Catalytic Component Research Articles

Abstract 5818: Cadherin complexes recruit PIWIL2 to suppress pro-tumorigenic transformation

Abstract Recent studies have shown that genomic instability, oncogene expression, and high mutation rates in more than 50% of tumors can be attributed to increased transposon activity. Transposons, also called transposable elements (TEs), are parasitic mobile DNA elements that make up 45% of the human genome and can cause DNA damage and gene mutations. The reasons for increased TE activity in somatic tumors are currently unknown. TE RNA transcripts are targeted for degradation by PIWI ribonucleases, which are members of the Argonaute superfamily of proteins, through regulation of small RNAs called piRNAs (PIWI-interacting RNAs). Although the function of the PIWI-piRNA pathway has been extensively studied in the germline, there is little understanding about the presence or functionality of the pathway in somatic tissues. We have evidence of a novel interaction of the adherens junctions of well-differentiated epithelial cells with PIWIL2 (PIWI-like RNA-Mediated Gene Silencing 2), a key catalytic component of the PIWI-piRNA complex. Through immunofluorescence staining, confocal microscopy, and co-immunoprecipitation studies, we found co-localization and association of PIWIL2, as well as of other key members of the PIWI complex, such as PIWIL4 and TDRD1, with E-cadherin and p120 catenin at adherens junctions of well-differentiated breast and colon epithelial cells, whereas this association is lost in cancer cells and patient tissues. Adherens junction disruption results in mis-localization of PIWIL2, PIWIL4, and TDRD1 from the adherens junctions and their accumulation either to the cytoplasm or to the nucleus. E-cadherin depletion particularly results in increased expression of the LINE1 transposon, which is the most abundant transposon in human cells, and in increased levels of γ-H2AX, an indicator of DNA damage. Our working hypothesis is that cadherin junctions of well-differentiated epithelial cells recruit and regulate the PIWIL2 complex to suppress transposon activity. Since both loss of junctional integrity and increased transposon activity are universal events in cancer, this study has the potential to deepen our understanding of the role of the PIWI-transposon pathway in somatic tumorigenesis. Citation Format: Alyssa Risner, Joyce Nair-Menon, Vamsi Gangaraju, Antonis Kourtidis. Cadherin complexes recruit PIWIL2 to suppress pro-tumorigenic transformation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5818.

Downregulation of MUS81 expression inhibits cell migration and maintains EBV latent infection through miR-BART9-5p in EBV-associated gastric cancer.

Epstein-Barr virus (EBV) infection is associated with the occurrence and development of gastric cancer (GC). Methyl methanesulfonate and ultraviolet-sensitive gene 81 (MUS81) is the catalytic component of a structure-specific endonuclease and plays an important role in chromosomal stability. However, the link between EBV infection and MUS81 remains unclear. In the present study, we found that MUS81 expression was much lower in EBV-associated GC cells than in EBV-negative GC. MUS81 acts as an oncogene in GC by inducing the cell migration and proliferation. Western blot and luciferase reporter assays revealed that miR-BART9-5p directly targeted MUS81 and downregulated its expression. Additionally, overexpression of MUS81 in EBV-positive GC cells inhibited the expression of EBV nuclear antigen 1 (EBNA1). EBNA1 is critical for the pathogenesis of EBV-associated tumors and the maintenance of a stable copy number of the viral genomes. Altogether, these results indicated that the lowering MUS81 expression might be a mechanism by EBV to maintain its latent infection.

Uncovering the gastrointestinal passage, intestinal epithelial cellular uptake, and AGO2 loading of milk miRNAs in neonates using xenomiRs as tracers

