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Chemistry: a European Journal

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https://www.readbyqxmd.com/read/29349863/experimental-observation-of-thermally-excited-triplet-states-of-heavier-group-15-element-centered-diradical-dianions
#1
Yong Fang, Li Zhang, Cheng Cheng, Yue Zhao, Manabu Abe, Gengwen Tan, Xinping Wang
One-electron reductions of Mes*As=Fl* (1; Fl* = 2,7-di-tert-butylfluorenylidene, Mes* = 2,4,6-tBu3C6H2) and diarsaalkenes [1,2-b]-IF(=AsMes*)2 (2; IF = indenofluorene) with potassium led to the isolation of the arsenic-centered radical anion salts 1K and 2K, respectively. The diradical dianion salts 2K2 and 3K2 were afforded by the reduction of 2 and 2,8-tBu2-[2,1-b]-IF(=AsMes*)2 (3) with an excess amount of KC8. The radicals have been investigated by single-crystal X-ray crystallography, EPR and UV-Vis absorption spectroscopy, along with theoretical calculations...
January 18, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29349830/synthesis-and-structure-of-a-longitudinally-twisted-hexacene
#2
Robert G Clevenger, Bharat Kumar, Elizabeth M Menuey, Kathleen Victoria Kilway
The addition of phenyllithium to a polycyclic quinone, 9,11,12,21,22,24-hexaphenyltetrabenzo[a,c,n,p]hexacene-10,23-di-one (10), followed by SnCl2-mediated reduction of the diol intermediate, yielded 9,10,11,12,21,22,23,24-octaphenyltetrabenzo-[a,c,n,p]hexacene (4). Crystallographic analysis of hexacene 4 showed it to possess a longitudinal twist of 184°, which was in good agreement with AM1 calculations. In addition to being the most twisted acene synthesized to this point, compound 4 contains within its substructure the most twisted naphthalene, anthracene, tetracene, and pentacene moieties described...
January 18, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29349825/synthesis-of-single-and-double-dibenzohelicenes-via-rhodium-catalyzed-intramolecular-2-2-2-and-2-1-2-1-cycloadditions
#3
Ryota Yamano, Yu Shibata, Ken Tanaka
Dibenzo[7]helicenes were synthesized with up to 99% ee via the rhodium(I)/binap complex-catalyzed enantioselective intramolecular [2+2+2] cycloaddition of 2-phenylnaphthalene-linked tryines. Additionally, [2+1+2+1] cycloaddition products, twisted anthracenes, were also synthesized by using difluorphos as a ligand. Although this compound is not configurationally stable at elevated temperature, the Scholl reaction of which afforded a configurationally stable double dibenzo[6]helicene. The thus obtained dibenzo[7]helicene exhibited good circularly polarized luminescence property and the double dibenzo[6]helicene exhibited high fluorescence quantum yield...
January 18, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29345775/versatile-modes-of-cooperative-b-h-bond-activation-reactions-in-ruthenium-carbene-complexes-addition-ring-opening-and-insertion
#4
Scharf T Lennart, Julia Weismann, Kai-Stephan Feichtner, Felix Lindl, Viktoria H Gessner
Cooperative B-H bond activation reactions with thio- and iminophosphoryl tethered ruthenium carbene complexes are reported. The complexes show surprisingly different reactivities towards the commonly employed boranes CatBH, PinBH and BH3∙LB as a result of different modes of metal ligand cooperation. While the iminophosphoryl system allows for selective 1,2-addition of the B-H bond across the Ru=C double bond, the sulfur analogue only delivers the 1,2-addition product for CatBH, while activation of BH3 and PinBH lead to further insertion reactions in one or more sides of the Ru-C-P-S-ring...
January 18, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29345774/rewiring-chemical-networks-based-on-dynamic-dithioacetal-and-disulfide-bonds
#5
Gaston Orrillo, Agustina La-Venia, Escalante Andrea, Ricardo L E Furlan
The control of the connectivity between nodes of synthetic networks is still largely unexplored. To address this point we take advantage of a simple dynamic chemical system with two exchange levels that are mutually connected and can be activated simultaneously or sequentially. Dithioacetals and disulfides can be exchanged simultaneously under UV light in the presence of a sensitizer. Crossover reactions between both exchange processes produce a fully connected chemical network. On the other hand, the use of acid, base or UV light connects different nodes allowing network rewiring...
