The efficient use of natural gas will require catalysts that can activate the first C–H bond of methane while suppressing complete dehydrogenation and avoiding overoxidation. We report that single ...iron sites embedded in a silica matrix enable direct, nonoxidative conversion of methane, exclusively to ethylene and aromatics. The reaction is initiated by catalytic generation of methyl radicals, followed by a series of gas-phase reactions. The absence of adjacent iron sites prevents catalytic C-C coupling, further oligomerization, and hence, coke deposition. At 136B kelvin, methane conversion reached a maximum at 48.1% and ethylene selectivity peaked at 48.4%, whereas the total hydrocarbon selectivity exceeded 99%, representing an atom-economical transformation process of methane. The lattice-confined single iron sites delivered stable performance, with no deactivation observed during a 60-hour test.
Autophagy is a highly conserved catabolic process cells use to maintain their homeostasis by degrading misfolded, damaged and excessive proteins, nonfunctional organelles, foreign pathogens and other ...cellular components. Hence, autophagy can be nonselective, where bulky portions of the cytoplasm are degraded upon stress, or a highly selective process, where preselected cellular components are degraded. To distinguish between different cellular components, autophagy employs selective autophagy receptors, which will link the cargo to the autophagy machinery, thereby sequestering it in the autophagosome for its subsequent degradation in the lysosome. Autophagy receptors undergo post‐translational and structural modifications to fulfil their role in autophagy, or upon executing their role, for their own degradation. We highlight the four most prominent protein modifications – phosphorylation, ubiquitination, acetylation and oligomerisation – that are essential for autophagy receptor recruitment, function and turnover. Understanding the regulation of selective autophagy receptors will provide deeper insights into the pathway and open up potential therapeutic avenues.
Selective autophagy receptors are essential for bridging the cellular cargo destined for degradation with autophagy machinery. As such, their role in autophagy is strictly regulated. In this review, we outline and discuss post‐translational (phosphorylation, ubiquitination, acetylation) and structural (oligomerisation) modifications involved in regulating the function of cargo receptors in selective autophagy, and highlight the importance of it in maintaining cellular fitness and homeostasis.
Developing supported single-site catalysts is an important goal in heterogeneous catalysis since the well-defined active sites afford opportunities for detailed mechanistic studies, thereby ...facilitating the design of improved catalysts. We present herein a method for installing Ni ions uniformly and precisely on the node of a Zr-based metal–organic framework (MOF), NU-1000, in high density and large quantity (denoted as Ni-AIM) using atomic layer deposition (ALD) in a MOF (AIM). Ni-AIM is demonstrated to be an efficient gas-phase hydrogenation catalyst upon activation. The structure of the active sites in Ni-AIM is proposed, revealing its single-site nature. More importantly, due to the organic linker used to construct the MOF support, the Ni ions stay isolated throughout the hydrogenation catalysis, in accord with its long-term stability. A quantum chemical characterization of the catalyst and the catalytic process complements the experimental results. With validation of computational modeling protocols, we further targeted ethylene oligomerization catalysis by Ni-AIM guided by theoretical prediction. Given the generality of the AIM methodology, this emerging class of materials should prove ripe for the discovery of new catalysts for the transformation of volatile substrates.
Transferring endo-dicyclopentadiene (endo-DCPD) into exo-isomer and exo-tricyclopentadiene (TCPD) has great potential in synthesizing high-density fuels, but microporous acidic zeolites show low ...activity due to the mass transfer limitation and shape selectivity. Herein, we successfully tuned HZSM-5 into high activity by generating hierarchical pores via alkali treatment. XRD, SEM, TEM, N2 adsorption/desorption and 27Al MAS NMR characterizations confirm that moderate alkali treatment removes the amorphous phase and producess mesopores connecting microchannels, but the framework collapses under rigorous conditions. NH3-TPD and pyridine adsorption IR indicate that the presence of mesopores increases the accessibility of acid sites in microchannles, especially for large molecules. In the isomerization of endo-DCPD, after the generation of hierarchical porosity, the inactive parent HZSM-5 shows a higher exo-DCPD yield than thiose of microporous Hβ and mesoporous Al-MCM-41. In the oligomerization reaction, hierarchical HZSM-5 shows a higher TCPD yield than that of Hβ and the yield is comparable to that of Al-MCM-41. Importantly, this work provides an easy way to produce exo-DCPD and TCPD with maximum yield respectively by adjusting the zeolite treatment and reaction conditions. Z5-70–0.5–1.0 shows the best performance for isomerization whereas Z5-80–0.5–1.0 possessing more mesopores is most suitable for oligomerization. The hierarchical porous zeolite shows excellent coke tolerance, and shows good stability in recycling.
Display omitted
•Hierarchical HZSM-5 was synthesized using alkali treatment.•Mesopores allow more acidic sites in microchannels that are accessible.•Hierarchical HZSM-5 is more active than Hβ and Al-MCM-41.•Highest exo-DCPD yield (50.6%) and selectivity (79.3%) are obtained.•Highest TCPD yield (36.3%) and catalytic selectivity (84%) are obtained.
The study of bacterial immune systems has recently gained momentum, revealing a fascinating trend: many systems form large supramolecular assemblies. Here, we examine the potential mechanisms ...underpinning the evolutionary success of these structures, draw parallels to eukaryotic immunity, and offer fresh perspectives to stimulate future research into bacterial immunity.
