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101.
Mandimutsira BS Ramdhanie B Todd RC Wang H Zareba AA Czernuszewicz RS Goldberg DP 《Journal of the American Chemical Society》2002,124(51):15170-15171
The synthesis and characterization of an oxomanganese(V) corrolazine, (TBP)8(Cz)Mn(V)O (2), are reported. This remarkably stable high-valent complex is obtained from the stoichiometric reaction of (TBP)8(Cz)Mn(III) (1) with m-CPBA and is easily purified by standard chromatographic methods on silica gel at room temperature. Complex 2 exhibits a diamagnetic 1H NMR spectrum indicative of a low-spin d2 Mn(V)O species. LDI-TOFMS of 2 shows the predicted isotopic envelope at m/z 1426.8. This envelope shifts to higher mass as expected after the facile exchange of the terminal oxo group with H218O. The resonance Raman spectrum of 2 either in solution or in the solid state shows a strongly enhanced Raman band for the stretching mode of the Mn-oxo bond, which also shifts as expected upon 18O substitution: 2(16O), 979 cm-1; 2(18O), 938 cm-1 (in CH2Cl2). Initial reactivity studies show that 2 rapidly transfers the terminal oxo ligand to PPh3, resulting in the quantitative formation of OPPh3 and concomitant reduction of 2 back to 1. Complex 2 is the first example of an oxomanganese(V)-porphyrinoid complex that can be isolated at room temperature. 相似文献
102.
Wang SH Mandimutsira BS Todd R Ramdhanie B Fox JP Goldberg DP 《Journal of the American Chemical Society》2004,126(1):18-19
The reaction between (TBP)8(Cz)Mn(III) (1) and the oxygen atom donors iodosylbenzene (PhIO) or p-cyanodimethylaniline-N-oxide (CDMANO) leads to the manganese(V)-oxo complex (TBP)8(Cz)Mn(V)O (2), which has been isolated and characterized previously. Under catalytic conditions with 1 as added catalyst and PhIO as oxidant, both sulfoxidation of PhSMe and epoxidation of cis-stilbene is observed, whereas with CDMANO no sulfoxidation takes place, suggesting that 2 is not the active oxidant. Examination of the independent reactivity of isolated 2 toward PhSMe and cis-stilbene supports this conclusion. A mechanism which relies on a novel type of oxidant involving Lewis acid activation of PhIO by the Mn(V)-oxo complex 2 accounts for these observations and is confirmed by 18O-labeling experiments. 相似文献
103.
Kumar P Lee TH Mehta A Sumpter BG Dickson RM Barnes MD 《Journal of the American Chemical Society》2004,126(11):3376-3377
Fluorescence intensity correlation measurements reveal that z-oriented nanostructures from single chains of a cyano-substituted polyphenylene vinylene (CN-PPV) polymer act as single-quantum emitters. Photon antibunching is observed for the first time on individual polymer nanostructures with a modulation depth exceeding 90%, providing definitive proof that radiative recombination of molecular excitons occurs at a single localized site within the folded polymer chain. 相似文献
104.
Bobby K. Antony Robert R. Gamache 《Journal of Quantitative Spectroscopy & Radiative Transfer》2007,105(1):148-163
Calculations of self-broadened half-widths and self-induced pressure shifts are made using the complex Robert-Bonamy formalism. The results of calculations using different approximations of the intermolecular potential indicate that this is a strong collision system. The effects of the imaginary components on the half-widths are studied. The temperature, vibrational, and rotational state dependence of the half-width are investigated. Results are compared with measurements from the database of self-broadening of water vapor [Gamache RR, Hartmann J-M. An intercomparison of measured pressure-broadening and pressure-shifting parameters of water vapor. Can J Chem 2004; 82: 1013-27]. 相似文献
105.
Enhancement of tribological performance of epoxy bulk composites and composite coatings using micro/nano fillers: a review
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Epoxies in the form of bulk and coatings have been used throughout the years for a wide spectrum of applications in various industries ranging from aerospace, oil and gas, petrochemical and marine to several others. Their use in tribological applications, those involving a range of contact conditions and where the requirement is exceptionally low wear and friction coefficient, is often limited by the properties of the pristine epoxy matrix such as low load bearing capacity combined with low thermal conductivity values. These properties have been improved by the addition of nano‐fillers, and numerous studies have been carried out in this regard. This paper presents a detailed review of the works carried out in the recent years where addition of nano‐fillers to formulate epoxy‐based composites and coatings has shown a substantial improvement in wear and friction properties thereby enhancing their potential to be used in demanding tribological applications such as solid lubricant in bearings, as wear‐resistant protective coatings in rotating and stationary equipment and for applications in the construction industry such as floorings and airport runway repairs. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
106.
