Magazine Articles |
Le Moal, E., Boer-Duchemin, E. (2020). La nano-optique sous la pointe d’un microscope à effet tunnel. Photoniques, 102, 31–34.
Résumé: Le microscope à effet tunnel (STM) n’est pas seulement un outil de sciences des surfaces qui produit de magnifiques images résolues à l’échelle atomique. Le courant tunnel sous la pointe du STM est également une source d’excitation optique extrêmement locale, ce qui en fait un extraordinaire outil de la nano-optique. Ici, nous donnons un aperçu des possibilités de cet outil en plasmonique et en électroluminescence, lorsque STM et microscopie optique sont associés dans un même instrument.
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Peer-reviewed Publications |
Aguillon, F., Marinica, D. C., & Borisov, A. G. (2020). Molecule Detection with Graphene Dimer Nanoantennas. J. Phys. Chem. C, 124(51), 28210–28219.
Résumé: Using the tight binding description of the electronic structure of graphene and a time-dependent quantum approach, we address the vibrational excitation of molecules in the near field of a graphene nanoantenna. The possibility of tuning the graphene plasmon frequency by electrostatic doping allows an efficient resonant excitation of the infrared (IR)-active vibrational modes via the coupling between the molecular dipole and plasmon near field. We show that for the carbon monoxide CO molecules placed in the gap of a dimer antenna formed by the 20 nm size graphene patches, an excitation of the υ=1←0 transition leads to a distinct molecular signature in the IR absorption spectrum of the system. A very small number of molecules down to a single molecule placed in the antenna gap can thus be detected. Along with IR-active vibrations, the inhomogeneity of the plasmonic near field allows vibrational excitation of IR-inactive molecules via molecular quadrupole. The resonant excitation of the N2 molecule vibration is thus observed in the calculated absorption spectra, albeit the molecule signature is essentially smaller than for the CO molecule. Obtained with molecules described on the ab initio quantum chemistry level, our results provide quantitative insights into the performance of graphene nanoflakes and their dimers for molecular sensing.
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Alyabyeva, N., Ouvrard, A., Bavencoffe, M., Lindfors-Vrejoiu, I., Kolomiytsev, A., Solodovnik, M., Ageev, O., & McGrouther, D. (2020). Control of binary states of ferroic orders in bi-domain BiFeO3 nanoislands. Appl. Phys. Lett., 116(19), 192904.
Résumé: Understanding switching mechanisms in multiferroics such as BiFeO3 (BFO) is an important challenge to control ferroic orders (ferroelectric or ferroelastic) as it could lead to the design of non-volatile memories based on magnetoelectric coupling. Here, we demonstrate an alternative way to control the binary states of ferroic orders by locally applying pressure and electric field in ferroelectric bi-domains confined in single BFO nanoislands. The study of the electronic transport properties and domain orientations using atomic force microscopy (AFM) based techniques enabled us to determine the electric and mechanical parameters at which ferroelectric and ferroelastic resistive switching can be observed. Nanoislands exhibited binary high and low resistance states without scaling effect, with high performance switching characteristics. Positive-forward rectifying behavior at high tip force was interpreted by the formation of a subsurface non-conductive interface due to the strain gradient. Ferroelastic switching at the surface was associated with a symmetry-breaking induced by electromechanical coupling between the AFM tip and the BFO thin film. It led to out-of-plane polarization pinning that allows performing only in-plane switching accompanied by nucleation and propagation of a conductive domain wall. The control of ferroic binary states by the electric field and pressure may pave the way for multilevel data storage devices.
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Babaze, A., Esteban, R., Aizpurua, J., & Borisov, A. G. (2020). Second-Harmonic Generation from a Quantum Emitter Coupled to a Metallic Nanoantenna. ACS Photonics, 7(3), 701–713.
Résumé: We use time-dependent density functional theory and a semiclassical model to study second-harmonic generation in a system comprising a quantum emitter and a spherical metallic nanoparticle, where the transition frequency of the quantum emitter is set to be resonant with the second harmonic of the incident frequency. The quantum emitter is shown to enable strong second-harmonic generation, which is otherwise forbidden because of symmetry constraints. The time-dependent density functional theory calculations allow one to identify the main mechanism driving this nonlinear effect, where the quantum emitter plays the role of an optical resonator that experiences the nonlinear near fields generated by the metallic nanoantenna located nearby. The influence of the intrinsic properties of the quantum emitter and the nanoantenna, together with the relative position of both in the coupled system, allows for a high degree of control of the nonlinear light emission. The main effects and contributions to this nonlinear process can be correctly captured by a semiclassical description developed in this work.
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Benseghir, Y., Lemarchand, A., Duguet, M., Mialane, P., Gomez-Mingot, M., Roch-Marchal, C., Pino, T., Ha-Thi, M. - H., Haouas, M., Fontecave, M., Dolbecq, A., Sassoye, C., & Mellot-Draznieks, C. (2020). Co-immobilization of a Rh Catalyst and a Keggin Polyoxometalate in the UiO-67 Zr-Based Metal–Organic Framework: In Depth Structural Characterization and Photocatalytic Properties for CO2 Reduction. Journal of the American Chemical Society, 142(20), 9428–9438.
Résumé: The Keggin-type polyoxometalate (POM) PW12O403– and the catalytic complex Cp*Rh(bpydc)Cl2 (bpydc = 2,2′-bipyridine-5,5′-dicarboxylic acid) were coimmobilized in the Zr(IV) based metal organic framework UiO-67. The POM is encapsulated within the cavities of the MOF by in situ synthesis, and then, the Rh catalytic complex is introduced by postsynthetic linker exchange. Infrared and Raman spectroscopies, 31P and 13C MAS NMR, N2 adsorption isotherms, and X-ray diffraction indicate the structural integrity of all components (POM, Rh-complex and MOF) within the composite of interest (PW12,Cp*Rh)@UiO-67. DFT calculations identified two possible locations of the POM in the octahedral cavities of the MOF: one at the center of a UiO-67 pore with the Cp*Rh complex pointing toward an empty pore and one off-centered with the Cp*Rh pointing toward the POM. 31P–1H heteronuclear (HETCOR) experiments ascertained the two environments of the POM, equally distributed, with the POM in interaction either with the Cp* fragment or with the organic linker. In addition, Pair Distribution Function (PDF) data were collected on the POM@MOF composite and provided key evidence of the structural integrity of the POM once immobilized into the MOF. The photocatalytic activity of the (PW12,Cp*Rh)@UiO-67 composite for CO2 reduction into formate and hydrogen were evaluated. The formate production was doubled when compared with that observed with the POM-free Cp*Rh@UiO-67 catalyst and reached TONs as high as 175 when prepared as thin films, showing the beneficial influence of the POM. Finally, the stability of the composite was assessed by means of recyclability tests. The combination of XRD, IR, ICP, and PDF experiments was essential in confirming the integrity of the POM, the catalyst, and the MOF after catalysis.
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Bizzocchi, L., Melosso, M., Giuliano, B. M., Dore, L., Tamassia, F., Martin-Drumel, M. - A., Pirali, O., Margulès, L., & Caselli, P. (2020). Submillimeter and Far-infrared Spectroscopy of Monodeuterated Amidogen Radical (NHD): Improved Rest Frequencies for Astrophysical Observations. The Astrophysical Journal Supplement Series, 247(2), 59.
Résumé: Observations of ammonia in interstellar environments have revealed high levels of deuteration, and all its D-containing variants, including ND3, have been detected in cold prestellar cores and around young protostars. The observation of these deuterated isotopologues is very useful for elucidating the chemical and physical processes taking place during the very early stages of star formation, as the abundance of deuterated molecules is highly enhanced in dense and cold gas. Nitrogen hydride radicals are key species lying at the very beginning of the reaction pathway leading to the formation of NH3 and organic molecules of prebiotic interest, but relatively little is known about their D-bearing isotopologues. To date, only ND has been detected in interstellar gas. To aid the identification of further deuterated nitrogen radicals, we have thoroughly reinvestigated the rotational spectrum of NHD by employing two different instruments: a frequency-modulation submillimeter spectrometer operating in the THz region and a synchrotron-based Fourier-transform infrared spectrometer operating in the 50–240 cm−1 frequency range. NHD was produced in a plasma of NH3 and D2. A wide range of rotational energy levels have been probed thanks to the observation of high-N (up to 15) and high-K a (up to 9) transitions. A global analysis including our new data and data from the literature has provided a comprehensive set of very accurate spectroscopic parameters. A highly reliable line catalog has been generated to assist archival data searches and future astronomical observations of NHD at submillimeter and THz regimes.
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Bocan, G. A., Breiss, H., Szilasi, S., Momeni, A., Staicu Casagrande, E. M., Gravielle, M. S., Sánchez, E. A., & Khemliche, H. (2020). Anomalous KCl(001) Surface Corrugation from Fast He Diffraction at Very Grazing Incidence. Phys. Rev. Lett., 125, 096101.
Résumé: We present theoretical and experimental evidence of an anomalous surface corrugation behavior in He-KCl(001) for incidence along ⟨110⟩. When the He normal energy decreases below 100 meV, i.e., He-surface distances Z>2 Å, the corrugation unexpectedly increases up to an impressive ≳85%. This is not due to van der Waals interactions but to the combination of soft potential effects and the evolution of He-cation and He-anion interactions with Z. This feature, not previously analyzed on alkali-halide surfaces, may favor the alignment properties of weakly interacting overlayers.
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Bossion, D., Ndengue, S., Meyer, H. - D., Gatti, F., & Scribano, Y. (2020). Theoretical investigation of the H + HD --> D + H2 chemical reaction for astrophysical applications: A state-to-state quasi-classical study. J Chem Phys, 153(8), 081102.
Résumé: We report a large set of state-to-state rate constants for the H + HD reactive collision, using Quasi-Classical Trajectory (QCT) simulations on the accurate H3 global potential energy surface of Mielke et al. [J. Chem. Phys. 116, 4142 (2002)]. High relative collision energies (up to approximately 56 000 K) and high rovibrational levels of HD (up to approximately 50 000 K), relevant to various non thermal equilibrium astrophysical media, are considered. We have validated the accuracy of our QCT calculations with a new efficient adaptation of the Multi Configuration Time Dependent Hartree (MCTDH) method to compute the reaction probability of a specific reactive channel. Our study has revealed that the high temperature regime favors the production of H2 in its highly rovibrationnally excited states, which can de-excite radiatively (cooling the gas) or collisionally (heating the gas). Those new state-to-state QCT reaction rate constants represent a significant improvement in our understanding of the possible mechanisms leading to the destruction of HD by its collision with a H atom.
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Boulet, C., & Ma, Q. (2020). Line shape parameters of PH3 transitions: Theoretical studies of self-broadened widths and line mixing effects. J. Chem. Phys., 152(21), 214305.
Résumé: Line mixing effects have been calculated in various parallel and perpendicular bands of self-broadened PH3 lines and compared with recent experimental data. The theoretical approach is an extension to symmetric tops with high inversion barrier of the formalism previously developed for NH3 [Q. Ma and C. Boulet, J. Chem. Phys. 144, 224303 (2016)]. The model takes into account the non-diagonality of the scattering operator within the line space as well as, in a correct way, the double degeneracy of the j, k levels when k ≠ 0. Transitions between such levels should be considered as doublets whose components may be coupled by the line mixing process. It has been shown that, at low pressure, the inversion of the experimental data will strongly depend on the splitting between the two components of a doublet. When it is significant, one can measure independently both the width of one component and the intra-doublet coupling matrix element. Otherwise, one can only measure the sum of these two elements. Comparisons with measurements show that the present formalism leads to accurate predictions of the experimental line shapes
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Cao, S., Zapata-Herrera, M., Campos, A., Le Moal, E., Marguet, S., Dujardin, G., Kociak, M., Aizpurua, J., Borisov, A. G., & Boer-Duchemin, E. (2020). Probing the Radiative Electromagnetic Local Density of States in Nanostructures with a Scanning Tunneling Microscope. ACS Photonics, 7(5), 1280–1289.
Résumé: A novel technique for the investigation of the radiative contribution to the electromagnetic local density of states is presented. The inelastic tunneling current from a scanning tunneling microscope (STM) is used to locally and electrically excite the plasmonic modes of a triangular gold platelet. The radiative decay of these modes is detected through the transparent substrate in the far field. Emission spectra, which depend on the position of the STM excitation, as well as energy-filtered emission maps for particular spectral windows are acquired using this technique. The STM-nanosource spectroscopy and microscopy results are compared to those obtained from spatially resolved electron energy loss spectroscopy (EELS) maps on similar platelets. While EELS is known to be related to the total projected electromagnetic local density of states, the light emission from the STM-nanosource is shown here to select the radiative contribution. Full electromagnetic calculations are carried out to explain the experimental STM data and provide valuable insight into the radiative nature of the different contributions of the breathing and edge plasmon modes of the nanoparticles. Our results introduce the STM-nanosource as a tool to investigate and engineer light emission at the nanoscale.
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Carniato, S., Bizau, J. - M., Cubaynes, D., Kennedy, E. T., Guilbaud, S., Sokell, E., McLaughlin, B., & Mosnier, J. - P. (2020). Vibrationally and Spin-Orbit-Resolved Inner-Shell X-ray Absorption Spectroscopy of the NH+ Molecular Ion: Measurements and ab Initio Calculations. Atoms, 8(4), 67.
Résumé: his article presents N2+ fragment yields following nitrogen K-shell photo-absorption in the NH+ molecular ion measured at the SOLEIL synchrotron radiation facility in the photon energy region 390–450 eV. The combination of the high sensitivity of the merged-beam, multi-analysis ion apparatus (MAIA) with the high spectral resolution of the PLEIADES beamline helped to resolve experimentally vibrational structures of highly excited [N1s−1H]*+ electronic states with closed or open-shell configurations. The assignment of the observed spectral features was achieved with the help of density functional theory (DFT) and post-Hartree Fock Multiconfiguration Self-Consistent-Field/Configuration Interaction (MCSCF/CI) ab-initio theoretical calculations of the N1s core-to-valence and core-to-Rydberg excitations, including vibrational dynamics. New resonances were identified compared to previous work, owing to detailed molecular modeling of the vibrational, spin-orbit coupling and metastable state effects on the spectra. The latter are evidenced by spectral contributions from the 4Σ− electronic state which lies 0.07 eV above the NH+2Π ground state.
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Carniato, S., Selles, P., Ferté, A., Berrah, N., Wuosmaa, A. H., Nakano, M., Hikosaka, Y., Ito, K., Žitnik, M., Bučar, K., Soejima, K., Jänkälä, K., Cubaynes, D., Bizau, J. - M., Andric, L., Khalal, M. A., Palaudoux, J., Lablanquie, P., & Penent, F. (2020). Single photon simultaneous K-shell ionization/excitation in C6H6: experiment and theory. J. Phys. B: At. Mol. Opt. Phys., 53(24), 244010.