The study of bacterial immune systems has recently gained momentum, revealing a fascinating trend: many systems form large supramolecular assemblies. Here, we examine the potential mechanisms underpinning the evolutionary success of these structures, draw parallels to eukaryotic immunity, and offer fresh perspectives to stimulate future research into bacterial immunity.
DFT and kMC calculations were combined to investigate the impact of the most commonly used organic template molecules both on the reaction energy profiles and the kinetics of formation of silica ...oligomers, as described by Caroline Mellot‐Draznieks, Carlos Nieto‐Draghi, and co‐workers in their Research Article on page 7111. The extended reaction path mechanism (258 equilibrium reactions and 242 chemical species) up to octameric species showed that organic templates produce higher concentrations of four‐membered‐ring intermediates.
The synthesis of macrocycles is severely impeded by concomitant oligomer formation. Here, we present a biomimetic approach that utilizes spatial confinement to increase macrocyclization selectivity ...in the ring-closing metathesis of various dienes at elevated substrate concentration up to 25 mM using an olefin metathesis catalyst selectively immobilized inside ordered mesoporous silicas with defined pore diameters. By this approach, the ratio between macro(mono)cyclization (MMC) product and all undesired oligomerization products (O) resulting from acyclic diene metathesis polymerization was increased from 0.55, corresponding to 35% MMC product obtained with the homogeneous catalyst, up to 1.49, corresponding to 60% MMC product. A correlation between the MMC/O ratio and the substrate-to-pore-size ratio was successfully established. Modification of the inner pore surface with dimethoxydimethylsilane allowed fine-tuning the effective pore size and reversing surface polarity, which resulted in a further increase of the MMC/O ratio up to 2.2, corresponding to >68% MMC product. Molecular-level simulations in model pore geometries help to rationalize the complex interplay between spatial confinement, specific (substrate and product) interaction with the pore surface, and diffusive transport. These effects can be synergistically adjusted for optimum selectivity by suitable surface modification.
Triplex nucleic acids have recently attracted interest as part of the rich “toolbox” of structures used to develop DNA‐based nanostructures and materials. This Review addresses the use of DNA ...triplexes to assemble sensing platforms and molecular switches. Furthermore, the pH‐induced, switchable assembly and dissociation of triplex‐DNA‐bridged nanostructures are presented. Specifically, the aggregation/deaggregation of nanoparticles, the reversible oligomerization of origami tiles and DNA circles, and the use of triplex DNA structures as functional units for the assembly of pH‐responsive systems and materials are described. Examples include semiconductor‐loaded DNA‐stabilized microcapsules, DNA‐functionalized dye‐loaded metal–organic frameworks (MOFs), and the pH‐induced release of the loads. Furthermore, the design of stimuli‐responsive DNA‐based hydrogels undergoing reversible pH‐induced hydrogel‐to‐solution transitions using triplex nucleic acids is introduced, and the use of triplex DNA to assemble shape‐memory hydrogels is discussed. An outlook for possible future applications of triplex nucleic acids is also provided.
DNA triplex structures are stabilized by Watson–Crick and Hoogsteen/reverse Hoogsteen interstrand interactions. This Review summarizes recently reported DNA‐triplex‐based systems and their application as switches, sensors, and for controlled drug delivery. In addition, the implementation of DNA triplex structures for the design of stimuli‐responsive materials is presented.
Infections by pathogens that contain DNA trigger the production of type-I interferons and inflammatory cytokines through cyclic GMP-AMP synthase, which produces 2'3'-cyclic GMP-AMP (cGAMP) that binds ...to and activates stimulator of interferon genes (STING; also known as TMEM173, MITA, ERIS and MPYS)
. STING is an endoplasmic-reticulum membrane protein that contains four transmembrane helices followed by a cytoplasmic ligand-binding and signalling domain
. The cytoplasmic domain of STING forms a dimer, which undergoes a conformational change upon binding to cGAMP
. However, it remains unclear how this conformational change leads to STING activation. Here we present cryo-electron microscopy structures of full-length STING from human and chicken in the inactive dimeric state (about 80 kDa in size), as well as cGAMP-bound chicken STING in both the dimeric and tetrameric states. The structures show that the transmembrane and cytoplasmic regions interact to form an integrated, domain-swapped dimeric assembly. Closure of the ligand-binding domain, induced by cGAMP, leads to a 180° rotation of the ligand-binding domain relative to the transmembrane domain. This rotation is coupled to a conformational change in a loop on the side of the ligand-binding-domain dimer, which leads to the formation of the STING tetramer and higher-order oligomers through side-by-side packing. This model of STING oligomerization and activation is supported by our structure-based mutational analyses.
Series of HY sorbents with different amounts and strength of Brønsted and Lewis acidic sites were prepared. Their adsorption performance in thiophene–benzene solution, pure benzene, and pure ...thiophene were evaluated, and the desulfurization mechanisms were studied. The results show that both thiophene and benzene could be effectively adsorbed through the interaction between Lewis acid sites and the conjugated π bond in these two molecules, and thus thiophene adsorption could be obviously competed by benzene on Lewis acidic sites. By contrast, on Brønsted acidic sites, thiophene can be efficiently adsorbed via H–S bond, which is stronger than the former interaction. Moreover, the middle strong Brønsted acid could cause thiophene oligomerization. Hence, for the desulfurization purpose by NaY zeolite in aromatic free system, its weak and middle strong Lewis acid should be increased, and for that in aromatic existing system, the Brønsted acid site with relative low strength should be promoted.
PDF
