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PubMed Journals Articles About "Exploring Magnetic Interaction Asymmetric Structures Based Chiral Clusters" RSS

07:41 EDT 22nd May 2019 | BioPortfolio

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Showing "Exploring Magnetic Interaction Asymmetric Structures Based Chiral Clusters" PubMed Articles 1–25 of 45,000+

Exploring the Magnetic Interaction of Asymmetric Structures Based on Chiral V Clusters.

Polyoxovanadates (III) are important class of polyoxometalates in molecular magnetism field, and particularly the systems which contain vanadium(III) centers. To date, only very few highly reduced vanadium polynuclear complexes were reported, which remains a significant challenge to synthesize novel polyoxovanadates, owing to the characteristics of easily oxidized vanadium(III). Herein, two unprecedented petaloid chiral octanuclear polyoxovanadates, l- and d-[HN(CH)](HN(CH)NH)(HO)(Vμ-OH)(SO)·2HO (L-, D-V)...


Asymmetric Synthesis of Chiral Flavan-3-Ols.

Flavan-3-ols are a series of natural products widely present in plants and show versatile biological activities. The structures of such compounds are characterized by owing two adjacent chiral centers and three rings. Their interesting structures and promising biological activities have driven increasing research developments toward the preparation of enantioenriched flavan-3-ols. This review summarizes the recent approaches for the asymmetric synthesis of chiral flavan-3-ols from two strategies in the cons...

Geometries, stabilities, and magnetic properties of CoB (n = 1-10) clusters.

The geometries, stabilities, and magnetic properties of CoB (n = 1-10) clusters were systematically investigated by performing spin-polarized density functional theory calculations. We found that doping B clusters with Co significantly changed their structures. CoB and CoB had planar and quasi-planar structures, while CoB and CoB had bipyramidal structures. CoB had a tubular structure. In analyses of the dissociation energies and the second-order differences in total energy of the clusters, CoB and CoB ...


Lutidine-Based Chiral Pincer Mn Catalysts for Enantioselective Hydrogenation of Ketones.

A series of Mn(I) complexes containing lutidine-based chiral pincer ligands with modular and tunable structures has been developed. The complex features unprecedentedly high activity (up to 9800 TON), broad substrate scope (81 examples), good functional group tolerance, and excellent enantioselectivity (85~98% ee) in the hydrogenation of various ketones, which are rare in earth-abundant metal catalyzed hydrogenation. The utilities of the protocol have been demonstrated in the asymmetric synthesis of a varie...

Chiral porphyrin imine manganese complex as catalyst for asymmetric epoxidation of styrene derivatives.

New chiral porphyrin imine was synthesized from (S)-3-benzyl-2-methyl-4-phenylbutanal according to dipyrromethane method using trifluoroacetic acid, BF etherate, and p-chloranil. Manganese complex of this chiral porphyrin imine ligand was used as catalyst in the asymmetric epoxidation of styrene derivatives possessing different substituents. Styrene derivatives possessing electron withdrawing groups gave the corresponding chiral epoxides in high yield up to 98% and ee up to 99%. The mechanism for the cataly...

Self-assembly of magnetic colloids with shifted dipoles.

The self-assembly of colloidal magnetic Janus particles with a laterally displaced (or shifted), permanent dipole in a quasi-two-dimensional system is studied using Brownian dynamics simulations. The rate of formation of clusters and their structures are quantified for several values of dipolar shift from the particle center, which is nondimensionalized using the particle's radius so that it takes values ranging from 0 to 1, and examined under different magnetic interaction strengths relative to Brownian mo...

Structures and magnetic properties of small Formula: see text and Co Cr (n  =  3-5) clusters.

Small cobalt clusters [Formula: see text] and their single chromium atom doped counterparts Co Cr (n  =  3-5) were studied mass spectrometrically by measuring the infrared multiple photon dissociation (IRMPD) spectra of the corresponding argon tagged complexes. The geometric and electronic structures of the [Formula: see text] and Co Cr (n  =  3-5) clusters as well as their Ar complexes were optimized by density functional theory (DFT) calculations. The obtained lowest energy structures were...

Emergence of complex chiral coordination clusters {CuNa} by using multiple ligands under oxidizing conditions.

Two chiral coordination clusters {CuII48Na12}, which can only be revealed by synchrotron single-crystal X-ray diffraction, were assembled unexpectedly from a system resembling the long-studied Fehling's solution. As the intricate structures themselves indicate, the ingenuity of using multiple ligands should inspire new strategies to fabricate new compounds.

Axially Chiral Cyclic Diphosphine Ligand-Enabled Palladium-Catalyzed Intramolecular Asymmetric Hydroarylation.

In transition metal-catalyzed asymmetric synthesis, enantioselectivity strongly depends on the structures of chiral ligands, so the development of new chiral ligands is crucial. Here, an efficient and highly enantioselective palladium-catalyzed intramolecular hydroarylation has been developed, and a new kind of N-heterocycles, 1H-pyrazolo[5,1-a]isoindol-2(8H)-ones containing a quaternary stereocenter, was prepared in high yields and excellent enantiomeric excess values. The reaction was effectively catalyze...

