No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Bioelectrocatalysis for Synthetic Applications: Utilities and Challenges
... However, homogenous catalytic systems are difficult to recycle, and nitrogenase is environmentally sensitive and costly. Immobilization techniques offer potential for improving the performance of tandem chemocatalytic and/or biocatalytic systems 14 . Indeed, hydrogels 15 and metal-organic frameworks (MOFs) 16 have been used to immobilize enzymes for bioelectrocatalysis reactions although they have not yet been demonstrated on tandem catalytic systems involving biocatalysts. ...
Two or more catalysts conducting multistep reactions in the same reactor, concurrent tandem catalysis, could enable (bio)pharmaceutical and fine chemical manufacturing to become much more sustainable. Herein we report that co-immobilization of metal nanoparticles and a biocatalytic system within a synthetic covalent organic framework capsule, COFcap-2, functions like an artificial cell in that, whereas the catalysts are trapped within 300-400 nm cavities, substrates/products can ingress/egress through ca. 2 nm windows. The COFcap-2 reactor is first coated onto an electrode surface and then used to prepare eleven homochiral amines using dinitrogen as a feedstock. The amines, including drug product intermediates and active pharmaceutical ingredient, are prepared in >99% enantiomeric excess under ambient conditions in water. Importantly, the COFcap-2 system is recycled 15 times with retention of performance, addressing the relative instability and poor recyclability of enzymes that has hindered their broad implementation for energy-efficient, low waste production of chemicals and (bio)pharmaceuticals.
Bioelectrocatalytic synthesis is the conversion of electrical energy into value‐added products using biocatalysts. These methods merge the specificity and selectivity of biocatalysis and energy‐related electrocatalysis to address challenges in the sustainable synthesis of pharmaceuticals, commodity chemicals, fuels, feedstocks and fertilizers. However, the specialized experimental setups and domain knowledge for bioelectrocatalysis pose a significant barrier to adoption. This review introduces key concepts of bioelectrosynthetic systems. We provide a tutorial on the methods of biocatalyst utilization, the setup of bioelectrosynthetic cells, and the analytical methods for assessing bioelectrocatalysts. Key applications of bioelectrosynthesis in ammonia production and small‐molecule synthesis are outlined for both enzymatic and microbial systems. This review serves as a necessary introduction and resource for the non‐specialist interested in bioelectrosynthetic research.
Biocatalysis is a highly valued enabling technology for pharmaceutical research and development as it can unlock synthetic routes to complex chiral motifs with unparalleled selectivity and efficiency. This perspective aims to review recent advances in the pharmaceutical implementation of biocatalysis across early and late-stage development with a focus on the implementation of processes for preparative-scale syntheses.
Simple petrochemical feedstocks are often the starting material for the synthesis of complex commodity and fine and specialty chemicals. Designing synthetic pathways for these complex and specific molecular structures with sufficient chemo-, regio-, enantio-, and diastereo-selectivity can expand the existing petrochemicals landscape. The two overarching challenges in designing such pathways are selective activation of chemically inert C–H bonds in hydrocarbons and systematic functionalization to synthesize complex structures. Multienzyme cascades are becoming a growing means of overcoming the first challenge. However, extending multienzyme cascade designs is restricted by the arsenal of enzymes currently at our disposal and the compatibility between specific enzymes. Here, we couple a bioelectrocatalytic multienzyme cascade to organocatalysis, which are two distinctly different classes of catalysis, in a single system to address both challenges. Based on the development and utilization of an anthraquinone (AQ)-based redox polymer, the bioelectrocatalytic step achieves regioselective terminal C–H bond oxyfunctionalization of chemically inert n-heptane. A second biocatalytic step selectively oxidizes the resulting 1-heptanol to heptanal. The succeeding inherently simple and durable l-proline-based organocatalysis step is a complementary partner to the multienzyme steps to further functionalize heptanal to the corresponding α-hydrazino aldehyde. The “three-stage” streamlined design exerts much control over the chemical conversion, which renders the collective system a versatile and adaptable model for a broader substrate scope and more complex C–H functionalization.
