Enhancement of catalytic activity of lipase-immobilized Fe3O4-chitosan microsphere for enantioselective acetylation of racemic 1-phenylethylamine

Abstract

Racemic 1-phenylethylamine was resolved by enantiomer selective acetylation using Fe3O4-chitosan microsphere (CTS)-glutaraldehyde-lipase in a solvent-free system under an alternating magnetic field. Magnetic chitosan microspheres (Fe3O4-CTS) were prepared via chemical co-precipitation and cross-linked with lipase using glutaraldehyde to form Fe3O4-CTS-glutaraldehyde-lipase particles. The magnetic, physicochemical, and textural characteristics of Fe3O4-CTS-glutaraldehyde-lipase particles were assessed by Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. The optimal immobilization conditions were 2.4 mg/mL lipase, 10 mg/mL Fe3O4-CTS-glutaraldehyde, pH 8.5, 35 °C, 3 h. The loading amount of lipase and the specific activity got to 132 mg/g carrier and 48 U/g. The optimal reaction conditions of the acylation reaction using Fe3O4-CTS-glutaraldehyde-lipase were 300 mmol/L 1-phenylethylamine, 150 mg immobilized lipase, 2 mL vinyl acetate, 12.6 ×g rotating speed, 40 °C, 8 h. The activity of the Fe3O4-CTS-glutaraldehyde-lipase particles and conversion were improved when they were exposed to an external alternating magnetic field. The optimum magnetic field was 12 Gs (500 Hz). The conversion, enantiomeric excess of (R)-N-(1-phenylethyl)acetamide, and E value reached 41.8%, 98.4%, and 264, respectively. Fe3O4-CTS-glutaraldehyde-lipase could be reused seven times. A kinetic model of the immobilized lipase-catalyzed resolution of 1-phenylethylamine was set up based on the ping-pong bi-bi mechanism. The kinetic constants were Vmax=1.62×10−2 mM/min, KA=2.84×10−4 mM, and KB=5.8×10−1 mM. The model data fit well with the experimental data.