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Atomic clusters

Jan Paulo T Zaragoza, Maxime A Siegler, David P Goldberg
High-valent metal-hydroxide species are invoked as critical intermediates in both catalytic, metal-mediated O2 activation (e.g., by Fe porphyrin in Cytochrome P450) and O2 production (e.g., by the Mn cluster in Photosystem II). However, well-characterized mononuclear MIV (OH) complexes remain a rarity. Herein we describe the synthesis of MnIV (OH)(ttppc) (3) (ttppc = tris(2,4,6-triphenylphenyl) corrole), which has been characterized by X-ray diffraction (XRD). The large steric encumbrance of the ttppc ligand allowed for isolation of 3...
March 15, 2018: Journal of the American Chemical Society
Pei-Yu Guo, Cai Sun, Ning-Ning Zhang, Li-Zhen Cai, Ming-Sheng Wang, Guo-Cong Guo
A photochromic compound with fast response to Mo-Kα (4 min) and Al-Kα (1 s) X-rays was synthesized using a cluster of high-Z atoms and a flexible viologen zwitterion. The coloration time of 1 s when exposed to soft X-rays is the recorded minimum for X-ray-induced photochromic materials, indicating a potential to detect low-energy X-rays.
March 15, 2018: Chemical Communications: Chem Comm
Esther Heid, Patricia A Hunt, Christian Schröder
Ground and excited state dipoles and polarizabilities of the chromophores N-methyl-6-oxyquinolinium betaine (MQ) and coumarin 153 (C153) in solution have been evaluated using time-dependent density functional theory (TD-DFT). A method for determining the atomic polarizabilities has been developed; the molecular dipole has been decomposed into atomic charge transfer and polarizability terms, and variation in the presence of an electric field has been used to evaluate atomic polarizabilities. On excitation, MQ undergoes very site-specific changes in polarizability while C153 shows significantly less variation...
March 15, 2018: Physical Chemistry Chemical Physics: PCCP
Joshua H Marks, Timothy B Ward, Michael A Duncan
Manganese oxide cluster cations are produced by laser vaporization in a pulsed nozzle source, and detected with time-of-flight mass spectrometry. The mass spectrum contains intense peaks for stoichiometries corresponding to (MnO)n+. Multiphoton photodissociation of these clusters yields smaller ions with the same stoichiometric ratio, either by sequential elimination of MnO units or by various fission processes with roughly equal efficiencies. Fragmentation of clusters containing excess oxygen also yields (MnO)n+ fragments...
March 14, 2018: Journal of Physical Chemistry. A
Udo Bauer, Florian Späth, Fabian Düll, Philipp Bachmann, Johann Steinhauer, Hans-Peter Steinrück, Christian Papp
We have investigated the adsorption and thermal reactivity of CO and C2H4 on well-defined bimetallic PtxAg1-x/Pt(111) surface alloys (with x = 0.67, 0.50, 0.38 and 0.32) using in situ synchrotron-based high resolution X-ray photoelectron spectroscopy. During low temperature (140 K) adsorption of CO, we find population of the energetically more stable Pt on-top site followed by the Pt bridge site, as known from clean Pt(111); CO does not adsorb on Ag facets under the applied conditions. The total CO coverage linearly decreases with Ag surface content...
March 14, 2018: Chemphyschem: a European Journal of Chemical Physics and Physical Chemistry
Alain Manceau, Jianxu Wang, Mauro Rovezzi, Pieter Glatzel, Xinbin Feng
Plant leaves serve both as a sink for gaseous elemental mercury (Hg) from the atmosphere and a source of toxic mercury to terrestrial ecosystems. Litterfall is the primary deposition pathway of atmospheric Hg to vegetated soils, yet the chemical form of this major Hg input remains elusive. We report the first observation of in vivo formation of mercury sulfur nanoparticles in intact leaves of 22 native plants from six different species across two sampling areas from China. The plants grew naturally in soils from a mercury sulfide mining and retorting region at ambient-air gaseous-Hg concentrations ranging from 131 ± 19 to 636 ± 186 ng m-3 and had foliar Hg concentration between 1...
March 14, 2018: Environmental Science & Technology
Agustín Bruzzese, Carles Gil, James A R Dalton, Jesús Giraldo
Lipids are becoming known as essential allosteric modulators of G protein-coupled receptor (GPCRs). However, how they exert their effects on GPCR conformation at the atomic level is still unclear. In light of recent experimental data, we have performed several long-timescale molecular dynamics (MD) simulations, totalling 24 μs, to rigorously map allosteric modulation and conformational changes in the β2 adrenergic receptor (β2AR) that occur as a result of interactions with three different phospholipids. In particular, we identify different sequential mechanisms behind receptor activation and deactivation, respectively, mediated by specific lipid interactions with key receptor regions...
