Two-Sided Impact of Water on the Relaxation of Inner-Valence Vacancies of Biologically Relevant Molecules

After ionization of an inner-valence electron of molecules, the resulting cationradicals store substantial internal energy which, if sufficient, can trigger ejection of an additional electron in an Auger decay usually followed by molecule fragmentation. In the environment, intermolecular Coulombic decay (ICD) and electron-transfer mediated decay (ETMD) are also operative, resulting in one or two electrons being ejected from a neighbor, thus preventing the fragmentation of the initially ionized molecule. These relaxation processes are investigated theoretically for prototypical heterocycle-water complexes of imidazole, pyrrole, and pyridine. It is found that the hydrogen-bonding site of the water molecule critically influences the nature and energetics of the electronic states involved, opening or closing certain relaxation processes of the inner-valence ionized system. Our results indicate that the relaxation mechanisms of biologically relevant systems with inner-valence vacancies on their carbon atoms can strongly depend on the presence of the electron-density donating or accepting neighbor, either water or another biomolecule.

Automated summary

After ionization, cation-radicals of molecules can release internal energy to trigger the ejection of additional electrons, leading to molecule fragmentation. However, intermolecular Coulombic decay (ICD) and electron-transfer mediated decay (ETMD) can prevent fragmentation by causing electrons to be ejected from neighboring molecules. The relaxation processes of imidazole, pyrrole, and pyridine complexes with water are affected by the hydrogen-bonding site of water molecules, which can open or close certain relaxation processes of ionized systems. The presence of electron-density donating or accepting neighbors, such as water or other biomolecules, can strongly affect the relaxation mechanisms of biologically relevant systems with inner-valence vacancies on carbon atoms.