C-coordinated O-carboxymethyl chitosan metal complexes: Synthesis, characterization and antifungal efficacy

Abstract

A novel type of O-carboxymethyl chitosan Schiff bases (O-CSPX) was synthesized via a condensation reaction. After the coordination reaction of cupric ions, zinc ions and nickel ions, metal complexes (O-CSPX-M) were achieved. The theoretical structure of O-CSPX-M calculated by Gaussian 09 reveals that the copper ions and nickel ions underwent dsp² hybridization, the zinc ions underwent sp³ hybridization, and they all coordinated by the carbon atom in the p-π conjugate group. Then, the structures were confirmed by FT-IR, ¹H NMR, CP-MAS ¹³C NMR, elemental analysis, DSC and XRD. The antifungal properties of O-CSPX-M against Phytophthora capsici (P. capsici), Gibberella zeae (G. zeae), Fusarium oxysporum (F. oxysporum) and Botrytis cinerea (B. cinerea) were evaluated at concentrations ranging from 0.05mg/mL to 0.40mg/mL. The experiments indicated that the derivatives have significantly enhanced antifungal activity after metal ions complexation compared with the original chitosan. Moreover, it was shown that 0.20mg/mL of O-CSPX-Cu can 100% inhibit the growth of P. capsici and 0.20mg/mL of O-CSPX-Ni can 87.5% inhibit the growth of B. cinerea. In addition, the phytotoxicity assay and cell viability assay were also evaluated. The experimental results may provide a novel direction for the development of metal fungicides.

Keywords: Acetic acid (PubChem CID: 176); Acetylacetone (PubChem CID: 31261); Antifungal; Chitosan (PubChem CID: 71853); Chitosan metal complex; Coordination; Cupric acetate monohydrate (PubChem CID: 165397); Diethyl ether (PubChem CID: 3283); Ethanol (PubChem CID: 702); Isonicotinamide (PubChem CID: 15074); Methanol (PubChem CID:887); Monochloroacetic acid (PubChem CID: 300); Nickel acetate tetrahydrate (PubChem CID: 62601); Nicotinamide (PubChem CID: 936); Sodium hydroxide (PubChem CID: 14798); Zinc acetate dihydrate (PubChem CID: 2724192).