March 13, 2018: Scientific Reports
Rebekka Haack, Stephan Schulz, Georg Jansen
Triggered by the observation of a short Bi⋯Bi distance and a BiTeBi bond angle of only 86.6° in the crystal structure of bis(diethylbismuthanyl)tellurane quantum chemical computations on interactions between neighboring Bi atoms in Te(BiR2 )2 molecules (R = H, Me, Et) and in (BiH3 )2 were undertaken. Bi⋯Bi distances atoms were found to significantly shorten upon inclusion of the d shells of the heavy metal atoms into the electron correlation treatment, and it was confirmed that interaction energies from spin component-scaled second-order Møller-Plesset theory (SCS-MP2) agree well with coupled-cluster singles and doubles theory including perturbative triples (CCSD(T))...
March 13, 2018: Journal of Computational Chemistry
Anthony M S Pembere, Xianhu Liu, Wei-Hua Ding, Zhixun Luo
We present here a further insight on the hydrogen evolution reactions (HER) of aluminum clusters with one and multiple water molecules. Along with natural bond orbital (NBO) and frontier molecular orbital (FMO) analysis, we compared the reactivities of both anionic and neutral Al13 , Al12 , Al7 and Al6 clusters with water in gas phase. It is found that charge transfer interactions between these typical Al clusters and H2 O initiate their reactions, allowing varied charge distribution on the cluster. With an emphasis on the typical Al6 cluster, we checked out the reactive intermediates, activated complexes, transition states, bond breaking and stereochemistry for it to react with two and four water molecules respectively...
March 12, 2018: Journal of Physical Chemistry. A
Natarajan Sathiyamoorthy Venkataramanan, Ambigapathy Suvitha
This study aims to cast light on the nature of interactions and cooperativity that exists in linear dimethyl sulfoxide (DMSO) clusters using dispersion corrected density functional theory. In the linear DMSO, DMSO molecules in the middle of the clusters are bound strongly than at the terminal. The plot of the total binding energy of the clusters vs the cluster size and mean polarizabilities vs cluster size shows an excellent linearity demonstrating the presence of cooperativity effect. The computed incremental binding energy of the clusters remains nearly constant, implying that DMSO addition at the terminal site can happen to form an infinite chain...
March 2, 2018: Journal of Molecular Graphics & Modelling
Zhao Tan, An Yong Li
A novel type of trivalent BNg five-membered cational species B5 Ngn 3+ (Ng = He~Rn, n = 1~5) has been found and investigated theoretically using the B3LYP and MP2 methods with the def2-QZVPPD and def2-TZVPPD basis sets. The geometry, harmonic vibrational frequencies, bond energies, charge distribution, bond nature, aromaticity, and energy decomposition analysis of these structures were reported. The calculated B-Ng bond energy is quite large (the averaged bond energy is in the range of 209.2~585.76 kJ mol-1 ) for heavy rare gases and increases with the Ng atomic number...
March 9, 2018: Journal of Molecular Modeling
Antonio Bauzá, Antonio Frontera
In this study the ability of metal clusters involving elements from group IB (Ag, Cu and Au) to favourably interact with π-systems of different size and electronic nature has been evaluated at the PBE0-D3/def2-TZVPP//PBE0-D3/def2-TZVP level of theory. We have used M9 clusters (M = Cu, Ag and Au) as σ-hole and σ-lump donors and benzene, trifluorobenzene and hexafluorobenzene as aromatic rings. In addition, we have expanded our study to the analysis of extended π-systems by using naphthalene and anthracene moieties as well as their corresponding perfluorinated derivatives...
March 9, 2018: Chemistry: a European Journal
Ling-Yan Ai, Hui-Yan Zhao, Hong-Man Ma, Jing Wang, Ying Liu
A stable Th -symmetry Ti12 C68 cage was systemically investigated using density functional theory. The structure of Ti12 C68 is a hollow cage with twelve TiC13 subunit of three pentagons and one hexagon. The calculated frequencies are in the range 95.1 cm-1 -1423.9 cm-1 . There are no imaginary frequencies, showing its kinetic stability. Ab initio molecular dynamics simulations demonstrate that the topological structure of cage-like Ti12 C68 cluster was well maintained when the effective temperature is up to 1139 K...
