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Biomolecules function in an aqueous environment. Elucidation of the hydration structures of biomolecules is hence important to understand their functions. Here, we investigated the hydration structure of lysozyme (Lys) in the gas phase by photodissociation and fluorescence spectroscopy in combination with droplet‐beam laser ablation mass spectrometry. We found that water molecules are held inside and on the surface of the Lys molecule, and the hydration structure around the tryptophan residue changes by photoexcitation. This study provides a novel method to observe the hydration structures of large biomolecules at the molecular level. [ABSTRACT FROM AUTHOR]

Hydrogen-bondedcomplexes of uric acid/9-methyluric acid (UA/9MUA)with melamine (MEL) are prepared by the combined technique of laserdesorption and supersonic-jet expansion, and their stable structuresare investigated by infrared spectroscopy and theoretical calculations.It is shown that the 1:1 complex formed between UA and MEL is of nonplanartype, in which the two chromophore planes are significantly foldedand thus allow for triple hydrogen-bonding interactions. An anomalouslybroad IR band is observed in the low-frequency range 2500–2800cm–1, which is taken as evidence for the formationof a strong hydrogen bond between one of the NH sites of UA and MEL.In the case of 9MUA, in which hydrogen bonding to the N9H site ofUA is blocked by the methyl group, two planar pairs formed of 9MUAand MEL are found to coexist. The nature of the multiple hydrogen-bondinginteractions in these complexes is discussed based on the naturalbond orbital analysis and compared with those of the guanine–cytosinebase pair. The results are expected to provide important informationon the structural characterization of urinary stones developed ininfants after ingesting MEL-contaminated formula. [ABSTRACT FROM AUTHOR]

Monohydration structures of the guanine-guanine and guanine-cytosine base pairs have been elucidated by IR-UV double resonance spectroscopy combined with ab initio calculations. The systems studied consist of the homodimer of 9-methylguanine and the heterodimer of 9-methylguanine and 1-methylcytosine in which the methyl group is introduced to mimic the presence of the sugar-phosphate backbone and to block specific tautomerization. The monohydrate of the homodimer is identified as that of the most stable symmetric structure formed by the keto tautomers of guanine, which demonstrates that the base pair structure is not influenced by the hydration. It is also shown that at least two structural isomers, one of which retains the Watson-Crick GC pair structure, contribute the monohydrated cluster of the heterodimer. Although stacked base pairs are suggested to be significantly stabilized by the addition of water, the result shows no clear indication for the presence of stacked monohydrates in either homodimer or heterodimer case.