Tailoring microenvironments of metal-enzyme cascade catalysts for efficient DKR reaction of chiral amine

Metal-enzyme integrated catalysts combine the high selectivity of enzyme catalysts with the broad substrate spectrum of metal catalysts and offer tremendous possibilities for chemoenzymatic cascade processes. However, the rational design of microenvironments in nanostructures that make metals and enzymes compatible for efficient activity still remains challenging. In this report, a nanocomposite catalyst was fabricated by integrating ultrafine Pd nanoparticles (Pd NPs) and Candida antarctica lipase B (CALB) on the hydrophobic polydopamine-coated SiO₂ (SP) to enhance the compatibility of enzyme-metal catalysts. In detail, Pd NPs were in situ reduced by PDA on the SP surface, and the obtained SP-loaded Pd (Pd/SP) was hydrophobically modified by octadecyltrimethoxysilane for the subsequent adsorption immobilization of CALB to prepare the integrated catalyst, CALB/mPd/SP. The hydrophobic PDA coating on SiO₂ not only stabilized the loaded ultrasmall Pd nanoparticles but also facilitated the activation of the immobilized lipase, which helped to improve the cascade catalytic efficiency of CALB/mPd/SP. Afterward, CALB/mPd/SP was used in a one-pot dynamic kinetic resolution (DKR) reaction of α-phenylethylamine with high conversion (>99 %), selectivity (93.9 %), and ee_p (>99 %). After 25 days of storage and 5 h of sonication, CALB/mPd/SP exhibited no significant reduction in the DKR catalytic activity. This study proposed a simple and sustainable method for the preparation of enzyme-metal cascade catalysts to enhance their stability and achieve significantly increased activity through interfacial microenvironmental modulation.