JACS Au最新文献

Electrolyte cations are conventionally viewed as inert spectators in electrocatalysis. However, a wealth of observations show that catalytic rates are often highly sensitive to cation identity. Despite their prevalence, these cation effects have resisted a unified mechanistic explanation, with different physical phenomena implicated across reaction chemistries, catalyst compositions, and choice of solvent. In this perspective, we describe a general framework for understanding cation effects in electrocatalysis based on electrostatics. We argue that cations influence reaction rates by modifying the strength of the electric field present at the catalyst surface, which alters the energetics of adsorbed intermediates and transition states according to their dipole moments and polarizabilities. The magnitude of this field depends on how cations arrange at the electrode surface, controlled by their size, shape, solvation, and packing efficiency. Cations that can arrange more densely result in a steeper potential drop at the electrode surface and consequently a stronger electric field. Our model further identifies two criteria for observing cation effects: (1) the operating potential must be negative of the electrode's potential of zero total charge, ensuring that cations accumulate at the interface, and (2) the energetics of the kinetically relevant elementary step must be field sensitive. This framework reconciles previously inconsistent trends, including why cation effects appear only for some catalysts, why reaction selectivity is sensitive to cation identity, and why activity can increase with cation size on certain metals but decrease on others. Supported by kinetic measurements, spectroscopy, and atomistic simulations, the model provides both conceptual value for building intuition about catalysis at charged interfaces and predictive value for anticipating trends for new reactions, catalysts, and electrolytes. We conclude by highlighting the importance of electric fields across electrochemical, thermochemical, and biological catalysis and propose that considering the electrostatic environment around active sites offers new opportunities for improving activity and selectivity.

Chemoenzymatic dynamic kinetic resolution (DKR), which combines a metal racemization catalyst with an enzyme, has been demonstrated as an elegant solution to deliver centrally and axially chiral products from their racemates. Bis-(hetero)-arenols have found wide applications as chiral organocatalysts, phosphine-containing ligands, and photoelectric materials. However, the current chemoenzymatic DKR strategy has not yet been applied to bis-(hetero)-arenols due to their more stable axial chirality and higher redox potential under oxidative conditions. Herein, we developed an efficient DKR method to access chiral bis-(hetero)-arenols from racemic derivatives under cooperative copper and enzyme catalysis. The utilization of copper catalysis successfully realized the racemization of bis-(hetero)-arenols under aerobic conditions, which was also compatible with enzyme catalysis, endowing the chemoenzymatic DKR with high efficiency and selectivity. In this way, not only a benzofuran moiety but also a benzothiophene or carbazole unit could be tolerated in the axial scaffold to deliver optically active products with high enantioselectivity. The methylene-locked axially chiral skeletons display potentially superior circularly polarized luminescence (CPL) as small organic optoelectronic molecules. Mechanistic investigations suggest that chirality inversion in bis-(hetero)-arenols proceeds via reversible single-electron oxidation, with the intermediacy of O-radical species to significantly decrease the energy barrier for axial rotation.

Triazolo-[5,5]-fused ring systems have attracted growing interest due to their diverse applications in biomedicine, agrochemicals, and, particularly, in energetic materials, owing to their rigid, nitrogen-rich architectures. However, efficient construction of these [5,5]-fused frameworks remains synthetically challenging, largely due to steric congestion and limited functional group compatibility. Here, we report a modular and operationally simple strategy involving the in situ generation of heteroaryl diazonium salts, followed by tandem nucleophilic addition and intramolecular cyclization with diazo compounds, to access three distinct classes of triazolo-[5,5]-fused heterocycles: triazolotriazoles, imidazotriazoles, and pyrazolotriazoles. Subsequent derivatization of these scaffolds furnishes high-nitrogen energetic compounds with excellent detonation properties, surpassing RDX in some cases and demonstrating strong potential as advanced gas-generating materials. This work establishes a versatile platform for the streamlined synthesis of structurally complex triazolo-[5,5]-fused heterocycles with broad implications for molecular design in energetic and functional materials.

Understanding how carbene reactivity is modulated by both the heteroarene scaffold and activation mode is critical for advancing selective functionalization strategies. Herein, we report a comparative study revealing the divergent reactivity of benzothiazole and benzisothiazole under both photochemical and metal-catalyzed carbene transfer conditions. Under photochemical conditions, free carbenes induce a stepwise transformation of benzothiazole involving initial carbon-atom exchange followed by carbon atom insertion, affording benzothiazoline and benzothiazine derivatives. In contrast, benzisothiazole undergoes direct monocarbon atom insertion, selectively forming ring-expanded products. Notably, metal-catalyzed carbene transfer does not proceed with aromatic benzothiazole but can efficiently engage its dearomatized intermediate through carbon atom insertion, enabling access to the same ring-expanded benzothiazine scaffolds with an expanded substrate scope. Mechanistic studies, including control experiments, isotope labeling, and DFT calculations, support the proposed pathways and clarify how scaffolds govern the distinct reactivity patterns. These findings highlight the complementary reactivity profiles of free and metal-bound carbenes and establish a structure- and activation-mode-guided platform for the selective functionalization of heteroaromatic systems.

