Comparative evaluation of the effect of cyclodextrins and pH on aqueous solubility of apigenin.

The aqueous solubility of a flavonoid, apigenin, was studied in the presence of first generation cyclodextrins (α-CyD, β-CyD, γ-CyD), ionic and nonionic synthetic derivatives of β-CyD, namely SBE-β-CyD, HP-β-CyD and RM-β-CyD at various physiological pH. The order of solubility enhancement was as follows: RM-β-CyD>SBE-β-CyD>γ-CyD>HP-β-CyD>β-CyD>α-CyD. The phase solubility diagrams of HP-β-CyD and SBE-β-CyD indicated Higuchi AL subtype behavior, suggesting 1:1 stoichiometry of the complex. In contrast, AP subtype, so higher order complex formation can be assumed in the case of RM-β-CyD and γ-CyD. The formation of inclusion complexes has been confirmed by absorption and fluorescence spectroscopic measurements. Increased antioxidant activity was observed due to the inclusion complexes. These results prove that synthetic derivatives of β-CyD will be potentially useful excipients in the development of drug delivery systems for healthcare products containing flavonoids.