Effect of N-Acetylcysteine on Volumetric and Viscometric Properties of Chitosan in Aqueous Acidic Solution

Abstract

Volumetric and viscometric studies of Chitosan-H20-CH3COOH and NAC (NAcetylcysteine)-Chitosan-[H20-CH3COOH] systems were investigated at 298.15 to 323.15 K at 5 K intervals. In a]l investigated systems concentrations of NAC were 0.10,0.50 & 1.00 mol.L' and concentrations of chitosan were 0.003, 0.006 & 0.012 mol.L* H20-CH3COOH mixed solvent was used for the experiment and H20 to CH3COOH ratios 9:1, 7:3 and 3:2 were maintained. Densities have been found to be increased with increasing concentration of both NAC and chitosan but decreased with increasing temperature. Densities were found to be increased with increasing the ratio of CH3COOH in Chitosan-H20-CH3COOH systems but this trend was not so significant is case of NAC-Chitosan-H20-CH3COOH systems. Density Values of NAC-Chitosan-[H20-CH3COOH] systems were remarkably higher than those Chitosan-H20-CH3COOH systems.The apparent molar volumes, φv of both Chitosan-H20-CH3COOH and NACChitosan-H20-CH3COOH systems were determined from the experimental density values data at 298.15 to 323.15 K at 5 intervals. The φv values were dependent upon concentration of NAC and chitosan in mixed solvents as well as the temperature. φv values have been found to be positive in all investigated systems. The φv values decreased throughout the whole concentration range for NAC and chitosan in their specific solvent systems. These results may be due to the solute—solvent, and solute—solute interaction through dipole-dipole interaction, ion-dipole interaction, hydrogen bond, hydrophilic or hydrophobic interaction among NAC, chitosan and aqueous acetic acid in the solutions. Besides, φv values were found to be increased with increasing temperature at any concentration of NAC and chitosan in solutions and this is may be due to increased thermal agitation at higher temperatures. Apparent molar volume at infinite dilution, φvo; apparent molar expansivity and Sv values were also determined. The φvo; values of chitosan-[H20-CH3COOH] systems decreased with increasing temperatures and increased with increasing the ratio of CH3COOH in H20-CH3COOH mixed solutions. At elevated temperatures cages in the investigated systems becomes less important hence the apparent molar volume at infinite dilution, φv3 decreased with increasing temperature. in addition, incorporation of more acetic acid ratio in Chitosan-H20-CH3COOH system hydrophobic-hydrophobic repulsion predominant over hydrogen bonding or dipole-dipoleinteraction. The apparent molar volume at infinite dilution gives an idea about the presence of solute—solvent interactions. The expansivity values are positive at all the investigated temperatures. Positive values indicate that, on heating some NAC and chitosan molecules may be released from the solvation layer of ion. It may also be conferred that the positive φEo;values may be originated from the hydrophobic character and steric effect of the NAC and chitosan in systems. As a whole there is a hydrophilic/hydrophobic balance among the solute and solvent molecules. S parameters contribute an idea about the prevailing solute—solute interactions in the mixtures. The negative and large in magnitude values of Sv in all investigated systems supports the weak solute-solute interaction present. Both Chitosan-H20-CHICOOH and NAC-Cli itosan-H20-CH3COOH systems showed rapid increase of viscosity values with the increase of chitosan and NAC concentrations but viscosities decreased with the increase of temperature. The increase of η values of with concentration of chitosan and NAC can be attributed to the increase in solute—solvent, and solute—solute interactions in solution. The small range of dissolution of chitosan and/or NAC in H2 0-Cl-13C00H might have intriguing aspects which may be the consequence of the great ability of H20 and Cl-13C00H to make hydrogen bond and dipole-dipole, ion-dipole interaction. In all cases with the increase of temperature internal energy of the systems increased as a result solute-solute or solute-solvent interaction may be depleted and viscosity values decreased.

The viscosity data were employed to determine A and B-coefficients; change of free energy, ∆G*; change of enthalpy. ∆H* and change of entropy,∆*. From these thermodynamic parameters state of the spontaneity of the investigated systems were known. Besides, negative A and positive B co-efficient suggesting that weak solute solute but strong solute-solvent interaction present. The change of free energy values for viscous flow,∆G* were found to be positive indicate that work has to be done to overcome the energy barrier for the flow process. The positive AH values indicate that work has to be done for all the investigated systems. The ∆S* values are negative for all the systems studied. This means that Chitosan-[H20-GH3COOH] and NACChitosan-[H20-CH3COOH]systems are regular than those of the pure one. Here one point may be remarked that as ∆S < 0 and ∆H> 0, so the processes are never spontaneous but the reverse process is always spontaneous.