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International audience; A bioelectrode for electroenzymatic synthesis was prepared, combining a layer for NADH regeneration and a renewable layer for enzymatic substrate reduction. The covalent immobilization of a rhodium complex mediator ([Cp*Rh(bpy)Cl]+) on the surface of a bucky paper electrode was achieved by following an original protocol in two steps. A bipyridine ligand was first grafted on the electrode by electro‐reduction of bipyridyl diazonium cations generated from 4‐amino‐2,2′‐bipyridine, and the complex was then formed by reaction with [RhCp*Cl2]2. A turnover frequency of 1.3 s−1 was estimated for the electrocatalytic regeneration of NADH by this immobilized complex, with a Faraday efficiency of 83 %. The bucky paper electrode was then overcoated by a bio‐doped porous layer made of glassy fibers with immobilized D‐sorbitol dehydrogenase. This assembly allowed for the efficient separation of the enzyme and the rhodium catalyst, which is a prerequisite for effective bioelectrocatalysis with such bioelectrochemical system, while allowing effective mass transport of NAD+/NADH cofactor from one layer to the other. Thereby, it was possible to reuse the same mediator‐functionalized bucky paper with three different enzyme layers. The bioelectrode was applied to the electroenzymatic reduction of D‐fructose to D‐sorbitol. A turnover frequency of 0.19 s−1 for the rhodium complex was observed in the presence of 3 mM D‐fructose and a total turnover number higher than 12000 was estimated.

Pyridoxal 5’‐phosphate (PLP)‐dependent enzymes are a versatile class of biocatalysts and feature a variety of industrial applications. However, PLP is light sensitive and can cause inactivation of enzymes in certain light conditions. As most of the PLP‐dependent enzymes are usually not handled in dark conditions, we evaluated the effect of visible light on the activity of PLP‐dependent enzymes during production as well as transformation. We tested four amine transaminases, from Chromobacterium violaceum, Bacillus megaterium, Vibrio fluvialis and a variant from Arthrobacter species as well as two lysine decarboxylases, from Selenomonas ruminantium and the LDCc from Escherichia coli. It appeared that five of these six enzymes suffered from a significant decrease in activity by up to 90 % when handled in laboratory light conditions. Surprisingly, only the amine transaminase variant from Arthrobacter species appeared to be unaffected by light exposure and even showed an activation to 150 % relative activity over the course of 6 h regardless of the light conditions., Careful with light: In this work, it is shown that the activity of PLP‐dependent enzymes can be affected by illumination, even by ordinary laboratory or sunlight. Most of the enzymes tested showed a significant loss of activity. Consequently, by performing enzyme production and reaction in the dark, the catalytic activity could be increased immensely. However, one PLP‐dependent enzyme appeared to be completely resistant to any type of illumination.

The development of sustainable processes for the valorization of byproducts and other waste streams remains an ongoing challenge in the field of catalysis. Racemic borneol, isoborneol and camphor are currently produced from α‐pinene, a side product from the production of cellulose. The pure enantiomers of these monoterpenoids have numerous applications in cosmetics and act as reagents for asymmetric synthesis, making an enzymatic route for their separation into optically pure enantiomers a desirable goal. Known short‐chain borneol‐type dehydrogenases (BDHs) from plants and bacteria lack the required specificity, stability or activity for industrial utilization. Prompted by reports on the presence of pure (−)‐borneol and (−)‐camphor in essential oils from rosemary, we set out to investigate dehydrogenases from the genus Salvia and discovered a dehydrogenase with high specificity (E>120) and high specific activity (>0.02 U mg−1) for borneol and isoborneol. Compared to other specific dehydrogenases, the one reported here shows remarkably higher stability, which was exploited to obtain the first three‐dimensional structure of an enantiospecific borneol‐type short‐chain dehydrogenase. This, together with docking studies, led to the identification of a hydrophobic pocket in the enzyme that plays a crucial role in the stereo discrimination of bornane‐type monoterpenoids. The kinetic resolution of borneol and isoborneol can be easily integrated into the existing synthetic route from α‐pinene to camphor thereby allowing the facile synthesis of optically pure monoterpenols from an abundant renewable source., Highly Specific Borneol‐Type Dehydrogenase: A borneol‐ type dehydrogenase with high specificity for borneol and isoborneol was characterized from the genome of Salvia rosmarinus. The crystallographic structure was determined, showing an hydrophobic pocket that plays a crucial role in the stereo discrimination of bornane‐type monoterpenoids.

