Volumetric and Solvation Properties of Glycyl-Glycine and Glycyl-l-leucine in Aqueous Acetate Solutions

The densities of glycyl-glycine (diglycine) and glycyl-l-leucine, in water and in aqueous sodium acetate, potassium acetate, magnesium acetate and calcium acetate solutions, were measured at 298.15 K. The apparent molar volumes, V1, and the partial molar volumes, V¯1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \bar{V}_{1} $$\end{document}, of diglycine and glycyl-l-leucine have been calculated. The solvation number, nS, of diglycine was also calculated. The limiting apparent molar volumes of the studied peptides were also analyzed in terms of the Setschenow relationship. The effect of the acetate salt solutions on the volumetric properties of the studied peptides was also discussed in terms of the Setschenow coefficients, k1. The results indicate that the limiting apparent molar volume in aqueous acetate solutions is higher than that in water and the values increase with the concentration of the co-solutes (NaA, KA, MgA and CaA). The results indicate that the peptide interactions are stronger with MgA/CaA than NaA/KA. Also the data suggest that the peptide interactions are stronger with NaA than KA and with MgA than CaA. Further, the limiting apparent molar volume values increase from diglycine to glycyl-l-leucine. It was also noted that the solvation numbers for the diglycine in aqueous acetate salt solutions are less than in water and decrease as the concentration of acetate salt increases.