B18-Core EXAFS
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Alexander
Parastaev
,
Valery
Muravev
,
Elisabet
Huertas Osta
,
Tobias F.
Kimpel
,
Jérôme F. M.
Simons
,
Arno J. F.
Van Hoof
,
Evgeny
Uslamin
,
Long
Zhang
,
Job J. C.
Struijs
,
Dudari B.
Burueva
,
Ekaterina V.
Pokochueva
,
Kirill V.
Kovtunov
,
Igor V.
Koptyug
,
Ignacio J.
Villar-Garcia
,
Carlos
Escudero
,
Thomas
Altantzis
,
Pei
Liu
,
Armand
Béché
,
Sara
Bals
,
Nikolay
Kosinov
,
Emiel J. M.
Hensen
Diamond Proposal Number(s):
[20715]
Abstract: A high dispersion of the active metal phase of transition metals on oxide supports is important when designing efficient heterogeneous catalysts. Besides nanoparticles, clusters and even single metal atoms can be attractive for a wide range of reactions. However, many industrially relevant catalytic transformations suffer from structure sensitivity, where reducing the size of the metal particles below a certain size substantially lowers catalytic performance. A case in point is the low activity of small cobalt nanoparticles in the hydrogenation of CO and CO2. Here we show how engineering of catalytic sites at the metal–oxide interface in cerium oxide–zirconium dioxide (ceria–zirconia)-supported cobalt can overcome this structure sensitivity. Few-atom cobalt clusters dispersed on 3 nm cobalt(II)-oxide particles stabilized by ceria–zirconia yielded a highly active CO2 methanation catalyst with a specific activity higher than that of larger particles under the same conditions.
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Nov 2022
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I03-Macromolecular Crystallography
I04-1-Macromolecular Crystallography (fixed wavelength)
I04-Macromolecular Crystallography
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Elizabeth L.
Bell
,
Ross
Smithson
,
Siobhan
Kilbride
,
Jake
Foster
,
Florence J.
Hardy
,
Saranarayanan
Ramachandran
,
Aleksander A.
Tedstone
,
Sarah J.
Haigh
,
Arthur A.
Garforth
,
Philip J. R.
Day
,
Colin
Levy
,
Michael P.
Shaver
,
Anthony P.
Green
Diamond Proposal Number(s):
[12788, 17773]
Abstract: The recent discovery of IsPETase, a hydrolytic enzyme that can deconstruct poly(ethylene terephthalate) (PET), has sparked great interest in biocatalytic approaches to recycle plastics. Realization of commercial use will require the development of robust engineered enzymes that meet the demands of industrial processes. Although rationally engineered PETases have been described, enzymes that have been experimentally optimized via directed evolution have not previously been reported. Here, we describe an automated, high-throughput directed evolution platform for engineering polymer degrading enzymes. Applying catalytic activity at elevated temperatures as a primary selection pressure, a thermostable IsPETase variant (HotPETase, Tm = 82.5 °C) was engineered that can operate at the glass transition temperature of PET. HotPETase can depolymerize semicrystalline PET more rapidly than previously reported PETases and can selectively deconstruct the PET component of a laminated multimaterial. Structural analysis of HotPETase reveals interesting features that have emerged to improve thermotolerance and catalytic performance. Our study establishes laboratory evolution as a platform for engineering useful plastic degrading enzymes.
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Aug 2022
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B18-Core EXAFS
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Diamond Proposal Number(s):
[22225]
Abstract: In recent years, noble metals atomically dispersed on solid oxide supports have become a frontier of heterogeneous catalysis. In pursuit of an ultimate atom efficiency, the stability of single-atom catalysts is pivotal. Here we compare two Pd/CeO2 single-atom catalysts that are active in low-temperature CO oxidation and display drastically different structural dynamics under the reaction conditions. These catalysts were obtained by conventional impregnation on hydrothermally synthesized CeO2 and one-step flame spray pyrolysis. The oxidized Pd atoms in the impregnated catalyst were prone to reduction and sintering during CO oxidation, whereas they remained intact on the surface of the Pd-doped CeO2 derived by flame spray pyrolysis. A detailed in situ characterization linked the stability of the Pd single atoms to the reducibility of the Pd–CeO2 interface and the extent of reverse oxygen spillover. To understand the chemical phenomena that underlie the metal–support interactions is crucial to the rational design of stable single-atom catalysts.
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Jun 2021
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E02-JEM ARM 300CF
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Lele
Peng
,
Ziyang
Wei
,
Chengzhang
Wan
,
Jing
Lin
,
Zhuo
Chen
,
Dan
Zhu
,
Daniel
Baumann
,
Haotian
Liu
,
Christopher S.
Allen
,
Xiang
Xu
,
Angus I.
