1,879 results match your criteria catalyses isomerization


Effect of External Surface Diffusion Barriers on Pt/Beta Catalyzed Isomerization of n-Pentane.

Angew Chem Int Ed Engl 2021 Apr 15. Epub 2021 Apr 15.

East China University of Science and Technology, School of Chemical Engineering, CHINA.

Zeolite crystals contain transport barriers on their external surface that hinder molecular uptake and processes that depend on it, such as catalysis and separations. However, the potentially dominant role of surface barriers in such processes is only emerging. In this work, we have developed a generalizable strategy to quantify the effect of surface barriers on zeolite catalysis. Read More

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Identification of extremely hard coke generation by low-temperature reaction on tungsten catalysts via Operando and in situ techniques.

Sci Rep 2021 Apr 13;11(1):8071. Epub 2021 Apr 13.

Center of Excellence On Catalysis and Catalytic Reaction Engineering, Department of Chemical Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok, 10330, Thailand.

The coke formation in the catalytic system mainly cause to the catalyst deactivate resulting the dramatic decreasing of the catalyst performance then the catalyst regeneration was required. In this study, adding MgO physically mixed with WO/SiO catalysts were prepared and compared with the ones prepared by physically mixing with SiO. Adding MgO affected the generation of new species of coke deposited on WO/SiO and MgO itself. Read More

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Multicatalytic Approach to One-Pot Stereoselective Synthesis of Secondary Benzylic Alcohols.

Org Lett 2021 Apr 12. Epub 2021 Apr 12.

University of Strasbourg, CNRS, ISIS UMR 7006, 8 Allée Gaspard Monge, 67000 Strasbourg, France.

One-pot procedures bear the potential to rapidly build up molecular complexity without isolation and purification of consecutive intermediates. Here, we report multicatalytic protocols that convert alkenes, unsaturated aliphatic alcohols, and aryl boronic acids into secondary benzylic alcohols with high stereoselectivities (typically >95:5 er) under sequential catalysis that integrates alkene cross-metathesis, isomerization, and nucleophilic addition. Prochiral allylic alcohols can be converted to any stereoisomer of the product with high stereoselectivity (>98:2 er, >20:1 dr). Read More

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Path Ensembles for Pin1-Catalyzed Cis-Trans Isomerization of a Substrate Calculated by Weighted Ensemble Simulations.

J Chem Theory Comput 2021 Apr 26;17(4):2522-2529. Epub 2021 Mar 26.

Department of Physics, Nippon Medical School, 1-7-1 Kyonan-cho, Musashino, Tokyo 180-0023, Japan.

Pin1 enzyme protein recognizes specifically phosphorylated serine/threonine (pSer/pThr) and catalyzes the slow interconversion of the peptidyl-prolyl bond between cis and trans forms. Structural dynamics between the cis and trans forms are essential to reveal the underlying molecular mechanism of the catalysis. In this study, we apply the weighted ensemble (WE) simulation method to obtain comprehensive path ensembles for the Pin1-catalyzed isomerization process. Read More

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Unlocking the Remarkable Influence of Intramolecular Group Rotation for Third-order Nonlinear Optical Properties.

Chem Asian J 2021 Apr 19;16(8):981-987. Epub 2021 Mar 19.

Green Catalysis Center and College of Chemistry, Zhengzhou University, 450001, Zhengzhou, P. R. China.

This work exposes for the first time the remarkable influence of intramolecular group rotation on third-order nonlinear optical (NLO) performance. In order to prove the role of group rotation, we designed and synthesized two photo-response compounds tetramethyl 5,5'-(((diazene-1,2-diylbis(4,1-phenylene))bis(oxy))bis(methylene))diisophthalate (1) and 5,5'-(((diazene-1,2-diylbis(4,1-phenylene))bis(oxy))bis(methylene))diisophthalic acid (2) and investigated their NLO performance under different substituent (benzyloxy group) rotation states. 1 and 2 have dynamic benzyloxy group rotation in dilute solution and shows reverse saturated absorption (RSA). Read More

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Efficient catalytic conversion of microalgae residue solid waste into lactic acid over a Fe-Sn-Beta catalyst.

Sci Total Environ 2021 Jun 27;771:144891. Epub 2021 Jan 27.

