Hydration numbers of α-alanine in an aqueous urea solution

Literature data on the apparent molar volumes I center dot of alanine in water and aqueous urea solutions at 298 K are analyzed. It is shown that the slope of the I center dot dependence on the alanine concentration is not dependent on the urea concentration. The standard partial volume of alanine increases linearly with the increase in the urea concentration (wt.%). The structural characteristics of hydrated complexes of alanine (hydration number, molar volume of water inside and outside the hydration sphere, and proper volume of alanine in solution) are given. The hydration number of alanine decreases by a factor of two in passing from water to a saturated (20m) urea solution. The effects of urea additions on the hydration numbers of alanine and glycine are compared.