Enzymatic Activation and Continuous Electrochemical Production of Methane from Dilute CO2 Sources with a Self-Healing Capsule.

Converting dilute CO2 source into value-added chemicals and fuels is a promising route to reduce fossil fuel consumption and greenhouse gas emission, but integrating electrocatalysis with CO2 capture still faced marked challenges. Herein, we show that a self-healing metal-organic macrocycle functionalized as an electrochemical catalyst to selectively produce methane from flue gas and air with the lowest applied potential so far (0.06 V vs reversible hydrogen electrode, RHE) through an enzymatic activation fashion. The capsule emulates the enzyme' pocket to abstract one in situ-formed CO2-adduct molecule with the commercial amino alcohols, forming an easy-to-reduce substrate-involving clathrate to combine the CO2 capture with electroreduction for a thorough CO2 reduction. We find that the self-healing system exhibited enzymatic kinetics for the first time with the Michaelis-Menten mechanism in the electrochemical reduction of CO2 and maintained a methane Faraday efficiency (FE) of 74.24% with a selectivity of over 99% for continuous operation over 200 h. A consecutive working lab at 50 mA·cm-2, in an eleven-for-one (10 h working and 1 h healing) electrolysis manner, gives a methane turnover number (TON) of more than 10,000 within 100 h. The integrated electrolysis with CO2 capture facilitates the thorough reduction of flue gas (ca. 13.0% of CO2) and first time of air (ca. 400 ppm of CO2 to 42.7 mL CH4 from 1.0 m3 air). The new self-healing strategy of molecular electrocatalyst with an enzymatic activation manner and anodic shifting of the applied potentials provided a departure from the existing electrochemical catalytic techniques.

Cluster-Cluster Co-Nucleation Induced Defective Polyoxometalate-Based Metal-Organic Frameworks for Efficient Tandem Catalysis.

The construction of defective sites is one of the effective strategies to create high-activity Metal-Organic frameworks (MOFs) catalysts. However, traditional synthesis methods usually suffer from cumbersome synthesis steps and disordered defect structures. Herein, a cluster-cluster co-nucleation (CCCN) strategy is presented that involves the in situ introduction of size-matched functional polyoxometalates (H6P2W18O62, {P2W18}) to intervene the nucleation process of cluster-based MOFs (UiO-66), achieving one-step inducement of exposed defective sites without redundant post-processing. POM-induced UiO-66 ({P2W18}-0.1@UiO-66) exhibits a classical reo topology for well-defined cluster defects. Moreover, the defective sites and the interaction between POM and skeletal cluster nodes are directly observed by Integrated Differential Phase Contrast in Scanning Transmission Electron Microscopy (iDPC-STEM). Owing to the molecular-level proximity between defective sites and POM in the same nano-reaction space, {P2W18}-0.1@UiO-66 exhibits efficient tandem catalysis in the preparation of γ-valerolactone (γ-GVL) from laevulinic acid (LA) by the combination of Lewis and Brønsted acids with 11 times higher performance than defective UiO-66 formed by conventional coordination modulation strategy. The CCCN strategy is applicable to different POM and has the potential to be extended to other cluster-based MOFs, which will pave a new way for the construction of functional MOFs with multi-centered synergistic catalysis.

A visible-light-catalyzed sulfonylation reaction of an aryl selenonium salt via an electron donor-acceptor complex.

An efficient synthesis of sulfone structures through selenonium salts and sodium sulfinates was developed. Under the irradiation of a blue LED lamp, the two substrates generate aryl and sulfonyl radicals through the activation of the intermediate electron donor acceptor (EDA) complex, thereby synthesizing aromatic, heteroaromatic and aliphatic sulfones in medium to good yields. The advantages of this strategy are metal-free, mild conditions and the leaving group is recycled to construct new selenonium salts.

Modifying Proton Relay into Bioinspired Dye-based Coordination Polymer for Photocatalytic Proton-Coupled Electron Transfer.