Sensitized triplet-triplet annihilation systems enable the efficient conversion of two low-energy photons from a low-intensity, noncoherent light source into one high-energy photon, opening avenues for diverse applications. The attachment of triisopropylsilylethynyl (TIPS-ethynyl) groups to aromatic compounds has led to the development of many annihilators with high upconversion quantum yields. Here, we synthesized a series of novel symmetrical biphenyls bearing silylethynyl substituents of varying sizes and evaluated them as annihilators in visible-to-UV upconversion systems. While all of these systems do not suffer from excimer formation issues, their upconversion performances differ significantly. Small substituents like trimethylsilylethynyl give similar upconversion quantum yields (up to ∼12%) as the TIPS-ethynyl groups, but the larger triphenylsilylethynyl substituents reduce the achievable quantum yields by half, which is likely due to additional nonradiative loss channels arising from altered energies of higher excited triplet states. The UV emission of the novel annihilators is hypsochromically shifted by about 20 nm relative to that of the TIPS-naphthalene benchmark UV annihilator, thereby reaching a highly attractive spectral region for bond activation photochemistry. Using the most efficient annihilator, bTIPS-BP, we achieved blue-to-UV upconversion-driven release of fluorescein from a photocage. In the greater context of photon upconversion and in view of other recent reports on substituent effects, our results indicate that several chromophore-specific effects must be understood for obtaining optimized systems.

A survey of the Protein Data Bank reveals that the arabinofuranosidase class of enzymes broadly restrict their substrate side chains to the gauche,gauche (gg) conformation that provides maximum electrostatic stabilization to oxocarbenium ion-like transition states and so employ the strategy reported previously for the majority of glycoside hydrolases, transglycosidases, and glycosyltransferases acting on pyranosyl substrates. The fructofuranosidases, ribonucleosidases, ribonucleoside phosphorylases, and nucleoside 2'-deoxyribosyltransferases, whose gg conformation is sterically hindered, restrict their substrate side chains to the next most positive charge-stabilizing gauche,trans (gt) conformation. These conclusions are supported by extensive literature studies on the mechanisms of C-N bond cleavage by members of the nucleosidase and nucleoside phosphorylase families and are discussed in terms of Warshel's concept of the electrostatic origin of the catalytic power of enzymes and the role of preorganized active sites.

Here, we report the NMR solution structure of the G-quadruplex (G4) folded by the 24-nt guanine-rich DNA sequence d-[AG₃AG₄A₂G₄TGA₂G₄A]. The sequence is originated from the first intron of the MAX gene, which encodes the transcription factor MAX, an obligate partner of the notorious oncoprotein MYC. The unimolecular G4 adopts a [3 + 1] hybrid topology containing all the three main loop types (propeller, diagonal, and lateral). Also, the three G-tetrads are stacked with the same polarity of the Hoogsteen hydrogen bond and anti-anti-anti-syn glycosidic configuration pattern. Both 5' and 3'-flanking regions contain one adenine residue. As far as we know, it is the first example of such a unique topology wherein all the nucleotides are not modified in either sugars or bases. In addition to the well-defined G-tetrad core, the diagonal loop contains a G·(A-G) triad, and a T·G base pair is formed within the lateral loop. Furthermore, the formation of the G4 is found to be stable under physiological conditions even without annealing and acts as a barrier to DNA polymerase. These findings provided deep insights into the G4 folding topology and a potential for targeting MAX G4.

The chemical industry is electrifying toward a net-zero emission future. Unfortunately, the catalyst manufacturing process remains almost untouched in the transition to electrification due to challenges in size controllability and powder handling. Herein, we reported a slurry electrolysis strategy for scale-up production of Cu nanocatalysts at the productivity of 15 g per hour with a Cu loading of 2.5 wt % in laboratory flow electrolyzers, while maintaining excellent controllability of particle size down to single atoms by regulating the nucleation and particle growth process via pulsed electrochemistry. Our strategy can be further extended to the synthesis of Ag and CuAg catalysts for diverse electrochemical applications. Further techno-economic analysis shows an extremely low greenhouse gas emission and production cost (0.03 kg_GHG and 16.4 USD per kg catalyst) compared to traditional approaches. This effectively addresses the productivity bottleneck in the electrosynthesis of nanocatalysts and paves the way for practical applications.

Iodonium salts have shown great potential as metal-free reagents in various transformations, offering a promising alternative to transition-metal-catalyzed arene amination. Herein, we report the design and synthesis of chromone-based iodonium salts (CMISs) and demonstrate their efficiency in selective chromone amination. Unlike the conventional ligand exchange/coupling pathway, mechanistic studies reveal a unique amination pathway specific to the chromone scaffold, in which the aryliodonium unit simultaneously facilitates N-Michael addition and the formation of a newfound chromone-derived strained alkyne intermediate, leading to mechanistic competition while directing product configuration. By further modulating the basicity and steric hindrance of amines, three distinct classes of aminated products ((Z)-2-(aminomethylene)-benzofuranones, β-aminochromones and α-aminochromones) were accessed.