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A Powerful Chiral Counterion Strategy for Asymmetric Transition Metal Catalysis
Hamilton, G. L.,Kang, E. J.,Mba, M.,Toste, F. D. American Association for the Advancement of Scienc 2007 Science Vol.317 No.5837
<P>Traditionally, transition metal-catalyzed enantioselective transformations rely on chiral ligands tightly bound to the metal to induce asymmetric product distributions. Here we report high enantioselectivities conferred by a chiral counterion in a metal-catalyzed reaction. Two different transformations catalyzed by cationic gold(I) complexes generated products in 90 to 99% enantiomeric excess with the use of chiral binaphthol-derived phosphate anions. Furthermore, we show that the chiral counterion can be combined additively with chiral ligands to enable an asymmetric transformation that cannot be achieved by either method alone. This concept of relaying chiral information via an ion pair should be applicable to a vast number of metal-mediated processes.</P>
Anovitz, L.M.,Lynn, G.W.,Cole, D.R.,Rother, G.,Allard, L.F.,Hamilton, W.A.,Porcar, L.,Kim, M.H. Pergamon Press ; Elsevier Science Ltd 2009 Geochimica et cosmochimica acta Vol.73 No.24
In this paper we report the results of a study using small angle and ultra-small angle neutron scattering techniques (SANS and USANS) to examine the evolution of carbonates during contact metamorphism. Data were obtained from samples collected along two transects in the metamorphosed Hueco limestone at the Marble Canyon, Texas, contact aureole. These samples were collected from the igneous contact out to ∼1700m. Scattering curves obtained from these samples show mass fractal behavior at low scattering vectors, and surface fractal behavior at high scattering vectors. Significant changes are observed in the surface and mass fractal dimensions as well as the correlation lengths (pore and grain sizes), surface area to volume ratio and surface Gibbs Free energy as a function of distance, including regions of the aureole outside the range of classic metamorphic petrology. A change from mass-fractal to non-fractal behavior is observed at larger scales near the outer boundary of the aureole that implies significant reorganization of pore distributions early in the metamorphic history. Surface fractal results suggest significant smoothing of grain boundaries, coupled with changes in pore sizes. A section of the scattering curve with a slope less than -4 appears at low-Q in metamorphosed samples, which is not present in unmetamorphosed samples. A strong spike in the surface area to volume ratio is observed in rocks near the mapped metamorphic limit, which is associated with reaction of small amounts of organic material to graphite. It may also represent an increase in pore volume or permeability, suggesting that a high permeability zone forms at the boundary of the aureole and moves outwards as metamorphism progresses. Neutron scattering data also correlate well with transmission electron microscopic (TEM) observations, which show formation of micro- and nanopores and microfractures during metamorphism. The scattering data are, however, quantifiable for a bulk rock in a manner that is difficult to achieve using high-resolution imaging (e.g. TEM). Thus, neutron scattering techniques provide a new approach to the analysis and study of metamorphism.
Colin M. Dinney,Lu-Dong Zhao,Charles D. Conrad,Jay M. Duker,Richard O. Karas,Zhibin Hu,Michele A. Hamilton,Thomas R. Gillis,Thomas M. Parker,Bing Fan,Andrew H. Advani,Fred B. Poordad,Paulette L. Fauce 한국미생물학회 2015 The journal of microbiology Vol.53 No.10
Chronic HBV infection is the leading cause of liver cirrhosis and hepatic cancer, but the individual responses toward HBV infection are highly variable, ranging from asymptomatic to chronic active hepatitis B inflammation. In this study, we hypothesized that the different individual responses to HBV infection was associated with differences in HBV-specific CD8+ T cell-mediated inflammation and cytotoxicity. Blood samples were collected from subjects with asymptomatic HBV-infection, subjects undergoing active chronic HBV flares (active CHB), and subjects with HBV-infected hepatocellular carcinoma (HBV-HCC). By tetramer staining, we found that all three groups had similar frequencies of HBVspecific CD8+ T cells. However, after HBV peptide stimulation, the HBV-specific CD8+ T cells in asymptomatic subjects had significantly stronger interferon gamma (IFN-γ), tumor necrosis factor alpha (TNF-α), and CD107a expression than those in active CHB and HBV-HCC patients. Examination of surface marker expression revealed that the PD-1-Tim-3- double-negative cell population was the main contributor to HBV-specific inflammation. In active CHB patients and HBV-HCC patients, however, the frequencies of activated PD-1-Tim-3- cells were significantly reduced. Moreover, the serum HBV DNA titer was not correlated with the frequencies of HBV-specific CD8+ T cells but was inversely correlated with the frequencies of IFN-g-expressing and CD107a-express cells in response to HBV stimulation. Together, our data demonstrated that the status of HBVspecific CD8+ T cell exhaustion was associated with different clinical outcomes of chronic HBV infection.