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.

Microcapsules with diverse wall structures may exhibit different performance in specific applications. In the present study, three kinds of mussel-inspired polydopamine (PDA) microcapsules with different wall structures have been prepared by a template-mediated method. More specifically, three types of CaCO3 microspheres (poly(allylamine hydrochloride), (PAH)-doped CaCO3; pure-CaCO3; and poly(styrene sulfonate sodium), (PSS)-doped CaCO3) were synthesized as sacrificial templates, which were then treated by dopamine to obtain the corresponding PDA-CaCO3 microspheres. Through treating these microspheres with disodium ethylene diamine tetraacetic acid (EDTA-2Na) to remove CaCO3, three types of PDA microcapsules were acquired: that was (1) PAH-PDA microcapsule with a thick (∼600 nm) and highly porous capsule wall composed of interconnected networks, (2) pure-PDA microcapsule with a thick (∼600 nm) and less porous capsule wall, (3) PSS-PDA microcapsule with a thin (∼70 nm) and dense capsule wall. Several characterizations confirmed that a higher degree in porosity and interconnectivity of the capsule wall would lead to a higher mass transfer coefficient. When serving as the carrier for catalase (CAT) immobilization, these enzyme-encapsulated PDA microcapsules showed distinct structure-related activity and stability. In particular, PAH-PDA microcapsules with a wall of highly interconnected networks displayed several significant advantages, including increases in enzyme encapsulation efficiency and enzyme activity/stability and a decrease in enzyme leaching in comparison with other two types of PDA microcapsules. Besides, this hierarchically structured PAH-PDA microcapsule may find other promising applications in biocatalysis, biosensors, drug delivery, etc.

Recent advances in enzyme-photo-coupled catalytic systems are reviewed and highlighted from the perspective of system engineering.

Artificial photosynthesis holds promise in producing solar fuels and chemicals. Although encouraging achievements have been made in the development of catalysts for reaction/ process modules in artificial photosynthesis, constructing a highly compatible complex reaction system remains a distant prospect. Herein, an artificial thylakoid is proposed and constructed by decorating the inner wall of protamine−titania (PTi) microcapsules with cadmium sulfide quantum dots (CdS QDs) for the photobiocoupled reduction of carbon dioxide (CO 2 ) via a single enzyme (formate dehydrogenase) and multiple enzymes (formate/formaldehyde/alcohol dehydrogenases). The size-selective capsule wall compartmentalizes photocatalytic oxidation and biocatalytic reduction, creating well-directed reaction sequences and protecting enzymes from deactivation. The favorable electronic coupling and band structure between CdS and PTi separate holes and electrons to afford an NADH regeneration rate of 4226 ± 121 μmol g −1 h −1 and optimized yield of 93.03 ± 3.84%. The photobiocoupled system achieves formate and methanol outputs of 1500 and 99 μM h −1 with a single enzyme and multiple enzymes, respectively. Our study may exploit a method for the construction of complex artificial catalytic systems with multiple reactions.

Solar energy conversion by photocatalysis holds promise in energy supply, but its efficiency is hindered by the mismatch in charge generation, transfer, and utilization. In natural photosynthesis, photosystem I (PSI) exhibits an intrinsic quantum efficiency of nearly 100% in solar energy conversion. The elaborate synergy of electron transfer and electron utilization guarantees the conversion of unstable excited electrons to stable electrons in reduced nicotinamide adenine dinucleotide phosphate (NADPH). To demonstrate this in vitro, we report a design of core−shell metal−organic frameworks (MOFs) as an "electron buffer tank" to coordinate electron transfer and electron utilization in photocatalysis. The electrons are generated via the irradiation on photosensitizers (2-aminoterephthalic acid, NH 2 -BDC) in the core and then transferred to Zr 6 O 8 clusters on the shell through the light-induced ligand-to-metal charge transfer mechanism. Neighboring reaction centers, [Cp*Rh(bpydc)H 2 O] 2+ , on the MOFs behave as the electron buffer tank and store these electrons in the form of hydrides for subsequent regeneration of reduced nicotinamide adenine dinucleotide (NADH). The electron lifetime is prolonged from nanoseconds to seconds, leading to 2.27-fold enhancement of electron availability and 2.08-fold enhancement of activity compared to the homogeneous reaction counterpart. The coupling of NADH regeneration and enzyme catalysis further enables the asymmetric reduction of carbonyl to chiral amine. The electron buffer tank concept may offer a generic strategy to coordinate mass transfer and chemical reaction in a broad range of catalytic processes.

