Given the high costs and stoichiometric amounts of reduced nicotinamide adenine dinucleotide (NADH) required by the many oxidoreductases used for organic synthesis and the pharmaceutical industry, there is a need for the efficient reductive regeneration of NADH from its oxidized form, NAD + . Bioelectrocatalytic methods for NADH regeneration involving diaphorase and a redox mediator have shown promise; however, strong reductive mediators needed for this system are scarce, generally unstable, and require downstream separation. The immobilization of diaphorase in cobaltocene-modified poly-(allylamine) redox polymer is presented which is capable of producing bioactive 1,4-NADH with yields between 97% and 100%, faradaic efficiencies between 78% and 99%, and turnover frequencies between 2091 h −1 and 3680 h −1 over a range of temperatures spanning 20 to 60 °C. By using this system, methanol and propanol production by an NADH-dependent alcohol dehydrogenase were enhanced 7.1-and 5.2-fold, respectively, compared with a negative control. Finally, the efficiency of this approach coupled with its high operational stability (91% of the maximum activity after five experimental cycles) renders it among the most promising means of NADH regeneration yet developed.
Aliphatic synthetic intermediates with high added value are generally produced from alkane sources (e.g., petroleum) by inert carbon–hydrogen (C−H) bond activation using classical chemical methods (i.e. high temperature, rare metals). As an alternative approach for these reactions, alkane monooxygenase from Pseudomonas putida (alkB) is able to catalyze the difficult terminal oxyfunctionalization of alkanes selectively and under mild conditions. Herein, we report an electrosynthetic system using an alkB biocathode which produces alcohols, epoxides, and sulfoxides through bioelectrochemical hydroxylation, epoxidation, sulfoxidation, and demethylation. The capacity of the alkB binding pocket to protect internal functional groups is also demonstrated. By coupling our alkB biocathode with a hydrogenase bioanode and using H2 as a clean fuel source, we have developed and characterized a series of enzymatic fuel cells capable of oxyfunctionalization while simultaneously producing electricity.
Atmospheric CO 2 is ac heap and abundants ource of carbonf or synthetic applications. However, the stability of CO 2 makes its conversion to other carbon compounds difficult and has prompted the extensive developmento fC O 2 reduction catalysts. Bioelectrocatalystsa re generally more selective, highly efficient, can operate under mild conditions, and use electricity as the sole reducing agent.I mproving the communication between an electrode and ab ioelectrocatalyst remains as ignificant area of development. Through the examples of CO 2 reduction catalyzed by electroactivee nzymesa nd whole cells, recent advancements in this area are compared and contrasted. Figure 5. (A) MWCNT-coated RVCs used to produce acetate by am ixed bacterial culture. Reproduced with permission from American Chemical Societyfrom Reference [50].(B) Agraphite felt electrode serves as artificial pilifor microbial electrosynthesis. Reproducedw ith permission from Elsevier from Reference [55].
Substrate channeling, where an intermediate in a multistep reaction is directed toward a reaction center rather than freely diffusing, offers several advantages when employed in catalytic cascades. Here we present a fusion enzyme comprised of an alcohol and aldehyde dehydrogenase, that is computationally designed to facilitate electrostatic substrate channeling using a cationic linker bridging the two structures. Rosetta protein folding software was utilized to determine an optimal linker placement, added to the truncated termini of the proteins, which is as close as possible to the active sites of the enzymes without disrupting critical catalytic residues. With improvements in stability, product selectivity (90%), and catalyst turnover frequency, representing 500-fold increased activity compared to the unbound enzymes and nearly 140-fold for a neutral-linked fusion enzyme, this design strategy holds promise for making other multistep catalytic processes more sustainable and efficient.
Aliphatic synthetic intermediates with high added value are generally produced from alkane sources (e.g., petroleum) by inert carbon-hydrogen (CÀH) bond activation using classical chemical methods (i.e. high temperature, rare metals). As an alternative approach for these reactions, alkane monooxygenase from Pseudomonas putida (alkB) is able to catalyze the difficult terminal oxyfunctionalization of alkanes selectively and under mild conditions. Herein, we report an electrosynthetic system using an alkB biocathode which produces alcohols, epoxides, and sulfoxides through bioelectrochemical hydroxylation, epoxidation, sulfoxidation, and demethylation. The capacity of the alkB binding pocket to protect internal functional groups is also demonstrated. By coupling our alkB biocathode with a hydrogenase bioanode and using H 2 as a clean fuel source, we have developed and characterized a series of enzymatic fuel cells capable of oxyfunctionalization while simultaneously producing electricity.
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