Ugi Four-Component Assembly Process: An Efficient Approach for One-Pot Multifunctionalization of Nanographene Oxide in Water and Its Application in Lipase Immobilization

Graphene-based materials are revealing the leading edge of advanced technology for their exceptional physical and chemical properties. Chemical manipulation on graphene surface to tailor its unique properties and modify atomic structures is being actively pursued. Therefore, the discovery of robust and general protocols to anchor active functionality on graphene basal plane is still of great interest. Multicomponent reactions promise an enormous level of interest due to addressing both diversity and complexity in combinatorial synthesis, in which more than two starting compounds react to form a product derived from entire inputs. In this article, we present the first covalent functionalization route beginning with carboxylated-graphene oxide through Ugi four-component assembly process (Ugi 4-CAP), in which amine, aldehyde, isocyanide, and acid components come together in a one-pot reaction to generate hydrophobic-, hydrophilic-, or amiphiphilic multifunctionalized graphene composites. Investigation on the covalent immobilization and biocatalytic activity of Bacillus thermocatenulatus lipase (BTL) on graphene surface showed the efficiency and competency of Ugi 4-CAP. The success of the multicomponent-coupling approach was confirmed by atomic force microscopy, Raman spectroscopy, UV–vis spectroscopy, Fourier transform infrared spectroscopy, 1 H NMR, energy-dispersive X-ray spectroscopy, scanning electron microscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy.