Development of a novel bi-enzymatic silver dendritic hierarchical nanostructure cascade catalytic system for efficient conversion of starch into gluconic acid

摘要

The natural cascade processes lead to inspire researchers to bring diverse biocatalysts together in an artificial way. In this work, we are going to introduce a brilliant double enzyme microsystem prepared from co-immobilization of glucose oxidase (GOD) and glucoamylase (GA) on silver dendrites hierarchical (Ag-DH) nanostructure through Ugi four-component reaction (Ugi-4CR) in water, as the green solvent at ambient temperature. The success preparation of the unique biocatalyst system was confirmed by FT-IR, UV-Vis, TGA, XRD, TEM, FE-SEM, AFM and elemental analysis. The properties of free and immobilized enzymes were investigated and compared. The immobilized GA and GOD had higher K_m (Michaelis constant) and lower V_(max) (maximum reaction velocity) than their native forms. The values of activation energy (E_a) for both the immobilized enzymes were smaller than those with native enzymes, implying that the immobilized enzymes are more temperature insensitive. The obtained double enzyme microsystem was employed as a biocatalyst for one pot transformation of starch to gluconic acid as an exclusive cascade reaction under mild conditions and in aqueous medium, and the final product obtained in high yield. Moreover, the artificial biomimetic microsystem exhibited high stability and reusability after eight cycles. These results demonstrated the feasibility of this approach for co-immobilization of enzyme on hierarchical structures may be extended to other biocatalytic cascades, thereby opening a new window for the other artificial biotransformations in chemistry.