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

Abstract

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 1 H and 13 C 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.

Synergistic Antifungal Activity of Dialdehyde Chitosan Loaded with Copper Metal‐Organic Framework (Cu‐MOF)

“…Additionally, the prolonged exposure of the agents has the potential to inhibit spore germination thus reducing the need for multiple applications of the fungicides. [3]…”

“…[2] Additionally, the traditional application of copper fungicides was faced with uncontrolled release of copper ions at initial applications and latter stages thus often exceeding the tolerance levels, decreasing the crop yield, and causing considerable pollution to soil and water. [3] It is because of this reason that there is a need to develop novel organic metal fungicides with low toxicity, and low metal content. To achieve this, metal-organic framework (MOFs) loaded onto polymeric matrices with proven antifungal activity such as chitosan are a promising alternative to conventional pesticides as they have enhanced antifungal and antibacterial properties, are biodegradable and can thus easily be removed from the environment.…”

“…[9,10] The cross-linking of Cs into MOF provides a new avenue for enhancing the antifungal activity of Cs via attachment activity to the target while also maintaining their degradation potential. [11] It is hypothesized that loading of MOF onto Cs ensures that the charged group such as NH 3 + present in Cs gets ionized in the acidic environment created by fungi thus damaging the pathogen cell membrane by releasing their metal ion in the cell and resulting in the leakage of reducing sugars, proteins, and degradation of their DNA and eventually reduces the cell viability. [12,13,14] The development of Cs-MOF gives the polymer a range of diverse and valuable properties for applications in agriculture in controlling and countering the resistance posed by pathogens by delaying the release of metal ions.…”

“…[23] Additionally, the stability of both the glycosidic bond and the acetylamino bond associated with Cs coupled with poor solubility hinders its reactivity and subsequent utilization in agriculture. [3,24] As a means of overcoming some of these limitations while increasing the application range of Cs, surface and structural modification have been extensively evaluated. Cs contains primary amine and hydroxyl functional groups and notably, periodate oxidation of Cs introduced carbonyl groups (C=O) in its structure which showed improved antifungal activities against Aspergillus spp and Candida spp.…”