Stereoselective Double Reduction of 3-Methyl-2-cyclohexenone, by Use of Palladium and Platinum Nanoparticles, in Tandem with Alcohol Dehydrogenase

NAD(H)-PEG Swing Arms Improve Both the Activities and Stabilities of Modularly-Assembled Transhydrogenases Designed with Predictable Selectivities

Protein engineering has been used to enhance the activities, selectivities, and stabilities of enzymes.  Frequently tradeoffs are observed, where improvements in some features can come at the expense of others.  Nature uses modular assembly of active sites for complex, multi-step reactions, and natural "swing arm" mechanisms have evolved to transfer intermediates between active sites.  Biomimetic polyethylene glycol (PEG) swing arms modified with NAD(H) have been explored to introduce synthetic swing arms into fused oxidoreductases.  Here we report that increasing NAD(H)-PEG swing arms can improve the activity of synthetic formate:malate oxidoreductases as well as the thermal and operational stabilities of the biocatalysts.  The modular assembly approach enables the K M values of new enzymes to be predictable, based on the parental enzymes.  We describe four unique synthetic transhydrogenases that have no native homologs, and this platform could be easily extended for the predictive design of additional synthetic cofactor-independent transhydrogenases.

Palladium and Copper: Advantageous Nanocatalysts for Multi-Step Transformations

Metal nanoparticles have been deeply studied in the last few decades due to their attractive physical and chemical properties, finding a wide range of applications in several fields. Among them, well-defined nano-structures can combine the main advantages of heterogeneous and homogeneous catalysts. Especially, catalyzed multi-step processes for the production of added-value chemicals represent straightforward synthetic methodologies, including tandem and sequential reactions that avoid the purification of intermediate compounds. In particular, palladium- and copper-based nanocatalysts are often applied, becoming a current strategy in the sustainable synthesis of fine chemicals. The rational tailoring of nanosized materials involving both those immobilized on solid supports and liquid phases and their applications in organic synthesis are herein reviewed.

Electrostatic Interaction-Induced Formation of Enzyme-on-MOF as Chemo-Biocatalyst for Cascade Reaction with Unexpectedly Acid-Stable Catalytic Performance

Combining biocatalytic and chemocatalytic reactions in a one-pot reaction not only avoids the tedious isolation of intermediates during the reactions but also provides a desirable alternative to extend the range of catalytic reactions. Here, we report a facile strategy to immobilize an enzyme, glucose oxidase (GOx), on PCN-222(Fe) induced by electrostatic interaction in which PCN-222(Fe) serves as both a support and chemocatalyst. The immobilization was confirmed through ζ potential measurement, confocal laser scanning microscopy, Fourier transform infrared spectrometry, and UV-vis spectroscopy. This chemo-biocatalyst was applied to a cascade reaction to catalyze glucose oxidation and ABTS (ABTS = 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (or pyrogallol) oxidation. The catalytic kinetics studies show that these chemo-biocatalytic cascade reactions obey the Michaelis-Menten equation, which indicates that the cascade reactions follow the typical enzymatic dynamic regulation process. Interestingly, GOx/PCN-222(Fe) exhibits an exceptional acid-stable catalytic performance as evidenced by circular dichroism spectroscopy where no significant structure change was observed toward acidic solutions with different pH values. GOx/PCN-222(Fe) also displays desirable recyclability since no significant loss of conversion rates was found after six repeated reactions. This work presents a convenient strategy to construct metal-organic framework based chemo-biocatalysts, which may find potential applications in sensing and nanomachines.