Mardi 23 septembre à 15h (heure de Paris)
Université de Cordoba
Cryogenic Ion Spectroscopy of Biologically Relevant Ions: From Nucleobase Radical Cations to NO Photodonor Anions
Understanding the photochemistry and photophysics of chromophores in nature is crucial for clarifying light’s interactions with biological systems. Light influences various biological processes, including human physiology, diagnosis, and therapy. Specifically, radical cations of nucleic bases in DNA can adopt different tautomeric forms, each with unique reactivity. Additionally, Photodynamic therapy relies on external light to activate chromophores (photosensitizers), which undergo reactions producing ROS, such as nitric oxide NO. Cold ion photodissociation spectroscopes with mass spectrometry provide a reliable approach to elucidate the molecular structures of biomolecular ions through comparison with theoretical calculations (DFT, TD DFT, or Coupled Clusters CC2 levels). In the first part of my work, we have used an original method to photo generate nucleobase radical cations by UV photo dissociation of complexes containing a silver ion. Electronic and vibrational isomer-selective spectroscopies determined the tautomer of the resulting nucleobase radical cation, providing precise experimental data to test and validate quantum chemical calculation methods on open-shell species. In the second part, I studied the meta-nitrophenolate, a model anionic NO photodonor. First, we investigated the monohydrated complex as a model of strong ionic hydrogen bonding, using anharmonic calculations to reproduce vibrational shifts. Next, meta-nitrophenolate and methylated and amino derivatives reveal that the substitution tunes the electronic excitation and still releases NO. Resonances below and above the electron affinity suggest a competition between photofragmentation and electron detachment processes.
Sous la direction de Gilles Grégoire et Gustavo Pino