State Key Laboratory of Pollution Control and Resources Reuse, Key Laboratory of Yangtze River Water Environment of Ministry of Education, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China. Electronic address:

Microalgae residue was efficiently converted into lactic acid with a high yield (33.9%) under mild reaction conditions (210 °C, 2 h) over a Fe-Sn-Beta catalyst. Under the action of homogeneous HO and distinct Lewis acid sites on the catalyst, the production of lactic acid from microalgae residue underwent three main reaction steps: hydrolysis, isomerization, and retro-aldol condensation. Read More

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An Amine-Assisted Ionic Monohydride Mechanism Enables Selective Alkyne -Semihydrogenation with Ethanol: From Elementary Steps to Catalysis.

J Am Chem Soc 2021 Mar 16;143(12):4824-4836. Epub 2021 Mar 16.

State Key Laboratory of Organometallic Chemistry, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China.

The selective synthesis of -alkenes in alkyne semihydrogenation relies on the reactivity difference of the catalysts toward the starting materials and the products. Here we report -selective semihydrogenation of alkynes with ethanol via a coordination-induced ionic monohydride mechanism. The EtOH-coordination-driven Cl dissociation in a pincer Ir(III) hydridochloride complex (NCP)IrHCl () forms a cationic monohydride, [(NCP)IrH(EtOH)]Cl, that reacts selectively with alkynes over the corresponding -alkenes, thereby overcoming competing thermodynamically dominant alkene - isomerization and overreduction. Read More

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Natural mineral bentonite as catalyst for efficient isomerization of biomass-derived glucose to fructose in water.

Sci Total Environ 2021 Mar 8;778:146276. Epub 2021 Mar 8.

School of Environmental Science and Engineering, State Key Lab of Metal Matrix Composites, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, China. Electronic address:

The development of inexpensive and efficient heterogeneous catalyst for the conversion of biomass including food and winery processing waste to value-added products is crucial in biorefinery. Glucose could be obtained via the hydrolysis of waste cellulose or starch-rich material, and the isomerization of glucose to fructose using either Lewis acid or Brønsted base catalysts is an important route in biorefinery. As a natural clay mineral, bentonite (Bt) is widely used as adsorption material and catalyst support, but how its intrinsic acid-base properties can impact the biomass conversion chemistry is still rarely reported. Read More

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Valorization of humins from food waste biorefinery for synthesis of biochar-supported Lewis acid catalysts.

Sci Total Environ 2021 Jun 14;775:145851. Epub 2021 Feb 14.

Department of Civil and Environmental Engineering, Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China. Electronic address:

To close the carbon loop of biomass waste valorization, it is imperative to utilize the unavoidable by-products such as humins, a carbonaceous residue with complex and heterogeneous composition. In this study, starch-rich rice waste was effectively converted into value-added chemicals (e.g. Read More

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BcfH Is a Trimeric Thioredoxin-Like Bifunctional Enzyme with Both Thiol Oxidase and Disulfide Isomerase Activities.

Antioxid Redox Signal 2021 Apr 12. Epub 2021 Apr 12.

Department of Biochemistry and Genetics, La Trobe Institute for Molecular Science, La Trobe University, Bundoora, Australia.

Thioredoxin (TRX)-fold proteins are ubiquitous in nature. This redox scaffold has evolved to enable a variety of functions, including redox regulation, protein folding, and oxidative stress defense. In bacteria, the TRX-like disulfide bond (Dsb) family mediates the oxidative folding of multiple proteins required for fitness and pathogenic potential. Read More

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Buchner Reaction/Azirine Modification Approach Toward Cycloheptatriene Containing Nitrogen Heterocyclic Scaffolds.

J Org Chem 2021 Mar 11;86(5):4098-4111. Epub 2021 Feb 11.

Saint Petersburg State University, Institute of Chemistry, 7/9 Universitetskaya nab., St. Petersburg 199034, Russia.

The reaction conditions for the Buchner reaction of 2-(diazoacetyl)-2-azirines with benzene leading to 2-(cyclohepta-2,4,6-trien-1-yl)-2-azirines have been found. The azirine fragment of these compounds was subsequently used to prepare 5-(cyclohepta-2,4,6-trien-1-yl)isoxazoles and α-(cyclohepta-2,4,6-triene-1-ylcarbonyl)-1-pyrroles. NMR and DFT calculations showed that the cycloheptatriene-norcaradiene valence isomerization in the corresponding moieties of synthesized azirines, isoxazoles, and pyrroles is very fast at room temperature. Read More

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Synthesis of 2-Oxazolines from Ring Opening Isomerization of 3-Amido-2-Phenyl Azetidines.

Molecules 2021 Feb 6;26(4). Epub 2021 Feb 6.

College of Chemistry, Beijing Normal University, Beijing 100875, China.