Résumé: Single photon simultaneous core ionization/core excitation (K−2V) of the Benzene molecule has been observed experimentally, using synchrotron radiation, by electron coincidence spectroscopy with a magnetic bottle time-of-flight electron spectrometer and reveals a rich spectrum. DFT and Post–Hartree–Fock calculations provide detailed assignments of K−2V states. The specific Auger decay of these states has also been determined experimentally with a new technique to improve the energy resolution.
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Carrascosa, H., Cruz-Díaz, G. A., Muñoz Caro, G. M., Dartois, E., & Chen, Y. - J. (2020). Photon-induced desorption of larger species in UV-irradiated methane ice. Mon Not R Astron Soc, 493(1), 821–829.
Résumé: At the low temperatures found in the interior of dense clouds and circumstellar regions, along with H2O and smaller amounts of species such as CO, CO2 or CH3OH, the infrared features of CH4 have been observed on icy dust grains. Ultraviolet (UV) photons induce different processes in ice mantles, affecting the molecular abundances detected in the gas phase. This work aims to understand the processes that occur in a pure CH4 ice mantle subjected to UV irradiation. We studied photon-induced processes for the different photoproducts arising in the ice upon UV irradiation. Experiments were carried out in ISAC, an ultra-high vacuum chamber equipped with a cryostat and an F-type UV lamp reproducing the secondary UV field induced by cosmic rays in dense clouds. Infrared spectroscopy and quadrupole mass spectrometry were used to monitor the solid and gas phases, respectively, during the formation, irradiation and warming-up of the ice. Direct photodesorption of pure CH4 was not observed. UV photons form CHx· and H· radicals, leading to photoproducts such as H2, C2H2, C2H6 and C3H8. Evidence for the photodesorption of C2H2 and photochemidesorption of C2H6 and C3H8 was found; the latter species is so far the largest molecule found to photochemidesorb. 13CH4 experiments were also carried out to confirm the reliability of these results.
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Chabot, M., Béroff, K., Dartois, E., Pino, T., & Godard, M. (2020). Coulomb Explosion of Polycyclic Aromatic Hydrocarbons Induced by Heavy Cosmic Rays: Carbon Chains Production Rates. The Astrophysical Journal, 888(1), 17.
Résumé: Cosmic rays (CRs) process the matter of the interstellar medium (ISM), not only modifying the interstellar matter but also injecting chemical species in the gas phase. In this work, we study the effect of CRs on astrophysical polycyclic aromatic hydrocarbons (PAHs). For events in which many electrons are stripped out from the PAHs, coulomb explosion takes place and carbon chains are produced. We computed PAH multi-ionization cross sections with a collisional model. We used another model to predict the fragmentation pattern following coulomb explosion. Experimental measurements were used to assess the validity of the calculations. The production rates of carbon chains were calculated using different CR fluxes and elemental compositions, to account for the variations expected in different astrophysical environments. PAHs with a range of sizes and levels of compactness were explored. As an average over the explored PAHs, the PAH lifetime with respect to a standard interstellar CR flux is found to be on the order of a few billion years. The production rates of chains (5–15 carbons) are slightly below the H2 ionization rate ζ. In the diffuse ISM, with 10% of the available cosmic carbon locked in PAHs, this process leads to carbon chain fractional abundances at steady state, in the range of 10−15–10−14, with a confidence interval of 1 order of magnitude. It reaches 10−13 in quiescent dense clouds. This is not sufficient to explain the observed abundances of carbon chains and complex organic molecules in dense clouds.
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Chin, A. W., Le Dé, B., Mangaud, E., Atabek, O., & Desouter-Lecomte, M. (2020). Role of the multiple-excitation manifold in a driven quantum simulator of an antenna complex. Phys. Rev. A, 102(2), 023708.
Résumé: Biomolecular light-harvesting antennas operate as nanoscale devices in a regime where the coherent interactions of individual light, matter, and vibrational quanta are nonperturbatively strong. The complex behavior arising from this could, if fully understood, be exploited for myriad energy applications. However, nonperturbative dynamics are computationally challenging to simulate, and experiments on biomaterials explore very limited regions of the nonperturbative parameter space. So-called quantum simulators of light-harvesting models could provide a solution to this problem, and here we employ the hierarchical equations-of-motion technique to investigate the recent superconducting experiments of Potočnik et al. [A. Potočnik et al., Nat. Commun. 9, 904 (2018)] used to explore excitonic energy capture. By explicitly including the role of optical driving fields, nonperturbative dephasing noise, and the full multiexcitation Hilbert space of a three-qubit quantum circuit, we predict the measurable impact of these factors on transfer efficiency. By analysis of the eigenspectrum of the network, we uncover a structure of energy levels that allows the network to exploit optical “dark” states and excited-state absorption for energy transfer. We also confirm that time-resolvable coherent oscillations could be experimentally observed, even under the strong, nonadditive action of the driving and optical fields.
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Corgier, R., Loriani, S., Ahlers, H., Posso-Trujillo, K., Schubert, C., Rasel, E. M., Charron, E., & Gaaloul, N. (2020). Interacting quantum mixtures for precision atom interferometry. New J. Phys., 22(12), 123008.
Résumé: We present a source engineering concept for a binary quantum mixture suitable as input for differential, precision atom interferometry with drift times of several seconds. To solve the non-linear dynamics of the mixture, we develop a set of scaling approach equations and verify their validity contrasting it to the one of a system of coupled Gross–Pitaevskii equations. This scaling approach is a generalization of the standard approach commonly used for single species. Its validity range is discussed with respect to intra- and inter-species interaction regimes. We propose a multi-stage, non-linear atomic lens sequence to simultaneously create dual ensembles with ultra-slow kinetic expansion energies, below 15 pK. Our scheme has the advantage of mitigating wave front aberrations, a leading systematic effect in precision atom interferometry.
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Coudert, L. H. (2020). Extreme anomalous centrifugal distortion in methylene. The Journal of Chemical Physics, 153, 144115.
Résumé: A new treatment is presented to account for the extreme anomalous centrifugal distortion displayed by the open-shell methylene radical. This new treatment is based on a four-dimensional approach in which both the overall rotation and the large amplitude bending mode are treated simultaneously. It accounts for the spin–rotation and spin–spin fine couplings, assumed to depend on the large amplitude bending coordinate, as well as for the hyperfine coupling. The new treatment is tested analyzing the available high-resolution data. 336 transitions, involving the ground and first excited vibrational states of the bending mode, are reproduced with a unitless standard deviation of 1.3, using 42 molecular constants. Compared to a previous analysis [S. Brünken et al., J. Chem. Phys. 123, 164315 (2005)], the present analysis is more satisfactory as it accounts for a larger dataset and the ratio of the number of data to the number of varied constants is larger. The present theoretical treatment also allows us to retrieve the bending potential and the main kinetic energy term.
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Dartois, E., Chabot, M., Bacmann, A., Boduch, P., Domaracka, A., & Rothard, H. (2020). Non-thermal desorption of complex organic molecules. Astronomy and Astrophysics, 634, A103.
Résumé: Aims. Methanol ice is embedded in interstellar ice mantles present in dense molecular clouds. We aim to measure the sputtering efficiencies starting from different ice mantles of varying compositions experimentally, in order to evaluate their potential impact on astrochemical models. The sputtering yields of complex organic molecules is of particular interest, since few mechanisms are efficient enough to induce a significant feedback to the gas phase.
Methods. We irradiated ice film mixtures made of methanol and carbon dioxide of varying ratios with swift heavy ions in the electronic sputtering regime. We monitored the evolution of the infrared spectra as well as the species released to the gas phase with a mass spectrometer. Methanol (12C) and isotopically labelled 13C-methanol were used to remove any ambiguity on the measured irradiation products.
Results. The sputtering of methanol embedded in carbon dioxide ice is an efficient process leading to the ejection of intact methanol in the gas phase. We establish that when methanol is embedded in a carbon-dioxide-rich mantle exposed to cosmic rays, a significant fraction (0.2–0.3 in this work) is sputtered as intact molecules. The sputtered fraction follows the time-dependent bulk composition of the ice mantle, the latter evolving with time due to the radiolysis-induced evolution of the bulk. If methanol is embedded in a carbon dioxide ice matrix, as the analyses of the spectral shape of the CO2 bending mode observations in some lines of sight suggest, the overall methanol sputtering yield is higher than if embedded in a water ice mantle. The sputtering is increased by a factor close to the dominant ice matrix sputtering yield, which is about six times higher for pure carbon dioxide ice when compared to water ice. These experiments are further constraining the cosmic-ray-induced ice mantle sputtering mechanisms important role in the gas-phase release of complex organic molecules from the interstellar solid phase.
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Dartois, E., Charon, E., Engrand, C., Pino, T., & Sandt, C. (2020). Mechanochemical synthesis of aromatic infrared band carriers. A&A, 637, A82.
Résumé: Context. Interstellar space hosts nanometre- to micron-sized dust grains, which are responsible for the reddening of stars in the visible. The carbonaceous-rich component of these grain populations emits in infrared bands that have been observed remotely for decades with telescopes and satellites. They are a key ingredient of Galactic radiative transfer models and astrochemical dust evolution. However, except for C60 and its cation, the precise carriers for most of these bands are still unknown and not well reproduced in the laboratory.
Aims: In this work, we aim to show the high-energy mechanochemical synthesis of disordered aromatic and aliphatic analogues provides interstellar relevant dust particles.
Methods: The mechanochemical milling of carbon-based solids under a hydrogen atmosphere produces particles with a pertinent spectroscopic match to astrophysical observations of aromatic infrared band (AIB) emission, linked to the so-called astrophysical polycyclic aromatic hydrocarbon hypothesis. The H/C ratio for the analogues that best reproduce these astronomical infrared observations lies in the 5 ± 2% range, potentially setting a constraint on astrophysical models. This value happens to be much lower than diffuse interstellar hydrogenated amorphous carbons, another Galactic dust grain component observed in absorption, and it most probably provides a constraint on the hydrogenation degree of the most aromatic carbonaceous dust grain carriers. A broad band, observed in AIBs, evolving in the 1350-1200 cm-1 (7.4-8.3 μm) range is correlated to the hydrogen content, and thus the structural evolution in the analogues produced.
Results: Our results demonstrate that the mechanochemical process, which does not take place in space, can be seen as an experimental reactor to stimulate very local energetic chemical reactions. It introduces bond disorder and hydrogen chemical attachment on the produced defects, with a net effect similar to the interstellar space very localised chemical reactions with solids. From the vantage point of astrophysics, these laboratory interstellar dust analogues will be used to predict dust grain evolution under simulated interstellar conditions, including harsh radiative environments. Such interstellar analogues offer an opportunity to derive a global view on the cycling of matter in other star forming systems.
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Debiossac, M., Roncin, P., & Borisov, A. G. (2020). Refraction of Fast Ne Atoms in the Attractive Well of a LiF(001) Surface. J. Phys. Chem. Lett., 11, 4564–4569.
Résumé: Ne atoms with energies of </=3 keV are diffracted under grazing angles of incidence from a LiF(001) surface. For a small momentum component of the incident beam perpendicular to the surface, we observe an increase in the elastic rainbow angle together with a broadening of the inelastic scattering profile. We interpret these two effects as the refraction of the atomic wave in the attractive part of the surface potential. We use a fast, rigorous dynamical diffraction calculation to find a projectile-surface potential model that enables a quantitative reproduction of the experimental data for </=10 diffraction orders. This allows us to extract an attractive potential well depth of 10.4 meV. Our results set a benchmark for more refined surface potential models that include the weak van der Waals region, a long-standing challenge in the study of atom-surface interactions.
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Dubosq, C., Calvo, F., Rapacioli, M., Dartois, E., Pino, T., Falvo, C., & Simon, A. (2020). Quantum modeling of the optical spectra of carbon cluster structural families and relation to the interstellar extinction UV bump. Astronomy and Astrophysics, 634, A62.
Résumé: Context. The UV bump observed in the interstellar medium extinction curve of galaxies has been assigned to π → π⋆ transitions within the sp2 conjugated network of carbon grains. These grains are commonly thought to be graphitic particles or polycyclic aromatic hydrocarbons. However, questions are still open regarding the shape and degree of amorphization of these particles, which could account for the variations in the 2175 Å astronomical bump. Optical spectra of graphitic and onion-like carbon structures were previously obtained from dielectric constant calculations based on oscillating dipole models. In the present study, we compute the optical spectra of entire populations of carbon clusters using an explicit quantum description of their electronic structure for each individual isomer.
Aims. Our aim is to determine the optical spectra of pure carbon clusters Cn=24,42,60 sorted into structural populations according to specific order parameters, namely asphericity and sp2 fraction, and to correlate these order parameters to the spectral features of the band in the region of the UV bump. Our comparison involves data measured for the astronomical UV bump as well as experimental spectra of carbon species formed in laboratory flames.
Methods. The individual spectrum of each isomer is determined using the time-dependent density functional tight-binding method. The final spectrum for a given population is obtained by averaging the individual spectra for all isomers of a given family. Our method allows for an explicit description of particle shape, as well as structural and electronic disorder with respect to purely graphitic structures.
Results. The spectra of the four main populations of cages, flakes, pretzels, and branched structures (Dubosq et al. 2019, A&A, 625, L11) all display strong absorption in the 2–8 eV domain, mainly due to π → π⋆ transitions. The absorption features, however, differ from one family to another and our quantum modeling indicates that the best candidates for the interstellar UV bump at 217.5 nm are cages and then flakes, while the opposite trend is found for the carbonaceous species formed in flame experiments; the other two families of pretzels and branched structures play a lesser role in both cases.
Conclusions. Our quantum modeling shows the potential contribution of carbon clusters with a high fraction of conjugated sp2 atoms to the astronomical UV bump and to the spectrum of carbonaceous species formed in flames. While astronomical spectra are better accounted for using rather spherical isomers such as cages, planar flake structures are involved as a much greater component in flame experiments. Interestingly, these flake isomers have been proposed as likely intermediates in the formation mechanisms leading to buckminsterfullerene, which was recently detected in space. This study, although restricted here to the case of pure carbon clusters, will be extended towards several directions of astronomical relevance. In particular, the ability of the present approach to deal with large-scale molecular systems at an explicit quantum level of electronic structure and its transferable character towards different charge states and the possible presence of heteroatoms makes it the method of choice to address the important case of neutral and ionic hydrogenated compounds.
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Dumur, F., Guerlin, A., Lehoux, A., Selvakannan, P. R., Miomandre, F., Méallet-Renault, R., Rebarz, M., Sliwa, M., Dumas, E., Le Pleux, L., Pellegrin, Y., Odobel, F., & Mayer, C. R. (2020). Mutual influence of gold and silver nanoparticles on Tris-(2,2′bipyridine)-Ru(II) core complexes: Post-functionalization processes, optical and electrochemical investigations. Applied Surface Science, 499(1), 143847.
