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75 items found (0 items not approved), displaying 1 to 10.[First/Prev] 1, 2, 3, 4, 5, 6, 7, 8 [Next/Last]

Instruments / Technical Area	Publication Details	Published
B18-Core EXAFS I11-High Resolution Powder Diffraction	Rational design of synergistic active sites for catalytic ethene/2-butene cross-metathesis in a rhenium-doped Y zeolite catalyst Pu Zhao , Lin Ye , Guangchao Li , Chen Huang , Simson Wu , Ping-luen Ho , Haokun Wang , Tatchamapan Yoskamtorn , Denis Sheptyakov , Giannantonio Cibin , Angus I. Kirkland , Chiu C. Tang , Anmin Zheng , Wenjuan Xue , Donghai Mei , Kongkiat Suriye , Shik Chi Edman Tsang Acs Catalysis DOI: 10.1021/acscatal.1c00524 Show Abstract ▼ Abstract: Synthesizing atomically dispersed synergistic active pairs is crucial yet challenging in developing highly active heterogeneous catalysts for various industrially important reactions. Here, a single molecular Re species is immobilized on the inner surface of a Y zeolite with Brønsted acid sites (BASs) within atomic proximity to form Re OMS–BAS active pairs for the efficient catalysis of olefin metathesis reactions (OMS: olefin metathesis site). The synergy within the active pairs is revealed by studying the coadsorption geometry of the olefin substrates over the active pairs by synchrotron X-ray and neutron powder diffraction. It is shown that the BAS not only facilitates olefin adsorption but also aligns the olefin molecule to the Re OMS for efficient intermediate formation. Consequently, for the cross-metathesis of ethene and trans-2-butene to propene, this catalyst shows high activity under mild reaction conditions without observable deactivation. The catalyst outperforms not only traditional ReOx-based catalysts but also the best industrially applicable WOx-based catalyst thus far that we discovered previously. The concept of using two isolated active sites of different functionalities within atomic proximity in a confined cavity can provide opportunities for designing synergistically catalytic materials.	Mar 2021
I03-Macromolecular Crystallography I04-1-Macromolecular Crystallography (fixed wavelength)	Substrate anchoring and flexibility reduction in CYP153AM.aq leads to highly improved efficiency toward octanoic acid Lea R. Rapp , Sérgio M. Marques , Erna Zukic , Benjamin Rowlinson , Mahima Sharma , Gideon Grogan , Jiri Damborsky , Bernhard Hauer Acs Catalysis DOI: 10.1021/acscatal.0c05193 Diamond Proposal Number(s): [9948] Open Access Show Abstract ▼ Abstract: Cytochrome P450 CYP153AM.aq from Marinobacter aquaeolei serves as a model enzyme for the terminal (ω-) hydroxylation of medium- to long-chain fatty acids. We have engineered this enzyme using different mutagenesis approaches based on structure-sequence-alignments within the 3DM database and crystal structures of CYP153AM.aq and a homologue CYP153AP.sp. Applying these focused mutagenesis strategies and site-directed saturation mutagenesis, we created a variant that ω-hydroxylates octanoic acid. The M.aqRLT variant exhibited 151-fold improved catalytic efficiency and showed strongly improved substrate binding (25-fold reduced Km compared to the wild type). We then used molecular dynamics simulations to gain deeper insights into the dynamics of the protein. We found the tunnel modifications and the two loop regions showing greatly reduced flexibility in the engineered variant were the main features responsible for stabilizing the enzyme–substrate complex and enhancing the catalytic efficiency. Additionally, we showed that a previously known fatty acid anchor (Q129R) interacts significantly with the ligand to hold it in the reactive position, thereby boosting the activity of the variant M.aqRLT toward octanoic acid. The study demonstrates the significant effects of both substrate stabilization and the impact of enzyme flexibility on catalytic efficiency. These results could guide the future engineering of enzymes with deeply buried active sites to increase or even establish activities toward yet unknown types of substrates.	Feb 2021
