Amine, thiol, and octyl functionalization of GO-Fe3O4 nanocomposites to enhance immobilization of lipase for transesterification

A novel immobilization support for Candida rugosa lipase Type VII (CRL7) is presented in the form of an octyl-functionalized magnetic graphene oxide nanocomposite (GO-Fe3O4). Immobilized lipase on this support is demonstrated to have 94.7% activity relative to free enzyme (34.5 U/mg-lipase), a transesterification yield of 89%, and a retained activity of 63% after 10 cycles. The octyl-functionalized GO-Fe3O4 nanocomposite (GO-Fe3O4@OTMS) is shown to perform better than graphene oxide (GO) and functionalized nanocomposites with amine and thiol groups. X-ray powder diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, Brunauer–Emmett–Teller method, and vibrating sample magnetometry were used to characterize the functionalized nanocomposites, demonstrating that Fe3O4 nanoparticles with an average crystallite size of 13.9 nm were deposited on GO layers. The Bradford assays showed that the amount of immobilized CRL7 was significantly increased from 187.4 mg lipase/g-nanocomposite for unfunctionalized GO-Fe3O4 to 328.6, 265.3, and 413.2 mg lipase/g-nanocomposite after functionalization of the nanocomposites (GO-Fe3O4) using (3-aminopropyl)trimethoxysilane, (3-mercaptopropyl)trimethoxysilane, and (3-octyl)trimethoxysilane, respectively. The hydrolytic specific activity and transesterification of the immobilized lipase on GO-Fe3O4 were greatly enhanced by the functionalization of the nanocomposite. The optimal pH for the relative activity of CRL7 was shifted from 7 for free CRL7 and immobilized CRL7 on GO and GO-Fe3O4 to 8 for the functionalized nanocomposite. Furthermore, functionalization was also shown to maintain higher relative activity at non-optimal pH and to improve thermal stability.