The development of efficient enzyme immobilization to promote their recyclability and activity is highly desirable. Zeolitic imidazolate framework‐8 (ZIF‐8) has been proved to be an effective platform for enzyme immobilization due to its easy preparation and biocompatibility. However, the intrinsic hydrophobic characteristic hinders its further development in this filed. Herein, a facile synthesis approach was developed to immobilize pepsin (PEP) on the ZIF‐8 carrier by using Ni²⁺ ions as anchor (ZIF‐8@PEP‐Ni). By contrast, the direct coating of PEP on the surface of ZIF‐8 (ZIF‐8@PEP) generated significant conformational changes. Electrochemical oxygen evolution reaction (OER) was employed to study the catalytic activity of immobilized PEP. The ZIF‐8@PEP‐Ni composite attains remarkable OER performance with an ultralow overpotential of only 127 mV at 10 mA cm⁻², which is much lower than the 690 and 919 mV overpotential values of ZIF‐8@PEP and PEP, respectively.
The electrochemical regeneration of the NADH cofactor was realized in a hybrid flow reactor coupling fuel cell technology and redox flow device, paying attention to the robust immobilization of all catalysts. The rhodium catalyst Rh(Cp∗)(bpy)Cl + was covalently immobilized on a MWCNT layer and the association with the gas diffusion electrode was carefully optimized. High stability and activity of the electrochemical system were assessed by cyclic voltammetry and amperometry in the flow reactor. Afterwards, the optimal cofactor regeneration was applied to NADH‐dependent biosynthesis using immobilized lactate dehydrogenase for the conversion of pyruvate to lactate in the flow cell in the presence of cofactor concentration as low as 10 µM. 79 % faradaic efficiency was achieved and remarkable total turnover number (TTN) were reached: 2500 and 18000 for the NADH cofactor and the Rh complex, respectively.
The electrochemical method of combining N2 and H2O to produce ammonia
(i.e., the electrochemical nitrogen reduction reaction [E-NRR]) continues
to draw attention as it is both environmentally friendly and well suited for
a progressively distributed farm economy. Despite the multitude of recent
works on the E-NRR, further progress in this field faces a bottleneck. On the
one hand, despite the extensive exploration and trial-and-error evaluation of
E-NRR catalysts, no study has stood out to become the stage protagonist. On
the other hand, the current level of ammonia production (microgram-scale) is
an almost insurmountable obstacle for its qualitative and quantitative determination,
hindering the discrimination between true activity and contamination.
Herein i) the popular theory and mechanism of the NRR are introduced;
ii) a comprehensive summary of the recent progress in the field of the E-NRR
and related catalysts is provided; iii) the operational procedures of the E-NRR
are addressed, including the acquisition of key metrics, the challenges faced,
and the most suitable solutions; iv) the guiding principles and standardized
recommendations for the E-NRR are emphasized and future research directions
and prospects are provided.
The sustainable capture and conversion of carbon dioxide (CO2) is key to achieving a circular carbon economy. Bioelectrocatalysis, which aims at using renewable energies to power the highly specific, direct transformation of CO2 into value added products, holds promise to achieve this goal. However, the functional integration of CO2‐fixing enzymes onto electrode materials for the electrosynthesis of stereochemically complex molecules remains to be demonstrated. Here, we show the electricity‐driven regio‐ and stereoselective incorporation of CO2 into crotonyl‐CoA by an NADPH‐dependent enzymatic reductive carboxylation. Co‐immobilization of a ferredoxin NADP⁺ reductase and crotonyl‐CoA carboxylase/reductase within a 2,2′‐viologen‐modified hydrogel enabled iterative NADPH recycling and stereoselective formation of (2S)‐ethylmalonyl‐CoA, a prospective intermediate towards multi‐carbon products from CO2, with 92±6 % faradaic efficiency and at a rate of 1.6±0.4 μmol cm⁻² h⁻¹. This approach paves the way for realizing even more complex bioelectrocatalyic cascades in the future.