Résumé: The synthesis, reactivity and properties of a series of four polypyridyl ruthenium complexes have been studied. These complexes were used to post-functionalize preformed 3 nm silver and gold nanoparticles (NPs) in water and in dichloromethane (DCM). We studied the influence of the grafted complexes on the formation process and stability of the colloidal solutions and we investigated the optical and electrochemical properties of the final nanocomposites. Among the series of four ruthenium complexes, three novel heteroleptic complexes (1–3) bearing one pyridine, one amine or two carboxydithioic acid pendant groups were synthesized and reacted with preformed Au-NPs and Ag-NPs. Results were compared to those obtained with the model [Ru(bpy)3]2+ complex (4). The strength of the interaction between the anchoring group and the surface of NPs influenced the size, shape and stability of the final nanocomposites. Polar solvent such as water induced aggregation and lead to unstable nanocomposites. Stationary and time resolved luminescence of grafted nanocomposites (1–3) showed that the luminescence of complexes were completely quenched (lifetime and emission quantum yield) in water by electron transfer processes, moreover electrical measurements rationalize that Ag nanocomposites exhibit the stronger quenching due to a lower oxidation potential. It also showed a current enhancement associated with double layer charging of the metal nanoparticle cores.
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Duverger, E., Boyer, A. - G., Sauriat-Dorizon, H., Sonnet, P., Stephan, R., Hanf, M. - C., & Riedel, D. (2020). Two-Dimensional Functionalized Ultrathin Semi-Insulating CaF2 Layer on the Si(100) Surface at a Low Temperature for Molecular Electronic Decoupling. ACS Appl. Mater. Interfaces, 12(26), 29661–29670.
Résumé: The ability to precisely control the electronic coupling/decoupling of adsorbates from surfaces is an essential goal. It is important for fundamental studies not only in surface science but also in several applied domains including, for example, miniaturized molecular electronic or for the development of various devices such as nanoscale biosensors or photovoltaic cells. Here, we provide atomic-scale experimental and theoretical investigations of a semi-insulating layer grown on a silicon surface via its epitaxy with CaF2. We show that, following the formation of a wetting layer, the ensuing organized unit cells are coupled to additional physisorbed CaF2 molecules, periodically located in their surroundings. This configuration shapes the formation of ribbons of stripes that functionalize the semiconductor surface. The obtained assembly, having a monolayer thickness, reveals a surface gap energy of ∼3.2 eV. The adsorption of iron tetraphenylporphyrin molecules on the ribbons of stripes is used to estimate the electronic insulating properties of this structure via differential conductance measurements. Density functional theory (DFT) including several levels of complexity (annealing, DFT + U, and nonlocal van der Waals functionals) is employed to reproduce our experimental observations. Our findings offer a unique and robust template that brings an alternative solution to electronic semi-insulating layers on metal surfaces such as NaCl. Hence, CaF2/Si(100) ribbon of stripe structures, whose lengths can reach more than 100 nm, can be used as a versatile surface platform for various atomic-scale studies of molecular devices.
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El Boujlaidi, A., Rochdi, N., Tchalala, R., Enriquez, H., Mayne, A. J., & Oughaddou, H. (2020). Growth and characterization of nickel oxide ultra-thin films. SURFACES AND INTERFACES, 18, 100433.
Résumé: The oxidation of the Ni(111) surface under ultrahigh-vacuum conditions is studied experimentally with low-energy electron diffraction and high-resolution X-ray photoelectron spectroscopy. Exposure of the clean Ni(111) surface to molecular oxygen at room temperature followed by annealing at 400 K leads to the formation of two different structures (2×2) and (3root3 × 3root3 )R30°, prior to the formation of the NiO(111) monolayer. The O 1s core levels indicate that the obtained oxide is terminated by oxygen atoms while the valence band measurements clearly reveal the band gap of NiO. The energy difference between the Fermi level and the maximum of the valance band is extracted and is found to be 0.47 eV.
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Gans, B., Hartweg, S., Garcia, G. A., Boyé-Péronne, S., Harper, O. J., Guillemin, J. - C., & Loison, J. - C. (2020). VUV photoionization of the CH2NC radical: adiabatic ionization energy and cationic vibrational mode wavenumber determinations. Phys. Chem. Chem. Phys., 22, 12496–12501.
Résumé: The photoelectron spectroscopy of CH2NC (isocyanomethyl) radical species is investigated for the first time between 9.3 and 11.2 eV in the vicinity of the first photoionizing transition X+1A1 ← X 2B1. The experiment combines a microwave discharge flow-tube reactor to produce the radicals through the CH3NC + F → CH2NC + HF reaction, a VUV synchrotron radiation excitation, and a double imaging electron/ion coincidence spectrometer which allows the recording of mass-selected threshold photoelectron spectra. Assignment of the observed vibrational structure of the CH2NC+ cation is guided by ab initio calculations and Franck–Condon simulations. From the experimental spectrum, the first adiabatic ionization energy of the CH2NC radical is measured as 9.439(6) eV. Fundamental wavenumbers are determined for several vibrational modes of the cation: 1+(CH2 symmetric stretch) = 2999(80) cm−1, 2+(NC stretch) = 1925(40) cm−1, 4+(H2C–N stretch) = 1193(40) cm−1, 6+(CNC out-of-plane bend) = 237(50) cm−1, and 8+(CH2 rock) = 1185(60) cm−1.
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Garcia, G. A., Loison, J. - C., Holzmeier, F., Gans, B., Alcaraz, C., Nahon, L., Wu, X., Zhou, X., Bodi, A., & Hemberger, P. (2020). Characterisation of the first electronically excited state of protonated acetylene C2H3 + by coincident imaging photoelectron spectroscopy. Molecular Physics, 119, e1825851.
Résumé: We present a combined experimental and theoretical study of the threshold photoelectron spectroscopy of the vinyl radical encompassing the first triplet excited state of the vinyl cation. The radicals were produced in a flow-tube reactor by hydrogen abstraction of C2H4 and CH4 using fluorine atoms generated in a microwave discharge. Vinyl was ionised with synchrotron vacuum ultraviolet radiation. A double imaging coincidence setup was used to record the threshold photoelectron spectrum. The experimental and simulated spectra show a marked adiabatic transition to the a ~ + 3A?? state with a short vibrational progression dominated by the C?=?C stretching mode. The adiabatic ionisation energy to this state is measured precisely at 10.747 ± 0.008?eV. In combination with the adiabatic ionisation energy to the X ~ + 1A1 state from the Active Thermochemical Tables (ATcT), we find a singlet?triplet gap of 2.27 ± 0.01?eV (219 ± 1?kJ mol?1). Calculated ionisation energies and Franck?Condon factors for the singlet A ~ + 1A?? excited state are also given.
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Goubet, M., Martin-Drumel, M. - A., Réal, F., Vallet, V., & Pirali, O. (2020). Conformational Landscape of Oxygen-Containing Naphthalene Derivatives. J. Phys. Chem. A, 124(22), 4484–4495.
Résumé: Polycyclic Aromatic Compounds (PACs) constitute an important class of molecules found in various environments and considered as important pollutants of the earth atmosphere. In particular, functionalization of PACs modify the ring aromaticity which greatly influence the chemical reactivity of these species. In this work we studied several oxygen-containing PACs, relevant to atmospheric chemistry. We investigated the conformational landscape of four naphthalene-derivative molecules --- namely 1- and 2-hydroxynaphthalene, and 1- and 2-naphthaldehyde --- by means of rotational and vibrational spectroscopy supported by quantum chemical calculations. For 1-hydroxynaphthalene and 1-naphthaldehyde, intramolecular hydrogen bonding and steric effects drive the conformational preferences while for 2-hydroxynaphthalene and 2-naphthaldehyde, the charge distributions allow to understand the conformational landscape. This work not only demonstrates how the localization of the substitution group in the ring influences the conformational relative energies and but also constitutes a step toward a better understanding of the different chemical reactivity of such functionalized PACs.
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Gutierrez-Quintanilla, A., Chevalier M, Platakyte, R., Ceponkus J, & Crepin, C. (2020). Intramolecular hydrogen tunneling in 2-chloromalonaldehyde trapped in solid para-hydrogen. Phys Chem Chem Phys, 20, 28658–28666.
Résumé: The internal dynamics of a 2-chloromalonaldehyde (2-ClMA) molecule, possessing a strong internal hydrogen bond (IHB), was examined by means of matrix isolation spectroscopy in a soft host: para-hydrogen (pH2). 2-ClMA is a chlorinated derivative of malonaldehyde (MA), a model molecule in hydrogen transfer studies, better suited to low temperature experiments than its parent molecule. The infrared absorption spectra of 2-ClMA isolated in pH2 exhibit temperature dependent structures which are explained as transitions occurring from split vibrational levels induced by hydrogen tunneling. The doublet components associated with higher and lower energy levels are changing reversibly with the increase/decrease of the matrix temperature. The ground state splitting is measured to be 7.9 +/- 0.1 cm(-1). The presence of oH2 impurities in the pH2 matrix close to the neighborhood of the 2-ClMA molecule is found to quench the H tunneling. The data provide a powerful insight into the dynamical picture of intramolecular hydrogen tunneling in a molecule embedded in a very weakly perturbing environment.
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Hammonds, M., Tran, T. - T., Tran, Y. H. H., Ha-Thi, M. - H., & Pino, T. (2020). Time-Resolved Resonant Raman Spectroscopy of the Photoinduced Electron Transfer from Ruthenium(II) Trisbipyridine to Methyl Viologen. The Journal of Physical Chemistry A, 124, 2736–2740.
Résumé: We report the first time-resolved resonant Raman (TR3) spectra of photoinduced charge transfer from [Ru(bpy)3]2+ to methyl viologen, with observations of vibrational structure. The presence of singly charged methyl viologen in solution is noted by the appearance of several spectroscopic lines, which are visible in the spectra following subtraction of reagent molecules. Assignments are confirmed using both density functional theory (DFT) calculations and literature values and are shown to be consistent with transient absorption spectroscopy data. This presents proof-of-concept for the application of TR3 in mechanistic studies of photocatalytic systems.
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Hamoudi, H., Berdiyorov, G. R., Ariga, K., & Esaulov, V. (2020). Bottom-up fabrication of the multi-layer carbon metal nanosheets. RSC ADVANCES, 10(13), 7987–7993.
Résumé: Ordered carbon composite materials have great potential for practical applications in many areas such as energy conversion, quantum computing, biotechnologies, and electronics. In this work, we demonstrate a state-of-the-art self-assembly driven building block approach to create new layered carbon-metal composite materials with advanced properties. We fabricate molecular nanocomposites using self-assembled metal intercalated multi-layers of dithiol derivatives. The obtained structures are analysed using different characterization tools (such as X-ray photoelectron and Raman spectroscopy and atomic force microscopy) and their electronic transport properties are studied by four-point probe measurements supplemented by density functional theory calculations. This work demonstrates a new strategy for low-cost, high-yield and eco-friendly nanofabrication of hybrid organometallic membranes.
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Harper, O. J., Boyé-Péronne, S., Garcia, G. A., Hrodmarsson, H. R., Loison, J. - C., & Gans, B. (2020). To see C2: Single-photon ionization of the dicarbon molecule. The Journal of Chemical Physics, 152(4), 041105.
Résumé: The C2 carbon cluster is found in a large variety of environments including flames, electric discharges, and astrophysical media. Due to spin-selection rules, assessing a complete overview of the dense vibronic landscape of the C2+ cation starting from the ground electronic state X 1Σg+ of the neutral is not possible, especially since the C2^+ ground state is of X+ 4Σg− symmetry. In this work, a flow-tube reactor source is employed to generate the neutral C2 in a mixture of both the lowest singlet X 1Σg+ and triplet a 3Πu electronic states. We have investigated the vibronic transitions in the vicinity of the first adiabatic ionization potential via one-photon ionization with vacuum ultraviolet synchrotron radiation coupled with electron/ion double imaging techniques. Using ab initio calculations and Franck-Condon simulations, three electronic transitions are identified and their adiabatic ionization energy is determined Ei(a+2Πu←X1Σ+g)=12.440(10) eV, Ei(X+4Σ−g←a3Πu)=11.795(10) eV, and Ei(a+2Πu ← a3Πu) = 12.361(10) eV. From the three origin bands, the following energy differences are extracted: ΔE(a − X) = 0.079(10) eV and ΔE(a+ − X+) = 0.567(10) eV. The adiabatic ionization potential corresponding to the forbidden one-photon transition X+ ← X is derived and amounts to 11.873(10) eV, in very good agreement with the most recent measurement by Krechkivska et al. [J. Chem. Phys. 144, 144305 (2016)]. The enthalpy of formation of the doublet ground state C2^+ cation in the gas phase is determined at 0 K, ΔfH0(0K)(C+2(Πu2))=2019.9(10) kJ mol−1. In addition, we report the first experimental ion yield of C2 for which only a simple estimate was used up to now in the photochemistry models of astrophysical media due to the lack of experimental data.
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Harper, O. J., Coudert, L. H., Loison, J. - C., Gans, B., Douin, S., Garcia, G. A., Guillemin, J. - C., & Boyé-Péronne, S. (2020). Quasi-symmetry effects in the threshold photoelectron spectrum of methyl isocyanate. The Journal of Chemical Physics, 153, 074308.
Résumé: The vacuum-ultraviolet threshold photoelectron spectrum of methyl isocyanate CH3NCO has been recorded from 10.4 eV to 12 eV using synchrotron radiation and a coincidence technique allowing for a mass-discrimination of the photoelectron signal. A significant improvement is achieved over previous investigations as this experimental setup leads to a much more resolved spectrum. Ten sharp peaks and a broad feature spanning 1.2 eV were recorded. This spectrum consists of X˜+2A″←X˜1A′
X
̃
+
2
A
″
←
X
̃
1
A
′
and Ã+2A′←X˜1A′
Ã
+
2
A
′
←
X
̃
1
A
′
ionizing transitions. For the former, the adiabatic ionization energy was determined experimentally to be 10.596(6) eV; for the latter, its value was estimated to be 10.759(50) eV. Seven sharp peaks could be assigned to vibrational modes of the cation X˜+2A″
X
̃
+
2
A
″
and neutral X˜1A′
X
̃
1
A
′
ground electronic states involving only the NCO group atoms. Theoretical modeling of the threshold photoelectron spectrum has proven difficult as methyl isocyanate is a non-rigid molecule displaying large amplitude internal rotation of the methyl group and ∠CNC bending mode, leading to the quasi-symmetry. With the help of ab initio calculations, a theoretical model in which these two large amplitude motions are included in addition to the five small amplitude vibrational modes involving NCO group atoms is proposed. Comparison with the experimental spectrum shows that the broad feature and the strongest peak line positions are well accounted for; their intensities are also fairly well reproduced after adjusting a few parameters.
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Hartmann, J. - M., Ma, J., Delahaye, T., Billard, F., Hertz, E., Wu, J., Lavorel, B., Boulet, C., & Faucher, O. (2020). Molecular alignment echoes probing collision-induced rotational-speed changes. Physical Review Research, 2(2), 023247.
