Concatenating Microbial, Enzymatic, and Organometallic Catalysis for Integrated Conversion of Renewable Carbon Sources.

The chemical industry can now seize the opportunity to improve the sustainability of its processes by replacing fossil carbon sources with renewable alternatives such as CO, biomass, and plastics, thereby thinking ahead and having a look into the future. For their conversion to intermediate and final products, different types of catalysts-microbial, enzymatic, and organometallic-can be applied. The first part of this review shows how these catalysts can work separately in parallel, each route with unique requirements and advantages.

Synthesis of Substituted Acyclic and Cyclic N-Alkylhydrazines by Enzymatic Reductive Hydrazinations.

Imine reductases (IREDs) provide promising opportunities for the synthesis of various chiral amines. Initially, asymmetric imine reduction was reported, followed by reductive aminations of aldehydes and ketones via imines. Herein we present the reductive amination of structurally diverse carbonyls and dicarbonyls with hydrazines (reductive hydrazination), catalyzed by the IRED from Myxococcus stipitatus.

Insights into electron transfer and bifurcation of the Synechocystis sp. PCC6803 hydrogenase reductase module.

The NAD-reducing soluble [NiFe] hydrogenase (SH) is the key enzyme for production and consumption of molecular hydrogen (H) in Synechocystis sp. PCC6803. In this study, we focused on the reductase module of the SynSH and investigated the structural and functional aspects of its subunits, particularly the so far elusive role of HoxE.

H-driven biocatalysis for flavin-dependent ene-reduction in a continuous closed-loop flow system utilizing H from water electrolysis.

Despite the increasing demand for efficient and sustainable chemical processes, the development of scalable systems using biocatalysis for fine chemical production remains a significant challenge. We have developed a scalable flow system using immobilized enzymes to facilitate flavin-dependent biocatalysis, targeting as a proof-of-concept asymmetric alkene reduction. The system integrates a flavin-dependent Old Yellow Enzyme (OYE) and a soluble hydrogenase to enable H-driven regeneration of the OYE cofactor FMNH.

Biocatalytic reductive amination as a route to isotopically labelled amino acids suitable for analysis of large proteins by NMR.

We demonstrate an atom-efficient and easy to use H-driven biocatalytic platform for the enantioselective incorporation of H-atoms into amino acids. By combining the biocatalytic deuteration catalyst with amino acid dehydrogenase enzymes capable of reductive amination, we synthesised a library of multiply isotopically labelled amino acids from low-cost isotopic precursors, such as HO and NH. The chosen approach avoids the use of pre-labeled H-reducing agents, and therefore vastly simplifies product cleanup.

Hydrogenase-based oxidative biocatalysis without oxygen.

Biocatalysis-based synthesis can provide a sustainable and clean platform for producing chemicals. Many oxidative biocatalytic routes require the cofactor NAD as an electron acceptor. To date, NADH oxidase (NOX) remains the most widely applied system for NAD regeneration.

Toward a synthetic hydrogen sensor in cyanobacteria: Functional production of an oxygen-tolerant regulatory hydrogenase in sp. PCC 6803.

Cyanobacteria have raised great interest in biotechnology, e.g., for the sustainable production of molecular hydrogen (H) using electrons from water oxidation.

Substrate-Gated Transformation of a Pre-Catalyst into an Iron-Hydride Intermediate [(NO)(CO)Fe(μ-H)Fe(CO)(NO)] for Catalytic Dehydrogenation of Dimethylamine Borane.

Continued efforts are made on the development of earth-abundant metal catalysts for dehydrogenation/hydrolysis of amine boranes. In this study, complex [K-18-crown-6-ether][(NO)Fe(μ-Pyr)(μ-CO)Fe(NO)] (, Pyr = 3-methylpyrazolate) was explored as a pre-catalyst for the dehydrogenation of dimethylamine borane (DMAB). Upon evolution of H from DMAB triggered by , parallel conversion of into [(NO)Fe(,'-PyrBHNMe)] () and an iron-hydride intermediate [(NO)(CO)Fe(μ-H)Fe(CO)(NO)] () was evidenced by X-ray diffraction/nuclear magnetic resonance/infrared/nuclear resonance vibrational spectroscopy experiments and supported by density functional theory calculations.

