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 N-H 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. (c) 2005 American Institute of Physics.