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121.
M. Fischer W. Knoche P. D. I. Fletcher B. H. Robinson N. C. White 《Colloid and polymer science》1980,258(6):733-742
Summary Complex formation between divalent metal ions and the hydrophilic murexide anion in the presence of anionic micelles has been employed to study aspects of micelle formation, the binding of divalent metal ions to micelles, and the kinetics of metal-complex formation in the presence of micelles.
With 8 figures and 1 table
Dedicated to Prof.G. Rehage on the occasion of his 60th birthday. 相似文献
Zusammenfassung Die Komplexbildung zweiwertiger Metallionen mit dem hydrophilen Indikator Murexid wurde in Gegenwart anionischer Mizellen untersucht. Die Indikatorreaktion wurde benutzt, um Aussagen über Mizellbildung, Bindung zweiwertiger Metallionen an Mizellen und die Kinetik der Metallkomplexbildung bei Anwesenheit von Mizellen zu erhalten.
With 8 figures and 1 table
Dedicated to Prof.G. Rehage on the occasion of his 60th birthday. 相似文献
122.
Klaus van Benthem Stephan Krämer Wilfried Sigle Manfred Rühle 《Mikrochimica acta》2002,138(3-4):181-193
An understanding of the correlation between microstructures and properties of materials require the characterization of the
material on many different length scales. Often the properties depend primarily on the atomistics of defects, such as dislocations
and interfaces. The different techniques of transmission electron microscopy allow the characterization of the structure and
of the chemical composition of materials with high spatial resolution to the atomic level: high resolution transmission electron
microscopy allows the determination of the position of the columns of atoms (ions) with high accuracy. The accuracy which
can be achieved in these measurements depends not only on the instrumentation but also on the quality of the transmitted specimen
and on the scattering power of the atoms (ions) present in the analyzed column.
The chemical composition can be revealed from investigations by analytical microscopy which includes energy dispersive X-ray
spectroscopy, mainly quantitatively applied for heavy elements, and electron energy-loss spectroscopy. Furthermore, the energy-loss
near-edge structure of EELS data results in information on the local band structure of unoccupied states of the excited atoms
and, therefore, on bonding. A quantitative evaluation of convergent beam electron diffraction results in information on the
electron charge density distribution of the bulk (defect-free) material.
The different techniques are described and applied to different problems in materials science. It will be shown that nearly
atomic resolution can be achieved in high resolution electron microscopy and in analytical electron microscopy. Recent developments
in electron microscopy instrumentation will result in atomic resolution in the foreseeable future. 相似文献
123.
Chiral salicylidenphenethylamines (R)‐HA or (S)‐HA , 2‐salicylidenfurfuryl‐imines HB , and 2‐salicylidenaminoethanol HC react with sodium hydride or sodium hexamethyldisilylamide to form the sodium complexes [Na(R)‐A] 4 · 0,5 Et 2 , [Na(S)‐A] 4 · 0,5 Et 2 O (1) , [NaB] 4 · 0,5 Ph‐Me (2) and [(dme)NaC] 4 (3) . In the presence of 18‐crown‐6 the complex [Na(18‐crown‐6)(thf) 2 ] 2 [Na 2 (C)] 4 · THF (4) can also be isolated. The crystal structure analyses of both 1 and 2 show that heterocubane structures with a Na4O4 frame work are formed. Additionally, the imine nitrogen atom is bonded at the Na atom which has the coordination number 4 in 1 . Additional coordination of the furfuryl oxygen atom results in the coordination number five for the sodium atom in 2 . In 3 which is also a tetramer, two Na2O2 units are connected via two imino‐ethanol bridges Na(1)‐N(=CH‐phenolat)‐CH2CH2‐OH‐Na(2A). The crystal structure analysis displays that 4 is an ionic compound consisting of two [(thf)2Na(18‐crown‐6)]+ cations and the dinuclear dianion [Na 2 (C) 4 ] 2? . Both 1 and 2 are carboxylation reagents which transfer CO2 to 2‐fluoropropiophenone. 1 is more active than 2 , but 3 and 4 are inactive. 相似文献
124.
Probing the water coordination of protein-targeted MRI contrast agents by pulsed ENDOR spectroscopy.
Stephan G Zech Wei-Chuan Sun Vincent Jacques Peter Caravan Andrei V Astashkin Arnold M Raitsimring 《Chemphyschem》2005,6(12):2570-2577
A novel methodology based on electron-nuclear double resonance (ENDOR) spectroscopy is used for the direct determination of the water coordination number (q) of gadolinium-based magnetic resonance imaging (MRI) contrast agents. Proton ENDOR spectra can be obtained at approximately physiological concentrations for metal complexes in frozen aqueous solutions either in the presence or absence of protein targets. It is shown that, depending on the structure of the co-ligand, the water hydration number of a complex in aqueous solution can be significantly different to when the complex is noncovalently bound to a protein. From the ENDOR spectra of the exchangeable protons, precise information on the metal-proton distance can be derived as well. These essential parameters directly correlate with the efficacy of MRI contrast agents and should therefore aid the development of novel, highly efficient compounds targeted to various proteins. 相似文献
125.
