Mo2C@C nanofibers film as durable self-supported electrode for efficient electrocatalytic hydrogen evolution

Self-supported electrocatalytic thin films consist 3D conducting network and well-embedded electrocatalysts, which endows the advantage in mass flow kinetics and durability for large-scale water splitting. Synthesis of such self-supported electrode still remains a big challenge due to the difficulty in the control over the 3D conducting network and the simultaneous growth of catalyst with well attachment on the conducting fibers. Herein, a self-supported Mo2C@carbon nanofibers (Mo2C@C NF) film has been successfully fabricated with outstanding electrocatalytic performance under optimized pyrolysis temperature and precursors mass ratio conditions. During the carbonation process, the Mo2C nanoparticles (~16 nm) are simultaneously grown and well dispersed on the inter-connected carbon nanofibers, which form 3D conducting network. The as-formed 3D carbon network is strong enough to support direct electrocatalytic application without additional ink or supporting substrates. This particular electrode structure facilitates easy access to the active catalytic sites, electron transfer, and hydrogen diffusion, resulting in the high hydrogen evolution reaction (HER) activity. A low overpotential of 86 mV is needed to achieve 10 mA cm-2 current density with outstanding kinetics metric (Tafel 43 mV dec-1) in 1M KOH. Additionally, the self-supported Mo2C@C NF film, a binder-free electrode, exhibits extraordinary stability of more than 340 h.

Interfacial-confined coordination to single-atom nanotherapeutics

Pursuing and developing effective methodologies to construct highly active catalytic sites to maximize the atomic and energy efficiency by material engineering are attractive. Relative to the tremendous researches of carbon-based single atom systems, the construction of bio-applicable single atom materials is still in its infancy. Herein, we propose a facile and general interfacial-confined coordination strategy to construct high-quality single-atom nanotherapeutic agent with Fe single atoms being anchored on defective carbon dots confined in a biocompatible mesoporous silica nanoreactor. Furthermore, the efficient energy conversion capability of silica-based Fe single atoms system has been demonstrated on the basis of the exogenous physical photo irradiation and endogenous biochemical reactive oxygen species stimulus in the confined mesoporous network. More importantly, the highest photothermal conversion efficiency with the mechanism of increased electron density and narrow bandgap of this single atom structure in defective carbon was proposed by the theoretical DFT calculations. The present methodology provides a scientific paradigm to design and develop versatile single atom nanotherapeutics with adjustable metal components and tune the corresponding reactions for safe and efficient tumor therapeutic strategy.

Mn, P Co doped Sharp-edged Mo2C Nanosheets Anchored on Porous Carbon for Efficient Electrocatalytic Hydrogen Evolution

Molybdenum carbide (Mo2C) has received great attention as a promising non-noble metal electrocatalyst for hydrogen evolution reaction (HER). The exposure of more catalytic sites and optimal Mo-H bonding strength via...

Non-metal boron atoms on CuB12 monolayer as efficient catalytic sites for urea production

Electrocatalytic C-N coupling reaction to convert CO2 and N2 into urea under mild conditions has been proposed to be a promising alternative experimentally, but the development of high-stable, low-cost and...

Synthesis of Mesoporous Zeolites and Their Opportunities in Heterogeneous Catalysis

Currently, zeolites are one of the most important classes of heterogeneous catalysts in chemical industries owing to their unique structural characteristics such as molecular-scale size/shape-selectivity, heterogenized single catalytic sites in the framework, and excellent stability in harsh industrial processes. However, the microporous structure of conventional zeolite materials limits their applications to small-molecule reactions. To alleviate this problem, mesoporous zeolitic frameworks were developed. In the last few decades, several methods have been developed for the synthesis of mesoporous zeolites; these zeolites have demonstrated greater lifetime and better performance than their bulk microporous counterparts in many catalytic processes, which can be explained by the rapid diffusion of reactant species into the zeolite framework and facile accessibility to bulky molecules through the mesopores. Mesoporous zeolites provide versatile opportunities not only in conventional chemical industries but also in emerging catalysis fields. This review presents many state-of-the-art mesoporous zeolites, discusses various strategies for their synthesis, and details their contributions to catalytic reactions including catalytic cracking, isomerization, alkylation and acylation, alternative fuel synthesis via methanol-to-hydrocarbon (MTH) and Fischer–Tropsch synthesis (FTS) routes, and different fine-chemical syntheses.

