Volumetric and Sound Velocity Studies of L-Serine, L-Asparagine and L-Glutamine in Aqueous Vitamin B6 Solution at Different Temperatures

Abstract

In this study, a simple volumetric and sound velocity method was used for the analysis of effect of vitamin B6 (pyridoxine) on the structure of amino acids (L-serine, L-asparagine and L-glutamine). Densities and sound velocities of L-serine, L-asparagine and L-glutamine in aqueous and in aqueous 0.05 mol.kg-1, 0.20 mol.kg-1, 0.35 mol.kg-1 and 0.50 mol.kg-1 vitamin B6 solutions have been studied at 293.15K to 318.15K with an interval of 5K. The density data have been used to calculate apparent molar volume (φv), limiting apparent molar volume (φv0), limiting apparent molar volume transfer (Δtrφv0), apparent molar expansibilities (Eφ0) and Helper’s constant (δEφ0/δT)p. The ultrasonic properties such as adiabatic compressibility (βs), apparent molar adiabatic compressibility (φk0), limiting apparent molar adiabatic compressibility (φk0), apparent molar adiabatic compressibility of transfer (Δtrφk0), acoustic impedance (Z) and hydration number (nH) have been calculated by densities and sound velocities data. The densities increase with the increase of concentration of amino acids. Densities of amino acids in aqueous vitamin B6 solutions are higher than that of amino acids in aqueous solution. The limiting apparent molar volumes (φv0) are positive at the studied temperatures for the binary and ternary mixtures indicate the presence of solute-solvent interactions. The smaller values of experimental slope (Sv) as compared to φv0 values suggest the dominance of solute-solvent interaction over the solute-solute interaction. The limiting apparent molar volume transfer (Δtrφv0) values of L-glutamine and L-asparagine in aqueous 0.2 mol.kg-1, 0.35 mol.kg-1 and 0.5 mol.kg-1 vitamin B6 solution are negative which suggest the dominance of ion-hydrophobic and hydrophobichydrophobic interactions. But Δtrφv0 values of L-serine in aqueous 0.05 mol.kg-1, 0.20 mol.kg-1, 0.35 mol.kg-1 and 0.50 mol.kg-1 vitamin B6 solutions positive which suggest the dominance of ion-hydrophilic and hydrophilic-hydrophilic interactions. The values of limiting apparent molar expansion (Eφ0) are positive. The Hepler’s constant (δEφ0/δT)p values of binary system are small negative for all studied amino acids. In ternary systems, the Hepler’s constant values are mainly positive. This suggest that amino acids in ternary solution are more structural than binary solution. The values of partial molar volumes (V2) increase with increasing of concentration of L-serine, L-asparagine and L-glutamine for the studied systems. The sound velocity increases with the increase of concentration of amino acids (L-serine, L-asparagine and L-glutamine). Sound velocities of amino acids in aqueous vitamin B6 solutions are higher than that of amino acids in aqueous solution. This indicate that the increase of compactness of the medium with the increase in amino acids and vitamin B6 concentration. The adiabatic compressibility (βs) decreases with the increase of concentration of amino acids. This indicates the water molecules around the amino acids are less compressible than the water molecules in the bulk solution. The negative apparent molar adiabatic compressibility (φk) values indicate the greater loss of structural compressibility of water. The values of limiting apparent molar adiabatic compressibility (φk0) are negative. The values of apparent molar adiabatic compressibility transfer (Δtrφk 0) are mainly negative. Negative values of Δtrφk0 indicate that increase in hydrophobic-hydrophobic and hydrophilic-hydrophobic group interactions. The small Sk values also indicates the dominating of solute-solvent interaction over solute-solute interaction. The increase of acoustic impedance, Z with the increase of concentration of amino acids indicates the presence of effective solute-solvent interactions. The positive hydration number (nH) indicate the appreciable solvation of solutes.