Solvent effect on the energetics of proton coupled electron transfer in guanine-cytosine pair in chloroform by mixed explicit and implicit solvation models

Abstract : The Watson-Crick hydrogen bonded pair formed by deoxyguanosine and deoxycytidine (GC) in chloroform has been analysed by classical Molecular Dynamics simulations, which shows the existence of several fairly stable solute/solvent hydrogen bonds. Time-Dependent Density Functional Theory (TD-DFT) calculations with M052X functional, including solvation effect by a mixed continuum/discrete model, show that solvent stabilizes G → C Charge Transfer excited states (CTGC). The Proton Transfer (PT) processes that can occur in CTGC have been mapped by TD-DFT combining State Specific and Linear Response implementations of the Polarizable Continuum Model. For the first time, the effect of explicit solute/solvent interactions on the PT is considered by studying models containing up to three CHCl3 molecules. Our study shows that PT from the N1 atom of G to the N3 of C is exoergonic also in solution but, at variance with what observed in gas-phase, a stable minimum is predicted for CTGC state in chloroform.