I02-Macromolecular Crystallography I03-Macromolecular Crystallography	Octahedral trifluoromagnesate, an anomalous metal fluoride species, stabilizes the transition state in a biological motor Mengyu Ge , Robert W. Molt , Huw T. Jenkins , G. Michael Blackburn , Yi Jin , Alfred A. Antson Acs Catalysis DOI: 10.1021/acscatal.0c04500 Diamond Proposal Number(s): [13587] Open Access Show Abstract ▼ Abstract: Isoelectronic metal fluoride transition state analogue (TSA) complexes, MgF3– and AlF4–, have proven to be immensely useful in understanding mechanisms of biological motors utilizing phosphoryl transfer. Here we report a previously unobserved octahedral TSA complex, MgF3(H2O)−, in a 1.5 Å resolution Zika virus NS3 helicase crystal structure. 19F NMR provided independent validation and also the direct observation of conformational tightening resulting from ssRNA binding in solution. The TSA stabilizes the two conformations of motif V of the helicase that link ATP hydrolysis with mechanical work. DFT analysis further validated the MgF3(H2O)− species, indicating the significance of this TSA for studies of biological motors.	Feb 2021
I03-Macromolecular Crystallography I04-Macromolecular Crystallography	Structure and mechanism of Pseudomonas aeruginosa PA0254/HudA, a prFMN-dependent pyrrole-2-carboxylic acid decarboxylase linked to virulence Karl A. P. Payne , Stephen A. Marshall , Karl Fisher , Stephen E. J. Rigby , Matthew J. Cliff , Reynard Spiess , Diego M. Cannas , Igor Larrosa , Sam Hay , David Leys Acs Catalysis DOI: 10.1021/acscatal.0c05042 Diamond Proposal Number(s): [12788] Open Access Show Abstract ▼ Abstract: The UbiD family of reversible (de)carboxylases depends on the recently discovered prenylated-FMN (prFMN) cofactor for activity. The model enzyme ferulic acid decarboxylase (Fdc1) decarboxylates unsaturated aliphatic acids via a reversible 1,3-cycloaddition process. Protein engineering has extended the Fdc1 substrate range to include (hetero)aromatic acids, although catalytic rates remain poor. This raises the question how efficient decarboxylation of (hetero)aromatic acids is achieved by other UbiD family members. Here, we show that the Pseudomonas aeruginosa virulence attenuation factor PA0254/HudA is a pyrrole-2-carboxylic acid decarboxylase. The crystal structure of the enzyme in the presence of the reversible inhibitor imidazole reveals a covalent prFMN–imidazole adduct is formed. Substrate screening reveals HudA and selected active site variants can accept a modest range of heteroaromatic compounds, including thiophene-2-carboxylic acid. Together with computational studies, our data suggests prFMN covalent catalysis occurs via electrophilic aromatic substitution and links HudA activity with the inhibitory effects of pyrrole-2-carboxylic acid on P. aeruginosa quorum sensing.	Feb 2021
	Spatial profiling of a Pd/Al2O3 catalyst during selective ammonia oxidation Donato Decarolis , Adam H. Clark , Tommaso Pellegrinelli , Maarten Nachtegaal , Evan Lynch , C. Richard A. Catlow , Emma K. Gibson , Alexandre Goguet , Peter P. Wells Acs Catalysis 50, 2141 - 2149 DOI: 10.1021/acscatal.0c05356 Open Access Show Abstract ▼ Abstract: The utilization of operando spectroscopy has allowed us to watch the dynamic nature of supported metal nanoparticles. However, the realization that subtle changes to environmental conditions affect the form of the catalyst necessitates that we assess the structure of the catalyst across the reactant/product gradient that exists across a fixed bed reactor. In this study, we have performed spatial profiling of a Pd/Al2O3 catalyst during NH3 oxidation, simultaneously collecting mass spectrometry and X-ray absorption spectroscopy data at discrete axial positions along the length of the catalyst bed. The spatial analysis has provided unique insights into the structure–activity relationships that govern selective NH3 oxidation—(i) our data is consistent with the presence of PdNx after the spectroscopic signatures for bulk PdNx disappear and that there is a direct correlation to the presence of this structure and the selectivity toward N2; (ii) at high temperatures, ≥400 °C, we propose that there are two simultaneous reaction pathways—the oxidation of NH3 to NOx by PdO and the subsequent catalytic reduction of NOx by NH3 to produce N2. The results in this study confirm the structural and catalytic diversity that exists during catalysis and the need for such an understanding if improvements to important emission control technologies, such as the selective catalytic oxidation of NH3, are to be made.	Feb 2021
