JACS Au最新文献

An electrochemically mediated enzyme process for nicotinamide adenine dinucleotide (NADH) oxidation and biosensing has been developed in which the oxygen-dependent activities of wild-type NADH oxidase are replaced by electrochemical regeneration of the flavin adenine dinucleotide (FAD) cofactor in the active site. Consequently, the present bioelectrocatalysis does not rely on a continuous oxygen supply through bubbling air or pure oxygen in biosynthetic applications, which reduces enzyme stability. The coupled electrochemical and enzymatic catalysis is achieved through a combination of enzyme immobilization on the electrode and electrochemical oxidation of FADH₂ in the active site mediated by the electron transfer mediator ferrocene carboxylic acid (FcCA). Furthermore, to minimize the effect of dissolved oxygen when the electrocatalytic process is exposed to air, we successfully designed mutations at the Leu40 and Cys42 sites of Leuconostoc mesenteroides (LmNOx) to block the oxygen passage into the active site and to eliminate the native FAD cofactor regeneration half-reaction. The engineered enzymes, whose activities are significantly reduced or inactive in solution, are electrocatalytically active toward conversion of NADH to NAD⁺, demonstrating successful FAD cofactor regeneration in the active site via electrochemistry. Finally, we developed two highly responsive electrochemical biosensors for NADH detection which has a superior substrate specific to standard detectors using metal electrodes, and comparable detection range and detection limit (1–3 μM).

Hydride shuttle catalysis has emerged as a powerful synthetic platform, enabling the selective formation of C–C bonds to yield sp³-rich structures. By virtue of the compelling reactivity of sterically encumbered Lewis acids from the frustrated Lewis pair regime, hydride shuttle catalysis enables the regioselective functionalization of alkyl amines at either the α- or β-position. In contrast to classical Lewis acid reactivity, the increased steric hindrance prevents interaction with the Lewis basic amine itself, instead leading to reversible abstraction of a hydride from the amine α-carbon. The created positive charge facilitates the occurrence of transformations before hydride rebound or a similar capture event happen. In this Perspective, we outline a broad selection of transformations featuring hydride shuttle catalysis, as well as the recently developed approach of inverse hydride shuttle catalysis. Both strategies give rise to a wide array of functionalized amines and offer elegant approaches to otherwise elusive bond formations.

Conjugated microporous polymers (CMPs) feature extended excellent porosity properties and fully conjugated electronic systems, making them highly effective for several uses, including photocatalysis, dye adsorption, CO₂ capture, supercapacitors, and so on. These polymers are known for their high specific surface area and adjustable porosity. To synthesize DHTP-CMPs (specifically TPE-DHTP CMP and Anthra-DHTP CMP) with abundant nitrogen (N) and oxygen (O) adsorption sites and spherical structures, we employed a straightforward Schiff-base [4 + 2] condensation reaction. This involved using 2,5-dihydroxyterephthalaldehyde (DHTP-2CHO) as the primary building block and phenolic OH group source, along with two distinct structures: 4,4′,4″,4”’-(ethene-1,1,2,2-tetrayl)tetraaniline (TPE-4NH₂) and 4,4′,4″,4”’-(anthracene-9,10-diylidenebis(methanediylylidene))tetraaniline (Anthra-4Ph-4NH₂). The synthesized Anthra-DHTP CMP had a remarkable BET surface area (BET_SA) of 431 m² g^–1. Additionally, it exhibited outstanding thermal stability, as shown by a T_d10 of 505 °C. Furthermore, for practical implementation, the Anthra-DHTP CMP demonstrates a significant capacity for capturing CO₂, measuring 1.85 mmol g^–1 at a temperature of 273 K and 1 bar. In a three-electrode test, the Anthra-DHTP CMP has a remarkable specific capacitance of 121 F g^–1 at 0.5 A g^–1. Furthermore, even after undergoing 5000 cycles, it maintains a capacitance retention rate of 79%. Due to their outstanding pore characteristics, abundant N and O, and conjugation properties, this Anthtra-DHTP CMP holds significant potential for CO₂ capture and supercapacitor applications. This work will pave the way for the development of materials based on DHTP-CMPs and their postmodification with additional groups, facilitating their use in photocatalysis, photodegradation, lithium battery applications, and so on.

