Driving a sustainable application of s-triazine ametryn and atrazine herbicides through multicomponent crystals with improved solubility

Abstract

Atrazine (ATZ) and ametryn (AMT) are poorly soluble s-triazine herbicides widely used worldwide as the main weed control (WC) method in crops. Herein, we report the highly soluble multicomponent crystals of these s-triazine herbicides, which were fabricated with the aim to provide safer and more eco-friendly formulations. The crystallization of ATZ with fumaric acid yielded hydrated (ATZ–H₂Fum·H₂O) and dehydrated (ATZ–H₂Fum) cocrystals with an herbicide : acid ratio of 2 : 1, whereas the combination of AMT with nitric and trifluoracetic acids resulted in the formation of two 1 : 1 salts (AMT–NO₃ and AMT–TFA, respectively). All solid forms were characterized in terms of their structural (single-crystal/powder X-ray diffraction and infrared spectroscopy), and physicochemical properties (thermal stability, phase transition, and solubility). Similarities between the crystal arrangements of these compounds could be seen in the formation of 1D-chains by the association of the s-triazine herbicide molecules and the ionizable portion of coformers. Thus, the crystal structures featured hydrophilic domains, breaking the original hydrophobic packing of the pure herbicides and, hence, increasing significantly the melting point and modifying the solubility compared to the parent forms. The new crystals ATZ–H₂Fum, AMT–NO₃, and AMT–TFA were 6-fold, 22-fold, and 14-fold, respectively, more soluble than their corresponding pure forms. The implication of these findings complies with enhanced sustainability in the crop production, whereby the herbicidal formulation utilizes highly soluble compounds, which could decrease the presence of undissolved solids or adjuvants, and thereby, reduce the dosage needed for WC.