January 18, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29345739/exact-mapping-from-many-spin-hamiltonians-to-giant-spin-hamiltonians
#6
Shadan Ghassemi Tabrizi, Alexei V Arbuznikov, Martin Kaupp
Exchange-coupled molecular spin clusters (e.g. single-molecule magnets) are routinely described in terms of a many-spin Hamiltonian (MSH) that considers individual spins, or a giant-spin Hamiltonian (GSH) that treats the system as a collective spin. When isotropic coupling is weak, the mapping MSH → GSH ('spin projection'), becomes non-trivial due to mixing of spin multiplets by anisotropic terms, an effect crucial for generating transverse magnetic anisotropy. Going beyond perturbational spin-projection schemes, based on exact diagonalization and canonical effective Hamiltonian theory, we construct a GSH that exactly matches the energies of the relevant (2S+1) states...
January 18, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29345002/remote-c-h-activation-of-various-n-heterocycles-using-a-single-template
#7
Guoqiang Yang, Dajian Zhu, Peng Wang, Ri-Yuan Tang, Jin-Quan Yu
A single simple ortho-sulfonyl benzonitrile template was developed to achieve remote C-H olefination of six different classes of N-heterocycles. We demonstrate that, by varying precatalysts and conditions, the same template can be applied to the remote C-H activation of six structurally distinct heterocyclic scaffolds, and the site-selectivity can be predicted based on distance and geometry. Furthermore, this new development shows that template-directed remote C-H activation are possible via macrocyclopalladation processes with smaller ring sizes...
January 18, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29344997/integration-of-open-metal-sites-and-lewis-basic-sites-for-construction-of-a-cu-mof-with-rare-chiral-oh-type-of-cage-for-high-performance-of-methane-purification
#8
Zhan Shi, Lingkun Meng, Ziyuan Niu, Chen Liang, XingLong Dong, Kang Liu, Guanghua Li, Chunguang Li, Yu Han, Shouhua Feng
A Cu MOF [Cu4(PMTD)2(H2O)3]·20H2O, 1, (Where PMTD is (1,4-phenylenebis(5-methyl-4H-1,2,4-triazole-3,4-diyl)bis(5-carboxylato-3,1-phenylene)bis(hydroperoxymethanide) with rare chiral Oh type of cage and dual functionalities of open metal sites and Lewis basic sites based on a designed U-shaped ligand was synthesized by hydrothermal method. It exhibits high-capacity of CO2, C2 and C3 hydrocarbon storage capacity under atmospheric pressure as well as high H2 (1.96% wt) adsorption capacity at 77K. Methane purification capacity was tested and verified step by step...
January 18, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29342326/mixed-fluorotryptophan-substitutions-at-the-same-residue-expand-the-versatility-of-%C3%A2-%C3%A2-f-protein-nmr-spectroscopy
#9
Calem Kenward, Kyungsoo Shin, Jan Rainey
The strategy of applying fluorine NMR to characterize ligand binding to a membrane protein prepared with mixtures of tryptophans substituted with F at different positions on the indole ring was tested. The ¹⁹F NMR behavior of 4-, 5-, 6-, and 7-fluorotryptophan were directly compared as a function of both micellar environment and fragment size for two overlapping apelin receptor (AR/APJ) segments - one with a single transmembrane (TM) helix and two tryptophan residues, the other with three TM helices and two additional tryptophan residues...
January 17, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29342315/oxidation-of-methylalumoxane-oligomers
#10
Harmen Zijlstra, Scott Collins, Jason Scott McIndoe
The anions formed from methylalumoxane (MAO) and suitable donors (e.g. octamethyltrisiloxane) are amenable to mass spectrometric (MS) analysis. Their composition as deduced from this data allows direct insight into the chemical transformations of their neutral precursors. One such process is oxidation, which is well-known to be facile for MAO without any clear idea of what actually occurs at a molecular level. Addition of O2 to MAO results in immediate gelation, but MS analysis reveals no corresponding change to the composition of the principal oligomeric anions...
