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排序方式: 共有225条查询结果,搜索用时 15 毫秒
61.
Woodroofe CC Masalha R Barnes KR Frederickson CJ Lippard SJ 《Chemistry & biology》2004,11(12):1659-1666
Esterification of fluorescent biosensors is a common strategy used to trap probes within the cell. Zinpyr-1 (ZP1) is a fluorescein-based bright fluorescent sensor for divalent zinc that is cell permeable without prior modification. We describe here the synthesis and characterization of ZP1 sensors containing a carboxylic acid or ethyl ester functionality at the 5 or 6 position of the fluorescein. The presence of an electronegative carboxylate decreases the proton-induced background fluorescence of the probe by lowering the pKa of the benzylic amines responsible for fluorescence quenching. The charged species ZP1(6-CO2-) is membrane-impermeant, whereas the permeability of the neutral ZP1(5/6-CO2Et) is similar to that of the parent sensor. Intracranial microinfusion of ZP1(6-CO2Et) into rat hippocampus produces reduced staining of vesicular zinc in neuropil and very clear delineation of zinc-positive injured neuronal somata and dendrites as compared with ZP1. 相似文献
62.
Zhang F Wolff MW Williams D Busch K Lang SC Murhammer DW Linhardt RJ 《Applied biochemistry and biotechnology》2001,90(2):125-136
Human secreted alkaline phosphatase (SEAP) was produced in a stablytransformed Spodoptera frugiperda Sf-9 insect cell line (Sfb4GalT) following infection with a recombinant Autographa californica multiple nuclear polyhedrovirus containing the SEAP gene under control of the polyhedrin promoter. An affinity chromatographic
column prepared by linking 4-aminobenzylphosphonic acid to histidyl-expoxy-Sepharose was used to isolate SEAP from the cell
supernatant following removal of cells and virus and 10-fold concentration through ultrafiltration. We found that the binding
of SEAP on the affinity matrix follows the Langmuir isotherm model. In addition, either recycling SEAP sample through the
column for 24 h or loading high SEAP concentrations resulted in a high-purity product. Some nonspecific binding of protein
on the matrix occurred when low concentrations of SEAP sample were loaded. Finally, we found that SEAP binding occurs rapidly,
i.e., within 30 min of adding the SEAP sample to the affinity matrix. 相似文献
63.
Peter M. Marley Tesfaye A. Abtew Katie E. Farley Gregory A. Horrocks Robert V. Dennis Peihong Zhang Sarbajit Banerjee 《Chemical science》2015,6(3):1712-1718
The classical orthorhombic layered phase of V2O5 has long been regarded as the thermodynamic sink for binary vanadium oxides and has found great practical utility as a result of its open framework and easily accessible redox states. Herein, we exploit a cation-exchange mechanism to synthesize a new stable tunnel-structured polymorph of V2O5 (ζ-V2O5) and demonstrate the subsequent ability of this framework to accommodate Li and Mg ions. The facile extraction and insertion of cations and stabilization of the novel tunnel framework is facilitated by the nanometer-sized dimensions of the materials, which leads to accommodation of strain without amorphization. The topotactic approach demonstrated here indicates not just novel intercalation chemistry accessible at nanoscale dimensions but also suggests a facile synthetic route to ternary vanadium oxide bronzes (MxV2O5) exhibiting intriguing physical properties that range from electronic phase transitions to charge ordering and superconductivity. 相似文献
64.
Expanding the Chemistry of Molecular U2+ Complexes: Synthesis,Characterization, and Reactivity of the {[C5H3(SiMe3)2]3U}− Anion 下载免费PDF全文
Cory J. Windorff Dr. Matthew R. MacDonald Dr. Katie R. Meihaus Dr. Joseph W. Ziller Prof. Jeffrey R. Long Prof. William J. Evans 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(2):772-782
The synthesis of new molecular complexes of U2+ has been pursued to make comparisons in structure, physical properties, and reactivity with the first U2+ complex, [K(2.2.2‐cryptand)][Cp′3U], 1 (Cp′=C5H4SiMe3). Reduction of Cp′′3U [Cp′′=C5H3(SiMe3)2] with KC8 in the presence of 2.2.2‐cryptand or 18‐crown‐6 generates [K(2.2.2‐cryptand)][Cp′′3U], 2‐K(crypt) , or [K(18‐crown‐6)(THF)2][Cp′′3U], 2‐K(18c6) , respectively. The UV/Vis spectra of 2‐K and 1 are similar, and they are much more intense than those of U3+ analogues. Variable temperature magnetic susceptibility data for 1 and 2‐K(crypt) reveal lower room temperature χMT values relative to the experimental values for the 5f3 U3+ precursors. Stability studies monitored by UV/Vis spectroscopy show that 2‐K(crypt) and 2‐K(18c6) have t1/2 values of 20 and 15 h at room temperature, respectively, vs. 1.5 h for 1 . Complex 2‐K(18c6) reacts with H2 or PhSiH3 to form the uranium hydride, [K(18‐crown‐6)(THF)2][Cp′′3UH], 3 . Complexes 1 and 2‐K(18c6) both reduce cyclooctatetraene to form uranocene, (C8H8)2U, as well as the U3+ byproducts [K(2.2.2‐cryptand)][Cp′4U], 4 , and Cp′′3U, respectively. 相似文献
65.
