Self-Assembly Mechanism of Avermectin B1a and Its Activity against Potato Rot Nematode

Many of the carriers used in the delivery of avermectin (Avm) B1a, a widely used crop pesticide, may lead to environmental safety problems. Here, we tested the self-assembly of Avm B1a without an exogenous excipient for improved environmental safety and drug activity. Our results showed that various solvents, including ethanol, methanol, acetone, dimethyl sulfoxide, and N,N-dimethylformamide, can be used to prepare Avm B1a self-assembled nanoparticles. Nuclear magnetic titration experiments revealed that the intermolecular hydrogen bond was the main binding force in Avm B1a self-assembly. Molecular dynamics simulations indicated that the number of hydrogen bonds increased to 10 and 20 in the assembly system of 16 and 32 Avm B1a molecules, respectively, over a period of 500 ns. The assembled Avm B1a presented a structured spherical shape, and particle size could be effectively regulated with the initial concentration. The permeability in soil and anti-UV degradation capacity were, respectively, 3.5 and 2.0 times higher for self-assembled nanoparticles with a size of 128 nm than for pure Avm B1a. The activity of nanoparticles against potato putrid stem nematode was higher than that of pure Avm B1a; in that, particles with a size of 128 nm exhibited the highest activity, and the 24 h and 48 h activity was, respectively, 16 and 20% higher than that of pure Avm B1a. In vivo fluorescence experiments showed that the fluorescence in nematodes increased with the increase in chemical concentration and time.