NADH Photosynthesis System with Affordable Electron Supply and Inhibited NADH Oxidation.

Photosynthesis offers a green approach for the recycling of nicotinamide cofactors primarily NADH in bio-redox reactions. Herein, we report an NADH photosynthesis system where the oxidation of biomass derivatives is designed as an electron supply module (ESM) to afford electrons and superoxide dismutase/catalase (SOD/CAT) cascade catalysis is designed as a reactive oxygen species (ROS) elimination module (REM) to inhibit NADH degradation. Glucose as the electron donor guarantees the reaction sustainability accompanied with oxidative products of gluconic acid and formic acid. Meanwhile, enzyme cascades of SOD/CAT greatly eliminate ROS, leading to a ≈2.00-fold elevation of NADH yield (61.1 % vs. 30.7 %). The initial reaction rate and turnover frequency (TOF) increased by 2.50 times and 2.54 times, respectively, compared with those systems without REM. Our study establishes a novel and efficient platform for NADH photosynthesis coupled to biomass-to-chemical conversion.

Carbonic Anhydrase-Embedded Hydrogen-Bonded Organic Frameworks Coating for Facilitated Offshore CO2 Fixation.

Exhausted emission of carbon dioxide (CO2 ) from ships or offshore platforms has become one of the major contributors to global carbon emissions. Enzymes such as carbonic anhydrase (CA) have been widely used for CO2 mineralization because of their high catalytic rate. However, CA in seawater is easy to inactivate and difficult to reuse. Immobilization would be a feasible solution to address the stability issue, which, however, may cause an increase of internal diffusion resistance and reduced catalytic activity. In this regard, design of high-performance biocatalysts for acquiring high catalytic activity and stability of CA is highly desirable. Herein, a monolithic catalyst of Filler-CA@Lys-HOF-1 (FCLH) was prepared by chemical sorption of CA on the surface of the Filler followed by the coating of Lys-HOF-1. The highest catalytic activity of FCLH was obtained by regulating the amount of HOF-1 monomer added. Due to the protection of Lys-HOF-1, the FCLH showed good tolerance against acidity and salinity, which could retain about 80.2 % of the original activity after 9 h incubation in simulated seawater. The catalytic activity of FCLH could retain 85.4 % of the initial activity after 10 cycles. Hopefully, our study can provide a promising biocatalyst for CO2 mineralization, which may drive down carbon emissions when used for CO2 capture and conversion on offshore platforms.

Synthesis of a Healthy Sweetener d-Tagatose from Starch Catalyzed by Semiartificial Cell Factories.

d-Tagatose is one of the several healthy sweeteners that can be a substitute for sucrose and fructose in our daily life. Whole cell-catalyzed phosphorylation and dephosphorylation previously reported by our group afford a thermodynamic-driven strategy to achieve tagatose production directly from starch with high product yields. Nonetheless, the poor structural stability of cells and difficulty in biocatalyst recycling restrict its practical application. Herein, an efficient and stable semiartificial cell factory (SACF) was developed by constructing an organosilica network (OSN) artificial shell on the cells bearing five thermophilic enzymes to produce tagatose. The OSN artificial shell, the thickness of which can be regulated by changing the tetraethyl silicate concentration, exhibited tunable permeability and superior mechanical strength. In contrast with cells, SACFs showed a relative activity of 99.5% and an extended half-life from 33.3 to 57.8 h. Over 50% of initial activity was retained after 20 reuses. The SACFs can catalyze seven consecutive reactions with tagatose yields of over 40.7% in field applications.

Modulating Catalytic Activity and Stability of Atomically Precise Gold Nanoclusters as Peroxidase Mimics via Ligand Engineering.

