IR-UV Double Resonance Spectroscopy of the Hydrated Clusters of Guanosine and 9-Methylguanine: Evidence for Hydration Structures Involving the Sugar Group

Infrared spectra of mono- and dihydrated clusters of guanosine (Gs) formed by laser desorption combined with supersonic jet cooling have been measured by the technique of IR-UV double resonance spectroscopy. The results are compared with those of 9-methylguanine (9MG), in which the sugar group of Gs is replaced with a methyl group, to elucidate the importance of the sugar group in the hydration structures. It is shown that the UV spectrum observed for the monohydrated cluster of Gs is composed of multiple structural isomers of larger stabilities. One of the monohydrates is identified to possess a hydration structure involving the 5'-OH group of the sugar and the amino group of the guanine moiety. The IR spectrum of the dihydrated clusters reveals that the 2'-OH group is significantly influenced by the addition of the second water, which suggests the possibility of specific dihydrate structures for Gs.