Reversible Glutamate Coordination to High-Valent Nickel Protects the Active Site of a [NiFe] Hydrogenase from Oxygen.

NAD-reducing [NiFe] hydrogenases are valuable biocatalysts for H-based energy conversion and the regeneration of nucleotide cofactors. While most hydrogenases are sensitive toward O and elevated temperatures, the soluble NAD-reducing [NiFe] hydrogenase from (SH) is O-tolerant and thermostable. Thus, it represents a promising candidate for biotechnological applications.

A hydrogen-driven biocatalytic approach to recycling synthetic analogues of NAD(P)H.

We demonstrate a recycling system for synthetic nicotinamide cofactor analogues using a soluble hydrogenase with turnover number of >1000 for reduction of the cofactor analogues by H. Coupling this system to an ene reductase, we show quantitative conversion of -ethylmaleimide to -ethylsuccinimide. The biocatalyst system retained >50% activity after 7 h.

From inert gas to fertilizer, fuel and fine chemicals: N reduction and fixation.

The 100th anniversary of a leading nitrogen fixation technology developer like CASALE SA is a reason to reflect over the 20th century successful solution of the problem of world food supply, and to look out for solutions for sustainable developments with respect to ammonia production. We review the role of nitrogen as essential chemical constituent in photosynthesis and biology, and component of ammonia as it is used as fertilizer for primary production by photosynthesis for farming and food supply and its future role as energy carrier. While novel synthesis methods and very advanced synchrotron based x-ray analytical techniques are being developed, we feel it is important to refer to the historical and economical context of nitrogen.

Crucial Role of the Chaperonin GroES/EL for Heterologous Production of the Soluble Methane Monooxygenase from Methylomonas methanica MC09.

Methane is a widespread energy source and can serve as an attractive C1 building block for a future bioeconomy. The soluble methane monooxygenase (sMMO) is able to break the strong C-H bond of methane and convert it to methanol. The high structural complexity, multiplex cofactors, and unfamiliar folding or maturation procedures of sMMO have hampered the heterologous production and thus biotechnological applications.

Catalytic and Spectroscopic Properties of the Halotolerant Soluble Methane Monooxygenase Reductase from Methylomonas methanica MC09.

The soluble methane monooxygenase receives electrons from NADH via its reductase MmoC for oxidation of methane, which is itself an attractive C1 building block for a future bioeconomy. Herein, we present biochemical and spectroscopic insights into the reductase from the marine methanotroph Methylomonas methanica MC09. The presence of a flavin adenine dinucleotide (FAD) and [2Fe2S] cluster as its prosthetic group were revealed by reconstitution experiments, iron determination and electron paramagnetic resonance spectroscopy.

Rewiring cyanobacterial photosynthesis by the implementation of an oxygen-tolerant hydrogenase.

Molecular hydrogen (H) is considered as an ideal energy carrier to replace fossil fuels in future. Biotechnological H production driven by oxygenic photosynthesis appears highly promising, as biocatalyst and H syntheses rely mainly on light, water, and CO and not on rare metals. This biological process requires coupling of the photosynthetic water oxidizing apparatus to a H-producing hydrogenase.

Hydroxy-bridged resting states of a [NiFe]-hydrogenase unraveled by cryogenic vibrational spectroscopy and DFT computations.

The catalytic mechanism of [NiFe]-hydrogenases is a subject of extensive research. Apart from at least four reaction intermediates of H/H cycling, there are also a number of resting states, which are formed under oxidizing conditions. Although not directly involved in the catalytic cycle, the knowledge of their molecular structures and reactivity is important, because these states usually accumulate in the course of hydrogenase purification and may also play a role during hydrogenase maturation.

Exploring Structure and Function of Redox Intermediates in [NiFe]-Hydrogenases by an Advanced Experimental Approach for Solvated, Lyophilized and Crystallized Metalloenzymes.

