THERMODYNAMICS OF QUERCETIN SOLVATION IN WATER-DIMETHYLSULFOXIDE SOLVENT

The distribution coefficients of quercetin (QCT) in water-dimethylsulfoxide solvents with a content of dimethylsulfoxide from 0.0 to 0.5 mol. fr. were determined by the method of interfacial distribution of the substance between two immiscible phases: aqueous or water-dimethylsulfoxide solution and n-hexane at 298.2 K. The distribution coefficients are less than one, which indicates a better solvation of quercetin in water and a water-dimethylsulfoxide solvent than in hexane. Changes in the distribution coefficients of quercetin are not correlated with a gradual increase in the content of dimethylsulfoxide (DMSO) in the solvent. Using the obtained values of the distribution coefficients, we calculated the changes in the Gibbs energy of re-solvation of quercetin in water-dimethylsulfoxide solvents. The dependence of the Gibbs energy of QCT re-solvation on the solvent composition has an extreme form with a minimum in the range of DMSO concentrations corresponding to 0.3 mol. fr. A comparative analysis of the effect of a water-dimethylsulfoxide solvent on the change in Gibbs energy of re-solvation of quercetin, nicotinamide and nicotinic acid was carried out. In the case of both nicotinamide and nicotinic acid, an extreme change is observed in the Gibbs energy of re-solvation of particles with a maximum in the region with a low content of non-aqueous component XDMSO ≈ 0.1 mol. fr. The main contribution to the weakening of the solvation of nicotinamide and nicotinic acid is due to the enthalpy component, and with increasing concentration of dimethylsulfoxide there is an increase in the contribution of entropy to the change in the Gibbs energy transfer. An extreme change in the Gibbs energy transfer of quercetin suggests that the minimum on the dependence ∆trGº(QCT) = F(χDMSO) is also a consequence of a change in the prevailing thermodynamic factor in the solvate state of quercetin.