Single Domain 10 nm Ferromagnetism Imprinted on Superparamagnetic Nanoparticles Using Chiral Molecules.

The rapid growth in demand for data and the emerging applications of Big Data require the increase of memory capacity. Magnetic memory devices are among the leading technologies for meeting this demand; however, they rely on the use of ferromagnets that creates size reduction limitations and poses complex materials requirements. Usually magnetic memory sizes are limited to 30-50 nm. Reducing the size even further, to the ≈10-20 nm scale, destabilizes the magnetization and its magnetic orientation becomes ...

Copper(II)-Catalyzed Asymmetric Photoredox Reactions: Enantioselective Alkylation of Imines Driven by Visible Light.

Asymmetric photoredox catalysis offers exciting opportunities to develop new synthetic approaches to chiral molecules through novel reaction pathways. Employing the first-row transition metal complexes as the chiral photoredox catalysts remains, however, a formidable challenge, although these complexes are economic, environmentally friendly, and often exhibit special reactivities. We report in this Article the development of one class of highly efficient asymmetric/photoredox bifunctional catalysts based on...

Aromatic Donor-Acceptor Interaction-Based Co(III)-salen Self-Assemblies and Their Applications in Asymmetric Ring Opening of Epoxides.

Aromatic donor-acceptor interaction as the driving force to assemble cooperative catalysts is described. Pyrene/naphthalenediimide functionalized Co(III)-salen complexes self-assembled into bimetallic catalysts through aromatic donor-acceptor interactions and showed high catalytic activity and selectivity in the asymmetric ring opening of various epoxides. Control experiments, nuclear magnetic resonance (NMR) spectroscopy titrations, mass spectrometry measurement, and X-ray crystal structure analysis confir...

Synthesis of Chiral Acyclic Nucleosides by Sharpless Asymmetric Dihydroxylation: Access to Cidofovir and Buciclovir.

An efficient method to construct chiral acyclic nucleosides via Sharpless asymmetric dihydroxylation of N-allylpyrimidines or N-alkenylpurines is reported. A range of chiral acyclic nucleosides with two adjacent hydroxyl groups present on the side chains could be produced in good yields (up to 97% yield) and excellent enantioselectivities (90-99% ee). The synthetic utility of the reaction was demonstrated by the catalytic asymmetric synthesis of (S)-Cidofovir and (R)-Buciclover.

Enantioselective Synthesis of C-N Axially Chiral N-Aryloxindoles by Asymmetric Rhodium-Catalyzed Dual C-H Activation.

The first enantioselective Satoh-Miura type reaction is reported. A variety of C-N axially chiral N-aryloxindoles have been enantioselectively synthesized by an asymmetric rhodium-catalyzed dual C-H activation reaction of N-aryloxindoles and alkynes. High yields and enantioselectivities were obtained (up to 99% yield and up to 99% ee). To the best of our knowledge, it is also the first example of asymmetric synthesis of C-N axially chiral compounds by transition-metal catalyzed asymmetric dual C-H activatio...

Cobalt-Catalyzed Enantioselective Hydroboration/Cyclization of 1,7-Enynes: Asymmetric Synthesis of Chiral Quinolinones Containing Quaternary Stereogenic Centers.

An asymmetric cobalt-catalyzed hydroboration/cyclization of 1,7-enynes to synthesize chiral six-membered N-heterocyclic compounds was developed. A variety of aniline-tethered 1,7-enynes react with pinacolborane to afford the corresponding chiral boryl-functionalized quinoline derivatives in high yields with high enantioselectivity. This cobalt-catalyzed asymmetric cyclization of 1,7-enyens provides a general approach to access a series of chiral quinoline derivatives containing quaternary stereocenters.

Asymmetric Synthesis of Griffipavixanthone Employing a Chiral Phosphoric Acid-Catalyzed Cycloaddition.

Asymmetric synthesis of the biologically active xanthone dimer griffipavixanthone (GPX) is reported along with its absolute stereochemistry determination. Synthesis of the natural product is accomplished via dimerization of a p-quinone methide (p-QM) using a chiral phosphoric acid (CPA) catalyst to afford a protected precursor in excellent diastereo- and enantioselectivity. Mechanistic studies, including an unbiased computational investigation of chiral ion-pairs using parallel tempering (PT), were performe...

P-Chiral Phosphorus Ligands Based on a 2,3-Dihydrobenzo d1,3oxaphosphole Motif for Asymmetric Catalysis.

Despite the rapid progress in the field of asymmetric catalysis, the search for new, efficient, and practical asymmetric catalytic transformations to facilitate the green synthesis of chiral natural products and drugs will continue to be a major ongoing effort in organic chemistry. Chiral phosphorus ligands have played a significant role in recent advances in transition-metal-catalyzed asymmetric transformations. However, there remain numerous challenging issues of reactivity and selectivity in catalysis. T...

