Theoretical study of GC+/GC base pair derivatives

The geometries of R (R = CH3, CH3O, F, NO2) substituted GC base pair derivatives and their cations have been optimized at B3LYP/6-31G* level and the substituent effects on the neutral and cationic geometric structures and energies have been discussed. The inner reorganization energies of various base pair derivatives and the native GC base pair have been calculated to discuss the substituent effects on the reorganization energy. NBO (natural bond orbital) analysis has been carried out on both the neutral and the cationic systems to investigate the differences of the charge distributions and the electronic structures. The outcomes indicate that 8-CH3O-G:C has the greatest reorganization energy and 8-NO2-G:C has the least, while the other substituted base pairs have a reorganization energy close to that of G:C. The one charge is mostly localized on guanine part after ionization and as high as 0.95e. The bond distances of N1-N3′andN2-O2′ in the cationic base pair derivatives shortened and that of O6-N4′ elongated as compared with the corresponding bond distances of the neutral GC base pair derivatives.