B18-Core EXAFS	CO2 reduction over Mo2 C-based catalysts Wijnand Marquart , Shaine Raseale , Gonzalo Prieto , Anna Zimina , Bidyut Bikash Sarma , Jan-dierk Grunwaldt , Michael Claeys , Nico Fischer Acs Catalysis DOI: 10.1021/acscatal.0c05019 Show Abstract ▼ Abstract: Four Mo-based catalysts were prepared via three different synthesis techniques supported on SiO2 and/or SBA-15. By means of complementary in situ characterization techniques, the carburization process and the final characteristics of these catalysts were investigated. Additionally, the four catalysts were evaluated for the activation of CO2 in the absence and presence of H2 (reverse water–gas shift, RWGS). The results suggest that CO2 reacts via a dissociation on the carbide surface, forming adsorbed oxygen surface species. Severe oxidation of the carbide into its oxidic phases (MoO2 or MoO3) only occurs at temperatures above 850 K in the presence of CO2. O2 dissociates on the carbide surface when introduced at low concentrations (1 vol %) at room temperature, but when exposed to higher concentrations, a strong exothermic bulk re-oxidation reaction occurs, forming MoO2. All four catalysts show high RWGS activity in terms of CO2 conversions with a minimum CO selectivity of 98% without any signs of bulk catalyst oxidation. Although minimal, the observed deactivation is suggested to be primarily due to phase changes between Mo2C allotropes (β-phase, oxycarbide, and η-phase) and/or sintering of the active phase.	Jan 2021
B18-Core EXAFS	Adsorbate-induced structural evolution of Pd catalyst for selective hydrogenation of acetylene Yanan Liu , Fengzhi Fu , Alan Mccue , Wilm Jones , Deming Rao , Junting Feng , Yufei He , Dianqing Li Acs Catalysis DOI: 10.1021/acscatal.0c03897 Show Abstract ▼ Abstract: This work describes the transformation of Pd species under reaction conditions to control the reactivity of heterogeneous catalysts, in which the real active sites for hydrogenation differ from simple Pd sites on a carbon nanofiber. Specifically, in the presence of C2H2/C2H4/H2 reaction mixtures, a permeable amorphous hydrocarbon overlayer is formed with simultaneous insertion of carbon atoms into the Pd lattice that drives the formation of low-coordinated Pd-carbide, thus providing more reactive Pd–Csub@Clayer sites (Csub: subsurface carbon; Clayer: carbon layer on the surface). The combination of these surface and subsurface effects hinders Pd-hydride, weakens ethylene adsorption confirmed by density functional theory (DFT) calculation, and thus improves catalytic behavior for selective hydrogenation of acetylene (93% ethylene selectivity at 100% conversion) with long-term stability. In the absence of hydrogen, a denser more crystalline overlayer is formed with severely restricted permeability, resulting in significantly lower activity. Moreover, by X-ray absorption spectroscopy (XAS) and in situ X-ray diffraction (XRD), it is demonstrated that different active sites dominate this catalytic reaction depending on the choice of adsorbate and exposure temperature. This work represents an alternative and arguably a simpler manner to design more reactive catalytic sites with the characteristics of long-term stability and facile preparation, which would enable promising industrial applications.	Dec 2020
I03-Macromolecular Crystallography I04-1-Macromolecular Crystallography (fixed wavelength) I04-Macromolecular Crystallography	Dissecting the mechanism of (R)-3-hydroxybutyrate dehydrogenase by kinetic isotope effects, protein crystallography, and computational chemistry Teresa F. G. Machado , Miha Purg , Stephen A. Mcmahon , Benjamin J. Read , Verena Oehler , Johan Åqvist , Tracey M. Gloster , Rafael G. Da Silva Acs Catalysis DOI: 10.1021/acscatal.0c04736 Show Abstract ▼ Abstract: The enzyme (R)-3-hydroxybutyrate dehydrogenase (HBDH) catalyzes the enantioselective reduction of 3-oxocarboxylates to (R)-3-hydroxycarboxylates, the monomeric precursors of biodegradable polyesters. Despite its application in asymmetric reduction, which prompted several engineering attempts of this enzyme, the order of chemical events