January 17, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29341382/synthesis-crystal-analysis-and-optoelectronic-properties-of-diazole-functionalized-acenes-and-azaacenes
#11
Jinchong Xiao, Huahang Pan, Tingting Song, Xiaomeng Yin, Pengcheng Jin
Doping heteroatoms into the skeletons of parent acenes can provide more chances to construct novel thermally and photo-stable organic π-conjugated semiconductors. Herein, a family of diazole-decorated acenes (APyS and APySe) and azaacenes (PyP, PyTh, PyPy, PyPh and PyAP) have been successfully synthesized through the classical reactions. Single crystal X-ray analyses showed that these as-formed diazole-modified derivatives adopted twisted topology configuration, whereas the azaacenes display reclining-chair architectures, besides twisted structure...
January 17, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29341369/structural-factors-affecting-binding-of-platinum-anticancer-agents-with-phospholipids-influence-of-charge-and-phosphate-clamp-formation
#12
Anil Kumar Gorle, Junyong Zhang, Qin Liu, Susan J Berners-Price, Nicholas P Farrell
We report a detailed NMR and DFT study of the interaction of polynuclear platinum anticancer agents (PPCs) with negatively charged phospholipids as a mechanism for their cellular uptake. The reactions of fully 15N-labelled [{trans-PtCl(NH3)2}2(-trans-Pt(NH3)2{NH2(CH2)6NH2}2)]4+ (15N-1, 1,0,1/t,t,t) and the dinuclear [{trans-PtCl(NH3)2}2{-H2N(CH2)6NH2}]2+ (15N-2, 1,1/t,t) with the sodium salt of 1,2-dihexanoyl-sn-glycero-3-phosphate (DHPA) were studied at 298 K, pH ~5.4, by [1H,15N] HSQC 2D NMR spectroscopy...
January 17, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29341353/fluorescence-redox-blinking-adaptable-to-structural-analysis-of-nucleic-acids
#13
Takafumi Miyata, Naohiko Shimada, Atsushi Maruyama, Kiyohiko Kawai
The phenomenon of "blinking" is unique to single-molecule fluorescence measurements. By designing a fluorophore with an appropriate dark state lifetime (τoff), we have devised a kinetic analysis based on the control of fluorescence blinking (KACB) to investigate the dynamics of biomolecules. By controlling the redox reaction based blinking (rKACB), we have previously investigated conformational dynamics of RNA at the single-molecule level. However, there have been little knowledge about suitable fluorescent molecules for rKACB, and the application of rKACB has been limited to the analysis of hairpins and duplex structures of nucleic acids...
January 17, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29341342/the-pentagonal-pyramidal-hexamethylbenzene-dication-the-many-shades-of-coordination-chemistry-at-carbon
#14
Johannes E M N Klein, Remco W A Havenith, Gerald Knizia
A recent report of the crystal structure of the pentagonal-pyramidal hexamethylbenzene dication C6(CH3)62+ by Malischewski and Seppelt [Angew. Chem. Int. Ed. 2017, 56, 368.] confirmed the structural proposal made in the first report of this compound in 1973 by Hogeveen and Kwant [Tetrahedron Lett. 1973, 14, 1665]. The widespread attention that this compound quickly gained led us to reinvestigate its electronic structure. Based on intrinsic bond orbital analysis, effective oxidation state analysis, ring current analysis and comparison to well established coordination complexes, we demonstrate that the central carbon atom behaves like a transition metal...
January 17, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29341333/br%C3%A3-nsted-base-catalyzed-umpolung-intramolecular-cyclization-of-alkynyl-imines
#15
Azusa Kondoh, Masahiro Terada
A novel "umpolung" intramolecular cyclization of alkynyl imines, in which the electrophilic imine sp2-carbon formally serves as a nucleophilic site, was developed under Brønsted base catalysis. The reaction involves the unprecedented catalytic generation of α-aminoester enolates from α-iminoesters via the 1,2-addition of the anion of a secondary phosphite to an imine moiety followed by the [1,2]-rearrangement of a dialkoxyphosphoryl moiety from carbon to nitrogen, which is a formal umpolung process, and the intramolecular addition to an alkyne...