Can green chemistry be the right reading key to let organocatalyst design take a step forward towards sustainable catalysis? What if the intriguing chemistry promoted by more engineered organocatalysts was carried on by using renewable and naturally occurring molecular scaffolds, or at least synthetic catalysts more respectful towards the principles of green chemistry? Within the frame of these questions, this Review will tackle the most commonly occurring organic chiral catalysts from the perspective of their synthesis rather than their employment in chemical methodologies or processes. A classification of the catalyst scaffolds based on their E factor will be provided, and the global E factor (EG factor) will be proposed as a new green chemistry metric to consider, also, the synthetic route to the catalyst within a given organocatalytic process.
In living cells, redox chains rely on nanoconfinement using tiny enclosures, such as the mitochondrial matrix or chloroplast stroma, to concentrate enzymes and limit distances that nicotinamide cofactors and other metabolites must diffuse. In a chemical analogue exploiting this principle, nicotinamide adenine dinucleotide phosphate (NADPH) and NADP⁺ are cycled rapidly between ferredoxin–NADP⁺ reductase and a second enzyme—the pairs being juxtaposed within the 5–100 nm scale pores of an indium tin oxide electrode. The resulting electrode material, denoted (FNR+E2)@ITO/support, can drive and exploit a potentially large number of enzyme‐catalysed reactions.
Enzymatic bioelectrocatalysis often requires an artificial redox mediator to observe significant electron transfer rates. The use of such mediators can add a substantial overpotential and obfuscate the protein’s native kinetics, which limits the voltage of a biofuel cell and alters the analytical peformance of biosensors. Herein, we describe a material for facilitating direct electrochemical communication with redox proteins based on a novel pyrene-modified linear poly(ethyleneimine). This method was applied for promoting direct bioelectrocatalytic reduction of O2 by laccase and, by immobilizing the catalytic subunit of nitrogenase (MoFe protein), to demonstrate the ATP-independent direct electroenzymatic reduction of N2 to NH3.
In this competitive age, when new industries sprout and decay in the span of a decade, we should reflect on how a company survives to celebrate its 350th anniversary. A prerequisite for survival in business is the ability to adapt to changing environments and tastes and to sense, anticipate and meet needs faster and better than the competition. This requires constant innovation as well as focused attention to execution. A company that continues to provide meaningful and profitable solutions to human problems has a chance to survive, even thrive, in a rapidly changing and highly competitive world.
Nitrogenases are the only enzymes known to reduce molecular nitrogen (N2) to ammonia (NH3). By using methyl viologen (N,N′-dimethyl-4,4′-bipyridinium) to shuttle electrons to nitrogenase, N2 reduction to NH3 can be mediated at an electrode surface. The coupling of this nitrogenase cathode with a bioanode that utilizes the enzyme hydrogenase to oxidize molecular hydrogen (H2) results in an enzymatic fuel cell (EFC) that is able to produce NH3 from H2 and N2 while simultaneously producing an electrical current. To demonstrate this, a charge of 60 mC was passed across H2 /N2 EFCs, which resulted in the formation of 286 nmol NH3 mg−1 MoFe protein, corresponding to a Faradaic efficiency of 26.4 %.
Natural photosynthesis is an effective route for the clean and sustainable conversion of CO2 into high-energy chemicals. Inspired by the natural process, a tandem photoelectrochemical (PEC) cell with an integrated enzyme-cascade (TPIEC) system was designed, which transfers photogenerated electrons to a multienzyme cascade for the biocatalyzed reduction of CO2 to methanol. A hematite photoanode and a bismuth ferrite photocathode were applied to fabricate the iron oxide based tandem PEC cell for visible-light-assisted regeneration of the nicotinamide cofactor (NADH). The cell utilized water as an electron donor and spontaneously regenerated NADH. To complete the TPIEC system, a superior three-dehydrogenase cascade system was employed in the cathodic part of the PEC cell. Under applied bias, the TPIEC system achieved a high methanol conversion output of 220 μm h−1, 1280 μmol g−1 h−1 using readily available solar energy and water.
The oxidation of alcohols to carbonyl compounds is one of the most fundamental reactions in synthetic organic chemistry. In order to achieve the realization of dehydrogenation reactions with high atomic efficiency, suitable catalysts and oxidants are considered as the key factors to obtain the optimum activity and aldehydes/ketones selectivity. This review aims to make an overview on the reasonable reaction mechanism and promising catalytic system of alcohols dehydrogenation.
