Natural enzyme cascades utilize electrostatic guidance as an effective technique to control the diffusion of charged reaction intermediates between catalytic active sites in a process known as substrate channeling. However, the limited understanding of channeling mechanisms has abated the application of this technique in artificial catalytic cascades. In this work, we utilize molecular dynamics simulations to describe the transport of anionic intermediates (e.g., oxalate and glucose-6-phosphate) on a theoretical cationic α-helix peptide bridge and identify rules for molecular-level design of electrostatic channeling. These simulations allowed us to elucidate a surface diffusion mechanism whereby the anionic intermediate undergoes discrete hydrogen-bonding interactions along adjacent cationic residues on the peptide bridge. Using MD simulations as a foundational blueprint, we synthesized an enzyme complex using a poly­(lysine) peptide chain as a cationic bridge between glucose-6-phosphate dehydrogenase and hexokinase. Stopped-flow lag time experiments demonstrate the ability of the artificially linked enzyme complex to facilitate electrostatic substrate channeling, while an analogous neutral poly­(glycine)-bridged complex was used as a control to isolate proximity effects from artificial substrate channeling.

Atomically dispersed (or single atom) iron-nitrogen-carbon (Fe-N-C) catalysts are promising alternatives to platinum group metals (PGM) nanoparticles supported on dispersed carbon as a cathode material in proton exchange membrane fuel cells. Here, the degradation mechanism of Fe-N-C catalysts, synthesized by the sacrificial support method (SSM), was investigated by conducting accelerated stress tests under "load cycling" protocol (i.e. from 0.6 to 1.0 V vs. the reversible hydrogen electrode, RHE).Electrocatalyst activity towards the oxygen reduction reaction (ORR) was studied for a SSM-derived material, obtained by a single pyrolysis under 7% H 2 atmosphere (Fe-HT 1 ) and juxtaposed to that of a catalyst derived from the same sample, but subjugated to a second pyrolysis under 10% NH 3 (noted as Fe-HT 2 ). Several findings can be highlighted:(i) the second pyrolysis results in a skewing of the mesopores size toward higher diameter, along with an increase in iron content and N-pyridinic moieties, leading to a combined benefit in terms of ORR activity and selectivity; (ii) the morphological changes of these catalysts during ageing are drastically different depending on whether they were exposed

Aimed toward the pursuit of manufacturing ammonia in a carbon-neutral and decentralized manner, the electrocatalytic nitrate reduction reaction (NO 3 RR) not only promises an effective route for carbon-neutral ammonia synthesis but also offers potential advantages to wastewater remediation. Here, we describe the efficacy of bioinspired, atomically dispersed catalysts for the NO 3 RR in aqueous media via a catalytic cascade. Compared to nanoparticles with extended catalytic surfaces, atomically dispersed catalysts are largely underexplored in this field, despite their intrinsic selectivity toward mono-nitrogen species over their dinitrogen counterparts. Herein, we specifically report on a series of nitrogen-coordinated mono-and bimetallic, atomically dispersed, iron-and molybdenum-based electrocatalysts for ammonia synthesis via the NO 3 RR. The key role of the *NO 2 /NO 2 − intermediates was identified both computationally and experimentally, wherein the Fe−N 4 sites and Mo−N 4 /*O− Mo−N 4 sites carried distinct associative and dissociative adsorption of NO 3 − molecules, respectively. By integrating individual Fe and Mo sites on a single bimetallic catalyst, the unique reaction pathways were synergized, achieving a Faradaic efficiency of 94% toward ammonia. Furthermore, the robustness of the bimetallic FeMo−N−C catalyst was highlighted by five consecutive 12 h electrolysis cycles with the Faradaic efficiency being maintained above 90% over the entire 60 h. The utilization of catalytic cascades, synergizing distinct reaction pathways on heterogeneous single-atom sites, is largely unconstrained by linear scaling relations of reaction intermediates and sheds light on designing electrocatalysts for highly selective, efficient, and durable ammonia synthesis.

Natural enzyme cascades are able to employ electrostatic channeling as an efficient mechanism for shuttling charged intermediates between sequential active sites. Application of channeling mechanisms to artificial cascades has drawn increasing attention for its potential to improve cascade design. We report a quantitative model of a two-step artificial metabolon that accounts for molecular-level complexity. Conversion of glucose to phospho-6-gluconolactone by hexokinase and glucose-6-phosphate dehydrogenase, covalently conjugated by a cationic oligopeptide bridge, is simulated and validated by comparison to stopped-flow lag time analysis. Specifically, molecular dynamics (MD) simulations enable the calculation of energy-determined surface equilibrium constants and surface diffusivity, and a kinetic Monte Carlo (KMC) model integrated all rate constants from MD (e.g., surface diffusion and desorption rate) and experiments (e.g., turnover frequency), to estimate the product evolution on an experimental time scale, starting from presteady state. Simulations, conducted as a function of ionic strength, compare well to experiment and indicate that bridge-enzyme leakage is a major limitation accounting for significant lag time increase. Reducing the energy barrier between the channeling pathway and binding pocket could further improve channeling efficiency. Bridge length is also found to have a significant effect on overall kinetics.

Group VI transition metal chalcogenides are the subject of increasing research interest for various electrochemical applications such as low-temperature water electrolysis, batteries, and supercapacitors due to their high activity, chemical stability, and the strong correlation between structure and electrochemical properties. Particularly appealing is their utilization as electrocatalysts for the synthesis of energy vectors and value-added chemicals such as C-based chemicals from the CO2 reduction reaction (CO2R) or ammonia from the nitrogen fixation reaction (NRR). This review discusses the role of structural and electronic properties of transition metal chalcogenides in enhancing selectivity and activity toward these two key reduction reactions. First, we discuss the morphological and electronic structure of these compounds, outlining design strategies to control and fine-tune them. Then, we discuss the role of the active sites and the strategies developed to enhance the activity of transition metal chalcogenide-based catalysts in the framework of CO2R and NRR against the parasitic hydrogen evolution reaction (HER); leveraging on the design rules applied for HER applications, we discuss their future perspective for the applications in CO2R and NRR. For these two reactions, we comprehensively review recent progress in unveiling reaction mechanisms at different sites and the most effective strategies for fabricating catalysts that, by exploiting the structural and electronic peculiarities of transition metal chalcogenides, can outperform many metallic compounds. Transition metal chalcogenides outperform state-of-the-art catalysts for CO2 to CO reduction in ionic liquids due to the favorable CO2 adsorption on the metal edge sites, whereas the basal sites, due to their conformation, represent an appealing design space for reduction of CO2 to complex carbon products. For the NRR instead, the resemblance of transition metal chalcogenides to the active centers of nitrogenase enzymes represents a powerful nature-mimicking approach for the design of catalysts with enhanced performance, although strategies to hinder the HER must be integrated in the catalytic architecture.