Molecular association of betaine and betaine hydrochloride in aqueous solutions - a study by Raman spectroscopy

Raman vibrational spectroscopy, at 298 K, has been used to study the hydrat ion of betaine hydrochloride and betaine in the concentration range 0.5-2 M . The observed changes in the internal vibrations of the solutes, namely, i n the C=O, COO- and C-H stretchings, and in the components of the O-H stret ching band are consonant with anionic water-betaine and betaine hydrochlori de dimeric species involving simultaneously hydrogen-bonding between two so lute and water molecules. In both cases, betaine hydrochloride and 'zwitter ionic' betaine behave like structure-makers promoting a larger association in the 'bulk' liquid water. (C) 2001 Elsevier Science B.V. All rights reser ved.