EFFECT OF THE H2O-EtOH AND H2O-DMSO SOLVENTS ON THE γ-CYCLODEXTRIN SOLVATION

Abstract

Cyclodextrins are cyclic molecules that consist of D-glucopyranose units connected by α-1,4 glycoside bonds. Cyclodextrins are already used in the composition of drugs to increase the solubility of active substances and are ever more in demand in technologies for the development of new hybrid materials for various industrial processes. A structural feature of cyclodextrins is the presence of a hydrophobic cavity capable of including hydrophobic molecules with the formation of molecular complexes both in solution and in the solid phase. Thermodynamic parameters of cyclodextrin solvation are necessary for the scientific selection of the solvent and prediction of the reactivity of cyclodextrins for carrying out processes with the greatest efficiency. In this regard, in this work, distribution coefficients of γ-cyclodextrin were determined by the method of distribution of the substance between two immiscible phases with a water-dimethyl sulfoxide (water-ethanol) solvent of variable composition and n-hexane and the changes in the Gibbs energy of re-solvation were calculated. The distribution coefficient of γ-CD in mixed solvents is higher than in water. The change in the Gibbs energy during the transfer of γ-CD from water to its mixture with dimethyl sulfoxide and ethanol indicates a weakening of the macrocycle solvation. A comparative analysis of the effect of H2O-EtOH and H2O-DMSO solvents on changes in the solvated state of β-cyclodextrin, hydroxypropyl-β-cyclodextrin, and γ-cyclodextrin was carried out. It was assumed that the changes in the solvated state of cyclodextrins have a major effect on the stability of molecular complexes of cyclodextrins with flavonoids rutin and quercetin in aqueous-ethanol media.