15,349 results match your criteria isomerization


An Isoxazole Strategy for the Synthesis of Fully Substituted Nicotinates.

J Org Chem 2021 Apr 13. Epub 2021 Apr 13.

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

A four-step quasi one-pot procedure for the preparation of fully substituted nicotinates from ketone enamines and 4-methylideneisoxazol-5-ones has been developed. The reaction sequence involves (1) reaction of 4-methylideneisoxazol-5-ones with ketone enamines with the formation of isoxazole-5-ols, (2) their O-methylation with diazomethane, (3) hydrogenative cleavage of the O-N bond in 5-methoxyisoxazoles under action of Mo(CO)/HO and simultaneous isomerization and condensation of the formed enamines, with the formation of dihydropyridines, and (4) aromatization of the latter. Read More

View Article and Full-Text PDF

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

View Article and Full-Text PDF

A Light-Operated Molecular Cable Car for Gated Ion Transport.

Angew Chem Int Ed Engl 2021 Apr 11. Epub 2021 Apr 11.

Key Labs for Advanced Materials, East China University of Science and Technology, CHINA.

Inspired by the nontrivial and controlled movements of molecular machines, we report an azobenzene-based molecular shuttle PR2 , which can perform light-gated ion transport across lipid membranes. The amphiphilicity and membrane-spanned molecular length enable PR2 to insert into the bilayer membrane and efficiently ferry K + (EC 50 = 4.1 µM) through the thermally driven stochastic shuttle motion of the crown ether ring along the axle. Read More

View Article and Full-Text PDF

Nitrogen monoxide as dopant for enhanced selectivity of isomeric monoterpenes in drift tube ion mobility spectrometry with H ionization.

Anal Bioanal Chem 2021 Apr 10. Epub 2021 Apr 10.

Institute for Instrumental Analytics and Bioanalytics, Mannheim University of Applied Sciences, Paul-Wittsack-Strasse 10, 68163, Mannheim, Germany.

The ion mobility spectra of the isomeric monoterpenes α-pinene, β-pinene, myrcene, and limonene in drift tube ion mobility spectrometry (IMS) with H radioactive ionization are highly similar and difficult to distinguish. The aim of this work was to enhance the selectivity of IMS by the addition of nitrogen monoxide (NO) as dopant and to investigate the underlying changes in ion formation responsible for the modified ion signals observed in the ion mobility spectra. Even though H-based-IMS systems have been used in hyphenation with gas chromatography (GC) for profiling of volatile organic compounds (VOCs), the investigation of ion formation still remains challenging and was exemplified by the investigated monoterpenes. Read More

View Article and Full-Text PDF

Effect of ligand backbone on the reactivity and mechanistic paradigm of non-heme iron(IV)-oxo during olefin epoxidation.

Angew Chem Int Ed Engl 2021 Apr 9. Epub 2021 Apr 9.

Indian Institute of Technology-Bombay, Department of Chemistry, Powai, 400076, Mumbai, INDIA.

Oxygen atom transfer (OAT) reactivity of a non-heme [Fe IV (2PyN2Q)(O)] 2+ ( 2 ) containing sterically bulky quinoline-pyridine pentadentate ligand (2PyN2Q) has been thoroughly studied with different olefins. The ferryl-oxo complex 2 shows excellent OAT reactivity during epoxidations. The steric encumbrance and electronic effect of the ligand influence the mechanistic shuttle between oxygen atom transfer pathway I (OAT) and isomerization pathway II (during the reaction stereo pure olefins), resulting in a mixture of cis - trans epoxide products. Read More

View Article and Full-Text PDF

From Photoinduced Supramolecular Polymerization to Responsive Organogels.

J Am Chem Soc 2021 Apr 8. Epub 2021 Apr 8.

Center for System Chemistry, Stratingh Institute for Chemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.