Proton-coupled electron transfer (PCET) imparts an energetic advantage over solo electron transfer in activating inert substances. Natural PCET enzyme catalysis generally requires tripartite preorganization of proton relay, substrate-bound active center, and redox mediator, making the processes efficient and precluding side reactions. Inspired by this, a heterogeneous photocatalytic PCET system was established to achieve higher PCET driving forces by modifying proton relays into anthraquinone-based anionic coordination polymers. The proximally separated proton relays and photoredox-mediating anthraquinone moiety allowed pre-assembly of inert substrate between them, merging proton and electron into unsaturated bond by photoreductive PCET, which enhanced reaction kinetics than the counter catalyst without proton relay. This photocatalytic PCET method was applied to a broad-scoped reduction of aryl ketones, unsaturated carbonyls, and aromatic compounds. The distinctive regioselectivities for the reduction of isoquinoline derivatives were found to occur on the carbon-ring sides. PCET-hydrogenated radical intermediate of quinoline could be trapped by alkene for proton relay-assisted Minisci addition, forming the pharmaceutical aza-acenaphthene scaffold within one step. When using heteroatom(X)-H/C-H compounds as proton-electron donors, this protocol could activate these inert bonds through photooxidative PCET to afford radicals and trap them by electron-deficient unsaturated compounds, furnishing the direct X-H/C-H functionalization.

Modifying the Oxidative Potentials of Imines in a Dye Loaded Capsule for Photocatalytic Cyclization with Hydrogen Evolution.

Modifying redox potential of substrates and intermediates to balance pairs of redox steps are important stages for multistep photosynthesis but faced marked challenges. Through co-clathration of iridium photosensitizer and imine substrate within one packet of a metal-organic capsule to shift the redox potentials of substrate, herein, we reported a multiphoton enzymatic strategy for the generation of heterocycles by intramolecular C-X hydrogen evolution cross-couplings. The cage facilitated a pre-equilibrium substrate-involving clathrate that cathodic shifts the oxidation potential of the substrate-dye-host ternary complex and configuration inversion of substrate via spatial constraints in the confined space. The new two photon excitation strategy enabled the precise control of the multistep electron transfer between each pair (photosensitizer, substrate and the capsule), endowing the catalytic system proceeding smoothly with an enzymatic fashion. Three kinds of 2-subsituted (-OH, -NH2 , and -SH) imines and N-aryl enamines all give the corresponding cyclization products efficiently under visible light irradiation, demonstrating the promising of the microenvironment driven thermodynamic activation in the host-dye-substrate ternary for synergistic combination of multistep photocatalytic transformations.

Engineering NH2-Cu-NH2 Triple-atom Sites in Defective MOFs for Selective Overall Photoreduction of CO2 into CH3COCH3.

Selective photoreduction of CO2 to multicarbon products, is an important but challenging task, due to high CO2 activation barriers and insufficient catalytic sites for C-C coupling. Herein, a defect engineering strategy for incorporating copper sites into the connected nodes of defective metal-organic framework UiO-66-NH2 for selective overall photo-reduction of CO2 into acetone. The Cu2+ site in well-modified CuN2O2 units served as a trapping site to capture electrons via efficient electron-hole separation, forming the active Cu+ site for CO2 reduction. Two NH2 groups in CuN2O2 unit adsorb CO2 and cooperated with copper ion to functionalize as a triple atom catalytic site, each interacting with one CO2 molecule to strengthen the binding of *CO intermediate to the catalytic site. The deoxygenated *CO attached to the Cu site interacted with *CH3 fixed at one amino group to form the key intermediate CO*-CH3, which interacted with the third reduction intermediate on another amino group to produce acetone. Our photocatalyst realizes efficient overall CO2 reduction to C3 product acetone CH3COCH3 with an evolution rate of 70.9 µmol gcat -1 h-1 and a selectivity up to 97 % without any adducts, offering a promising avenue for designing triple-atomic sites to producing C3 product from photosynthesis with water.

Enzyme-Inspired Coordination Polymers for Selective Oxidization of C(sp3)-H Bonds via Multiphoton Excitation.

