| 1. |
- Afewerki, Samson, et al.
(author)
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Highly Enantioselective Control of Dynamic Cascade Transformations by Dual Catalysis : Asymmetric Synthesis of Polysubstituted Spirocyclic Oxindoles
- 2015
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In: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 5:2, s. 1266-1272
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Journal article (peer-reviewed)abstract
- The highly enantioselective (up to >99.5:0.5 er) synthesis of polysubstituted spirocyclic oxindoles with four new contiguous stereocenters, including the spiro all-carbon quaternary center, is disclosed. It is accomplished by the highly stereoselective control of a dynamic conjugate/intramolecular allylic alkylation relay sequence based on the synergistic cooperation of metal and chiral amine catalysts in which the careful selection of organic Nand, metal complex, and chiral amine is essential. The intermolecular C-C bond-forming step occurred only when both the metal and chiral amine catalysts were present.
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| 2. |
- Agasti, Soumitra, et al.
(author)
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Orthogonal Selectivity in C–H Olefination : Synthesis of Branched Vinylarene with Unactivated Aliphatic Substitution
- 2019
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In: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 9:10, s. 9606-9613
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Journal article (peer-reviewed)abstract
- Oxidative coupling is a useful tool to synthesize vinylarenes. Despite remarkable successes in linear vinylarene, branched vinylarene synthesis has remained underdeveloped. Overcoming this limitation, herein, we report a chelation-assisted oxidative coupling to generate branched olefinated product in high yield. Exclusive branched selectivity was obtained using alkenyl carboxylic acid. Detailed experimental studies combined with computational investigations suggest that beta-migratory insertion, followed by a decarboxylation pathway is operative for the overall transformation.
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| 3. |
- Albinsson, David, 1990, et al.
(author)
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Shedding light on CO oxidation surface chemistry on single Pt catalyst nanoparticles inside a nanofluidic model pore
- 2021
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In: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 11:4, s. 2021-2033
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Journal article (peer-reviewed)abstract
- Investigating a catalyst under relevant application conditions is experimentally challenging and parameters like reaction conditions in terms of temperature, pressure, and reactant mixing ratios, as well as catalyst design, may significantly impact the obtained experimental results. For Pt catalysts widely used for the oxidation of carbon monoxide, there is keen debate on the oxidation state of the surface at high temperatures and at/above atmospheric pressure, as well as on the most active surface state under these conditions. Here, we employ a nanoreactor in combination with single-particle plasmonic nanospectroscopy to investigate individual Pt catalyst nanoparticles localized inside a nanofluidic model pore during carbon monoxide oxidation at 2 bar in the 450-550 K temperature range. As a main finding, we demonstrate that our single-particle measurements effectively resolve a kinetic phase transition during the reaction and that each individual particle has a unique response. Based on spatially resolved measurements, we furthermore observe how reactant concentration gradients formed due to conversion inside the model pore give rise to position-dependent kinetic phase transitions of the individual particles. Finally, employing extensive electrodynamics simulations, we unravel the surface chemistry of the individual Pt nanoparticles as a function of reactant composition and find strongly temperature-dependent Pt-oxide formation and oxygen spillover to the SiO2 support as the main processes. These results therefore support the existence of a Pt surface oxide in the regime of high catalyst activity and demonstrate the possibility to use plasmonic nanospectroscopy in combination with nanofluidics as a tool for in situ studies of individual catalyst particles.
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| 4. |
- Amrein, Beat A., et al.
(author)
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Expanding the catalytic triad in epoxide hydrolases and related enzymes
- 2015
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In: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 5:10, s. 5702-5713
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Journal article (peer-reviewed)abstract
- Potato epoxide hydrolase 1 exhibits rich enantio- and regioselectivity in the hydrolysis of a broadrange of substrates. The enzyme can be engineered to increase the yield of optically pureproducts, as a result of changes in both enantio- and regioselectivity. It is thus highly attractive inbiocatalysis, particularly for the generation of enantiopure fine chemicals and pharmaceuticals.The present work aims to establish the principles underlying the activity and selectivity of theenzyme through a combined computational, structural, and kinetic study, using the substratetrans-stilbene oxide as a model system. Extensive empirical valence bond simulations have beenperformed on the wild-type enzyme together with several experimentally characterized mutants.We are able to computationally reproduce the differences in activities between differentstereoisomers of the substrate, and the effects of mutations in several active-site residues. Inaddition, our results indicate the involvement of a previously neglected residue, H104, which iselectrostatically linked to the general base, H300. We find that this residue, which is highlyconserved in epoxide hydrolases and related hydrolytic enzymes, needs to be in its protonatedform in order to provide charge balance in an otherwise negatively-charged active site. Our datashow that unless the active-site charge balance is correctly treated in simulations, it is notpossible to generate a physically meaningful model for the enzyme that can accurately reproduceactivity and selectivity trends. We also expand our understanding of other catalytic residues,demonstrating in particular the role of a non-canonical residue, E35, as a “backup-base” in theabsence of H300. Our results provide a detailed view of the main factors driving catalysis andregioselectivity in this enzyme, and identify targets for subsequent enzyme design efforts.
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| 5. |
- Aqvist, Johan, et al.
