Effect of γ-cyclodextrin derivative complexation on the physicochemical properties and antimicrobial activity of hinokitiol
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The aim of this study was to evaluate the physicochemical properties of solid dispersion on mixtures of hinokitiol (HT) and γ-cyclodextrin (γ-CD) and of HT and (2-hydroxypropyl)-γ-cyclodextrin (HP-γ-CD). Differential scanning calorimetry revealed that coground HT/γ-CD at a molar ratio of 1:1 and HT and HP-γ-CD at molar ratios of 1:1 and 1:2 lacked an endothermic peak due to melting of HT crystals. Powder x-ray diffraction revealed that HT crystal showed a halo pattern respectively, by mixing and grinding of the CDs and HT. Thus, coground HT/γ-CD and HT/HP-γ-CD at a molar ratio of 1:1 had molecular interaction. Assessment of dissolution revealed that ground mixtures had improved dissolution of HT compared to HT crystals, ground HT alone, and physical mixtures containing HT. 1H-1H NOESY NMR suggested that the 7-membered ring and isopropyl group of HT were located within the cavity of γ-CD and HP-γ-CD. The antimicrobial tests indicated that ground mixtures exhibited a minimum inhibitory concentration (MIC) of 20 μg/mL against Bacillus subtilis, 40 μg/mL against Staphylococcus aureus, and 20 μg/mL against Escherichia coli. GMs were found to have 4 times more antimicrobial activity than HT crystals. Ground mixtures also exhibited MIC of 160 μg/mL against Pseudomonas aeruginosa and they were found to 2 times more antimicrobial activity than HT crystals. Improvement in antimicrobial activity with the formation of inclusion complexes is presumably due to increase the solubility of HT as a result of the formation of HT/CD inclusion complexes.
KeywordsHinokitiol Cyclodextrin Ground mixture Molecular interaction Antimicrobial activity
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Conflicts of interest
The authors declare no conflict interest.
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