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.

We have employed IR-UV double resonance spectroscopy to identify the tautomeric and isomeric structures of uric acid and its monohydrated clusters which are produced by the techniques of laser-desorption and supersonic-jet cooling. The IR spectrum obtained for bare uric acid exhibits four distinct NH stretching transitions assignable to those of the most stable triketo form. We have also observed the two most stable monohydrated clusters, each with uric acid in the triketo form and water bonded to either the N3H or N9H site. It is demonstrated that the R2PI spectra of these monohydrates can be separated by using the IR-purified spectroscopic method.

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Nucleosides that consist of base and sugar moieties can adopt two main conformations, syn and anti, about the glycosidic bond. We have investigated the conformational properties of guanine nucleosides in the gas phase by using laser desorption combined with IR-UV double resonance spectroscopy. In guanosine, syn conformation is preferred as a result of internal hydrogen bonding between the 5'-OH group of the sugar and the N3 site of the guanine moiety. We have therefore employed a chemically modified nucleoside 5'-O-ethylguanosine, in which possible glycosyl bond conformations are restricted upon ethylation of the 5'-OH group. The result shows that anti conformer is stabilized by the formation of hydrogen bonding involving the 2'-OH group.

Infrared spectra of mono- and dihydrated clusters of 2'-deoxyguanosine (2'-dGs), which are formed by laser desorption combined with supersonic jet-cooling, have been measured by the technique of IR-UV double resonance spectroscopy. The structures of these hydrates are compared with those reported for guanosine (Gs) to elucidate the importance of the 2'-hydroxy group in the hydration. It is shown that monohydrated structures observed for 2'-dGs are similar to those of Gs, indicating no significant influence by the absence of 2'-OH group. For the dihydrated cluster, two structural isomers are identified and assigned to the dihydrates with the guanine moiety is in the keto form, which are consistent with the lowest-energy structures derived from theoretical calculations. Comparison with the results for Gs suggests that the presence of 2'-OH group leads to the stabilization of specific dihydrate structures involving the sugar group.