To study metalloenzymes in detail, we developed a new experimental setup allowing the controlled preparation of catalytic intermediates for characterization by various spectroscopic techniques. The in situ monitoring of redox transitions by infrared spectroscopy in enzyme lyophilizate, crystals, and solution during gas exchange in a wide temperature range can be accomplished as well. Two O -tolerant [NiFe]-hydrogenases were investigated as model systems.

Correction: H as a fuel for flavin- and HO-dependent biocatalytic reactions.

Correction for 'H2 as a fuel for flavin- and H2O2-dependent biocatalytic reactions' by Ammar Al-Shameri et al., Chem. Commun.

H as a fuel for flavin- and HO-dependent biocatalytic reactions.

The soluble hydrogenase from Ralstonia eutropha provides an atom efficient regeneration system for reduced flavin cofactors using H as an electron source. We demonstrated this system for highly selective ene-reductase-catalyzed C[double bond, length as m-dash]C-double bond reductions and monooxygenase-catalyzed epoxidation. Reactions were expanded to aerobic conditions to supply HO for peroxygenase-catalyzed hydroxylations.

Powering Artificial Enzymatic Cascades with Electrical Energy.

We have developed a scalable platform that employs electrolysis for an in vitro synthetic enzymatic cascade in a continuous flow reactor. Both H and O were produced by electrolysis and transferred through a gas-permeable membrane into the flow system. The membrane enabled the separation of the electrolyte from the biocatalysts in the flow system, where H and O served as electron mediators for the biocatalysts.

Formyltetrahydrofolate Decarbonylase Synthesizes the Active Site CO Ligand of O-Tolerant [NiFe] Hydrogenase.

[NiFe] hydrogenases catalyze the reversible oxidation of molecular hydrogen into two protons and two electrons. A key organometallic chemistry feature of the NiFe active site is that the iron atom is co-coordinated by two cyanides (CN) and one carbon monoxide (CO) ligand. Biosynthesis of the NiFe(CN)(CO) cofactor requires the activity of at least six maturation proteins, designated HypA-F.

How to make the reducing power of H available for in vivo biosyntheses and biotransformations.

Solar-driven electrolysis enables sustainable production of molecular hydrogen (H), which represents a cheap and carbon-free reductant. Knallgas bacteria like Ralstonia eutropha are able to split H to supply energy in form of ATP and NADH, which can be subsequently used to power reactions of interest. R.

O-tolerant [NiFe]-hydrogenases of Ralstonia eutropha H16: Physiology, molecular biology, purification, and biochemical analysis.

Dioxygen-tolerant [NiFe]-hydrogenases are defined by their ability to catalyze the reaction, H⇌2H+2e even in the presence of O. Catalytic and probably also noncatalytic mechanisms protect their active sites from being inactivated by reactive oxygen species, which makes them attractive subjects of investigation from both fundamental and applied perspectives. Prominent representatives of the O-tolerant [NiFe]-hydrogenases have been isolated from the chemolithoautotrophic model organism Ralstonia eutropha H16, which can thrive in a simple mineral medium supplemented with the gases H, O, and CO.

Enzymatic and spectroscopic properties of a thermostable [NiFe]‑hydrogenase performing H-driven NAD-reduction in the presence of O.

Biocatalysts that mediate the H-dependent reduction of NAD to NADH are attractive from both a fundamental and applied perspective. Here we present the first biochemical and spectroscopic characterization of an NAD-reducing [NiFe]‑hydrogenase that sustains catalytic activity at high temperatures and in the presence of O, which usually acts as an inhibitor. We isolated and sequenced the four structural genes, hoxFUYH, encoding the soluble NAD-reducing [NiFe]‑hydrogenase (SH) from the thermophilic betaproteobacterium, Hydrogenophilus thermoluteolus TH-1 (Ht).

Synchrotron-based Nickel Mössbauer Spectroscopy.

We used a novel experimental setup to conduct the first synchrotron-based (61)Ni Mössbauer spectroscopy measurements in the energy domain on Ni coordination complexes and metalloproteins. A representative set of samples was chosen to demonstrate the potential of this approach. (61)NiCr2O4 was examined as a case with strong Zeeman splittings.