Ligand-Engineered Rearrangement of Active Sites in Silver-Based MOFs for Improved CO2 Capture.

The electronic structures and geometries of nanometer-sized silver clusters Ag„ (n = 2–6) have been examined in the framework of self-consistent-field local density functional theory SCC-DV-Xx. The results show that there is a quantum size effect in silver clusters Agn. The binding energies per atom, Eb, for Agn increase monotonically with cluster size. There are transitions from a one-dimensional linear structure to a two-dimensional planar structure and then to a three-dimensional stereo structure from smaller silver clusters to larger ones. Both the binding energy differences, ∆Eb, between the neighbouring silver clusters and the highest occupied molecular orbital (HOMO) energies show these alternate features. The results indicate that the geometry factor takes an important role in the growth of nanometer-sized silver clusters. The steps from the one-dimensional linear structure (Ag2) to the two-dimensional planar structure (Ag3) and from the two-dimensional planar structure (Ag4) to the three-dimensional stereo structure (Ag5) are the hardest steps for the growth of these nanometer-sized silver clusters. After Ag5, it is easier to grow by one silver atom for nanometer-sized silver clusters. The transition between structures of different dimensional numbers can be treated as a kind of phase change. The results show the smallest development centre ( ) of the photographic process is the three-dimensional stereo structure of minimum size.

Insulin-degrading enzyme (IDE) exists primarily as a dimer being unique among the zinc metalloproteases in that it exhibits allosteric kinetics with small synthetic peptide substrates. In addition the IDE reaction rate is increased by small peptides that bind to a distal site within the substrate binding site. We have generated mixed dimers of IDE in which one or both subunits contain mutations that affect activity. The mutation Y609F in the distal part of the substrate binding site of the active subunit blocks allosteric activation regardless of the activity of the other subunit. This effect shows that substrate or small peptide activation occurs through a cis effect. A mixed dimer composed of one wild-type subunit and the other subunit containing a mutation that neither permits substrate binding nor catalysis (H112Q) exhibits the same turnover number per active subunit as wild-type IDE. In contrast, a mixed dimer in which one subunit contains the wild-type sequence and the other contains a mutation that permits substrate binding, but not catalysis (E111F), exhibits a decrease in turnover number. This indicates a negative trans effect of substrate binding at the active site. On the other hand, activation in trans is observed with extended substrates that occupy both the active and distal sites. Comparison of the binding of an amyloid β peptide analog to wild-type IDE and to the Y609F mutant showed no difference in affinity, indicating that Y609 does not play a significant role in substrate binding at the distal site.

Sluggish kinetics severely limit the development of potassium-ion hybrid capacitors (PIHCs). Exposing active sites is recognized as an ideal strategy to resolve this issue, but the corresponding ma...

The mitochondrial ATP synthase couples the flow of protons with the phosphorylation of ADP. A class of mutations, the mitochondrial genome integrity (mgi) mutations, has been shown to uncouple this process in the yeast mitochondrial ATP synthase. Four mutant forms of the yeast F(1) ATPase with mgi mutations were crystallized; the structures were solved and analyzed. The analysis identifies two mechanisms of structural uncoupling: one in which the empty catalytic site is altered and in doing so, apparently disrupts substrate (phosphate) binding, and a second where the steric hindrance predicted between γLeu83 and β(DP) residues, Leu-391 and Glu-395, located in Catch 2 region, is reduced allowing rotation of the γ-subunit with less impedance. Overall, the structures provide key insights into the critical interactions in the yeast ATP synthase involved in the coupling process.