(author)
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Conserved Motifs in Different Classes of GTPases Dictate their Specific Modes of Catalysis
- 2016
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In: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 6:3, s. 1737-1743
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Journal article (peer-reviewed)abstract
- The GTPase superfamily of enzymes that hydrolyze GTP have a number of conserved sequence regions (the so-called "G-motifs"), and several of the subfamilies also require catalytic activation by specific GTPase-activating proteins. In the translational GTPases involved in protein synthesis, this activating function is instead accomplished by their interaction with the ribosome. Despite these similarities, there are distinct differences regarding some of the amino acid residues making up the GTPase active sites. This raises the question of whether or not the catalytic mechanisms of different types of GTPases are identical. We report herein extensive computer simulations of both the intrinsic GTP hydrolysis reaction of Ras and the considerably faster reaction activated by the interaction with RasGAP. The results of these calculations are compared to earlier simulations of GTP hydrolysis by EF-Tu on the ribosome and show that the favored reaction pathways are strongly dependent on the composition of the active site. By computing Arrhenius plots for the temperature dependence of the calculated free energy profiles, we further show that different mechanistic pathways are associated with distinct differences in activation entropies and enthalpies. The activation parameters are in good agreement with experimental data, and we conclude that calculations of Arrhenius plots from computer simulations can be very useful for dissecting the energetics of enzyme catalysis.
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| 6. |
- Araujo, Rafael, et al.
(author)
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Supervised AI and Deep Neural Networks to Evaluate High-Entropy Alloys as Reduction Catalysts in Aqueous Environments
- 2024
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In: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 14:6, s. 3742-3755
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Journal article (peer-reviewed)abstract
- Competitive surface adsorption energies on catalytic surfaces constitute a fundamental aspect of modeling electrochemical reactions in aqueous environments. The conventional approach to this task relies on applying density functional theory, albeit with computationally intensive demands, particularly when dealing with intricate surfaces. In this study, we present a methodological exposition of quantifying competitive relationships within complex systems. Our methodology leverages quantum-mechanical-guided deep neural networks, deployed in the investigation of quinary high-entropy alloys composed of Mo-Cr-Mn-Fe-Co-Ni-Cu-Zn. These alloys are under examination as prospective electrocatalysts, facilitating the electrochemical synthesis of ammonia in aqueous media. Even in the most favorable scenario for nitrogen fixation identified in this study, at the transition from O and OH coverage to surface hydrogenation, the probability of N2 coverage remains low. This underscores the fact that catalyst optimization alone is insufficient for achieving efficient nitrogen reduction. In particular, these insights illuminate that system consideration with oxygen- and hydrogen-repelling approaches or high-pressure solutions would be necessary for improved nitrogen reduction within an aqueous environment.
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| 7. |
- Armillotta, Francesco, et al.
(author)
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Single Metal Atom Catalysts and ORR : H-Bonding, Solvation, and the Elusive Hydroperoxyl Intermediate
- 2022
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In: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 12:13, s. 7950-7959
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Journal article (peer-reviewed)abstract
- The widely investigated oxygen reduction reaction (ORR) is well-known to proceed via two competing routes, involving two or four electrons, and yielding different reaction products, respectively. Both pathways are believed to share a common, elusive intermediate, namely, the hydroperoxyl radical. By exploiting a cobalt single-atom biomimetic model catalyst, based on a self-assembled monolayer of Co-porphyrins grown on an almost free-standing graphene sheet, we identify, in situ at room temperature in O2+H2O atmosphere, a hydroperoxyl-water cluster that is stabilized at the Co single-metal atom catalytic site. We show that the interplay between charge transfer, dipole and H-bonding, and water solvation behavior actually determines the hydroperoxyl-water complex stability, the Co-OOH bonding geometry, and, prospectively, opens to the engineered control of the selectivity of ORR pathways.
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| 8. |
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| 9. |
- Babucci, Melike, et al.
(author)
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Tuning the Selectivity of Single-Site Supported Metal Catalysts with Ionic Liquids
- 2017
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In: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 7:10, s. 6969-6972
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Journal article (peer-reviewed)abstract
- 1,3-Dialkylimidazolium ionic liquid coatings act as electron donors, increasing the selectivity for partial hydrogenation of 1,3-butadiene catalyzed by iridium complexes supported on high-surface-area gamma-Al2O3. High-energy-resolution fluorescence detection X-ray absorption near-edge structure (HERFD XANES) measurements quantify the electron donation and are correlated with the catalytic activity and selectivity. The results demonstrate broad opportunities to tune electronic environments and catalytic properties of atomically dispersed supported metal catalysts.
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| 10. |
- Bagnall, Andrew J., et al.
(author)
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Molecular Engineering of Electrocatalytic Nanomaterials for Hydrogen Evolution : The Impact of Structural and Electronic Modifications of Anchoring Linkers on Electrocatalysis
- 2024
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In: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 14:8, s. 5630-5638
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Journal article (peer-reviewed)abstract
- The anticipated shortage of an increasing number of critical elements, especially metals, requires a shift toward molecularly defined materials with low metal loadings. More particularly, surface-anchored molecular catalysts are attractive to prospectively enable cost-effective electrochemical hydrogen evolution. However, the design of ligands integrating specific anchoring unit(s) for the immobilization of molecular catalysts can be challenging and has direct consequences for the intrinsic properties of the grafted complex. In this work, two cobalt tetraazamacrocyclic complexes bearing pyrene anchoring groups at different positions on the macrocyclic ligands were synthesized. The pyrene unit allows for simple immobilization and electrochemical characterization of the two complexes on multi-walled carbon nanotube-based electrodes. Thorough electrochemical and electrocatalytic investigation demonstrates important differences between the two closely related catalysts in terms of catalyst loading, catalytic response, and stability over time, with a significantly higher stability observed at pH 7 than at pH 2.
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