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Xinghong Dai, Danyang Gong, Hanyoung Lim, Jonathan Jih, Ting-Ting Wu, Ren Sun, Z Hong Zhou
Kaposi's sarcoma-associated herpesvirus (KSHV) causes Kaposi's sarcoma, a cancer that commonly affects patients with AIDS and which is endemic in sub-Saharan Africa. The KSHV capsid is highly pressurized by its double-stranded DNA genome, as are the capsids of the eight other human herpesviruses. Capsid assembly and genome packaging of herpesviruses are prone to interruption and can therefore be targeted for the structure-guided development of antiviral agents. However, herpesvirus capsids-comprising nearly 3,000 proteins and over 1,300 Å in diameter-present a formidable challenge to atomic structure determination and functional mapping of molecular interactions...
January 17, 2018: Nature
Harris Hyun-Soo Kim
This study examines factors associated with the physical health of Korea's growing immigrant population. Specifically, it focuses on the associations between ethnic networks, community social capital, and self-rated health (SRH) among female marriage migrants. For empirical testing, secondary analysis of a large nationally representative sample (NSMF 2009) is conducted. Given the clustered data structure (individuals nested in communities), a series of two-level random intercepts and slopes models are fitted to probe the relationships between SRH and interpersonal (bonding and bridging) networks among foreign-born wives in Korea...
January 17, 2018: International Journal of Environmental Research and Public Health
Xiaoxiao Hu, Peiquan Xu, Hongying Gong, Guotao Yin
Tungsten trioxide (WO₃) nanorods are synthesized on the surface of graphene (GR) sheets by using a one-step in-situ hydrothermal method employing sodium tungstate (Na₂WO₄·2H₂O) and graphene oxide (GO) as precursors. The resulting WO₃/GR nanocomposites are characterized by X-ray diffraction, Raman spectroscopy, transmission electron microscopy, scanning electron microscopy and X-ray photoelectron spectroscopy. The results confirm that the interface between WO₃ nanorod and graphene contains chemical bonds...
January 17, 2018: Materials
Chuanlong Lin, Xue Yong, John S Tse, Jesse S Smith, Stanislav V Sinogeikin, Curtis Kenney-Benson, Guoyin Shen
We report the results of in situ structural characterization of the amorphization of crystalline ice Ih under compression and the relaxation of high-density amorphous (HDA) ice under decompression at temperatures between 96 and 160 K by synchrotron x-ray diffraction. The results show that ice Ih transforms to an intermediate crystalline phase at 100 K prior to complete amorphization, which is supported by molecular dynamics calculations. The phase transition pathways show clear temperature dependence: direct amorphization without an intermediate phase is observed at 133 K, while at 145 K a direct Ih-to-IX transformation is observed; decompression of HDA shows a transition to low-density amorphous ice at 96 K and ∼1  Pa, to ice Ic at 135 K and to ice IX at 145 K...
September 29, 2017: Physical Review Letters
Wilbert J Smit, Fujie Tang, M Alejandra Sánchez, Ellen H G Backus, Limei Xu, Taisuke Hasegawa, Mischa Bonn, Huib J Bakker, Yuki Nagata
Phase-resolved sum-frequency generation measurements combined with molecular dynamics simulations are employed to study the effect of temperature on the molecular arrangement of water on the basal face of ice. The topmost monolayer, interrogated through its nonhydrogen-bonded, free O-H stretch peak, exhibits a maximum in surface H-bond density around 200 K. This maximum results from two competing effects: above 200 K, thermal fluctuations cause the breaking of H bonds; below 200 K, the formation of bulklike crystalline interfacial structures leads to H-bond breaking...
September 29, 2017: Physical Review Letters
Mostafa Youssef, Krystyn J Van Vliet, Bilge Yildiz
We demonstrate a thermodynamic formulation to quantify defect formation energetics in an insulator under a high electric field. As a model system, we analyzed neutral oxygen vacancies (color centers) in alkaline-earth-metal binary oxides using density functional theory, Berry phase calculations, and maximally localized Wannier functions. The work of polarization lowers the field-dependent electric Gibbs energy of formation of this defect. This is attributed mainly to the ease of polarizing the two electrons trapped in the vacant site, and secondarily to the defect induced reduction in bond stiffness and softening of phonon modes...
