Heat capacities of transfer of some amino acids and peptides from water to aqueous urea solution

Abstract

Integral enthalpies of solution at low concentrations of several amino acids and peptides in 2 and 6M urea solutions have been determined at 25 and 35°C. These data have been used to derive the enthalpies of transfer (at 25 and 35°C) and heat capacities of transfer (at 30°C) of these amino acids and peptides from water to aqueous urea solutions. Furthermore, the enthalpies of transfer and heat capacities of transfer per CH₂ group and per peptide group - CONH - have also been estimated. These results show that while the enthalpies and heat capacities of transfer per CH₂ group are positive and negative, respectively, the reverse is true for -CONH - group. The implications of these results in the mechanism of the denaturation of proteins by urea are discussed.