Immobilisation of lipase on the surface of magnetic nanoparticles and non-porous glass beads for regioselective acetylation of prednisolone

Magnetic nanoparticles (MNPs) were prepared by co-precipitation of Fe⁺³/Fe⁺² (2:1; molar ratio) with a mean size of 40 ± 5 nm. Scanning electron microscopy, dynamic light scattering, X-ray diffraction, vibrating sample magnetometer and thermogravimetric analysis were used to characterise the MNPs. The MNPs and also hydroxylated nonporous glass beads were similarly functionalised with the aid of glutaraldehyde to be cross-linked to lipase originated from Thermomyces lanuginosus (TLL). The yield and efficiency for immobilised lipase on the MNPs were calculated as 72 ± 2.4 and 63 ± 3.5%, whereas a yield and efficiency of 60 ± 2.1 and 55 ± 4.1%, respectively, were measured for the corresponding parameters of the immobilised enzyme on the glass beads. When the immobilised TLL was compared with its free form, Michaelis-Menten kinetics indicated an insignificant change in the Michaelis constant (K_m) and a drastic decrease in the maximum substrate conversion rate (V_max). The immobilised TLL and six other commercial lipases were then checked for regioselective acetylation of prednisolone. The highest and lowest yields of the product were observed for Novozym 435 and immobilised TLL on the glass beads, respectively. Immobilised TLL retained its bioacetylation activity of prednisolone in five successive catalytic processes.