Kinetic Resolution of Allylic Alcohol with Chiral BINOL-based Alkoxides: A Combination of Experimental and Theoretical Studies.

The development and characterization of enantioselective catalytic kinetic resolution of allylic alcohols through asymmetric isomerization with chiral BINOL derivatives-based alkoxides as bifunctional Brønsted base catalyst were described in the study. A number of chiral BINOL derivatives-based alkoxides were synthesized and their structure-enantioselectivity correlation study in asymmetric isomerization identified a promising chiral Brønsted base catalyst, which afforded various chiral secondary allylic ...

Chiral Brønsted acid catalyzed metal free asymmetric direct reductive amination using 1-hydrosilatrane.

The asymmetric direct reductive amination of prochiral ketones with aryl amines using 1-hydrosilatrane with a chiral Brønsted acid catalyst is reported. This is the first known example of chiral Brønsted acid catalyzed asymmetric reductive amination using a silane as the hydride source. The reaction features a highly practical reducing reagent and proceeds efficiently at room temperature without specialized reaction setup or equipment to exclude air or moisture. This method provides high conversion and ee...

Optically active inverse opal photonic crystals.

Chiral photonic crystals have been a widely investigated topic in chemistry, physics and biology. Till now, the researches about chiral photonic crystals are conducted on the objects of helical structures, while the chiral photonic crystals made of periodic chiral media remain unexplored experimentally. In this work, we have successfully constructed three-dimensional chiral polymer inverse opal photonic crystals (3D CPIOPCs) by a template-based method. Impressively, the 3D CPIOPCs exhibit emerging circular ...

Assembling a Hybrid Pd-Catalyst from Chiral Anionic Co(III)-Complex and Ligand for Asymmetric C(sp3)-H Functionalization.

An unusual hybrid palladium catalyst containing an anionic chiral Co(III) complex and a chiral phosphoramidite ligand shows high capacity of catalyzing the asymmetric thioamide-directed C(sp3)-H arylation and delivers excellent levels of yield and enantioselectivity (up to 99% yield, 99% ee). A significant synergy of chiral ligand and anion in the stereochemical control has been observed. Mechanistic investigations have revealed both the nature of the C-H activation and the origin of the enantioselectivity.

Formal Asymmetric Cycloaddition of Activated α,β-Unsaturated Ketones with α-Diazomethylphosphonate Mediated by a Chiral Silver SPINOL Phosphate Catalyst.

An efficient method for preparing highly functionalized chiral nonspiro-phosphonylpyrazolines via an asymmetric formal 1,3-dipolar cycloaddition reaction of α-diazomethylphosphonate with activated, acyclic α,β-unsaturated ketones, bearing an additional nitrile electron-withdrawing group, has been developed, utilizing an in situ generated chiral silver phosphate catalyst, affording excellent stereoselectivities (up to 98% ee, 99:1 dr) and yields (up to 95%). A stepwise mechanism is proposed based upon den...

Chiral DMAP-N-oxides as Acyl Transfer Catalysts: Design, Synthesis, and Application in Asymmetric Steglich Rearrangement.

A DMAP-N-oxide, featuring an α-amino acid as the chiral source, was developed, synthesized and applied in asymmetric Steglich rearrangement. A series of O-acylated azlactones afforded C-acylated azlactones possessing a quaternary stereocenter in high yields (88-97% yields) and excellent enantioselectivities (90-97% ee). Compared to the widespread use of pyridine nitrogen, which serves as the nucleophilic site in the asymmetric acyl transfer reaction, we discovered that chiral DMAP-N-oxides, in which the ox...

Anomalous Nonreciprocal Electrical Transport on Chiral Magnetic Order.

Nonreciprocal flow of conduction electrons is systematically investigated in a monoaxial chiral helimagnet CrNb_{3}S_{6}. We found that such directional dichroism of the electrical transport phenomena, called the electrical magnetochiral (EMC) effect, occurs in a wide range of magnetic fields and temperatures. The EMC signal turns out to be considerably enhanced below the magnetic ordering temperature, suggesting a strong influence of the chiral magnetic order on this anomalous EMC transport property. The E...

Cu/Chiral Phosphoric Acid-Catalyzed Asymmetric Three-Component Radical-Initiated 1,2-Dicarbofunctionalization of Alkenes.

An asymmetric intermolecular, three-component radical-initiated dicarbofunctionalization of 1,1-diarylalkenes with diverse carbon-centered radical precursors and electron-rich heteroaromatics by a copper(I) and chiral phosphoric acid cooperative catalysis strategy has been developed, providing straightforward access to chiral triarylmethanes bearing quaternary all-carbon stereocenters with high efficiency as well as excellent chemo- and enantioselectivity. The key to success is not only the introduction of ...


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