State- and time-resolved observation of ultrafast intermolecular proton transfer in hydrated biomolecules.

Zhou, Jiaqi; Wu, Lu; Belina, Michal; Skitnevskaya, Anna D; Jia, Shaokui; Xue, Xiaorui; Hao, Xintai; Zeng, Qingrui et al. · Nat Commun · 2025

basic_science · Level V

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Abstract

Proton transfer underpins number of chemical and biochemical processes, yet its sub-100 fs dynamics have rarely been captured in real time. Here, we report direct and time-resolved observation of ionizing radiation-induced proton transfer in a heteroaromatic hydrate: the pyrrole-water complex. Both the electron-impact and strong-field laser experiments create a locally and doubly charged pyrrole unit (C<sub>4</sub>H<sub>5</sub>N<sup>2+</sup>), which immediately (within 60 fs) donates a proton to the adjacent H<sub>2</sub>O, generating deprotonated C<sub>4</sub>H<sub>4</sub>N<sup>+</sup> and hydronium H<sub>3</sub>O<sup>+</sup> cations that subsequently undergo Coulomb explosion. The electron-impact experiments directly revealed initial states and provided dynamical insights through fragment ions and electron coincidence momentum imaging. The strong-field femtosecond laser experiments tracked the ultrafast dynamics of proton transfer; complementary ab initio calculations unraveled the dynamical details. The 50-60 fs proton transfer qualifies as one of the fastest acid-base reactions observed to date. This study offers a novel perspective on radiation-induced proton transfer in hydrated biomolecules.