Synthesis and Characterization of Slow-Release Chitosan Oligosaccharide Pyridine Schiff Base Copper Complexes with Antifungal Activity

Herein, a series of chitosan oligosaccharide copper complexes modified with pyridine groups (CPSx-Cu complexes) were successfully prepared via the Schiff base reaction and ion complexation reaction for slow-release fungicide. The structures of the synthesized derivatives were characterized via Fourier transform infrared spectroscopy and ¹H and ¹³C nuclear magnetic resonance spectroscopy, and the unit configuration of the complexes was calculated using Gaussian software. The slow-release performance experiment demonstrated that the cumulative copper ion release rate of CPSx-Cu complexes was dependent on the type of substituents on the pyridine ring. Furthermore, the in vitro and in vivo antifungal activities of the CPSx-Cu complexes were investigated. At a concentration of 0.4 mg/mL, CPSx-Cu complexes completely inhibited the growth of Pythium vexans and Phytophthora capsici. Results indicated that CPSx-Cu complexes with slow-release ability exhibited better antifungal activity than thiodiazole-copper and copper sulfate basic. This study confirmed that combining chitosan oligosaccharide with bioactive pyridine groups and copper ions is an effective approach to further developing slow-release copper fungicides, providing new possibilities for the application of copper fungicides in green agriculture. This study lays the foundation for further studies on biogreen copper fungicides.