Suppression of X-Ray-Induced Radiation Damage to Biomolecules in Aqueous Environments by Immediate Intermolecular Decay of Inner-Shell Vacancies

TL;DR

This study reveals that immediate intermolecular electronic decay in aqueous environments can prevent radiation-induced damage to biomolecules by outpacing Auger decay, highlighting a protective mechanism relevant for understanding radiation effects.

Contribution

It demonstrates that direct intermolecular electronic decay occurs immediately after inner-shell ionization, providing a new insight into radiation protection mechanisms in aqueous environments.

Findings

Intermolecular decay outpaces Auger decay in aqueous environments.

Charge delocalization occurs rapidly, reducing fragmentation.

Protective effects are observable immediately after ionization.

Abstract

The predominant reason for the damaging power of high-energy radiation is multiple ionization of a molecule, either direct or via the decay of highly excited intermediates, as e.g., in the case of X-ray irradiation. Consequently, the molecule is irreparably damaged by the subsequent fragmentation in a Coulomb explosion. In an aqueous environment, however, it has been observed that irradiated molecules may be saved from fragmentation presumably by charge and energy dissipation mechanisms. Here, we show that the protective effect of the environment sets in even earlier than hitherto expected, namely immediately after single inner-shell ionization. By combining coincidence measurements of the fragmentation of X-ray-irradiated microsolvated pyrimidine molecules with theoretical calculations, we identify direct intermolecular electronic decay as the protective mechanism, outrunning the usually dominant Auger decay. Our results demonstrate that such processes play a key role in charge delocalization and have to be considered in investigations and models on high-energy radiation damage in realistic environments.