JACS Au最新文献

The regiospecific ring expansion of 2H-azetines into halogenated pyrroles is disclosed. Simple reaction sequences have been developed to conceptualize this 4 → 5 skeletal editing strategy, taking advantage of the inherent reactivity of double bonds present in the initial four-membered ring systems. Detailed density functional theory (DFT) calculations are presented to explain this unusual rearrangement. Such a reaction design allows for the preparation of highly substituted halogenated pyrrole derivatives.

Protein tyrosine phosphatases (PTPs) are a family of enzymes that play important roles in regulating cellular signaling pathways. The activity of these enzymes is regulated by the motion of a catalytic loop that places a critical conserved aspartic acid side chain into the active site for acid-base catalysis upon loop closure. These enzymes also have a conserved phosphate-binding loop that is typically highly rigid and forms a well-defined anion-binding nest. The intimate links between loop dynamics and chemistry in these enzymes make PTPs an excellent model system for understanding the role of loop dynamics in protein function and evolution. In this context, archaeal PTPs, which have often evolved in extremophilic organisms, are highly understudied, despite their unusual biophysical properties. We present here an engineered chimeric PTP (ShufPTP) generated by shuffling the amino acid sequence of five extant hyperthermophilic archaeal PTPs. Despite ShufPTP's high sequence similarity to its natural counterparts, it presents a suite of unique properties, including high flexibility of the phosphate binding P-loop, facile oxidation of the active-site cysteine, mechanistic promiscuity, and, most notably, hyperthermostability, with a denaturation temperature likely >130 °C (>8 °C higher than the highest recorded growth temperature of any archaeal strain). Our combined structural, biochemical, biophysical, and computational analysis provides insight both into how small steps in evolutionary space can radically modulate the biophysical properties of an enzyme and showcases the tremendous potential of archaeal enzymes for biotechnology, to generate novel enzymes capable of operating under extreme conditions.

The supramolecular self-assembly of uric acid (UA), the end product of purine metabolism, underlies crystal deposition in gout and kidney diseases. However, the intermediate states linking soluble UA to crystalline phases remain poorly defined. Here, we report that UA self-assembles into amyloid-like fibrils that coexist with crystalline forms and exhibit cytotoxicity. Native ion mobility spectrometry-mass spectrometry (IMS-MS) reveals discrete UA oligomers up to 60-mers, suggesting a stepwise assembly process. Optical and electron microscopy distinguish between fibrous and crystalline morphologies, with the fibrillar network acting as a potential scaffold for nucleation. We demonstrate that allopurinol, beyond its known function as a xanthine oxidase inhibitor, directly perturbs UA aggregation. Allopurinol alters the thermodynamics of self-assembly, suppressing fibril formation and promoting crystallization into a more stable anhydrous polymorph. In contrast, epigallocatechin gallate (EGCG) suppresses both fibrillation and crystallization. X-ray diffraction confirms the formation of a distinct anhydrous crystal phase in the presence of allopurinol, analogous to that found in patient-derived deposits. These findings expand the chemical understanding of UA phase behavior and polymorphism and establish cytotoxic UA fibrils as drug-modifiable intermediates. Modulating small-molecule-driven metabolite self-assembly provides a mechanistic basis for rational intervention in gout and other disorders characterized by metabolite aggregation.

(Pybox)Os is found to catalyze alkene hydrovinylation, effecting the dimerization of ethylene, tail-to-tail coupling of propene and 1-butene, and cross-coupling of ethylene with higher α-olefins. This reactivity contrasts with the previously reported dehydrogenative coupling of ethylene to give butadiene catalyzed by the isoelectronic fragment (Phebox)-Ir. The reaction mechanism was investigated through computational and experimental means. Both the Os- and Ir-catalyzed reactions proceed through a [2 + 2 + 1] cyclization of the corresponding bis-olefin complex to yield an experimentally observed metallacyclopentane intermediate. In both cases, the metallacyclopentane undergoes β-H elimination, via a dechelated κ²-pincer-ligated intermediate, to yield a σ-π-but-3-enyl hydride complex or derivative. Both the greater reactivity and the distinct chemoselectivity of the Os system relative to the Ir system are attributable to C-H reductive elimination by the σ-π-but-3-enyl hydride having a barrier for Os much lower than that for Ir. This lower barrier to C-H elimination for Os is unexpected given that the thermodynamic driving force for elimination is much less for Os than for Ir. Computational studies of model complexes were conducted, comparing (Pybox)-Os-(L)-(CH₃)-(H) with the isoelectronic (Phebox)-Ir-(L)-(CH₃)-(H). The results indicate that the more facile kinetics with Os relative to Ir may be general for C-H elimination from six-coordinate d⁶ complexes of the two metals, as well as for the microscopic reverse, i.e., C-H addition to the corresponding four-coordinate d⁸ species.