Résumé: We show that the decays with pressure of the rotational alignment echoes induced in
N
2
O
-He gas mixtures by two ultrashort laser pulses with various delays show detailed information about collision-induced changes of the rotational speed of the molecules. Measurements and classical calculations consistently demonstrate that collisions reduce the echo amplitude all the more efficiently when the echo appears late. We quantitatively explain this behavior by the filamentation of the classical rotational phase space induced by the first pulse and the narrowing of the filaments with time. The above-mentioned variation of the echo decay then reflects the ability of collisions to change the molecular rotation speed by various amounts, enabling refined tests of models for the dissipation induced by intermolecular forces. We also demonstrate that the collision-induced changes of the rotational speed within the filaments are the classical equivalents of the nonsecular transfers among quantum coherences, thus evidencing the correspondence between the classical and quantum worlds.
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Hartweg, S., Loison, J. - C., Boyé-Péronne, S., Gans, B., Holland, D. M. P., Garcia, G. A., Nahon, L., & Pratt, S. T. (2020). Photoionization of C4H5 Isomers. The Journal of Physical Chemistry A, 124, 6050–6060.
Résumé: Single-photon, photoelectron–photoion coincidence spectroscopy is used to record the mass-selected ion spectra and slow photoelectron spectra of C4H5 radicals produced by the abstraction of hydrogen atoms from three C4H6 precursors by fluorine atoms generated by a microwave discharge. Three different C4H5 isomers are identified, with the relative abundances depending on the nature of the precursor (1-butyne, 1,2-butadiene, and 1,3-butadiene). The results are compared with our previous work using 2-butyne as a precursor [Hrodmarsson, H. R. J. Phys. Chem. A 2019, 123, 1521−1528]. The slow photoelectron spectra provide new information on the three radical isomers that is in good agreement with previous experimental and theoretical results [Lang, M. J. Phys. Chem. A 2015, 119, 3995−4000; Hansen, N. J. Phys. Chem. A 2006, 110, 3670–3678]. The energy scans of the C4H5 photoionization signal are recorded with substantially better resolution and signal-to-noise ratio than those in earlier work, allowing the observation of autoionizing resonances based on excited states of the C4H5 cation. Photoelectron images recorded at several energies are also reported, providing insight into the decay processes of these excited states. Finally, in contrast to the earlier work using 2-butyne as a precursor, where H-atom abstraction was the only observed process, F- and H-atom additions to the present precursors are also observed through the detection of C4H6F, C4H5F, and C4H7.
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Hartwig, B., Lange, M., Poblotzki, A., Medel, R., Zehnacker, A., & Suhm, M. A. (2020). The reduced cohesion of homoconfigurational 1,2-diols. PCCP, 22(3), 1122–1136.
Résumé: By a combination of linear FTIR and Raman jet spectroscopy, racemic trans-1,2-cyclohexanediol is shown to form an energetically unrivalled S4-symmetric heterochiral dimer in close analogy to 1,2-ethanediol. Analogous experiments with enantiopure trans-1,2-cyclohexanediol reveal the spectral signature of at least three unsymmetric homochiral dimers. A comparison to signal-enhanced spectra of 1,2-ethanediol and to calculations uncovers at least three transiently homochiral dimer contributions as well. In few of these dimer structures, the intramolecular OH⋯O contact present in monomeric 1,2-diols survives, despite the kinetic control in supersonic jet expansions. This provides further insights into the dimerisation mechanism of conformationally semi-flexible molecules in supersonic jets. Racemisation upon dimerisation is shown to be largely quenched under jet cooling conditions, whereas it should be strongly energy-driven at higher temperatures. The pronounced energetic preference for heterochiral aggregation of vicinal diols is also discussed in the context of chirality-induced spin selectivity.
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Hirata, K., Mori, Y., Ishiuchi, S. -ichi, Fujii, M., & Zehnacker, A. (2020). Chiral discrimination between tyrosine and β-cyclodextrin revealed by cryogenic ion trap infrared spectroscopy. PCCP, 22(43), 24887–24894.
Résumé: Complexes of permethylated β-cyclodextrin (β-MCD) with the two enantiomers of protonated tyrosine (l- and d-TyrH+) are studied by cryogenic ion trap infrared photo-dissociation spectroscopy. The vibrational spectra in the OH/NH stretch and fingerprint regions are assigned based on density functional theory calculations. The spectrum of both l- and d-TyrH+ complexes contains features characteristic of a first structure with ammonium and acid groups of the amino acid simultaneously interacting with the β-MCD, the phenolic OH remaining free. A second structure involving additional interaction between the phenolic OH and the β-MCD is observed only for the complex with d-TyrH+. The larger abundance of the d-TyrH+ complex in the mass spectrum is tentatively explained in terms of (1) better insertion of d-TyrH+ within the cavity with the hydrophobic aromatic moiety less exposed to hydrophilic solvent molecules and (2) a stiff structure involving three interaction points, namely the ammonium, the phenolic OH and the carboxylic acid OH, which is not possible for the complex with l-TyrH+. The recognition process does not occur through size effects that induce complementarity to the host molecule but specific interactions. These results provide a comprehensive understanding of how the cyclodextrin recognises a chiral biomolecule.
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Hrodmarsson, H. R., Gans, B., Boyé-Péronne, S., Garcia, G. A., Nahon, L., Pratt, S. T., & Holland, D. M. P. (2020). The effect of autoionization on the HBr+ X 2Π3/2,1/2 state photoelectron angular distributions. Chemical Physics, 539, 110961.
Résumé: A double-imaging photoelectron-photoion spectrometer and synchrotron radiation have been used to measure the HBr+ X 2Π3/2 v+ = 0, 1, 2 and the 2Π1/2 v+ = 0 state photoelectron angular distributions, as characterized by the anisotropy parameter β, the total ion yield, and the threshold photoelectron spectrum. Particular attention has been focussed on the photon energy range between the 2Π3/2 and the 2Π1/2 spin–orbit components of the ground ionic state. This region encompasses Rydberg states, belonging to series converging onto the upper 2Π1/2 ionization limit, which may decay by autoionization into the 2Π3/2 ionization continuum. A detailed study has been performed on the effects of autoionization on the 2Π3/2 v+ = 0 state photoelectron angular distributions. The observed energy dependent variations in the β-values exhibit a regular pattern that correlates with excitation into members of a very broad d-type Rydberg series. Additional rapid variations in the β-parameters, which occur over a narrow energy range, appear to coincide with sharp autoionizing Rydberg states belonging to s, p and d series. The present experimental results for the HBr+ X 2Π3/2 v+ = 0 state photoelectron anisotropy parameter are compared to previously reported theoretical predictions and to earlier studies of the Kr+ 4p5 2P3/2 state β-parameter. The threshold photoelectron spectrum of the X 2Π3/2 v+ = 0 band exhibits partially resolved rotational structure. A simulation of this structure yields an ionization threshold of 11.6673 ± 0.0010 eV, which is consistent with previous measurements.
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Humberg, N., Bretel, R., Eslam, A., Le Moal, E., & Sokolowski, M. (2020). Hydrogen-Bonded One-Dimensional Chains of Quinacridone on Ag(100) and Cu(111): The Role of Chirality and Surface Bonding. J. Phys. Chem. C, 124(45), 24861–24873.
Résumé: The adsorption and ordering of the prochiral molecule quinacridone (QA) on the Ag(100) and Cu(111) surfaces were studied by low-energy electron diffraction and scanning tunneling microscopy. Upon adsorption, the molecules form parallel homochiral chains of flat-lying molecules linked together via hydrogen bonds on both surfaces, but these chains show significant surface-dependent differences concerning their lateral order. On both substrates, the chains are not thermodynamically stable but only metastable and stabilized by kinetic barriers. On the Ag(100) surface, annealing induces a phase transition to a highly ordered and heterochiral structure with a reduced density of hydrogen bonds. The related loss of bonding energy is overcompensated by a stronger bonding to the substrate, yielding a commensurate structure. For QA on Ag(100), we propose that during the initial chain formation and the phase transition upon annealing, the molecules can change their handedness by rotating around their long axes. In contrast, the initial chain formation and the phase transitions of QA on the Cu(111) surface appear to be subject to stronger kinetic limitations. These are explained by stronger substrate molecule interactions on Cu(111), which reduce the diffusion and the possibility for a change of handedness in comparison to QA on Ag(100). We discuss how the intermolecular hydrogen bonds, the 2D chirality, and the different chemical reactivities of the two surfaces [Ag(100) and Cu(111)] influence the structural formation of QA aggregates. We compare our results to the results for QA on Ag(111) reported previously by Wagner et al. [JPCC2014, 118, 10911-10920].
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Imani, Z., Mundlapati, V. R., Goldsztejn, G., Brenner, V., Gloaguen, E., Guillot, R., Baltaze, J. P., Le Barbu-Debus, K., Robin, S., Zehnacker, A., Mons, M., & Aitken, D. J. (2020). Conformation control through concurrent N–H⋯S and N–H⋯O=C hydrogen bonding and hyperconjugation effects. CHEMICAL SCIENCE, 11(34), 9191–9197.
Résumé: In addition to the classical N-HMIDLINE HORIZONTAL ELLIPSISO-C non-covalent interaction, less conventional types of hydrogen bonding, such as N-HMIDLINE HORIZONTAL ELLIPSISS, may play a key role in determining the molecular structure. In this work, using theoretical calculations in combination with spectroscopic analysis in both gas phase and solution phase, we demonstrate that both these H-bonding modes exist simultaneously in low-energy conformers of capped derivatives of Attc, a thietane alpha-amino acid. 6-Membered ring inter-residue N-HMIDLINE HORIZONTAL ELLIPSISS interactions (C6(gamma)), assisted by hyperconjugation between the thietane ring and the backbone, combine with 5-membered ring intra-residue backbone N-HMIDLINE HORIZONTAL ELLIPSISO-C interactions (C5) to provide a C5-C6(gamma)feature that stabilizes a planar geometry in the monomer unit. Two contiguous C5-C6(gamma)features in the planar dimer implicate an unprecedented three-centre H-bond of the type C-OMIDLINE HORIZONTAL ELLIPSISH(N)MIDLINE HORIZONTAL ELLIPSISSR2, while the trimer adopts two C5-C6(gamma)features separated by a Ramachandran alpha-type backbone configuration. These low-energy conformers are fully characterized in the gas phase and support is presented for their existence in solution state.
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Jänkälä, K., Lablanquie, P., Andric, L., Khalal, M. A., Palaudoux, J., Penent, F., Bizau, J. - M., Cubaynes, D., Guilbaud, S., Ito, K., Bučar, K., Žitnik, M., Huttula, M., Kaneyasu, T., & Hikosaka, Y. (2020). Core-hole spectator Auger decay. Phys. Rev. A, 101(2), 023413.
Résumé: For an atomic state with two electrons missing from different core orbitals one may assume that the deeper hole decays first. However, it is quite probable that the double core-hole state will decay by emission of a slow Auger electron where the deeper core hole remains a spectator, especially if the outer core hole can be filled by Coster-Kronig transition, while the deeper cannot. We study here the competition of both Auger decay channels in a model system, the 1s2s2p6(3s/3p) states of Ne+ ions. As the phenomenon can take place in any decay chain involving multiple core-excited states it can be critical to understand the ion yields, the electron and x-ray emission spectra, and the molecular fragmentation.
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Joseph, J., Holzmeier, F., Bresteau, D., Spezzani, C., Ruchon, T., Hergott, J. - F., Tcherbakoff, O., D’Oliveira, P., Houver, J. - C., & Dowek, D. (2020). Angle-resolved studies of XUV–IR two-photon ionization in the RABBITT scheme. J. Phys. B: At. Mol. Opt. Phys., 53, 184007.
Résumé: Reconstruction of attosecond beating by interference of two-photon transitions (RABBITT) is an established technique for studying time-delay in photoionization of atoms and molecules. It has been recently extended to angle-resolved studies, accessing diverse fingerprint observables of the attosecond photoemission dynamics within the bound-continuum and continuum–continuum transitions. In this work, we address the general form of the ISB(θ,τ) two-photon photoelectron angular distributions (PADs) associated to the RABBITT sideband signal, as a function of the emission angle θ, and the delay τ between the XUV attosecond pulse train and the infrared (IR) dressing field at play in the RABBITT scheme. Relying on the expansion in Legendre polynomials, the PAD is synthesized in terms of a reduced set of coefficients which fully describe both its static (τ-independent) and dynamic (τ-dependent) components and enables us to retrieve any observable characterizing the PAD. This unified framework streamlines the comparison between different experimental or theoretical data sets and emphasizes how some observables depend on the experimental conditions. Along with the modelled analysis, we report new results of angle-resolved RABBITT direct ionization of the np valence orbital of Ar(3p6) and Ne(2p6), employing electron-ion coincidence momentum spectroscopy at the new Attolab facility. In this case, the nine coefficients synthesizing the PAD are further linked to the magnitude and phase of the transition dipole matrix elements, providing a fundamental test of theoretical predictions. Similarities and differences are found between Ar and Ne in the explored low energy region, up to 20 eV above the ionization threshold, where the electron dynamics is most sensitive to electronic correlation. Further interpretation of these results would benefit from a comparison with advanced many-body theoretical simulations.
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Kena Zhao, T. G., Caifen Wang, Yong Zhou, Ting Xiong, Li Wu, Xue Li, Priyanka Mittal, Senlin Shi, Ruxandra Gref. (2020). Glycoside scutellarin enhanced CD-MOF anchoring for laryngeal delivery. Acta Pharm Sin B, 10(9), 1709.
Résumé: It is essential to develop new carriers for laryngeal drug delivery in light of the lack of therapy in laryngeal related diseases. When the inhalable micron-sized crystals of gamma-cyclodextrin metal-organic framework (CD-MOF) was utilized as dry powder inhalers (DPIs) carrier with high fine particle fraction (FPF), it was found in this research that the encapsulation of a glycoside compound, namely, scutellarin (SCU) in CD-MOF could significantly enhance its laryngeal deposition. Firstly, SCU loading into CD-MOF was optimized by incubation. Then, a series of characterizations were carried out to elucidate the mechanisms of drug loading. Finally, the laryngeal deposition rate of CD-MOF was 57.72 +/- 2.19% improved by SCU, about two times higher than that of CD-MOF, when it was determined by Next Generation Impactor (NGI) at 65 L/min. As a proof of concept, pharyngolaryngitis therapeutic agent dexamethasone (DEX) had improved laryngeal deposition after being co-encapsulated with SCU in CD-MOF. The molecular simulation demonstrated the configuration of SCU in CD-MOF and its contribution to the free energy of the SCU@CD-MOF, which defined the enhanced laryngeal anchoring. In conclusion, the glycosides-like SCU could effectively enhance the anchoring of CD-MOF particles to the larynx to facilitate the treatment of laryngeal diseases.
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Le Barbu-Debus, K., Bowles, J., Jähnigen, S., Clavaguéra, C., Calvo, F., Vuilleumier, R., & Zehnacker, A. (2020). Assessing cluster models of solvation for the description of vibrational circular dichroism spectra: synergy between static and dynamic approaches. PCCP, 22, 26047–26068.