The results of international assessments such as the Trends in International Mathematics and Science Study (TIMSS) are often reported as rankings of nations. Focusing solely on national rank can result in invalid inferences about the relative quality of educational systems that can, in turn, lead to negative consequences for teachers and students. This study seeks an alternative data analysis method that allows for improved inferences about international performance on the TIMSS. In this study, four classroom teachers categorized a sample of TIMSS items by the cognitive domains of knowing and applying using the definitions provided by the TIMSS 2011 Assessment Frameworks. Items of different cognitive domains were analyzed separately. This disaggregation allowed for more valid inferences to be made about student performance. Results showed almost no significant difference between the performance of U.S. students and the students of five other nations. Additionally, no differences were observed in U.S. students' performance on knowing items and applying items, although students from some sample nations performed significantly better on knowing items. These results suggest that policy makers, educators, and citizens should be cautious when interpreting the results of TIMSS rank tables. 相似文献
66.
Katie A. Edwards Katherine J. Meyers Barbara Leonard Antje J. Baeumner 《Analytical and bioanalytical chemistry》2013,405(12):4017-4026
Myoglobin is one of several cardiac markers which become elevated in the blood following an acute myocardial infarction and can aid in the diagnosis of a heart attack. Here, a sandwich immunoassay for myoglobin was developed, including a thorough optimization of fluorescent dye-encapsulating liposomes versus enzymatic amplification (alkaline phosphatase and horseradish peroxidase) at each step. The optimized microtiter plate-based assay was capable of detecting as low as 11.3 pg/mL myoglobin and was successfully applied for the quantification of myoglobin in human serum. In comparison to enzymatic approaches, the liposomes demonstrated lower limits of detection, significantly reduced limits of quantification, improved signal discrimination through substantial signal enhancement, and reduced assay time. Liposomes were stable and functional at ambient temperatures for over 400 days. Finally, ease of use was greater due to lack of reliance on additional reagents, non-time-based signal enhancement, and excellent photostability. Optimal conditions identified for enzymatic approaches can also be used for liposome amplification, which makes substitution of these liposomes into existing assays straightforward. Thus, the extensive studies carried out here suggest that liposomes may be incorporated into formats currently utilizing enzymatic enhanced fluorescence with a potential for increased performance on various levels.
Sandwich immunoassay for the cardiac marker myoglobin. Excellent performance of fluorescent dye-encapsulating liposomes for signal enhancement versus enzymes using commercially available fluorescent substrates was demonstrated. 相似文献
67.
Simona E. Hunyadi Murph Catherine J. Murphy Hector R. Colon-Mercado Ricardo D. Torres Katie J. Heroux Elise B. Fox Lucas B. Thompson Richard T. Haasch 《Journal of nanoparticle research》2011,13(12):6347-6364
In this article, we report the precise control of the size, shape, and surface morphology of Au–Pt nanocatalysts (cubes, blocks,
octahedrons, and dogbones) synthesized via a seed-mediated approach. Gold “seeds” of different aspect ratios (1–4.2), grown
by a silver-assisted approach, were used as templates for high-yield production of novel Au–Pt nanocatalysts at a low temperature
(40 °C). Characterization by electron microscopy (SEM, TEM, HRTEM), energy dispersive X-ray analysis, UV–Vis spectroscopy,
zeta-potential (surface charge), atomic force microscopy, X-ray photoelectron spectroscopy, and inductively coupled plasma
mass spectrometry were used to better understand their physico-chemical properties, preferred reactivities and underlying
nanoparticle growth mechanism. A rotating disk electrode was employed to evaluate the Au–Pt nanocatalysts electrochemical
performance in the oxygen reduction reaction (ORR) and the methanol oxidation reaction of direct methanol fuel cells. The
results indicate the Au–Pt dogbones are partially and in some cases completely unaffected by methanol poisoning during the
evaluation of the ORR. The ORR performance of the octahedron particles in the absence of MeOH is superior to that of the Au–Pt
dogbones and Pt-black; however, its performance is affected by the presence of MeOH. 相似文献
68.