In-depth understanding and rational manipulation of the electron transfer process and molecule diffusion process are critical to promote the overall photocatalytic efficiency. In our study, core@shell photocatalysts that embody graphitic carbon nitride (GCN) core and amorphous titania (a-TiO2) nanoshell are prepared to elucidate and coordinate the electron transfer and molecule diffusion for the regeneration of nicotinamide adenine dinucleotide (NADH) with [Cp*Rh­(bpy)­H2O]2+ as the redox mediator. The GCN core absorbs visible light to generate electron–hole pairs, whereas the a-TiO2 nanoshell facilitates the transfer of photogenerated electrons from GCN to the a-TiO2 surface for NADH regeneration, which also enables the diffusion of electron donor molecules (triethanolamine, TEOA) from the a-TiO2 surface to GCN for consuming the holes left on GCN. The transfer of photogenerated electrons and the diffusion of electron donor molecules are coordinated by finely tuning the thickness of the a-TiO2 nanoshell. Under the optimized nanoshell thickness of ∼2.1 nm, the GCN@a-TiO2 photocatalyst exhibits the highest NADH regeneration yield of 82.1% after a 10 min reaction under LED light (405 nm), over 200% higher than that of the GCN photocatalyst. Combined with the highly controllable and mild features of the bioinspired mineralization method, our study may offer a facile and generic strategy to design high performance photocatalysts through rational coordination of different substances/species transport processes.

In this study, a method inspired by polyphenol chemistry is developed for the facile preparation of microcapsules under mild conditions. Specifically, the preparation process includes four steps: formation of the sacrificial template, generation of the polyphenol coating on the template surface, cross-linking of the polyphenol coating by cationic polymers, and removal of the template. Tannic acid (TA) is chosen as a representative polyphenol coating precursor for the preparation of microcapsules. The strong interfacial affinity of TA contributes to the formation of polyphenol coating through oxidative oligomerization, while the high reactivity of TA is in charge of reacting/cross-linking with cationic polymer polyethylenimine (PEI) through Schiff base/Michael addition reaction. The chemical/topological structures of the resultant microcapsules are simultaneously characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier Transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), etc. The wall thickness of the microcapsules could be tailored from 257±20 nm to 486±46 nm through changing the TA concentration. The microcapsules are then utilized for encapsulating glucose oxidase (GOD), and the immobilized enzyme exhibits desired catalytic activity and enhanced pH and thermal stabilities. Owing to the structural diversity and functional versatility of polyphenols, this study may offer a facile and generic method to prepare microcapsules and other kinds of functional porous materials.

Photoenzymatic coupled catalysis, integrating semiconductor photocatalysis and enzymatic catalysis, exhibits great potential for light-driven synthesis. To make photocatalyst and enzyme at play concertedly, nicotinamide-based cofactors have been widely used as electron carrier. However, these cofactors are easily oxidized into enzymatically inactive form by photo-generated holes. Herein, oxidation mechanism of NADH, one typical nicotinamide-based cofactor, by photo-generated holes was reported. With CdS, g-C3N4 and BiVO4 as hole generators, NADH is oxidized into NAD + or fragmented into ADP-ribose derivatives through multi-step electron transfer. Importantly, fragmentation reaction is inhibited with dopamine and neutral red to coordinate electron transfer between NADH and photo-generated holes.