September 22, 2017: Physical Review Letters
Suman Dana, Anup Mandal, Harekrishna Sahoo, Sumitava Mallik, Gowri Sankar Grandhi, Mahiuddin Baidya
A straightforward synthesis of 2-styrylbenzoic acids from aryl carboxylic acids is disclosed through a carboxylate-assisted coupling under Ru(II) catalysis. This protocol is simple and exhibits broad scope with high tolerance of common organic functional groups, providing good to excellent yields of diverse olefinated products. The efficacy of this protocol has been showcased through sequential syntheses of isochromanone, isocoumarin, and formal synthesis of anacardic acid derivative in good yields.
January 17, 2018: Organic Letters
Cheng-Yi Chen, Fengxian He, Guangrong Tang, Huiqing Yuan, Ning Li, Jinmin Wang, Roger Faessler
An efficient synthesis of quinazolines based on an iron-catalyzed C(sp3)-H oxidation and intramolecular C-N bond formation using tert-BuOOH as the terminal oxidant is described. The reaction of readily available 2-alkylamino benzonitriles with various organometallic reagents led to 2-alkylamino N-H ketimine species. The FeCl2-catalyzed C(sp3)-H oxidation of the alkyl group employing tert-BuOOH followed by intramolecular C-N bond formation and aromatization afforded a wide variety of 2,4-disubstituted quinazolines in good to excellent yields...
January 17, 2018: Journal of Organic Chemistry
Saumyak Mukherjee, Sayantan Mondal, Ashish Anilrao Deshmukh, Balasubramanian Gopal, Biman Bagchi
Self-assembly of proteins often gives rise to interesting quasi-stable structures that serve important biological purposes. Insulin hexamer is such an assembly. While monomer is the biologically active form of insulin, hexamer serves as the storehouse of the hormone. The hexamer also prevents the formation of higher order aggregates. While several studies explored the role of bivalent metal ions like Zn2+, Ca2+ etc. in the stabilization of the hexameric form, the role of water molecules has been ignored. We combine molecular dynamics simulations, quantum calculations and X-ray analyses to discover that a team of approximately ten water molecules confined inside a barrel-shaped nano-cavity at the center of insulin hexamer is one of the major causes that account for the unusual stability of the biomolecular assembly...
January 17, 2018: Journal of Physical Chemistry. B
Yu Liu, Qiao-Lin Wang, Cong-Shan Zhou, Biquan Xiong, Pan-Liang Zhang, Chang-An Yang, Ke-Wen Tang
A novel visible-light-mediated ipso-carboacylation of N-(p-methoxyaryl)propiolamides with acyl chloride has been established for the synthesis of diverse 3-acylspiro[4,5]trienones with high selectivity and efficiency. This method represents a new difunctionalization of alkynes through cross coupling of the acyl chloride C-Cl bonds with an ipso-aromatic carbon by simultaneously forming two new carbon-carbon bonds and one carbon-oxygen double bond.
January 17, 2018: Journal of Organic Chemistry
Rachel A Harris, Jody C May, Craig A Stinson, Yu Xia, John A McLean
The increasing focus on lipid metabolism has revealed a need for analytical techniques capable of structurally characterizing lipids with a high degree of specificity. Lipids can exist as any one of a large number of double bond positional isomers, which are indistinguishable by single-stage mass spectrometry alone. Ozonolysis reactions coupled to mass spectrometry have previously been demonstrated as a means for localizing double bonds in unsaturated lipids. Here we describe an online, solution-phase reactor using ozone produced via a low-pressure mercury lamp, which generates aldehyde products diagnostic of cleavage at a particular double bond position...
January 17, 2018: Analytical Chemistry
Christoph Heinz, J Patrick Lutz, Eric M Simmons, Michael M Miller, William R Ewing, Abigail G Doyle
This report describes a three-component, Ni-catalyzed reductive coupling that enables the convergent synthesis of tertiary benzhydryl amines, which are challenging to access by traditional reductive amination methodologies. The reaction makes use of iminium ions generated in situ from the condensation of secondary N-trimethylsilyl amines with benzaldehydes, and these species undergo reaction with several distinct classes of organic electrophiles. The synthetic value of this process is demonstrated by a single-step synthesis of antimigraine drug flunarizine (Sibelium®) and high yielding derivatization of paroxetine (Paxil®) and metoprolol (Lopressor®)...
