Chitosan based metal-chelated copolymer nanoparticles: Laccase immobilization and phenol degradation studies

Immobilization improves the stability and reusability of enzymes. In this study, laccase, which is a green biocatalyst, was immobilized onto Cu (II)-chelated chitosan nanoparticles via adsorption and successfully applied to remove phenol from aqueous solution. Cu (II)-chelated chitosan-graft-poly (glycidyl methacrylate) nanoparticles were prepared using poly (ethylene imine), PEI, which is employed as both a spacer arm and metal chelator and used to immobilize laccase by coordination. Properties of chitosan based nanoparticles were characterized using FTIR, TGA, SEM and zeta-sizer analysis. The maximum laccase loading capacity of Cu (II)-chelated chitosan based nanoparticles (CHT-PGMA-PEI-Cu (II) NPs) was calculated as 65.75 ± 2.51 mg/g. This immobilized system exhibited broad pH and temperature profiles, and better stability and reusability than free enzyme; after eight cycles of continuous use, the activity of the immobilized enzyme remained above 50 ± 0.62%. The Km and Vmax values of free and immobilized laccase were 0.055 mM, 0.070 mM, and 0.19 U/mg, 0.14 U/mg, respectively. The catalytic efficiencies (Vmax/KM) of the free and immobilized laccase were 3.45 and 2.0, respectively. Feasibility of the laccase immobilized system in the removal of phenol was investigated in a batch system. The results showed that the CHT-PGMA-PEI-Cu (II) NPs have great potential for industrial applications. More than 96% of phenol was removed with laccase immobilized metal chelated NPs in the presence of mediator, ABTS, indicating that the metal-chelated chitosan based NPs is a promising support for both laccase immobilization and further applications in the removal of phenolic compounds. Laccase immobilization mechanism is attributed to metal-chelated adsorption. PEI was used as a flexible spacer-arm for moving laccase molecules away from the surface of chitosan based NPs and also acts as a metal chelator. The Cu(II) is a kind of strong Lewis acid that has high binding capacity with strong Lewis bases like histidine residues which are abundantly exposed surface of laccase. [Display omitted] •Immobilized laccase on metal-chelated chitosan based nanoparticles was developed for phenol degradation.•Phenol was removed above 80% in 4 h by metal-chelated copolymer nanoparticles.•2,2′-azino-bis(3-ethylbenzthiazoline-6- sulfonic acid) as mediator enhances the phenol degradation efficiency.