Ab initio calculations of solvent effects on guanine and thioguanine tautomerism

Abstract

The molecular geometries and the relative energies of the ten most stable tautomers of guanine (G1, G2, G3...etc.) and thioguanine (TG1, TG2, TG3...etc.) have been investigated at the HF/3-21G and HF/6-31G** levels in the gas phase and in solution. Electron-correlation contributions have been determined at the MP2/6-31G** level in the gas phase. The solvent effects have been investigated by self-consistent reaction field (SCRF) theory. The introduction of a dielectric medium has an effect on the relative stability order of guanine and thioguanine tautomers. The results are discussed in terms of known experimental results.