Raman spectroscopic study on the structure of water in aqueous solution of α,ω-amino acids

The structure and hydrogen bonding of water in an aqueous solution of various α,ω-amino acids were analyzed using the contours of the OH stretching in the polarized Raman spectra. From the relative intensity of the collective band (C value) corresponding to a long-range coupling of the OH stretching in the aqueous amino acid solutions, the number of hydrogen bonds disrupted due to the presence of one amino acid molecule (Ncorr value) was evaluated. The Ncorr value for glycine was slightly positive, whereas with an increase in the number of methylene groups between ammonium and carboxylate groups, the Ncorr value gradually increased. These results suggest that the species with proximal anionic and cationic groups do not disturb the hydrogen-bonded network structure of water significantly, probably due to the counteraction of the electrostatic hydration effect attributable to the anionic and cationic groups.