Journal of the American Chemical Society最新文献

Lignin is the largest renewable resource for aromatics, and the quest to understand enzymatic lignin modification has never been more important. A recently recognized group of single-domain type-3 copper enzymes, named ortho-methoxyphenolases (o-MPs, EC 1.14.18.13) and previously referred to as short polyphenol oxidases (PPOs), found in filamentous fungi can sequentially o-hydroxylate and oxidize guaiacyl-type phenols into methoxy-o-quinones. A subset of these enzymes also targets syringyl-type phenols and, via an unprecedented oxidative o-demethoxylation mechanism, funnels these into the same methoxy-o-quinones generated from guaiacyl-type compounds. Here, we demonstrate that fungal o-methoxyphenolases also cleave bonds in lignin model dimers representing the abundant β-O-4'-linked substructures of lignin, having guaiacyl and, in some cases, syringyl terminal phenolic groups. Based on advanced liquid chromatography-mass spectrometry (LC-MS), nuclear magnetic resonance (NMR) analysis, and isotope labeling, we propose a mechanism in which the enzymatic formation of methoxy-o-quinone moieties in the model dimers triggers intramolecular rearrangements that lead to different types of bond cleavage, where C1-Cα cleavage predominates. Additionally, β-ether breakage and formation of Cα-ketone groups occur. We investigate the influence of pH and reductants on reaction pathways and identify strategies to steer the reaction toward either depolymerization or oxyfunctionalization of the dimers without interunit bond cleavage. The enzymes also target Cα-oxidized model dimers, albeit at lower rates. The findings of this study demonstrate the potential of using fungal o-methoxyphenolases for catalyzing selective ortho-hydroxylation and two-electron oxidation of lignin components and provide a new foundation for developing enzyme-based lignin valorization strategies.

Fundamental limitations in structural reversibility and electrochemical performance have rendered anode materials a critical bottleneck for proton batteries and capacitors. While the rational design of intrinsic properties for metal oxides offers a promising route for advanced proton storage, the simultaneous realization of high-power and low-temperature operability remains a grand challenge. We show that topochemical preintercalation of protons and confined lattice water in hydrated molybdenum bronze modifies host lattice rearrangement and enables ultrafast proton-coupled electron transfer. Ion-fluid cointercalation mediates electrochemical reaction pathways to an unconventional three-proton insertion mechanism, enabling a state-of-the-art specific capacity of 407 mAh g^-1, ultrahigh-rate capability exceeding 1000 C (500 A g^-1), and ultralow-temperature adaptability (194.2 mAh g^-1 at -80 °C). Comprehensive in situ crystal and interface evolution methods and theoretical calculations reveal a highly reversible and homogeneous protonation mechanism and enhanced interfacial transport, suppressing heterogeneous and unstable reaction kinetics of pristine MoO₃. The hybrid proton capacitor with such a molybdenum bronze anode shows an unprecedented ultrahigh-power and ultralow-temperature performance, with excellent stability for over 2000 cycles at -80 °C. This work highlights physicochemical insights on preintercalation topochemistry in modulating charge carrier-host interactions and provides electrode design principles for high-rate and low-temperature nonmetallic ion storage.

Dynamic covalent bonds (DCBs) enable reversible bond formation/cleavage, offering exciting possibilities for smart and adaptive materials, yet challenges such as slow kinetics and stringent conditions required for the reverse reaction currently hinder their broader use. We present a novel C-N σ-bond with exceptional reversibility and ultrafast kinetics (t_1/2 = 200 ms) across diverse primary aliphatic amine substrates, occurring spontaneously under ambient conditions without catalysts or external energy input, which is enabled by remarkably low activation barriers and near-equilibrium energetics. We showcase this transformative DCB's versatility in reversible gas-fixation, programmable transamination, and construct the first reversible chemical probes for real-time quantitative tracking of spatiotemporal histamine dynamics in live cells and in vivo within the brain under inflammatory pathology. This work redefines C-N σ-bonds as dynamic linkages, opening avenues for innovation in organic chemistry, adaptive materials, and dynamic biosystems.