Controlling supramolecular polymerization by external stimuli holds great potential toward the development of responsive soft materials and manipulating self-assembly at the nanoscale. Photochemical switching offers the prospect of regulating the structure and properties of systems in a noninvasive and reversible manner with spatial and temporal control. In addition, this approach will enhance our understanding of supramolecular polymerization mechanisms; however, the control of molecular assembly by light remains challenging. Read More

View Article and Full-Text PDF

Influence of Lipidation on the Folding and Stability of Collagen Triple Helices-An Experimental and Theoretical Study.

J Am Chem Soc 2021 Apr 8. Epub 2021 Apr 8.

Laboratory of Organic Chemistry, ETH Zurich, D-CHAB, Vladimir-Prelog-Weg 3, 8093 Zurich, Switzerland.

The folding of triple-helical collagen, the most abundant protein in nature, relies on the nucleation and propagation along the strands. Hydrophobic moieties are crucial for the folding and stability of numerous proteins. Instead, nature uses for collagen a trimerization domain and - prolyl isomerases to facilitate and accelerate triple helix formation. Read More

View Article and Full-Text PDF

Insights into the Decomposition and Oxidation Chemistry of -Xylene in Laminar Premixed Flames.

J Phys Chem A 2021 Apr 8. Epub 2021 Apr 8.

Key Laboratory for Power Machinery and Engineering of MOE, School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China.

This work reports an experimental and kinetic modeling investigation on laminar premixed flame of -xylene at 0.04 atm and equivalence ratios of 0.75, 1. Read More

View Article and Full-Text PDF

Carbazole-Cyanobenzene Dyes Electrografted to Carbon or Indium-Doped Tin Oxide Supports for Visible Light-Driven Photoanodes and Olefin Isomerizations.

ACS Appl Mater Interfaces 2021 Apr 7. Epub 2021 Apr 7.

Department of Chemistry, University of Alberta, 11227 Saskatchewan Drive, Edmonton, Alberta T6G 2G2, Canada.

The organic carbazole-cyanobenzene push-pull dye 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene was derivatized and attached to carbon or indium-doped tin oxide (ITO) electrodes by simple diazonium electrografting. The surface-bound dye is active and stable for the visible light photosynthetic isomerization of a wide range of functionalized stilbene and cinnamic acid derivatives. Up to 87,000 net turnovers were obtained for the isomerization of -stilbene. Read More

View Article and Full-Text PDF

Analysis of Peptide Stereochemistry in Single Cells by Capillary Electrophoresis-Trapped Ion Mobility Spectrometry Mass Spectrometry.

Anal Chem 2021 Apr 7. Epub 2021 Apr 7.

Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States.

Single cell analysis strives to probe molecular heterogeneity in morphologically similar cell populations through quantitative or qualitative measurements of genetic, proteomic, or metabolic products. Here, we applied mass analysis of single neurons to investigate cell-cell signaling peptides. The multiplicity of endogenous cell-cell signaling peptides is a common source of chemical diversity among cell populations. Read More

View Article and Full-Text PDF

Cis-Trans Isomerization and Thermal Decomposition Mechanisms of a Series of N ( = 4, 8, 10, 11) Chain-Catenated Energetic Crystals.

J Phys Chem A 2021 Apr 6. Epub 2021 Apr 6.

Institute for Computation in Molecular and Materials Science and Department of Chemistry, Nanjing University of Science and Technology, Nanjing 210094, China.

Nitrogen-rich compounds based on heteroaromatic rings with different lengths of nitrogen chains are at the forefront of the energetic materials field. We studied the decomposition processes and reaction kinetics of a series of N ( = 4, 8, 10, 11) chain-catenated energetic crystals at various temperatures (2400-3000 K) based on a combinational strategy based on density functional tight binding molecular dynamics (DFTB-MD) simulations and density functional theory (DFT). The results show that the thermal decomposition and reaction kinetics are dependent on both the temperature and nitrogen chain's length. Read More

View Article and Full-Text PDF

Collision-induced dissociation of [UO (NO )(O )] and reactions of product ions with H O and O.

J Mass Spectrom 2021 May;56(5):e4720

Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, Pennsylvania, USA.