Metal nanoclusters (NCs), composed of a metal core and protecting ligands, show promising potentials as enzyme mimics for producing fuels, pharmaceuticals, and valuable chemicals, etc. Herein, we explore the critical role of ligands in modulating the peroxidase mimic activity and stability of Au NCs. A series of Au15(SR)13 NCs with various thiolate ligands [SR = N-acetyl-l-cysteine (NAC), 3-mercaptopropionic acid (MPA), or 3-mercapto-2-methylpropanoic acid (MMPA)] are utilized as model catalysts. It is found that Au15(NAC)13 shows higher structural stability than Au15(MMPA)13 and Au15(MPA)13 against external stimuli (e.g., pH, oxidants, and temperature) because of the intramolecular hydrogen bonds. More importantly, detailed enzymatic kinetics data show that the catalytic activity of Au15(NAC)13 is about 4.3 and 2.7 times higher than the catalytic activity of Au15(MMPA)13 and Au15(MPA)13, respectively. Density functional theory (DFT) calculations reveal that the Au atoms on the motif of Au NCs should be the active centers, whereas the superior peroxidase mimic activity of Au15(NAC)13 should originate from the emptier orbitals of Au atoms because of the electron-withdrawing effect of acetyl amino group in NAC. This work demonstrates the ligand-engineered electronic structure and functionality of atomically precise metal NCs, which afford molecular and atomic level insights for artificial enzyme design.

Hierarchically Structured CA@ZIF-8 Biohybrids for Carbon Dioxide Mineralization.

Carbonic anhydrase (CA) is a powerful biocatalyst for carbon dioxide (CO2) mineralization, of which immobilization is usually used for maintaining its catalytic activity against harsh external stimuli. However, the incorporated materials for CA immobilization would commonly increase the internal diffusion resistance during the catalytic process, thereby decreasing the catalytic efficiency. In our study, poly-L-glutamic acid (PLGA) as the structure regulator was used to induce the synthesis of CA@zeolitic imidazolate framework-8 (CA@ZIF-8) biohybrids. The introduction of PLGA that could coordinate with Zn2+ interfered the crystallization of ZIF-8, thereby changing the morphological structure of CA@ZIF-8 biohybrids. With the increase of PLGA amount from 0 to 60 mg, PLGA(x)-CA@ZIF-8 biohybrids were gradually transformed from a dodecahedron structure to a 3D lamellar nano-flower structure, which caused elevated exposed surface area. Accordingly, the loading ratio was increased from 34.6 to 49.8 mg gcat-1, while the catalytic activity was elevated from 20.6 to 23.4%. The CO2 conversion rate was enhanced by nearly two folds compared to PLGA(0)-CA@ZIF-8 under the optimized condition. The final CaCO3 yield could reach 5.6 mg mgcat-1, whereas the reaction system could remain above 80% of the initial reaction activity after 8 cycles.

Supported Pt Enabled Proton-Driven NAD(P)+ Regeneration for Biocatalytic Oxidation.

The utilization of biocatalytic oxidations has evolved from the niche applications of the early 21st century to a widely recognized tool for general chemical synthesis. One of the major drawbacks that hinders commercialization is the dependence on expensive nicotinamide adenine dinucleotide (NAD(P)+) cofactors, and so, their regeneration is essential. Here, we report the design of carbon-supported Pt catalysts that can regenerate NAD(P)+ by proton-driven NAD(P)H oxidation with concurrent hydrogen formation. The carbon support was modified to tune the electronic nature of the Pt nanoparticles, and it was found that the best catalyst for NAD(P)+ regeneration (TOF = 581 h-1) was electron-rich Pt on carbon. Finally, the heterogeneous Pt catalyst was applied in the biocatalytic oxidation of a variety of alcohols catalyzed by different alcohol dehydrogenases. The Pt catalyst exhibited good compatibility with the biocatalytic system. Its NAD(P)+ regeneration function successfully supported biocatalytic conversion from alcohols to corresponding ketone or lactone products. This work provides a promising strategy for chemical synthesis via NAD(P)+-dependent pathways utilizing a cooperative inorganic-enzymatic catalytic system.

Thylakoid Membrane-Inspired Capsules with Fortified Cofactor Shuttling for Enzyme-Photocoupled Catalysis.

