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atomic structure

Michael J Walsh, Wenming Tong, Hadas Katz-Boon, Paul Mulvaney, Joanne Etheridge, Alison M Funston
The phenomenon of symmetry breaking-in which the order of symmetry of a system is reduced despite manifest higher-order symmetry in the underlying fundamental laws-is pervasive throughout science and nature, playing a critical role in fields ranging from particle physics and quantum theory to cosmology and general relativity. For the growth of crystals, symmetry breaking is the crucial step required to generate a macroscopic shape that has fewer symmetry elements than the unit cell and/or seed crystal from which it grew...
November 16, 2017: Accounts of Chemical Research
Emilia Caselli, Chiara Romagnoli, Rachel A Powers, Magdalena A Taracila, Alexandra A Bouza, Hollister C Swanson, Kali A Smolen, Francesco Fini, Bradley J Wallar, Robert A Bonomo, Fabio Prati
Boronic acids are attracting a lot of attention as -lactamase inhibitors, and in particular compound S02030 (Ki = 44 nM) proved to be a good lead compound against ADC-7 (Acinetobacter Derived Cephalosporinase), one of the most significant resistance determinants in A. baumannii. The atomic structure of the ADC-7/S02030 complex highlighted the importance of critical structural determinants for recognition of the boronic acids. Herein, to elucidate the role in recognition of the R2-carboxylate, which mimics the C3/C4 found in -lactams, we designed, synthesized, and characterized six derivatives of S02030 (3a)...
November 16, 2017: ACS Infectious Diseases
Liang Huang, Chengpeng Jiao, Liqiong Wang, Zili Huang, Feng Liang, Simin Liu, Yuhua Wang, Haijun Zhang, Shaowei Zhang
ISOBAM-104 protected Rh/Ag bimetallic nanoparticles (NPs) with average diameter less than 3.0 nm were synthesized by a co-reduction method. Ultraviolet-visible (UV-Vis) spectroscopy, transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and x-ray photoelectron spectroscopy (XPS) were employed to characterize the structure, particle size, and electronic structure of the prepared bimetallic NPs. The catalytic activities of prepared bimetallic NPs for hydrogen generation from hydrolysis of a basic KBH4 solution were evaluated in detail...
November 16, 2017: Nanotechnology
Rajesh V Chopdekar, Vivek K Malik, Alexander Kane, Apurva Mehta, Elke Arenholz, Yayoi Takamura
The extent of interfacial charge transfer and the resulting impact on magnetic interactions were investigated as a function of sublayer thickness in La<sub>0.7</sub>Sr<sub>0.3</sub>MnO<sub>3</sub>/La<sub>0.7</sub>Sr<sub>0.3</sub>CoO<sub>3</sub> ferromagnetic superlattices. Element-specific soft x-ray magnetic spectroscopy reveals that the electronic structure is altered within 5-6 unit cells of the chemical interface, and can lead to a synthetic ferromagnet with strong magnetic coupling between the sublayers...
November 16, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Heesoo Park, Fahhad H Alharbi, Stefano Sanvito, Nouar Tabet, Fedwa El-Mellouhi
In the quest for non-toxic and stable perovskites for solar cells, we conduct a systematic study of the effect of chalcogen content in oxychalcogenide perovskite using density functional theory (DFT) and quasi-particle perturbation theory. We explore the changes in the electronic structure due to the substitution of O atoms in NaNbO 3 and NaTaO 3 perovskite structures with various chalcogen (S, Se, Te) at different concentrations. Interestingly, the introduction of the chalcogen atoms results in a drastic reduction of the electronic band gap, making some of them fall within the visible range of the solar spectrum...
November 16, 2017: Chemphyschem: a European Journal of Chemical Physics and Physical Chemistry
Congming Zou, Wei Huang, Gaokun Zhao, Xiao Wan, Xiaodong Hu, Yan Jin, Junying Li, Junjun Liu
Tyrosinase is a type-3 copper enzyme that is widely distributed in plants, fungi, insects, and mammals. Developing high potent inhibitors against tyrosinase is of great interest in diverse fields including tobacco curing, food processing, bio-insecticides development, cosmetic development, and human healthcare-related research. In the crystal structure of Agaricus bisporus mushroom tyrosinase, there is an oxygen atom bridging the two copper ions in the active site. It is unclear whether the identity of this bridging oxygen is a water molecule or a hydroxide anion...
October 28, 2017: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
Julian Cruz-Borbolla, Esteban Garcia-Ochoa, Jayanthi Narayanan, Pablo Maldonado-Rivas, Thangarasu Pandiyan, José M Vásquez-Pérez
The capacity of 2,6-bis[((2-pyridylmethyl)oxy)methyl)]pyridine (BPMMP) to inhibit the corrosion of mild carbon steel in HCl was analyzed. In a polarization study, both the cathodic and anodic currents were appreciably decreased in the presence of BPMMP, suggesting that this ligand is effective at inhibiting corrosion at the metal surface. This conclusion is consistent with the results of impedance analysis, where only one time constant corresponding to one depressed capacitive loop was detected, and the diameter of the impedance plot was directly related to the concentration of BPMMP...
