On the formulation of disulfide herbicides based on aminophenoxazinones: polymeric nanoparticle formulation and cyclodextrin complexation to combat crop yield losses

Abstract

Background: The resistance of weeds to herbicides is a significant issue in ensuring future food supply. Specific examples are Plantago lanceolata, Portulaca oleracea and Lolium rigidum, which mainly infect rice, wheat, barley and pastures, and cause high yield losses every year. In this regard, natural products and their mimics have provided new hope as a result of their different modes-of-action, activity at low concentrations and reduced pollution effects relative to conventional herbicides. However, the poor water solubility and physicochemical properties of these compounds limit their broad application. These problems can be addressed by formulation techniques, and encapsulation appears to be of great interest. Results: Disulfide herbicides inspired by aminophenoxazinones have been formulated with 2-hydroxypropyl-β-cyclodextrin (HP-β-CD), γ-CD and polymeric nanoparticles (NPs). In silico studies were employed to identify which complexes would be generated and complex formation was confirmed by nuclear magnetic resonance spectroscopy. Solubility diagrams were generated to assess any improvement in water solubility, which was enhanced 2–13-fold. Scanning electron microscopy and energy-dispersive X-ray spectra confirmed the success of the formulation process for the nanoparticles. Formulated compounds were evaluated in an in vitro wheat coleoptile bioassay, with almost 100% elongation inhibition achieved using only water for the bioassay. Specific in vitro testing on weed phytotoxicity showed that the application of core/shell NPs is highly effective in the fight against P. lanceolata seed germination. Conclusions: The formulation of disulfide herbicides with CD complexes and NPs led to an enhancement in water solubility and bioactivity. These systems can be applied in pre-emergent mode against P. lanceolata, using only water to prepare the sample, and they showed better activity than the positive controls. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.