Reactivity of 2,2-Diphenyl-1-picrylhydrazyl Solubilized in Water by beta-Cyclodextrin and Its Methylated Derivative

Abstract

A stable radical, 2,2-diphenyl-1-picrylhydrazyl (DPPH center dot), frequently used as a reactivity model of reactive oxygen species, was successfully solubilized in water by forming an inclusion complex with beta-cyclodextrin (beta-CD), but the yield was less than 1%. When beta-CD was replaced with 2,6-di-O-methyl-beta-cyclodextrin (DM-beta-CD), the solubility of DPPH center dot in water improved significantly. However, the reactivity of DM-beta-CD-solubilized DPPH center dot toward water-soluble antioxidants, such as ascorbate, Trolox, and caffeic acid, was significantly lower than that of beta CD-solubilized DPPH center dot due to the steric hindrance of the methyl groups in DM-beta-CD. Therefore, beta-CD-solubilized DPPH center dot is suitable for evaluating the innate activity of water-soluble antioxidants.