Valerie Paprocki Peter Hrobrik Katie L. M. Harriman Martin S. Luff Thomas Kupfer Martin Kaupp Muralee Murugesu Holger Braunschweig 《Angewandte Chemie (International ed. in English)》2020,59(31):13109-13115
The π coordination of arene and anionic heteroarene ligands is a ubiquitous bonding motif in the organometallic chemistry of d‐block and f‐block elements. By contrast, related π interactions of neutral heteroarenes including neutral bora‐π‐aromatics are less prevalent particularly for the f‐block, due to less effective metal‐to‐ligand backbonding. In fact, π complexes with neutral heteroarene ligands are essentially unknown for the actinides. We have now overcome these limitations by exploiting the exceptionally strong π donor capabilities of a neutral 1,4‐diborabenzene. A series of remarkably robust, π‐coordinated thorium(IV) and uranium(IV) half‐sandwich complexes were synthesized by simply combining the bora‐π‐aromatic with ThCl4(dme)2 or UCl4, representing the first examples of actinide complexes with a neutral boracycle as sandwich‐type ligand. Experimental and computational studies showed that the strong actinide–heteroarene interactions are predominately electrostatic in nature with distinct ligand‐to‐metal π donation and without significant π/δ backbonding contributions. 相似文献
69.
Let \(\varphi \) be an arbitrary linear-fractional self-map of the unit disk \({\mathbb {D}}\) and consider the composition operator \(C_{-1, \varphi }\) and the Toeplitz operator \(T_{-1,z}\) on the Hardy space \(H^2\) and the corresponding operators \(C_{\alpha , \varphi }\) and \(T_{\alpha , z}\) on the weighted Bergman spaces \(A^2_{\alpha }\) for \(\alpha >-1\). We prove that the unital C\(^*\)-algebra \(C^*(T_{\alpha , z}, C_{\alpha , \varphi })\) generated by \(T_{\alpha , z}\) and \(C_{\alpha , \varphi }\) is unitarily equivalent to \(C^*(T_{-1, z}, C_{-1, \varphi }),\) which extends a known result for automorphism-induced composition operators. For maps \(\varphi \) that are not automorphisms of \({\mathbb {D}}\), we show that \(C^*(C_{\alpha , \varphi }, {\mathcal {K}}_{\alpha })\) is unitarily equivalent to \(C^*(C_{-1, \varphi }, {\mathcal {K}}_{-1})\), where \({\mathcal {K}}_{\alpha }\) and \({\mathcal {K}}_{-1}\) denote the ideals of compact operators on \(A^2_{\alpha }\) and \(H^2\), respectively, and apply existing structure theorems for \(C^*(C_{-1, \varphi }, {\mathcal {K}}_{-1})/{\mathcal {K}}_{-1}\) to describe the structure of \(C^*(C_{\alpha , \varphi }, {\mathcal {K}}_{\alpha })/\mathcal {K_{\alpha }}\), up to isomorphism. We also establish a unitary equivalence between related weighted composition operators induced by maps \(\varphi \) that fix a point on the unit circle. 相似文献
70.
Banner LT Danila DC Sharpe K Durkin M Clayton B Anderson B Richter A Pinkhassik E 《Langmuir : the ACS journal of surfaces and colloids》2008,24(20):11464-11473
Using temporary self-assembled scaffolds to preorganize building blocks is a potentially powerful method for the synthesis of organic nanostructures with programmed shapes. We examined the underlying phenomena governing the loading of hydrophobic monomers into lipid bilayer interior and demonstrated successful control of the amount and ratio of loaded monomers. When excess styrene derivatives or acrylates were added to the aqueous solution of unilamellar liposomes made from saturated phospholipids, most loading occurs within the first few hours. Dynamic light scattering and transmission electron microscopy revealed no evidence of aggregation caused by monomers. Bilayers appeared to have a certain capacity for accommodating monomers. The total volume of loaded monomers is independent of monomer structure. X-ray scattering showed the increase in bilayer thickness consistent with loading monomers into bilayer interior. Loading kinetics is inversely proportional to the hydrophobicity and size of monomers. Loading and extraction kinetic data suggest that crossing the polar heads region is the rate limiting step. Consideration of loading kinetics and multiple equilibria are important for achieving reproducible monomer loading. The total amount of monomers loaded into the bilayer can be controlled by the loading time or length of hydrophobic lipid tails. The ratio of loaded monomers can be varied by changing the ratio of monomers used for loading or by the time-controlled replacement of a preloaded monomer. Understanding and controlling the loading of monomers into bilayers contributes to the directed assembly of organic nanostructures. 相似文献