November 15, 2017: Journal of Molecular Modeling
Richard Denk, Alberto Lodi-Rizzini, Shudong Wang, Michael Hohage, Peter Zeppenfeld, Jinming Cai, Roman Fasel, Pascal Ruffieux, Reinhard Franz Josef Berger, Zongping Chen, Akimitsu Narita, Xinliang Feng, Klaus Müllen, Roberto Biagi, Valentina De Renzi, Deborah Prezzi, Alice Ruini, Andrea Ferretti
The bottom-up fabrication of graphene nanoribbons (GNRs) has opened new opportunities to specifically tune their electronic and optical properties by precisely controlling their atomic structure. Here, we address excitation in GNRs with periodic structural wiggles, the so-called chevron GNRs. Based on reflectance difference and high-resolution electron energy loss spectroscopies together with ab initio simulations, we demonstrate that their excited-state properties are of excitonic nature. The spectral fingerprints corresponding to different reaction stages in their bottom-up fabrication are also unequivocally identified, allowing us to follow the exciton build-up from the starting monomer precursor to the final GNR structure...
November 16, 2017: Nanoscale
Hee-Kyung Kim, Sung-Hun Kim
PURPOSE: The purpose of this study was to compare the optical properties of pre-colored dental monolithic zirconia ceramics of various thicknesses sintered in a microwave and those in a conventional furnace. MATERIALS AND METHODS: A2-shade of pre-colored monolithic zirconia ceramic specimens (22.0 mm × 22.0 mm) in 3 thickness groups of 0.5, 1.0, and 1.5 mm were divided into 2 subgroups according to the sintering methods (n=9): microwave and conventional sintering...
October 2017: Journal of Advanced Prosthodontics
Gulsum Sayin Ozel, Mehmet Burak Guneser, Ozgur Inan, Ayce Unverdi Eldeniz
PURPOSE: Bacterial adhesion on provisional crown materials retained for a long time can influence the duration for which permanent prosthetic restorations can be healthily worn in the oral cavity. The aim of this study was to compare seven different commonly used provisional crown materials with regard to Streptococcus mutans and Candida albicans surface adhesion. MATERIALS AND METHODS: For each group, twenty specimens of the provisional fixed prosthodontic materials TemDent (Schütz), Imıdent (Imıcryl), Tab 2000 (Kerr), Structur Premium (Voco), Systemp (Ivoclar Vivadent), Acrytemp (Zhermack), and Takilon-BBF (Takilon) were prepared (diameter, 10...
October 2017: Journal of Advanced Prosthodontics
Sebastian Dillinger, Jennifer Mohrbach, Gereon Niedner-Schatteburg
We present the cryogenic (26 K) IR spectra of selected [Nin(N2)m](+) (n = 5-20, m = 1 - mmax), which strongly reveal n- and m-dependent features in the N2 stretching region, in conjunction with density functional theory modeling of some of these findings. The observed spectral features allow us to refine the kinetic classification [cf. J. Mohrbach, S. Dillinger, and G. Niedner-Schatteburg, J. Chem. Phys. 147, 184304 (2017)] and to define four classes of structure related surface adsorption behavior: Class (1) of Ni6(+), Ni13(+), and Ni19(+) are highly symmetrical clusters with all smooth surfaces of equally coordinated Ni atoms that entertain stepwise N2 adsorption up to stoichiometric N2:Nisurface saturation...
November 14, 2017: Journal of Chemical Physics
Sergey V Ryazantsev, Daniil A Tyurin, Vladimir I Feldman, Leonid Khriachtchev
We report on the preparation and vibrational characterization of the C2H3⋯CO2 complex, the first example of a stable intermolecular complex involving vinyl radicals. This complex was prepared in Ar and Kr matrices using UV photolysis of propiolic acid (HC3OOH) and subsequent thermal mobilization of H atoms. This preparation procedure provides vinyl radicals formed exclusively as a complex with CO2, without the presence of either CO2 or C2H3 monomers. The absorption bands corresponding to the ν5(C2H3), ν7(C2H3), ν8(C2H3), ν2(CO2), and ν3(CO2) modes of the C2H3⋯CO2 complex were detected experimentally...
November 14, 2017: Journal of Chemical Physics
V A Levashov
We studied the connection between the structural relaxation and viscosity for a binary model of repulsive particles in the supercooled liquid regime. The used approach is based on the decomposition of the macroscopic Green-Kubo stress correlation function into the correlation functions between the atomic level stresses. Previously we used the approach to study an iron-like single component system of particles. The role of vibrational motion has been addressed through the demonstration of the relationship between viscosity and the shear waves propagating over large distances...