Legitimate use of legal intranasal decongestants containing l-methamphetamine may complicate interpretation of urine drug tests positive for amphetamines. Our study hypotheses were that
commonly used immunoassays would produce no false-positive results and a recently developed enantiomer-specific gas chromatography–mass
spectrometry (GC–MS) procedure would find no d-amphetamine or d-methamphetamine in urine following controlled Vicks VapoInhaler administration at manufacturer's recommended doses. To evaluate
these hypotheses, 22 healthy adults were each administered one dose (two inhalations in each nostril) of a Vicks VapoInhaler
every 2 h for 10 h on Day 1 (six doses), followed by a single dose on Day 2. Every urine specimen was collected as an individual
void for 32 h after the first dose and assayed for d- and l-amphetamines specific isomers with a GC–MS method with >99% purity of R-(−)-α-methoxy-α-(trifluoromethyl)phenylacetyl derivatives and 10 µg/L lower limits of quantification. No d-methamphetamine or d-amphetamine was detected in any urine specimen by GC–MS. The median l-methamphetamine maximum concentration was 62.8 µg/L (range: 11.0–1,440). Only two subjects had detectable l-amphetamine, with maximum concentrations coinciding with l-methamphetamine peak levels, and always ≤4% of the parent's maximum. Three commercial immunoassays for amphetamines EMIT® II Plus, KIMS® II and DRI® had sensitivities, specificities and efficiencies of 100, 97.8, 97.8; 100, 99.6, 99.6 and 100, 100, 100%, respectively. The
immunoassays had high efficiencies, but our first hypothesis was not affirmed. The EMIT® II Plus assay produced 2.2% false-positive results, requiring an enantiomer-specific confirmation.
The integration of redox enzymes on electrode surfaces enables the use of renewable energy for highly specific bioelectrochemical synthesis. Herein, we investigate the oxidation of glucose to gluconic acid on a bioanode, combining electrochemical and enzymatic components. Gluconic acid is a valuable chemical widely used in the industry. The bioanode consists of a redox hydrogel film of polyethylenimine (PEI) containing ferrocene (Fc) as a mediator, glycerol diglycidyl ether (GDGE) as a cross-linker, and the enzyme glucose oxidase (GOx). Optimization of the enzyme and cross-linker loading in the redox film led to faradaic efficiencies up to 96 ± 5 % for gluconate. The oxygen-free setup was highly stable for quantitative electrosynthesis, yielding gluconate concentrations of 6.4 ± 0.25 mmol L-1. Moreover, this catalase-free anaerobic system showed no production of H2O2 within 24 h, thereby eliminating the deactivation of the GOx caused by H2O2 and a high enzyme performance, with a turnover frequency (TOF) of 5 x10-3 s-1. This is the first quantitative bioelectrosynthesis of gluconate in an entirely anaerobic environment with electrode stability of at least 8 h.
The development of efficient enzyme immobilization to promote their recyclability and activity is highly desirable. Zeolitic imidazolate framework‐8 (ZIF‐8) has been proved to be effective platforms for enzyme immobilization due to its easy preparation and biocompatibility. However, the intrinsic hydrophobic characteristic hinders its further development in this filed. Herein, a facile synthesis approach was developed to immobilize pepsin (PEP) on the ZIF‐8 carrier by using Ni2+ ions as anchor (ZIF‐8@PEP‐Ni). By contrast, the direct coating of PEP on the surface of ZIF‐8 (ZIF‐8@PEP) engendered significant conformational changes. Electrochemical oxygen evolution reaction (OER) was employed to study the catalytic activity of immobilized PEP. The ZIF‐8@PEP‐Ni composite attains remarkable OER performance with an ultralow overpotential of only 127 mV at 10 mA•cm‐2, which is much lower than the 690 and 919 mV•cm‐2 overpotential values of ZIF‐8@PEP and PEP, respectively.