Enzyme-photocoupled catalytic systems (EPCSs), combining the natural enzyme with a library of semiconductor photocatalysts, may break the constraint of natural evolution, realizing sustainable solar-to-chemical conversion and non-natural reactivity of the enzyme. The overall efficiency of EPCSs strongly relies on the shuttling of energy-carrying molecules, e.g., NAD+/NADH cofactor, between active centers of enzyme and photocatalyst. However, few efforts have been devoted to NAD+/NADH shuttling. Herein, we propose a strategy of constructing a thylakoid membrane-inspired capsule (TMC) with fortified and tunable NAD+/NADH shuttling to boost the enzyme-photocoupled catalytic process. The apparent shuttling number (ASN) of NAD+/NADH for TMC could reach 17.1, ∼8 times as high as that of non-integrated EPCS. Accordingly, our TMC exhibits a turnover frequency (TOF) of 38 000 ± 365 h-1 with a solar-to-chemical efficiency (STC) of 0.69 ± 0.12%, ∼6 times higher than that of non-integrated EPCS.

General framework for enzyme-photo-coupled catalytic system toward carbon dioxide conversion.

High emission of carbon dioxide (CO2) has aroused global concern due to the 'greenhouse effect'. The conversion of CO2 to valuable chemicals/materials is an indispensable route toward 'carbon neutrality'. Enzyme-photo-coupled catalytic systems (EPCCSs), integrating synthetic library of semiconductor photocatalyst and natural database of enzyme, have emerged as a green and powerful platform toward CO2 conversion. Herein, we discuss the recent progress in design and application of EPCCSs for CO2 conversion from the perspective of pathway engineering, reaction engineering and system engineering. We firstly summarize the explored pathways of EPCCSs for converting CO2 to C1 and C2+ products. Secondly, we discuss the matching of kinetics between photocatalytic and enzymatic reactions in EPCCSs. Thirdly, we unveil the complex interplay between photocatalytic and enzymatic modules, and further demonstrate the strategy of compartmentalization to eliminate the negative interactions. Lastly, we conclude with the perspective on the opportunities and challenges of EPCCSs for CO2 conversion.

Enzyme-photo-coupled catalytic systems.

Efficient chemical transformation in a green, low-carbon way is crucial for the sustainable development of modern society. Enzyme-photo-coupled catalytic systems (EPCS) that integrate the exceptional selectivity of enzyme catalysis and the unique reactivity of photocatalysis hold great promise in solar-driven 'molecular editing'. However, the involvement of multiple components and catalytic processes challenged the design of efficient and stable EPCS. To show a clear picture of the complex catalytic system, in this review, we analyze EPCS from the perspective of system engineering. First, we disintegrate the complex system into four elementary components, and reorganize these components into biocatalytic and photocatalytic ensembles (BE and PE). By resolving current accessible systems, we identify that connectivity and compatibility between BE and PE are two crucial factors that govern the performance of EPCS. Then, we discuss the origin of undesirable connectivity and low compatibility, and deduce the possible solutions. Based on these understandings, we propose the designing principles of EPCS. Lastly, we provide a future perspective of EPCS.

Interactions Between Microplastics and Heavy Metals in Aquatic Environments: A Review.

Microplastics (MPs), tiny particles broken down from larger pieces of plastics, have accumulated everywhere on the earth. As an inert carbon stream in aquatic environment, they have been reported as carriers for heavy metals and exhibit diverse interactive effects. However, these interactions are still poorly understood, especially mechanisms driving these interactions and how they pose risks on living organisms. In this mini review, a bibliometric analysis in this field was conducted and then the mechanisms driving these interactions were examined, especially emphasizing the important roles of microorganisms on the interactions. Their combined toxic effects and the potential hazards to human health were also discussed. Finally, the future research directions in this field were suggested. This review summarized the recent research progress in this field and highlighted the essential roles of the microbes on the interactions between MPs and heavy metals with the hope to promote more studies to unveil action mechanisms and reduce/eliminate the risks associated with MP presence.

Intensifying Electron Utilization by Surface-Anchored Rh Complex for Enhanced Nicotinamide Cofactor Regeneration and Photoenzymatic CO2 Reduction.

