Abstract
Cyclodextrin inclusion complexes have been successfully used to encapsulate essential oils, improving their physicochemical properties and pharmacological effects. Besides being well-known for its effects on cats and other felines, catnip (Nepeta cataria) essential oil demonstrates repellency against blood-feeding pests such as mosquitoes. This study evaluates the tick repellency of catnip oil alone and encapsulated in β-cyclodextrin, prepared using the co-precipitation method at a 1:1 molar ratio. The physicochemical properties of this inclusion complex were characterized using GC-FID for encapsulation efficiency and yield and SPME/GC-MS for volatile emission. Qualitative assessment of complex formation was done by UV-Vis, FT-IR, 1H NMR, and SEM analyses. Catnip oil at 5% (v/v) demonstrated significant tick repellency over time, being comparable to DEET as used in commercial products. The prepared [catnip: β-CD] inclusion complex exerted significant tick repellency at lower concentration of the essential oil (equivalent of 1% v/v). The inclusion complex showed that the release of the active ingredient was consistent after 6 h, which could improve the effective repellent duration. These results demonstrated the effective tick repellent activity of catnip essential oil and the successful synthesis of the inclusion complex, suggesting that β-CDs are promising carriers to improve catnip oil properties and to expand its use in repellent formulations for tick management.
Highlights
Cyclodextrins (CDs) are important carrier molecules for the synthesis of different types of inclusion complexes
The amount of surface oil concentration in the complexes was far less than the total oil concentration, which indicates that the encapsulation was highly efficient (>99%) and the overall oil measured in the complexes was contained within the inclusion complex
We have reported the use of catnip essential oil to synthesize an inclusion complex with cyclodextrins according to the co-precipitation method
Summary
Cyclodextrins (CDs) are important carrier molecules for the synthesis of different types of inclusion complexes. They are macrocyclic oligosaccharides composed of 6–8 glucose units to form a ring (named α-, β-, and γ-CD respectively). The arrangement of the OH and H groups is such that the central inner cavity is somewhat lipophilic, and the outer surface is hydrophilic. This makes cyclodextrins an ideal substrate to formulate inclusion complexes containing small hydrophobic active ingredients and improve their solubility in aqueous media. Synthetic methods currently available are simple, require no (or limited amount of) organic solvents and no additional purification or cleanup steps, and use non-toxic materials, which makes the preparation of β-cyclodextrin inclusion complexes a desired and environmentally friendly process that falls into the green-synthesis approach [17,18]
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