Nature's blueprint provides the fundamental principles for expanding the use of abundant metals in catalysis; however, mimicking both the structure and function of copper enzymes simultaneously in one artificial system for selective C-H bond oxidation faces marked challenges. Herein, we report a new approach to the assembly of artificial monooxygenases utilizing a binuclear Cu2S2Cl2 cluster to duplicate the identical structure and catalysis of the CuA enzyme. The designed monooxygenase Cu-Cl-bpyc facilitates well-defined redox potential that initially activated O2via photoinduced electron transfer, and generated an active chlorine radical via a ligand-to-metal charge transfer (LMCT) process from the consecutive excitation of the in situ formed copper(II) center. The chlorine radical abstracts a hydrogen atom selectively from C(sp3)-H bonds to generate the radical intermediate; meanwhile, the O2•- species interacted with the mimic to form mixed-valence species, giving the desired oxidization products with inherent product selectivity of copper monooxygenases and recovering the catalyst directly. This enzymatic protocol exhibits excellent recyclability, good functional group tolerance, and broad substrate scope, including some biological and pharmacologically relevant targets. Mechanistic studies indicate that the C-H bond cleavage was the rate-determining step and the cuprous interactions were essential to stabilize the active oxygen species. The well-defined structural characters and the fine-modified catalytic properties open a new avenue to develop robust artificial enzymes with uniform and precise active sites and high catalytic performances.

Modifying Enzymatic Substrate Binding within a Metal-Organic Capsule for Supramolecular Catalysis.

Supramolecular catalysis is established to modify reaction kinetics by substrate encapsulation, but manipulating the thermodynamics of electron-transfer reactions remains unexplored. Herein, we reported a new microenvironment-shielding approach to induce an anodic shift in the redox potentials of hydrazine substrates, reminiscent of the enzymatic activation for N-N bond cleavage within a metal-organic capsule H1. Equipped with the catalytic active cobalt sites and substrate-binding amide groups, H1 encapsulated the hydrazines to form the substrate-involving clathration intermediate, triggering the catalytic reduction N-N bond cleavage when electrons were acquired from the electron donors. Compared with the reduction of free hydrazines, the conceptual molecular confined microenvironment decreases the Gibbs free energy (up to -70 kJ mol-1), which is relevant to the initial electron-transfer reaction. Kinetic experiments demonstrate a Michaelis-Menten mechanism, which involves the formation of the pre-equilibrium of substrate-binding, followed by bond cleavage. Then, the distal N is released as NH3 and the product is squeezed. Integrating fluorescein into H1 enabled the photoreduction of N2H4 with an initial rate of ca. 1530 nmol min-1 into ammonia, comparable to that of natural MoFe proteins; thus, the approach provides an attractive manifold toward mimicking enzymatic activation.

Enzyme Grafting with a Cofactor-Decorated Metal-Organic Capsule for Solar-to-Chemical Conversion.

Semi-artificial approaches to solar-to-chemical conversion can achieve chemical transformations that are beyond the capability of natural enzymes, but face marked challenges to facilitate in vivo cascades, due to their inevitable need for cofactor shuttling and regeneration. Here, we report on an enzyme grafting strategy to build a metal-organic capsule-docking artificial enzyme (metal-organic-enzyme, MOE) that comprised the self-assembly of a cofactor-decorated capsule and the supramolecular enzyme-recognition features between the enzyme scaffold and the capsule to bypass cofactor shuttling and regeneration. The incorporated NADH mimics within the metal-organic capsule interacted with the imine intermediate that formed from the condensation of the amines and the dehydrogenation of alcohol substrates in the microenvironment to form complexes within the capsule and subsequently served as an in situ-generated photoresponsive cofactor. Upon illumination, the photoresponsive cofactor facilitates efficient proton/electron transport between the inner space (supramolecular hydrogenation) and outer space (enzymatic dehydrogenation) of the capsule to dehydrogenize the alcohols and hydrogenize the imine intermediates, respectively, circumventing the conventionally complex multistep cofactor shuttling and regeneration. The semi-artificial enzyme endows the conversion of diverse types of alcohol to amine products in both aqueous/organic solutions and Escherichia coli with high efficiency, offering a wide range of opportunities for sustainable and environmentally friendly biomanufacturing of commodity and fine chemicals.

Optically Pure Double-Stranded Dinuclear Ir(III) Metallohelices Enabled Chirality-Induced Photodynamic Responses.

