Description
Biomolecular radiation damage is a natural process caused by high-energy photons, in which a core excited/ionized state is formed. These intermediate states can be experimentally reproduced by interaction of X-ray radiation with biochemically relevant molecules and further studied by the means of X-ray absorption spectroscopy (XAS) or Auger Electron Spectroscopy. Additionally, theoretical methods such as LR-TDDFT [1] or RASPT2 can provide additional information about the character of these excited states. They can also describe more complex processes, such as charge transfer, where the excited electron is delocalized from the virtual orbital into the surrounding solvent.
In our research, we focused on propylamine, a simple model of organic amine, that can be used as a proxy for general amines [2] or for chains of amino acids. RAES spectra were measured at the DESY synchrotron (P04 beamline) for both gas-phase, solvated propylamine and protonated propylamine. Theoretical XAS (X-ray absorption spectra) were modeled for the 1s orbital of nitrogen atom using mainly LR-TDDFT.
In the gas-phase, there were three distinct pre-edge peaks, respectively corresponding to the σ*- and two Rydberg states. All of these states were diffused around the molecule. Transferring the propylamine to solvent, the diffused core-excited states remained, which lead to observation of charge-transfer-to-solvent states in both neutral and protonated propylamine. However, the shape of the spectrum itself changed, where in solvated propylamine, the intensity of these pre-edge peaks lowered drastically and in propylammonium they were also shifted to higher energies.
1 Herbert, J. M. Phys. Chem. Chem. Phys. 2024, 26, 3755-3794
2 Ekimova, M.; Kubin, M.; Ochmann, M.; Ludwig, J.; Huse, N.; Wernet, P.; Odelius, M.; Nibbering, E. T. J; J. Phys. Chem. B 2018, 122, 7737-7746
