Xylanase immobilization on magnetite and magnetite core/shell nanocomposites using two different flexible alkyl length organophosphonates: Linker length and shell effect on enzyme catalytic activity

Abstract

Magnetite and magnetite core/shell (Fe₃O₄/SiO₂) nanoparticles were synthesized and functionalized with two different alkyl chain length linkers that were 3-Phosphonopropionic acid (3-PPA) and 16-Phosphonohexadecanoic acid (16-PHDA). Xylanase (EC 3.2.1.8, endo-1,4-xylanase, endo-1), was immobilized on as synthesized bare and silica coated magnetite nanoparticles via well-known EDC coupling. Transmission Electron Microscopy (TEM), Field Emission Scanning Electron Microscopy (FESEM), X-Ray Diffraction Spectroscopy (XRD), X-ray Photoelectron Spectroscopy (XPS), Dynamic Light Scattering (DLS) and Thermogravimetric analysis (TGA) techniques were utilized to characterize all the modifications. The flexible linker chain length plays a vital role in the catalytic attributes of the immobilized enzyme. Result shows that long chain alkyl linker grafted magnetite and magnetite core/silica shell nanoparticles exhibited a superior performance in terms of lower K_m, higher catalytic efficiency and better reusability. Furthermore, the immobilized xylanase shows improved tolerability performance at a wide range of pH and temperature. Silica-coated magnetite nanoparticles bound xylanase through 16-PHDA retained 90% of its initial activity after 10 consecutive cycles, further emphasize on the beneficial effect of linker chain length and inert silica coating.

Keywords: 16-Phosphonohexadecanoic acid; 3-Phosphonopropionic acid; Magnetite and silica coated magnetite nanoparticles; Xylanase.