Metal-assisted proton transfer reaction in base pairs.

We investigated the proton-transfer reactions in guanine-cytosine (GC) pairs with density functional theories. In the GC pair bound to cis-platin, the barrier height of proton-transfer reaction dramatically decreases in comparison with the GC pair without the cis-platin. This is because (a) successive processes of charge transfer from G to cisplatin thereby stabilizing both the GC and G*C pairs and (b) an additional hydrogen bond between G and the ligand of Pt atom. In two GC pairs bound to the cis-platin, the single proton-transfer reaction occurs in one of the two GC pairs. No simultaneous single proton-transfer reaction can occur in both base pairs. From the geometry optimization, two different single proton-transferred structures (cis-(CG*)d-Pt-(GC)p and cis-(CG)d-Pt-(G*C)p, where * means a proton donor of G) are as stable as the original structures (CG)d-Pt-(GC)p.