BackgroundHuman breast milk has a high microRNA (miRNA) content. It remains unknown whether and how milk miRNAs might affect intestinal gene regulation and homeostasis of the developing microbiome after initiating enteral nutrition. However, this requires that relevant milk miRNA amounts survive the gastrointestinal (GI) passage, are taken up by cells, and become available to the RNA interference machinery. It seems important to dissect the fate of these miRNAs after oral ingestion and GI passage. ObjectivesOur goal was to analyze the potential transmissibility of milk miRNAs via the gastrointestinal system in neonate humans and a porcine model in vivo to contribute to the discussion of whether milk miRNAs could influence gene regulation in neonates and thus might vertically transmit developmental relevant signals. MethodsWe performed cross-species profiling of miRNAs via deep sequencing and utilized dietary xenobiotic taxon-specific milk miRNA (xenomiRs) as tracers in human and porcine neonates, followed by functional studies in primary human fetal intestinal epithelial cells using adenovirus-type 5-mediated miRNA gene transfer. ResultsMammals share many milk miRNAs yet exhibit taxon-specific miRNA fingerprints. We traced bovine-specific miRNAs from formula nutrition in human preterm stool and 9 d after the onset of enteral feeding in intestinal cells (ICs) of preterm piglets. Thereafter, several xenomiRs accumulated in the ICs. Moreover, a few hours after introducing enteral feeding in preterm piglets with supplemented reporter miRNAs (cel-miR-39-5p/-3p), we observed their enrichment in blood serum and in argonaute RISC catalytic component 2 (AGO2)-immunocomplexes from intestinal biopsies. ConclusionsMilk-derived miRNAs survived GI passage in human and porcine neonates. Bovine-specific miRNAs accumulated in ICs of preterm piglets after enteral feeding with bovine colostrum/formula. In piglets, colostrum supplementation with cel-miR-39-5p/-3p resulted in increased blood concentrations of cel-miR-39-3p and argonaute RISC catalytic component 2 (AGO2) loading in ICs. This suggests the possibility of vertical transmission of miRNA signaling from milk through the neonatal digestive tract.

Beyond Purification: Highly Efficient and Selective Conversion of NO into Ammonia by Coupling Continuous Absorption and Photoreduction under Ambient Conditions.

Although the selective catalytic reduction technology has been confirmed to be effective for nitrogen oxide (NOx) removal, green and sustainable NOx re-utilization under ambient conditions is still a great challenge. Herein, we develop an on-site system by coupling the continuous chemical absorption and photocatalytic reduction of NO in simulated flue gas (CNO = 500 ppm, GHSV = 18,000 h-1), which accomplishes an exceptional NO conversion into value-added ammonia with competitive conversion efficiency (89.05 ± 0.71%), ammonia production selectivity (95.58 ± 0.95%), and ammonia recovery efficiency (>90%) under ambient conditions. The anti-poisoning capacities, including the resistance against factors of H2O, SO2, and alkali/alkaline/heavy metals, are also achieved, which presents strong environmental practicability for treating NOx in flue gas. In addition, the critical roles of corresponding chemical absorption and catalytic reduction components are also revealed by in situ characterizations. The emerging strategy herein not only achieves a milestone efficiency for sustainable NO purification but also opens a new route for contaminant resourcing in the near future of carbon neutrality.

Erythrocyte-Derived microRNAs: Emerging Players in Cardiovascular and Metabolic Disease.

Recent studies have demonstrated a novel function of red blood cells (RBCs) beyond their classical role as gas transporters, that is, RBCs undergo functional alterations in cardiovascular and metabolic disease, and RBC dysfunction is associated with hypertension and the development of cardiovascular injury in type 2 diabetes, heart failure, preeclampsia, familial hypercholesterolemia/dyslipidemia, and COVID-19. The underlying mechanisms include decreased nitric oxide bioavailability, increased arginase activity, and reactive oxygen species formation. Of interest, RBCs contain diverse and abundant micro (mi)RNAs. microRNA expression pattern in RBCs reflects the expression in the whole blood, serum, and plasma. microRNA levels in RBCs have been found to be altered in various cardiovascular and metabolic diseases, which contributes to the development of cardiovascular complications. Evidence has shown that RBC-derived miRNAs interact with the cardiovascular system via extracellular vesicles and argonaute RISC catalytic component 2 as carriers. Alteration of RBC-to-vascular communication via miRNAs may serve as potential disease mechanism for vascular complications. The present review summarizes RBCs and their released miRNAs as potential mediators of cardiovascular injury. We further focus on the possible mechanisms by which RBC-derived miRNAs regulate cardiovascular function. A better understanding of the function of RBC-derived miRNAs will increase insights into the disease mechanism and potential targets for the treatment of cardiovascular complications.