Adenosine triphosphate (ATP) provides the driving force necessary for critical biological functions in all living organisms. In synthetic biocatalytic reactions, this cofactor is recycled in situ using high-energy stoichiometric reagents, an approach that generates waste and poses challenges with enzyme stability. On the other hand, an electrochemical recycling system would use electrons as a convenient source of energy. We report a method that uses electricity to turn over enzymes for ATP generation in a simplified cellular respiration mimic. The method is simple, robust, and scalable, as well as broadly applicable to complex enzymatic processes including a four-enzyme biocatalytic cascade in the synthesis of the antiviral molnupiravir.
Selective functionalization of aliphatic C-H bonds, ubiquitous in molecular structures, could allow ready access to diverse chemical products. While enzymatic oxygenation of C-H bonds is well established, the analogous enzymatic nitrogen functionalization is still unknown; nature is reliant on preoxidized compounds for nitrogen incorporation. Likewise, synthetic methods for selective nitrogen derivatization of unbiased C-H bonds remain elusive. In this work, new-to-nature heme-containing nitrene transferases were used as starting points for the directed evolution of enzymes to selectively aminate and amidate unactivated C(sp3)-H sites. The desymmetrization of methyl- and ethylcyclohexane with divergent site selectivity is offered as demonstration. The evolved enzymes in these lineages are highly promiscuous and show activity toward a wide array of substrates, providing a foundation for further evolution of nitrene transferase function. Computational studies and kinetic isotope effects (KIEs) are consistent with a stepwise radical pathway involving an irreversible, enantiodetermining hydrogen atom transfer (HAT), followed by a lower-barrier diastereoselectivity-determining radical rebound step. In-enzyme molecular dynamics (MD) simulations reveal a predominantly hydrophobic pocket with favorable dispersion interactions with the substrate. By offering a direct path from saturated precursors, these enzymes present a new biochemical logic for accessing nitrogen-containing compounds.
We report the reprogramming of nonheme iron enzymes to catalyze an abiological C(sp3)‒H azidation reaction through iron-catalyzed radical relay. This biocatalytic transformation uses amidyl radicals as hydrogen atom abstractors and Fe(III)‒N3 intermediates as radical trapping agents. We established a high-throughput screening platform based on click chemistry for rapid evolution of the catalytic performance of identified enzymes. The final optimized variants deliver a range of azidation products with up to 10,600 total turnovers and 93% enantiomeric excess. Given the prevalence of radical relay reactions in organic synthesis and the diversity of nonheme iron enzymes, we envision that this discovery will stimulate future development of metalloenzyme catalysts for synthetically useful transformations unexplored by natural evolution.
Nicotinamide adenine dinucleotide(NAD(P)H) is a metabolically interconnected redox cofactor serving as a hydride source for the majority of oxidoreductases, and consequently constituting a significant cost factor for bioprocessing. Much research has been devoted to the development of efficient, affordable, and sustainable methods for the regeneration of these cofactors through chemical, electrochemical, and photochemical approaches. However, the enzymatic approach using formate dehydrogenase is still the most abundantly employed in industrial applications, even though it suffers from system complexity and product purity issues. In this review, we summarize non-enzymatic and enzymatic electrochemical approaches for cofactor regeneration, then discuss recent developments to solve major issues. Issues discussed include Rh-catalyst mediated enzyme mutual inactivation, electron-transfer rates, catalyst sustainability, product selectivity and simplifying product purification. Recently reported remedies are discussed, such as heterogeneous metal catalysts generating H⁺ as the sole byproduct or high activity and stability redox-polymer immobilized enzymatic systems for sustainable organic synthesis.
Bioelectrocatalysis is an interdisciplinary research field combining biocatalysis and electrocatalysis via the utilization of materials derived from biological systems as catalysts to catalyze the redox reactions occurring at an electrode. Bioelectrocatalysis synergistically couples the merits of both biocatalysis and electrocatalysis. The advantages of biocatalysis include high activity, high selectivity, wide substrate scope, and mild reaction conditions. The advantages of electrocatalysis include the possible utilization of renewable electricity as an electron source and high energy conversion efficiency. These properties are integrated to achieve selective biosensing, efficient energy conversion, and the production of diverse products. This review seeks to systematically and comprehensively detail the fundamentals, analyze the existing problems, summarize the development status and applications, and look toward the future development directions of bioelectrocatalysis. First, the structure, function, and modification of bioelectrocatalysts are discussed. Second, the essentials of bioelectrocatalytic systems, including electron transfer mechanisms, electrode materials, and reaction medium, are described. Third, the application of bioelectrocatalysis in the fields of biosensors, fuel cells, solar cells, catalytic mechanism studies, and bioelectrosyntheses of high-value chemicals are systematically summarized. Finally, future developments and a perspective on bioelectrocatalysis are suggested.