Solar-driven photocatalytic regeneration of cofactors, including reduced nicotinamide adenine dinucleotide (NADH), reduced nicotinamide adenine dinucleotide phosphate (NADPH), and reduced flavin adenine dinucleotide (FADH2), could ensure the sustainable energy supply of enzymatic reactions catalyzed by oxidoreductases for the efficient synthesis of chemicals. However, the elevation of cofactor regeneration efficiency is severely hindered by the inefficient utilization of electrons transferred on the surface of photocatalysts. Inspired by the phenomenon of ferredoxin-NADP+ reductase (FNR) anchoring on thylakoid membrane, herein, a homogeneous catalyst of rhodium (Rh) complex, [Cp∗Rh(bpy)H2O]2+, was anchored on polymeric carbon nitride (PCN) mediated by a tannic acid/polyethyleneimine (TA/PEI) adhesive layer, acquiring PCN@TA/PEI-Rh core@shell photocatalyst. Illuminated by visible light, electrons were excited from the PCN core, then transferred through the TA/PEI shell, and finally captured by the surface-anchored Rh for instant utilization during the regeneration of NADH. The TA/PEI-Rh shell could facilitate the electron transfer from the PCN core and, more importantly, achieved ~1.3-fold elevation of electron utilization efficiency compared with PCN. Accordingly, the PCN@TA/PEI-Rh afforded the NADH regeneration efficiency of 37.8% after 20 min reaction under LED light (405 nm) illumination, over 1.5 times higher than PCN with free Rh. Coupling of the NADH regeneration system with formate dehydrogenase achieved continuous production of formate from carbon dioxide (CO2). Our study may provide a generic and effective strategy to elevate the catalytic efficiency of a photocatalyst through intensifying the electron utilization.

Hierarchically Porous Biocatalytic MOF Microreactor as a Versatile Platform towards Enhanced Multienzyme and Cofactor-Dependent Biocatalysis.

Metal-organic frameworks (MOFs) have recently emerged as excellent hosting matrices for enzyme immobilization, offering superior physical and chemical protection for biocatalytic reactions. However, for multienzyme and cofactor-dependent biocatalysis, the subtle orchestration of enzymes and cofactors is largely disrupted upon immobilizing in the rigid crystalline MOF network, which leads to a much reduced biocatalytic efficiency. Herein, we constructed hierarchically porous MOFs by controlled structural etching to enhance multienzyme and cofactor-dependent enzyme biocatalysis. The expanded size of the pores can provide sufficient space for accommodated enzymes to reorientate and spread within MOFs in their lower surface energy state as well as to decrease the inherent barriers to accelerate the diffusion rate of reactants and intermediates. Moreover, the developed hierarchically porous MOFs demonstrated outstanding tolerance to inhospitable surroundings and recyclability.

Mussel-Inspired pH-Switched Assembly of Capsules with an Ultrathin and Robust Nanoshell.

Enclosed films, also called capsules, bearing an ultrathin and robust nanoshell have sparked much interest for use in many applications, for which facile preparation methods are urgently pursued. Inspired by the pH-programmed adhesion/cohesion of mussel-secreted foot proteins, polyphenol/polyamine capsules with an ultrathin and robust nanoshell are fabricated through a pH-switched assembly on sacrificial calcium carbonate (CaCO3) templates. Polyphenols adhere to the templates at pH 6.0 and rapidly cohere with polyamines at pH 8.0. The pH-switched assembly process is accomplished in only a few minutes where multiple instances of electrostatic interactions and chemical conjugation between polyphenols and polyamines occur. As a result, the capsules exhibit a nanoshell thickness of ∼10 nm and a superior mechanical strength of ∼1.575 GPa (elasticity modulus). Cell mimics are prepared through encasing enzymes in the lumen and present an activity recovery of ∼70% along with little activity decline during reuse. Amine or phenolic groups on the nanoshell of capsules are then applied to induce the generation of titania or silver nanoparticles, which may expand the applications of the capsules to the photo- and biorelated realms. Our study not only deepens the understanding of the adhering process of mussels but also offers a generic method toward functional materials for diverse applications.

