Enhancing adsorption capacity and herbicidal efficacy of 2,4-D through supramolecular self-assembly: Insights from cocrystal engineering to solution chemistry

Highly water-soluble pesticides have garnered significant attention due to their poor durability and severe environmental damage caused by easy leaching. Cocrystallization based on a supramolecular self-assembly mechanism has been demonstrated to be an effective method for tuning the dissolution of pharmaceuticals and agrochemicals. However, as a strategy to tune the properties of solid materials, cocrystal engineering appears to be challenging to apply to many liquid formulations of pesticides. Herein, cocrystal of the 2,4-dichlorophenoxyacetic acid (2,4-D) and phenazine (PHE) were developed to explore whether supramolecular assembly in the solid state could be extended to the solution. In the crystalline state, the cocrystal reduced the solubility and dissolution rate of 2,4-D by 71.51 % and 50.55 %, respectively. Notably, when applied in solution, 2,4-D - PHE cocrystal exhibits greater soil adsorption capacity and lower leaching characteristics than pure 2, 4-D. Specifically, only 75% of the cocrystal was leached when 2,4-D was fully leached. Under simulated rainfall, the biological activity experiments in the greenhouse demonstrated that the control efficacy of cocrystal was almost twice as that of the pure 2,4-D. Additionally, two-dimensional NOE Spectroscopy (2D NOESY) and molecular simulations were employed to reveal the mechanism of supramolecular assembly in crystal lattice and aqueous solution. This work reveals that cocrystal engineering is a promising strategy for bridging solid-state and solution chemistry through supramolecular self-assembly to improve the persistence and decrease the off-target threat of highly water-soluble pesticides.