Abstract
The covalent binding of xylanase to silica-coated modified magnetite nanoparticles via cyanuric chloride activation was investigated. The structure, size, and magnetic properties of the support and immobilized xylanase were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectra (FTIR), thermo-gravimetric analysis (TGA) and vibrating sample magnetometer (VSM) analysis. The TEM images showed that the xylanase immobilized on functionalized magnetic nanoparticles (xylanase-MNPs) possessed three dimensional core–shell structures with an average diameter of ∼9nm. The FTIR and XPS results demonstrated the successful immobilization of xylanase on functionalized MNPs. Results from Bradford protein assay and TGA indicated that xylanase was covalently attached to the surface of modified magnetic nanoparticles with immobilization yield of 280mg enzyme/gMNPs. The VSM analysis revealed that Fe3O4, Fe3O4@SiO2 and xylanase-MNPs had high saturation magnetization of 69.4, 63.84 and 46.56emu/g, respectively. Enzymatic activity, reusability, thermo-stability, pH-stability, and storage stability of the immobilized xylanase were found significantly superior to those of the free one. The xylanase-MNPs exhibited maximal catalytic activity at pH 6.5 and 60°C and the immobilized enzymes were found to keep as high as 80% of the activity of free ones. Notably, xylanase-MNPs showed quite impressive stability, even after 9 reaction cycles, it could still retain about 65% of the initial activity. The measurement of Michaelis–Menten parameters (Km and vmax) also revealed the considerable improvement of immobilized enzyme. The results suggested that xylanase-MNPs could be used in an interesting range of application allowing both using in broader temperature and pH ranges, facilitating long-term storage, while permitting magnetic recovery of the enzyme for reuse or purification of the product.
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