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

Abstract

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 φ ), partial molar volumes V φ 0 , transfer volumes Δ V φ 0 and hydration number ( n H ) are evaluated using density data. Adiabatic compressibility ( β s), change (Δ β s), and relative change in compressibility (Δ β s/ β 0), apparent molar compressibility ( K φ ), partial molar compressibility K φ 0 , transfer compressibility Δ K φ 0 , and hydration number ( n H) have been calculated using ultrasonic speed data. The linear correlation of V φ 0 , Δ V φ 0 , K φ 0 and Δ K φ 0 for a homologous series of amino acids have been used utilised to calculate the contribution of charged end groups ( NH 3 + , COO −), CH 2 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.