# Surprising Radiolytic Stability of 8-Thiomethyladenine in an Aqueous Solution

## TL;DR

A modified nucleobase called 8-thiomethyladenine remains stable in water when exposed to high X-ray doses, but degrades in acetonitrile, suggesting proton transfer in water stabilizes it.

## Contribution

The study reveals proton transfer in water as a key factor in stabilizing radical anions of modified nucleobases, impacting radiosensitization.

## Key findings

- ASCH3 remains radiolytically stable in aqueous solution up to 300 Gy X-ray exposure.
- Electron-induced degradation of ASCH3 occurs in aprotic acetonitrile, indicating proton transfer stabilizes its radical anion in water.
- The dissociation of the S-CH3 bond is the main reaction channel in the radical anion of ASCH3.

## Abstract

8-Thiomethyladenine (ASCH3), a potentially
radiosensitizing
modified nucleobase, has been synthesized in a reaction between 8-thioadenine
and methyl iodide. Despite favorable dissociative electron attachment
(DEA) characteristics, the radiolysis of an aqueous solution of ASCH3 with a dose of X-ray amounting to as much as 300 Gy leads
to no effects. Nevertheless, crossed electron-molecule beam experiments
in the gas phase on ASCH3 confirm the theoretical findings
regarding the stability of its radical anion, namely, the most abundant
reaction channel is related to the dissociation of the S-CH3 bond in the respective anion. Furthermore, electron-induced degradation
of ASCH3 has been observed in aprotic acetonitrile, which
is strong evidence for the involvement of proton transfer (PT) in
stabilizing the radical anion in an aqueous solution. These findings
demonstrate that PT in water can be the main player in deciding the
radiosensitizing properties of modified nucleobases/nucleosides.