Halide assays are important for the study of enzymatic dehalogenation, a topic of great industrial and scientific importance. Here we describe the development of a very sensitive halide assay that can detect less than a picomole of bromide ions, making it very useful for quantifying enzymatic dehalogenation products. Halides are oxidised under mild conditions using the vanadium‐dependent chloroperoxidase from Curvularia inaequalis, forming hypohalous acids that are detected using aminophenyl fluorescein. The assay is up to three orders of magnitude more sensitive than currently available alternatives, with detection limits of 20 nM for bromide and 1 μM for chloride and iodide. We demonstrate that the assay can be used to determine specific activities of dehalogenases and validate this by comparison to a well‐established GC‐MS method. This new assay will facilitate the identification and characterisation of novel dehalogenases and may also be of interest to those studying other halide‐producing enzymes., How sensitive! A simple, safe, and very sensitive assay for enzymatic dehalogenation is presented. The halides produced by dehalogenases are generally very unreactive and thus hard to detect. We use hydrogen peroxide and a haloperoxidase to activate halides to hypohalous acids, which are easily detected using the sensitive fluorogenic probe aminophenyl fluorescein.

Saudi Aramco is gratefully acknowledged for financial support.The authors acknowledge G&W Mineral Resources and ActiveMinerals International LCC for providing them with the claymineral samples used in this study. The authors wish to acknowl-edge and thank Sandra Ramirez Cherbuy for the graphicalabstract’s illustration.

Multi-step enzyme reactions offer considerable cost and productivity benefits. Process models offer a route to understanding the complexity of these reactions, and allow for their optimization. Despite the increasing prevalence of multi-step biotransformations, there are few examples of process models for enzyme reactions. From a toolbox of characterized enzyme parts, we demonstrate the construction of a process model for a seven enzyme, three step biotransformation using isolated enzymes. Enzymes for cofactor regeneration were employed to make thisin vitroreaction economical. Good modelling practice was critical in evaluating the impact of approximations and experimental error. We show that the use and validation of process models was instrumental in realizing and removing process bottlenecks, identifying divergent behavior, and for the optimization of the entire reaction using a genetic algorithm. We validated the optimized reaction to demonstrate that complex multi-step reactions with cofactor recycling involving at least seven enzymes can be reliably modelled and optimized.Significance statementThis study examines the challenge of modeling and optimizing multi-enzyme cascades. We detail the development, testing and optimization of a deterministic model of a three enzyme cascade with four cofactor regeneration enzymes. Significantly, the model could be easily used to predict the optimal concentrations of each enzyme in order to get maximum flux through the cascade. This prediction was strongly validated experimentally. The success of our model demonstrates that robust models of systems of at least seven enzymes are readily achievable. We highlight the importance of following good modeling practice to evaluate model quality and limitations. Examining deviations from expected behavior provided additional insight into the model and enzymes. This work provides a template for developing larger deterministic models of enzyme cascades.

Preparing catalysts with highly dispersed metal nanoparticles and narrow particle size distribution has been in the focus of numerous studies. Besides size and size distribution, the location of metal nanoparticles within and local metal loading of the support can have significant impact on catalytic performance. This study revealed that great variations in Pt loading between individual Pt/zeolite Y crystals occurred irrespective of the metal deposition method, namely ion‐exchange (IE) or incipient wetness impregnation (IWI). The variation in Pt loading was found to be directly related to different Si/Al ratios of individual zeolite crystals. Results indicate that this Si/Al variation was likely induced by post‐synthesis treatments, commonly performed to introduce mesoporosity. In view of the great importance of zeolite‐based catalysts for oil refining, understanding the origin of such metal loading heterogeneities may lead to further improvement of zeolite‐based catalytic performance.

