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The inclusion complex between asiaticoside (AC), an active substance from the medicinal plant Centella asiatica L., and 2-hydroxypropyl-β-cyclodextrin (HPβCD) was investigated. The phase solubility profiles of AC in distilled water and 90:10 (v/v) mixture of 80 vol.% acetic acid and N,N-dimethylacetamide (DMAc) both in the absence and the presence of HPβCD were classified as AL-type and indicated a 1:1 molar ratio of the AC/HPβCD complex. The 1:1 stoichiometric molar ratio of the complex was confirmed by both the 1D and the 2D 1H-nuclear magnetic resonance spectrometry. Unlike the highly crystalline nature of the native AC, the stoichiometric AC/HPβCD complex powder was amorphous in nature. The average diameters of the self-assembling aggregates of the AC/HPβCD complex, a priori prepared at various HPβCD to AC molar ratios of 0.5, 1, and 2, in the solution state, were about 2.4, 3.3, and 3.8 μm, respectively. The solvent-cast CA films containing these complexes showed strong evidence of the aggregates on their surfaces. The maximal cumulative released amounts of AC, a sparingly water-soluble substance, from the CA films containing a mixture of AC/HPβCD of varying molar ratios (i.e., 1:0.5, 1:1, and 1:2) in the phosphate buffer saline solution (PBS) containing 10% (v/v) methanol (i.e., P/B/M medium) were 2.2, 3.9, and 5.8% (based on the actual weights of the film specimens), respectively, which were clearly an increasing function of the HPβCD content in the films. |
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