Hydration number of glycine in aqueous solution: an experimental estimate.

An experimental estimate of hydration number, N(H), of glycine in aqueous solution is given by using the calorimetric methodology developed by us earlier, which is briefly reviewed. We found NH to be 7+/-0.6 for glycine presumably in the zwitter ion form, 10+/-1 for sodium glycinate, and 5+/-0.4 for glycine hydrochloride. Both glycine and sodium glycinate seem to work purely as a hydration center without altering the nature of the bulk H2O away from the hydration shell. Glycine hydrochloride, in addition to the role of hydration center, seems also to act as a typical hydrophilic species such as polyols, urea, or polyethylene glycols. Hence, the effect of the latter on H2O is of a long range, like other hydrophilic species.