Crackled nanocapsules: the "imperfect" structure for enzyme immobilization.

Herein, the first example of crackled organosilica nanocapsules (CONs) is reported to directly immobilize enzymes without any further chemical modification. Enzymes are adsorbed on both the exterior and interior surfaces of CONs, integrating the merits of adsorption and encapsulation. When used for Candida rugosa lipase (CRL) immobilization, the CONs displayed higher enzyme loading, lower enzyme leaching, and elevated enzyme activity, compared to the conventional non-crackled nanocapsules/particles.

Nanoporous Phyllosilicate Assemblies for Enzyme Immobilization.

Physical/chemical adsorption is well-known as a facile and effective method for enzyme immobilization, while ideal adsorbents with a high structural stability, high loading capacity, and low leaching ratio are still under exploration. In this study, nanoporous assemblies of two-dimensional (2D) copper phyllosilicate (L-CuSiO3) are prepared as an adsorbent to immobilize horseradish peroxidase (HRP) for phenol-containing wastewater treatment. Specifically, the robust chemical bonds of Si-O-Si and Si-O-Cu in L-CuSiO3 ensure its superior structural stability; the well-developed porous structure endows L-CuSiO3 assemblies with a high specific surface area of 611.7 cm3 g-1, which enables a fast and high enzyme loading of 140 mg g-1 within 4 h, and the well-distributed Cu(II) ions ensure the stable attachment of enzyme through Cu(II)-arginine (in HRP) coordination with a leaching ratio less than 10%. Meanwhile, the scaling assembly of L-CuSiO3 renders the resultant biocatalyst (HRP-loaded L-CuSiO3 assemblies) ease-of-recycling performance. Given the above features, the HRP-loaded L-CuSiO3 assemblies exhibit a better stability and 2-fold higher activity by contrast with HRP adsorbed on conventional mesoporous SiO2 and SiO2 nanoparticles, and it also acted as an efficient bioreactor in the application of catalytical removal of phenol pollutants from wastewater. Our L-CuSiO3 assemblies show great potential in immobilization of enzymes for industrial biocatalysis.

Plant polyphenol-inspired nano-engineering topological and chemical structures of commercial sponge surface for oils/organic solvents clean-up and recovery.

In our study, plant polyphenol-inspired chemistry is explored to nano-engineer the topological and chemical structures of commercial melamine sponge surface for preparing superhydrophobic sponges. Briefly, tannic acid (TA, a typical plant polyphenol) is applied to induce the co-assembly of silica nanoparticles (SiO2) and silver ions (Ag+) to form SiO2@TA@Ag nanostructures on a melamine sponge surface. After further chemical fluorination, the superhydrophobic sponge with a "lotus leaf-mimic" surface is formed. Surface topological/chemical structures, superhydrophobic property and anti-combustion characteristics of the sponge are examined by a series of characterization techniques, including scanning electron microscopy, X-ray photoelectron spectroscopy, water contact angle measurements, combustion/heating test, etc. The superhydrophobic sponge presents an adsorption capacity of 69-153 times of its own weight toward various oils/organic solvents, and exhibits excellent recycling ability evidenced by over 100-cycled uses. Continuous oil/water separation apparatus is also set up through equipping the superhydrophobic sponge on a peristaltic pump, realizing the clean-up of oils and organic solvents from water continuously. Together with the facile, easy-to-scale-up and substrate non-selective features of plant polyphenol-inspired chemistry, the superhydrophobic sponge and the surface nano-engineering method would hold great promise for the effective treatment of oil spillages and organic discharges, achieving high sustainability to energy and environment.

Shielding of Enzymes on the Surface of Graphene-Based Composite Cellular Foams Through Bioinspired Mineralization.