Cryo-EM structure of the four-subunit Rhodobacter sphaeroides cytochrome bc1 complex in styrene maleic acid nanodiscs

Cytochrome bc1 complexes are ubiquinol:cytochrome c oxidoreductases, and as such, they are centrally important components of respiratory and photosynthetic electron transfer chains in many species of bacteria and in mitochondria. The minimal complex has three catalytic components, which are cytochrome b, cytochrome c1, and the Rieske iron-sulfur subunit, but the function of mitochondrial cytochrome bc1 complexes is modified by up to eight supernumerary subunits. The cytochrome bc1 complex from the purple phototrophic bacterium Rhodobactersphaeroides has a single supernumerary subunit called subunit IV, which is absent from current structures of the complex. In this work we use the styrene-maleic acid copolymer to purify the R. sphaeroides cytochrome bc1 complex in native lipid nanodiscs, which retains the labile subunit IV, annular lipids, and natively bound quinones. The catalytic activity of the four-subunit cytochrome bc1 complex is threefold higher than that of the complex lacking subunit IV. To understand the role of subunit IV, we determined the structure of the four-subunit complex at 2.9 Å using single particle cryogenic electron microscopy. The structure shows the position of the transmembrane domain of subunit IV, which lies across the transmembrane helices of the Rieske and cytochrome c1 subunits. We observe a quinone at the Qo quinone-binding site and show that occupancy of this site is linked to conformational changes in the Rieske head domain during catalysis. Twelve lipids were structurally resolved, making contacts with the Rieske and cytochrome b subunits, with some spanning both of the two monomers that make up the dimeric complex.

Photocatalytic C-O Coupling Enzymes That Operate via Intramolecular Electron Transfer.

Efficient and environmentally friendly conversion of light energy for direct utilization in chemical production has been a long-standing goal in enzyme design. Herein, we synthesized artificial photocatalytic enzymes by introducing an Ir photocatalyst and a Ni(bpy) complex to an optimal protein scaffold in close proximity. Consequently, the enzyme generated C-O coupling products with up to 96% yields by harvesting visible light and performing intramolecular electron transfer between the two catalysts. We systematically modulated the catalytic activities of the artificial photocatalytic cross-coupling enzymes by tuning the electrochemical properties of the catalytic components, their positions, and distances within a protein. As a result, we discovered the best-performing mutant that showed broad substrate scopes under optimized conditions. This work explicitly demonstrated that we could integrate and control both the inorganic and biochemical components of photocatalytic biocatalysis to achieve high yield and selectivity in valuable chemical transformations.

BaTiO3 Functional Perovskite as Photocathode in Microbial Fuel Cells for Energy Production and Wastewater Treatment.

Microbial fuel cells (MFCs) provide new opportunities for the sustainable production of energy, converting organic matter into electricity through microorganisms. Moreover, MFCs play an important role in remediation of environmental pollutants from wastewater with power generation. This work focuses on the evaluation of ferroelectric perovskite materials as a new class of non-precious photocatalysts for MFC cathode construction. Nanoparticles of BaTiO3 (BT) were prepared and tested in a microbial fuel cell (MFC) as photocathode catalytic components. The catalyst phases were synthesized, identified and characterized by XRD, SEM, UV-Vis absorption spectroscopy, P-E hysteresis and dielectric measurements. The maximum absorption of BT nanoparticles was recorded at 285 nm and the energy gap (Eg) was estimated to be 3.77 eV. Photocatalytic performance of cathodes coated with BaTiO3 was measured in a dark environment and then in the presence of a UV-visible (UV-Vis) light source, using a mixture of dairy industry and domestic wastewater as a feedstock for the MFCs. The performance of the BT cathodic component is strongly dependent on the presence of UV-Vis irradiation. The BT-based cathode functioning under UV-visible light improves the maximum power densities and the open circuit voltage (OCV) of the MFC system. The values increased from 64 mW m-2 to 498 mW m-2 and from 280 mV to 387 mV, respectively, showing that the presence of light effectively improved the photocatalytic activity of this ceramic. Furthermore, the MFCs operating under optimal conditions were able to reduce the chemical oxygen demand load in wastewater by 90% (initial COD = 2500 mg L-1).

