Aqueous solvation of glutathione probed by UV resonance Raman spectroscopy

The specific interactions of water molecules with the tripeptide glutathione are investigated by UV Resonance Raman spectroscopy taking advantage of its sensitivity and selectivity. The peptide-solvent interactions at different chemical sites of glutathione, i.e. the peptide backbone and the side groups of the molecule, are investigated. With the aim of gaining new insights on the mechanism regulating the hydration of glutathione, intimately related to its biological functionality, the spectra of the tripeptide solutions are examined as a function of different concentration, pH and temperature. The Amide and the OH stretching spectral regions result very sensitive to the variations of the explored experimental parameters. Our observations provide a picture of the hydrogen-bonding network around glutathione. The number and the strength of hydrogen bonds increase in the deprotonated form of tripeptide that exhibits also a more marked capacity in decreasing the intermolecular order of water in its hydration shell. According to this view, a progressive reduction in the strength of hydrogen bond interactions on amide sites is probed upon the increment of thermal motion, accompanied by conformational changes involving the trans-cis isomerization of glutathione.