Thermo-acoustical and volumetric studies on interionic interactions of l-histidine in aqueous maltose solutions at different temperatures

Abstract

Apparent molar volumes, Vφ and adiabatic compressibilities, Ks, φ of l-histidine in the concentration range (0.0 to 0.18 mol kg−1) in maltose solutions ranging from pure water to 20.0 mass % of maltose have been calculated at 298.15, 303.15, 308.15 and 313.15 K from precise measurements of density and speed of sound. At infinite dilution apparent molar volumes, Vφ0, and apparent molar adiabatic compressibilities, Ks, φ0, of l-histidine have been also evaluated. Transfer volumes, ΔtrVφ0, and transfer adiabatic compressibilities, ΔtrKs, φ0, at infinite dilution from water to aqueous maltose solutions have been also calculated. Solute-solvent interaction has been confirmed with the positive value of Vφ in all the systems. Besides the reported values of Ks, φ were negative for l-histidine in aqueous-maltose solutions, indicating that the water molecules around ionic charged groups of amino acids are less compressible than the water molecules in the bulk solution. Interaction between saccharides and proteins molecules is expected to create polar environment, which helps to increase the hydrophobic interactions because of stabilizing the protein. The results indicate there exists strong solute–solvent (hydrophilic–ionic group and hydrophilic–hydrophilic group) interactions in these systems, which increase with increasing in saccharide concentration. It has also been observed that l-histidine acts as structure maker in aqueous-maltose solvents.