Novel magnetic nanoparticles for the hydrolysis of starch with Bacillus licheniformis α-amylase

Novel magnetic nanoparticles with an average size of 350-400 nm with N-methacryloyl-(L)-phenylalanine (MAPA) as a hydrophobic monomer were prepared by the surfactant-free emulsion polymerization of 2-hydroxyethyl methacrylate, MAPA, and magnetite in an aqueous dispersion medium. MAPA was synthesized from methacryloyl chloride and L-phenylalanine methyl ester. The specific surface area of the nonporous magnetic nanoparticles was found to be 580 m ²/g. Magnetic poly[2-hydroxyethyl methacrylate-N-methacryloyl-(L)- phenylalanine] nanoparticles were characterized by Fourier transform infrared spectroscopy, electron spin resonance, atomic force microscopy, and transmission electron microscopy. Elemental analysis of MAPA for nitrogen was estimated as 4.3 × 10^-3 mmol/g of nanoparticles. Then, magnetic nano-poly[2-hydroxyethyl methacrylate-N-methacryloyl-(L)-phenylalanine] nanoparticles were used in the adsorption of Bacillus licheniformis α-amylase in a batch system. With an optimized adsorption protocol, a very high loading of 705 mg of enzyme/g nanoparticles was obtained. The adsorption phenomena appeared to follow a typical Langmuir isotherm. The inverse of enzyme affinity for free amylase (181.82 mg/mL) was higher than that for immobilized enzyme (81.97 mg/mL). Storage stability was found to increase with adsorption. It was observed that the enzyme could be repeatedly adsorbed and desorbed without a significant loss in the adsorption amount or enzyme activity.