Partial molar volume and partial molar compressibility of four homologous α-amino acids in aqueous sodium fluoride solutions at different temperatures

Density and ultrasonic speed of four amino acids (glycine, L-alanine, L-valine, and L-leucine) in aqueous sodium fluoride solutions {(0.1 to 0.5) M} have been measured at T =(308.15. 313.15, and 318.15) K. Apparent molar volumes (V-phi), partial molar volumes (V-phi(0)), transfer volumes (Delta V-phi(0)) and hydration number (n(H)) are evaluated using density data. Adiabatic compressibility (beta(s)), change (Delta beta(s)), and relative change in compressibility (Delta beta(s)/beta(0)), apparent molar compressibility (K-phi). partial molar compressibility (K-phi(0)). transfer compressibility (Delta K-phi(0)), and hydration number (n(H)) have been calculated using ultrasonic speed data. The linear correlation of V-phi(0), Delta V-phi(0), K-phi(0) and Delta K-phi(0) for a homologous series of amino acids have been used utilised to calculate the contribution of charged end groups (NH3+, COO-), CH2 group and other alkyl chain of the amino acids. The analysis shows that the ion-ion interactions are much stronger than ion-hydrophobic interactions over the entire concentration range of sodium fluoride. It is observed that sodium fluoride has a strong dehydration effect on amino acids. (C) 2011 Elsevier Ltd. All rights reserved.