Densities and Partial Molar Volumes of Some Amino Acids and Diglycine in Aqueous n-Propanol Solutions at 25°C

Abstract

Apparent molar volumes, Vφ, of glycine, DL-α-alanine, DL-α-amino-n-butyric acid, L-valine, L-leucine, and diglycine in water and in 1.0, 2.0, 3.0, 4.0, 5.0, and 6.0 mB [molality of n-propanol in water (mol-kg−1)] aqueous solutions of n-propanol have been obtained from densities of their solutions at 25 °C measured by using a precise vibrating-tube digital densimeter. The calculated partial molar volumes of amino acids and diglycine at infinite dilution, V2,mo, have been used to obtain the corresponding transfer volumes, ΔtrV2,mo, from water to different n-propanol–water mixtures. ΔtrV2,mo values are positive for glycine, DL-α- alanine, and diglycine (except at lower concentration ∼1.0 mB), negative for L-valine, and both positive and negative for the remaining amino acids over the concentration range studied. The side-chain contributions and hydration numbers have been calculated from V2,mo data. Interaction coefficients have also been obtained from the McMillan–Mayer approach and the data have been interpreted in terms of various interactions.