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排序方式: 共有846条查询结果,搜索用时 15 毫秒
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2.
Daria E. Lonsdale Geoffrey Johnston‐Hall Amanda Fawcett Craig A. Bell Carl N. Urbani Michael R. Whittaker Michael J. Monteiro 《Journal of polymer science. Part A, Polymer chemistry》2007,45(16):3620-3625
In this work, we propose that retardation in vinyl acetate polymerization rate in the presence of toluene is due to degradative chain transfer. The transfer constant to toluene (Ctrs) determined using the Mayo method is equal to 3.8 × 10?3, which is remarkably similar to the value calculated from the rate data, assuming degradative chain transfer (2.7 × 10?3). Simulations, including chain‐length‐dependent termination, were carried out to compare our degradative chain transfer model with experimental results. The conversion–time profiles showed excellent agreement between experiment and simulation. Good agreement was found for the Mn data as a function of conversion. The experimental and simulation data strongly support the postulate that degradative chain transfer is the dominant kinetic mechanism. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3620–3625, 2007 相似文献
3.
Amanda J. Ziegler Craig C. McLauchlan Cyndi R. Sosnowski Albert W. Herlinger 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(2):o132-o134
The title compound (H2DTMSP[EBP]), C14H36O6P2Si2, was crystallized by the slow evaporation of a solution in a 20:1 mixture of pentane and acetone. The H2DTMSP[EBP] molecule lies about an inversion center. In the solid state, the molecule exists in an anti configuration, with the molecular backbone C—C bond located on an inversion center. The compound exists in the solid state as hydrogen‐bonded infinite sheets in the ab plane, unlike the methylene analogue, which exists as hydrogen‐bonded infinite chains, demonstrating an `even–odd' effect of the length of the backbone alkyl chain. 相似文献
4.
Haes AJ Zhao J Zou S Own CS Marks LD Schatz GC Van Duyne RP 《The journal of physical chemistry. B》2005,109(22):11158-11162
A novel method to produce solution-phase triangular silver nanoparticles is presented. Ag nanoparticles are prepared by nanosphere lithography and are subsequently released into solution. The resulting nanoparticles are asymmetrically functionalized to produce either single isolated nanoparticles or dimer pairs. The structural and optical properties of Ag nanoparticles have been characterized. Mie theory and the Discrete Dipole Approximation method (DDA) have been used to model and interpret the optical properties of the released Ag nanoparticles. 相似文献
5.
E. M. Araújo Renata Barbosa Amanda D. Oliveira Crislene R. S. Morais T. J. A. deMélo A. G. Souza 《Journal of Thermal Analysis and Calorimetry》2007,87(3):811-814
Polyethylene/montmorillonite clay nanocomposites were obtained via direct
melt intercalation. The clay was organically modified with four different
types of quaternary ammonium salts. The objective of this work is to study
the use of montmorillonite clay in the production of nanocomposites by means
on rheological, mechanical and crystallization properties of nanocomposites
and to compare to the properties of the matrix and PE/unmodified clay nanocomposites.
In general, the tensile test showed that the yield strength and modulus of
the nanocomposites are close to the pure PE. Apparently, the mixture with
Dodigen salt seems to be more stable than the pure PE and PE/unmodified clay. 相似文献
6.
Although a number of computational studies have examined the relative stability of icosahedral and decahedral gold clusters from 1 to 3 nm in size, few studies have focussed on the variety of face-centered cubic (fcc) nanoparticles in this size regime. In most cases small fcc gold particles are assumed to adopt the truncated octahedral shape, but in light of the fact that the shape and structure of gold nanoparticles is known to vary, the relative stability of fcc polyhedra may change with size. Presented here are results of first-principles calculations investigating the preferred shape of gold particles less than 3 nm in size. Our results indicate that the equilibrium shape of fcc gold nanoparticles less than 1 nm is the cuboctahedron, but this shape rapidly becomes energetically unstable with respect to the truncated octahedron, octahedron and truncated cube shapes as the size increases. 相似文献
7.
