Effects of sugar solutions on the activity coefficients of aromatic amino acids and their N-acetyl esters.

Activity coefficients of N -acetyl ethyl esters of phenylalanine, tyrosine, and tryptophan have been determined
in aqueous sucrose and glucose solutions. Similar measurements have been carried out with phenylalanine,
tyrosine. and tryptophan in sucrose solution. The oompounds show increased activity coefficients
(decrease in solubility or "sugaring out") in the solutions studied. The molar free energy of transfer,
of these compounds from water to sugar solutions has positive values and indicates increased hydrophobicity
in sugar solutions. The delta Ftr value is found to remain unaltered over a considerable range of temperature.
These observations have been utilized to explain the thermal stability of protein in aqueous sugar solutions.