B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS
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Diamond Proposal Number(s):
[35264]
Open Access
Abstract: The distribution of elements within alloy nanoparticles is a critical parameter for their electrocatalytic performance. Here, we use the case of a Pt3Ni alloy to show that this elemental distribution can dynamically respond to the applied potential, leading to strongly potential-dependent catalytic properties. Starting from the Pt3Ni core and Pt shell structure that forms in acid electrolyte due to Ni leaching, our electrochemical X-ray photoelectron spectroscopy measurements show that the Ni atoms can be reversibly moved between the core of the particles and the near-surface region using the applied potential. Through potential jump measurements, we show that this Ni migration modulates the hydrogen evolution reaction activity of the particles by over 30%. These observations highlight the potential of incorporating in situ restructuring of alloys as the final step in electrocatalyst design.
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Jul 2025
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I24-Microfocus Macromolecular Crystallography
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Diamond Proposal Number(s):
[36008]
Abstract: Transaldolases are essential enzymes across all life domains, facilitating the exchange of aldol fragments in metabolic processes. AprG, a transaldolase in the apramycin biosynthetic pathway, catalyzes the incorporation of C7′ and C8′ moieties into the bicyclic octose core. Unlike canonical transaldolases, the AprG product exhibits unique stereochemical inversion, whose mechanism remains unclear. Here, by taking snapshots of AprG at different stages of the reaction, we identified active site residues essential for each reaction step. Strikingly, we discovered a 7′-epimer of the AprG product, directly implicating this inversion in the enzyme’s mechanism and uncovering a key aspect of product inhibition. This unexpected epimer sheds a light on the stereochemical plasticity of transaldolases. Additionally, donor analogue studies provided insights into substrate recognition. These findings enhance our mechanistic understanding of AprG and suggest strategies for engineering biocatalysts with tailored stereochemical properties. More broadly, this work provides a framework for modifying transaldolase activity, expanding its potential applications in chemoenzymatic synthesis and metabolic engineering.
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Jul 2025
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B18-Core EXAFS
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Diamond Proposal Number(s):
[34632]
Abstract: Bimetallic palladium (Pd) and gold (Au) systems are active for promoting the selective oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA), a key building block for producing polyethylene furanoate, a biobased polymer to substitute poly(ethylene terephthalate). Here, an FDCA yield of ∼99% was achieved over a physical mixture of 1.5 wt % Au/C and 1.5 wt % Pd/C (Pd/Au molar ratio of 5:1) under mild conditions (90 °C, 1 bar O2), outperforming bimetallic core–shell Au@Pd/C (∼90% FDCA yield) or alloyed AuPd/C (∼73% FDCA yield) systems. To gain insights into the synergy between the two monometallic catalysts, a series of kinetic studies were conducted employing either HMF or its intermediates as substrates in catalytic oxidation systems over either Pd/C or Au/C. The results show distinct selectivity preference of the two catalysts: Pd/C favors the 2,5-diformylfuran pathway (DFF), while Au/C follows the 5-hydroxymethyl-2-furancarboxylic acid (HFCA) pathway, as well as the presence of base-induced Cannizzaro disproportionation (CD) reactions. The advantage of the physical mixture system is largely attributed to the synergy between the two metals, which promotes the DFF pathway (over the HFCA route) and suppresses CD reactions, facilitating a more rapid progression of the overall oxidation cascade process. Catalyst recycling studies reveal deactivation of the physical mixture system (FDCA yield dropped to 62% after 3 cycles), with detailed comparative characterization of the fresh and used catalysts identifying operando Pd leaching and subsequent deposition onto Au/C, forming a core (Au)–shell (Pd) structure, as the origin of the diminished activity. Our findings challenge the conventional view regarding the alloy superiority in the selective oxidation of HMF, showing that systems based on simple physical mixtures of monometallic catalysts could be a more effective and practical strategy for progressing FDCA production via selective HMF oxidation.
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Jun 2025
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B18-Core EXAFS
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Adrián
García-Zaragoza
,
José Luis
Del Río-Rodríguez
,
Christian
Cerezo-Navarrete
,
Silvia
Gutiérrez-Tarriño
,
M. Asunción
Molina
,
Lucy
Costley-Wood
,
Jaime
Mazarío
,
Bruno
Chaudret
,
Luis M.
Martínez-Prieto
,
Andrew M.