Bioelectrocatalysis is a green, sustainable, efficient method to produce value-added chemicals, clean biofuels and degradable materials. As an alternative approach to modern biomanufacturing technology, bioelectrocatalysis fully combines the merits of both biocatalysis and electrocatalysis to realize the green, efficient production of target products from electricity. Here, we review the development status of bioelectrocatalysis, discussing the current challenges and looking toward future development directions. First, we detail the structure, function and modification methods of bioelectrocatalysis. Next, we describe the mechanism of electron transfer, including mediated electron transfer and directed electron transfer. Third, we discuss the impact of the electrode on bioelectrocatalysis. Then we analyse and summarize the application of bioelectrocatalysis methods in the production of chemicals, biofuels and materials. Finally, we detail future developments and perspectives on bioelectrocatalysis for electrosynthesis. Electrochemical reactions can provide necessary redox equivalents for biocatalysis. In this Review, Minteer and co-workers summarize the current status and challenges of enzymatic and microbial bioelectrocatalysis for the green and efficient production of target products using electricity.
Due to the high costs and stoichiometric amounts of reduced nicotinamide adenine dinucleotide (NADH) required by the many oxidoreductases used for organic synthesis and the pharmaceutical industry, there is a need for the efficient reductive regeneration of NADH from its oxidized form, NAD+. Bioelectrocatalytic methods for NADH regeneration involving diaphorase and a redox mediator have shown promise; however, strong reductive mediators needed for this system are scarce, generally unstable, and require downstream separation. The immobilization of diaphorase in cobaltocene-modified poly(allylamine) redox polymer is presented which is capable of producing bioactive 1,4-NADH with yields between 97% and 100%, faradaic efficiencies between 78% and 99%, and turnover frequencies between 2091 h-1 and 3680 h-1 over the range of temperatures spanning 20 °C to 60 °C. By using this system, methanol and propanol production by an NADH-dependent alcohol dehydrogenase were enhanced 7.1- and 5.2-fold, respectively, compared to a negative control. Finally, the efficiency of this approach coupled with its high operational stability (91% of the maximum activity after five experimental cycles) renders it among the most promising means of NADH regeneration yet developed.
Enantiomerically pure chiral amines are of increasing value in the preparation of bioactive compounds, pharmaceuticals, and agrochemicals. ω-transaminase (ω-TA) is an ideal catalyst for asymmetric amination, because of its excellent enanti-oselectivity and wide substrate scope. In order to shift the equilibrium of reactions catalyzed by ω-TA to the side of amine product, an upgraded N2 fixation system based on bioelectrocatalysis was developed to realize the conversion from N2 to chiral amine intermediates. The produced NH3 was in situ reacted by L-alanine dehydrogenase to perform the alanine generation with NADH as a coenzyme. ω-TA transferred the amino group from alanine to ketone substrates and finally produced the desired chiral amine intermediates. The cathode of the upgraded N2 fixation system supplied enough re-ducing power to synchronously realize the regeneration of reduced methyl viologen (MV.+) and NADH for the nitrogenase and L-alanine dehydrogenase. The co-product, pyruvate, was consumed by L-alanine dehydrogenase to regenerate alanine and push the equilibrium to the side of the amine. After 10 hours of reaction, the concentration of 1-methyl-3-phenylpropylamine achieved 0.54 mM with the highest faradaic efficiency of 27.6% and >99% enantiomeric excess (eep). Due to the wide substrate scope and excellent enantioselectivity of ω-TA, the upgraded N2 fixation system has great po-tential to produce a variety of chiral amine intermediates for pharmaceuticals and other applications.
