On the interactions of hydrated metal cations (Mg2+, Mn2+, Ni2+, Zn2+) with guanine-cytosine Watson-Crick and guanine-guanine reverse-Hoogsteen DNA base pairs

Interactions between hydrated divalent metal cations (Mg2+, Mn2+, Ni2+, and Zn2+) and guanine-cytosine Watson-Crick and guanine-guanine reverse-Hoogsteen base pairs have been investigated systematically in this paper. The influence of hydrated divalent metal cations coordinated to N7 of guanine on the structures, electron density topological properties, charges, the interaction energies, and the proton transfers of the base pairs has been studied in detail at the B3LYP/6-31++G(d,p) level of theory. Furthermore, the interaction energies were refined at the electron correlated MP2/6-31++G(d,p) theory level. The energy penalty of changing the water coordination number of the metal cation in GC related complexes was also discussed. Our results show that the base pairs prefer to bind the transition metal cations (Zn2+, Mn2+, and Ni2+) rather than Mg2+, although many properties of Mn2+ are similar to those of Mg2+. The influences of hydrated Zn2+ on the base pairs are almost the same as those of hydrated Ni2+. For Ni2+ and Mg2+, the total energy of the complex with higher coordination number of metal cation is higher than the corresponding one with lower coordination number of metal cation, but for Mn2+ and Zn2+, the complex with lower coordinated metal cation is more stable. For the four divalent metal cations, we found that the energy penalties of changing their coordination numbers could correlate with the experimental ratios of unwinding and rewinding of DNA helix induced by them.