Investigation on the interactions between enantiomers of chiral drugs and biomolecules can help precisely understand their biological behaviors in vivo and provide insights into the design of new drugs. Herein, we designed and synthesized a pair of optically pure, cationic, double-stranded dinuclear Ir(III)-metallohelices (Λ2R4-H and Δ2S4-H), and their dramatic enantiomer-dependent photodynamic therapy (PDT) responses were thoroughly studied in vitro and in vivo. Compared to the mononuclear enantiomeric or racemic [Ir(ppy)2(dppz)][PF6] (Λ-/Δ-Ir, rac-Ir) that with high dark toxicity and low photocytotoxicity index (PI) values, both of the optically pure metallohelices displayed negligible toxicity in the dark while exhibiting very distinctive light toxicity upon light irradiation. The PI value of Λ2R4-H was approximately 428, however, Δ2S4-H significantly reached 63,966. Interestingly, only Δ2S4-H was found to migrate from mitochondria to nucleus after light irradiation. Further proteomic analysis verified that Δ2S4-H activated the ATP-dependent migration process after light irradiation, and subsequently inhibited the activities of the nuclear proteins such as superoxide dismutase 1 (SOD1) and eukaryotic translation initiation factor 5A (EIF5A) to trigger the accumulation of superoxide anions and downregulate mRNA splicing processes. Molecular docking simulations suggested that the interactions between metallohelices and nuclear pore complex NDC1 dominated the migration process. This work presents a new kind of Ir(III) metallohelices-based agent with the highest PDT efficacy, highlights the importance of metallohelices' chirality, and provides inspirations for the future design of chiral helical metallodrugs.

Ultrathin 2D Cerium-Based Metal-Organic Framework Nanosheet That Boosts Selective Oxidation of Inert C(sp3 )H Bond through Multiphoton Excitation.

The development of methodologies for inducing and tailoring activities of catalysts is an important issue in various catalysis. The ultrathin 2D monolayer metal-organic framework (MOF) nanosheets with more accessible active sites and faster diffusion obtained by exfoliating 3D layered MOFs are of great potential as heterogeneous catalysts, but the rational design and preparation of 3D layered MOFs remains a grand challenge. Herein, a novel weak electrostatic interaction strategy to construct a 3D layered cerium-bearing MOF by coordinating chlorine-capped cerium nodes and linear photoactive methyl viologen (MV+ ) organic linkers is used. Under multiphoton excitation, the MV+ ligands and CeCl chromophores are triggered consecutively to form the high activity chlorine radical (Cl• ) for activation of inert C(sp3 )H bond through a hydrogen atom transfer. Benefiting from framework confinement effects, synergistic effects of two active sites and/or flexibility of the ultrathin framework nanosheets with high surface utilization, the observed activities increase in the order CeCl3 /MV+  < bulk 3D MOF crystals < 2D MOF nanosheets in photocatalysis. This work not only contributes a new strategy to construct 3D layered MOFs and their ultrathin nanosheets but also paves the way to use nanostructured MOFs to handle synergy of multiple molecular catalysts.

Harnessing Radicals in Confined Supramolecular Environments Made Possible by MOFs.

Researching and utilizing radical intermediates in organic synthetic chemistry have innovated discoveries in methodology and theory. Reactions concerning free radical species opened new pathways beyond the frame of the two-electron mechanism while commonly characterized as rampant processes lacking selectivity. As a result, research in this field has always focused on the controllable generation of radical species and determining factors of selectivity. Metal-organic frameworks (MOFs) have emerged as compelling candidates as catalysts in radical chemistry. From a catalytic point of view, the porous nature of MOFs entails an inner phase for the reaction that could offer possibilities for the regulation of reactivity and selectivity. From a material science perspecti ve, MOFs are organic-inorganic hybrid materials that integrate functional units in organic compounds and complex forms in the tunable long-ranged periodic structure. In this account, we summarized our progress in the application of MOFs in radical chemistry in three parts: (1) The generation of radical species; (2) The weak interactions and site selectivity; (3) Regio- and stereo-selectivity. The unique role of MOFs play in these paradigms is demonstrated in a supramolecular narrative through the analyses of the multi-constituent collaboration within the MOF and the interactions between MOFs and the intermediates during the reactions.