Chiral 2-oxazolines are valuable building blocks and famous ligands for asymmetric catalysis. The most common synthesis involves the reaction of an amino alcohol with a carboxylic acid. In this paper, an efficient synthesis of 2-oxazolines has been achieved via the stereospecific isomerization of 3-amido-2-phenyl azetidines. Read More

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February 2021

Diastereoselective and Stereodivergent Synthesis of 2-Cinnamylpyrrolines Enabled by Photoredox-Catalyzed Iminoalkenylation of Alkenes.

Angew Chem Int Ed Engl 2021 Apr 10;60(17):9672-9679. Epub 2021 Mar 10.

State Key Laboratory of Analytical Chemistry for Life Science, Jiangsu Key Laboratory of Advanced Organic Materials, Chemistry and Biomedicine Innovation Center (ChemBIC), School of Chemistry and Chemical Engineering, Nanjing University, Nanjing, 210023, China.

A photoredox-catalyzed iminoalkenylation of γ-alkenyl O-acyl oximes has been developed. Readily available alkenylboronic acids serve as alkenylation reagents, leading to densely functionalized pyrrolines. Both (E)- and (Z)-cinnamylpyrrolines are accessible depending on the reaction solvent. Read More

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Enantioselective Nickel-Catalyzed anti-Arylmetallative Cyclizations onto Acyclic Ketones.

Chemistry 2021 Apr 5;27(19):5897-5900. Epub 2021 Mar 5.

The GlaxoSmithKline Carbon Neutral Laboratories for, Sustainable Chemistry, University of Nottingham, Jubilee Campus, Triumph Road, Nottingham, NG7 2TU, UK.

Domino reactions involving nickel-catalyzed additions of (hetero)arylboronic acids to alkynes, followed by cyclization of the alkenylnickel intermediates onto tethered acyclic ketones to give chiral tertiary-alcohol-containing products in high enantioselectivities, are described. The reversible E/Z isomerization of the alkenylnickel intermediates enables overall anti-arylmetallative cyclization to occur. The ring system of the products are substructures of certain diarylindolizidine alkaloids. Read More

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Highly Colored Boron-Doped Thiazolothiazoles from the Reductive Dimerization of Boron Isothiocyanates.

Angew Chem Int Ed Engl 2021 Mar 3;60(12):6446-6450. Epub 2021 Feb 3.

Institute for Inorganic Chemistry, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074, Würzburg, Germany.

Reduction of (CAAC)BBr (NCS) (CAAC=cyclic alkyl(amino)carbene) in the presence of a Lewis base L yields tricoordinate (CAAC)LB(NCS) borylenes which undergo reversible E/Z-isomerization. The same reduction in the absence of L yields deep blue, bis(CAAC)-stabilized, boron-doped, aromatic thiazolothiazoles resulting from the dimerization of dicoordinate (CAAC)B(NCS) borylene intermediates. Read More

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Iron Catalyzed Double Bond Isomerization: Evidence for an Fe /Fe Catalytic Cycle.

Chemistry 2021 Apr 15;27(19):5972-5977. Epub 2021 Mar 15.

School of Chemistry, University of Bath, Claverton Down, Bath, BA2 7AY, UK.

Iron-catalyzed isomerization of alkenes is reported using an iron(II) β-diketiminate pre-catalyst. The reaction proceeds with a catalytic amount of a hydride source, such as pinacol borane (HBpin) or ammonia borane (H N⋅BH ). Reactivity with both allyl arenes and aliphatic alkenes has been studied. Read More

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Effective synthesis of bicyclodienes via palladium-catalyzed asymmetric allylic alkylation and ruthenium-catalyzed cycloisomerization.

Authors:
Nizam Havare

Turk J Chem 2020 16;44(6):1445-1462. Epub 2020 Dec 16.

Department of Chemistry, School of Humanities & Sciences, Stanford University, Stanford, California 94305-5580 United States.

[n.3.0]Bicycles (n = 3-6) can be synthesized using palladium-catalyzed asymmetric allylic alkylation followed by ruthenium-catalyzed cycloisomerization. Read More

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December 2020

Racing against unwanted isomerization.

Science 2021 01;371(6527):345-346

Department of Chemistry, Duke University, Durham, NC 27708, USA.

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January 2021

Brønsted-Acid-Catalyzed Intramolecular Carbonyl-Olefin Reactions: Interrupted Metathesis vs Carbonyl-Ene Reaction.

J Org Chem 2021 Feb 21;86(3):3008-3016. Epub 2021 Jan 21.

Department of Chemistry, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109, United States.