Over the last decade, there has been significant research in electrochemical reduction of CO2, but it has been difficult to develop catalysts capable of C-C bond formation. Here, we report bioelectrocatalysis of vanadium nitrogenase from Azoto-bacter vinelandii, where cobaltocenium derivatives transfer electrons to the catalytic VFe protein, independent of ATP-hydrolysis. In this bioelectrochemical system, CO2 is reduced to ethylene (C2H4) and propene (C3H6), by a single metalloenzyme.
Ein künstliches Photosynthesesystem wurde durch Kombination einer photoelektrochemischen Zelle mit einer Multienzymkaskade konstruiert. J. K. Lee, C. B. Park und Mitarbeiter nutzen in ihrer Zuschrift (DOI: 10.1002/ange.201611379) Wasser als Elektronendonor, eine Hämatit-Photoanode und eine Bismutferrit-Photokathode zur Regenerierung von NADH mit sichtbarem Licht sowie eine Kaskade aus drei Dehydrogenasen für die hoch selektive und schnelle Umwandlung von Kohlendioxid in Methanol.
Natural photosynthesis is an effective route for the clean and sustainable conversion of CO2 into high-energy chemicals. Inspired by the natural process, a tandem photoelectrochemical (PEC) cell with an integrated enzyme-cascade (TPIEC) system was designed, which transfers photogenerated electrons to a multienzyme cascade for the biocatalyzed reduction of CO2 to methanol. A hematite photoanode and a bismuth ferrite photocathode were applied to fabricate the iron oxide based tandem PEC cell for visible-light-assisted regeneration of the nicotinamide cofactor (NADH). The cell utilized water as an electron donor and spontaneously regenerated NADH. To complete the TPIEC system, a superior three-dehydrogenase cascade system was employed in the cathodic part of the PEC cell. Under applied bias, the TPIEC system achieved a high methanol conversion output of 220 μm h(-1) , 1280 μmol g(-1) h(-1) using readily available solar energy and water.
Biocatalysis has made tremendous advances in the field of synthesis of industrially important products and intermediates. Cofactors are an important part of many enzymes which are involved in biocatalysis. These cofactors are expensive and stoichiometric addi- tions are not economically feasible. This necessitates the in situ cofactor regeneration in biocatalytic pro- cesses. Various methods of regeneration of NAD(H)/ NADP(H), an important class of cofactors, have been reviewed in this article. We discuss their salient fea- tures, suitability for current bioprocesses, drawbacks and scope of improvement.
By mimicking key processes of Darwinian evolution in the test tube, we can explore enzyme functions never required in the natural environment. This laboratory is developing efficient strategies for directing the evolution of enzymes in vitro, using random mutagenesis and gene recombination coupled with screening for improved variants. By accumulating beneficial mutations over multiple generations, very large increases in enzyme properties such as activity and stability have been achieved. From the large variant libraries generated, we are also able to determine the extent to which such properties are correlated. Many of the molecular solutions that arise from these experiments have been and will be unanticipated, thereby providing new insight into the molecular mechanisms of protein folding and enzyme catalysis. Furthermore, methods that have been developed for in vitro evolution will be applicable to understanding molecular events in 'natural' evolution. An example is the use of in vitro random recombination and library screening to identify the specific mutations responsible for functional differences in proteins in the background of numerous neutral or even deleterious mutations.
Biological nitrogen fixation is catalyzed by the nitrogenase enzyme system which consists of
two metalloproteins, the iron (Fe-) protein and the molybdenum-iron (MoFe-) protein. Together, these
proteins mediate the ATP-dependent reduction of dinitrogen to ammonia. Recent crystallographic analyses
of Fe-protein and MoFe-protein have revealed the polypeptide fold and the structure and organization of
the unusual metal centers in nitrogenase. These structure provide a molecular framework for addressing
the mechanism of the nitrogenase-catalyzed reaction. General features of the nitrogenase system, including
conformational coupling of nucleotide hydrolysis, aspects of the cluster structures, and the general spatial
organization of redox centers within the protein subunits, are relevant to a wide range of biochemical
systems.