Environmental catalysis has attracted great interest in air and water purification. Selective catalytic reduction with ammonia (NH₃-SCR) as a representative technology of environmental catalysis is of significance to the elimination of nitrogen oxides (NO _x ) emitting from stationary and mobile sources. However, the evolving energy landscape in the nonelectric sector and the changing nature of fuel in motor vehicles present new challenges for NO _x catalytic purification over the traditional NH₃-SCR catalysts. These challenges primarily revolve around the application limitations of conventional industrial NH₃-SCR catalysts, such as V₂O₅-WO₃(MoO₃)/TiO₂ and chabazite (CHA) structured zeolites, in meeting both the severe requirements of high activity at ultralow temperatures and robust resistance to the wide array of poisons (SO₂, HCl, phosphorus, alkali metals, and heavy metals, etc.) existing in more complex operating conditions of new application scenarios. Additionally, volatile organic compounds (VOCs) coexisting with NO _x in exhaust gas has emerged as a critical factor further impeding the highly efficient reduction of NO _x . Therefore, confronting the challenges inherent in current NH₃-SCR technology and drawing from the established NH₃-SCR reaction mechanisms, we discern that the strategic manipulation of the properties of surface acidity and redox over NH₃-SCR catalysts constitutes an important pathway for increasing the catalytic efficiency at low temperatures. Concurrently, the establishment of protective sites and confined structures combined with the strategies for triggering antagonistic effects emerge as imperative items for strengthening the antipoisoning potentials of NH₃-SCR catalysts. Finally, we contemplate the essential status of selective synergistic catalytic elimination technology for abating NO _x and VOCs. By virtue of these discussions, we aim to offer a series of innovative guiding perspectives for the further advancement of environmental catalysis technology for the highly efficient NO _x catalytic purification from nonelectric industries and motor vehicles.

Metal nitrides (MNs) are attracting enormous attention in the electrocatalytic nitrogen reduction reaction (NRR) because of their rich lattice nitrogen (N_lat) and the unique ability of N_lat vacancies to activate N₂. However, continuing controversy exists on whether MNs are catalytically active for NRR or produce NH₃ via the reductive decomposition of N_lat without N₂ activation in the in situ electrochemical conditions, let alone the rational design of high-performance MN catalysts. Herein, we focus on the common rocksalt-type MN(100) catalysts and establish a quantitative theoretical framework based on the first-principles microkinetic simulations to resolve these puzzles. The results show that the Mars-van Krevelen mechanism is kinetically more favorable to drive the NRR on a majority of MNs, in which N_lat plays a pivotal role in achieving the Volmer process and N₂ activation. In terms of stability, activity, and selectivity, we find that MN(100) with moderate formation energy of N_lat vacancy (E _vac) can achieve maximum activity and maintain electrochemical stability, while low- or high-E _vac ones are either unstable or catalytically less active. Unfortunately, owing to the five-coordinate structural feature of N_lat on rocksalt-type MN(100), this maximum activity is limited to a yield of NH₃ of only ∼10^-15 mol s^-1 cm^-2. Intriguingly, we identify a volcano-type activity-regulating role of the local structural features of N_lat and show that the four-coordinate N_lat can exhibit optimal activity and overcome the performance limitation, while less coordinated N_lat fails. This work provides, arguably for the first time, an in-depth theoretical insight into the activity and stability paradox of MNs for NRR and underlines the importance of reaction kinetic assessment in comparison with the prevailing simple thermodynamic analysis.

The overall significance of loop motions for enzymatic activity is generally accepted. However, it has largely remained unclear whether and how such motions can control different steps of catalysis. We have studied this problem on the example of the mobile active site β₁α₁-loop (loop1) of the (βα)₈-barrel enzyme HisF, which is the cyclase subunit of imidazole glycerol phosphate synthase. Loop1 variants containing single mutations of conserved amino acids showed drastically reduced rates for the turnover of the substrates N′-[(5′-phosphoribulosyl) formimino]-5-aminoimidazole-4-carboxamide ribonucleotide (PrFAR) and ammonia to the products imidazole glycerol phosphate (ImGP) and 5-aminoimidazole-4-carboxamide-ribotide (AICAR). A comprehensive mechanistic analysis including stopped-flow kinetics, X-ray crystallography, NMR spectroscopy, and molecular dynamics simulations detected three conformations of loop1 (open, detached, closed) whose populations differed between wild-type HisF and functionally affected loop1 variants. Transient stopped-flow kinetic experiments demonstrated that wt-HisF binds PrFAR by an induced-fit mechanism whereas catalytically impaired loop1 variants bind PrFAR by a simple two-state mechanism. Our findings suggest that PrFAR-induced formation of the closed conformation of loop1 brings active site residues in a productive orientation for chemical turnover, which we show to be the rate-limiting step of HisF catalysis. After the cyclase reaction, the closed loop conformation is destabilized, which favors the formation of detached and open conformations and hence facilitates the release of the products ImGP and AICAR. Our data demonstrate how different conformations of active site loops contribute to different catalytic steps, a finding that is presumably of broad relevance for the reaction mechanisms of (βα)₈-barrel enzymes and beyond.

