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Chemistry: a European Journal

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https://www.readbyqxmd.com/read/28334469/stereoisomerism-of-bis-sigma-zincane-complexes-evidence-for-an-intramolecular-pathway
#1
Mark Richard Crimmin, Olga Ekkert, Andrew White
The first bis(sigma-zincane) complexes, heterotrimetallic species [M(CO)4(2-HZnBDI)2], have been prepared (BDI = 2-{2,6-i-Pr2C6H3NCMe}2CH). For M = Cr a single stereoisomer is observed in solution and the solid-state. For M = Mo and W, cis and trans isomers where found to reversibly interconvert at 297 K. Despite the huge steric demands of the ligand on zinc, in all cases the cis isomer was found to be the most thermodynamically stable. The activation parameters for the isomerization when M = Mo are H‡ = 20...
March 23, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28334464/revealing-the-origin-of-the-efficiency-of-the-de-novo-designed-kemp-eliminase-hg-3-17-by-comparison-with-the-former-developed-hg-3
#2
Vicent Moliner, Katarzyna Swiderek, Iñaki Tuñón, Joan Bertran
The design of new biocatalysts is a goal in biotechnology to improve the rate, selectivity and environmental impact of industrial chemical processes. In this regard, the use of computational techniques has provided valuable assistance in the design of new enzymes with remarkable catalytic activity. In this paper, hybrid QM/MM Molecular Dynamics simulations have allowed getting an insight into the origin of the limited efficiency of a computationally designed enzyme for the Kemp elimination; the HG-3. Comparison of results derived from this enzyme with those of a more evolved protein containing additional point mutations, HG-3...
March 23, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28334462/flexibility-and-stability-of-metal-coordination-macromolecules
#3
Xiao-Song Wang, Dapeng Liu, Diya Gen, Heyang Jiang, Nicholas Lanigan
The effect of chain structure on flexibility and stability of the macromolecules containing weak P-Fe metal coordination bonds is studied. Migration insertion polymerization (MIP) of FpCXFp (1) and PR2CYPR2 (2) (Fp: CpFe(CO)2; CX and CY: alkyl spacers; P: phosphine; R: phenyl or isopropyl) generates P(1/2), in which the P-Fe and Fe-P bonds with opposite bonding direction are alternatively arranged in the backbone. On the other hand, P(FpCXP) synthesized from AB-type monomers (FpCXP) has P-Fe bonds arranged in the same direction...
March 23, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28334455/ceric-cyclopentadienides-bearing-alkoxy-aryloxy-chlorido-or-iodido-co-ligands
#4
Reiner Anwander, David Schneider, Frank Edelmann, Nicole Harmgarth
A series of heteroleptic tris(cyclopentadienyl) CeIV complexes has been isolated and crystallographically characterized, implying a broad accessibility of such organocerium(IV) compounds. The oxidation of complexes CpMe3Ce(thf) and Cp'3Ce(thf) (CpMe = C5H4Me, Cp' = C5H4SiMe3), bearing monosubstituted electron-poor cyclopentadienyl ligands, with either 0.5 equiv. 1,4-benzoquinone or C2Cl6 gave the cerium(IV) hydroquinolate and chloride complexes CpMe3Ce(OC6H4O)CeCpMe3, Cp'3Ce(OC6H4O)CeCp'3, as well as CpMe3CeCl and Cp'3CeCl, respectively...
March 23, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28332756/a-fluorescent-sensing-of-nerve-agent-simulant-with-dual-emissions-at-wide-ph-range-in-aqueous-solution
#5
Youngsam Kim, Yoon Jeong Jang, Sandip V Mulay, Thuy-Tien T Nguyen, David G Churchill
A new 1,8-naphthalimide-based fluorescent probe for the detection of diethyl cyanophosphonate, a very common nerve agent simulant, was designed, synthesized and characterized fully. The probe showed around 50-fold enhancement of fluorescence intensity over other nerve agent simulants. Importantly, the probe is able to work under aqueous conditions at wide pH range. Two reactive groups, the oxime and phenol, allowed a dual emission with different kinetic reaction. The reaction of diethyl cyanophosphonate with the oxime group occurred in advance; the resulting time-response of fluorescence enhancement was observed within ~30 s...