Fragrance and flavor industries could not imagine business without aldehydes. Processes for their commercial production raise environmental and ecological concerns. The chemical reduction of organic acids to aldehydes is challenging. To fulfill the demand of a mild and selective reduction of carboxylic acids to aldehydes, carboxylic acid reductases (CARs) are gaining importance. We identified two new subtype IV fungal CARs from Dichomitus squalens CAR (DsCAR) and Trametes versicolor CAR (Tv2CAR) in addition to literature known Trametes versicolor CAR (TvCAR). Expression levels were improved by the co‐expression of GroEL‐GroES with either the trigger factor or the DnaJ‐DnaK‐GrpE system. Investigation of the substrate scope of the three enzymes revealed overlapping substrate‐specificities. Tv2CAR and DsCAR showed a preferred pH range of 7.0 to 8.0 in bicine buffer. TvCAR showed highest activity at pH 6.5 to 7.5 in MES buffer and slightly reduced activity at pH 6.0 or 8.0. TvCAR appeared to tolerate a wider pH range without significant loss of activity. Type IV fungal CARs optimal temperature was in the range of 25–35 °C. TvCAR showed a melting temperature (Tm) of 55 °C indicating higher stability compared to type III and the other type IV fungal CARs (Tm 51–52 °C). Finally, TvCAR was used as the key enzyme for the bioreduction of 3,4‐dihydroxyphenylacetic acid to the antioxidant 3‐hydroxytyrosol (3‐HT) and gave 58 mM of 3‐HT after 24 h, which correlates to a productivity of 0.37 g L−1 h−1., Expanding the toolbox: Fragrance and flavor industries could not imagine business without aldehydes. Mild and selective reduction of carboxylic acids to aldehydes is achieved with new carboxylic acid reductase enzymes (CARs).

Functionalization of aromatic compounds by acylation has considerable significance in synthetic organic chemistry. As an alternative to chemical Friedel‐Crafts acylation, the C‐acyltransferase from Pseudomonas protegens has been found to catalyze C−C bond formation with non‐natural resorcinol substrates. Extending the scope of acyl donors, it is now shown that the enzyme is also able to catalyze C−S bond cleavage prior to C−C bond formation, thus aliphatic and aromatic thioesters can be used as acyl donors. It is worth to mention that this reaction can be performed in aqueous buffer. Identifying ethyl thioacetate as the most suitable acetyl donor, the products were obtained with up to >99 % conversion and up to 88 % isolated yield without using additional base additives; this represents a significant advancement to prior protocols.

Electrochemical conversion of CO2 is an attractive alternative to releasing it to the atmosphere. Catalysts derived from electroreduction of metal oxides are often more active than when starting with metallic phase catalyst. The origin of this effect is not yet clear. Using ZnO nanorods, we show that the initial structure of the oxide as well as the electrolyte medium have a profound impact on the structure of the catalytic active Zn phase, and thereby the selectivity of the catalysts. ZnO nanorods with various aspect ratios were electrochemically reduced in different electrolytes leading to metallic Zn with different structures; a sponge‐like structure, nanorods and nanoplates. The sponge‐like Zn produced syngas with H2 : CO=2, and some formate, the nanorods produced only syngas with H2 : CO=1, while Zn nanoplates exhibited 85 % selectivity towards CO. These results open a pathway to design new electrocatalysts with optimized properties by modifying the structure of the starting material and the electroreduction medium., The structure to evolve: Electron micrographs illustrates the evolution of Zn structure from the electroreduction of ZnO nanorods, and the effects on the product selectivity in the CO2 electroreduction. This work shows that the structure/morphology, and hence product selectivity of oxide‐derived Zn catalysts in CO2 electroreduction, can be tuned by changing the structure/aspect ratio of the staring ZnO nanorods and the reduction condition.

