Thermodynamics of inclusion complexes between cyclodextrins and isoniazid

Complex formation of α- and β-cyclodextrins with isoniazid, a antituberculous pharmaceutical, is studied using such methods as calorimetry and 1H NMR at 298.15 K. On the basis of the obtained experimental data, it is shown that α- and β-cyclodextrins form 1 : 1 inclusion complexes with isoniazid, which are characterized by low stability in aqueous solution. Along with this, deeper penetration of isoniazid into the cavity of β-cyclodextrin, accompanied by more intensive dehydration of the reagents, is observed. The results are interpreted in terms of influence of structure of reagents and their state in solution on the binding mode, driving forces, and thermodynamic parameters of the complex formation.