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Semi‐biological photosynthesis combines synthetic photosensitizers with microbial catalysts to produce sustainable fuels and chemicals from CO2. However, the inefficient transfer of photoexcited electrons to microbes leads to limited CO2 utilization, restricting the catalytic performance of such biohybrid assemblies. Here, we introduce a biological engineering solution to address the inherently sluggish electron uptake mechanism of a methanogen, Methanosarcina barkeri (M. barkeri), by coculturing it with an electron transport specialist, Geobacter sulfurreducens KN400 (KN400), an adapted strain rich with multiheme c‐type cytochromes (c‐Cyts) and electrically conductive protein filaments (e‐PFs) made of polymerized c‐Cyts with enhanced capacity for extracellular electron transfer (EET). Integration of this M. barkeri‐KN400 co‐culture with a synthetic photosensitizer, carbon nitride, demonstrates that c‐Cyts and e‐PFs, emanating from live KN400, transport photoexcited electrons efficiently from the carbon nitride to M. barkeri for methanogenesis with remarkable long‐term stability and selectivity. The demonstrated cooperative interaction between two microbes via direct interspecies electron transfer (DIET) and the photosensitizer to assemble a semi‐biological photocatalyst introduces an ecosystem engineering strategy in solar chemistry to drive sustainable chemical reactions. [ABSTRACT FROM AUTHOR]

Precious metal complexes remain ubiquitous in photoredox catalysis (PRC) despite concerted efforts to find more earth‐abundant catalysts and replacements based on 3d metals in particular. Most otherwise plausible 3d metal complexes are assumed to be unsuitable due to short‐lived excited states, which has led researchers to prioritize the pursuit of longer excited‐state lifetimes through careful molecular design. However, we report herein that the C−H arylation of pyrroles and related substrates (which are benchmark reactions for assessing the efficacy of photoredox catalysts) can be achieved using a simple and readily accessible octahedral bis(diiminopyridine) cobalt complex, [1‐Co](PF6)2. Notably, [1‐Co]2+ efficiently functionalizes both chloro‐ and bromoarene substrates despite the short excited‐state lifetime of the key photoexcited intermediate *[1‐Co]2+ (8 ps). We present herein the scope of this C−H arylation protocol and provide mechanistic insights derived from detailed spectroscopic and computational studies. These indicate that, despite its transient existence, reduction of *[1‐Co]2+ is facilitated via pre‐assembly with the NEt3 reductant, highlighting an alternative strategy for the future development of 3d metal‐catalyzed PRC. [ABSTRACT FROM AUTHOR]

A general synthetic sequence involving simply prepared starting materials provides rapid access to diverse, novel tricyclic architectures inspired by pleuromutilin. SmII-mediated radical cyclization cascades of dialdehydes, prepared using a new, one-pot, copper-catalyzed double organomagnesium addition to β-chlorocyclohexenone, proceed with complete sequence selectivity and typically with high diastereocontrol to give analogues of the target core. Our expedient approach (ca. 7 steps) allows non-traditional, de novo synthetic access to analogues of the important antibacterial that can't be prepared from the natural product by semisynthesis. [ABSTRACT FROM AUTHOR]

Flavohemoglobins (flavoHbs) constitute a distinct class of chimeric hemoglobins in which a globin domain is coupled with a ferredoxin reductase such as FAD- and NADH-binding modules. Structural features and active site of heme and reductase domains are highly conserved in various flavoHbs. A new class of flavoHbs, displaying crucial differences in functionally conserved regions of heme and reductase domains, have been identified in mycobacteria. Mining of microbial genome data indicated that the occurrence of such flavoHbs might be restricted to a small group of microbes unlike conventional flavoHbs that are widespread among prokaryotes and lower eukaryotes. One of the representative flavoHbs of this class, encoded by Rv0385 gene (MtbFHb) of Mycobacterium tuberculosis, has been cloned, expressed, and characterized. The ferric and deoxy spectra of MtbFHb displayed a hexacoordinate state indicating that its distal site may be occupied by an intrinsic amino acid or an external ligand and it may not be involved in nitric oxide detoxification. Phylogenetic analysis revealed that mycobacterial flavoHbs constitute a separate cluster distinct from conventional flavoHbs and may have novel function(s). © 2011 IUBMB IUBMB Life, 63(5): 337-345, 2011 [ABSTRACT FROM AUTHOR]

Cellobiose dehydrogenase (CDH) is an extracellular flavocytochrome containing flavin andb-type heme, and plays a key role in cellulose degradation by filamentous fungi. To investigate intermolecular electron transfer from CDH to cytochrome c, Phe166, which is located in the cytochrome domain and approaches one of propionates of heme, was mutated to Tyr, and the thermodynamic and kinetic properties of the mutant (F166Y) were compared with those of the wild-type (WT) enzyme. The mid-point potential of heme in F166Y was measured by cyclic voltammetry, and was estimated to be 25 mV lower than that of WT at pH 4.0. Although presteady-state reduction of flavin was not affected by the mutation, the rate of subsequent electron transfer from flavin to heme was halved in F166Y. When WT or F166Y was reduced with cellobiose and then mixed with cytochrome c, heme re-oxidation and cytochrome creduction occurred synchronously, suggesting that the initial electron is transferred from reduced heme to cytochrome c. Moreover, in both enzymes the observed rate of the initial phase of cytochrome creduction was concentration dependent, whereas the second phase of cytochrome creduction was dependent on the rate of electron transfer from flavin to heme, but not on the cytochrome cconcentration. In addition, the electron transfer rate from flavin to heme was identical to the steady-state reduction rate of cytochrome cin both WT and F166Y. These results clearly indicate that the first and second electrons of two-electron-reduced CDH are both transferred via heme, and that the redox reaction of CDH involves an electron-transfer chain mechanism in cytochrome creduction. [ABSTRACT FROM AUTHOR]