Abstract
This study searched for a new pre-formulation based on the natural compound from the class of the avermectins, named abamectin (ABA), in order to improve its action against Aedes aegypti larvae by complexation with β-cyclodextrin (βCD). Concerning the low aqueous solubility of ABA, even in the presence of βCD, it was also invoked the strategy of working with hydrophobic nanoprecipitates (HNPs). For these purposes, molecular and supramolecular characterizations of 1:1 ABA/βCD complex and evaluation of its toxicity against A. aegypti larvae were performed. In the physical-chemistry characterizations, changes in the infrared spectra and thermal profiles in relation to precursors confirmed the occurrence of interactions between ABA and βCD in solid state. Nuclear magnetic resonance (NMR) data suggest the inclusion of ABA in βCD via benzofuran ring. Isothermal titration calorimetry (ITC) experiments allowed to verify the formation of complex with a 1:1 stoichiometry, which was entropy driven. The dynamic light scattering and zeta potential data from inclusion compounds demonstrated changes in the size of the ABA/βCD HNP if compared with the ABA HNP. Finally, the results for biological assays demonstrate that the strategy to prepare the inclusion compound led to an increase in the larvicidal activity in relation to free ABA.
Highlights
Avermectins (AVMs) are pentacyclic lactones obtained by fermentation from Streptomyces avermitilis cultures, belonging to one of the most abundant genres of microorganisms in soil.[1]
We have recently studied the combination of β-cyclodextrin[12,13,14] with insecticides from the class of benzoylphenylureas (BPUs)[15] and from the class of avermectins,[16] in order to produce hydrophobic nanoprecipitates, which can be used against A. aegypti in larval stages, with lower effective dosages
The infrared spectra and thermal analysis indicated the occurrence of interaction between ABA and βCD in solid state
Summary
Avermectins (AVMs) are pentacyclic lactones obtained by fermentation from Streptomyces avermitilis cultures, belonging to one of the most abundant genres of microorganisms in soil.[1]. DLS experiments were performed in a Malvern Zetasizer Nano ZS particle analyzer (Malvern Instruments Ltd., Malvern, Worcestershire, UK), using polyethylene square cells to measure the average hydrodynamic diameter (Dh) of ABA, ABA/βCD hydrophobic nanoprecipitates spontaneously formed by the mixture of their DMSO solutions in water.
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