Application of ionic liquids in CO2 capture and electrochemical reduction: A review

As a new type of green solvent with non-volatility, high thermal stability, high conductivity and various adjustable properties, ionic liquid (IL) has been widely used in the capture and electrochemical reduction of carbon dioxide (CO2). To date, many studies have been made to investigate CO2 capture by using different types of ILs and CO2 electrochemical reduction (CO2ER) with ILs as either electrolyte or other catalytic active components. Some structure–activity relationships between the structure and adsorption or catalytic properties of ILs have been found. Herein, the absorption performances and mechanisms of conventional ILs, amino-functionalized ILs, non-amino functionalized ILs and supported ILs for CO2 capture, as well as the performances and action mechanisms of ILs as the electrolyte, electrolyte additive, and/or electrode modifier in the process of CO2ER are summarized. Many researches indicate that the unique interaction between the anion or cation of IL and CO2 has a significant contribution to promote the absorption and conversion of CO2. However, the ILs used for CO2 capture and electrochemical reduction should be further explored. Especially, a more in-depth investigation of the adsorption and catalytic mechanisms with the help of quantum chemical calculation, molecular simulation, and in situ characterization techniques is necessary. It is expected to design and develop more efficient ILs used for CO2 capture and conversion on a large scale.

Understanding the synergistic effect of Ni/Al2O3 on CO2 adsorption and sintering properties of CaO in sorption-enhanced steam reforming process

Sorption-enhanced steam reforming with in-situ CO2 removal by high temperature solid sorbents is an environmentally friendly and sustainable approach for hydrogen production. Ca-Ni-Al bifunctional materials with both catalytic activity and sorption activity have received extensive attention recently. However, the synergistic effect of Ni/Al2O3 on the CO2 adsorption and sintering properties of CaO sorbents have not been studied, and the atomistic mechanisms behind them still remain unclear. Here, we investigated the synergistic effect of Ni/Al2O3 on the carbonation properties and sintering resistance of CaO sorbents by experiments combined with density functional theory (DFT) calculations. Results show that the phase transformation for reduction of NiO and NiAl2O4 to Ni promotes the reaction between CaO and Al2O3, which is beneficial to the formation of the inert framework Ca12Al14O33. After adding 5 % and 15 % Ni, the BET specific surface area decreases from 11.85 to 7.59 and 4.51 m2/g, respectively. The catalytic component Ni is dispersed on the CaO surface, which blocks the pore structure and eventually leads to a decrease in CO2 capture capacity. Under high temperature calcination, Ni aggravates the sintering of CaO, which is not conducive to cyclic adsorption. The Al2O3 support can effectively improve the pore structure and maintain cycle stability of CaO sorbents. DFT calculations suggest that the catalytic component Ni, the Al2O3 support and the Ni-Al2O3 bi-component have little effect on the CO2 adsorption activity. The Ni significantly weakens the adsorption energy of Ca4O4 cluster on CaO surface from −2.58 eV to −1.57 eV, resulting in the growth of CaO grains. The strong interaction between Ca4O4 cluster and Al2O3 surface with the adsorption energy of −7.34 eV makes Ca4O4 cluster migration difficult, thereby inhibiting the agglomeration and sintering of CaO particles. Meanwhile, the addition of Ni component does not significantly reduce the anti-sintering ability of Al2O3 support on CaO sorbents. For Ni-Ca-Al bifunctional materials, the strong interaction between Ni-Ca is not conducive to the carbonation performance of CaO sorbents and the strong interaction between Ni-Al should be appropriately avoided to weaken the efficacy of Al2O3 support, which was confirmed by experiments.

In situ growth of ZnO nanorods on monolithic diesel particulate filters and supporting potassium for catalytic soot combustion

Soot particulate is one of the most important pollutants emitted from diesel engines. A monolithic wall-flow diesel particulate filter (DPF) is a commercial technology for the removal of soot via filtration and subsequent combustion with/without catalysts. Herein, in situ grown ZnO nanorods on DPFs are applied to improve both soot and potassium (K)-based catalyst dispersion efficiency and thus enhancing the activity of DPF regeneration. The pretreatment and hydrothermal synthesis procedures for the homogenously covered ZnO nanorod arrays were specifically investigated on aluminum titanate (Al2TiO5) and silicon carbide (SiC) and compared with cordierite (Mg2Al4Si5O18). Potassium carbonate (K2CO3) is further supported on these monolithic substrates with in situ grown ZnO nanorods acting as catalytic active components for soot combustion. The coexistence of in situ grown ZnO nanorods and K active species on the three monoliths leads to much better soot combustion activity than those bare monoliths. The ZnO nanorods can not only trap soot to improve the contact efficiency between soot and catalysts, but also disperse the active K species. This demonstrates a promising strategy to develop highly active catalytic DPF for diesel soot removal.

