Exploring novel slow-release organic copper fungicides

Copper fungicides have been widely used due to their wide sterilization spectrum, low cost and low drug resistance.

However, their toxicity to plant growth and damage to the environment cannot be ignored. Therefore, developing novel, low toxicity biogenic copper fungicide is necessary.

Recently, Dr. Liu Weixiang of Prof. Li Pengcheng's team from the Institute of Oceanology of the Chinese Academy of Sciences (IOCAS) provided new insights into the design and synthesis of slow-release organic copper fungicides based on chitooligosaccharide (COS).

The study was published in Carbohydrate Polymers on May 26.

Graphical abstract. Credit: Carbohydrate Polymers (2022). DOI: 10.1016/j.carbpol.2022.119663

The researchers proposed that the construction of a conjugated system is a feasible method for the design and synthesis of slow-release COS copper complexes. They synthesized pyridinylcarbonyl chitooligosaccharide ligands (pCOSx) and their copper complexes (pCOSx-Cu).

Results showed that a slowly dissociated coordination bond was formed between the nitrogen atom of pyridyl and Cu²⁺ in pCOSx-Cu because of the formulation of a p-π-π conjugated system in pCOSx.

From the perspective of Phytophthora capsici Leonian control, pCOS2-Cu synthesized by isonicotinoyl chloride exhibited the best antifungal activity and root protection effect. When the concentration was 0.8 mg/mL, pCOS2-Cu completely inhibited the growth of mycelium in vitro.

Researchers also found that pCOSx-Cu had better antifungal activity, lower toxicity and lower metal content than commercially available copper fungicides. In addition, due to the introduction of COS, the root activity of seedlings increased with higher pCOSx-Cu concentration.

Chitooligosaccharide metal complexes have different physicochemical properties and biological activities due to their structural diversity, yet the relationship between their slow-release performances and molecular structures has not been elucidated.

With this regard, pyridinylcarbonyl chitooligosaccharide copper complexes with different conjugated systems were constructed in this study, and their slow-release performances and biological activities were further explored. "This will help us to understand the structure-activity relationship of chitooligosaccharide copper complexes," said Dr. Liu, first author of the study.

"The pyridinylcarbonyl chitooligosaccharide copper complexes possess good biological activity and environmental sustainability; it offers the possibility for use in the comprehensive management of crop fungal diseases," said Prof. Li. This discovery lays a foundation for the in-depth study of green copper fungicides based on marine biomacromolecules.

More information: Weixiang Liu et al, Synthesis and antifungal activity of slow-release pyridinylcarbonyl chitooligosaccharide copper complexes, Carbohydrate Polymers (2022). DOI: 10.1016/j.carbpol.2022.119663