Structural Characterization of 6-Thioguanosine and Its Monohydrate in the Gas Phase

Detailed structural analysis of 6-thioguanosine (6TGs) in relation to its tautomerization and sugar conformation is performed in the gas phase using UV and IR spectroscopy combined with ab initio calculations. We have observed a thiol tautomer of 6TGs with its sugar moiety in the syn conformation that is stabilized by a strong intramolecular H-bonding between O5'H of the sugar and N3 atom of the guanine moiety. This observation is consistent with previous results for guanosine (Gs) in which the corresponding enol form is solely detected. We have also identified a monohydrate of 6TGs consisting of a thiol tautomer with the water linking guanine moiety and sugar OH group. It is demonstrated that hydration behavior of 6TGs is significantly different from that of Gs as a result of a weaker H-bonding ability of the thiol group.