March 23, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28332743/nitrene-radical-approach-to-saturated-heterocycles-cobalt-porphyrin-catalysed-intramolecular-ring-closing-c-h-amination-of-aliphatic-azides
#6
Bas de Bruin, Petrus F Kuijpers, Martijn J Tiekink, Willem B Breukelaar, Daniël L J Broere, Nicolaas P van Leest, Jarl Ivar van der Vlugt, Joost N H Reek
Cobalt porphyrin catalysed intramolecular ring-closing C-H bond amination enables direct synthesis of various N-heterocycles from aliphatic azides. Pyrrolidines, oxazolidines imidazolidines, isoindolines and tetrahydroisoquinoline can be obtained in good to excellent yields in a single reaction step with an air and moisture stable catalyst. Kinetic studies of the reaction in combination with DFT calculations reveal a metallo-radical-type mechanism involving rate limiting azide activation to form the key cobalt(III)-nitrene radical intermediate...
March 23, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28332741/robust-stimuli-responsive-membranes-prepared-from-a-blend-of-polysulfone-and-a-graft-copolymer-bearing-binary-side-chains-with-thermo-and-ph-responsive-switching-behavior
#7
Lei Miao, Yuanyuan Tu, Yang Yang, Shudong Lin, J W Hu, Min Zhang, Yue Li, Fei Li, Yangmiao Mo
Reported herein is the fabrication of a stimuli-responsive membrane exhibiting independent pH- and temperature-responsive behavior that was prepared from a blend of commercial polysulfone with a functional amphiphilic binary graft copolymer denoted as polysulfone-graft-(poly(isopropylacrylamide-co-acrylic acid)-random-poly(methyl acrylate) (or PSf-g-(P(NIPAAm-co-AA)-r-PMMA)). This series of two graft copolymers with different lengths of P(NIPAAm-co-AA) side-chains were respectively designed and enriched on the membrane surface to serve as thermo- and pH-responsive "on/off" switches...
March 23, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28332263/synthesis-of-ortho-azophenols-by-formal-dehydrogenative-coupling-of-phenols-and-hydrazines-or-hydrazides
#8
Jean-Philip George Lumb, Kenneth Virgel N Esguerra
Azophenols are important chromophores and reagents in organic synthesis, with applications as pigments and molecular switches. Herein, we describe a catalytic aerobic process that couples phenols and hydrazines or hydrazides for their synthesis. The key aromatic C-N bond is formed via condensation between the hydrazine or hydrazide and an ortho-quinone, which triggers a redox-isomerization to install the azo functionality. Notable features include rapid access to highly functionalized azophenols with a range of electronic configurations, including "push-pull" systems, under conditions that employ simple, un-activated substrates, occur at room temperature using an earth-abundant and commercially available copper-catalyst, and produce water as the only stoichiometric byproduct...
March 22, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28332244/a-fluorine-18-radiolabelling-method-enabled-by-rhenium-i-complexation-circumvents-the-requirement-of-anhydrous-conditions
#9
Mitchell Ashley Klenner, Giancarlo Pascali, Bo Zhang, Tiffany Russel Sia, Lawson Kyle Spare, Anwen M Krause-Heuer, Janice Aldrich-Wright, Ivan Greguric, Adam Guastella, Massimiliano Massi, Benjamin Hugh Fraser
Azeotropic distillation is typically required to achieve fluorine-18 radiolabelling during the production of positron emission tomography (PET) imaging agents. However, this time consuming process also limits fluorine-18 incorporation, due to radioactive decay of the isotope and its adsorption to the drying vessel. In addressing these limitations, we herein report the fluorine-18 radiolabelling of one model rhenium(I) complex, which is significantly improved under conditions that do not require azeotropic drying...
March 22, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28332232/paper-based-colorimetric-sensor-system-for-high-throughput-screening-of-c-h-borylation
#10
Han-Sung Kim, Min Sik Eom, Min Su Han, Sunwoo Lee
A paper-based colorimetric sensor system (PBCSS) was developed to detect the amount of bis(pinacolato)diboron (B2Pin2) and applied as a high-throughput screening protocol in Ir-catalyzed C-H borylation. First, 96 ligands were screened for the borylation of benzene, and then 12 of them were selected and tested for five substrates. These reaction mixtures were spotted in the PBCSS, showing a blue-violet color. The value of the gray scale of each reaction was obtained from these colored spots and converted to the extent of conversion of B2Pin2...
