RESUMO
The aim of this research is to obtain new data about the complexation between ß-cyclodextrin (ß-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 ß-CD ([BAâß-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 [BAâß-CD] molecular complex formation. Quantum chemical calculations of the interaction energy between ß-CD and BA as well as the structure of the [BAâß-CD] complex and the energy of ß-CD and BA interaction in vacuum and in the medium of water, methanol and dimethylsulfoxide solvents are carried out. The stability of [BAâß-CD] complex in H2O-EtOH and H2O-DMSO solvents, obtained by different methods, are compared. The thermodynamic parameters of the [BAâß-CD] molecular complexation as well as the reagent solvation contributions in H2O-EtOH and H2O-DMSO mixtures were analyzed by the solvation-thermodynamic approach.
RESUMO
Noncatalyzed, regio- and stereoselective hypochlorite oxidation of 3-aminothieno[2,3-b]pyridine-2-carboxamides is presented. Unexpectedly, the oxidation proceeded by different mechanistic pathways, and different products were formed, depending on the nature of solvents used. A possible mechanism, the structure of products, kinetics and dynamics of intramolecular processes, and biological activity of products are discussed.