The Effect of Some Mono and Bivalent Metal Cations on the Individual Hydrogen Bond Energies in A-T and G-C Base Pairs

The effect of interactions of various Ia and IIa cations with two positions of the adenine-thymine (A-T) and guanine-cytosine (G-C) base pairs on the geometries and individual hydrogen bond (HB) energies have been investigated by using the atoms in molecules (AIM) method at the B3LYP/6-311++G(d,p) level of theory. The cations that possess higher charge/radius (q/rad) ratio make higher changes on the individual HB energies and the total binding energies of G-C base pair, while no meaningful changes are observed for the A-T base pair. The effect of coordination with cations on the H-bond energies of A-T type complexes, especially in the X'-A-T derivatives, is slight and different from the GC complexes. The changes of total binding energies are most important in the presence of bivalent cations. The estimated individual EHBs are in good agreement with the results of natural bond orbital (NBO) analysis and also with the structural parameters of HBs.