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atomic structure

Xiaotian Zhang, Tanushree H Choudhury, Mikhail Chubarov, Yu Xiang, Bhakti Jariwala, Fu Zhang, Nasim Alem, Gwo-Ching Wang, Joshua A Robinson, Joan M Redwing
A multi-step diffusion-mediated process was developed to control the nucleation density, size and lateral growth rate of WSe2 domains on c-plane sapphire for the epitaxial growth of large area monolayer films by gas source chemical vapor deposition (CVD). The process consists of an initial nucleation step followed by an annealing period in H2Se to promote surface diffusion of tungsten-containing species to form oriented WSe2 islands with uniform size and controlled density. The growth conditions were then adjusted to suppress further nucleation and laterally grow the WSe2 islands to form a fully coalesced monolayer film in less than one hour...
January 17, 2018: Nano Letters
Hongxian Liu, Zhenxing Fang, Yongfei Su, Yuanli Suo, Shuping Huang, Yongfan Zhang, Kaining Ding
We have systematically investigated the electronic structures and activation capacities of BiOBr {001} facets with different atomic terminations by means of DFT methods. Our calculations reveal that oxygen vacancies (OVs) give a significant boost in band edges of the O-terminated BiOBr {001} facets, and excess electrons induced by OVs could exceed the reduction potentials of high-energy N2 intermediates. Interestingly, the Bi-terminated BiOBr {001} facets may be good candidates for photocatalytic nitrogen fixation due to the stronger activation ability of N2 molecules comparing with O-terminated BiOBr {001} facets with OVs...
January 17, 2018: Chemistry, An Asian Journal
Julien Frouin, Antoine Languillaume, Justine Mas, Delphine Mieulet, Arnaud Boisnard, Axel Labeyrie, Mathilde Bettembourg, Charlotte Bureau, Eve Lorenzini, Muriel Portefaix, Patricia Turquay, Aurore Vernet, Christophe Périn, Nourollah Ahmadi, Brigitte Courtois
Salinity tolerance is an important quality for European rice grown in river deltas. We evaluated the salinity tolerance of a panel of 235 temperate japonica rice accessions genotyped with 30,000 SNP markers. The panel was exposed to mild salt stress (50 mM NaCl; conductivity of 6 dS m-1) at the seedling stage. Eight different root and shoot growth parameters were measured for both the control and stressed treatments. The Na+ and K+ mass fractions of the stressed plants were measured using atomic absorption spectroscopy...
2018: PloS One
Melinda M Diver, Leanne Pedi, Akiko Koide, Shohei Koide, Stephen B Long
The maturation of RAS GTPases and approximately 200 other cellular CAAX proteins involves three enzymatic steps: addition of a farnesyl or geranylgeranyl prenyl lipid to the cysteine (C) in the C-terminal CAAX motif, proteolytic cleavage of the AAX residues and methylation of the exposed prenylcysteine residue at its terminal carboxylate. This final step is catalysed by isoprenylcysteine carboxyl methyltransferase (ICMT), a eukaryote-specific integral membrane enzyme that resides in the endoplasmic reticulum...
January 17, 2018: Nature
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
Gaozhi Chen, Yang Liu, Regina Goetz, Lili Fu, Seetharaman Jayaraman, Ming-Chang Hu, Orson W Moe, Guang Liang, Xiaokun Li, Moosa Mohammadi
The ageing suppressor α-klotho binds to the fibroblast growth factor receptor (FGFR). This commits FGFR to respond to FGF23, a key hormone in the regulation of mineral ion and vitamin D homeostasis. The role and mechanism of this co-receptor are unknown. Here we present the atomic structure of a 1:1:1 ternary complex that consists of the shed extracellular domain of α-klotho, the FGFR1c ligand-binding domain, and FGF23. In this complex, α-klotho simultaneously tethers FGFR1c by its D3 domain and FGF23 by its C-terminal tail, thus implementing FGF23-FGFR1c proximity and conferring stability...
January 17, 2018: Nature
Shuai Zhang, Chen-Guang Wang, Ming-Yang Li, Di Huang, Lain-Jong Li, Wei Ji, Shiwei Wu
The atomic and electronic structure of intrinsic defects in a WSe_{2} monolayer grown on graphite was revealed by low temperature scanning tunneling microscopy and spectroscopy. Instead of chalcogen vacancies that prevail in other transition metal dichalcogenide materials, intrinsic defects in WSe_{2} arise surprisingly from single tungsten vacancies, leading to the hole (p-type) doping. Furthermore, we found these defects to dominate the excitonic emission of the WSe_{2} monolayer at low temperature. Our work provided the first atomic-scale understanding of defect excitons and paved the way toward deciphering the defect structure of single quantum emitters previously discovered in the WSe_{2} monolayer...
July 28, 2017: Physical Review Letters
Jordan Muscatello, Enrique Chacón, Pedro Tarazona, Fernando Bresme
The interfacial thermal resistance determines condensation-evaporation processes and thermal transport across material-fluid interfaces. Despite its importance in transport processes, the interfacial structure responsible for the thermal resistance is still unknown. By combining nonequilibrium molecular dynamics simulations and interfacial analyses that remove the interfacial thermal fluctuations we show that the thermal resistance of liquid-vapor interfaces is connected to a low density fluid layer that is adsorbed at the liquid surface...
