Journal of the American Chemical Society最新文献

Oxygen vacancies (V_O) in metal oxide electrocatalysts are widely recognized as key contributors to enhanced hydrogen evolution reaction (HER) activity, yet their precise function during catalysis remains elusive. Here, we investigate V_O-rich Co₃O₄ (a transition-metal oxide with moderate activity) and V_O-rich RuO₂ (a high-performance oxide catalyst) as model catalysts to elucidate the dynamic evolution of V_O during alkaline HER. Electrochemical analysis demonstrates that V_O-rich oxides exhibit significantly enhanced intrinsic HER activity compared to their V_O-poor counterparts. Comprehensive operando spectroscopies, ex situ characterizations, and ab initio molecular dynamics (AIMD) simulations reveal that V_O is not inert but is dynamically consumed during HER, facilitating extensive surface hydroxylation. Such surface hydroxylation and reconstruction optimize water molecule adsorption and dissociation, regulate interfacial water distribution, and enhance the connectivity of the hydrogen-bond network at the interface, collectively shifting the reaction pathway from Volmer-Heyrovsky to Volmer-Tafel. These synergistic effects lead to accelerated reaction kinetics and superior HER performance. This work supports the generality of the proposed mechanism across oxide electrocatalysts with vastly different intrinsic activities, provides new insights into the structural dynamics of V_O, and highlights the critical role of its induced surface hydroxylation in regulating the interfacial water and hydrogen-bond network, thereby boosting electrocatalytic hydrogen evolution.

Efforts to improve C₂₊ selectivity in CO₂ electroreduction have increasingly focused on strategies that deliberately induce catalyst surface reconstruction to create and maintain active sites. Among these, approaches using anodic pulses have gained particular attention for their ability to modulate the copper catalyst surface in situ. However, the underlying Cu surface reconstruction mechanisms triggered by anodic polarization still remain unclear. Here, we show that applying anodic potentials to copper can lead to two distinct surface reconstructions: surface oxide formation or metal dissolution, each defining a different reconstruction pathway with contrasting impacts on product selectivity. Oxide-derived reconstruction transiently enhances C₂ over C₁ selectivity but gradually loses effectiveness during operation, while dissolution-redeposition reconstruction continuously forms C₂-selective sites, resulting in a progressive increase in C₂ selectivity over time. Leveraging this mechanistic understanding, we implement electrolyte engineering by introducing trace Cu²⁺ ions under cathodic conditions to directly activate the dissolution-redeposition pathway without anodic bias. This strategy drives a dynamic electrochemical interface that sustains active-site regeneration and enables controllable selectivity, offering an energy-efficient alternative.

Indoleamine 2,3-dioxygenase (IDO) is a heme-dependent enzyme that catalyzes the first, rate-limiting step of the kynurenine pathway─the oxidation of l-tryptophan to N-formylkynurenine (NFK). IDO-catalyzed depletion of tryptophan levels and accumulation of kynurenine pathway metabolites is an important control mechanism of the immune responses in cells. IDO has been considered as a dioxygenase because two atoms of oxygen are inserted into the substrate. Here, we use LC-MS and NMR to examine the reactivity of human IDO (hIDO) with l-tryptophan (l-Trp) and several other tryptophan analogues. Alongside dioxygenase activity, we identify a concurrent pathway of heme-dependent monooxygenase activity in the reaction of hIDO with l-Trp, leading to the formation of a cyclic 3a-hydroxy-1,2,3,3a,8,8a-hexahydropyrrolo[2,3-b]indole-2-carboxylic acid (HPIC) species. Reaction profiles for the reaction of hIDO with other tryptophan analogues are likewise examined. Formation of HPIC from l-Trp is reproduced in HeLa cells induced to overexpress hIDO, indicating that this dual dioxygenase/monooxygenase reactivity also occurs biologically. Notably, the reaction of hIDO with β-[3-benzo(b)thienyl]-l-alanine (S-l-Trp)─a known inhibitor ─yielded only the cyclic HPIC analogue, suggesting that IDO activity can be selectively directed toward the monooxygenase pathway. Molecular dynamics simulations underscore the critical role of substrate plasticity within the active site of hIDO, while DFT calculations provide a mechanistic rationalization for the observed product distributions. Together, the data demonstrate dual dioxygenase/monooxygenase functionality for human IDO. As the overall gatekeeper for control of tryptophan levels in cells, the findings provide mechanistic information on relevance to therapeutic strategies focused on IDO inhibition.

Precise control of chemo- and regioselectivity in intermolecular difunctionalization of alkenes remains a long-standing challenge in organic synthesis. Here, we report a heterogeneous cobalt single-atom-site catalyst that enables selective 1,2-sulfonamidoazidation of styrenes. The system features good functional group tolerance and excellent recyclability. By leveraging the characteristics of single-atom-site catalysis, this work provides a valuable platform for achieving highly selective, efficient, and sustainable styrene functionalization.