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61.
Dyke JM Levita G Morris A Ogden JS Dias AA Algarra M Santos JP Costa ML Rodrigues P Andrade MM Barros MT 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(5):1665-1676
The thermal decompositions of methyl azidoformate (N3COOMe), ethyl azidoformate (N3COOEt) and 2-azido-N,N-dimethylacetamide (N3CH2CONMe2) have been studied by matrix isolation infrared spectroscopy and real-time ultraviolet photoelectron spectroscopy. N2 appears as an initial pyrolysis product in all systems, and the principal interest lies in the fate of the accompanying organic fragment. For methyl azidoformate, four accompanying products were observed: HNCO, H2CO, CH2NH and CO2, and these are believed to arise as a result of two competing decomposition routes of a four-membered cyclic intermediate. Ethyl azidoformate pyrolysis yields four corresponding products: HNCO, MeCHO, MeCHNH and CO2, together with the five-membered-ring compound 2-oxazolidone. In contrast, the initial pyrolysis of 2-azido-N,N-dimethyl acetamide, yields the novel imine intermediate Me2NCOCH=NH, which subsequently decomposes into dimethyl formamide (HCONMe2), CO, Me2NH and HCN. This intermediate was detected by matrix isolation IR spectroscopy, and its identity confirmed both by a molecular orbital calculation of its IR spectrum, and by the temperature dependence and distribution of products in the PES and IR studies. Mechanisms are proposed for the formation and decomposition of all the products observed in these three systems, based on the experimental evidence and the results of supporting molecular orbital calculations. 相似文献
62.
Proton transfer in bacteriorhodopsin from the cytoplasm to the extracellular side is initiated from protonated asp96 in the cytoplasmic region toward the deprotonated Schiff base. This occurs in the transition from the photocycle late M state to the N state. To investigate this proton-transfer process, a quantum mechanics/molecular mechanics (QM/MM) model is constructed from the bacteriorhodopsin E204Q mutant crystal structure. Three residues, asp96, asp85, and thr89, as well as most of the retinal chromophore and the Schiff base link of lys216 are treated quantum mechanically and connected to the remaining classical protein through linker atom hydrogens. Structural transformation in the M state results in the formation of a water channel between the Schiff base and asp96. Since a part of this channel is lined with hydrophobic residues, there has been a question on the mechanism of proton transfer in a hydrophobic channel. Ab initio dynamics using the CHARMM/GAMESS methodology is used to simulate the transfer of the proton through a partially hydrophobic channel. Once sufficient water molecules are added to the channel to allow the formation of a single chain of waters from asp96 to the Schiff base, the transfer occurs as a fast (less than a picosecond) concerted event irrespective of the protonation state of asp85. Dynamic transfer of the proton from asp96 to the nearest water initiates the organization of a strongly bonded water chain conducive to the transfer of the proton to the Schiff base nitrogen. 相似文献
63.
M. Rubesch A. L. Clobes M. L. Morris R. D. Koob 《Journal of mass spectrometry : JMS》1971,5(3):237-248
The ionic fragmentation of twelve partially fluorinated β-diketones, RCOCH2COCF3 was studied with a medium resolution mass spectrometer. In addition to the anticipated fragmentation by β-cleavage, a number of interesting rearrangements are observed. [CF3COCH2CO]+., an ion common to all of the compounds investigated, decomposes predominantly by elimination of HF. When R is an alkyl group containing hydrogen γ to the adgacent carbonyl, the McLafferty rearrangement occurs. The [RCOCH2CO]+.ion eliminates neutral RH when R is phenyl, thienyl, or cyclopropyl. An intense metastable peak, absent when R is an alkyl substituent, accompanies the rearrangement in these three compounds. A number of fragments characteristic of the R substituent are also observed in many cases. This is interpreted as indicating a considerable degree of charge localization on the R moiety. 相似文献
64.
T. A. Nichols J. S. Morris V. L. Spate C. J. Tharp C. K. Baskett T. L. Horsman M. M. Mason T. P. Cheng 《Journal of Radioanalytical and Nuclear Chemistry》1998,235(1-2):65-69
A global radionuclide monitoring system is being engineered as part of a multi-technology verification system for the Comprehensive
Nuclear Test Ban Treaty. The system detects airborne radioactive aerosols and gases that can indicate nuclear weapons test
debris. The backbone of the system is a network of 80 remote detection stations that utilize high-volume air sampling and
high-resolution gamma spectrometry to provide in-situ assay and near-real time reporting. These stations are linked to the
International Data Centre, which is a central data processing hub where raw spectral data is automatically processed, analyzed,
and disseminated to the states parties. Measurements are categorized based on spectral content to determine which contain
anomalous anthropogenic radionuclides that require intensive radiochemical analysis at a certified laboratory. The resulting
system has the capability to measure microbecquerel concentrations of radionuclides and provide accessible data products within
minutes of field measurements. During the past year of international operations, the minimum detectable concentrations and
spectroscopy processing statistics were recorded as a function of geographical location and time. The results show that this
system is an effective tool for nuclear test monitoring, as well as other applications such as radiological emergency response,
public health monitoring, and scientific research. 相似文献
65.