Kirkland
,
Imran
Shakir
,
Zeyad
Almutairi
,
Sarah
Tolbert
,
Bruce
Dunn
,
Yu
Huang
,
Philippe
Sautet
,
Xiangfeng
Duan
Diamond Proposal Number(s):
[23956]
Abstract: The fundamental kinetics of the electrocatalytic sulfur reduction reaction (SRR), a complex 16-electron conversion process in lithium–sulfur batteries, is so far insufficiently explored. Here, by directly profiling the activation energies in the multistep SRR, we reveal that the initial reduction of sulfur to the soluble polysulfides is relatively easy owing to the low activation energy, whereas the subsequent conversion of the polysulfides into the insoluble Li2S2/Li2S has a much higher activation energy, contributing to the accumulation of polysulfides and exacerbating the polysulfide shuttling effect. We use heteroatom-doped graphene as a model system to explore electrocatalytic SRR. We show that nitrogen and sulfur dual-doped graphene considerably reduces the activation energy to improve SRR kinetics. Density functional calculations confirm that the doping tunes the p-band centre of the active carbons for an optimal adsorption strength of intermediates and electroactivity. This study establishes electrocatalysis as a promising pathway to tackle the fundamental challenges facing lithium–sulfur batteries.
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Sep 2020
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B18-Core EXAFS
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Diamond Proposal Number(s):
[20715]
Abstract: Metal–support interactions have a strong impact on the performance of heterogeneous catalysts. Specific sites at the metal–support interface can give rise to unusual high reactivity, and there is a growing interest in optimizing not only the properties of metal particles but also the metal–support interface. Here, we demonstrate how varying the particle size of the support (ceria–zirconia) can be used to tune the metal–support interactions, resulting in a substantially enhanced CO2 hydrogenation rate. A combination of X-ray diffraction, X-ray absorption spectroscopy, near-ambient pressure X-ray photoelectron spectroscopy, transmission electron microscopy and infrared spectroscopy provides insight into the active sites at the interface between cobalt and ceria–zirconia involved in CO2 hydrogenation to CH4. Reverse oxygen spillover from the support during treatment in hydrogen results in the generation of oxygen vacancies. Stabilization of cobalt particles by ceria–zirconia particles of intermediate size leads to oxygen spillover to the support during the CO2 and CO dissociation steps, followed by further hydrogenation of the resulting intermediates on cobalt.
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May 2020
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E01-JEM ARM 200CF
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Haohong
Duan
,
Jin-Cheng
Liu
,
Ming
Xu
,
Yufei
Zhao
,
Xue-Lu
Ma
,
Juncai
Dong
,
Xusheng
Zheng
,
Jianwei
Zheng
,
Christopher
Allen
,
Mohsen
Danaie
,
Yung-Kang
Peng
,
Titipong
Issariyakul
,
Dongliang
Chen
,
Angus
Kirkland
,
Jean-Charles
Buffet
,
Jun
Li
,
Shik Chi Edman
Tsang
,
Dermot
O'Hare
Diamond Proposal Number(s):
[16969, 17397]
Abstract: Although molecular dinitrogen (N2) is widely used as a carrier or inert gas for many catalytic reactions, it is rarely considered as a catalytic promoter. Here, we report that N2 could be used to reduce the activation energy for catalytic hydrodeoxygenation over ruthenium-based catalysts. Specifically, we report a 4.3-fold activity increase in the catalytic hydrodeoxygenation of p-cresol to toluene over a titanium oxide supported ruthenium catalyst (Ru/TiO2) by simply introducing 6 bar N2 under batch conditions at 160 °C and 1 bar hydrogen. Detailed investigations indicate that N2 can be adsorbed and activated on the metallic ruthenium surface to form hydrogenated nitrogen species, which offer protic hydrogen to lower the activation energy of direct carbonaromatic–oxygen bond scission and the hydrogenation of hydroxy groups. Thus, by employing different ruthenium catalysts, including Ru/TiO2, Ru/Al2O3, Ru/ZrO2 and Ru/C, we demonstrate that N2 promotion of hydrodeoxygenation can be regarded as a general strategy.
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Oct 2019
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I04-Macromolecular Crystallography
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Rory
Little
,
Fernanda C. R.
Paiva
,
Robert
Jenkins
,
Hui
Hong
,
Yuhui
Sun
,
Yuliya
Demydchuk
,
Markiyan
Samborskyy
,
Manuela
Tosin
,
Finian J.
Leeper
,
Marcio V. B.
Dias
,
Peter F.
Leadlay
Abstract: Enzymes that catalyse remarkable Diels–Alder-like [4+2] cyclizations have been previously implicated in the biosynthesis of spirotetronate and spirotetramate antibiotics. Biosynthesis of the polyether antibiotic tetronasin is not expected to require such steps, yet the tetronasin gene cluster encodes enzymes Tsn11 and Tsn15, which are homologous to authentic [4+2] cyclases. Here, we show that deletion of Tsn11 led to accumulation of a late-stage intermediate, in which the two central rings of tetronasin and four of its twelve asymmetric centres remain unformed. In vitro reconstitution showed that Tsn11 catalyses an apparent inverse-electron-demand hetero-Diels–Alder-like [4+2] cyclization of this species to form an unexpected oxadecalin compound that is then rearranged by Tsn15 to form tetronasin. To gain structural and mechanistic insight into the activity of Tsn15, the crystal structure of a Tsn15-substrate complex has been solved at 1.7 Å resolution.