Immobilization of enzyme on the surface of graphene-based composite cellular foams (GCCFs) is commonly prone to acquire stable and ultrahigh loading of enzymes and fast transport of substrates during the catalytic process. In this chapter, we reported a method of preparing GCCFs through combination of redox assembly and biomimetic mineralization with in situ enzyme immobilization. Briefly, GCCFs were first prepared through redox assembly of graphene oxide (GO) nanosheets enabled by polyethyleneimine (PEI). The cationic PEI in the resultant reduced GO/PEI (rGO/PEI) cellular foams acted as the mineralization-inducing agent could catalyze the condensation of silicate to form silica (biomimetic silicification) on the reduced graphene oxide (rGO) surface, where enzyme (with penicillin G acylase as model enzyme) is in situ entrapped and shielded within the silica network. Enzymes could be stably resided on the surface of GCCFs without any leaching against a broad range of pH values (3.5-10.0). GCCFs show a three-dimensional (3D) porous structure, which facilitates the fast transfer of substrate and, thereby, leads to desirable catalytic activity. Combined with the monolithic feature, GCCFs exhibit ease of recyclability and superior thermal/recycling stabilities during the catalytic synthesis of 6-aminopenicillanic acid (6-APA, an important pharmaceutical intermediate) compared to free enzyme and enzyme adsorbed on rGO/PEI cellular foams.

Bioinspired construction of multi-enzyme catalytic systems.

Enzyme catalysis, as a green, efficient process, displays exceptional functionality, adaptivity and sustainability. Multi-enzyme catalysis, which can accomplish the tandem synthesis of valuable materials/chemicals from renewable feedstocks, establishes a bridge between single-enzyme catalysis and whole-cell catalysis. Multi-enzyme catalysis occupies a unique and indispensable position in the realm of biological reactions for energy and environmental applications. Two complementary strategies, i.e., compartmentalization and substrate channeling, have been evolved by living organisms for implementing the complex in vivo multi-enzyme reactions (MERs), which have been applied to construct multi-enzyme catalytic systems (MECSs) with superior catalytic activity and stabilities in practical biocatalysis. This tutorial review aims to present the recent advances and future prospects in this burgeoning research area, stressing the features and applications of the two strategies for constructing MECSs and implementing in vitro MERs. The concluding remarks are presented with a perspective on the construction of MECSs through rational combination of compartmentalization and substrate channeling.

One-pot fabrication of chitin-shellac composite microspheres for efficient enzyme immobilization.

In this study, all-natural composite microspheres were fabricated through adding shellac into chitin solution followed by self-assembly via thermally-induced phase separation. The pore structure of the composite microspheres was altered into wedge-shape from ink-bottle-shape of the chitin microspheres, whereas, the crystalline structure of these two kinds of microspheres remained unaltered. The as-fabricated chitin-shellac composite microspheres were used for enzyme immobilization through adsorption. And yeast alcohol dehydrogenase (YADH) was chosen as the model enzyme, which is a multimer consisting of 4 subunits. The loading capacity of the as-prepared composite microspheres was up to 79.0mg/g (enzyme/carrier). The immobilized enzyme exhibited a comparable catalytic activity compared to its free counterpart and maintained 49.3% of its initial activity after 54days' storage at 4°C while the free enzyme lost all its activity.

Combination of Redox Assembly and Biomimetic Mineralization To Prepare Graphene-Based Composite Cellular Foams for Versatile Catalysis.

Graphene-based materials with hierarchical structures and multifunctionality have gained much interest in a variety of applications. Herein, we report a facile, yet universal approach to prepare graphene-based composite cellular foams (GCCFs) through combination of redox assembly and biomimetic mineralization enabled by cationic polymers. Specifically, cationic polymers (e.g., polyethyleneimine, lysozyme, etc.) could not only reduce and simultaneously assemble graphene oxide (GO) into cellular foams but also confer the cellular foams with mineralization-inducing capability, enabling the formation of inorganic nanoparticles (e.g., silica, titania, silver, etc.). The GCCFs show highly porous structure and appropriate structural stability, where nanoparticles are well distributed on the surface of the reduced GO. Through altering polymer/inorganic pairs, a series of GCCFs are synthesized, which exhibit much enhanced catalytic performance in enzyme catalysis, heterogeneous chemical catalysis, and photocatalysis compared to nanoparticulate catalysts.