Proton-Induced Charge Transfer on Imidazole and 2- Aminoimidazole. Role of the Substituent and Influence of Stepwise Hydration.

Abstract

The behaviour of potential prebiotic species in space is of main concern in the chemistry at the origin of life. Their reactivity or stability in spatial conditions, under strong UV radiations or ion bombardments remains an open question and needs wide investigations. As protons are by far the most abundant ions in space, we focus presently on proton-induced collisions on imid-azole and 2-aminoimidazole evidenced as important prebiotic RNA intermediates. Uncon-strained full optimization of the structures was performed with B3LYP/cc-pVTZ model chem-istry. The calculations were performed in a wide collision energy range in order to model vari-ous astrophysical environments, from eV in the interstellar medium, up to keV for solar winds or supernovae shock-wave protons. Such study drives for the first time a theoretical insight on the influence of the amino substituent on the proton-induced charge transfer. We evaluated besides the role of icy grain environments through a cluster approach modelling the effect of a stepwise microhydration on the process. Comparisons with oxygenated and sulfurated ana-logues address further qualitative trends on the respective stability or reactivity of such heter-ocycles which may be of tremendous interest in prebiotic chemistry. Charge transfer appears effectively quite efficient for imidazole compounds and their sulfurated analogue compared to the oxygenated heterocycle.