AdamJ. Rucklidge GeorgeE. Morris AlexandraM.Z. Slawin DavidJ. Cole‐Hamilton 《Helvetica chimica acta》2006,89(8):1783-1800
Palladium complexes of [1,2‐phenylenebis(methylene)]bis[di(tert‐butyl)phosphine] ( 1 ) catalyze the methoxycarbonylation of vinyl acetate (= ethenyl acetate) in the presence of methanesulfonic acid (Scheme 1). High selectivities to ester products can be obtained if free phosphine ligand is in excess over the amount of added acid (Table 1). Selectivities to methyl 2‐acetoxypropanoate, a precursor to lactate esters, can be as high as 3.6 : 1 at low temperature and pressure (Table 2). Replacing tBu by iPr groups leads to less‐active catalysts and lower selectivities to the branched product. Replacing the phenylene moiety by a naphthalenediyl moiety also gives lower activity, but with similar selectivity to the phenylene‐based analogues. Linear hydrocarbon‐chain linkers as the backbone instead of the phenylenebis(methylene) linker leads to poor catalysis, except for a propane‐1,3‐diyl linker, which gives good rates but poor branched selectivity (Table 5). The effect of different reaction conditions on the catalysis is discussed. The syntheses of the new xylene‐based diphosphines 2 – 5 with one to four iPr groups replacing the tBu groups at the P‐atoms of 1 and of the ligands 6 and 7 based on 1,2‐ and 2,3‐dimethylnaphthalene are also described (Schemes 2 and 3). 相似文献
66.
C. E. Morris 《Shock Waves》1991,1(3):213-222
A history of the shock-wave equation-of-state (EOS) studies at Los Alamos is given. Particular emphasis is placed on the pioneering research in the 1950s where many of the experimental techniques and methods of analysis were developed, which we now take for granted. A brief review of shock-wave physics is given, which illustrates important hydrodynamic and thermodynamic concepts. Recent studies on the EOS of Ti are presented with emphasis on the-to- phase transition. VISAR wave profiles for polycrystalline Ni and singlecrystal Ni are presented to determine the strengths of these materials under pressure. Low-density polystyrene foam Hugoniot experiments are described and results analyzed.This article was processed using Springer-Verlag TEX Shock Waves macro package 1990. 相似文献
67.
68.
E. J. Ansaldo J. Boyle Ch. Niedermayer G. D. Morris J. H. Brewer C. E. Stronach R. S. Cary 《Zeitschrift für Physik B Condensed Matter》1992,86(3):317-318
Three distinct electronic states were detected for positive muons (+) after implantation into a C60 powder sample. About 40% of the + remained in the bare (diamagnetic) state, essentially an interstitial charged point particle. The rest of the muons were found to thermalize predominantly in two muonium (Mu=+ e–) atomic species. A vacuum Mu state, with hyperfine coupling close to that of free Mu, most likely at the molecular center, and a muonic substituted radical, i.e. a hydrogen-like Mu addition to double bonds on the carbon rings. This opens up a rich subfield of fullerene spectroscopy using muons. 相似文献
69.
We present a study of finite-size effects in a model exhibiting a first-order temperature-driven symmetry-breaking structural phase transition in theL
× cylindrical geometry in theL
limit. Exact studies demonstrate the applicability of our scaling ansatz even in the one-dimensional limit, making this model ideal for studying finite-size effects. The scaling ansatz, similar to the previously developed ansatz for field-driven transitions, demonstrates that latent heat is crucial in driving these transitions. This ansatz is supported by a 2×2 phenomenological transfer matrix based upon the symmetries of the system; this produces an analytic free energy which has the scaling form. Order parameter probability distributions show that the high- and low-temperature phases coexist only in a small finite-size-affected regime near the bulk transition temperature; this regime vanishes exponentially fast asL
diverges. 相似文献
70.
Ronald Grigg Anne HodgsonJames Morris Visuvanathar Sridharan 《Tetrahedron letters》2003,44(5):1023-1026
A novel sequential palladium/ruthenium-catalysed four component process is described involving carbonylation of an aryl/heteroaryl iodide followed by allenylation to generate (π-allyl) palladium species which are intercepted by nitrogen nucleophiles to afford 1,6-dienes. Subsequent Ring-Closing Metathesis (RCM) affords C-acyl-N-heterocycles in good yield. These heterocycles proved to be active dipolarophiles in sequential and cascade 1,3-dipolar cycloaddition reactions (1,3-DC) as exemplified by reactions with nitrones and azomethine ylides. 相似文献