Encapsulation of benzene carboxylic acids using cyclodextrins

The encapsulation of medicinal substances in various polymers is a common way to increase their thermal, hydrolytic, and chemical stability. However, the bioavailability of the encapsulated drugs decreases. The solution to this important problem can be the preparation of nanocapsules of medicinal substances using complexing agents, for example, cyclodextrins. The purpose of this work is to study the possibility of encapsulation of benzoic, salicylic, and β-resorcylic acids using α- and β-cyclodextrins. The interaction of benzene carboxylic acids with cyclodextrins in aqueous solutions at 20–30 оС has been studied by spectrophotometry. The formation of complexes with a composition of 1:1 in the cyclodextrin – benzene carboxylic acid systems has been proven. The stability constants of the complexes and the main thermodynamic parameters of complex formation have been calculated. It has been shown that the nature of changes in the spectral characteristics of benzene carboxylic acids in the presence of cyclodextrins can be used to predict the possibility of aromatic organic compounds encapsulation. The determining role of the complementarity of geometric parameters of cyclodextrins and benzene carboxylic acids in the preparation of inclusion complexes with features of nanocapsules has been found. The prospects of using β-cyclodextrin for encapsulation of benzene carboxylic acids have been demonstrated. The complexes of β-cyclodextrin with benzene carboxylic acids were synthesized and studied by IR spectroscopy, X-ray analysis and derivatography. The formation of two types of complexes in the β-cyclodextrin – benzene carboxylic acid system was established. The first type of complexes is formed due to nonspecific interactions between the hydrophobic cavity of β-cyclodextrin and the benzene carboxylic acid molecule, the second type is due to specific interactions between the functional groups of molecules. Benzoic and salicylic acids form nanocapsules with β-cyclodextrin, and their hydrolytic and thermal stability increases. Complexes of the second type acquire the properties of a new compound: β-resorcylic acid loses its individuality, forming strong supramolecular structures with β-cyclodextrin.