Studies on β-cyclodextrin inclusion complex of curcumin

Formation of inclusion complex of curcumin with beta-cyclodextrin (beta-CD) has been characterized by change in the absorption spectrum, blue shifted fluorescence spectrum and increase in fluorescence intensity. The spectral changes could be fitted to 1:1 complex formation with estimated binding constant of 2.6 +/- 0.3 x 10(2) M-1. At high concentrations (> 4 mM) the data indicated formation of 1:2 complex. Fluorescence measurements in the temperature range from 293 to 323 K showed a steady decrease in binding constant with increase in temperature, from which the thermodynamic parameters Delta H and Delta S, for the 1:1 complexation have been estimated to be -8.5 kJ/mol and - 0.02 kJ/mol/K respectively. Kinetics of binding was studied by stopped flow technique from which the binding constants for 1:1 and 1:2 complex formation could be resolved as 6.87 x 10(2) M-1 and 6.8 x 10(4) M-2. Further, influence of such inclusion complex on change in superoxide radical scavenging property of curcumin was examined using xanthine/ xanthine oxidase assay.