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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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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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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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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B18-Core EXAFS
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Antonis M.
Messinis
,
Stephen L. J.
Luckham
,
Peter P.
Wells
,
Diego
Gianolio
,
Emma K.
Gibson
,
Harry M.
O’brien
,
Hazel A.
Sparkes
,
Sean A.
Davis
,
June
Callison
,
David
Elorriaga
,
Oscar
Hernandez-fajardo
,
Robin B.
Bedford
Diamond Proposal Number(s):
[15151]
Abstract: Iron-catalysed cross-coupling is undergoing explosive development, but mechanistic understanding lags far behind synthetic methodology. Here, we find that the activity of iron–diphosphine pre-catalysts in the Negishi coupling of benzyl halides is strongly dependent on the diphosphine, but the ligand does not appear to be coordinated to the iron during turnover. This was determined using time-resolved in operando X-ray absorption fine structure spectroscopy employing a custom-made flow cell and confirmed by 31P NMR spectroscopy. While the diphosphine ligands tested are all able to coordinate to iron(ii), in the presence of excess zinc(ii)—as in the catalytic reaction—they coordinate predominantly to the zinc. Furthermore, combined synthetic and kinetic investigations implicate the formation of a putative mixed Fe–Zn(dpbz) species before the rate-limiting step of catalysis. These unexpected findings may not only impact the field of iron-catalysed Negishi cross-coupling, but potentially beyond to reactions catalysed by other transition metal/diphosphine complexes.
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Dec 2018
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I03-Macromolecular Crystallography
I04-Macromolecular Crystallography
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Diamond Proposal Number(s):
[13587]
Abstract: Artificial metalloenzymes that contain protein-anchored synthetic catalysts are attracting increasing interest. An exciting, but still unrealized advantage of non-covalent anchoring is its potential for reversibility and thus component recycling. Here we present a siderophore–protein combination that enables strong but redox-reversible catalyst anchoring, as exemplified by an artificial transfer hydrogenase (ATHase). By linking the iron(iii)-binding siderophore azotochelin to an iridium-containing imine-reduction catalyst that produces racemic product in the absence of the protein CeuE, but a reproducible enantiomeric excess if protein bound, the assembly and reductively triggered disassembly of the ATHase was achieved. The crystal structure of the ATHase identified the residues involved in high-affinity binding and enantioselectivity. While in the presence of iron(iii), the azotochelin-based anchor binds CeuE with high affinity, and the reduction of the coordinated iron(iii) to iron(ii) triggers its dissociation from the protein. Thus, the assembly of the artificial enzyme can be controlled via the iron oxidation state.
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Aug 2018
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E02-JEM ARM 300CF
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Huilong
Fei
,
Juncai
Dong
,
Yexin
Feng
,
Christopher
Allen
,
Chengzhang
Wan
,
Boris
Volosskiy
,
Mufan
Li
,
Zipeng
Zhao
,
Yiliu
Wang
,
Hongtao
Sun
,
Pengfei
An
,
Wenxing
Chen
,
Zhiying
Guo
,
Chain
Lee
,
Dongliang
Chen
,
Imran
Shakir
,
Mingjie
Liu
,
Tiandou
Hu
,
Yadong
Li
,
Angus I.
Kirkland
,
Xiangfeng
Duan
,
Yu
Huang
Diamond Proposal Number(s):
[16967]
Abstract: Single-atom catalysts (SACs) have recently attracted broad research interest as they combine the merits of both homogeneous and heterogeneous catalysts. Rational design and synthesis of SACs are of immense significance but have so far been plagued by the lack of a definitive correlation between structure and catalytic properties. Here, we report a general approach to a series of monodispersed atomic transition metals (for example, Fe, Co, Ni) embedded in nitrogen-doped graphene with a common MN4C4 moiety, identified by systematic X-ray absorption fine structure analyses and direct transmission electron microscopy imaging. The unambiguous structure determination allows density functional theoretical prediction of MN4C4 moieties as efficient oxygen evolution catalysts with activities following the trend Ni > Co > Fe, which is confirmed by electrochemical measurements. Determination of atomistic structure and its correlation with catalytic properties represents a critical step towards the rational design and synthesis of precious or nonprecious SACs with exceptional atom utilization efficiency and catalytic activities.
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Jan 2018
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