Exploring the potential of nanosized oxides of zinc and tin as recyclable catalytic components for the synthesis of cyclic organic carbonates under atmospheric CO2 pressure

Nanomaterials based on tin (IV) oxide (SnO2) and zinc oxide (ZnO) were investigated in the search for active, environmentally benign, and inexpensive materials for the crucial reaction of CO2 cycloaddition to epoxides to afford cyclic carbonates. In particular, nanoparticles (NPs), nanorods (NRs), nanosheets (NSs) and microplates (µPLs) were prepared and used in combination with small amounts of TBAI (tetrabutylammonium iodide) as the nucleophile. Different from the general case of metal oxides, often requiring harsh reaction conditions, the most active compound in this study, SnO2-NPs, served as an active material for the cycloaddition of CO2 to several terminal epoxides under atmospheric pressure at moderate temperatures (60–80 °C) and could also be employed for converting internal epoxides under harsher conditions. Importantly, SnO2-NPs could also be used in the presence of impure CO2 feeds (20% methane in CO2) resembling low calorific landfill gas and could be recycled and reused. Overall, SnO2-NPs represent a promising, readily available, and inexpensive metal oxide-based material to produce cyclic carbonates under atmospheric CO2 pressure.

Early transcriptional and epigenetic divergence of CD8+ T cells responding to acute versus chronic infection.

During a microbial infection, responding CD8+ T cells give rise to effector cells that provide acute host defense and memory cells that provide sustained protection. An alternative outcome is exhaustion, a state of T cell dysfunction that occurs in the context of chronic infections and cancer. Although it is evident that exhausted CD8+ T (TEX) cells are phenotypically and molecularly distinct from effector and memory CD8+ T cells, the factors regulating the earliest events in the differentiation process of TEX cells remain incompletely understood. Here, we performed single-cell RNA-sequencing and single-cell ATAC-sequencing of CD8+ T cells responding to LCMV-Armstrong (LCMV-Arm) or LCMV-Clone 13 (LCMV-Cl13), which result in acute or chronic infections, respectively. Compared to CD8+ T cells that had undergone their first division in response to LCMV-Arm (Div1ARM) cells, CD8+ T cells that had undergone their first division in response to LCMV-Cl13 (Div1CL13) expressed higher levels of genes encoding transcription factors previously associated with exhaustion, along with higher levels of Ezh2, the catalytic component of the Polycomb Repressive Complex 2 (PRC2) complex, which mediates epigenetic silencing. Modulation of Ezh2 resulted in altered expression of exhaustion-associated molecules by CD8+ T cells responding to LCMV-Cl13, though the specific cellular and infectious contexts, rather than simply the level of Ezh2 expression, likely determine the eventual outcome. Taken together, these findings suggest that the differentiation paths of CD8+ T cells responding to acute versus chronic infections may diverge earlier than previously appreciated.

Insight into the role of [C2C1mim][OAc] and AgNO3 in the reaction of propargylic alcohols, CO2, and 2-aminoethanols

The chemical fixation of CO2 has attracted elevated attentions since it is a promising pathway to solve the serious environmental pollution and fuel shortage. The three-component reaction of CO2, propargyl alcohols, and 2-aminoethanols is one of the most attractive candidates due to the wide applications and extreme importance of products. However, the reaction mechanism is desired to explore due to the complicated catalytic components and substrates. In addition, contribution of each catalytic component and actual catalytic component are still not clear. The mechanism of title reaction catalyzed by AgNO3/[C2C1mim][OAc] is elucidated by the density functional theory (DFT). In addition, the catalytic routes of AgNO3/[C4C1mim][OAc], AgNO3/[DBUH][OAc], AgNO3/[C2C1mim][NO3], and AgNO3/[C2C1mim][ClO4] are also considered to unfold the contribution of cation and anion. The atoms in molecule (AIM) and noncovalent interactions (NCI) are calculated for some important configurations to deeply understand the difference among various catalysts. To elucidate these issues is favorable to explore the more robust catalysts for this reaction.

