The aim of this research is to obtain new data about the complexation between β-cyclodextrin (β-CD) and benzoic acid (BA) as a model reaction of the complex formation of hydrophobic molecules with cyclodextrins (CDs) in various media. This research may help developing cyclodextrin-based pharmaceutical formulations through the choice of the appropriate solvent mixture that may be employed in the industrial application aiming to control the reactions/processes in liquid phase. In this paper, NMR results for the molecular complex formation between BA and β-CD ([BA⊂β-CD]) in D2O-DMSO-d6 and in D2O-EtOH have shown that the stability of the complex in the H2O-DMSO-d6 varies within the experimental error, while decreases in H2O-EtOH. Changes in the Gibbs energy of BA resolvation in water and water–dimethylsulfoxide mixtures have been obtained and have been used in the analysis of the reagent solvation contributions into the Gibbs energy changes of the [BA⊂β-CD] molecular complex formation. Quantum chemical calculations of the interaction energy between β-CD and BA as well as the structure of the [BA⊂β-CD] complex and the energy of β-CD and BA interaction in vacuum and in the medium of water, methanol and dimethylsulfoxide solvents are carried out. The stability of [BA⊂β-CD] complex in H2O-EtOH and H2O-DMSO solvents, obtained by different methods, are compared. The thermodynamic parameters of the [BA⊂β-CD] molecular complexation as well as the reagent solvation contributions in H2O-EtOH and H2O-DMSO mixtures were analyzed by the solvation-thermodynamic approach.

The paper reports the spectrofluorimetric and calorimetric study of binding of two hydrophobic biologically active molecules with antioxidant ability, flavonoids quercetin, and curcumin, to human serum albumin (HSA) in water, aqueous DMSO (0.05 and 0.1 mol. fraction of DMSO), and aqueous ethanol (0.05 mol. fraction of EtOH). Both flavonoids induce the quenching of HSA fluorescence. The stability constants of associates, as well as the changes in enthalpy of the reaction between quercetin and protein, were evaluated. The influence of solvent composition and additions of hydroxypropyl-β-cyclodextrin as a solubilizer of hydrophobic molecules, on the association processes is discussed. Supplementary Information The online version contains supplementary material available at 10.1007/s10973-022-11216-8.

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