Direct detection of a single[4Fe-4S]cluster in a tungsten-containing enzyme:Electrochemical conversion of CO_(2) into formate by formate dehydrogenase

The conversion of CO_(2) into fuels and valuable chemicals is one of the central topics to combat climate change and meet the growing demand for renewable energy.Herein,we show that the formate dehydrogenase from Clostridium ljungdahlii(ClFDH)adsorbed on electrodes displays clear characteristic voltammetric signals that can be assigned to the reduction and oxidation potential of the[4Fe-4S]^(2+/+)cluster under nonturnover conditions.Upon adding substrates,the signals transform into a specific redox center that engages in catalytic electron transport.ClFDH catalyzes rapid and efficient reversible interconversion between CO_(2) and formate in the presence of substrates.The turnover frequency of electrochemical CO_(2) reduction is determined as 1210 s^(-1) at 25℃ and pH 7.0,which can be further enhanced up to 1786 s^(-1) at 50℃.The Faradaic efficiency at−0.6 V(vs.standard hydrogen electrode)is recorded as 99.3%in a 2-h reaction.Inhibition experiments and theoretical modeling disclose interesting pathways for CO_(2) entry,formate exit,and OCN−competition,suggesting an oxidation-state-dependent binding mechanism of catalysis.Our results provide a different perspective for understanding the catalytic mechanism of FDH and original insights into the design of synthetic catalysts.

Hydrogenase as the basis for green hydrogen production and utilization

Hydrogenase is a paradigm of highly efficient biocatalyst for H_(2) production and utilization evolved in nature. A dilemma is that despite the high activity and efficiency expected for hydrogenases as promising catalysts for the hydrogen economy, the poor oxygen tolerance and low yield of hydrogenases largely hinder their practical application. In these years, the enigmas surrounding hydrogenases regarding their structures, oxygen tolerance, mechanisms for catalysis, redox intermediates, and proton-coupled electron transfer schemes have been gradually elucidated;the schemes, which can well couple hydrogenases with other highly efficient(in)organic and biological catalysts to build novel reactors and drive valuable reactions, make it possible for hydrogenases to find their niches. To see how scientists put efforts to tackle this issue and design novel reactors in the fields where hydrogenases play crucial roles, in this review,recent advances were summarized, including different strategies for protecting enzyme molecules from oxygen, enzyme-based assembling systems for H_(2) evolution in the photoelectronic catalysis, enzymatic biofuel cells for H_(2) utilization and storage and the efficient electricity-hydrogen-carbohydrate cycle for high-purity hydrogen and biofuel automobiles. Limitations and future perspectives of hydrogenasebased applications in H_(2) production and utilization with great impact are discussed. In addition, this review also provides a new perspective on the use of biohydrogen in healthcare beyond energy.

Decoding and quantitative detection of antibiotics by a luminescent mixed-lanthanide-organic framework

Due to the potential risk of antibiotics to the environment,the development of inexpensive,simple,and reliable antibiotic detection methods is significant but also faces challenges.In this work,several lanthanide-organic frameworks(LOFs),constructed from lanthanide ions(Eu3+and/or Tb3+)and 1,3,5-benzene-tricarboxylic acid(BTC),were synthesized by solvothermal method.LOF-S3 with comparable emission peaks of 5D4→7F5(Tb3+,545 nm)and 5D0→7F2(Eu3+,618 nm)was selected as a luminescent sensor.In this system,the highly efficient energy transferred from the organic linker to lanthanide ions and from Tb3+to Eu3+occurs.LOF-S3 sensor was capable of decoding antibiotics by distinguishable emission intensity ratios.Therefore,a two-dimensional decoded map of antibiotics was established.The linear relationship between antibiotic concentration and emission intensity ratio indicated the quantitative determination of antibiotics was feasible.As a typical analyte,the response mechanism of nalidixic acid(NA)was investigated in detail.The competition of NA and BTC for UV light absorption,as well as the binding propensity of NA and Tb,affected the organic linkers-to-lanthanide ions and Tb-to-Eu energy transfer,resulting in the change of fluorescence intensity ratio.The self-calibrating mixed-LOF sensor overcame the uncontrollable errors of the traditional absolute emission intensity method and generated stable luminescent signals in multiple cycles.Furthermore,the integration of LOF-S3 with polymer fibers enabled the formation of a LOF-polymer fibrous composite with fluorescence detection capability,which is a promising portable sensor for practical applications.