in the active site, their contributions to limit the reaction rate, and interactions between the enzyme and non-native 3-oxocarboxylates have not been explored. Here, a combination of kinetic isotope effects, protein crystallography, and quantum mechanics/molecular mechanics (QM/MM) calculations were employed to dissect the HBDH mechanism. Initial velocity patterns and primary deuterium kinetic isotope effects establish a steady-state ordered kinetic mechanism for acetoacetate reduction by a psychrophilic and a mesophilic HBDH, where hydride transfer is not rate limiting. Primary deuterium kinetic isotope effects on the reduction of 3-oxovalerate indicate that hydride transfer becomes more rate limiting with this non-native substrate. Solvent and multiple deuterium kinetic isotope effects suggest hydride and proton transfers occur in the same transition state. Crystal structures were solved for both enzymes complexed to NAD+:acetoacetate and NAD+:3-oxovalerate, illustrating the structural basis for the stereochemistry of the 3-hydroxycarboxylate products. QM/MM calculations using the crystal structures as a starting point predicted a higher activation energy for 3-oxovalerate reduction catalyzed by the mesophilic HBDH, in agreement with the higher reaction rate observed experimentally for the psychrophilic orthologue. Both transition states show concerted, albeit not synchronous, proton and hydride transfers to 3-oxovalerate. Setting the MM partial charges to zero results in identical reaction activation energies with both orthologues, suggesting the difference in activation energy between the reactions catalyzed by cold- and warm-adapted HBDHs arises from differential electrostatic stabilization of the transition state. Mutagenesis and phylogenetic analysis reveal the catalytic importance of His150 and Asn145 in the respective orthologues.	Dec 2020
B18-Core EXAFS	Preparation of solid solution and layered IrOx–Ni(OH)2 oxygen evolution catalysts: toward optimizing iridium efficiency for OER Jonathan Ruiz Esquius , Gerardo Algara-siller , Simon J. Freakley , Robert Schlögl , Graham J. Hutchings , Ioannis Spanos Acs Catalysis DOI: 10.1021/acscatal.0c03866 Diamond Proposal Number(s): [18701] Show Abstract ▼ Abstract: Minimizing iridium loading in oxygen evolution reaction (OER) catalysts, without impairing electrocatalytic activity and stability is crucial to reduce the cost of water electrolysis. In this work, two Ir0.5Ni0.5Ox mixed oxide catalysts with layered and solid solution morphologies were prepared by modifying a facile hydrothermal methodology. The catalytic OER activity and stability of the Ir–Ni catalyst with a homogeneous distribution (IrNi-HD) was seriously compromised compared to pure IrOx due to the high concentration of surface nickel prone to corrosion under reaction conditions. However, the design of layered IrOx–Ni(OH)x (IrNi-LY) with Ir at the exposed surface allowed a 50% reduction in the molar concentration of the precious metal on the electrode compared to IrOx without impairing the catalytic activity or stability. As a result, IrNi-LY outperformed IrOx in activity when normalized to the Ir mass.	Nov 2020
	α-tertiary dialkyl ether synthesis via reductive photocatalytic α-functionalization of alkyl enol ethers Jamie A. Leitch , Thomas Rossolini , Tatiana Rogova , Darren J. Dixon Acs Catalysis DOI: 10.1021/acscatal.0c02584 Show Abstract ▼ Abstract: The photocatalytic construction of C(sp3)-rich α-tertiary dialkyl ethers through the reductive α-functionalization of alkyl enol ether substrates with conjugated alkenes in the presence of a Hantzsch ester terminal reductant under blue LED irradiation, is described. Pivoting on oxocarbenium ion generation via an initial TMSCl-facilitated protic activation of the enol ether substrate, subsequent single electron transfer delivers the putative nucleophilic α-oxy tertiary radical capable of productively combining with a variety of alkene substrates. The reductive functionalization strategy was simple to perform, efficient, broad in scope with respect to both alkene acceptor and enol ether donor fragments and delivered a wide range of complex α-tertiary dialkyl ether architectures.	Sep 2020

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