Beale
,
Pascual
Oña-Burgos
Diamond Proposal Number(s):
[34632]
Open Access
Abstract: Reducing CO2 to CO via the reverse water–gas shift (RWGS) reaction is a promising strategy for carbon capture and utilization (CCU). In this study, tailored magnetic catalysts were designed through the pyrolysis of a Co-based MOF to form well-defined nanoparticles. As a result, carbon-encapsulated cobalt nanoparticles (Co@C) and palladium-doped cobalt nanoparticles (CoPd/Co@C) were synthesized and thoroughly characterized using a variety of techniques, including in situ X-ray absorption and diffraction experiments. These carbon-based catalysts were simultaneously used as heating agents and catalysts for the magnetically induced RWGS reaction, exhibiting remarkable activity and selectivity for syngas production. CO2 conversions of 61.1% and 71.1% were obtained for Co@C and CoPd/Co@C (63 mT, 2 kW, 320 kHz), respectively. Using magnetic induction heating (MIH), these catalysts operate at lower local temperatures and with greater energy efficiency than conventional thermal heating, while achieving superior CO production efficiency. Notably, CoPd/Co@C achieved highly satisfactory CO production efficiency (478.5 mLCO/kW·h), demonstrating a significant improvement compared to the analogous process utilizing magnetically induced heating. Furthermore, CoPd/Co@C exhibited unwavering stability, maintaining its performance for more than 200 h without significant degradation or need for reactivation. This study highlights the potential of MIH for industrial applications in CO2 reduction, offering a more renewable and economically viable alternative to traditional methods.
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May 2025
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I20-Scanning-X-ray spectroscopy (XAS/XES)
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Diamond Proposal Number(s):
[24399]
Open Access
Abstract: The catalytic conversion of C–H to C–F bonds is a critical synthetic transformation of relevance to the pharmaceutical, agrochemical, and medicinal chemical industries. When coupled with an oxidant and a fluorine donor, biomimetic Mn-porphyrins have been shown to be capable of achieving this reaction. However, the definition of the active forms of these fluorinating Mn-porphyrins remains an unsolved challenge, which limits mechanistic understanding of the process and makes it challenging to systematically design better catalytic materials. Herein, we present a combination of kinetic, spectroscopic, and theoretical studies focused on alkane fluorination over Mn-containing porphyrins. Specifically, by correlating kinetic studies with resonance Raman, UV–vis, and high-energy resolution fluorescence detected X-ray absorption spectroscopic analysis of the various states of the catalyst, we provide evidence that a 6-coordinated Mn(IV) complex with −F and −OI(F)Ar axial ligands is the active species responsible for selective fluorination via Hydrogen Atom Transfer. This active state is distinct from the Mn═O species previously proposed to be the active intermediates for alkane fluorination and oxidation.
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Mar 2025
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B18-Core EXAFS
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Diamond Proposal Number(s):
[34632]
Open Access
Abstract: Ethylene produced from steam cracking includes an acetylene impurity of 0.5–3%, harming the downstream polymerization process. To achieve polymer-grade ethylene, acetylene must be removed by chemoselective hydrogenation to ethylene without overhydrogenation to ethane. The current state-of-the-art process uses supported Pd nanoparticles (NPs) and toxic CO injections to poison the active sites, which is expensive and shows poor ethylene selectivity. To tackle this issue, the use of single-atom catalysts can offer a way to simultaneously improve selectivity through preferential desorption of ethylene over its hydrogenation and minimize cost. In particular, single-atom cobalt catalysis can address both of these issues. However, to date, single-atom cobalt has not been tested for this reaction. Herein, we present a cost-effective monometallic, cobalt-anchored zeolite Y (Co1@Y) catalyst, synthesized via an in situ hydrothermal method, holding isolated active cobalt atoms that efficiently and selectively hydrogenate acetylene to ethylene. Characterization techniques proved the absence of NPs and the presence of single-atom cobalt sites. The catalyst achieved an ethylene selectivity of 90 ± 2% at full acetylene conversion, with a stable performance for over 400 h. Co1@Y achieved TOFethylene greater than the previously reported zeolite-supported single-atom catalysts by ∼5 times. Varying the dispersion of cobalt from an NP to a single atom modified the reaction mechanism from associative to dissociative, remarkably improving catalytic activity and selectivity. This strategy can be extended to other relatively inactive metals and other hydrogenation reactions.
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Feb 2025
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E02-JEM ARM 300CF
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Diamond Proposal Number(s):
[32035]
Open Access
Abstract: Bimetallic manganese–ruthenium nanoparticles of defined Mn:Ru ratios were prepared on an imidazolium-based supported ionic liquid phase. Characterization of the resulting MnxRu100–x@SILP materials by electron microscopy evidenced the formation of small (1.3–3.6 nm) and well-dispersed nanoparticles (NPs) containing Mn and Ru in the expected ratios. X-ray absorption spectroscopy (XAS) studies revealed that no significant levels of alloying occurred in these NPs that contain mainly oxidized Mn species and metallic Ru, consistent with the immiscibility of the two metals and the high oxophilicity of Mn. The hydrogenation performance of MnxRu100–x@SILP materials was probed using benzylideneacetone as model substrate containing three distinct reducible moieties. Albeit the two metals are present in distinct phases, the Mn:Ru ratio was found to have a strong impact on activity and selectivity with trends similar to what was previously reported for alloyed FexRu100–x@SILP and CoxRu100–x@SILP catalysts. In particular, a sharp switch of 6-membered aromatic ring hydrogenation between Mn15Ru85 (full ring hydrogenation) and Mn25Ru75 (no ring hydrogenation) was observed. These results demonstrate that alloying is not a requirement to observe synergistic effects from the combination of 3d metals and noble metals in NPs, opening new opportunities for the development of bimetallic catalysts for selective hydrogenation.
