Paper Title
PHOTOSTABILITY OF THE GUANINE-CYTOSINE BASE PAIR WITH RESPECT TO THE OUT-OF-PLANE H-TRANSFER: A CC2 LEVEL STUDY

Abstract
We performed a theoretical study of the out-of-plane excited-state intermolecular proton transfer between the nucleic acid bases guanine (G) and cytosine (C) in the Watson-Crick model. The level of computation is CC2/aug-cc-pVDZ. The mechanism of the process was followed by using the Linear interpolation in internal coordinates approach. For this purpose we optimized the ground-state equilibrium geometry of the Watson-Crick G-C base pair and the conical intersection S0/S1 of the out-of-plane H-transfer at the CASSCF(6,6)/6-31G level of theory. The results showed an energy barrier along the 1πσ* excited-state reaction path of the mechanism which hinders the proton transfer process. This fact is in support of the photostability of the base pair. RUNNING TITLE: OUT-OF-PLANE PROTON TRANSFER IN GUANINE-CYTOSINE Keywords - Coupled-cluster calculations; Cytosine; Excited states; Guanine; Photostability; Proton transfer.