March 8, 2018: Scientific Reports
J Janata, Z Kamenik, R Gazak, S Kadlcik, L Najmanova
Covering: up to 2017This review covers the biosynthetic and evolutionary aspects of lincosamide antibiotics, antitumour pyrrolobenzodiazepines (PBDs) and the quorum-sensing molecule hormaomycin. These structurally and functionally diverse groups of complex natural products all incorporate rarely occurring 4-alkyl-l-proline derivatives (APDs) biosynthesized from l-tyrosine through an unusual specialized pathway catalysed by a common set of six proteins named Apd1-Apd6. We give an overview of APD formation, which involves unusual enzyme activities, and its incorporation, which is based either on nonribosomal peptide synthetase (PBDs, hormaomycin) or a unique hybrid ergothioneine-dependent condensation system followed by mycothiol-dependent sulphur atom incorporation (lincosamides)...
March 8, 2018: Natural Product Reports
K Vijay Reddy, Snehanshu Pal
The dependence of creep deformation behavior of nickel bicrystal specimens on grain boundary (GB) complexion was investigated by performing a simulated bending creep test using molecular dynamics methods. Strain burst phenomena were observed during the low temperature [500 K, i.e., <0.3 * melting point of nickel (Tm )] bending creep process. Atomic strain and dislocation analyses showed that the time of occurrence of strain burst depends on how easily GB migration happens in bicrystal specimens. Specimens with kite monolayer segregation GB complexion were found to be stable at low temperature (500 K), whereas specimens with split-kite GB complexion were stable at a comparatively higher temperature (900 K)...
March 7, 2018: Journal of Molecular Modeling
Leah G Dodson, Michael Charles Thompson, J Mathias Weber
We explore the structures of [Ti(CO2 )y ]- cluster anions using infrared photodissociation spectroscopy and quantum chemistry calculations. The existence of spectral signatures of metal carbonyl CO stretching modes shows that insertion of titanium atoms into C-O bonds represents an important reaction during the formation of these clusters. In addition to carbonyl groups, the infrared spectra show that the titanium center is coordinated to oxalato, carbonato, and oxo ligands, which form along with the metal carbonyls...
March 7, 2018: Journal of Physical Chemistry. A
Sean T Hunt, Yuriy Román-Leshkov
Conspecuts Commercial and emerging renewable energy technologies are underpinned by precious metal catalysts, which enable the transformation of reactants into useful products. However, the noble metals (NMs) comprise the least abundant elements in the lithosphere, making them prohibitively scarce and expensive for future global-scale technologies. As such, intense research efforts have been devoted to eliminating or substantially reducing the loadings of NMs in various catalytic applications. These efforts have resulted in a plethora of heterogeneous NM catalyst morphologies beyond the traditional supported spherical nanoparticle...
March 6, 2018: Accounts of Chemical Research
Jinming Guo, Georg Haberfehlner, Julian Rosalie, Lei Li, María Jazmin Duarte, Gerald Kothleitner, Gerhard Dehm, Yunbin He, Reinhard Pippan, Zaoli Zhang
Oxygen contamination is a problem which inevitably occurs during severe plastic deformation of metallic powders by exposure to air. Although this contamination can change the morphology and properties of the consolidated materials, there is a lack of detailed information about the behavior of oxygen in nanocrystalline alloys. In this study, aberration-corrected high-resolution transmission electron microscopy and associated techniques are used to investigate the behavior of oxygen during in situ heating of highly strained Cu-Fe alloys...
March 5, 2018: Nature Communications
Luděk Vyšín, Tomáš Burian, Egor Ukraintsev, Marie Davídková, Michael E Grisham, Scott Heinbuch, Jorge J Rocca, Libor Juha
In this study, we examined dose-rate effects on strand break formation in plasmid DNA induced by pulsed extreme ultraviolet (XUV) radiation. Dose delivered to the target molecule was controlled by attenuating the incident photon flux using aluminum filters as well as by changing the DNA/buffer-salt ratio in the irradiated sample. Irradiated samples were examined using agarose gel electrophoresis. Yields of single- and double-strand breaks (SSBs and DSBs) were determined as a function of the incident photon fluence...
March 5, 2018: Radiation Research
Alexander Ovchinnikov, Svilen Bobev
The Ga- and In-substituted bismuthides Ca11 Gax Bi10-x , Ca11 Inx Bi10-x , Yb11 Gax Bi10-x , and Yb11 Inx Bi10-x (x < 2) can be readily synthesized employing molten Ga or In metals as fluxes. They crystallize in the tetragonal space group I4/mmm and adopt the Ho11 Ge10 structure type (Pearson code tI84; Wyckoff sequence n2 m j h2 e2 d). The structural response to the substitution of Bi with smaller and electron-poorer In or Ga has been studied by single-crystal X-ray diffraction methods for the case of Ca11 Inx Bi10-x [x = 1...
March 1, 2018: Acta Crystallographica. Section C, Structural Chemistry
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