July 28, 2017: Physical Review Letters
Josef Grenz, Arne Köhler, Alexander Schwarz, Roland Wiesendanger
We demonstrate that the magnetic nano-Skyrmion lattice on the Fe monolayer on Ir(111) and the positions of the Fe atoms can be resolved simultaneously using magnetic exchange force microscopy. Thus, the relation between magnetic and atomic structure can be determined straightforwardly by evaluating the Fourier transformation of the real space image data. We further show that the magnetic contrast can be mapped on a Heisenberg-like magnetic interaction between tip and sample spins. Since our imaging technique is based on measuring forces, our observation paves the way to study Skyrmions or other complex spin textures on insulating sample systems with atomic resolution...
July 28, 2017: Physical Review Letters
E Miles Stoudenmire, Steven R White
We introduce a hybrid approach to applying the density matrix renormalization group to continuous systems, combining a grid approximation along one direction with a finite Gaussian basis set for the remaining two directions. This approach is especially useful for chainlike molecules, where the grid is used in the long direction. For hydrogen chain systems, the computational time scales approximately linearly with the number of atoms, as we show with near-exact minimal basis set calculations with up to 1000 atoms...
July 28, 2017: Physical Review Letters
R Smith, Tz Kokalova, C Wheldon, J E Bishop, M Freer, N Curtis, D J Parker
Excited states in certain atomic nuclei possess an unusual structure, where the dominant degrees of freedom are those of α clusters rather than individual nucleons. It has been proposed that the diffuse 3α system of the ^{12}C Hoyle state may behave like a Bose-Einstein condensate, where the α clusters maintain their bosonic identities. By measuring the decay of the Hoyle state into three α particles, we obtained an upper limit for the rare direct 3α decay branch of 0.047%. This value is now at a level comparable with theoretical predictions and could be a sensitive probe of the structure of this state...
September 29, 2017: Physical Review Letters
Zongfang Wu, Agata Płucienik, Felix E Feiten, Matthias Naschitzki, Walter Wachsmann, Sandy Gewinner, Wieland Schöllkopf, Volker Staemmler, Helmut Kuhlenbeck, Hans-Joachim Freund
Vibrational action spectroscopy employing infrared radiation from a free-electron laser has been successfully used for many years to study the vibrational and structural properties of gas phase aggregates. Despite the high sensitivity of this method no relevant studies have yet been conducted for solid sample surfaces. We have set up an experiment for the application of this method to such targets, using infrared light from the free-electron laser of the Fritz Haber Institute. In this Letter, we present first results of this technique with adsorbed argon and neon atoms as messengers...
September 29, 2017: Physical Review Letters
Ivan Kozyryev, Nicholas R Hutzler
Precision searches for time-reversal symmetry violating interactions in polar molecules are extremely sensitive probes of high energy physics beyond the standard model. To extend the reach of these probes into the PeV regime, long coherence times and large count rates are necessary. Recent advances in laser cooling of polar molecules offer one important tool-optical trapping. However, the types of molecules that have been laser cooled so far do not have the highly desirable combination of features for new physics searches, such as the ability to fully polarize and the existence of internal comagnetometer states...
September 29, 2017: Physical Review Letters
Jisong Yao, Jing Ge, Bo-Ning Han, Kun-Hua Wang, Hong-Bin Yao, Hao-Lei Yu, Jian-Hai Li, Bai-Sheng Zhu, Jizhong Song, Chen Chen, Qun Zhang, Haibo Zeng, Yi Luo, Shu-Hong Yu
Inorganic perovskite CsPbBr3 nanocrystals (NCs) are emerging, highly attractive light emitters with high color purity and good thermal stability for light-emitting diodes (LEDs). Their high photo/electroluminescence efficiencies are very important for fabricating efficient LEDs. Here, we propose a novel strategy to enhance the photo/electroluminescence efficiency of CsPbBr3 NCs through doping of heterovalent Ce3+ ions via a facile hot-injection method. The Ce3+ cation was chosen as the dopant for CsPbBr3 NCs by virtue of its similar ion radius and formation of higher energy level of conduction band with bromine in comparison with the Pb2+ cation to maintain the integrity of perovskite structure without introducing additional trap states...
January 17, 2018: Journal of the American Chemical Society
Vladimir Gevorgyan, Maxim Ratushnyy, Marvin Parasram, Yang Wang
A novel mild, visible light-induced Pd-catalyzed hydrogen atom translocation/atom transfer radical cyclization (HAT/ATRC) cascade has been developed. This protocol involves a 1,5-HAT process of previously unknown hybrid vinyl Pd-radical intermediates leading to iodomethyl carbo- and heterocyclic structures.
January 16, 2018: Angewandte Chemie
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
Piotr Aleksander Guńka, Michał Hapka, Michael Hanfland, Maciej Dranka, Grzegorz Chałasiński, Janusz Zachara
Investigations into the helium permeation of arsenolite, the cubic, molecular arsenic(III) oxide polymorph As₄O₆, were carried out in order to understand how and why arsenolite helium clathrate As₄O₆∙2He is formed. High-pressure synchrotron X-ray diffraction experiments on arsenolite single crystals revealed that the permeation of helium into non-porous arsenolite depends on the time during which the crystal is subjected to high pressure and on the crystal history. The single crystal was totally transformed into As₄O₆·2He within 45 h under 5 GPa...
January 17, 2018: Chemphyschem: a European Journal of Chemical Physics and Physical Chemistry
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
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
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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