Three-Dimensional Neodymium Metal-Organic Framework for Catalyzing the Cyanosilylation of Aldehyde and the Synthesis of 2,3-Dihydroquinazolin-4(1H)-one Derivatives.

In this work, a novel 3D lanthanide metal-organic framework (Ln-MOF) Nd-cdip (H4cdip = 5,5'-carbonyldiisophthalic acid) was successfully synthesized, which could be used as an efficient heterogeneous catalyst for cyanosilylation and the synthesis of 2,3-dihydroquinazolin-4(1H)-one derivatives at room temperature based on the Lewis acid sites in the channels of the MOF. Moreover, Nd-cdip had an excellent turnover number (500) for catalyzing cyanosilylation in no solvent condition. Nd-cdip could be reused in both of the above-mentioned reactions at least five times without a significant decrease in yield. The possible mechanism of cyanosilylation catalyzed by Nd-cdip was studied by using the luminescence properties of Tb-cdip, which has the same structure and functions as Nd-cdip. Furthermore, both reactions catalyzed by Nd-cdip were fitted to zero-order dynamics.

Surface Engineering of TiO2 Nanosheets to Boost Photocatalytic Methanol Dehydrogenation for Hydrogen Evolution.

Low-cost high-efficiency H2 evolution is indispensable for its large-scale applications in the future. In the research, we expect to build high active photocatalysts for sunlight-driven H2 production by surface engineering to adjust the work function of photocatalyst surfaces, adsorption/desorption ability of substrates and products, and reaction activation energy barrier. Single-atom Pt-doped TiO2-x nanosheets (NSs), mainly including two facets of (001) and (101), with loading of Pt nanoparticles (NPs) at their edges (Pt/TiO2-x-SAP) are successfully prepared by an oxygen vacancy-engaged synthetic strategy. According to the theoretical simulation, the implanted single-atom Pt can change the surface work function of TiO2, which benefits electron transfer, and electrons tend to gather at Pt NPs adsorbed at (101) facet-related edges of TiO2 NSs for H2 evolution. Pt/TiO2-x-SAP exhibits ultrahigh photocatalytic performance of hydrogen evolution from dry methanol with a quantum yield of 90.8% that is ∼1385 times higher than pure TiO2-x NSs upon 365 nm light irradiation. The high H2 generation rate (607 mmol gcata-1 h-1) of Pt/TiO2-x-SAP is the basis for its potential applications in the transportation field with irradiation of UV-visible light (100 mW cm-2). Finally, lower adsorption energy for HCHO on Ti sites originated from TiO2 (001) doping single-atom Pt is responsible for high selective dehydrogenation of methanol to HCHO, and H tends to favorably gather at Pt NPs on the TiO2 (101) surface to produce H2.

Visible-light-mediated α-amino alkylation of ketimines and aldimines for the synthesis of 1,2-diamines.

A visible-light-mediated protocol to prepare 1,2-diamines has been successfully explored based on the photoredox/Brønsted acid co-catalyzed α-amino alkylations of imines with tertiary amines. Both ketimines and aldimines are applicable to this transformation. Various 1,2-diamines with different functional groups were produced in moderate to excellent yields. Moreover, this approach could be performed on a gram scale, showing its practicality.

Visible light-mediated three-component functionalization of olefins with sulfoxyimidoylsulfonium salt for the synthesis of ß-amino alcohols and amino ethers.

A new strategy involving three-component functionalization of olefins with sulfoxyimidoylsulfonium salt and a nucleophilic reagent for the synthesis of ß-amino alcohols and ß-amino ethers by photoredox catalysis was developed. The sulfoxyimidoylsulfonium salt is important and serves as the N-centred radical precursor. ß-Amino alcohols and ß-amino ethers bearing various functional groups are synthesized in good yields under mild conditions. Furthermore, the advantages of this strategy are greater safety, no additives, and easy to obtain raw materials.

A Diode-Like Dye-Cu Anisotropic Junction in a Coordination Polymer as a Logic State Ratchet for Intratumor Redox Photomodulation.

