Volumetric and Sound Velocity Studies on L-Lysine and L-Arginine in Aqueous Sodium Benzoate Solution at Different Temperature

Abstract

In this study, a general volumetric and sound velocity method was used to analyze the effects of sodium benzoate (SB) on the structure of essential amino acids (L-lysine, L-arginine). Densities and sound velocities of L-lysine and L-arginine in aqueous and in aqueous 0.05 mol.kg-1, 0.2 mol.kg-1, 0.35 mol.kg-1 and 0.5 mol.kg-1 SB solutions have been studied at 293.15K to 313.15K 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 ( 0  E ) and Helper’s constant ( E / T) p 0    . The acoustic properties such as adiabatic compressibility (βs), apparent molar adiabatic compressibility (k), limiting apparent molar adiabatic compressibility (φk 0), apparent molar adiabatic compressibility transfer (Δtrφk 0), 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 SB solutions are higher than that of amino acids in aqueous solution. The limiting apparent molar volumes (φv 0) and the values of experimental slope (Sv) are positive. The smaller values of Sv as compared to φv 0 values suggest the dominance of solute-solvent interaction over the solute-solute interaction. The limiting apparent molar volume transfer (Δtrφv 0) values of L-lysine and L-arginine in SB solutions are negative. This indicate that ion-hydrophobic and hydrophobichydrophobic group interaction are dominating over the hydrophilic-hydrophilic interaction. The values of limiting apparent molar expansion ( 0  E ) are positive. These trends in limiting apparent molar expansions for these amino acids in each concentration of SB solutions indicating the presence of solute-solvent interaction. The Hepler’s constant p ( E / T) 0    values of binary system are entirely positive for all studied amino acids suggest the studied systems act as structure makers. In ternary system some values are small negative and some values are positive. Hepler’s constant p ( E / T) 0    in ternary solutions indicating the structure making properties of amino acids in SB solutions. The values of partial molar volumes (V̅ 2) increase with increasing of concentration of L-lysine, L-arginine for the studied systems. As the concentration of amino acids increases, the adiabatic compressibility (βs) decreases. 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 implying a greater ordering effect by the solute on the solvent. Δtrφk 0 values of L-lysine are positive whereas Δtrφk 0 of L-arginine are negative. This indicate that hydrophilichydrophilic and ion-hydrophilic interaction are dominating for L-lysine systems whereas hydrophobic-hydrophobic and ion-hydrophobic interactions are dominating for L-arginine systems. The small Sk values also indicates the solute-solvent interactions. The increase in acoustic impedance Z, indicates the presence of effective solvent-solvent interactions with the increase in solution concentration. The positive hydration number (nH) values indicate an admirable solubility of the solutes. Water molecules around amino acids have less shrinkage than water molecules in bulk solutions. The compressive strength of the ternary solution is less than that of the binary solution. This result suggests that the proteins or peptides generated from the studied amino acids will be denatured in ternary SB solutions.