Thorough understanding of reconstructed active sites evolving from their initial states is crucial for a variety of catalytic reactions, as it not only promotes an atomic-level comprehension of the catalytic mechanism but also guides the design of practically usable catalysts. In particular under electrochemical operation, the reconstruction phenomenon of surface sites during reactions. After reconstruction, the active site is no longer the original pristine structure but rather the newly formed surface site. Exploring surface reconstruction under Operando catalytic conditions can aid in a better understanding of the active sites and catalytic pathways, helping designing more efficient catalyst systems.Atomically dispersed catalysts (ADCs), specifically the ones based on carbon, show tremendous potential in critical electrochemical reactions, including the hydrazine oxidation reaction (HzOR), which exhibits zero-carbon emissions and possesses a high energy density, presents considerable promise for the application of hydrazine fuel cells with improved power density. The dynamic reconstruction of atomically dispersed catalytic sites during electrocatalytic processes has emerged as a subject of intensive investigation. On one hand, knowledge of the reconstruction process is crucial, as it provides deep insights into the atomically dispersed active site and catalytic mechanism, laying a firm basis for material innovation. On the other hand, atomically dispersed catalytic sites have clear and uniform coordination structures, making them ideal quasi-model catalysts for revealing reconstruction mechanisms of active sites. However, discovering these reconstruction behaviors has focused primarily on metallic atomically dispersed catalytic sites so far, leaving non-metallic ones much unexplored, despite the fact that their performance in catalysis is comparable to or even superior to that of costly noble metals. An accurate vision of active sites during reactions is vital in developing non-metallic atomically dispersed catalysts; from a scientific perspective, it is essential to extract information about possible dynamic reconstruction processes in non-metallic atomically dispersed catalytic sites, similar to that of metallic ones.Combining ex situ high resolution electron microscopy and in situ X-ray adsorption spectroscopy to monitor the structurally uniform and well-defined single atomic site of atomically dispersed catalyst as an ideal model system could provide valuable atomic insights to active sites and the corresponding catalytic reaction mechanism. In situ techniques, particularly operando near and extended X-ray absorption fine structure (EXAFS and XANES) spectroscopies, in which the probe parameters such as the edge intensity, “white line”, and its energy position are affected by spectator species adsorbed on the electrode surface and intermediates formed upon reaction, may deliver chemical fingerprints that capture evolution of active sites during reactionIn this study, we synthesized a carbonaceous, non-metallic atomically dispersed selenium (Se) catalyst and confirmed the atomically dispersed configuration of Se in a SeC4 configuration. The as-prepared Se ADCs was found active in the hydrazine oxidation reaction (HzOR) in alkaline media (-114 mV (vs. reversible hydrogen electrode) at a current density of 1 mA cm-2), even surpassing that of noble-metal platinum (Pt) catalysts. Using the Se ADCs as a quasi-model catalyst, in situ X-ray absorption spectroscopy and Fourier-Transform infrared spectroscopy were used to trace the dynamic reconstruction process of atomically dispersed Se catalytic sites. We found that pristine SeC4 will pre-adsorb an *OH ligand in alkaline aqueous solutions, and the electrochemical oxidation of the N2H4 molecule will subsequently occur on the opposite side of the OH-SeC4. Theoretical calculations suggest that the pre-adsorbed *OH group pulls electrons from the Se site, resulting in a more positively charged Se and a higher polarity of Se-C bonds, and consequently higher surface reactivity toward HzOR. Our findings provide valuable insights into the reconstruction mechanism of atomically dispersed semimetallic catalytic sites and promote their practical use in a wide range of energy systems. Figure 1

Magnetocatalysis: The Interplay between the Magnetic Field and Electrocatalysis

Surface Coordination Decouples Hydrogenation Catalysis on Supported Metal Catalysts

Syngas production over La0.9NiyAl11.95-yO19-δ catalysts during C14-alkane partial oxidation: Effects of sulfur and polycyclic aromatic hydrocarbons

Catalytic action of platinum on coke burning

Structure of the Whole Cytosolic Region of ATP-Dependent Protease FtsH

Thiamine diphosphate-dependent enzymes are involved in a wide variety of metabolic pathways. The molecular mechanism behind active site communication and substrate activation, observed in some of these enzymes, has since long been an area of debate. Here, we report the crystal structures of a phenylpyruvate decarboxylase in complex with its substrates and a covalent reaction intermediate analogue. These structures reveal the regulatory site and unveil the mechanism of allosteric substrate activation. This signal transduction relies on quaternary structure reorganizations, domain rotations, and a pathway of local conformational changes that are relayed from the regulatory site to the active site. The current findings thus uncover the molecular mechanism by which the binding of a substrate in the regulatory site is linked to the mounting of the catalytic machinery in the active site in this thiamine diphosphate-dependent enzyme.

The development of highly efficient, multifunctional catalysts featuring cooperative active sites is a complex yet vital endeavor. This study introduces an innovative approach through in situ polymerization, where flexible, cross-linked ionic polymers are synthesized within the channels of flexible, porous polymeric porphyrins. This process yields a series of interwoven frameworks endowed with dual catalytic active sites. The uniqueness of these catalysts lies in the synergistic interaction between metalated porphyrins and ionic components, greatly boosting their catalytic efficiency in the cycloaddition of CO2 and epoxides. The bifunctional catalysts not only surpass the individual constituents in performance but also demonstrate a significant superiority over their physical mixture. The structural flexibility and high density of active sites in these catalysts enable synergistic effects, leading to exceptional catalytic performance. This research marks a substantial leap in catalyst design, introducing a novel method for crafting bifunctional catalysts with dual-activation capabilities.

