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X-ray crystallography shows the gold atoms in [R3PAu{SC(OMe)=NC6H4NO2-4}] (R = Et, Cy, Ph; 1-3, respectively) and [(Ph2P-R-PPh2){AuSC(OMe)=NC6H4NO2-4}(2)] (R = CH2, (CH2)2, (CH2)3, (CH2)4, Fc; 4-8, respectively) are linearly coordinated by phosphorus and thiolate-sulfur; weak intramolecular Au...O interactions are featured in all structures. The smaller ethyl substituents in 1 allow for supramolecular association via Au...S and Au...Au interactions that are not found in 2 and 3, which contain larger phosphorus-bound Cy and Ph groups, respectively. Intramolecular Au...Au interactions are found in the dppm, dppe, dppp, and Fc structures but not in the dppp analogue, for which an anti conformation was found. The structures have been correlated with the results from photophysical study conducted in the solid state. Thus, photoexcitation of 1-7 with lambda > 350 in the solid state and in solution produces green and blue luminescence, respectively. The spectra in each medium are remarkably similar to each other, and so the emission energy and excitation maxima observed for 1-7 appear to be independent of the nature of the ancillary phosphines, as well as the presence or absence of Au...Au interactions, either intermolecularly or intramolecularly. 相似文献
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Spin‐label electron spin resonance (ESR) has emerged as a powerful tool to characterize protein dynamics. One recent advance is the development of ESR for resolving dynamical components that occur or coexist during a biological process. It has been applied to study the complex structural and dynamical aspects of membranes and proteins, such as conformational changes in protein during translocation from cytosol to membrane, conformational exchange between equilibria in response to protein‐protein and protein‐ligand interactions in either soluble or membrane environments, protein oligomerization, and temperature‐ or hydration‐dependent protein dynamics. As these topics are challenging but urgent for understanding the function of a protein on the molecular level, the newly developed ESR methods to capture individual dynamical components, even in low‐populated states, have become a great complement to other existing biophysical tools. 相似文献
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We study the bifurcation diagrams of (classical) positive solutions u with |u |∞ ∈ (0, ∞) of the p -Laplacian Dirichlet problem (φp (u ′(x)))′ + λfq (u (x))) = 0, –1 ≤ x ≤ 1, u (–1) = 0 = u (1), where p > 1, φp (y) = |y |p –2 y, (φp (u ′))′ is the one-dimensional p -Laplacian, λ > 0 is a bifurcation parameter, and the nonlinearity fq (u) = |1 – u |q is defined on [0, ∞) with constant q > 0. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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The focus-shaping technique of a cylindrically polarized vortex beam by a high numerical-aperture lens is reported. Such a polarized vortex beam is decomposed into radial and azimuthal polarization. It is shown that the total intensity distribution in the focal region is dependent not only on the numerical-aperture maximal angle and the polarization rotation angle but also on the topological charge. By choosing the proper combination of parameters, the adjustably confined flat-topped focus and focal hole can be obtained. The focus-shaping technique may find wide applications, such as optical tweezers, laser printing and material processing. 相似文献
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Dr. Feng‐Chun Lo Chang‐Chih Hsieh Dr. Manuel Maestre‐Reyna Prof. Chin‐Yu Chen Dr. Tzu‐Ping Ko Prof. Yih‐Chern Horng Yei‐Chen Lai Prof. Yun‐Wei Chiang Chih‐Mao Chou Cheng‐Hung Chiang Prof. Wei‐Ning Huang Dr. Yi‐Hung Lin Prof. D. Scott Bohle Prof. Wen‐Feng Liaw 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(28):9768-9776
Molecular mechanisms underlying the repair of nitrosylated [Fe–S] clusters by the microbial protein YtfE remain poorly understood. The X‐ray crystal structure of YtfE, in combination with EPR, magnetic circular dichroism (MCD), UV, and 17O‐labeling electron spin echo envelope modulation measurements, show that each iron of the oxo‐bridged FeII–FeIII diiron core is coordinatively unsaturated with each iron bound to two bridging carboxylates and two terminal histidines in addition to an oxo‐bridge. Structural analysis reveals that there are two solvent‐accessible tunnels, both of which converge to the diiron center and are critical for capturing substrates. The reactivity of the reduced‐form FeII–FeII YtfE toward nitric oxide demonstrates that the prerequisite for N2O production requires the two iron sites to be nitrosylated simultaneously. Specifically, the nitrosylation of the two iron sites prior to their reductive coupling to produce N2O is cooperative. This result suggests that, in addition to any repair of iron centers (RIC) activity, YtfE acts as an NO‐trapping scavenger to promote the NO to N2O transformation under low NO flux, which precedes nitrosative stress. 相似文献
6.