The substitution of catalytic metals by p‐block main elements has a tremendous impact not only in the fundamentals but also in the economic and ecological fingerprint of organic reactions. Here we show that few‐layer black phosphorous (FL‐BP), a recently discovered and now readily available 2D material, catalyzes different radical additions to alkenes with an initial turnover frequency (TOF0) up to two orders of magnitude higher than representative state‐of‐the‐art metal complex catalysts at room temperature. The corresponding electron‐rich BP intercalation compound (BPIC) KP6 shows a nearly twice TOF0 increase with respect to FL‐BP. This increase in catalytic activity respect to the neutral counterpart also occurs in other 2D materials (graphene vs. KC8) and metal complex catalysts (Fe0 vs. Fe2− carbon monoxide complexes). This reactive parallelism opens the door for cross‐fertilization between 2D materials and metal catalysts in organic synthesis., Phosphorene catalyzes with extraordinary activity radical additions to alkenes, faster than optimized metal catalysts, opening the door for future applications of 2D heteroatom materials in organic synthesis.

A biphasic process for the hydrogenation of aldehydes was developed using a well‐defined iron (II) PNP pincer complex as model system to investigate the performance of various ionic liquids. A number of suitable hydrophobic ionic liquids based on the N(Tf)2 − anion were identified, allowing to immobilize the iron (II) catalyst in the ionic liquid layer and to facilitate the separation of the desired alcohols. Further studies showed that targeted Brønsted basic ionic liquids can eliminate the need of an external base to activate the catalyst.

Cobalt‐loaded MFI zeolite showed distinct activity for direct methylation of benzene with methane into toluene. High activity was found at around 0.6 of Co/Al molar ratio. Incorporation of carbon from methane into the methyl group of toluene was confirmed with isotope tracer experiments and mass spectroscopy. Ammonia infrared‐mass spectroscopy temperature‐programmed desorption, transmission electron microscopy, X‐ray absorption near edge spectroscopy and extended X‐ray absorption fine structure indicated that Lewis acidic divalent (+II of oxidation state) Co species mono‐atomically dispersed on the ion exchange site of MFI zeolite was the active species.

Discovery and development of enzymes for the synthesis of chiral amines have been a hot topic for basic and applied aspects of biocatalysts. Based on our X‐ray crystallographic analyses of porcine kidney D‐amino acid oxidase (pkDAO) and its variants, we rationally designed a new variant that catalyzed the oxidation of (S)‐4‐Cl‐benzhydrylamine (CBHA) from pkDAO and obtained it by functional high‐throughput screening with colorimetric assay. The variant I230A/R283G was constructed from the variant R283G which had completely lost the activity for D‐amino acids, further gaining new activity toward (S)‐chiral amines with the bulky substituents. The variant enzyme (I230A/R283G) was characterized to have a catalytic efficiency of 1.85 s−1 for (S)‐CBHA, while that for (R)‐1‐phenylethylamine was diminished 10‐fold as compared with the Y228L/R283G variant. The variant was efficiently used for the synthesis of (R)‐CBHA in 96 % ee from racemic CBHA by the deracemization reaction in the presence of reducing agent such as NaBH4 in water. Furthermore, X‐ray crystallographic analysis of the new variant complexed with (S)‐CBHA, together with modelling study clearly showed the basis of understanding the structure‐activity relationship of pkDAO.

Herein, we introduce a new class of bench‐stable N‐heterocyclic carbene (NHC) nickel‐precatalysts for homogeneous nickel‐catalysis. The nickel(II) complexes are readily activated to Ni0 in situ under mild conditions, via a proposed Heck‐type mechanism. The precatalysts are shown to facilitate carbonyl‐ene, hydroalkenylation, and amination reactions.