January 17, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29341313/title-synthesis-of-%C3%AE-l-fucopyranoside-presenting-glycoclusters-and-investigation-of-their-interaction-with-recombinant-photorhabdus-asymbiotica-lectin-phl
#16
Jančaříková Gita, Mihály Herczeg, Eva Fujdiarová, Josef Houser, Katalin E Kövér, Anikó Borbás, Michaela Wimmerová, Magdolna Csávás
Photorhabdus asymbiotica is a gram-negative bacterium that is not only as effective an insect pathogen as other members of the genus, but it also causes serious diseases in humans. The recently identified lectin PHL from P. asymbiotica verifiably modulates an immune response of humans and insects, which supports the idea that the lectin might play an important role in the host-pathogen interaction. Dimeric PHL contains up to seven L-fucose specific binding sites per monomer, and in order to target multiple binding sites of PHL, α-L-fucoside-containing di-, tri- and tetravalent glycoclusters were synthesized...
January 17, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29341307/chemical-and-enzymatic-strategies-for-bacterial-and-mammalian-cell-surface-engineering
#17
Xiaobao Bi, Juan Yin, Ashley Chen Guanbang, Chuan-Fa Liu
Cell surface serves important functions such as the regulation of cell-cell and cell-environment interactions. The understanding and manipulation of the cell surface is important for a wide range of fundamental studies of cellular behavior and for biotechnological and medical applications. With the rapid advance of biology, chemistry and materials science, many strategies have been developed for the functionalization of bacterial and mammalian cell surfaces. Here, we review the recent development of chemical and enzymatic approaches to cell surface engineering with particular emphasis on discussing the advantages and limitations of each of these strategies...
January 17, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29341305/plasmid-templated-control-of-dna-cyclodextrin-nanoparticle-morphology-through-molecular-vector-design-for-effective-gene-delivery
#18
Laura Gallego-Yerga, Juan M Benito, Laura Blanco-Fernández, María Martínez-Negro, Itziar Vélaz, Emilio Aicart, Elena Junquera, Carmen Ortiz Mellet, Conchita Tros de Ilarduya, Jose M Garcia Fernandez
Engineering self-assembled superstructures through complexation of plasmid DNA (pDNA) and single-isomer nanometric size macromolecules (molecular nanoparticles) is a promising strategy for gene delivery. Notably, the functionality and overall architecture of the vector can be precisely moulded at the atomic level by chemical tailoring, enabling unprecedented opportunities for structure/self-assembling/pDNA delivery relationship studies. Beyond this notion, by judiciously preorganizing the functional elements in cyclodextrin (CD)-based molecular nanoparticles through covalent dimerization, here we demonstrate that the morphology of the resulting nanocomplexes (CDplexes) can be tuned, from spherical to ellipsoidal, rod-type or worm-like nanoparticles, which makes it possible to gain understanding of their shape-dependent transfection properties...
January 17, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29341304/enantioselective-synthesis-of-aminodiols-by-sequential-rh-catalysed-oxyamination-kinetic-resolution-expanding-the-substrate-scope-of-amidine-based-catalysis
#19
Joan Guasch, Irene Giménez, Ignacio Funes-Ardoiz, Isabel Matheu, Feliu Maseras, Sergio Castillón, Yolanda Díaz, Miguel Bernús
Regio- and stereoselective oxyamination of dienes through a tandem rhodium catalysed aziridination-nucleophilic opening affords racemic oxazolidinone derivatives, which undergo a kinetic resolution acylation process using ABCs (amidine-based catalysts) achieving s values up to 117. This protocol was applied to the enantioselective synthesis of sphingosine.
January 17, 2018: Chemistry: a European Journal
https://www.readbyqxmd.com/read/29341302/twisted-charge-transfer-antennas-for-ultra-bright-terbium-iii-and-dysprosium-iii-bioprobes
#20
Anh Thy Bui, Amandine Roux, Alexei Grichine, Alain Duperray, Chantal Andraud, Olivier Maury
The design of original twisted charge transfer antennas where a non planar geometry is enforced thanks to one or two bulky ortho-Me substituents allows us to prepare the corresponding ultra-bright Tb(III) and Dy(III) bioprobes. The brightness of the Tb(III) derivative compares well with that of the benchmark Tb-Lumi4 complex. The first bio-imaging experiments with a Dy(III) luminescent bioprobe are also reported.
January 17, 2018: Chemistry: a European Journal
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