Hydration of monosaccharides studied by Raman scattering

We report a Raman spectroscopy study of glucose, fructose, and mannose. The spectra have been recorded for the dry powders and for solutions in H2O and D2O and commented in the so-called fingerprint region of the spectra (200-1,400 cm(-1)), in order to study the influence of the interaction with water on the solute vibrational modes. We have evidenced splitting of some bands, due to the presence of different anomers in solution. The isotopic substitution of the solvent has allowed in some instances to confirm the band assignment and, in other cases, to propose new assignments. Importantly, the isotopic substitution of the solvent has evidenced differences in the interaction of the investigated monosaccharides with water, which are rationalized as due to a balance between the inertia of the oscillator due to H-bonding and bond strength. In particular, glucose and fructose interact strongly with water, whereas in the case of mannose, we have observed a weaker interaction with water and a different behaviour of its anomers.