Fabrication of a magnetic nanoparticle embedded NH2-MIL-88B MOF hybrid for highly efficient covalent immobilization of lipase

Abstract

Metal–organic frameworks (MOFs), a class of porous hybrid materials composed of metal ions and organic ligands, have been studied for a variety of applications. In this work, for the first time, magnetic MOFs are developed for lipase immobilization. A general one-step in situ hydrothermal route is developed for the construction of MOFs encapsulating superparamagnetic Fe₃O₄ nanoparticles. The integration of Fe₃O₄ nanoparticles into the MOFs exhibits many interesting inherent properties including a porous nature, easy functionalization as well as strong superparamagnetism. Here Candida rugosa lipase (CRL) is covalently attached to amino-rich magnetic MOFs. The resulting magnetic MOFs are characterized by means of field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and vibrating sample magnetometer (VSM) measurements. Then the enzymatic activities of the immobilized CRL are compared with free CRL. The immobilized CRL presented a wider pH tolerance and excellent thermal stability than free CRL. The Michaelis–Menten kinetic constant (K_m) and maximum reaction velocity (V_max) for both free and immobilized lipase are investigated. The loading amount of CRL on the magnetic MOFs was 280 mg per g of support and the immobilized CRL was efficiently recycled for up to nine cycles.