Tailored mutants of phenylalanine ammonia‐lyase from Petroselinum crispum (PcPAL) were created and tested in ammonia elimination from various sterically demanding, non‐natural analogues of phenylalanine and in ammonia addition reactions into the corresponding (E)‐arylacrylates. The wild‐type PcPAL was inert or exhibited quite poor conversions in both reactions with all members of the substrate panel. Appropriate single mutations of residue F137 and the highly conserved residue I460 resulted in PcPAL variants that were active in ammonia elimination but still had a poor activity in ammonia addition onto bulky substrates. However, combined mutations that involve I460 besides the well‐studied F137 led to mutants that exhibited activity in ammonia addition as well. The synergistic multiple mutations resulted in substantial substrate scope extension of PcPAL and opened up new biocatalytic routes for the synthesis of both enantiomers of valuable phenylalanine analogues, such as (4‐methoxyphenyl)‐, (napthalen‐2‐yl)‐, ([1,1′‐biphenyl]‐4‐yl)‐, (4′‐fluoro‐[1,1′‐biphenyl]‐4‐yl)‐, and (5‐phenylthiophene‐2‐yl)alanines.

We study the allylic oxidation of cyclohexene with dioxygen under mild conditions in the presence of transition-metal catalysts. The catalysts are comprised of nanometric metal oxide particles supported on porous nitrogen-doped carbons (M/N:C, where M = V, Cr, Fe, Co, Ni, Cu, Nb, Mo, and W). Most of these metal oxides give only moderate conversions, whereof the majority of the products are over-oxidation products. Co/N:C and Cu/N:C, however, give 70-80% conversion and 40-50% selectivity to the ketone product, cyclohexene-2-one. Control experiments using free-radical scanvengers shows that the oxidation follows the expected free-radical pathway in almost all cases. Surprisingly, the catalytic cycle in the presence of Cu/N:C does not involve free-radical species in solution. Optimisation of this catalyst gives >85% conversion with >60% selectivity to the allylic ketone, at 70 °C and 10 bar oxygen pressure. Scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction studies show that the active particles have a cupric oxide/cuprous oxide core/shell structure, with a correspondingly high TOF of ca. 1500 h-1. We attribute the high performance of this Cu/N:C catalyst to a facile surface reaction between adsorbed cyclohexenyl hydroperoxide molecules and activated oxygen species.

Colloids with controlled dimensions, morphology and composition can be used to obtain supported metal catalysts with desired characteristics. Yet, removal of capping agents which block active metal sites in such catalysts can be challenging: mild methods often result in incomplete removal of capping agents, whereas harsher methods can cause change in particle size or morphology or cause metal segregation for bimetallic particles. Here we provide evidence that polyvinylpyrrolidone used as a stabilizing agent for gold colloids is present both on the metal and the support surface after colloid deposition on the TiO2 support. The polymer adsorbed on Au sites blocks their catalytic activity if it cannot be desorbed/decomposed under reaction conditions. Polyvinylpyrrolidone can be removed completely from the active gold surface of Au/TiO2 without particle growth using a number of mild treatment methods described in this work, despite only partial removal (≈45 %) of the stabilizer from the bulk of Au/TiO2 can be achieved. The remaining >50 % of polyvinylpyrrolidone resides exclusively on the TiO2 support and has no effect on the optical properties and catalytic activity of gold nanoparticles. The treated catalysts demonstrate catalytic activity and selectivity similar to those of a catalyst prepared by impregnation. These findings are important for further advancing the preparation of well‐defined supported catalysts using metal colloids.