January 17, 2018: Journal of the American Chemical Society
Qun Jing, Guang Yang, Zhaohui Chen, Xiaoyu Dong, Yunjing Shi
In this paper, a joint strategy was proposed to investigate the microscopic origin of the second-harmonic-generation (SHG) response in nonpolar ABCO3F compounds. The SHG coefficients of ABCO3F were evaluated using finite-field and sum-over-states methods. The tendency of the obtained SHG tensors is in good agreement with the powder SHG response. The atomic contribution was investigated using variation of the atomic charges and bandwidth of occupied atomic states. The results show that oxygen states play a key role in determining the SHG response, and the neighboring divalent cations exert a indirect influence via covalent interaction...
January 17, 2018: Inorganic Chemistry
Fernando Albericio, Saba Alapour, Beatriz G de la Torre, Deresh Ramjugernath, Neil Anthony Koorbanally
Considerable attention has been devoted to fluorinated compounds due to their unique and interesting properties. Many modern pharmaceuticals contain fluorinated substituents, which are commonly synthesized using selective fluorinating reagents. Decafluorobiphenyl (DFBP) as a fluorinated linker is susceptible to nucleophilic attack. This nucleophilic reaction has been widely studied using various nucleophiles. Sulfur and nitrogen containing nucleophiles have been of particular interest, especially in bioconjugated reactions...
January 17, 2018: Bioconjugate Chemistry
Martin Andreas Robert George, Nguyen Xuan Truong, Marco Savoca, Otto Dopfer
We report the spectroscopic characterization of protonated monosilanol (SiH3OH2+) isolated in the gas phase, thus providing the first experimental determination of the structure and bonding of a member of the elusive silanole family. The SiH3OH2+ ion is generated in a silane/water plasma expansion, and its structure is derived from the IR photodissociation (IRPD) spectrum of its Ar cluster measured in a tandem mass spectrometer. The chemical bonding in SiH3OH2+ is analyzed by density functional theory (DFT) calculations, providing detailed insight into the nature of the dative H3Si+-OH2 bond...
January 17, 2018: Angewandte Chemie
Ulrich S Schubert, Ronny Tepper
The halogen bond is a supramolecular interaction between a Lewis-acidic region of a covalently bound halogen and a Lewis base. It has been studied widely in silico and experimentally in the solid state; however, solution phase applications have attracted enormous interest in the last years. This Minireview highlights selected recent developments of halogen bond interactions in solution with focus on the use of halogen bond receptors in anion recognition and sensing, anion templated self-assembly as well as in organo-catalysis...
January 17, 2018: Angewandte Chemie
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
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
Vivek Sinha, Bruno Pribanic, Bas de Bruin, Monica Trincado, Hansjörg Grützmacher
Coordination of the diazadiene diolefin ligand trop2dad to ruthenium leads to various complexes of composition [Ru(trop2dad)(L)]. DFT studies indicate that the closed-shell singlet (CSS), open-shell singlet (OSS) and triplet electronic structures of this species are close in energy, with the OSS state being the lowest in energy for all tested functionals. Singlet state CASSCF calculations reveal a significant multireference character for these complexes. The closed-shell singlet wavefunction dominates, but these complexes have a significant (~8-16%) open-shell singlet [d7 Ru(I)(L)(trop2dad●-] contribution mixed into the ground state...
January 17, 2018: Chemistry: a European Journal
Mauricio Cattaneo, Christine Schiewer, Anne Schober, Sebastian Dechert, Inke Siewert, Franc Meyer
[1,2]dithiino[4,3-b:5,6-b']dipyridine (1) and its protonated open form 3,3'-dithiol-2,2'-bipyridine (2) were synthesised and their interconversion investigated. The X-ray structure of 2 revealed an anti orientation of the two pyridine units and a zwitterionic form. In depth electrochemical studies in combination with DFT calculations lead to a comprehensive picture of the redox chemistry of 1 in the absence and presence of protons. Initial one electron reduction at E1 = -1.97 V results in the formation of the radical anion 1red with much elongated S-S bond, which readily undergoes further reduction at E2 = -2...
January 17, 2018: Chemistry: a European Journal
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