The effects of water-soluble polymers on hydroxypropyl-β-cyclodextrin solubilization of oleanolic acid and ursolic acid

The objective of this study was to investigate the influence of water-soluble polymers on the complex formation of hydroxypropyl-β-cyclodextrin (HP-β-CD) with oleanolic acid (OA) and ursolic acid (UA), two insoluble isomeric triterpenic acids. The interactions of OA and UA with HP-β-CD in water-soluble polymer solutions were studied by ultraviolet (UV) spectrophotometry. Phase-solubility studies were carried out to evaluate the solubilizing power of HP-β-CD, in association with water-soluble polymers, towards OA and UA. UV spectra indicated that the absorption intensity decreased upon the addition of HP-β-CD both in the absence and presence of water-soluble polymers. Stability constants were also calculated from the UV spectra. When water-soluble polymers were added, both the solubilization effect and the complexation efficiency (CE) of HP-β-CD with the isomers decreased. The experimental results suggested that the addition of water-soluble polymers inhibit the solubilization effect of HP-β-CD with OA and UA.