Lewis acid catalysts have been shown to promote carbonyl-olefin metathesis through a critical four-membered-ring oxetane intermediate. Recently, Brønsted-acid catalysis of related substrates was similarly proposed to result in a transient oxetane, which fragments within a single elementary step via a postulated oxygen-atom transfer mechanism. Herein, careful quantum chemical investigations show that Brønsted acid (triflic acid, TfOH) instead invokes a mechanistic switch to a carbonyl-ene reaction, and oxygen-atom transfer is uncompetitive. Read More

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February 2021

Diverse Reactivity of Hypersilylsilylene with Boranes and Three-Component Reactions with Aldehyde and HBpin.

Inorg Chem 2021 Feb 18;60(3):1654-1663. Epub 2021 Jan 18.

Inorganic Chemistry and Catalysis Division, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pashan, Pune 411008, India.

The recently reported hypersilylsilylene PhC(NBu)SiSi(SiMe) () reacts with BH, 9-BBN, and PhBCl to yield the respective Lewis acid base adducts , respectively. Compound undergoes isomerization to form a ring expansion product . The same silylene was found to initially form an adduct with HBpin () and subsequently isomerized to via the rupture of the B-H bond of HBpin (), where the hydride was bound to the carbon atom of the amidinate ligand and the Bpin unit was attached to the silicon center. Read More

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February 2021

Efficient Palladium-Catalyzed Carbonylation of 1,3-Dienes: Selective Synthesis of Adipates and Other Aliphatic Diesters.

Angew Chem Int Ed Engl 2021 Apr 3;60(17):9527-9533. Epub 2021 Mar 3.

Leibniz-Institut für Katalyse e. V., Albert-Einstein-Straße 29a, 18059, Rostock, Germany.

The dicarbonylation of 1,3-butadiene to adipic acid derivatives offers the potential for a more cost-efficient and environmentally benign industrial process. However, the complex reaction network of regioisomeric carbonylation and isomerization pathways, make a selective and direct transformation particularly difficult. Here, we report surprising solvent effects on this palladium-catalysed process in the presence of 1,2-bis-di-tert-butylphosphin-oxylene (dtbpx) ligands, which allow adipate diester formation from 1,3-butadiene, carbon monoxide, and methanol with 97 % selectivity and 100 % atom-economy under scalable conditions. Read More

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TM1385 from Thermotoga maritima functions as a phosphoglucose isomerase via cis-enediol-based mechanism with active site redundancy.

Biochim Biophys Acta Proteins Proteom 2021 Apr 7;1869(4):140602. Epub 2021 Jan 7.

Department of Chemistry, University of Virginia, Charlottesville, VA, USA. Electronic address:

Phosphoglucose isomerases (PGIs) belong to a class of enzymes that catalyze the reversible isomerization of glucose-6-phosphate to fructose-6-phosphate. PGIs are crucial in glycolysis and gluconeogenesis pathways and proposed as serving additional extracellular functions in eukaryotic organisms. The phosphoglucose isomerase function of TM1385, a previously uncharacterized protein from Thermotoga maritima, was hypothesized based on structural similarity to established PGI crystal structures and computational docking. Read More

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Enantioselective Addition of α-Nitroesters to Alkynes.

Angew Chem Int Ed Engl 2021 02 7;60(9):4599-4603. Epub 2021 Jan 7.

Department of Chemistry, University of California, Irvine, Irvine, CA, 92697, USA.

By using Rh-H catalysis, we couple α-nitroesters and alkynes to prepare α-amino-acid precursors. This atom-economical strategy generates two contiguous stereocenters, with high enantio- and diastereocontrol. In this transformation, the alkyne undergoes isomerization to generate a Rh -π-allyl electrophile, which is trapped by an α-nitroester nucleophile. Read More

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February 2021

Chemistry of Unsymmetrical C1-Substituted Oxabenzonorbornadienes.

Curr Org Synth 2021 Jan 5. Epub 2021 Jan 5.

Guelph-Waterloo Center for Graduate Work in Chemistry and Biochemistry, Department of Chemistry, University of Guelph, Guelph, Ontario, N1G 2W1. Canada.

Oxabenzonorbornadiene (OBD) is a useful synthetic intermediate which can be readily activated by transition metal complexes with great face selectivity due to its dual-faced nature and intrinsic angle strain on the alkene. To date, the understanding of transition-metal catalyzed reactions of OBD itself has burgeoned; however, this has not been the case for unsymmetrical OBDs. Throughout the development of these reactions, the nature of C1-substituent has proven to have a profound effect on both the reactivity and selectivity of the outcome of the reaction. Read More

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January 2021

The deactivation of acidic sites of NiMo/B O -Al O catalysts during vegetable oil hydrodeoxygenation studied by EPR spectroscopy.