International audience; Gold and silver are miscible over the entire composition range, and form an attractive combination for fundamental studies on bimetallic catalysts. Au–Ag catalysts have shown synergistic effects for different oxidation and liquid-phase hydrogenation reactions, but have rarely been studied for gas-phase hydrogenation. In this study 3 nm particles of Au, Ag and Au–Ag supported on silica (SBA-15) were investigated as catalysts for selective hydrogenation of butadiene in an excess of propene. The Au catalyst was over an order of magnitude more active than the Ag catalyst at 120 °C. The initial activity of the Au–Ag catalysts scaled linearly with the Au-content, suggesting a direct correlation between the surface and overall compositions of the nanoparticles and the absence of synergistic effects. All Au-containing catalysts were highly selective to butenes (>99.9 %). The Au catalysts were stable, whereas the Au–Ag catalysts lost about half of their activity during 20 h run time at 200 °C, but the initial activity was restored by a consecutive oxidation-reduction treatment. Near ambient pressure x-ray photoelectron spectroscopy showed that exposure to H2 at elevated temperatures led to a gradual enrichment of the surface of the Au–Ag nanoparticles by Ag. These observations highlight the importance of considering progressive atomic rearrangements in bimetallic nanocatalysts under reaction conditions.

One of the major requirements in solid acid and base catalyzed reactions is that the reactants, intermediates or activated complexes cooperate with several functions of catalyst support. In this work the remarkable bifunctional behavior of the defective UiO‐66(Zr) metal organic framework is shown for acid‐base pair catalysis. The active site relies on the presence of coordinatively unsaturated zirconium sites, which may be tuned by removing framework linkers and by removal of water from the inorganic bricks using a dehydration treatment. To elucidate the amphoteric nature of defective UiO‐66, the Oppenauer oxidation of primary alcohols has been theoretically investigated using density functional theory (DFT) and the periodic approach. The presence of acid and basic centers within molecular distances is shown to be crucial for determining the catalytic activity of the material. Hydrated and dehydrated bricks have a distinct influence on the acidity and basicity of the active sites. In any case both functions need to cooperate in a concerted way to enable the chemical transformation. Experimental results on UiO‐66 materials of different defectivity support the theoretical observations made in this work.

Catalysts for methanol synthesis from CO2 and H2 have been produced by two main methods: co‐precipitation and supercritical anti‐solvent (SAS) precipitation. These two methods are compared, along with the behaviour of copper supported on Zn, Mg, Mn, and Ce oxides. Although the SAS method produces initially active material with high Cu specific surface area, they appear to be unstable during reaction losing significant amounts of surface area and hence activity. The CuZn catalysts prepared by co‐precipitation, however, showed much greater thermal and reactive stability than the other materials. There appeared to be the usual near‐linear dependence of activity upon Cu specific area, though the initial performance relationship was different from that post‐reaction, after some loss of surface area. The formation of the malachite precursor, as reported before, is important for good activity and stability, whereas if copper oxides are formed during the synthesis and ageing process, then a detrimental effect on these properties is seen.

Carboxylic acid reductase enzymes (CARs) meet the demand in synthetic chemistry for a green and regiospecific route to aldehydes from their respective carboxylic acids. However, relatively few of these enzymes have been characterized. A sequence alignment with members of the ANL (Acyl‐CoA synthetase/ NRPS adenylation domain/Luciferase) superfamily of enzymes shed light on CAR functional dynamics. Four unstudied enzymes were selected by using a phylogenetic analysis of known and hypothetical CARs, and for the first time, a thorough biochemical characterization was performed. Kinetic analysis of these enzymes with various substrates shows that they have a broad but similar substrate specificity. Electron‐rich acids are favored, which suggests that the first step in the proposed reaction mechanism, attack by the carboxylate on the α‐phosphate of adenosine triphosphate (ATP), is the step that determines the substrate specificity and reaction kinetics. The effects of pH and temperature provide a clear operational window for the use of these CARs, whereas an investigation of product inhibition by NADP+, adenosine monophosphate, and pyrophosphate indicates that the binding of substrates at the adenylation domain is ordered with ATP binding first. This study consolidates CARs as important and exciting enzymes in the toolbox for sustainable chemistry and provides specifications for their use as a biocatalyst.