Heme enzymes catalyze several key reactions in nature. O₂ reduction and peroxidation are two such reactions crucial for respiration and oxidation of organic and inorganic substrates in nature, respectively. Over the last several decades, there has been a focused effort to generate small-molecule analogues which mimic these reactions. Small-molecule mimics of these metallo-enzymes may find potential use as an oxygen reduction reaction (ORR) catalyst in a fuel cell and as a catalyst for decontamination of wastewater in addition to providing deeper insights into the reactivity of the enzyme they mimic. An iron porphyrin with a pendant imidazole group appears to catalyze both these reactions quite efficiently. On the one hand, the pendant imidazole group provides a binding site for both H₂O₂ and the substrate, which results in efficient peroxidase catalysis that shows an enzyme-like "ping-pong" mechanism which is extremely rare in a small molecule. On the other hand, the pendant imidazole aids stabilization of intermediates during the ORR and facilitates O-O bond cleavage, resulting in fast catalysis with a high selectivity for 4e^-/4H⁺ ORR under homogeneous as well as heterogeneous conditions. The reactive species produced during the ORR can oxidize organic substrates, acting like an oxygenase.

Alkaline earth metal oxides are economically attractive, earth-abundant sorbents for CO₂ capture. In particular, MgO is a promising CO₂ sorbent for applications in the intermediate temperature range (200-400 °C). However, MgO requires the addition of promoters such as alkali metal nitrates or carbonates to overcome the slow kinetics of CO₂ sorption. It has been observed experimentally that the addition of K₂CO₃ increases the CO₂ uptake of MgO, yet its role remains poorly understood; this is a critical knowledge gap for the design of more efficient sorbents. In this work, using a combination of in situ XRD and Raman spectroscopy, we gain insight into the CO₂ uptake mechanism of K₂CO₃-promoted MgO, which proceeds in two steps. An initial rapid CO₂ uptake (within 1 min) occurs via the formation of a potassium-rich amorphous carbonate phase (K₂CO₃·xMgCO₃·yH₂O). This is followed by a slower CO₂ capture step, in which the intermediate K-rich phase transforms into a magnesium-rich amorphous carbonate, along with the formation of small amounts of crystalline (hydrated and anhydrous) carbonates such as K₂CO₃, baylissite (K₂Mg-(CO₃)₂·4H₂O), and nesquehonite (MgCO₃·3H₂O). In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis reveals that surface hydroxides, which remain on the MgO surface even after a thermal treatment at 720 °C in N₂, facilitate the formation of hydrated carbonates at 315 °C in dry CO₂. However, the presence of steam during carbonation lowers the CO₂ uptake and inhibits the second CO₂ uptake step, most likely by stabilizing the K-rich amorphous intermediate. Cyclic CO₂ uptake and regeneration experiments reveal the crucial role of a high K₂CO₃ dispersion within the sorbent for maintaining good cyclic stability.

Water splitting in quasi-neutral electrolytes (5 ≤ pH ≤ 10) offers advantages over highly alkaline or acidic electrolytes by improving operational safety, simplifying maintenance, and enabling the use of diverse natural water sources. Such electrolytes suggest promise for large-scale applications, especially considering their widened catalyst scope. However, kinetically restrained oxygen evolution reaction (OER) catalysts exhibit decreased electrochemical performance in these conditions, marked by reduced activity and increased overpotential. This problem has been primarily addressed by exploring catalyst design without proper consideration of the electrolyte; its role is often undervalued and overlooked. Electrolyte parameters, including ionic species, pH, physicochemical properties, etc., profoundly impact the OER. If not properly chosen, catalyst surface interactions, local pH swings, and factors like mass transport can become nonideal. Therefore, quasi-neutral electrolytes must be methodically selected for a given system. In this perspective, we present the challenges faced in quasi-neutral electrolytes and emphasize points of consideration for quasi-neutral OER electrolytes by systematically reviewing the literature. First, we explore buffers and local pH, and the surface interactions between the catalyst and the electrolyte. Next, we discuss electrolyte additives and their promise to enhance the OER by altering the electric double layer and hydrogen bonding environment. Lastly, we address the critical role of mass transport through the lens of physicochemical properties and external parameters. Overall, a strategic approach, encompassing an informed choice of an electrolyte and modification of its properties, is suggested for enhancing OER performance to drive quasi-neutral electrochemical water splitting innovations.

[This corrects the article DOI: 10.1021/jacsau.4c00986.].

[This corrects the article DOI: 10.1021/jacsau.5c00675.].

Electron transfer between adsorbates and surfaces determines the binding strength and reactivity of chemical moieties on materials designed for separations and catalysis. To quantify electron exchange, the extent of charge transfer resulting from ammonia adsorption on a Ru surface was measured by isopotential electron titration (IET) on a Ru catalytic condenser, where isopotential conditions were maintained between Ru and silicon separated by an insulating HfO₂ layer during gas phase ammonia adsorption. Charge transfer upon ammonia adsorption on a Ru catalytic condenser increased from 40 to 1200 nC/cm² at 75 and 225 °C, respectively. Charge transfer measurements provided a direct estimate of ammonia adsorption thermodynamics on Ru without knowing surface coverages a priori, revealing an adsorption enthalpy of -53 ± 10 kJ/mol and entropy of -61 ± 26 J/mol·K. Combining experimentally-measured charge transfer with kinetic Monte Carlo simulations informed adsorbate surface coverages determined that 0.058 electrons were transferred to the Ru surface for each molecular ammonia adsorption event (δ_NH3 = 0.058 ± 0.005 e^-/NH₃ ^*), consistent with calculated Bader charges. The ability to measure the extent of charge transfer for adsorbed species provides a fundamental descriptor to understand existing and new chemically functional surfaces, providing a foundational method for the emerging field of thermochemical surface coulometry.