Résumé: Solvation effects are essential for defining the shape of vibrational circular dichroism (VCD) spectra. Several approaches have been proposed to include them into computational models for calculating VCD signals, in particular those resting on the “cluster-in-a-liquid” model. Here we examine the capabilities of this ansatz on the example of flexible (1S,2S)-trans-1-amino-2-indanol solvated in dimethyl sulfoxide (DMSO). We compare cluster sets obtained from static calculations with results from explicit molecular dynamics (MD) trajectories based on either force field (FF) or first-principles (FP) methods. While the FFMD approach provides a broader sampling of configurational space, FPMD and time-correlation functions of dipole moments account for anharmonicity and entropy effects in the VCD calculation. They provide a means to evaluate the immediate effect of the solvent on the spectrum. This survey singles out several challenges associated with the use of clusters to describe solvation effects in systems showing shallow potential energy surfaces and non-covalent interactions. Static structures of clusters involving a limited number of solvent molecules satisfactorily capture the main effects of solvation in the bulk limit on the VCD spectra, if these structures are correctly weighted. The importance of taking into consideration their fluxionality, i.e. different solvent conformations sharing a same hydrogen bond pattern, and the limitations of small clusters for describing the solvent dynamics are discussed.
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Le Barbu-Debus, K., Scuderi, D., Lepère, V., & Zehnacker, A. (2020). Homochiral vs. heterochiral sodium core dimers of tartaric acid esters: A mass spectrometry and vibrational spectroscopy study. Journal of Molecular Structure, 1205, 127583.
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Le Sech, C., Le Sech C, Hirayama, R., & Hirayama R. (2020). Dual aspect of radioenhancers and free radical scavengers. Free Radic Biol Med, .
Résumé: Combining an external beam of ionizing particles with agents to augment the dose effects of cell damages for therapeutic purpose is an important goal of radiotherapy. This last decade intensive works have focused on metal compounds or metal nanoparticles as radiosensitizers to increase the oxidative damages under irradiation. In principle the nanoparticles can be coated with a functionalized shell, to achieve a specific targeting of the tissues, making such approach attractive. The functionalized coating is made of polymers. These molecules are able to scavenge the free radicals, thus, the coating can decrease the overall efficacy of the radiation. The purpose of the present model is to analyse the role of free hydroxyl radicals in the dual behaviour of the added agent. Consideration of the efficiency of the added agents versus the Linear Energy Transfer – LET – of the ionizing particles is made. It is shown that an efficient agent combined with a low-LET particle beams might become less efficient when high-LET particles like heavy-ions are used. These general considerations should be useful to optimize the design of the nanoparticles to be combined with the different kind of ionizing particles.
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Lefebvre, R., & Atabek, O. (2020). Progress toward full optical control of ultracold-molecule formation: Role of scattering Feshbach resonances. Phys. Rev. A, 101(6), 063406.
Résumé: Feshbach resonances play a major role in translationally cold-molecule preparation. In this context, their laser control is of crucial importance. This work is devoted to the depiction of some basic mechanisms of such a control using intense, short laser pulses and referring to nonlinear multiphoton processes. Our goal is to adiabatically transport a Feshbach resonance onto a zero-width resonance, the characteristics of which have already been discussed in the literature. Three processes are then addressed: (i) during the rise of the pulse and its plateau, the preparation of a so-called laser bound molecule (LBM) still stable, but structurally different from the standard chemically bound molecule; (ii) during the pulse switching off, an adiabatic transport of this LBM on a very few excited vibrational levels, and (iii) concomitantly, a filtration strategy to photodissociate all these levels except one, giving thus rise to but a single field-free excited vibrational state. With or without an eventual stimulated Raman adiabatic passage technique to bring all the population to the ground rovibrational state, this opens an alternate for a full optical control of ultracold-molecule formation. The illustrative example, offering the potentiality to be transposed to other diatomics, is H_2^+.
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Li, X., Porcino, M., Martineau-Corcos, C., Guo, T., Xiong, T., Zhu, W. F., Patriarche, G., Pechoux, C., Perronne, B., Hassan, A., Kummerle, R., Michelet, A., Zehnacker-Rentien, A., Zhang, J. W., & Gref, R. (2020). Efficient incorporation and protection of lansoprazole in cyclodextrin metal-organic frameworks. International Journal of Pharmaceutics, 585, 119442.
Résumé: Lansoprazole (LPZ) is an acid pump inhibitor, which readily degrades upon acidic or basic conditions and under heating. We investigated here LPZ stability upon incorporation in particles made of cyclodextrin metal-organic frameworks (CD-MOFs). LPZ loaded CD-MOFs were successfully synthesized, reaching high LPZ payloads of 23.2 +/- 2.1 wt%, which correspond to a molar ratio of 1:1 between LPZ and gamma-CD. The homogeneity of LPZ loaded CD-MOFs in terms of component distribution was confirmed by elemental mapping by STEM-EDX. Both CTAB, the surfactant used in the CD-MOFs synthesis, and LPZ compete for their inclusion in the CD cavities. CTAB allowed obtaining regular cubic particles of around 5 μm with 15 wt% residual CTAB amounts. When LPZ was incorporated, the residual CTAB amount was less than 0.1 wt%, suggesting a higher affinity of LPZ for the CDs than CTAB. These findings were confirmed by molecular simulations. Vibrational circular dichroism studies confirmed the LPZ incorporation inside the CDs. Solid-state NMR showed that LPZ was located in the CDs and that it remained intact even after three years storage. Remarkably, the CD-MOFs matrix protected the drug upon thermal decomposition. This study highlights the interest of CD-MOFs for the incorporation and protection of LPZ.
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Li, X., Salzano, G., Qiu, J., Menard, M., Berg, K., Theodossiou, T., Ladaviere, C., & Gref, R. (2020). Drug-Loaded Lipid-Coated Hybrid Organic-Inorganic “Stealth” Nanoparticles for Cancer Therapy. Front Bioeng Biotechnol, .
Résumé: Hybrid porous nanoscale metal organic frameworks (nanoMOFs) made of iron trimesate are attracting increasing interest as drug carriers, due to their high drug loading capacity, biodegradability, and biocompatibility. NanoMOF surface modification to prevent clearance by the innate immune system remains still challenging in reason of their high porosity and biodegradable character. Herein, FDA-approved lipids and poly(ethylene glycol) (PEG)-lipid conjugates were used to engineer the surface of nanoMOFs by a rapid and convenient solvent-exchange deposition method. The resulting lipid-coated nanoMOFs were extensively characterized. For the first time, we show that nanoMOF surface modification with lipids affords a better control over drug release and their degradation in biological media. Moreover, when loaded with the anticancer drug Gem-MP (Gemcitabine-monophosphate), iron trimesate nanoMOFs acted as “Trojan horses” carrying the drug inside cancer cells to eradicate them. Most interestingly, the PEG-coated nanoMOFs escaped the capture by macrophages. In a nutshell, versatile PEG-based lipid shells control cell interactions and open perspectives for drug targeting.
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Liu, P., Yin, L., Zhang, Z., Ding, B., Shi, Y., Li, Y., Zhang, X., Song, X., Guo, Y., Chen, L., Chen, X., Gainullin, I. K., & Esaulov, V. A. (2020). Anomalous neutralization characteristics in Na+ neutralization on Al(111) surfaces. PHYSICAL REVIEW A, 101(3), 032706.
Résumé: The jellium model of free electron gas and its extended version have been widely used to understand the neutralization of alkali-metal ions on metal surfaces. We report an unexpected deviation from its prediction that we observed in the neutralization of Na+ ions scattering from an Al(111) surface. We find that the neutralization probability decreases monotonically with increasing ion velocity for the specular scattering condition, which is consistent with the well-known parallel velocity effect. However, the neutralization probability exhibits an unexpected bell shape with the variation of outgoing angle for a given incident energy. Calculations based on the jellium model using the rate equation and including the dynamic parallel velocity effect are presented. Their results agree with the velocity dependence of the neutral fraction, but completely fail in reproducing the angle dependence. This anomalous angle dependence could be due to the appearance of inelastic processes, corresponding to inner 2p electron promotion in hard encounters with Al atoms for large incidence angles, when the interatomic distances become small. This can lead to the formation of autoionizing Na states that result in the formation of extra Na+ ions, not accounted for in the jellium model.
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Ludwig, M., Aguirregabiria, G., Ritzkowsky, F., Rybka, T., Marinica, D. C., Aizpurua, J., Borisov, A. G., Leitenstorfer, A., & Brida D. (2020). Sub-femtosecond electron transport in a nanoscale gap. Nat. Phys., 16, 341–345.
Résumé: The strong fields associated with few-cycle pulses can drive highly nonlinear phenomena, allowing the direct control of electrons in condensed matter systems. In this context, by employing near-infrared single-cycle pulse pairs, we measure interferometric autocorrelations of the ultrafast currents induced by optical field emission at the nanogap of a single plasmonic nanocircuit. The dynamics of this ultrafast electron nanotransport depends on the precise temporal field profile of the optical driving pulse. Current autocorrelations are acquired with sub-femtosecond temporal resolution as a function of both pulse delay and absolute carrier-envelope phase. Quantitative modelling of the experiments enables us to monitor the spatiotemporal evolution of the electron density and currents induced in the system and to elucidate the physics underlying the electron transfer driven by strong optical fields in plasmonic gaps. Specifically, we clarify the interplay between the carrier-envelope phase of the driving pulse, plasmonic resonance and quiver motion.
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Ludwig, M., Kazansky, A. K., Aguirregabiria, G., Marinica, D. C., Falk, M., Leitenstorfer, A., Brida, D., Aizpurua, J., & Borisov, A. G. (2020). Active control of ultrafast electron dynamics in plasmonic gaps using an applied bias. Phys. Rev. B, 101(24), 241412.
Résumé: In this joint experimental and theoretical study we demonstrate coherent control of the optical field emission and electron transport in plasmonic gaps subjected to intense single-cycle laser pulses. Our results show that an external THz field or a minor dc bias, orders of magnitude smaller than the optical bias owing to the laser field, allows one to modulate and direct the electron photocurrents in the gap of a connected nanoantenna operating as an ultrafast nanoscale vacuum diode for lightwave electronics. Using time-dependent density functional theory calculations we elucidate the main physical mechanisms behind the observed effects and show that an applied dc field significantly modifies the optical field emission and quiver motion of photoemitted electrons within the gap. The quantum many-body theory reproduces the measured net electron transport in the experimental device, which allows us to establish a paradigm for controlling nanocircuits at petahertz frequencies.
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Ma, J., Zhang, H., Lavorel, B., Billard, F., Wu, J., Boulet, C., Hartmann, J. - M., & Faucher, O. (2020). Ultrafast collisional dissipation of symmetric-top molecules probed by rotational alignment echoes. Physical Review A, 101(4), 043417.
Résumé: We experimentally and theoretically investigate the ultrafast collisional dynamics of a symmetric-top molecule (
C2H6) in pure gas and mixtures with He at high density by employing the rotational alignment echo created by a pair of time-delayed intense laser kicks. The decrease of the amplitude of the echo when increasing the delay between the two laser pulses, reflecting the collisional relaxation of the system, is measured by probing the transient birefringence induced in the medium. The theoretical predictions, carried using purely classical molecular dynamics simulations, reproduce well the observed features, as demonstrated previously for a linear molecule. The analysis shows that the dissipation of the ethane alignment, despite the fact that this species has an extra rotational degree of freedom as compared to a linear molecule, barely involves more complex collisional relaxation channels due to characteristics of the C2H6−C2H6 and C2H6−He interactions. However, our findings reveal that the dissipative dynamics of a symmetric-top molecule can be properly approached using the recently discovered rotational alignment echoes, which, so far, have been only tested for probing rotational decoherence of simpler (linear) molecules.
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Martin-Drumel, M. - A., Porterfield, J. P., Goubet, M., Asselin, P., Georges, R., Soulard, P., Nava, M., Changala, B., Billinghurst, B. E., Pirali, O., McCarthy, M. C., & Baraban, J. H. (2020). Synchrotron-Based High Resolution Far-Infrared Spectroscopy of trans-Butadiene. The Journal of Physical Chemistry A, 124(12), 2427–2435.
Résumé: The high resolution far-infrared spectrum of trans-butadiene has been re-investigated by Fourier-transform spectroscopy at two synchrotron radiation facilities, SOLEIL and the Canadian Light Source, at temperatures ranging from 50 to 340 K. Beyond the well-studied bands, two new fundamental bands lying below 1100 cm-1, ν10 and ν24, have been assigned using a combination of cross-correlation (ASAP software) and Loomis-Wood type (LWWa software) diagrams. While the ν24 analysis was rather straightforward, ν10 exhibits obvious signs of a strong perturbation, presumably owing to interaction with the dark ν9+ν12 state. Effective rotational constants have been derived for both the v10 = 1 and v24 = 1 states. Since only one weak, infrared active fundamental band (ν23) of trans-butadiene remains to be observed at high resolution in the far-infrared, searches for the elusive gauche conformer can now be undertaken with considerably greater confidence in the dense ro-vibrational spectrum of the trans form.
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Melosso, M., Belloche, A., Martin-Drumel, M. - A., Pirali, O., Tamassia, F., Bizzocchi, L., Garrod, R. T., Müller, H. S. P., Menten, K. M., Dore, L., & Puzzarini, C. (2020). Far-infrared laboratory spectroscopy of aminoacetonitrile and first interstellar detection of its vibrationally excited transitions⋆. Astronomy & Astrophysics, 641, A160.
Résumé: Context. Aminoacetonitrile, a molecule detected in the interstellar medium only toward the star-forming region Sagittarius B2 (Sgr B2), is considered an important prebiotic species; in particular, it is a possible precursor of the simplest amino acid glycine. To date, observations have been limited to ground state emission lines, whereas transitions from within vibrationally excited states remained undetected.
Aims. We wanted to accurately determine the energies of the low-lying vibrational states of aminoacetonitrile, which are expected to be populated in Sgr B2(N1), the main hot core of Sgr B2(N). This step is fundamental in order to properly evaluate the vibration-rotation partition function of aminoacetonitrile as well as the line strengths of the rotational transitions of its vibrationally excited states. This is necessary to derive accurate column densities and secure the identification of these transitions in astronomical spectra.
Methods. The far-infrared ro-vibrational spectrum of aminoacetonitrile has been recorded in absorption against a synchrotron source of continuum emission. Three bands, corresponding to the lowest vibrational modes of aminoacetonitrile, were observed in the frequency region below 500 cm−1. The combined analysis of ro-vibrational and pure rotational data allowed us to prepare new spectral line catalogs for all the states under investigation. We used the imaging spectral line survey ReMoCA performed with ALMA to search for vibrationally excited aminoacetonitrile toward Sgr B2(N1). The astronomical spectra were analyzed under the local thermodynamic equilibrium (LTE) approximation.