Optimization and execution of chemical reactions are to a large extend based on experience and chemical intuition of a chemist. The chemical intuition is rooted in the phenomenological Le Chatelier's principle that teaches us how to shift equilibrium by manipulating the reaction conditions. To access the underlying thermodynamic parameters and their condition‐dependencies from the first principles is a challenge. Here, we present a theoretical approach to model non‐standard free energies for a complex catalytic CO2 hydrogenation system under operando conditions and identify the condition spaces where catalyst deactivation can potentially be suppressed. Investigation of the non‐standard reaction free energy dependencies allows rationalizing the experimentally observed activity patterns and provides a practical approach to optimization of the reaction paths in complex multicomponent reactive catalytic systems., Operando modeling: Optimization and execution of chemical reactions are to a large extend based on experience and chemical intuition of a chemist. Herewith we present a practical computational approach to investigate condition‐dependencies of reaction free energies in reactive multicomponent multiphase solutions. This method can be readily used to rationally select starting parameters for experimental catalyst tests.

A novel laboratory setup for combined operando X‐ray diffraction and Raman spectroscopy of catalytic solids with online product analysis by gas chromatography is presented. The setup can be used with a laboratory‐based X‐ray source, which results in important advantages in terms of time‐on‐stream that can be measured, compared to synchrotron‐based experiments. The data quality was much improved by the use of a relatively high‐energy MoKα radiation instead of the more conventional CuKα radiation. We have applied the instrument to study the long‐term deactivation of Co/TiO2 Fischer–Tropsch synthesis (FTS) catalysts. No sign of Co sintering or bulk oxidation was found during the experiments. However, part of the metallic Co was converted into cobalt carbide (Co2C), at elevated pressure (10 bar). Furthermore, graphitic‐like coke species are clearly formed during FTS at atmospheric pressure, whereas at elevated pressure fluorescence hampered the interpretation of the measured Raman spectra.

The mono(μ-oxo) dicopper cores present in the pores of Cu-ZSM-5 are active for the partial oxidation of methane to methanol. However, copper on the external surface reduces the ratio of active, selective sites to unselective sites. More efficient catalysts are obtained by controlling the copper deposition during synthesis. Herein, the external exchange sites of ZSM-5 samples were passivated by bis(trimethylsilyl) trifluoroacetamide (BSTFA) followed by calcination, promoting selective deposition of intraporous copper during aqueous copper ion exchange. At an optimum level of 1-2 wt % SiO2, IR studies showed a 64 % relative reduction in external copper species and temperature-programmed oxidation analysis showed an associated increase in the formation of methanol compared with unmodified Cu-ZSM-5 samples. It is, therefore, reported that the modified zeolites contained a significantly higher proportion of active, selective copper species than their unmodified counterparts with activity for partial methane oxidation to methanol.

Trioxo‐rhenium complexes are well known catalysts for the deoxydehydration (DODH) of vicinal diols (glycols). In this work, we report on the DODH of diols and biomass‐derived polyols using CpttReO3 as a new catalyst (Cptt=1,3‐di‐tert‐butylcyclopentadienyl). The DODH reaction was optimized using 2 mol % of CpttReO3 and 3‐octanol as both reductant and solvent. The CpttReO3 catalyst exhibits an excellent activity for biomass‐derived polyols. Specifically, glycerol is almost quantitatively converted to allyl alcohol and mucic acid gives 75 % of muconates at 91 % conversion. In addition, the loading of CpttReO3 can be reduced to 0.1 mol % to achieve a turn‐over number as high as 900 per Re when using glycerol as substrate. Examination of DODH reaction profiles by NMR spectroscopy indicates that catalysis is related to Cp‐ligand release, which raises questions on the nature of the actual catalyst.

