Activity coefficients of the peptide and the electrolyte in ternary systems water plus glycylglycine+NaCl,+NaBr,+KCl and +KBr at 298.2 K

The activity coefficients of glycylglycine in four aqueous electrolyte solu tions (+NaCl, +NaBr, +KCl and +KBr) were obtained at 298.2 K. The mean ioni c activity coefficient of the electrolyte in aqueous solutions containing t he peptide was determined from measurements of the potential differences of a cation and an anion ion-selective-electrode, each vs. a double junction reference electrode. The results show that the nature of the anion has a ma jor effect on the activity coefficients of glycylglycine. Comparison of act ivity coefficient data for glycylglycine with literature data for glycine, both in aqueous NaCl solutions, indicates that the effect of the electrolyt e is larger for the peptide than for the amino acid. For the peptide, in al l cases, the effect of the electrolyte is more important at low molalities of the electrolyte. The Wilson equation was used to correlate the activity coefficient data obtained. The correlation results were satisfactory for th e region of concentrated electrolyte. (C) 2001 Elsevier Science B.V. All ri ghts reserved.