March 22, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28328176/glucose-responsive-supramolecular-vesicles-based-on-water-soluble-pillar-5-arene-and-pyridylboronic-acid-derivative-for-controlled-insulin-delivery
#11
Lei Gao, Tingting Wang, Keke Jia, Xuan Wu, Chenhao Yao, Wei Shao, Dongmei Zhang, Xiao-Yu Hu, Leyong Wang
The stimuli-responsive behavior of supramolecular nanocarriers is crucial for their potential applications as smart drug delivery systems. We hereby constructed a glucose-responsive supramolecular drug delivery system constructed by the host-guest interaction between a water-soluble pillar[5]arene (WP5) and a pyridylboronic acid derivative (G) for insulin delivery and controlled release at physiological condition, which represents the ideal treatment of diabetes mellitus. The drug loading and in vitro drug release experiments demonstrated that large molecular weight insulin could be successfully encapsulated into the vesicles with high loading efficiency, which to the best of our knowledge, is the first example of small size supramolecular vesicles with excellent encapsulation capacity of large protein molecule...
March 22, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28326640/catalytic-enantioselective-synthesis-of-protecting-group-free-1-5-benzothiazepines
#12
Sara Meninno, Chiara Volpe, Alessandra Lattanzi
A one-pot enantioselective route to N-unprotected 2,3-dihydro-1,5-benzothiazepinones, by an organocatalyzed sulfa-Michael reaction of readily available α,β-unsaturated N-acyl pyrazoles with 2-aminothiophenols followed by silica-gel-catalyzed lactamization, has been developed. The method proceeds under mild conditions at room temperature and it requires only 1 mol % catalyst loading, to give 2-aryl/alkyl-substituted 1,5-benzothiazepines in generally good to excellent yields and enantioselectivities. The process, used for a short synthesis of antidepressant drug (R)-(-)-thiazesim, represents the first method to access enantioenriched unprotected 1,5-benzotiazepines, which are useful for rapid derivatization in drug discovery...
March 22, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28326635/structure-enabled-discovery-of-a-stapled-peptide-inhibitor-to-target-the-oncogenic-transcriptional-repressor-tle1
#13
Sally McGrath, Marcello Tortorici, Ludovic Drouin, Savade Solanki, Lewis Vidler, Isaac Westwood, Peter Gimeson, Rob vanMontfort, Swen Hoelder
TLE1 is an oncogenic transcriptional co-repressor that exerts its repressive effects through binding of transcription factors. Inhibition of this protein-protein interaction represents a putative cancer target but no small molecule inhibitors have been published for this challenging interface. In this manuscript, we report the structure enabled design and synthesis of a constrained peptide inhibitor of TLE1. Our design featured introduction of a four carbon atom linker into the peptide epitope found in many TLE1 binding partners...
March 22, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28326622/synthesis-and-reduction-of-sterically-encumbered-mesoionic-carbene-stabilized-aryldihaloboranes
#14
Merle Arrowsmith, Julian Böhnke, Holger Braunschweig, Haopeng Gao, Marc-André Légaré, Valerie Paprocki, Jens Seufert
Sterically hindered, in situ generated 1,3,4-substituted 1,2,3-triazol-5-ylidene mesoionic carbenes (MICs) were employed to stabilize a number of aryl- and heteroaryldihaloboranes, as well as the first MIC-supported diborane. Reduction of borane adducts of the 1-(2,6-diisopropylphenyl)-3-methyl-4-tert-butyl-1,2,3-triazol-5-ylidene ligand with KC8 in non-coordinating solvents led to intramolecular C-H- and, C-C-activation at an isopropyl residue of the supporting ligand. DFT calculations showed that each of these activation reactions proceed via a different isomer of a borylene intermediate...
March 22, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28326629/solvent-controlled-phase-transition-of-a-co-ii-organic-framework-from-achiral-to-chiral-and-two-to-three-dimen-sion
#15
Xing-Po Wang, Wen-Miao Chen, Xiao-Yu Li, Cyril Rajnák, Zhen-Yu Feng, Mohamedally Kurmoo, Roman Boča, Chunjiang Jia, Chen-Ho Tung, Di Sun
We report an unprecedented reversible dynamic transformation in a metal-organic framework involving bond formation that is accompanied by two important structural changes, achiral to chiral and two- to three-dimension. Using two bent organic lig-ands (diimpym = 4,6-di(1H-imidazol-1-yl)pyrimidine; H2npta = 5-nitroisophthalic acid) and CoII(NO3)2*6H2O the coordination pol-ymer Co(diimpym)(npta)*CH3OH, 1*CH3OH, was obtained sol-vothermally. Its structure consisting of knitted pairs of square layers (44-sql) of five-coordinated Co, disordered methanol and crystallizing in achiral Pbca space group at room temperature undergoes a single-crystal to single-crystal (SC-SC) transfor-mation to a 3D interpenetrated framework (pcu) of six-coordinated Co and ordered methanol in chiral P212121 space group below 220 K...
