Effect of pressure on tautomers' equilibrium in supercooled glibenclamide drug: analysis of fragility behavior.

In this work, we investigated the relaxation dynamics of supercooled and glassy glibenclamide drug in conditions of high compression using broadband dielectric spectroscopy. Glibenclamide, an oral antidiabetic drug, belongs to the group of organic compounds which reveal amide-imidic acid tautomerism. Our studies reveal that application of pressure does not change the shape of dielectric loss spectrum of this pharmaceutical, whereas it probably influences the tautomers' concentration in the examined sample. Because every tautomer may influence the unique physical properties like the glass transition temperature, we have also focused on the analysis of pressure dependence of fragility, m(P)(P). In contradiction to the others active pharmaceutical ingredients (API) like verapamil hydrochloride, indomethacin or ibuprofen, in the case of glibenclamide drug slightly increasing trend of fragility was observed. On the other hand, pressure measurements confirmed the validity of suggestions concerning the origins of two secondary relaxations in glibenclamide presented in our previous paper (Wojnarowska et al. Mol. Pharmaceutics 2010, 7, 1692-1707). It is worth noting that until now the system which reveals tautomerism has never been analyzed in condition of high compression.