Results. Almost 11 000 lines have been assigned during the analysis of the laboratory spectrum of aminoacetonitrile, thanks to which the vibrational energies of the v11 = 1, v18 = 1, and v17 = 1 states have been determined. The whole dataset, which includes high J and Ka transitions, is well reproduced within the experimental accuracy. Reliable spectral predictions of pure rotational lines can now be produced up to the THz region. On the basis of these spectroscopic predictions, we report the interstellar detection of aminoacetonitrile in its v11 = 1 and v18 = 1 vibrational states toward Sgr B2(N1) in addition to emission from its vibrational ground state. The intensities of the identified v11 = 1 and v18 = 1 lines are consistent with the detected v = 0 lines under LTE at a temperature of 200 K for an aminoacetonitrile column density of 1.1 × 1017 cm−2.
Conclusions. This work shows the strong interplay between laboratory spectroscopy exploiting (sub)millimeter and synchrotron-based far-infrared techniques, and observational spectral surveys to detect complex organic molecules in space and quantify their abundances.
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Melosso, M., Bizzocchi, L., Adamczyk, A., Canè, E., Caselli, P., Colzi, L., Dore, L., Giuliano, B. M., Guillemin, J. - C., Martin-Drumel, M. - A., Pirali, O., Pietropolli Charmet, A., Prudenzano, D., Rivilla, V. M., & Tamassia, F. (2020). Extensive ro-vibrational analysis of deuterated-cyanoacetylene (DC3N) from millimeter-wavelengths to the infrared domain. JQSRT, 254, 107221.
Résumé: Cyanoacetylene, the simplest cyanopolyyne, is an abundant interstellar molecule commonly observed in a vast variety of astronomical sources. Despite its importance as a potential tracer of the evolution of star-forming processes, the deuterated form of cyanoacetylene is less observed and less studied in the laboratory than the main isotopologue. Here, we report the most extensive spectroscopic characterization of DC3N to date, from the millimeter domain to the infrared region. Rotational and ro-vibrational spectra have been recorded using millimeter-wave frequency-modulation and Fourier-transform infrared spectrometers, respectively. All the vibrational states with energy up to 1015 cm−1 have been analyzed in a combined fit, where the effects due to anharmonic resonances have been adequately accounted for. The analysis contains over 6500 distinct transition frequencies, from which all the vibrational energies have been determined with good precision for many fundamental, overtone, and combination states. This work provides a comprehensive line catalog for astronomical observations of DC3N.
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Melosso, M., Bizzocchi, L., Sipilä, O., Giuliano, B. M., Dore, L., Tamassia, F., Martin-Drumel, M. - A., Pirali, O., Redaelli, E., & Caselli, P. (2020). First detection of NHD and ND2 in the interstellar medium -- Amidogen deuteration in IRAS 16293–2422. A&A, 641, A153.
Résumé: Context. Deuterium fractionation processes in the interstellar medium (ISM) have been shown to be highly efficient in the family of nitrogen hydrides. To date, observations have been limited to ammonia (NH2D, NHD2, ND3) and imidogen radical (ND) isotopologues.
Aims. We want to explore the high-frequency windows offered by the Herschel Space Observatory to search for deuterated forms of the amidogen radical NH2 and to compare the observations against the predictions of our comprehensive gas-grain chemical model.
Methods. Making use of the new molecular spectroscopy data recently obtained at high frequencies for NHD and ND2, we searched for both isotopologues in the spectral survey toward the Class 0 protostar IRAS 16293-2422, a source in which NH3, NH, and their deuterated variants have previously been detected. We used the observations carried out with HIFI (Heterodyne Instrument for the Far-Infrared) in the framework of the key program “Chemical Herschel surveys of star forming regions” (CHESS).
Results. We report the first detection of interstellar NHD and ND2. Both species are observed in absorption against the continuum of the protostar. From the analysis of their hyperfine structure, accurate excitation temperature and column density values are determined. The latter were combined with the column density of the parent species NH2 to derive the deuterium fractionation in amidogen. We find a high deuteration level of amidogen radical in IRAS 16293-2422, with a deuterium enhancement about one order of magnitude higher than that predicted by earlier astrochemical models. Such a high enhancement can only be reproduced by a gas-grain chemical model if the pre-stellar phase preceding the formation of the protostellar system has a long duration: on the order of one million years.
Conclusions. The amidogen D/H ratio measured in the low-mass protostar IRAS 16293-2422 is comparable to that derived for the related species imidogen and much higher than that observed for ammonia. Additional observations of these species will provide more insights into the mechanism of ammonia formation and deuteration in the ISM. Finally, we indicate the current possibilities to further explore these species at submillimeter wavelengths.
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Mery, M., Chen, L., Valdés, J. E., & Esaulov, V. A. (2020). On the determination of stopping cross-sections in ion scattering in solids and deviations from standard models. RADIATION EFFECTS AND DEFECTS IN SOLIDS, 175(1-2), 160–176.
Résumé: When atomic particles traverse solids they suffer energy losses due to elastic scattering from nuclei and excitation of electron-hole pairs. These are referred to as nuclear and electronic stoppings respectively. In this paper we discuss methods of determining energy losses and 'stopping' cross-sections in ion transmission through thin films, as well as in large angle and grazing backscattering from surfaces. This is done on the basis of deterministic simulations of ion scattering by following ion trajectories as they pass through the solid and sample regions of different electron densities depending on the distance from atomic nuclei. The ab initio calculated electron densities in the crystal are used to determine the stopping power, as predicted by the free electron gas model, and including a threshold value for d electron excitation. We discuss some aspects that are not included in standard descriptions based on the use of free electron models and averaged effective electron densities. In this context, we point out the possibility of inelastic processes involving inner-shell excitations, and briefly summarise main findings.
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Panadés-Barrueta, R. L., & Peláez, D. (2020). Low-rank sum-of-products finite-basis-representation (SOP-FBR) of potential energy surfaces. The Journal of Chemical Physics, 153, 234110.
Résumé: The sum-of-products finite-basis-representation (SOP-FBR) approach for the automated multidimensional fit of potential energy surfaces (PESs) is presented. In its current implementation, the method yields a PES in the so-called Tucker sum-of-products form, but it is not restricted to this specific ansatz. The novelty of our algorithm lies in the fact that the fit is performed in terms of a direct product of a Schmidt basis, also known as natural potentials. These encode in a non-trivial way all the physics of the problem and, hence, circumvent the usual extra ad hoc and a posteriori adjustments (e.g., damping functions) of the fitted PES. Moreover, we avoid the intermediate refitting stage common to other tensor-decomposition methods, typically used in the context of nuclear quantum dynamics. The resulting SOP-FBR PES is analytical and differentiable ad infinitum. Our ansatz is fully general and can be used in combination with most (molecular) dynamics codes. In particular, it has been interfaced and extensively tested with the Heidelberg implementation of the multiconfiguration time-dependent Hartree quantum dynamical software package.
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Pandey, A. K., Papagiannouli, I., Sanson, F., Baynard, E., Demailly, J., Kazamias, S., Pittman, M., Neveu, O., Lucas, B., Le Marec, A., Klisnick, A., Calisti, A., Larroche, O., Ros, D., & Guilbaud, O. (2020). Towards subpicosecond pulses from solid target plasma based seeded soft X-ray laser. Opt Express, 28(20), 28924.
Résumé: We investigate the coherence of plasma-based soft X-ray laser (XRL) for different conditions that can alter the electron density in the gain region. We first measure the source temporal coherence in amplified spontaneous emission (ASE) mode. We develop a data analysis procedure to extract both its spectral width and pulse duration. These findings are in agreement with the spectral line shape simulations and seeded operation experimental results. Utilizing the deduced spectral width and pulse duration in a one-dimensional Bloch-Maxwell code, we reproduce the experimental temporal coherence properties of the seeded-XRL. Finally, we demonstrate efficient lasing in ASE and seeded mode at an electron density two times higher than the routine conditions. In this regime, using Bloch-Maxwell modeling, we predict the pulse duration of the seeded XRL to be approximately 500fs.
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Penent, F., Cubaynes, D., Lablanquie, P., Palaudoux, J., Guilbaud, S., Moustier, O., Guigand, J., & Bizau, J. - M. (2020). Modification of a Cylindrical Mirror Analyzer for High Efficiency Photoelectron Spectroscopy on Ion Beams. Atoms, 8(4), 63.
Résumé: An existing cylindrical mirror analyzer (CMA) that was initially equipped with eight channeltrons detectors has been modified to install large micro-channel plate detectors to perform parallel detection of electrons on an energy range corresponding to ~12% of the mean pass energy. This analyzer is dedicated to photoelectron spectroscopy of ions ionized by synchrotron radiation. The overall detection efficiency is increased by a factor of ~20 compared to the original analyzer. A proof of principle of the efficiency of the analyzer has been done for Xe5+ and Si+ ions and will allow photoelectron spectroscopy on many other ionic species.
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Pérez-Mellor, A., Le Barbu-Debus, K., & Zehnacker, A. (2020). Solid-state synthesis of cyclo LD-diphenylalanine: A chiral phase built from achiral subunits. Chirality, 32(5), 693–703.
Résumé: Abstract The solid-state structure of LL/DD or LD/DL diphenylalanine diluted in KBr pellets is studied by infrared (IR) absorption and vibrational circular dichroism (VCD) spectroscopy. The structure depends on the absolute configuration of the residues. The natural LL diphenylalanine exists as a mixture of neutral and zwitterionic structures, depending on the humidity of the sample, while mostly the zwitterion is observed for LD diphenylalanine whatever the experimental conditions. The system undergoes spontaneous cyclization upon heating at 125°C, resulting to the formation of a diketopiperazine (DKP) dipeptide as the only product. The reaction is faster for LD than for LL diphenylalanine. As expected, LL and DD diphenylalanine react to form the LL and DD enantiomers of cyclo diphenylalanine. Interestingly, the DKP dipeptides formed from the LD or DL diphenylalanine show unexpected optical activity, with opposite VCD spectra for the products formed from the LD and DL reagents. This is explained in terms of chirality synchronization between the monomers within the crystal, which retain the symmetry of the reagent, resulting to the formation of a new chiral phase made from transiently chiral molecules.
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Raseev, G., Achlan, M. (2020). MIM thin film stack: flux enhancement due to coupling of surface plasmon polariton with wave guide modes. J. Phys. D: Appl. Phys., 53(50), 505303.
Résumé: A theoretical study is presented of the dispersion of surface plasmon polariton (SPP) and wave guide (WG) modes of a metal-insulator-metal (MIM) thin film stack. We study the dispersion of the reflectance and of the transmitted flux, originating from a local excitation source, of an asymmetric MIM air-Au-SiO2-Au-Ti-glass material system in the infrared and visible spectral region for a wide range of SiO2 and gold thicknesses, $d{\mathrm{SiO}2}$ and $d{\mathrm{Au}}$. In comparison to reference stacks of air-Au-glass or air-SiO2-glass, between 1.4 and 2.0 eV, the transmitted flux intensity is enhanced 12 or 25 times, in the emission direction of the in-plane wave vector $k\rho/k0\approx$1.05 and for a thickness of $d{\mathrm{SiO}2}\in$[300–700] nm, respectively. This enhancement is attributed to the coupling, through the avoided crossings, between the SPP${\mathrm{air}}$ and WG modes. As the fields of the SPP$_{\mathrm{air}}$ and WG modes are located in different regions of space the enhancement is nearly independent of the number of nodes in the WG mode. In summary we have identified sets of parameters giving rise to the observables enhancement. Therefore the present MIM thin film stack is a simple and a versatile system for the use in applications.
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Roncin, P. (2020). Revisiting atomic collisions physics with highly charged ions, a tribute to Michel Barat. Journal of Physics B: Atomic, Molecular and Optical Physics, 53, 202001.
Résumé: Michel Barat passed away in November 2018 at the age of 80 after a rich career in atomic and molecular collisions. He had participated actively in formalizing the electron promotion model, contribuing to low energy reactive collisions at the frontier of chemistry. He investigated electron capture mechanisms by highly charged ions (HCI), switched to collision induced cluster dissociation and finally to UV laser induced fragmentation mechanisms of biological molecules. During this highly active time he created a laboratory, organized ICPEAC and participated actively in the administration of research. This paper covers the 10 years when he mentored my scientific activity in the blossoming field of electron capture by
HCI. In spite of an impressive number of open channels, Michel found a way to capture the important parameters and to simplify the description of several electron capture processes; orientation propensity, electron promotion, true double electron capture, transfer ionisation, transfer excitation, formation of Rydberg states, and electron capture by metastable states. Each time Michel established fruitful collaborations with other groups.
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Rukmana, T. I., Moran, G., Méallet-Renault, R., Clavier, G., Kunieda, T., Ohtani, M., Demura, T., Yasukuni, R., & Hosokawa, Y. (2020). Photoinjection of fluorescent nanoparticles into intact plant cells using femtosecond laser amplifier. APL Photonics, 5, 066104.
Résumé: The introduction of nanoparticles to intact plant cells is promising as a transporting technique of a wide range of functional molecules. Among various molecular delivery methods, femtosecond laser photoinjection possesses target selectivity at a single cell level and is potentially applicable for many types of materials. However, for plant cells, the vacuoles’ turgor pressure and the thick cell wall limit the application of photoinjection to only small objects. In this work, we overcome these limitations by employing a single pulse irradiation from a femtosecond laser amplifier. After laser irradiation on intact tobacco BY-2 cells, 80 nm fluorescent nanoparticles dispersed in a cell culture medium were successfully injected into their cytoplasm. This breakthrough would lead to a vast utilization of nanoparticles containing functional molecules for single cell manipulation in plant physiological study and genetic engineering. Such an injection was observed even when the laser pulse was focused neither on the cell wall nor on the cell membrane, but beside the cells. With these results, we suggest pore formation on the cell membrane by instantaneous deformation induced by an intense femtosecond laser pulse as an injection mechanism of nanoparticles. Reported photomechanical effects of the amplified femtosecond laser on the permeability of the biological membrane would offer new perspectives in biophotonics.
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Rukmana, T. I., Yasukuni, R., Moran, G., Méallet-Renault, R., Clavier, G., Kunieda, T., Ohtani, M., Demura, T., & Hosokawa, Y. (2020). Direct observation of nanoparticle diffusion in cytoplasm of single plant cells realized by photoinjection with femtosecond laser amplifier. Applied Physics Express, 13(11), 117002.
Résumé: Diffusion is an important process for molecular transport inside plant cells. Recent advancement in plant physiological study demands verification of the diffusion process at the single cell level. In this work, the real-time intracellular diffusion of nanoparticles in the cytoplasm of single plant cells was realized using photoinjection with femtosecond laser amplifier. The diffusion behavior was analyzed by estimating the diffusion coefficient in cytoplasm. In addition, the effect of particle size to the photoinjection efficiency and diffusion was evaluated. Surprisingly, the intercellular diffusion of nanoparticles between single plant cells was also directly observed.
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Sautrot-Ba, P., Jockusch, S., Nguyen, T. - T. - T., Grande, D., Chiapionne, A., Abbad-Andaloussi, S., Pan, M., Méallet-Renault, R., & Versace, D. - L. (2020). Photoinduced synthesis of antibacterial hydrogel from aqueous photoinitiating system. European Polymer Journal, 138(5), 109936.
