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

Racemic 1-phenylethylamine was resolved by enantiomer selective acetylation using Fe 3 O 4 -chitosan microsphere (CTS)-glutaraldehyde-lipase in a solvent-free system under an alternating magnetic field. Magnetic chitosan microspheres (Fe 3 O 4 -CTS) were prepared via chemical co-precipitation and cross-linked with lipase using glutaraldehyde to form Fe 3 O 4 -CTS-glutaraldehyde-lipase particles. The magnetic, physicochemical, and textural characteristics of Fe 3 O 4 -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 Fe 3 O 4 -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 Fe 3 O 4 -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 Fe 3 O 4 -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. Fe 3 O 4 -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 V max =1.62×10 −2 mM/min, K A =2.84×10 −4 mM, and K B =5.8×10 −1 mM. The model data fit well with the experimental data.