Synthesis and Characterization of β-Cyclodextrin-Essential Oil Inclusion Complexes for Tick Repellent Development

Abstract

Essential oils (EOs) are used in several pest management applications. Due to their volatility, EOs may experience bioactivity reduction, thus requiring protection to extend their properties. In the present study, we investigated the inclusion complex formation (IC) of β-cyclodextrin (β-CD) with selected EOs with known tick repellent activity using two co-precipitation methods. ICs were characterized by evaluating EO mass concentration and inclusion efficiency (% IE) and other instrumental methods. Co-precipitation method 2 yielded the highest EO mass concentration (88 ± 6 μg/mg β-CD) for the 1:1 molar ratio geranium Egyptian EO IC. The EO volatile release over time from the ICs was investigated by headspace SPME/GC-MS analysis. ICs were also tested in tick repellency bioassays. ICs reported significant tick repellent activity, with lemongrass IC performing best overall. Method 1 showed the best combination of high mass concentration EO, controlled volatile release, and tick repellency with lemongrass EO. The results demonstrated that β-CD had selectively encapsulated different EOs. Moreover, the formation of ICs may improve EO tick repellent properties protecting the active ingredients and providing a better, long-lasting repellent action. These findings will allow the development of more effective naturally derived repellent products to protect individuals from tick bites and prevent tick-borne illnesses.

Novel β-Cyclodextrin and Catnip Essential Oil Inclusion Complex and Its Tick Repellent Properties

“…The results of the 1 H NMR spectroscopy showed a change in the chemical shift for the protons on the inside of the β-cyclodextrin cavity (e.g., H-3 and H-5). This indicates that the chemical environment inside the cavity has changed as a result of the successful encapsulation of catnip oil inside the cyclodextrin cavity [ 9 , 40 ]. The chemical shifts of both β-cyclodextrin and the inclusion complex and their differences are shown in Table 3 .…”

“…The inclusion complexes in this study were prepared with a 1:1 molar ratio for β-cyclodextrin and catnip oil (or nepetalactone, as the main constituent and active ingredient). This molar ratio has been previously demonstrated to be effective for both other iridoid compounds (i.e., genipin [ 43 ]) and other monoterpenoids [ 6 , 40 ]. To determine the molar ratio, nepetalactone was used to approximate a molar amount of catnip oil.…”

“…This is further supported by the 1 H NMR results, which show that the protons on the inside of the cyclodextrin cavity have shifted up-field. The inclusion of the oil within the cyclodextrin cavity has a shielding effect on the H-3 and H-5 through intermolecular interactions [ 9 , 40 ]. The same change in chemical shift is not observed with other protons on the outside of the cyclodextrin as expected, since the surface oil extraction and analysis showed that there was not a significant amount on the outside of the cavity.…”

“…Although the concentration of the active ingredient was low, the [catnip: β-CD] inclusion complex performed even better than the unencapsulated oil at similar concentrations, repelling 86% of tested ticks. The encapsulation of essential oils and other aromatic molecules has been reported to improve their physical properties, retaining or even enhancing their biological properties, such as exerting repellent action against arthropods [ 40 , 49 ]. Results from the SPME/GC-MS showed that the release of catnip volatiles from the [catnip: β-CD] inclusion complex reaches a plateau after 6 h, remaining consistent after an initial drop to about 60% of the initial amount.…”

“…The hexanes layer was collected, and the aqueous layer was extracted twice more with 1 mL of hexane for a total of 3 extractions. The organic layers were combined for each sample (final volume was 3.5 mL), dried with Na 2 SO 4 , and filtered using cotton wool [ 40 ].…”