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1. Highly efficient deoxydehydration and hydrodeoxygenation on MoS2-supported transition metal atoms through a C-H activation mechanism

   https://doi.org/10.1021/acscatal.0c02669  

   Xi, Yongjie; Heyden, Andreas (July 2020, ACS Catalysis)

   Deoxydehydration (DODH) is an efficient process for the removal of vicinal OH groups of a diol or polyol. Conventional DODH reactions usually take place at a single-site MOx (M=Re, Mo, V etc.) active center, which proceed through a diol condensation step, an alkene extrusion step and a catalyst regeneration (or reduction) step. Here, we suggest that MoS2-supported transition metal atoms allow for the DODH reaction to occur through an alternative mechanism, whereby the C-H bond of a diol is activated first, which facilitates the C-OH bond cleavage on a neighboring carbon. The removal of the second OH group is also facile over the proposed catalysts. Our kinetic studies suggest that the DODH of ethylene glycol on Ru2/MoS2, Ir2/MoS2 and Ru3/MoS2 are highly active with predicted turnover frequencies of over 1/s. Thus, our study suggests a possible approach for the design of highly active DODH catalysts. Apart from being a DODH catalyst, the proposed MoS2-supported catalysts are also highly active as hydrodeoxygenation catalyst for the removal of alcohol OH groups. 

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2. Photoenzymatic Hydrogenation of Heteroaromatic Olefins Using ‘Ene’‐Reductases with Photoredox Catalysts

   https://doi.org/10.1002/anie.202003125  

   Nakano, Yuji; Black, Michael J.; Meichan, Andrew J.; Sandoval, Braddock A.; Chung, Megan M.; Biegasiewicz, Kyle F.; Zhu, Tianyu; Hyster, Todd K. (April 2020, Angewandte Chemie International Edition)

   Abstract Flavin‐dependent ‘ene’‐reductases (EREDs) are highly selective catalysts for the asymmetric reduction of activated alkenes. This function is, however, limited to enones, enoates, and nitroalkenes using the native hydride transfer mechanism. Here we demonstrate that EREDs can reduce vinyl pyridines when irradiated with visible light in the presence of a photoredox catalyst. Experimental evidence suggests the reaction proceeds via a radical mechanism where the vinyl pyridine is reduced to the corresponding neutral benzylic radical in solution. DFT calculations reveal this radical to be “dynamically stable”, suggesting it is sufficiently long‐lived to diffuse into the enzyme active site for stereoselective hydrogen atom transfer. This reduction mechanism is distinct from the native one, highlighting the opportunity to expand the synthetic capabilities of existing enzyme platforms by exploiting new mechanistic models. 

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3. The roles of chalcogenides in O ₂ protection of H ₂ ase active sites

   https://doi.org/10.1039/D0SC02584D  

   Yang, Xuemei; Darensbourg, Marcetta Y. (September 2020, Chemical Science)

   null (Ed.)

   At some point, all HER (Hydrogen Evolution Reaction) catalysts, important in sustainable H 2 O splitting technology, will encounter O 2 and O 2 -damage. The [NiFeSe]-H 2 ases and some of the [NiFeS]–H 2 ases, biocatalysts for reversible H 2 production from protons and electrons, are exemplars of oxygen tolerant HER catalysts in nature. In the hydrogenase active sites oxygen damage may be extensive (irreversible) as it is for the [FeFe]–H 2 ase or moderate (reversible) for the [NiFe]–H 2 ases. The affinity of oxygen for sulfur, in [NiFeS]–H 2 ase, and selenium, in [NiFeSe]–H 2 ase, yielding oxygenated chalcogens results in maintenance of the core NiFe unit, and myriad observable but inactive states, which can be reductively repaired. In contrast, the [FeFe]–H 2 ase active site has less possibilities for chalcogen-oxygen uptake and a greater chance for O 2 -attack on iron. Exposure to O 2 typically leads to irreversible damage. Despite the evidence of S/Se-oxygenation in the active sites of hydrogenases, there are limited reported synthetic models. This perspective will give an overview of the studies of O 2 reactions with the hydrogenases and biomimetics with focus on our recent studies that compare sulfur and selenium containing synthetic analogues of the [NiFe]–H 2 ase active sites. 

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4. A single diiron enzyme catalyses the oxidative rearrangement of tryptophan to indole nitrile

   https://doi.org/10.1038/s41557-024-01603-z  

   Adak, Sanjoy; Ye, Naike; Calderone, Logan_A; Duan, Meng; Lubeck, Wilson; Schäfer, Rebecca_J_B; Lukowski, April_L; Houk, K_N; Pandelia, Maria-Eirini; Drennan, Catherine_L; et al (September 2024, Nature Chemistry)

   Abstract Nitriles are uncommon in nature and are typically constructed from oximes through the oxidative decarboxylation of amino acid substrates or from the derivatization of carboxylic acids. Here we report a third nitrile biosynthesis strategy featuring the cyanobacterial nitrile synthase AetD. During the biosynthesis of the eagle-killing neurotoxin, aetokthonotoxin, AetD transforms the 2-aminopropionate portion of 5,7-dibromo-l-tryptophan to a nitrile. Employing a combination of structural, biochemical and biophysical techniques, we characterized AetD as a non-haem diiron enzyme that belongs to the emerging haem-oxygenase-like dimetal oxidase superfamily. High-resolution crystal structures of AetD together with the identification of catalytically relevant products provide mechanistic insights into how AetD affords this unique transformation, which we propose proceeds via an aziridine intermediate. Our work presents a unique template for nitrile biogenesis and portrays a substrate binding and metallocofactor assembly mechanism that may be shared among other haem-oxygenase-like dimetal oxidase enzymes. 

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5. Molecularly imprinted artificial esterases with highly specific active sites and precisely installed catalytic groups

   https://doi.org/10.1039/C8OB01584H  

   Hu, Lan; Zhao, Yan (January 2018, Organic & Biomolecular Chemistry)

   A difficult challenge in synthetic enzymes is the creation of substrate-selective active sites with accurately positioned catalytic groups. Covalent molecular imprinting in cross-linked micelles afforded such active sites in protein-sized, water-soluble nanoparticle catalysts. Our method allowed a systematic tuning of the distance of the catalytic group to the bound substrate. The catalysts displayed enzyme-like kinetics and easily distinguished substrates with subtle structural differences. 

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