Preparation, characterization, and study of the antimicrobial activity of a Hinokitiol-copper(II)/γ-cyclodextrin ternary complex

Objectives: The aim of the current study was to prepare a ternary complex of hinokitiol (HT), a metal ion (Cu (II)) and gamma-cyclodextrin (gamma CD) via coprecipitation and to assess its physicochemical properties and the effects of complexation on the antimicrobial activity of HT. Methods: Single-crystal X-ray structural analysis, powder X-ray diffraction (PXRD), near-infrared (NIR) absorption spectroscopy, and electron spin resonance (ESR) spectroscopy were performed to assess the complex in a solid state. Agar dilution was used to determine the minimum inhibitory concentration (MIC) of HT-Cu complex and the ternary inclusion complex with respect to Escherichia coli, Bacillus subtilis, Staphylococcus aureus, and Pseudomonas aeruginosa. Key findings: A ternary HT Cu/gamma CD inclusion complex formed as a result of coprecipitation. Results of an antimicrobial test revealed that the ternary HT-Cu/gamma CD inclusion complex had increased antimicrobial activity compared to that of HT alone. The level of antibacterial activity of ternary complex had action equivalent to that of an HT/gamma CD inclusion complex. Conclusions: The antimicrobial action of HT can presumably be capitalized on by including HT in CD without a metal in certain applications. The current results should provide a basis for use of hinokitiol as a human and environmentally friendly antimicrobial. (C) 2019 Elsevier B.V. All rights reserved.