Hydrated cations present in the electrochemical double layer (EDL) are known to play a crucial role in electrocatalytic CO2 reduction (CO2R), and numerous studies have attempted to explain how the cation effect contributes to the complex CO2R mechanism. CO2R is a structure sensitive reaction, indicating that a small fraction of total surface sites may account for the majority of catalytic turnover. Despite intense interest in specific cation effects, probing site-specific, cation-dependent solvation structures remains a significant challenge. In this work, CO adsorbed on Au is used as a vibrational Stark reporter to indirectly probe solvation structure using vibrational sum frequency generation (VSFG) spectroscopy. Two modes corresponding to atop adsorption of CO are observed with unique frequency shifts and potential-dependent intensity profiles, corresponding to direct adsorption of CO to inactive surface sites, and in situ generated CO produced at catalytic active sites. Analysis of the cation-dependent Stark tuning slopes for each of these species provides estimates of the hydrated cation radius upon adsorption to active and inactive sites on the Au electrode. While cations are found to retain their bulk hydration shell upon adsorption at inactive sites, catalytic active sites are characterized by a single layer of water between the Au surface and the electrolyte cation. We propose that the drastic increase in catalytic performance at active sites stems from this unique solvation structure at the Au/electrolyte interface. Building on this evidence of a site-specific EDL structure will be critical to understand the connection between cation-dependent interfacial solvation and CO2R performance.

Graphene and its hybrid nanocomposite: A Metamorphoses elevation in the field of tissue engineering

ConspectusLithium-sulfur batteries (LSBs), recognized for their high energy density and cost-effectiveness, offer significant potential for advancement in energy storage. However, their widespread deployment remains hindered by challenges such as sluggish reaction kinetics and the shuttle effect of lithium polysulfides (LiPSs). By the introduction of catalytic materials, the effective adsorption of LiPSs, smooth surface migration behavior, and significantly reduced conversion energy barriers are expected to be achieved, thereby sharpening electrochemical reaction kinetics and fundamentally addressing the aforementioned challenges. However, driven by practical application targets, the demand for higher loadings and reduced electrolyte parameters inevitably exacerbates the burden on catalytic materials during their service. Additionally, given that catalytic materials contribute negligible electrochemical capacity, their incorporation inevitably increases the mass of nonactive components for reducing the energy density of LSBs. A meticulous insight into the lithium-sulfur catalytic reaction reveals that the conversion of LiPSs is dominated by active sites on the surfaces of catalytic materials. These microregions provide the necessary electron and ion transport for the conversion reaction of LiPSs, with their efficacy and quantity directly impacting the conversion efficiency. In light of these considerations, the strategic optimization of active sites emerges as a paramount pathway toward promoting the performance of LSBs while concurrently mitigating unnecessary mass. Here, we outline three strategies developed by our group to optimize active sites of catalytic materials: (1) Augmenting active sites by customizing structural modulation and precise dimensional control to maximize exposure. Emphasis has been placed on the approaches for material synthesis and the essence of reactions for achieving this strategy. (2) Regulating the microenvironment of active sites by integrating the coordination refinement, long-range atomic interactions, metal-support interactions, and other electronic regulation strategies, thereby providing an elevation in the intrinsic catalytic performance. (3) Implementing a self-cleaning mechanism for active sites to counteract deactivation by designing a tandem adsorption-migration-transformation pathway of sulfur contained within the molecular domain. Throughout this process, the intrinsic mechanisms driving performance enhancement through active site optimization strategies have been prominently emphasized, which encompass aspects such as electronic structure, atomic composition, and molecular configuration and significantly expand the comprehension of Li-S catalytic chemistry. Subsequently, considerations demanding heightened attention in future processes of active site optimization for catalytic materials have been delineated, including the in situ evolution patterns and resistance to the poisoning of active sites. It is noteworthy that given the similarity between Li-S catalysis chemistry and traditional electrocatalytic processes, this Account elucidates the concept of active site optimization by drawing insights from representative works and our own works in the field of electrocatalysis, which is relatively rare in previous reviews of LSBs. The proposed insights contribute to uncovering the intrinsic mechanisms of Li-S catalysis chemistry and introducing innovative ideas into active site optimization, ultimately advancing energy density and stability in LSBs.