Enhanced specificity mutations perturb allosteric signaling in CRISPR-Cas9

CRISPR-Cas9 is a molecular tool with transformative genome editing capabilities. At the molecular level, an intricate allosteric signaling is critical for DNA cleavage, but its role in the specificity enhancement of the Cas9 endonuclease is poorly understood. Here, multi-microsecond molecular dynamics is combined with solution NMR and graph theory-derived models to probe the allosteric role of key specificity-enhancing mutations. We show that mutations responsible for increasing the specificity of Cas9 alter the allosteric structure of the catalytic HNH domain, impacting the signal transmission from the DNA recognition region to the catalytic sites for cleavage. Specifically, the K855A mutation strongly disrupts the allosteric connectivity of the HNH domain, exerting the highest perturbation on the signaling transfer, while K810A and K848A result in more moderate effects on the allosteric communication. This differential perturbation of the allosteric signal correlates to the order of specificity enhancement (K855A > K848A ~ K810A) observed in biochemical studies, with the mutation achieving the highest specificity most strongly perturbing the signaling transfer. These findings suggest that alterations of the allosteric communication from DNA recognition to cleavage are critical to increasing the specificity of Cas9 and that allosteric hotspots can be targeted through mutational studies for improving the system's function.

Review: Clay-Modified Electrodes in Heterogeneous Electro-Fenton Process for Degradation of Organic Compounds: The Potential of Structural Fe(III) as Catalytic Sites

Advanced oxidation processes are considered as a promising technology for the removal of persistent organic pollutants from industrial wastewaters. In particular, the heterogeneous electro-Fenton (HEF) process has several advantages such as allowing the working pH to be circumneutral or alkaline, recovering and reusing the catalyst and avoiding the release of iron in the environment as a secondary pollutant. Among different iron-containing catalysts, studies using clay-modified electrodes in HEF process are the focus in this review. Fe(III)/Fe(II) within the lattice of clay minerals can possibly serve as catalytic sites in HEF process. The description of the preparation and application of clay-modified electrodes in the degradation of model pollutants in HEF process is detailed in the review. The absence of mediators responsible for transferring electrons to structural Fe(III) and regenerating catalytic Fe(II) was considered as a milestone in the field. A comprehensive review of studies investigating the use of electron transfer mediators as well as the mechanism behind electron transfer from and to the clay mineral structure was assembled in order to uncover other milestones to be addressed in this study area.

Allosteric regulation of the proteasomes catalytic sites by the proteasome activator PA28gamma/REGgamma

Proteasome Activator 28γ (PA28γ) is a member of the 11S family of proteasomal regulators that is constitutively expressed in the nucleus and is implicated in certain cancers, lupus, rheumatoid arthritis, and Poly-glutamine neurodegenerative diseases. However, how PA28γ functions in protein degradation remains unclear. Though PA28γs mechanism has been investigated for some time, many alternative hypotheses have not been tested: e.g. 1) substrate selection, 2) allosteric upregulation of the Trypsin-like catalytic site, 3) allosteric inhibition of the Chymotrypsin- and Caspase-like catalytic sites, 4) conversion of the Chymotrypsin- or Caspase-like sites to new Trypsin-like catalytic sites, and 5) gate-opening in combination with these. The purpose of this study was to conclusively determine how PA28γ regulates proteasome function. Here, we rigorously and definitively show that PA28γ uses an allosteric mechanism to upregulate the proteolytic activity of the 20S proteasomes Trypsin-like catalytic site. Using a constitutively open channel proteasome, we were able to dissociate gating affects from catalytic affects demonstrating that the PA28γ-increases the affinity (Km) and Vmax for Trypsin-like peptide substrates. Mutagenesis of PA28γ also reveals that it does not select for (i.e. filter) peptide substrates, and does not change the specificity of the other active sites to trypsin-like. Further, using Cryo-EM we were able to visualize the C7 symmetric PA28γ-20S proteasome complex at 4.4A validating it's expected 11S-like quaternary structure and proteasome binding mode. The results of this study provide unambiguous evidence that PA28γ functions by allosterically upregulating the T-L like site in the 20S proteasome.