Résumé: A new photoactivable material based on polyethylene imine with allyl functions (A-PEI monomer) was synthesized to develop new hydrogel. The water-based photoinitiating system consisting of anthraquinone-2-sulfonic acid (AQS) and N-methyldiethanol amine (MDEA) was studied by laser flash photolysis and electron paramagnetic resonance. LED@385 nm exposure of this combination of AQS with MDEA in aqueous medium has led to the formation of α-aminoalkyl radicals which were able to cross-link the acrylamide and A-PEI to generate new antibacterial materials in reduced time and under air. Interestingly, the addition of the multifunctional A-PEI monomer to acrylamide derived monomers has led to faster gel formation and an increase of the instantaneous G’ modulus value. The resulting hydrogel containing quaternary ammonium groups on its surface has demonstrated excellent anti-adherence and biocide properties against Escherichia coli and Staphylococcus aureus.
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Si, Y., Grazon, C., Clavier, G., Rieger, J., Tian, Y., Audibert, J. - F., Sclavi, B., & Méallet-Renault, R. (2020). Fluorescent Copolymers for Bacterial Bioimaging and Viability Detection. ACS Sensors, 5(9), 2843–2851.
Résumé: Novel fluorescent labels with high photostability and high biocompatibility are required for microbiological imaging and detection. Here, we present a green fluorescent polymer chain (GFPC), designed to be nontoxic and water-soluble, for multicolor bioimaging and real-time bacterial viability determination. The copolymer is synthesized using a straightforward one-pot reversible addition–fragmentation chain-transfer (RAFT) polymerization technique. We show that GFPC does not influence bacterial growth and is stable for several hours in a complex growth medium and in the presence of bacteria. GFPC allows the labeling of the bacterial cytoplasm for multicolor bacterial bioimaging applications. It can be used in combination with propidium iodide (PI) to develop a rapid and reliable protocol to distinguish and quantify, in real time, by flow cytometry, live and dead bacteria.
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Siddharth Sivankutty, I. C. H., Nicolas Bourg, Guillaume Dupuis, Sandrine Lévêque-Fort. (2020). Supercritical angle fluorescence for enhanced axial sectioning in STED microscopy. Methods, 174, 20–26.
Résumé: We demonstrate subwavelength axial sectioning on biological samples with a stimulated emission depletion (STED) microscope combined with supercritical angle fluorescence (SAF) detection. SAF imaging is a powerful technique for imaging the membrane of the cell based on the direct exploitation of the fluorophore emission properties. Indeed, only when fluorophores are close to the interface can their evanescent near-field emission become propagative and be detected beyond the critical angle. Therefore, filtering out the SAF emission from the undercritical angle fluorescence (UAF) emission in the back focal plane of a high-NA objective lens permits nanometer axial sectioning of fluorescent emitters close to the coverslip. When combined with STED microscopy, a straightforward gain in axial resolution can be reached without any alteration of the STED beam path. Indeed, STED-SAF implementation only requires a modification in the detection path of the STED microscope and thus could be widely implemented.
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Strom, A. I., Gutierrez-Quintanilla A, Chevalier, M., Ceponkus J, Crepin, C., & Anderson DT. (2020). Matrix Isolation Spectroscopy and Nuclear Spin Conversion of Propyne Suspended in Solid Parahydrogen. J Phys Chem A, 124(22), 4471–4483.
Résumé: Parahydrogen (pH2) quantum solids are excellent matrix isolation hosts for studying the rovibrational dynamics and nuclear spin conversion (NSC) kinetics of molecules containing indistinguishable nuclei with nonzero spin. The relatively slow NSC kinetics of propyne (CH3CCH) isolated in solid pH2 is employed as a tool to assign the rovibrational spectrum of propyne in the 600-7000 cm(-1) region. Detailed analyses of a variety of parallel (DeltaK = 0) and perpendicular (DeltaK=+/-1) bands of propyne indicate that the end-over-end rotation of propyne is quenched, but K rotation of the methyl group around the C3 symmetry axis still persists. However, this single-axis K rotation is significantly hindered for propyne trapped in solid pH2 such that the energies of the K rotational states do not obey simple energy-level expressions. The NSC kinetics of propyne follows first-order reversible kinetics with a 287(7) min effective time constant at 1.7 K. Intensity-intensity correlation plots are used to determine the relative line strengths of individual ortho- and para-propyne rovibrational transitions, enabling an independent estimation of the ground vibrational state effective A'' constant of propyne.
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Szczepaniak, U., Gutiérrez-Quintanilla, A., Crépin, C., Guillemin, J. - C., Turowski, M., Custer, T., & Kołos, R. (2020). Spectroscopy of methylcyanodiacetylene revisited. Solid parahydrogen and solid neon matrix studies. Journal of Molecular Structure, 1218, 128437.
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Szczepaniak, U., Ozaki, K., Tanaka, K., Ohnishi, Y., Wada, Y., Guillemin, J. - C., Crépin, C., Kołos, R., Morisawa, Y., Suzuki, H., & Wakabayashi, T. (2020). Phosphorescence excitation mapping and vibrational spectroscopy of HC9N and HC11N cyanopolyynes in organic solvents. Journal of Molecular Structure, 1214, 128201.
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Talotta, F., Morisset, S., Rougeau, N., Lauvergnat, D., & Agostini, F. (2020). Internal Conversion and Intersystem Crossing with the Exact Factorization. Journal of Chemical Theory and Computation, 16(8), 4833–4848.
Résumé: We present a detailed derivation of the generalized coupled-trajectory mixed quantum-classical (G-CT-MQC) algorithm based on the exact-factorization equations. The ultimate goal is to propose an algorithm that can be employed for molecular dynamics simulations of nonradiative phenomena, as the spin-allowed internal conversions and the spin-forbidden intersystem crossings. Internal conversions are nonadiabatic processes driven by the kinetic coupling between electronic states, whereas intersystem crossings are mediated by the spin–orbit coupling. In this paper, we discuss computational issues related to the suitable representation for electronic dynamics and the different natures of kinetic and spin–orbit coupling. Numerical studies on model systems allow us to test the performance of the G-CT-MQC algorithm in different situations.
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Talotta, F., Morisset, S., Rougeau, N., Lauvergnat, D., & Agostini, F. (2020). Spin-Orbit Interactions in Ultrafast Molecular Processes. Physical Review Letters, 124(3), 033001.
Résumé: We investigate spin-orbit interactions in ultrafast molecular processes employing the exact factorization of the electron-nuclear wave function. We revisit the original derivation by including spin-orbit coupling, and show how the dynamics driven by the time-dependent potential energy surface alleviates inconsistencies arising from different electronic representations. We propose a novel trajectory-based scheme to simulate spin-forbidden non-radiative processes, and we show its performance in the treatment of excited-state dynamics where spin-orbit effects couple different spin multiplets.
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Tchalala, M. R., Enriquez, H., Bendounan, A., Mayne, A. J., Dujardin, G., Kara, A., Ali, M. A., & Oughaddou, H. (2020). Tip-induced oxidation of silicene nano-ribbons. NANOSCALE ADVANCES, 2, 2309–2314.
Résumé: We report on the oxidation of self-assembled silicene nanoribbons grown on the Ag (110) surface using scanning tunneling microscopy and high-resolution photoemission spectroscopy. The results show that silicene nanoribbons present a strong resistance towards oxidation using molecular oxygen. This can be overcome by increasing the electric field in the STM tunnel junction above a threshold of +2.6 V to induce oxygen dissociation and reaction. The higher reactivity of the silicene nanoribbons towards atomic oxygen is observed as expected. The HR-PES confirm these observations: even at high exposures of molecular oxygen, the Si 2p core-level peaks corresponding to pristine silicene remain dominant, reflecting a very low reactivity to molecular oxygen. Complete oxidation is obtained following exposure to high doses of atomic oxygen; the Si 2p core level peak corresponding to pristine silicene disappears.
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Tiouitchi, G., Ali, M. A., Benyoussef, A., Hamedoun, M., Lachgar, A., Kara, A., Ennaoui, A., Mahmoud, A., Boschini, F., Oughaddou, H., El Moutaouakil, A., El Kenz, A., & Mounkachi, O. (2020). Efficient production of few-layer black phosphorus by liquid-phase exfoliation. Royal Society Open Source, 7(10), 201210.
Résumé: Phosphorene is a new two-dimensional material that has recently attracted much attention owing to its fascinating electrical, optical, thermal and chemical properties. Here, we report on high-quality exfoliation of black phosphorus nanosheets, with controllable size produced in large quantities by liquid-phase exfoliation using N-methyl-2-pyrrolidone (NMP) as a solvent under ambient conditions. The as-synthesized few layers show a great potential for solar energy conversion based on the optical results shown in this work.
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Tiouitchi, G., ElManjli, E., Mounkachi, O., Mahmoud, A., Boschini, F., Kara, A., Oughaddou, H., Hamedoun, M., Benyoussef, A., & Ait Ali, M. (2020). From Amorphous Red Phosphorus to a Few Layers of Black Phosphorus: A Low-cost and Efficient Preparation Process. JORDAN JOURNAL OF PHYSICS, 13(2), 149–155.
Résumé: In this work, we present an efficiency synthesis method of phosphorene from red phosphorus by means of black phosphorus. The latter was synthesized by using copper, tin, tin iodide and red phosphorus as precursor at low pressure-temperature. Characterizations with powder X-ray diffraction, scanning electron microscopy (SEM), energy dispersive spectrometry (EDX), high-resolution TEM (HR-TEM) and Raman spectroscopy were performed to confirm the high quality and purity of black phosphorus crystal. Liquid phase method was used to exfoliate black phosphorus to phosphorene in N-methyl-2-pyrrolidone (NMP) as solvent. Atomic force microscopy and STEM were used to confirm the exfoliation of black phophorus in a few layers of phophorene.
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Tong, Y., Bouaziz, M., Oughaddou, H., Enriquez, H., Chaouchi, K., Nicolas, F., Kubsky, S., Esaulov, V., & Bendounan, A. (2020). Phase transition and thermal stability of epitaxial PtSe2 nanolayer on Pt(111). RSC ADVANCES, 10(51), 30934–30943.
Résumé: This work relates to direct synthesis of the two-dimensional (2D) transition metal dichalchogenide (TMD) PtSe2 using an original method based on chemical deposition during immersion of a Pt(111) surface into aqueous Na2Se solution. Annealing of the sample induces significant modifications in the structural and electronic properties of the resulting PtSe2 film. We report systematic investigations of temperature dependent phase transitions by combining synchrotron based high-resolution X-ray photoemission (XPS), low temperature scanning tunnelling microscopy (LT-STM) and low energy electron diffraction (LEED). From the STM images, a phase transition from TMD 2H-PtSe2 to Pt2Se alloy monolayer structure is observed, in agreement with the LEED patterns showing a transition from (4 × 4) to (√3 × √3)R30° and then to a (2 × 2) superstructure. This progressive evolution of the surface reconstruction has been monitored by XPS through systematic de-convolution of the Pt4f and Se3d core level peaks at different temperatures. The present work provides an alternative method for the large scale fabrication of 2D transition metal dichalchogenide films.
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Tong, Y., Bouaziz, M., Zhang, W., Obeid, B., Loncle, A., Oughaddou, H., Enriquez, H., Chaouchi, K., Esaulov, V., Chen, Z., Xiong, H., Cheng, Y., & Bendounan, A. (2020). Evidence of new 2D material: Cu2Te. 2D MATERIALS, 7(3), 035010.
Résumé: The number of two-dimensional (2D) materials has grown steadily since the discovery of graphene. Each new 2D material demonstrated unusual physical properties offering a large flexibility in their tailoring for high-tech applications. Here, we report on the formation and characterization of an uncharted 2D material: 'Cu2Te alloy monolayer on Cu(111) surface'. We have successfully grown a 2D binary Te-Cu alloy using a straightforward approach based on chemical deposition method. Low electron energy diffraction (LEED) and scanning tunneling microscopy (STM) results reveal the existence of a well-ordered alloy monolayer characterized by (√3 × √3)R30° superstructure, while the x-ray photoemission spectroscopy (XPS) measurements indicate the presence of single chemical environment of the Te atoms associated with the Te-Cu bonding. Analysis of the valence band properties by angle resolved photoemission spectroscopy (ARPES); in particular the electronic states close to the Fermi level suggests a strong hybridization between Te and Cu electronic states leading to an appearance of new dispersive bands localized at the surface alloy, which is confirmed by first-principles calculations. These bands are strongly influenced by the surface reconstruction and undergo a back-folding at the boundaries of the reduced surface Brillouin zone (SBZ). More interesting, a band gap of about 0.91 eV and a Rashba splitting in the conduction band are obtained. These findings taken together clearly prove the presence of 2D-type electron system within the Cu2Te alloy layer, which is promising for spintronic application.
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Tran, T. - T., Rabah, J., Ha-Thi, M. - H., Allard, E., Nizinski, S., Burdzinski, G., Aloïse, S., Fensterbank, H., Baczko, K., Nasrallah, H., Vallée, A., Clavier, G., Miomandre, F., Pino, T., & Méallet-Renault, R. (2020). Photoinduced Electron Transfer and Energy Transfer Processes in a Flexible BODIPY-C60 Dyad. The Journal of Physical Chemistry B, 124(42), 9396–9410.
Résumé: A new donor–acceptor dyad composed of a BODIPY (4,4′-difluoro-4-bora-3a,4a-diaza-s-indacene) donor and a fullerene C60 acceptor has been synthesized and characterized. This derivative has been prepared using a clickable fullerene building block that bears an alkyne moiety and a maleimide unit. The post-functionalization of the maleimide group by a BODIPY thiol leads to a BODIPY-C60 dyad, leaving the alkyne moiety for further functional arrangement. On the basis of the combination of semi-empirical and density functional theory (DFT) calculations, spectroelectrochemical experiments, and steady-state and time-resolved spectroscopies, the photophysical properties of this new BODIPY-C60 dyad were thoroughly studied. By using semi-empirical calculations, the equilibrium of three conformations of the BODIPY-C60 dyad has been deduced, and their molecular orbital structures have been analyzed using DFT calculations. Two short fluorescence lifetimes were attributed to two extended conformers displaying variable donor–acceptor distances (17.5 and 20.0 Å). Additionally, the driving force for photoinduced electron transfer from the singlet excited state of BODIPY to the C60 moiety was calculated using redox potentials determined with electrochemical studies. Spectroelectrochemical measurements were also carried out to investigate the absorption profiles of radicals in the BODIPY-C60 dyad in order to assign the transient species in pump–probe experiments. Under selective photoexcitation of the BODIPY moiety, occurrences of both energy and electron transfers were demonstrated for the dyad by femtosecond and nanosecond transient absorption spectroscopies. Photoinduced electron transfer occurs in the folded conformer, while energy transfer is observed in extended conformers.
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Turbet, M., Boulet, C., & Karman, T. (2020). Measurements and semi-empirical calculations of CO2 + CH4 and CO2 + H2 collision-induced absorption across a wide range of wavelengths and temperatures. Application for the prediction of early Mars surface temperature. Icarus, 346, 113762.