Redox logic materials offer new avenues to modulate intracellular pathologic redox environment area-specifically, but the unambiguity of redox logic states and their unidirectional and repetitive switchability are challenging to realize. By merging a bistable diisophthalic phenazine dye ligand with CuII salt, a multistable coordination polymer (CP) was constructed, of which the dye-Cu anisotropic junction achieved the diode-like unidirectional electron transfer and logic state ratchet for the first time. Radical cationic CP maintained OFF status with low toxicity in healthy tissues, but was reduced to the neutral SERVO state by the overexpressed glutathione (GSH) in hypoxic tumors. After photoirradiation, the stabilized charge-separated ON status promoted photo-Fenton reaction for reactive oxygen species (ROS) signal transduction, and simultaneously recovered the initial state for catalytic signal amplification of ROS, furnishing intratumor redox photomodulation for therapy.

A Platinum(II)-Based Molecular Cage with Aggregation-Induced Emission for Enzymatic Photocyclization of Alkynylaniline.

Enzymes facilitate chemical conversions through the collective activity of aggregated components, but the marriage of aggregation-induced emission (AIE) with molecular containers to emulate enzymatic conversion remains challenging. Herein, we report a new approach to construct a PtII -based octahedral cage with AIE characteristics for the photocyclization of alkynylaniline by restricting the rotation of the pendant phenyl rings peripheral to the PtII corner. With the presence of water, the C-H⋅⋅⋅π interactions involving the triphenylphosphine fragments resulted in aggregation of the molecular cages into spherical particles and significantly enhanced the PtII -based luminescence. The kinetically inert Pt-NP chelator, with highly differentiated redox potentials in the ground and excited states, and the efficient coordination activation of the platinum corner facilitated excellent catalysis of the photocyclization of alkynylaniline. The enzymatic kinetics and the advantages of binding and activating substrates in an aqueous medium provide a new avenue to develop mimics for efficient photosynthesis.

Urea-Functionalized Fe4 L6 Cages for Supramolecular Gold Catalyst Encapsulation to Control Substrate Activation Modes.

The excellent catalytic performances of enzymes in terms of activity and selectivity are an inspiration for synthetic chemists and this has resulted in the development of synthetic containers for supramolecular catalysis. In such containers the local environment and pre-organization of catalysts and substrates leads to control of the activity and selectivity of the catalyst. Herein we report a supramolecular strategy to encapsulate single catalysts in a urea-functionalized Fe4 L6 cage, which can co-encapsulate a functionalized urea substrate through hydrogen bonding. Distinguished selectivity is obtained, imposed by the cage as site isolation only allows catalysis through π activation of the substrate and as a result the selectivity is independent of catalyst concentration. The encapsulated catalyst is more active than the free analogue, an effect that can be ascribed to transitionstate stabilization rather than substrate pre-organization, as revealed by the MM kinetic data. The simple strategy reported here is expected to be of general use in many reactions, for which the catalyst can be functionalized with a sulfonate group required for encapsulation.

Synthesis of a Lanthanide Metal-Organic Framework and Its Fluorescent Detection for Phosphate Group-Based Molecules Such as Adenosine Triphosphate.

Adenosine triphosphate (ATP) is an important kind of metabolized biological molecule that is formed in organisms, especially in mitochondria, is used universally as energy, and is one of the most significant multifunctional biological molecules. Metal-organic frameworks (MOFs) have been widely used in many applications such as gas storage and separation, drug delivery, heterogeneous catalysis, chemical sensors, etc. Remarkably, lanthanide MOFs (Ln-MOFs), which display large pores, multiple dimensions, and unique lanthanide luminescence properties, are widely used as chemical sensors. A novel three-dimensional probe, Eu2(sbdc)3(H2O)3 (Eu-sbdc), was successfully self-assembled with Eu(NO3)3·6H2O and 5,5-dioxo-5H-dibenzo[b,d]thiophene-3,7-dicarboxylic acid (H2sbdc). The Ln-MOF Eu-sbdc can quickly and effectively optically detect ATP via a luminescent quenching mechanism. The Ksv value of Eu-sbdc is 1.02 × 104 M-1, and the lower detection limit of Eu-sbdc for ATP is 20 µM, which is more sensitive to ATP. Its mechanism of monitoring ATP might be a dynamic or static quenching process. Eu-sbdc could effectively and quickly recognize ATP with high sensitivity.