Metal nitrides (MNs) are attracting enormous attention in the electrocatalytic nitrogen reduction reaction (NRR) because of their rich lattice nitrogen (N_lat) and the unique ability of N_lat vacancies to activate N₂. However, continuing controversy exists on whether MNs are catalytically active for NRR or produce NH₃ via the reductive decomposition of N_lat without N₂ activation in the in situ electrochemical conditions, let alone the rational design of high-performance MN catalysts. Herein, we focus on the common rocksalt-type MN(100) catalysts and establish a quantitative theoretical framework based on the first-principles microkinetic simulations to resolve these puzzles. The results show that the Mars-van Krevelen mechanism is kinetically more favorable to drive the NRR on a majority of MNs, in which N_lat plays a pivotal role in achieving the Volmer process and N₂ activation. In terms of stability, activity, and selectivity, we find that MN(100) with moderate formation energy of N_lat vacancy (E_vac) can achieve maximum activity and maintain electrochemical stability, while low- or high-E_vac ones are either unstable or catalytically less active. Unfortunately, owing to the five-coordinate structural feature of N_lat on rocksalt-type MN(100), this maximum activity is limited to a yield of NH₃ of only ∼10^–15 mol s^–1 cm^–2. Intriguingly, we identify a volcano-type activity-regulating role of the local structural features of N_lat and show that the four-coordinate N_lat can exhibit optimal activity and overcome the performance limitation, while less coordinated N_lat fails. This work provides, arguably for the first time, an in-depth theoretical insight into the activity and stability paradox of MNs for NRR and underlines the importance of reaction kinetic assessment in comparison with the prevailing simple thermodynamic analysis.

The overall significance of loop motions for enzymatic activity is generally accepted. However, it has largely remained unclear whether and how such motions can control different steps of catalysis. We have studied this problem on the example of the mobile active site β₁α₁-loop (loop1) of the (βα)₈-barrel enzyme HisF, which is the cyclase subunit of imidazole glycerol phosphate synthase. Loop1 variants containing single mutations of conserved amino acids showed drastically reduced rates for the turnover of the substrates N'-[(5'-phosphoribulosyl) formimino]-5-aminoimidazole-4-carboxamide ribonucleotide (PrFAR) and ammonia to the products imidazole glycerol phosphate (ImGP) and 5-aminoimidazole-4-carboxamide-ribotide (AICAR). A comprehensive mechanistic analysis including stopped-flow kinetics, X-ray crystallography, NMR spectroscopy, and molecular dynamics simulations detected three conformations of loop1 (open, detached, closed) whose populations differed between wild-type HisF and functionally affected loop1 variants. Transient stopped-flow kinetic experiments demonstrated that wt-HisF binds PrFAR by an induced-fit mechanism whereas catalytically impaired loop1 variants bind PrFAR by a simple two-state mechanism. Our findings suggest that PrFAR-induced formation of the closed conformation of loop1 brings active site residues in a productive orientation for chemical turnover, which we show to be the rate-limiting step of HisF catalysis. After the cyclase reaction, the closed loop conformation is destabilized, which favors the formation of detached and open conformations and hence facilitates the release of the products ImGP and AICAR. Our data demonstrate how different conformations of active site loops contribute to different catalytic steps, a finding that is presumably of broad relevance for the reaction mechanisms of (βα)₈-barrel enzymes and beyond.

Molecular hosts with functional cavities can emulate enzymatic behavior through selective encapsulation of substrates, resulting in high chemo-, regio-, and stereoselective product formation. It is still challenging to synthesize enzyme-mimicking hosts that exhibit a narrow substrate scope that relies upon the recognition of substrates based on the molecular size. Herein, we introduce a Pd₄ self-assembled water-soluble molecular capsule [M ₄ L ₂] (MC) that was formed through the self-assembly of a ligand L (4',4‴'-(1,4-phenylene)bis(1',4'-dihydro-[4,2':6',4″-terpyridine]-3',5'-dicarbonitrile)) with the acceptor cis-[(en)Pd(NO₃)₂] [en = ethane-1,2-diamine] (M). The molecular capsule MC showed size-selective recognition towards xylene isomers. The redox property of MC was explored for efficient and selective oxidation of one of the alkyl groups of m-xylene and p-xylene to their corresponding toluic acids using molecular O₂ as an oxidant upon photoirradiation. Employing host-guest chemistry, we demonstrate the homogeneous catalysis of alkyl aromatics to the corresponding monocarboxylic acids in water under mild conditions. Despite homogeneous catalysis, the products were separated from the reaction mixtures by simple filtration/extraction, and the catalyst was reused. The larger analogues of the alkyl aromatics failed to bind within the MC's hydrophobic cavity, resulting in a lower/negligible reaction outcome. The present study represents a facile approach for selective photo-oxidation of xylene isomers to their corresponding toluic acids in an aqueous medium under mild conditions.