Role of the Hydrogen Bond on the Internal Conversion of Photoexcited Adenosine
Résumé
Experiments and theory have revealed that hydrogen bonds modify the excited-state lifetimes of nucleosides compared to nucleobases. Nevertheless, how these bonds impact the internal conversion is still unsettled. This work simulates the nonadiabatic dynamics of adenosine conformers in the gas phase with and without hydrogen bonds between the sugar and adenine moieties. The isomer containing the hydrogen bond (syn) exhibits a significantly shorter excited-state lifetime than the one without it (anti). However, internal conversion through electron-driven proton transfer between sugar and adenine plays only a minor (although non-negligible) role in the photophysics of adenosine. Either with or without hydrogen bonds, photodeactivation preferentially occurs following the ring puckering pathways. The role of the hydrogen bond is to avoid the sugar rotation relative to adenine, shortening the distance to the ring puckering internal conversion.