Johnson RD Navratil M Poe BG Xiong G Olson KJ Ahmadzadeh H Andreyev D Duffy CF Arriaga EA 《Analytical and bioanalytical chemistry》2007,387(1):107-118
Bulk studies are not suitable to describe and study cell-to-cell variation, which is of high importance in biological processes
such as embryogenesis, tissue differentiation, and disease. Previously, capillary electrophoresis with laser-induced fluorescence
detection (CE-LIF) was used to measure the properties of organelles isolated from millions of cells. As such, these bulk measurements
reported average properties for the organelles of cell populations. Similar measurements for organelles released from single
cells would be highly relevant to describe the subcellular variations among cells. Toward this goal, here we introduce an
approach to analyze the mitochondria released from single mammalian cells. Osteosarcoma 143B cells are labeled with either
the fluorescent mitochondrion-specific 10-N-nonyl acridine orange (NAO) or via expression of the fluorescent protein DsRed2. Subsequently, a single cell is introduced
into the CE-LIF capillary where the organelles are released by a combined treatment of digitonin and trypsin. After this treatment,
an electric field is applied and the released organelles electromigrate toward the LIF detector. From an electropherogram,
the number of detected events per cell, their individual electrophoretic mobilities, and their individual fluorescence intensities
are calculated. The results obtained from DsRed2 labeling, which is retained in intact mitochondria, and NAO labeling, which
labels all mitochondria, are the basis for discussion of the strengths and limitations of this single-cell approach.
Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users 相似文献
107.
Kazuhiko Fukui Bobby G. Sumpter Donald W. Noid Chao Yang Robert E. Tuzun 《Journal of Polymer Science.Polymer Physics》2000,38(13):1812-1823
A complete set of frequencies for the density of states spectrum g(ω) is obtained for 6000‐atom polymer particles involving all 18,000 degrees of freedom. We efficiently generate the particle using molecular dynamics and molecular mechanics, and systematically analyze the spectra and thermal properties as a function of chain lengths: from one to 100 monomers. The density of states spectrum g(ω) shows a higher number of low‐frequency modes for the polymer particle with a smaller chain length, which results in a higher heat capacity at low temperature. Gibbs free energy was also calculated for the formation of a particle from a crystal as a function of temperature to evaluate thermal stability of those systems. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1812–1823, 2000 相似文献
108.
Robert E. Tuzun Donald W. Noid Bobby G. Sumpter 《Journal of computational chemistry》1997,18(14):1804-1811
Simple and very efficient formulas are presented for four-body out-of-plane bend (used in MM2 and MM3 force fields) and improper torsion (used in the MM4 force field) internal coordinates and their first and second derivatives. The use of a small set of bend and stretch intermediates allows for order of magnitude decreases in calculation time for potential energies and their first and second derivatives, which are required in molecular mechanics calculations. The formulas are eminently suitable for use in molecular simulations of systems with complicated bond networks. © 1997 John Wiley & Sons, Inc. J Comput Chem 18 : 1804–1811, 1997 相似文献
109.
Robert E. Tuzun Bobby G. Sumpter Donald W. Noid 《Macromolecular theory and simulations》1998,7(2):203-209
In a recent study we found the classical dynamics of a polyethylene (PE) chain to exhibit low dimensional chaos at temperatures as low as a few Kelvin. These results strongly suggest that classical molecular dynamic simulations in polymer systems can grossly overestimate vibrational motion, which consequently results in disordered structures. In contrast, quantum mechanical calculations using Internal Coordinate Quantum Monte Carlo (an improved method with an initial conjecture for the correct wave function) indicate that the quantum ground state for a three-dimensional model PE chain is far more rigid than determined from molecular dynamics (MD) simulations, even at energies as low as a small fraction of the ground state energy. This result casts uncertainty on the reliability of MD estimates of dynamical or structural quantities relevant to the study of some macromolecular systems. 相似文献
110.
Xuanyu Zhang Rui You Zeyue Wei Xiao Jiang Jiuzhong Yang Yang Pan Peiwen Wu Qingdong Jia Zhenghong Bao Lei Bai Mingzhou Jin Bobby Sumpter Victor Fung Weixin Huang Zili Wu 《Angewandte Chemie (International ed. in English)》2020,59(21):8042-8046
Although hexagonal boron nitride (h‐BN) has recently been identified as a highly efficient catalyst for the oxidative dehydrogenation of propane (ODHP) reaction, the reaction mechanisms, especially regarding radical chemistry of this system, remain elusive. Now, the first direct experimental evidence of gas‐phase methyl radicals (CH3.) in the ODHP reaction over boron‐based catalysts is achieved by using online synchrotron vacuum ultraviolet photoionization mass spectroscopy (SVUV‐PIMS), which uncovers the existence of gas‐phase radical pathways. Combined with density functional theory (DFT) calculations, the results demonstrate that propene is mainly generated on the catalyst surface from the C?H activation of propane, while C2 and C1 products can be formed via both surface‐mediated and gas‐phase pathways. These observations provide new insights towards understanding the ODHP reaction mechanisms over boron‐based catalysts. 相似文献