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Inclusion complexes and photo-stability studies of pyrazinamide with cyclodextrins: Spectrophotometric and kinetic determination of stability constant

A.M.El kosasy, O.A.A.Ghonim, M.F.Ayada, L.E.Abdel-Fattah

The present study offers valuable information in comparing two methods for determination of stability constants of inclusion complexes of two hosts; -cyclodextrin (-CD) and 2-hydroxypropyl--cyclodextrin (HP--CD) as complexation reagentswith Pyrazinamide (PZA) acting as the same ‘‘guest’’ molecule. The stoichiometry of the complex formation was examined by applying the continuous variation (Job plot) method and a 1:1 molar ratio has been identified for both complexes, at the examined concentrations. The formation of the complexes was investigated and confirmed by 1H NMR spectrometry. Stability constantsKst of the inclusion complexes were determined spectrophotometrically according to the spectral changes of PZA absorbance due to complexation and kinetically as a function of the changes in the rate constant of PZA photodegradation. The photodegradation rate constants for the free and complexed forms were also calculated.