We report a sustainable in vitro system for enzyme-based photohydrogen production. The [FeFe]-hydrogenase HydA1 from Chlamydomonas reinhardtii was tested for photohydrogen production as a proton-reducing catalyst in combination with eight different photosensitizers. Using the organic dye 5-carboxyeosin as a photosensitizer and plant-type ferredoxin PetF as an electron mediator, HydA1 achieves the highest light-driven turnover number (TON ) yet reported for an enzyme-based in vitro system (2.9×10 mol(H ) mol(cat) ) and a maximum turnover frequency (TOF ) of 550 mol(H ) mol(HydA1) s . The system is fueled very effectively by ambient daylight and can be further simplified by using 5-carboxyeosin and HydA1 as a two-component photosensitizer/biocatalyst system without an additional redox mediator.
The sustainable capture and conversion of carbon dioxide (CO2) is key to achieving a circular carbon economy. Bioelectrocatalysis, which aims at using renewable energies to power the highly specific, direct transformation of CO2 into value added products, holds promise to achieve this goal. However, the functional integration of CO2‐fixing enzymes onto electrode materials for the electrosynthesis of stereochemically complex molecules remains to be demonstrated. Here, we show the electricity‐driven regio‐ and stereoselective incorporation of CO2 into crotonyl‐CoA by an NADPH‐dependent enzymatic reductive carboxylation. Co‐immobilization of a ferredoxin NADP+ reductase and crotonyl‐CoA carboxylase/reductase within a 2,2′‐viologen‐modified hydrogel enabled iterative NADPH recycling and stereoselective formation of (2S)‐ethylmalonyl‐CoA, a prospective intermediate towards multi‐carbon products from CO2, with 92±6 % faradaic efficiency and at a rate of 1.6±0.4 μmol cm−2 h−1. This approach paves the way for realizing even more complex bioelectrocatalyic cascades in the future.
While bimetallic azacryptands are known to selectively coordinate CO, there is little knowledge on how different substitution patterns of the azacryptand cage structure influence CO coordination. Stopped-flow UV-vis spectroscopy, electrochemical analysis and DFT calculations were performed on a series of dinickel azacryptands and showed different rates of CO coordination to the complexes. We herein present data showing that the different flexibility of the azacryptands is directly responsible for the difference in the CO uptake capability of dinickel azacryptand complexes.
Redox‐active polymers for wiring NADPH recycling and CO2‐fixating enzymes create a bioelectrocatalytic volume on electrodes for the regio‐ and stereoselective incorporation of CO2 into complex molecules via C−C bond formation at high current densities. Details of the study are presented in the Research Article by Michael Richter, Nicolas Plumeré et al. on page 21056.
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