Study of the Inclusion Complexation of B – Cyclodextrin –Metronidazole and Determination of its Stability Constant (K) by U.V. Visible Spectroscopy

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In this research inclusion complexation between the drug metronidazole as the guest molecule and b - cyclodextrin as the host molecule at pH=6.5, 7, 7.4 and lmax= 319 nm by using U.V.-Visible spectroscopy was investigated. Two different concentrations of metronidazole were used. 5 mL solutions consisting of a known and constant amount of metronidazole (in the first series of experiments with concentration of [3.88 x 10-5 mol/L] and in the second series of experiments, with saturated solution) and varying amounts of b - cyclodextrin were prepared in 0.1 M phosphate buffer (pH 7.4). The final solutions had b - cyclodextrin concentrations between 0.0011 M and 0.015 M. U.V. spectrum of each solution was taken at lmax= 319 nm. The absorbances at lmax= 319 nm were recorded and plotted against b - cyclodextrin concentrations. From the graph, the concentrations of free and bound metronidazole and free b - cyclodextrin were calculated by using the Beer-Lambert law. In the case of unsaturated solution of metronidazole, a stability constant of K= 37.7 ± 8.16 mol/L and in the case of saturated solution of metronidazole, a stability constant constat of K=57 mol/L was obtained.

b - cyclodextrn; metronidazole; inclusion complex; stability constant