November 14, 2017: Journal of Chemical Physics
Naveen Kumar, Martin Peter Andersson, Dirk van den Ende, Frieder Mugele, Igor Siretanu
High resolution Atomic Force Microscopy is used to map the surface charge on the basal planes of kaolinite nanoparticles in an ambient solution of variable pH and NaCl or CaCl2 concentration. Using DLVO theory with charge regulation we determine from the measured force-distance curves the surface charge distribution on both the silica-like and the gibbsite-like basal plane of the kaolinite particles. We observe that both basal planes do carry charge that varies with pH and salt concentration. The silica facet was found to be negatively charged at pH 4 and above, whereas the gibbsite facet is positively charged at pH below 7, and negatively charged at pH above 7...
November 15, 2017: Langmuir: the ACS Journal of Surfaces and Colloids
Simon Budzak, Giovanni Scalmani, Denis Jacquemin
We present an investigation of the excited-state structural parameters determined for a large set of small compounds with the dual goals of defining reference values for further works and assessing the quality of the geometries obtained with relatively cheap computational approaches. In the first stage, we compare the excited-state geometries obtained with ADC(2), CC2, CCSD, CCSDR(3), CC3 and CASPT2 and large atomic basis sets. It is found that CASPT2 and CC3 results are generally in very good agreement with one another (typical differences of ca...
November 15, 2017: Journal of Chemical Theory and Computation
Manar M Shoshani, Robert Beck, Xiaoping Wang, Matthew J McLaughlin, Samuel A Johnson
Tetranuclear Ni complexes were synthesized with bonding to BH, NR, and O in atypical surface-like geometries. The previously reported electron-deficient cluster [((i)Pr3P)Ni]5H6 (1) reacts with N-methylmorpholine oxide to give [((i)Pr3P)Ni]4H4(μ4-O) (2), which contains O coordinated in the center of a square-plane arrangement of Ni atoms. Reaction of 1 with benzonitrile gave the square-planar tetranuclear Ni cluster [((i)Pr3P)Ni]4H4(μ4-NCH2Ph) (3), which contains an imido donor in a square-based-pyramidal geometry...
November 15, 2017: Inorganic Chemistry
Tianhan Liu, Timothy D Keiper, Xiaolei Wang, Guang Yang, Daniel T Hallinan, Jianhua Zhao, Peng Xiong
The ability to create micro/nano patterns of organic self-assembled monolayers (SAMs) on semiconductor surfaces is crucial for fundamental studies and applications in a number of emerging fields in nanoscience. Here, we demonstrate the direct patterning of thiolate SAMs on oxide-free GaAs surface by dip-pen nanolithography (DPN) and micro-contact printing (μCP), facilitated by a process of surface etching and passivation of the GaAs. A quantitative analysis on the molecular diffusion on GaAs was conducted by examining the writing of nanoscale dot and line patterns by DPN, which agrees well with surface diffusion models...
November 15, 2017: ACS Applied Materials & Interfaces
Yoshiko Nakahara, Tatsuro Toda, Asuka Matsunami, Yoshihito Kayaki, Shigeki Kuwata
The NNN and NCN pincer-type ruthenium(II) complexes featuring two protic pyrazol-3-yl arms with a trifluoromethyl (CF3) group at the 5-position were synthesized and structurally characterized to evaluate the impact of the substitution on the properties and catalysis. The Brønsted acidity increased by the highly electron-withdrawing CF3 pendants was demonstrated by the protonation-deprotonation experiments. By contrast, the infrared spectra of the carbonyl derivatives as well as the cyclic voltammogram indicated that the electron density of the ruthenium atom is little influenced by the CF3 group...
November 15, 2017: Chemistry, An Asian Journal
Sina Saravi, Alexander N Poddubny, Thomas Pertsch, Frank Setzpfandt, Andrey A Sukhorukov
We propose the concept of atom-mediated spontaneous parametric down-conversion, in which photon-pair generation can take place only in the presence of a single two-level emitter, relying on the bandgap evanescent modes of a nonlinear periodic waveguide. Using a guided signal mode, an evanescent idler mode, and an atom-like emitter with the idler's transition frequency embedded in the structure, we find a heralded excitation mechanism, in which the detection of a signal photon outside the structure heralds the excitation of the embedded emitter...
November 15, 2017: Optics Letters
Irena Milosevic, Amarnath Jayaprakash, Brigitte Greenwood, Birgit van Driel, Sami Rtimi, Paul Bowen
This work focuses on the development of a facile and scalable wet milling method followed by heat treatment to prepare fluorinated and/or N-doped TiO₂ nanopowders with improved photocatalytic properties under visible light. The structural and electronic properties of doped particles were investigated by various techniques. The successful doping of TiO₂ was confirmed by X-ray photoelectron spectroscopy (XPS), and the atoms appeared to be mainly located in interstitial positions for N whereas the fluorination is located at the TiO₂ surface...
November 15, 2017: Nanomaterials
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