Résumé: Reducing atmospheres have recently emerged as a promising scenario to warm the surface of early Mars enough to drive the formation of valley networks and other ancient aqueous features that have been detected so far on the surface of Mars. Here we present a series of experiments and calculations to better constrain CO2 + CH4 and CO2 + H2 collision-induced absorptions (CIAs) as well as their effect on the prediction of early Mars surface temperature. First, we carried out a new set of experimental measurements (using the AILES line of the SOLEIL synchrotron) of both CO2 + CH4 and CO2 + H2 CIAs. These measurements confirm the previous results of Turbet et al. (2019), Icarus vol. 321, while significantly reducing the experimental uncertainties. Secondly, we fitted a semi-empirical model to these CIAs measurements, allowing us to compute the CO2 + CH4 and CO2 + H2 CIAs across a broad spectral domain (0–1500 cm−1) and for a wide range of temperatures (100–600 K). Last, we performed 1-D numerical radiative-convective climate calculations (using the LMD Generic Model) to compute the surface temperature expected on the surface of early Mars for several CO2, CH4 and H2 atmospheric contents, taking into account the radiative effect of these revised CIAs. These calculations demonstrate that thick CO2 + H2-dominated atmospheres remain a viable solution for warming the surface of Mars above the melting point of water, but not CO2 + CH4-dominated atmospheres. Our calculated CO2 + CH4 and CO2 + H2 CIA spectra and predicted early Mars surface temperatures are provided to the community for future uses.
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Versace, D. - L., Moran, G., Belqat, M., Spangenberg, A., Méallet-Renault, R., Abbad-Andaloussi, S., Brezová, V., & Malval, J. - P. (2020). Highly Virulent Bactericidal Effects of Curcumin-Based μ-Cages Fabricated by Two-Photon Polymerization. ACS Applied Materials & Interfaces, 12(4), 5050–5057.
Résumé: A new antibacterial strategy is reported based on two-photon fabrication of three-dimensional curcumin-embedded μ-cages. Such devices were designed to entrap and kill Staphylococcus aureus bacteria upon visible light irradiation. The proposed concept mainly relies on the pivotal role of curcumin, which is sequentially used as a two-photon active free radical initiator and as a photogenerator of reactive oxygen species within the cage μ-volumes. We show that these μ-cages exhibit extremely high antimicrobial properties, leading to 95% bacteria mortality after only 10 min visible irradiation. A preconcentration mechanism of photogenerated oxygen species is proposed to account for this highly performing bactericidal effect whose virulence can be strikingly switched on by increasing the light exposure time from 5 to 10 min.
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Wakamura, T., Wu, N. J., Chepelianskii, A. D., Gueron, S., Och, M., Ferrier, M., Taniguchi, T., Watanabe, K., Mattevi, C., & Bouchiat, H. (2020). Spin-Orbit-Enhanced Robustness of Supercurrent in Graphene/WS2 Josephson Junctions. PHYSICAL REVIEW LETTERS, 125(26), 266801.
Résumé: We demonstrate the enhanced robustness of the supercurrent through graphene-based Josephson junctions in which strong spin-orbit interactions (SOIs) are induced. We compare the persistence of a supercurrent at high out-of-plane magnetic fields between Josephson junctions with graphene on hexagonal boron-nitride and graphene on WS{2}, where strong SOIs are induced via the proximity effect. We find that in the shortest junctions both systems display signatures of induced superconductivity, characterized by a suppressed differential resistance at a low current, in magnetic fields up to 1 T. In longer junctions, however, only graphene on WS{2} exhibits induced superconductivity features in such high magnetic fields, and they even persist up to 7 T. We argue that these robust superconducting signatures arise from quasiballistic edge states stabilized by the strong SOIs induced in graphene by WS_{2}.
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Wang, J., Ding, B., Song, X., Shi, Y., Guo, X., Liu, X., Wang, L., Wei, M., Liu, P., Liu, Y., Hu, B., Valdés, J. E., Esaulov, V. A., Chen, L., Guo, Y., & Chen, X. (2020). Nuclear versus electronic energy loss in slow Ar ion scattering on a Cu (100) surface: Experiment and simulations. PHYSICAL REVIEW A, 102(1), 012805.
Résumé: In the scattering and stopping of heavy ions on a few surface layers in solids, contributions of the electronic and nuclear energy losses can become comparable. In this work we present a study of 0.6-5-keV Ar ion scattering on a Cu (100) surface. Energy-loss spectra were measured and displayed some changes as the incident ion energy changes. Thus, a structured spectrum is observed at the higher energies. We analyze the characteristics of the spectra and contributions from the nuclear and electronic energy-loss components using both a Monte Carlo kinetics simulation assuming an averaged electron density and a semiclassical deterministic simulation with an inhomogeneous electron density in the solid. The general features of the experimental spectra were well reproduced, and semiclassical simulations allow us to identify contributions from trajectories coming from below and on top of the surface atomic layer. The relative contribution of nuclear energy loss and electronic energy loss (EEL) were delineated and a more refined analysis of the EEL for different trajectories is presented.
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Zhang, W., Enriquez, H., Zhang, X., Mayne, A. J., Bendounan, A., Dappe, Y. J., Kara, A., Dujardin, G., & Oughaddou, H. (2020). Blue phosphorene reactivity on the Au(111) surface. NANOTECHNOLOGY, 31(49), 495602.
Résumé: The synthesis of blue phosphorene by molecular beam epitaxy (MBE) has recently come under the spotlight due to its potential applications in electronic and optoelectronic devices. However, this synthesis remains a significant challenge. The surface reactivity between the P atoms and the Au atoms should be considered for the P/Au(111) system. In the MBE process, the temperature of the substrate is a key parameter for the growth of blue phosphorene. During the initial growth stage, irregularly shaped Phosphorus clusters grow on top of Au(111) surface at room temperature. When the substrate temperature is increased, these clusters transform into a phosphorene-like structure with a honeycomb lattice. An atom exchange reaction is observed between the P and first layer Au atoms under thermal activation at higher temperature, where the P atoms replace Au atoms to form a blue phosphorene structure within the top Au layer and at the step edges.
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Zhang, W., Enriquez, H., Tong, Y., Mayne, A. J., Bendounan, A., Dappe, Y. J., Kara, A., Dujardin, G., & Oughaddou, H. (2020). Phosphorus Pentamers: Floating Nanoflowers form a 2D network. ADVANCED FUNCTIONAL MATERIALS, 30, 2004531.
Résumé: An experimental investigation of a new polymorphic 2D single layer of phosphorus on Ag(111) is presented. The atomically-resolved scanning tunneling microscopy images show a new 2D material composed of freely-floating phosphorus pentamers organized into a 2D layer, where the pentamers are aligned in close-packed rows. The scanning tunneling spectroscopy measurements reveal a semiconducting character with a band gap of 1.20 eV. This work presents the formation at low temperature of a new polymorphic 2D phosphorus layer composed of a floating 2D pentamer structure. The smooth curved terrace edges and a lack of any clear crystallographic orientation with respect to the Ag(111) substrate at room temperature indicates a smooth potential energy surface that is reminiscent of a liquid-like growth phase. This is confirmed by density functional theory calculations that find a small energy barrier of only 0.17 eV to surface diffusion of the pentamers (see Supporting Information). The formation of extended, homogeneous domains is a key ingredient to opening a new avenue to integrate this new 2D material into electronic devices.
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Zhang, Z., Zhang Z, Gatti, F., Gatti F, Zhang, D. H., & Zhang DH. (2020). Full-dimensional quantum mechanical calculations of the reaction probability of the H + CH4 reaction based on a mixed Jacobi and Radau description. J Chem Phys, 152(20), 201101.
Résumé: A full-dimensional time-dependent wave packet study using mixed polyspherical Jacobi and Radau coordinates for the title reaction has been reported. The non-reactive moiety CH3 has been described using three Radau vectors, whereas two Jacobi vectors have been used for the bond breaking/formation process. A potential-optimized discrete variable representation basis has been employed to describe the vibrational coordinates of the reagent CH4. About one hundred billion basis functions have been necessary to achieve converged results. The reaction probabilities for some initial vibrational states are given. A comparison between the present approach and other methods, including reduced and full-dimensional ones, is also presented.
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Actes de Conférences |
Aguilar-Galindo, F., Díaz-Tendero, S., & Borisov, A. G. (2020). Resonant anionic states of organic molecules adsorbed on metal surfaces. In Journal of Physics: Conference Series (Vol. 1412, 202015).
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Palaudoux, J., Penent, F., Khalal, M., Jänkälä, K., Keskinen, J., Huttula, M., Bizau, J. - M., Cubaynes, D., Guilbaud, S., Zitnik, M., Bucar, K., Ito, K., Andric, L., & Lablanquie, P. (2020). Auger decay of Rubidum atom after 3d-shell ionization. In Journal of Physics: Conference Series (Vol. 1412, 152037).
Résumé: We present here the different Auger decay paths following 3d inner-shell ionization of Rubidium atom and we observe the peculiar behaviour and correlation effects due to the outer, unpaired 5s electron. This electron can be submitted to shake-up during 3d ionization. Also shake-up and shake-down of the outer electron are observed in the Auger decay. Cascade double Auger decay is the dominant process leading to Rb3+ ion.
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Staicu Casagrande, E. M., Momeni, A., & Khemliche, H. (2020). Fast atom interaction with surfaces at grazing incidence: classical and quantum scattering applied to thin film growth. In Journal of Physics: Conference Series (Vol. 1412, 202010). IOP.
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Chapitres de Livres |
I Christodoulou, C. S., R Gref. (2020). Metal-organic frameworks for drug delivery: Degradation mechanism and in vivo fate. In Metal-Organic Frameworks for Biomedical Applications (pp. 467–489).
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Gref, R., Delomenie C, Maksimenko A, Gouadon E, Percoco, G., Lati E, Desmaele, D., Zouhiri, F., & Couvreur P. (2020). Vitamin C-squalene bioconjugate promotes epidermal thickening and collagen production in human skin. (Vol. 10).
Résumé: Vitamin C (Vit C) benefits to human skin physiology notably by stimulating the biosynthesis of collagen. The main cutaneous collagens are types I and III, which are less synthesized with aging. Vit C is one of the main promotors of collagen formation but it poorly bypasses the epidermis stratum corneum barrier. To address this challenge, we developed a lipophilic version of Vit C for improving skin diffusion and delivery. Vit C was covalently conjugated to squalene (SQ), a natural lipid of the skin, forming a novel Vit C-SQ derivative suitable for cream formulation. Its biological activity was investigated on human whole skin explants in an ex vivo model, through histology and protein and gene expression analyses. Results were compared to Vit C coupled to the reference lipophilic compound palmitic acid, (Vit C-Palmitate). It was observed that Vit C-SQ significantly increased epidermal thickness and preferentially favored collagen III production in human skin after application for 10 days. It also promoted glycosaminoglycans production in a higher extent comparatively to Vit C-Palmitate and free Vit C. Microdissection of the explants to separate dermis and epidermis allowed to measure higher transcriptional effects either in epidermis or in dermis. Among the formulations studied, the strongest effects were observed with Vit C-SQ.
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Li X, Porcel, E., Menendez-Miranda, M., Qiu, J., Yang, X., Serre, C., Pastor, A., Desmaele, D., Lacombe S, & Gref, R. (2020). Highly Porous Hybrid Metal-Organic Nanoparticles Loaded with Gemcitabine Monophosphate: a Multimodal Approach to Improve Chemo- and Radiotherapy. (Vol. 15).
Résumé: Nanomedicine recently emerged as a novel strategy to improve the performance of radiotherapy. Herein we report the first application of radioenhancers made of nanoscale metal-organic frameworks (nanoMOFs), loaded with gemcitabine monophosphate (Gem-MP), a radiosensitizing anticancer drug. Iron trimesate nanoMOFs possess a regular porous structure with oxocentered Fe trimers separated by around 5 A (trimesate linkers). This porosity is favorable to diffuse the electrons emitted from nanoMOFs due to activation by gamma radiation, leading to water radiolysis and generation of hydroxyl radicals which create nanoscale damages in cancer cells. Moreover, nanoMOFs act as “Trojan horses”, carrying their Gem-MP cargo inside cancer cells to interfere with DNA repair. By displaying different mechanisms of action, both nanoMOFs and incorporated Gem-MP contribute to improve radiation efficacy. The radiation enhancement factor of Gem-MP loaded nanoMOFs reaches 1.8, one of the highest values ever reported. These results pave the way toward the design of engineered nanoparticles in which each component plays a role in cancer treatment by radiotherapy.
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Usami, N., Usami N, Hirayama, R., Hirayama R, Kobayashi, K., Kobayashi K, Furusawa, Y., Furusawa Y, Le Sech, C., & Le Sech C. (2020). Combination of agents modifying effects in hadrontherapy: modelization of the role of HO degrees free radicals..
Résumé: Purpose: A study is presented of the irradiation of cancerous cervical cell line HeLa loaded with a platinum salt, betamethasone and deoxyglucose. The presence of the platinum increases the free-radical concentration and augments the cell death rate, whereas betamethasone or deoxyglucose induces radiosensitization by the alteration of metabolic pathways. Two by two combinations of these chemicals are made to investigate the possible benefit when two radiosensitizers are present. A model is proposed to understand the results of the presence of two modifying agents on the dose effects.Materials and methods: The cells were incubated for 6 h in the presence of the following molecules: dichloro terpyridine platinum, concentration C = 350 muM, betamethasone and deoxyglucose with concentrations of C = 0.2 muM and C = 6 mM, respectively. The cells were subsequently irradiated by carbon C(6+) ion 290 MeV/amu up to a dose of 2.5 Gy, under atmospheric conditions.Results: The presence of the platinum salt or bethamethasone augments the cell death rate. The combination of betamethasone with the platinum salt also increases the cell death rate, but less than for the platinum salt alone. The explanation is that any radiosensitizer also behaves as a scavenger of free radicals. This dual behavior should be considered in any optimization of the design of radiosensitizers when different ionizing particles are used.
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Villemagne, B., Machelart A, Tran, N. C., Flipo M, Moune, M., Leroux F, Piveteau, C., Wohlkonig A, Wintjens, R., Li X, Gref R, Brodin P, Deprez, B., Baulard AR, & Willand, N. (2020). Fragment-Based Optimized EthR Inhibitors with in Vivo Ethionamide Boosting Activity. (Vol. 6).
Résumé: Killing more than one million people each year, tuberculosis remains the leading cause of death from a single infectious agent. The growing threat of multidrug-resistant strains of Mycobacterium tuberculosis stresses the need for alternative therapies. EthR, a mycobacterial transcriptional regulator, is involved in the control of the bioactivation of the second-line drug ethionamide. We have previously reported the discovery of in vitro nanomolar boosters of ethionamide through fragment-based approaches. In this study, we have further explored the structure-activity and structure-property relationships in this chemical family. By combining structure-based drug design and in vitro evaluation of the compounds, we identified a new oxadiazole compound as the first fragment-based ethionamide booster which proved to be active in vivo, in an acute model of tuberculosis infection.
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