Exploring the interactional behavior of N-acetylcysteine in aqueous-dimethylsulfoxide solutions: A physicochemical and computational study

In order to determine the molecular interactions, the volumetric and viscometric characteristics of N-Acetyl-L-Cysteine (NAC) (∼0.10 to ∼1.00) mol.kg−1 solutions in water, dimethylsulfoxide (DMSO), and aqueous solution of DMSO (DMSO-H2O) have been investigated at temperatures between 298.15 and 318.15 K at 5 K interval. From the density data Apparent molar volume (φv), apparent molar expansivity (φE0), apparent molar volume at infinite dilution (φv0), and transfer apparent molar volume (φv,tr0) have been evaluated. Apparent molar volume (φv) of NAC decreased for all the investigated systems with concentration but increased with temperatures. Negative Sv values for all the systems indicate the weak solute-solute interactions. Positive and small negative values of Hepler constant, (∂2 φv0/ ∂T2) showed that NAC possess structure-making capabilities in ternary solutions. With increasing the concentration of NAC viscosities of all the solutions increased but decreased as the temperature rises. Viscosity coefficient (B, D), as well as the derivative of the B coefficient, (∂B/∂T), values have been calculated using the viscosity data and demonstrated the structure making properties of the investigated systems. Thermodynamic characteristics such as change in free energy (ΔG∗), change in enthalpy (ΔH∗), and change in entropy (ΔS∗) for viscous flow have established that all the processes are nonspontaneous at low temperatures and spontaneous at high temperatures. Computational analysis also confirmed that the solution is being formed by a hydrophilic bond through solute-solvent interaction.