We report the solution‐phase electrochemistry of seven half‐sandwich iridium(III) complexes with varying pyridine‐alkoxide ligands to quantify electronic ligand effects that translate to their activity in catalytic water oxidation. Our results unify some previously reported electrochemical data of Cp*Ir complexes by showing how the solution speciation determines the electrochemical response: cationic complexes show over 1 V higher redox potentials that their neutral forms in a distinct demonstration of charge accumulation effects relevant to water oxidation. Building on previous work that analysed the activation behaviour of our pyalk‐ligated Cp*Ir complexes 1–7, we assess their catalytic oxygen evolution activity with sodium periodate (NaIO4) and ceric ammonium nitrate (CAN) in water and aqueous tBuOH solution. Mechanistic studies including H/D kinetic isotope effects and reaction progress kinetic analysis (RPKA) of oxygen evolution point to a dimer‐monomer equilibrium of the IrIV resting state preceding a proton‐coupled electron transfer (PCET) in the turnover‐limiting step (TLS). Finally, true electrochemically driven water oxidation is demonstrated for all catalysts, revealing surprising trends in activity that do not correlate with those obtained using chemical oxidants.

Fungal ferulic acid decarboxylases (FDCs) belong to the UbiD-family of enzymes and catalyse the reversible (de)carboxylation of cinnamic acid derivatives through the use of a prenylated flavin cofactor. The latter is synthesised by the flavin prenyltransferase UbiX. Herein, we demonstrate the applicability of FDC/UbiX expressing cells for both isolated enzyme and whole-cell biocatalysis. FDCs exhibit high activity with total turnover numbers (TTN) of up to 55000 and turnover frequency (TOF) of up to 370 min−1. Co-solvent compatibility studies revealed FDC's tolerance to some organic solvents up 20 % v/v. Using the in-vitro (de)carboxylase activity of holo-FDC as well as whole-cell biocatalysts, we performed a substrate profiling study of three FDCs, providing insights into structural determinants of activity. FDCs display broad substrate tolerance towards a wide range of acrylic acid derivatives bearing (hetero)cyclic or olefinic substituents at C3 affording conversions of up to >99 %. The synthetic utility of FDCs was demonstrated by a preparative-scale decarboxylation.

Imine reductases (IREDs) have recently become a primary focus of research in biocatalysis, complementing other classes of amine‐forming enzymes such as transaminases and amine dehydrogenases. Following in the footsteps of other research groups, we have established a set of IRED biocatalysts by sequence‐based in silico enzyme discovery. In this study, we present basic characterisation data for these novel IREDs and explore their activity and stereoselectivity using a panel of structurally diverse cyclic imines as substrates. Specific activities of >1 U/mg and excellent stereoselectivities (ee>99 %) were observed in many cases, and the enzymes proved surprisingly tolerant towards elevated substrate loadings. Co‐expression of the IREDs with an alcohol dehydrogenase for cofactor regeneration led to whole‐cell biocatalysts capable of efficiently reducing imines at 100 mM initial concentration with no need for the addition of extracellular nicotinamide cofactor. Preparative biotransformations on gram scale using these ‘designer cells’ afforded chiral amines in good yield and excellent optical purity.

Dynamic kinetic resolution (DKR) reactions in which a stereoselective enzyme and a racemization step are coupled in one pot would represent powerful tools for the production of enantiopure amines through enantioconvergence of racemates. The exploitation of DKR strategies is currently hampered by the lack of effective, enzyme‐compatible and scalable racemization strategies for amines. In the present work, the proof of concept of a fully biocatalytic method for amine racemization is presented. Both enantiomers of the model compound 1‐methyl‐3‐phenylpropylamine could be racemized in water and at room temperature using a couple of wild‐type, non‐proprietary, enantiocomplementary amine transaminases and a minimum amount of pyruvate/alanine as a co‐substrate couple. The biocatalytic simultaneous parallel cascade reaction presented here poses itself as a customizable amine racemization system with potential for the chemical industry in competition with traditional transition‐metal catalysis.

A series of well‐defined copper(I) complexes bearing ring‐expanded N‐heterocyclic carbene (NHC) ligands has been applied to the azide–alkyne cycloaddition reaction. The obtained results notably showed that the six‐membered NHC ligands outperform well‐established five‐membered ones. [CuI(Mes‐6)] displayed a remarkable catalytic activity while respecting the strict criteria for click reactions.