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Oct 2019
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B18-Core EXAFS
E01-JEM ARM 200CF
I20-Scanning-X-ray spectroscopy (XAS/XES)
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Margherita
Macino
,
Alexandra J.
Barnes
,
Sultan M.
Althahban
,
Ruiyang
Qu
,
Emma K.
Gibson
,
David J.
Morgan
,
Simon J.
Freakley
,
Nikolaos
Dimitratos
,
Christopher J.
Kiely
,
Xiang
Gao
,
Andrew M.
Beale
,
Donald
Bethell
,
Qian
He
,
Meenakshisundaram
Sankar
,
Graham J.
Hutchings
Diamond Proposal Number(s):
[15151, 22776]
Abstract: The catalytic activities of supported metal nanoparticles can be tuned by appropriate design of synthesis strategies. Each step in a catalyst synthesis method can play an important role in preparing the most efficient catalyst. Here we report the careful manipulation of the post-synthetic heat treatment procedure—together with control over the metal loading—to prepare a highly efficient 0.2 wt% Pt/TiO2 catalyst for the chemoselective hydrogenation of 3-nitrostyrene. For Pt/TiO2 catalysts with 0.2 and 0.5 wt% loading levels, reduction at 450 °C induces the coverage of TiOx over Pt nanoparticles through a strong metal–support interaction, which is detrimental to their catalytic activities. However, this can be avoided by following calcination treatment with reduction (both at 450 °C), allowing us to prepare an exceptionally active catalyst. Detailed characterization has revealed that the peripheral sites at the Pt/TiO2 interface are the most likely active sites for this hydrogenation reaction.
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Sep 2019
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I04-1-Macromolecular Crystallography (fixed wavelength)
I04-Macromolecular Crystallography
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Ombeline
Mayol
,
Karine
Bastard
,
Lilian
Beloti
,
Amina
Frese
,
Johan
Turkenburg
,
Jean-Louis
Petit
,
Aline
Mariage
,
Adrien
Debard
,
Virginie
Pellouin
,
Alain
Perret
,
Véronique
De Berardinis
,
Anne
Zaparucha
,
Gideon
Grogan
,
Carine
Vergne-Vaxelaire
Diamond Proposal Number(s):
[9948]
Abstract: The asymmetric reductive amination of ketones enables the one-step synthesis of chiral amines from readily available starting materials. Here we report the discovery of a family of native NAD(P)H-dependent amine dehydrogenases (nat-AmDHs) competent for the asymmetric reductive amination of aliphatic and alicyclic ketones, adding significantly to the biocatalytic toolbox available for chiral amine synthesis. Studies of ketone and amine substrate specificity and kinetics reveal a strong preference for aliphatic ketones and aldehydes, with activities of up to 614.5 mU mg−1 for cyclohexanone with ammonia, and 851.3 mU mg−1 for isobutyraldehyde with methylamine as the amine donor. Crystal structures of three nat-AmDHs (AmDH4, MsmeAmDH and CfusAmDH) reveal the active site determinants of substrate and cofactor specificity and enable the rational engineering of AmDH4 for the generated activity towards pentan-2-one. Analysis of the three-dimensional catalytic site distribution among bacterial biodiversity revealed a superfamily of divergent proteins with representative specificities ranging from amino acid substrates to hydrophobic ketones.
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Mar 2019
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I03-Macromolecular Crystallography
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Diamond Proposal Number(s):
[12342]
Abstract: Oxygen heterocycles—in particular, tetrahydropyrans (THPs) and tetrahydrofurans—are common structural features of many biologically active polyketide natural products. Mupirocin is a clinically important antibiotic isolated from Pseudomonas fluorescens and is assembled on a THP ring, which is essential for bioactivity. However, the biosynthesis of this moiety has remained elusive. Here, we show an oxidative enzyme-catalysed cascade that generates the THP ring of mupirocin. Rieske non-haem oxygenase (MupW)-catalysed selective oxidation of the C8–C16 single bond in a complex acyclic precursor is combined with an epoxide hydrolase (MupZ) to catalyse the subsequent regioselective ring formation to give the hydroxylated THP. In the absence of MupZ, a five-membered tetrahydrofuran ring is isolated, and model studies are consistent with cyclization occurring via an epoxide intermediate. High-resolution X-ray crystallographic studies, molecular modelling and mutagenesis experiments of MupZ provide insights into THP ring formation proceeding via an anti-Baldwin 6-endo-tet cyclization.
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Dec 2018
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