The interaction of the most stable guanine tautomers with water. The structure and properties of monohydratesElectronic supplementary information (ESI) available: Geometries of a guanine moiety in isolated molecules and monohydrates of the Gua9, Gua7 and Gua9* tautomers (Tables S1, S2 and S3). See http://www.rsc.org/suppdata/cp/b2/b205351a/

A comprehensive computational study of all stable monohydrates of the oxo-amino N9H (Gua9), oxo-amino N7H (Gua7), and hydroxy-imino N9H (Gua9*) tautomers of guanine has been performed at the MP2/6-31G(d) level of theory. Five stable complexes for the Gua9 tautomer and seven for the Gua7 and Gua9* tautomers have been revealed. They can be divided into three groups. The first group includes hydrates where the nucleobase appears to act as a proton donor and acceptor simultaneously. The second group contains hydrates where guanine is either a proton donor or a proton acceptor. Two additional complexes of water with the Gua7 and Gua9* tautomers are stabilized by non-conventional hydrogen bonds: C–H⋯O and N⋯H–O with participation of the nitrogen atom of the amino group. All hydrogen bonds between the nucleobase and water are rather weak. It was demonstrated that the geometry of the amino and carbonyl groups and the N1–C6 bond are the most sensitive to interactions with water.