TERT promoter mutations and methylation for telomerase activation in urothelial carcinomas: New mechanistic insights and clinical significance.

Telomerase, an RNA-dependent DNA polymerase synthesizing telomeric TTAGGG sequences, is primarily silent in normal human urothelial cells (NHUCs), but widely activated in urothelial cell-derived carcinomas or urothelial carcinomas (UCs) including UC of the bladder (UCB) and upper track UC (UTUC). Telomerase activation for telomere maintenance is required for the UC development and progression, and the key underlying mechanism is the transcriptional de-repression of the telomerase reverse transcriptase (TERT), a gene encoding the rate-limiting, telomerase catalytic component. Recent mechanistic explorations have revealed important roles for TERT promoter mutations and aberrant methylation in activation of TERT transcription and telomerase in UCs. Moreover, these TERT-featured genomic and epigenetic alterations have been evaluated for their usefulness in non-invasive UC diagnostics, recurrence monitoring, outcome prediction and response to treatments such as immunotherapy. Importantly, the detection of the mutated TERT promoter and TERT mRNA as urinary biomarkers holds great promise for urine-based UC liquid biopsy. In the present article, we review recent mechanistic insights into altered TERT promoter-mediated telomerase activation in UCs and discuss potential clinical implications. Specifically, we compare differences in senescence and transformation between NHUCs and other types of epithelial cells, address the interaction between TERT promoter mutations and other factors to affect UC progression and outcomes, evaluate the impact of TERT promoter mutations and TERT-mediated activation of human endogenous retrovirus genes on UC immunotherapy including Bacillus Calmette-Guérin therapy and immune checkpoint inhibitors. Finally, we suggest the standardization of a TERT assay and evaluation system for UC clinical practice.

Heterogenous carboxyl-functionalized bilayer ionic liquids/polyoxometalate catalysts for extractant-free oxidative desulfurization

Heterogenous carboxyl-functionalized bilayer ionic liquids/polyoxometalate catalysts were synthesized. The optimized catalyst SiO2(50 nm)-BiIL-PW(Keggin-type) was characterized via FT-IR, XRD, Raman, UV–vis-DRS, XPS, TG, SEM-EDX, TEM, contact angle and N2 adsorption/desorption. Characterization results illuminate that polyoxometalate anions are grafted successfully onto the surface of carrier. The catalyst exhibits good amphiphilicity for both sulphur-containing compounds and hydrogen peroxide. With optimized catalyst, 100% sulfur removal can all be achieved for four model fuels including less active BT using a 4:1 molar ratio of n(H2O2)/n(S) and a low temperature of 40 °C free of extractant, which could be attributed to the better quasi homogeneous microenvironment provided by bilayer ionic liquids. Reaction results demonstrate that polyoxometalate and carrier have significant effects on the catalytic activities. Keggin-type phosphotungstate and 50 nm silica are superior for the desulfurization. ICP-MS analysis and the characterizations of recovered catalyst show no significant leaching of catalytic active component. No decrease was observed in catalytic efficiency after the 8th cycle in scale-up experiments.

Human SMARCA5 is continuously required to maintain nucleosome spacing

Genetic models suggested that SMARCA5 was required for DNA-templated events including transcription, DNA replication, and DNA repair. We engineered a degron tag into the endogenous alleles of SMARCA5, a catalytic component of the imitation switch complexes in three different human cell lines to define the effects of rapid degradation of this key regulator. Degradation of SMARCA5 was associated with a rapid increase in global nucleosome repeat length, which may allow greater chromatin compaction. However, there were few changes in nascent transcription within the first 6h of degradation. Nevertheless, we demonstrated a requirement for SMARCA5 to control nucleosome repeat length at G1/S and during the S phase. SMARCA5 co-localized with CTCF and H2A.Z, and we found a rapid loss of CTCF DNA binding and disruption of nucleosomal phasing around CTCF binding sites. This spatiotemporal analysis indicates that SMARCA5 is continuously required for maintaining nucleosomal spacing.

Structural correlations of nitrogenase active sites using nuclear resonance vibrational spectroscopy and QM/MM calculations.