March 21, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28324643/unsymmetrical-iron-p-nh-p-catalysts-for-the-asymmetric-pressure-hydrogenation-of-aryl-ketones
#16
Robert Harold Morris, Samantha Alizabeth Michelle Smith, Paraskevi Olympia Lagaditis, Alan J Lough, Anne Lüpke
The reductive amination of -dialkylphosphine acetaldehydes with enantiopure -aminophosphines is a new, versatile route to unsymmetrical tridentate (pincer) ligands P-NH-P'. Four new ligands PR2CH2CH2NHCHR'CHR''PPh2 (R = iPr, Cy, R' = Ph, CH(CH3)2, R'' = Ph, H) prepared in this way are used to make the iron(II) complexes mer-FeCl2(CO)(P-NH-P') and mer-FeCl(H)(CO)(P-NH-P'). The hydride complex with the rigid ligand with R'= R''= Ph is an efficient and highly enantioselective homogeneous asymmetric pressure hydrogenation (APH) catalyst...
March 21, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28324628/linear-trinuclear-cobalt-complexes-with-o-phenylene-bis-silylamido-ligands
#17
Kirill Yu Monakhov, Jan van Leusen, Paul Koegerler, Emilie-Laure Zins, Esmaïl Alikhani, Moniek Tromp, Andreas Danopoulos, Pierre Braunstein
Transamination of [Co{N(SiMe3)2}2]2 with C6H4(NHSiiPr3)2 gave the linear trinuclear [(Coter{N(SiMe3)2}{μ-η-(o-C6H4(κNSiiPr3)2)2}Coint)] (1) (Coter, Coint = terminal, internal Co, respectively), with 3-coordinate Coter, and Coint 'sandwiched' between the o-phenylenes of the two ligands; experimental and computational data support CoII centres and ditopic o-amido-imino-cyclohexen-allyl ligands; magnetic studies reveal intermetallic ferromagnetic interactions and single-molecule magnet (SMM) character. One-electron reduction of 1 gave the salt 4 with the anion isostructural to 1...
March 21, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28324621/quantum-chemical-dissection-of-the-shortest-p-o%C3%A2-%C3%A2-%C3%A2-i-halogen-bond-the-decisive-role-of-crystal-packing-effects
#18
Milan Kivala, Tobias A Schaub, Rebecca Sure, Frank Hampel, Stefan Grimme
We report on a supramolecular arrangement comprising a bridged triarylphoshine oxide and an aryl iodide that features the shortest ever reported P=O···I halogen bond of 2.683(5) Å in the solid state. X-ray crystallographic analysis together with modern quantum chemical methods were enlisted to dissect the individual contributions that compelled this exceptionally short halogen bond pointing out the decisive role of crystal packing effects.
March 21, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28322472/molecular-chemistry-and-engineering-of-boron-modified-polyorganosilazanes-as-new-processable-and-functional-sibcn-precursors
#19
Samuel Bernard, Antoine Viard, Diane Fonblanc, Marion Schmidt, Abhijeet Lale, Chrystelle Salameh, Anne Soleilhavoup, Mélanie Wynn, Philippe Champagne, Sophie Cerneaux, Florence Babonneau, Georges Chollon, Fabrice Rossignol, Christel Gervais
A series of boron-modified polyorganosilazanes was synthesized from a poly(vinylmethyl-co-methyl)silazane and controlled borane dimethyl sulfide amounts. The role of the chemistry behind their syntheses has been studied in details by solid-state NMR, FT-IR and elemental analyses. Then, the intimate relationship between the chemistry and the processability of these polymers was discussed. Polymers with low boron contents display the appropriate requirements for facile processing in solution such as impregnation of host carbon materials resulting in the design of mesoporous monoliths with high specific surface area after pyrolysis...
March 21, 2017: Chemistry: a European Journal
https://www.readbyqxmd.com/read/28319647/cancer-specific-intracellular-reductive-activation-of-anticancer-pt-iv-prodrugs
#20
Andriy Mokhir, Viktor Reshetnikov, Steffen Daum
Since cellular uptake of anticancer Pt(II)- and Pt(IV)-drugs occurs via different mechanisms, the latter ones can exhibit substantial activity towards cells, which have either intrinsic or acquired resistance towards Pt(II)-drugs. However, this positive effect is diminished due to reductive activation of Pt(IV)-drugs in extracellular space that can be one of the reasons why they were not yet approved for clinical use despite over 60 clinical trials conducted worldwide. Herein we suggest a solution to this problem by achieving highly specific intracellular versus extracellular prodrug reduction...
March 20, 2017: Chemistry: a European Journal
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