Sequence-dependent proton-transfer reaction in stacked GC pair II: The origin of stabilities of proton-transfer products

The stabilities of products for proton-transfer reactions in stacked two guanine(G)–cytosine(C) pairs are discussed by means of Hartree–Fock, MP2 and density functional methods. The stacking energy of the original 5′-d(CpG)-3′ (CG/GC) differs from that of single proton-transfer (SPT) product. On the other hand, the stacking energy of the original 5′-d(GpG)-3′ (GC/GC) is essentially equal to the double proton-transfer (DPT) products. The dispersion forces of both CG/GC and its SPT product are similar to each other. Not only dispersion force but also Coulomb attraction contributes to the stability of the SPT product of CG/GC.