A new insight into the structure and stability of Hoogsteen hydrogen-bonded G-tetrad: an ab initio SCF study

Hoogsteen-bonded guanine tetrad (G-tetrad) has been studied at the HF/6-311G(d, p) and B3LYP/6-311G(d, p) levels of theory. The optimized structure of G-tetrad is significantly different from the traditionally suggested structure. Bifurcated hydrogen bonds are predicted to be responsible for the formation of internal G–G pairs in G-tetrad. The calculated stabilization energy of 62 kcal/mol at the HF/6-311G(d, p) level suggests that a quite stable G-tetrad is formed through four pairs of bifurcated H-bonds. Inclusion of electron correlation (the B3LYP/6-311G(d, p) approach) recovers only 4 kcal/mol of additional stabilization energy. The electrostatic potential map of G-tetrad shows significant concentration of negative charges in the central area of the G-tetrad. The neutralization of this charge by a cation placed in this central area is expected to bring an auxiliary stabilization of the G-tetrad.