Photocatalysis with Chalcogen Bonds

In a recent prebiotically plausible synthesis of 2'-deoxyribose-2-thiouridine, UV irradiation and aqueous bisulfide were employed to conduct the photoreduction of 2',2-thioanhydrouridine, resulting in the formation of the non-canonical thiopyrimidine nucleoside. To elucidate the molecular mechanisms governing the synthesis, we conducted ab initio molecular dynamics simulations and photochemical calculations. Our findings demonstrate that thioanhydrouridine can readily establish intermolecular non-covalent interactions with bisulfide anions, known as chalcogen bonds. Upon UV excitation, in such a thioanhydrouridine-uridine encounter complex, selective excited-state electron transfer can be triggered from bisulfide to the C2'-S bond of thioanhydrouridine, leading to a photoreduction process. In this work, for the first time, we demonstrate that small anions might form stable intermolecular chalcogen contacts with chromophores and, importantly, could serve as electron donor chemical species, which are activated only in a UV-rich environment.