Water is a radiation protection agent for ionised pyrrole

TL;DR

This study demonstrates that a single water molecule can significantly protect ionised pyrrole from radiation damage by reducing fragmentation, highlighting water's role as a natural radiation protection agent for biomolecules.

Contribution

The paper provides experimental evidence that a hydrogen-bonded water molecule shields ionised pyrrole from damage, revealing a specific molecular mechanism of radiation protection.

Findings

Water reduces pyrrole fragmentation upon ionisation.

Protection involves dissociative water release or electron/proton transfer.

Single water molecule provides significant radiation shielding.

Abstract

Radiation-induced damage of biological matter is an ubiquitous problem in nature. The influence of the hydration environment is widely discussed, but its exact role remains elusive. Utilising well defined solvated-molecule aggregates, we experimentally observed a hydrogen-bonded water molecule acting as a radiation protection agent for ionised pyrrole, a prototypical aromatic biomolecule. Pure samples of pyrrole and pyrrole(H$_2$O) were outer-valence ionised and the subsequent damage and relaxation processes were studied. Bare pyrrole ions fragmented through the breaking of C-C or N-C covalent bonds. However, for pyrrole(H$_2$O)$^+$, we observed a strong protection of the pyrrole ring through the dissociative release of neutral water or by transferring an electron or proton across the hydrogen bond. Overall, a single water molecule strongly reduces the fragmentation probability and thus the persistent radiation damage of singly-ionised pyrrole.