Studies on Volumetric and Ultrasonic Properties of L-Lysine, L-Ornithine and Glycine in Aqueous Fructose Solution at Different Temperatures

Abstract

In this study, the interaction of amino acids (glycine, L-ornithine and L-lysine) in water and aqueous fructose solution has been determined by using volumetric and sound velocity method. Interactions of glycine, L-ornithine and L-lysine in aqueous fructose solution play an important role to understand biochemical process in living cells. Densities and sound velocities of glycine, L-ornithine and L-lysine in water and in aqueous 0.05 mol.kg-1, 0.20 mol.kg-1, 0.35 mol.kg-1 and 0.50 mol.kg-1 fructose 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 (φv 0), limiting apparent molar volume transfer (Δtrφv 0), apparent molar expansibilities (δφv 0/δT)p and Hepler’s constant (δ2φv 0/δT2)p. The acoustic properties such as adiabatic compressibility (βs), apparent molar adiabatic compressibility (k), limiting apparent molar adiabatic compressibility (φk 0), apparent molar adiabatic compressibility of transfer (Δtrφk 0), acoustic impedance (Z), relative association (RA) and hydration number (nH) have been calculated by densities and sound velocities data. The densities increase with the increase of concentration of amino acids (glycine, L-ornithine and L-lysine). Densities of glycine, L-ornithine and L-lysine in aqueous fructose solutions are higher than that of glycine, L-ornithine and L-lysine in aqueous solution. The smaller values of experimental slope (Sv) as compared to limiting apparent molar volume (φv 0) values suggest the dominance of solute-solvent interaction over the solute-solute interaction. The true volume (φv 0) of amino acids are found to be order of L-lysine > L-ornithine > glycine. The limiting apparent molar volume transfer (Δtrφv 0) values of glycine, L-ornithine and L-lysine are positive which suggest the dominance of ion-hydrophilic and hydrophilichydrophilic interactions over the hydrophobic-hydrophobic and ion-hydrophobic interaction. The values of limiting apparent molar expansion (δφv 0/δT)p are positive. Hepler’s constant (δ2φv 0/δT2)p values are small negative for all studied amino acids in binary and ternary system suggest the studied systems act as structure maker. The values of partial molar volumes ( 2) increase with increasing of concentration of glycine, L-ornithine and L-lysine for the studied systems. This trend of 2 indicates solute-solvent interactions increase with increasing concentration of amino acids. The sound velocity increases with the increase of concentration of L-lysine, L-ornithine and glycine. This may be attributed to the increase of compactness of the medium with the increase in amino acids concentration. Sound velocities of L-lysine, L-ornithine and glycine in aqueous fructose solutions are higher than that of L-lysine, L-ornithine and glycine in aqueous solution. The adiabatic compressibility (βs) decreases with the increase of concentration of L-lysine, L-ornithine and glycine. 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 (k) values indicate the greater loss of structural compressibility of water. The values of limiting apparent molar adiabatic compressibility (φk 0) are negative. The values of apparent molar adiabatic compressibility transfer (Δtrφk 0) are positive which suggest the existence of strong solute-solvent interaction. At lower concentration, negative values of Δtrφk 0 indicate that increase in hydrophobic-hydrophobic group interactions. The small Sk values also indicates the dominating of solute-solvent interactions over solute-solute interaction. The acoustic impedance, Z increases with the increase of concentration of amino acids. The relative association, RA decreases linearly with increasing the concentration of solute. The positive hydration number (nH) values indicate an appreciable solvation of solutes. Therefore, the water molecules around amino acids are less compressible than water molecules in the bulk solution. The compressibility of ternary solution is lower than binary solution. This result suggests that the proteins or peptides generated from the studied amino acids will be denatured in ternary fructose solution.