Ding‐Ru Yei Huei‐Kuan Fu Wen‐Yi Chen Feng‐Chih Chang 《Journal of Polymer Science.Polymer Physics》2006,44(2):347-358
Polybenzoxazine (PBZ), which has a structure similar to that of phenolic resin, is formed through the thermal self‐curing of benzoxazine, that is through a heterocyclic ring opening reaction that requires no catalyst and releases no condensation byproducts. We have used the solvent blending method to prepare PBZ/clay nanocomposites possessing various clay contents. We synthesized a monofunctional benzoxazine monomer (MBM) and then treated the clay with this intercalation agent. The results of X‐ray diffraction (XRD) analysis indicated that MBM intercalated into the galleries of the clay; the nanocomposite possessed an exfoliated structure at 3% clay content. To better understand the curing kinetics of the PBZ/clay nanocomposites, we performed dynamic and isothermal differential scanning calorimetry (DSC) measurements. We describe the thermodynamics of the curing process, using all three of the Kissinger, Ozawa, and Kamal models. The Kissinger and Ozawa methods gave fairly close results for the calculated activation energies, which decreased upon increasing the clay content. The Kamal method, based on an autocatalytic model, suggested a total reaction order of between 2.4 and 2.8. The glass transition temperature (Tg) decreased upon increasing the clay content. Thermogravimetric analysis (TGA) indicated that the nanocomposites have higher decomposition temperatures than does the pristine PBZ; this finding suggests an enhancement in their thermal stability. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 347–358, 2006 相似文献
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Huei‐Kuan Fu Chih‐Feng Huang Shiao‐Wei Kuo Han‐Ching Lin Ding‐Ru Yei Feng‐Chih Chang 《Macromolecular rapid communications》2008,29(14):1216-1220
Novel low surface free energy materials of polybenzoxazine/organically modified silicate nanocomposites have been prepared and characterized. The CPC (cetylpyridinium chloride)/clay10%/poly(3‐phenyl‐3,4‐dihydro‐2H‐1,3‐benzoxazine) (PP‐a) material possesses an extremely low surface free energy (12.7 mJ · m−2) after 4 h curing at 200 °C, which is even lower than that of poly(tetrafluoroethylene) (22.0 mJ · m−2) calculated on the basis of the three‐liquid geometric method. X‐Ray photoelectron spectroscopy (XPS) shows a higher silicon content on the surface of the nanocomposites than for an average composition, which implies that the clay is more preferentially enriched on the outermost layer. In addition, the glass transition temperature (Tg) of the polybenzoxazine (PP‐a) in the nanocomposite is 22.6 °C higher and its thermal decomposition temperature is also 31.5 °C higher than the pure PP‐a. This finding provides a simple way to prepare low surface energy and high thermal stability materials.
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Recent experimental efforts focused on near-field coherent vortex dynamics, and their impact on stabilization of a lifted jet diffusion flame in the hysteresis region are reported. Simultaneous jet flow and flame visualizations are conducted first to obtain a global feature of flow/flame interaction. The statistical liftoff heights are calculated by a DIP (digital image processing) method. The gas concentration and velocity distributions induced by the vortex evolution as well as the corresponding flame front motion are deduced from phase-averaged measurements of planar Mie-scattering gas concentration images, LDV and ion-signals, respectively. The planar gas concentration technique employed here extends our previous work (Chao et al. 1990, 1991 a) to include phase-averaging. Results of the experiments show that the most probable flame base locations in the hysteresis region are at the coherent vortex roll-up and pairing locations. The deeply entrained air lump caused by large-scale vortices during roll-up and pairing is the main obstruction to flame propagation back to the nozzle exit and causes the hysteresis phenomenon. 相似文献
10.
We study the bifurcation diagrams of classical positive solutions u with ‖u‖∞∈(0,∞) of the p-Laplacian Dirichlet problem