The biological conversion of N2 to NH3 is accomplished by the nitrogenase family, which is collectively comprised of three closely related but unique metalloenzymes. In the present study, we have employed a combination of the synchrotron-based technique of 57Fe nuclear resonance vibrational spectroscopy together with DFT-based quantum mechanics/molecular mechanics (QM/MM) calculations to probe the electronic structure and dynamics of the catalytic components of each of the three unique M N2ase enzymes (M = Mo, V, Fe) in both the presence (holo-) and absence (apo-) of the catalytic FeMco clusters (FeMoco, FeVco and FeFeco). The results described herein provide vibrational mode assignments for important fingerprint regions of the FeMco clusters, and demonstrate the sensitivity of the calculated partial vibrational density of states (PVDOS) to the geometric and electronic structures of these clusters. Furthermore, we discuss the challenges that are faced when employing NRVS to investigate large, multi-component metalloenzymatic systems, and outline the scope and limitations of current state-of-the-art theory in reproducing complex spectra.

In situ formation of TiB2 and TiH2 catalyzed Li/Mg based dual-cation borohydride with a low onset dehydrogenation temperature below 100 °C

Chemical complex borohydride is a promising hydrogen storage material due to its large gravimetric and volumetric hydrogen capacities. However, the high dehydrogenation temperature and sluggish kinetics still place strong restrictions on its practical application in the hydrogen storage field. In this work, a synergetic approach of partial cation substitution and catalysis is developed to enhance the hydrogen storage properties of LiBH4. The Li/Mg based dual-cation borohydride (LiMg2(BH4)5, LMBH) was successfully synthesized by wet chemical ball milling of LiBH4 and MgCl2. The optimal (LMBH (4.5:1) sample, LiBH4 and MgCl2 in molar ratios of 4.5:1, possesses a maximum hydrogen desorption capacity (11.27 wt%) and the outstanding initial decomposition temperature (∼250 °C). Importantly, the LMBH (4.5:1) doped with TiF3 shows a remarkable onset dehydrogenation temperature as low as 97.2 °C, which is about 190 °C lower than that of pristine LiBH4. The LMBH (4.5:1) doped with TiF3 system releases 7.98 wt% H2 within 170 min below 350 °C. And the dehydrogenation product of doped composite can reversibly absorb ∼4.72 wt% H2 at a relatively moderate temperature of 280 °C, which is substantially lower than the reversible hydrogen absorption temperature of previous modified borohydride systems. Based on the structural characteristic analyses, the TiF3 reacts with LMBH (4.5:1) to in-situ form actual catalytic components of TiB2 and TiH2 as the actual catalysts for LMBH (4.5:1), resulting in the improved hydrogen re/dehydrogenation properties. The synergetic modification of Li/Mg dual-cation substitution and TiB2/TiH2 catalysis may lead to the development of light-metal borohydrides with outstanding hydrogen storage properties.

Solvent‐Polarity‐Induced Assembly of Calixarene‐Capped Titanium‐Oxo Clusters with Catalytic Activity in the Oxygenation of Sulfides

AbstractFour calixarene‐coordinated titanium‐oxo clusters, namely, [Ti4(C6A)2(μ3‐O)2(DMF)2] (CIAC‐258), [Ti8(H3C6A)4(C6H5PO3)8(μ2‐O)4]4− (CIAC‐259), [Ti6(TC4A)3(μ2‐O)3 (OiPr)6] (CIAC‐260) and [Ti6(H2TC4A)4(C6H5PO3)4(μ2‐O)5(DMF)2]2− (CIAC‐261) were obtained, which feature sandwich‐like, windmill‐like, triangular, and tetrahedral structures, respectively. The polarity of the solvent determines the involvement of the auxiliary ligand phenylphosphonic acid in the formation of the products and their structures. Compounds CIAC‐258 and CIAC‐261 exhibit good catalytic performance in the selective oxidation of sulfides to sulfoxides with H2O2 as the oxidant, which can be attributed to the Ti active sites coordinated by exchangeable DMF molecules. Moreover, density functional theory (DFT) calculations revealed that the Ti‐hydroperoxo species formed by the interaction of the Ti active site in CIAC‐258 or CIAC‐261 and H2O2 is the most likely catalytic active component during the catalytic sulfoxidation process.