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Feb 2025
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I03-Macromolecular Crystallography
I04-Macromolecular Crystallography
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Diamond Proposal Number(s):
[37236]
Open Access
Abstract: Reductive amination is one of the most synthetically direct routes to access chiral amines. Several Imine Reductases (IREDs) have been discovered to catalyze reductive amination (Reductive Aminases or RedAms), yet they are dependent on the expensive phosphorylated nicotinamide adenine dinucleotide cofactor NADPH and usually more active at basic pH. Here, we describe the discovery and synthetic potential of an IRED from Rhodococcus erythropolis (RytRedAm) that catalyzes reductive amination between a series of medium to large carbonyl and amine compounds with conversions of up to >99% and 99% enantiomeric excess at neutral pH. RytRedAm catalyzes the formation of a substituted γ-lactam and N-methyl-1-phenylethanamine with stereochemistry opposite to that of fungal RedAms, giving the (S)-enantiomer. This enzyme remarkably uses both NADPH and NADH cofactors with KM values of 15 and 247 μM and turnover numbers kcat of 3.6 and 9.0 s–1, respectively, for the reductive amination of hexanal with allylamine. The crystal structure obtained provides insights into the flexibility to also accept NADH, with residues R35 and I69 diverging from that of other IREDs/RedAms in the otherwise conserved Rossmann fold. RytRedAm thus represents a subfamily of enzymes that enable synthetic applications using NADH-dependent reductive amination to access complementary chiral amine products.
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Dec 2024
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I03-Macromolecular Crystallography
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Abstract: The assembly of artificial metalloenzymes (ArMs) provides a second coordination sphere around a metal catalyst. Such a well-defined microenvironment can lead to an enhancement of the activities and selectivity of the catalyst. Herein, we present the development of artificial hydroxylase (ArHase) by embedding an Fe-TAML (TAML = tetraamide macrocyclic ligand) catalyst into a human carbonic anhydrase II (hCAII). Incorporation of the Fe-TAML catalyst ([BS-Fe-bTAML]–) within hCAII enhanced the total turnover number (TTON) for the hydroxylation of benzylic C–H bonds. After engineering a thermostable variant of hCAII (hCAIITS), the resulting ArHase, [BS-Fe-bTAML]–·hCAIITS, was subjected to directed evolution using cell lysates in a 384-well format. After three rounds of laboratory evolution, the best-performing variants exhibited enhancement in the initial rate (124.4 min–1) and in the TTON (2629 TTON) for the hydroxylation of benzylic C–H bonds compared to that of the free cofactor. We surmise that an arginine residue introduced in the course of directed evolution engages in hydrogen bonding with [BS-Fe-bTAML]–. This study highlights the potential of relying on a thermostable host protein to improve the catalytic performance of hCAII-based ArMs.
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Nov 2024
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I03-Macromolecular Crystallography
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Diamond Proposal Number(s):
[20303]
Open Access
Abstract: Ene reductases (EREDs) catalyze asymmetric reduction with exquisite chemo-, stereo-, and regioselectivity. Recent discoveries led to unlocking other types of reactivities toward oxime reduction and reductive C–C bond formation. Exploring nontypical reactions can further expand the biocatalytic knowledgebase, and evidence alludes to yet another variant reaction where flavin mononucleotide (FMN)-bound ERs from the old yellow enzyme family (OYE) have unconventional activity with α,β-dicarbonyl substrates. In this study, we demonstrate the nonconventional stereoselective monoreduction of α,β-dicarbonyl to the corresponding chiral hydroxycarbonyl, which are valuable building blocks for asymmetric synthesis. We explored ten α,β-dicarbonyl aliphatic, cyclic, or aromatic compounds and tested their reduction with five OYEs and one nonflavin-dependent double bond reductase (DBR). Only GluER reduced aliphatic α,β-dicarbonyls, with up to 19% conversion of 2,3-hexanedione to 2-hydroxyhexan-3-one with an R-selectivity of 83% ee. The best substrate was the aromatic α,β-dicarbonyl 1-phenyl-1,2-propanedione, with 91% conversion to phenylacetylcarbinol using OYE3 with R-selectivity >99.9% ee. Michaelis–Menten kinetics for 1-phenyl-1,2-propanedione with OYE3 gave a turnover kcat of 0.71 ± 0.03 s–1 and a Km of 2.46 ± 0.25 mM. Twenty-four EREDs from multiple classes of OYEs and DBRs were further screened on 1-phenyl-1,2-propanedione, showing that class II OYEs (OYE3-like) have the best overall selectivity and conversion. EPR studies detected no radical signal, whereas NMR studies with deuterium labeling indicate proton incorporation at the benzylic carbonyl carbon from the solvent and not the FMN hydride. A crystal structure of OYE2 with 1.5 Å resolution was obtained, and docking studies showed a productive pose with the substrate.
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Oct 2024
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