Molecular chaperones, folding catalysts, and the recovery of active recombinant proteins fromE. coli
Jeffrey G. Thomas Amanda Ayling François Baneyx 《Applied biochemistry and biotechnology》1997,66(3):197-238
The high-level expression of recombinant gene products in the gramnegative bacteriumEscherichia coli often results in the misfolding of the protein of interest and its subsequent degradation by cellular proteases or its deposition
into biologically inactive aggregates known as inclusion bodies. It has recently become clear that in vivo protein folding
is an energy-dependent process mediated by two classes of folding modulators. Molecular chaperones, such as the DnaK-DnaJ-GrpE
and GroEL-GroES systems, suppress off-pathway aggregation reactions and facilitate proper folding through ATP-coordinated
cycles of binding and release of folding intermediates. On the other hand, folding catalysts (foldases) accelerate rate-limiting
steps along the protein folding pathway such as thecis/trans isomerization of peptidyl-prolyl bonds and the formation and reshuffling of disulfide bridges. Manipulating the cytoplasmic
folding environment by increasing the intracellular concentration of all or specific folding modulators, or by inactivating
genes encoding these proteins, holds great promise in facilitating the production and purification of heterologous proteins.
Purified folding modulators and artificial systems that mimic their mode of action have also proven useful in improving the
in vitro refolding yields of chemically denatured polypeptides. This review examines the usefulness and limitations of molecular
chaperones and folding catalysts in both in vivo and in vitro folding processes. 相似文献
8.
Detection of a biomarker for Alzheimer's disease from synthetic and clinical samples using a nanoscale optical biosensor 总被引:9,自引:0,他引:9
Haes AJ Chang L Klein WL Van Duyne RP 《Journal of the American Chemical Society》2005,127(7):2264-2271
A nanoscale optical biosensor based on localized surface plasmon resonance (LSPR) spectroscopy has been developed to monitor the interaction between the antigen, amyloid-beta derived diffusible ligands (ADDLs), and specific anti-ADDL antibodies. Using the sandwich assay format, this nanosensor provides quantitative binding information for both antigen and second antibody detection that permits the determination of ADDL concentration and offers the unique analysis of the aggregation mechanisms of this putative Alzheimer's disease pathogen at physiologically relevant monomer concentrations. Monitoring the LSPR-induced shifts from both ADDLs and a second polyclonal anti-ADDL antibody as a function of ADDL concentration reveals two ADDL epitopes that have binding constants to the specific anti-ADDL antibodies of 7.3 x 10(12) M(-1) and 9.5 x 10(8) M(-1). The analysis of human brain extract and cerebrospinal fluid samples from control and Alzheimer's disease patients reveals that the LSPR nanosensor provides new information relevant to the understanding and possible diagnosis of Alzheimer's disease. 相似文献
9.
In vivo imaging is a powerful approach to study biological processes. Beyond cellular methods, in vivo studies allow for biological stimuli (small molecules or proteins) to be studied in their native environment. This has the potential to aid in the discovery of new biology and guide the development of diagnostics and therapies for diseases. To ensure selectivity and an observable readout, the probe development field is shifting towards activity-based sensing (ABS) approaches and near-infrared (NIR) imaging modalities. This perspective will highlight recent in vivo ABS applications that utilize NIR imaging platforms. In vivo imaging is a powerful approach to study biological processes. 相似文献
10.
Reaction of a (237)Np(V) stock solution in the presence of oxalic acid, calcium chloride, and sodium hydroxide under hydrothermal conditions produces single crystals of a neptunium(V) oxalate, Na(2)NpO(2)(C(2)O(4))OH.H(2)O. The structure consists of one-dimensional chains running down the a axis and is the first example of a neptunium(V) oxalate compound containing hydroxide anions. 相似文献