We recently reported a detailed investigation of the collision-induced dissociation (CID) of [UO (NO ) ] and [UO (NO ) (O )] in a linear ion trap mass spectrometer (J. Mass Spectrom. DOI:10. Read More

View Article and Full-Text PDF

A hollow visible-light-responsive surface molecularly imprinted polymer for the detection of chlorpyrifos in vegetables and fruits.

Food Chem 2021 Mar 23;355:129656. Epub 2021 Mar 23.

The Key Laboratory of Applied Chemistry of Chongqing Municipality, College of Chemistry and Chemical Engineering, Southwest University, Chongqing 400715, PR China. Electronic address:

A visible-light-responsive azobenzene derivative, 3,5-dichloro-4-((2,6-dichloro-4-(methacryloyloxy)phenyl)diazenyl)benzoic acid, was synthesized and used as the functional monomer to fabricate a visible-light-responsive core-shell structured surface molecularly imprinted polymer (PS-co-PMAA@VSMIP). After removal of the sacrificial PS-co-PMAA core, a hollow structured surface molecularly imprinted polymer (HVSMIP) was obtained. Both the PS-co-PMAA@VSMIP and HVSMIP were used for the detection of chlorpyrifos, a moderately toxic organophosphate pesticide. Read More

View Article and Full-Text PDF

Isomerization of 5-(2-Azirin-2-yl)oxazoles: An Atom-Economic Approach to 4-Pyrrolo[2,3-]oxazoles.

Molecules 2021 Mar 26;26(7). Epub 2021 Mar 26.

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

An atom economical method for the preparation of variously substituted 4-pyrrolo[2,3-]oxazoles was developed on the basis of thermal isomerization of 5-(2-azirin-2-yl)oxazoles. The latter were prepared by Rh(oct) catalyzed reaction of 2-(3-aryl/heteroaryl)-2-diazoacetyl-2-azirines with a set of substituted acetonitriles, benzonitriles, acrylonitrile and fumaronitrile. According to DFT calculations the transformation of 5-(2-azirin-2-yl)oxazole to 4-pyrrolo[2,3-]oxazole occurs through the nitrenoid-like transition state to give a 3a-pyrrolo[2,3-]oxazole intermediate, followed by 1,5-H-shift. Read More

View Article and Full-Text PDF

Targeting Pin1 for Modulation of Cell Motility and Cancer Therapy.

Biomedicines 2021 Mar 31;9(4). Epub 2021 Mar 31.

Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Kaohsiung Medical University Hospital, Kaohsiung Medical University, Kaohsiung 80708, Taiwan.

Peptidyl-prolyl isomerase NIMA-interacting 1 (Pin1) specifically binds and isomerizes the phosphorylated serine/threonine-proline (pSer/Thr-Pro) motif, which leads to changes in protein conformation and function. Pin1 is widely overexpressed in cancers and plays an important role in tumorigenesis. Mounting evidence has revealed that targeting Pin1 is a potential therapeutic approach for various cancers by inhibiting cell proliferation, reducing metastasis, and maintaining genome stability. Read More

View Article and Full-Text PDF

Effect of Iodine Filler on Photoisomerization Kinetics of Photo-Switchable Thin Films Based on PEO-BDK-MR.

Polymers (Basel) 2021 Mar 9;13(5). Epub 2021 Mar 9.

Leibniz Institut für Analytische Wissenschaften-ISAS-e.V., Bunsen-Kirchhoff-Straße 11, 44139 Dortmund, Germany.

We report the effect of an iodine filler on photoisomerization kinetics of photo-switchable PEO-BDK-MR thin films. The kinetics of photoisomerization and time progression of PEO-BDK-MR/I nanocomposite thin films are investigated using UV-Vis, FTIR spectroscopies, and modified mathematical models developed using new analytical methods. Incorporating iodine filler into the PEO-BDK-MR polymeric matrix enhances the isomerization energy barrier and considerably increases the processing time. Read More

View Article and Full-Text PDF