The Activity Coefficients of Amino Acids and Peptides in Aqueous Solutions Containing Guanidinium Chloride

Six systems of the type amino acidor peptide-guanidinium chloride-water have been investigated over wide solute molality ranges using vapor pressure osmometry. The amino acids used were glycine and L-leucine, while the peptides were diglycine, triglycine, glycyl-L-leucine and L-leucyl-L-leucine. Equations for the ratios of the activity coefficients of these compounds in the salt solutions and water, respectively, were obtained in terms of the molalities of the solutes. The activity coefficient ratios for glycine are not much below one, whereas those for i.-leucine are considerably smaller reflecting the presence of the leucyl side chain. The activity coefficient ratios for the peptides are generally smaller than those for the amino acids which can be attributed to . the presence of the peptide group.