Studies on Volumetric and Sound Velocity of L-proline and L-lysine in Aqueous Nicotinamide Solution at Different Temperature

Abstract

In this study, volumetric and sound velocity method was used for the analysis of effect of vitamin B3 (nicotinamide) on the structure of essential amino acids (L-proline and Llysine). Densities and sound velocities of L-proline and L- lysine in water and in aqueous 0.03 mol.kg-1, 0.045 mol.kg-1, 0.06 mol.kg-1 and 0.09 mol.kg-1 nicotinamide 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. Densities of amino acids in aqueous nicotinamide solutions are higher than that of amino acids in aqueous solution. The increase of density with concentration of amino acids can be attributed to solute-solvent interaction. The limiting apparent molar volumes (φv 0) are positive at the studied temperatures for the binary and ternary mixtures indicate the presence of solute-solvent interactions. 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-proline are negative which suggest the existence of ion-hydrophobic and hydrophobic-hydrophobic group interaction. But Δtrφv 0 values of L- lysine are positive which suggest the existence of ionhydrophilic and hydrophilic-hydrophilic interactions. The values of limiting apparent molar expansion (δφv 0/δT)p are positive which suggest the presence of solute-solvent interactions in solutions of amino acids in nicotinamide. Hepler’s constant (δ2φv 0/δT2)p values are small negative for all studied amino acids suggest the studied systems act as structure makers. The values of partial molar volumes ( 2) increase with increasing of concentration of L-proline 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-proline and L- lysine. This may be attributed to the increase of compactness of the medium with the increase in amino acids concentration. Sound velocities of amino acids in aqueous nicotinamide solutions are higher than that of amino acids in aqueous solution. The adiabatic compressibility (βs) decreases with the increase of concentration of L-proline and L- lysine. 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 ion-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 solution. The relative association, RA decreases linearly with increasing the concentration of solute indicates the increase of solute-solvent interaction. 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 less than binary solution. This result suggests that the proteins or peptides generated from the studied amino acids that will be denatured in ternary nicotinamide solution.