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

摘要

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 V0, transfer volumes ΔV0 and hydration number (n_H) are evaluated using density data. Adiabatic compressibility (β_s), change (Δβ_s), and relative change in compressibility (Δβ_s/β _0), apparent molar compressibility (K_φ), partial molar compressibility K0, transfer compressibility ΔK0, and hydration number (n_H) have been calculated using ultrasonic speed data. The linear correlation of V0,ΔV0,K0 and ΔK0 for a homologous series of amino acids have been used utilised to calculate the contribution of charged end groups (NH3+, 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.