Sergii Afonin Alexander Frey Sybille Bayerl Dahlia Fischer Parvesh Wadhwani Sevil Weinkauf Anne S Ulrich 《Chemphyschem》2006,7(10):2134-2142
Cell-penetrating peptides (CPPs) are short polycationic sequences that can translocate into cells without disintegrating the plasma membrane. CPPs are useful tools for delivering cargo, but their molecular mechanism of crossing the lipid bilayer remains unclear. Here we study the interaction of the HIV-derived CPP TAT (48-60) with model membranes by solid-state NMR spectroscopy and electron microscopy. The peptide induces a pronounced isotropic (31)P NMR signal in zwitterionic DMPC, but not in anionic DMPG bilayers. Octaarginine and to a lesser extent octalysine have the same effect, in contrast to other cationic amphiphilic membrane-active peptides. The observed non-lamellar lipid morphology is attributed to specific interactions of polycationic peptides with phosphocholine head groups, rather than to electrostatic interactions. Freeze-fracture electron microscopy indicates that TAT(48-60) induces the formation of rodlike, presumably inverted micelles in DMPC, which may represent intermediates during the translocation across eukaryotic membranes. 相似文献
126.
Vitamin-B12-Catalyzed C, C-Bond Formation: Synthesis of Jasmonates via Sequential Radical Reaction The Cbl-catalyzed electroreduction of 3-(2′-bromo-1′-ethoxyethoxy)cyclopenten ( 1a ) in presence of 1-cyanovinyl-acetate ( 8 ) gave, in a sequential radical reaction (5-exo-trig-cyclization of 1a followed by addition to 8 ), 1-cyano-2-(2′-ethoxy-hexahydro-2′H-cyclopenta[b] furan-4′-yl)ethyl acetate ( 10a ). This intermediate was transformed to methyl jasmonate ( 7 ; four steps) and epituberolide ( 9 ; three steps) in 20 and 31% yield, respectively, from cyclopent-2-en-l-ol. 相似文献
127.
Heinz Berner Hermann Vyplel Gerhard Schulz Gernot Fischer 《Monatshefte für Chemie / Chemical Monthly》1985,116(10):1165-1176
2-Hydroxy-19,20-dihydropleuromutilin (10) undergoes a stereospecific ketolisomerisation when treated with base under phase/transfer conditions (11, 12). The subsequent reductive elimination of the 3-acetoxygroup afforded mutilin with a 1,2-transposed ketofunction (13). 相似文献
128.
P. Placke V. Edel L. Reversat R. Richert E. W. Fischer 《Colloid and polymer science》1995,273(12):1156-1162
Structural relaxations of an electrorheological fluid (ERF) due to changes in the applied electrical field strength or shear rate are observed on time scales 1 s<t<40 000 s. Commercial ERFs consisting of mesoscopic polyurethane particles in a silicone oil matrix were studied by three different experimental techniques in order to obtain and compare the characteristic relaxation times. It is demonstrated that dielectric spectroscopy, viscosimetry and light transmission experiments represent the same results concerning the structural relaxation phenomena of ERFs when electrical fields are applied. The tendency of strong induced dipoles to align the particles in the direction of the field increases the effective dipole moment and therefore , the shear viscosity and the amount of light transmitted along the field direction in an ITO/glass sandwich cell. The optical experiment is capable of resolving fast processes within the first 1 ms if large electrical fields are applied. The effects of electrophoresis and shearing, which both counteract the field induced structures, are also addressed. 相似文献
129.
Stephan Wehner 《Archive for Mathematical Logic》1995,34(3):183-196
To date the problem of finding a general characterization of injective enumerability of recursively enumerable (r.e) classes of r.e. sets has proved intractable. This paper investigates the problem for r.e. classes of cofinite sets. We state a suitable criterion for r.e. classesC such that there is a boundn with |-A|n for allAC. On the other hand an example is constructed which shows that Lachlan's condition (F) does not imply injective enumerability for r.e. classes of cofinite sets. We also look at a certain embeddability property and show that it is equivalent with injective enumerability for certain classes of cofinite sets. At the end we present a reformulation of property (F).Thank you for technical support, Wolfgang Eppler, for intellectual support, Alistair Lachlan, and for proof-reading, Martin Kummer. Thanks also to the anonymous referee 相似文献
130.