Magn Reson Chem 2020 Dec 23. Epub 2020 Dec 23.

Center of New Chemical Technologies BIC, Boreskov Institute of Catalysis, Omsk, Russia.

This paper presents the study results of NiMo/B O -Al O (0-30% wt. of B O ) catalysts for vegetable oil hydrodeoxygenation before and after catalytic tests by different electron paramagnetic resonance (EPR) methodologies. For the initial catalysts, the concentration of Brønsted acidic sites (BAS) determined by probe EPR with perylene increases linearly with an increase in the modifier (B O ) content in the samples. Read More

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December 2020

Dissecting the Conformational Dynamics of the Bile Acid Transporter Homologue ASBT.

J Mol Biol 2021 02 13;433(4):166764. Epub 2021 Jan 13.

Graduate Institute of Biochemistry, National Chung Hsing University, Taichung City 40227, Taiwan, ROC; Rong Hsing Research Center for Translational Medicine, National Chung Hsing University, 145 Xinda Rd., South Dist., Taichung City 40227, Taiwan, ROC; Ph.D. Program in Transnational Medicine, National Chung Hsing University, 145 Xinda Rd., South Dist., Taichung City 40227, Taiwan, ROC. Electronic address:

Apical sodium-dependent bile acid transporter (ASBT) catalyses uphill transport of bile acids using the electrochemical gradient of Na as the driving force. The crystal structures of two bacterial homologues ASBT and ASBT have previously been determined, with the former showing an inward-facing conformation, and the latter adopting an outward-facing conformation accomplished by the substitution of the critical Na-binding residue glutamate-254 with an alanine residue. While the two crystal structures suggested an elevator-like movement to afford alternating access to the substrate binding site, the mechanistic role of Na and substrate in the conformational isomerization remains unclear. Read More

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February 2021

Photo-induced energy transfer relay of N-heterocyclic carbene catalysis: an asymmetric α-fluorination/isomerization cascade.

Chem Commun (Camb) 2021 Jan;57(6):729-732

Department of Chemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong SAR, China.

The geometric configuration of olefin products is often driven by thermodynamic control in synthesis. Methods enabling switching of cis/trans selectivity are rare. Recently, photosensitized approaches have emerged as a powerful tool for accomplishing this task. Read More

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January 2021

Prolyl isomerization controls activation kinetics of a cyclic nucleotide-gated ion channel.

Nat Commun 2020 12 16;11(1):6401. Epub 2020 Dec 16.

Weill Cornell Medicine, Department of Anesthesiology, 1300 York Avenue, New York, NY, 10065, USA.

SthK, a cyclic nucleotide-modulated ion channel from Spirochaeta thermophila, activates slowly upon cAMP increase. This is reminiscent of the slow, cAMP-induced activation reported for the hyperpolarization-activated and cyclic nucleotide-gated channel HCN2 in the family of so-called pacemaker channels. Here, we investigate slow cAMP-induced activation in purified SthK channels using stopped-flow assays, mutagenesis, enzymatic catalysis and inhibition assays revealing that the cis/trans conformation of a conserved proline in the cyclic nucleotide-binding domain determines the activation kinetics of SthK. Read More

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December 2020

Manganese-Catalyzed Hydroboration of Terminal Olefins and Metal-Dependent Selectivity in Internal Olefin Isomerization-Hydroboration.

Inorg Chem 2021 Jan 16;60(1):494-504. Epub 2020 Dec 16.

Schulich Faculty of Chemistry, Technion-Israel Institute of Technology, Technion City, 3200008 Haifa, Israel.

In the past decade, the use of earth-abundant metals in homogeneous catalysis has flourished. In particular, metals such as cobalt and iron have been used extensively in reductive transformations including hydrogenation, hydroboration, and hydrosilylation. Manganese, on the other hand, has been considerably less explored in these reductive transformations. Read More

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January 2021

trans-3-Methylglutaconyl CoA isomerization-dependent protein acylation.

Biochem Biophys Res Commun 2021 01 4;534:261-265. Epub 2020 Dec 4.

Department of Biochemistry and Molecular Biology, Mail Stop 0330, 1664 N. Virginia Street, University of Nevada, Reno, NV, 89557, USA. Electronic address:

3-methylglutaconic (3MGC) aciduria is associated with a growing number of discrete inborn errors of metabolism. Herein, an antibody-based approach to detection/quantitation of 3MGC acid has been pursued. When trans-3MGC acid conjugated keyhole limpet hemocyanin (KLH) was inoculated into rabbits a strong immune response was elicited. Read More

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January 2021