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31.
Meyer F Demeshko S Leibeling G Kersting B Kaifer E Pritzkow H 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(5):1518-1526
Pyrazolate-based dinucleating ligands with thioether-containing chelate arms have been used for the synthesis of a family of novel tetranuclear nickel(II) complexes [L2Ni4(N3)3(O2CR)](ClO4)2 that incorporate three azido bridges and one carboxylate (R = Me, Ph). Molecular structures have been elucidated by X-ray crystallography in four cases, revealing Ni4 cores with a unique topology in which two of the azido ligands adopt an unusual mu3-1,1,3 bridging mode. The compounds were further characterized by mass spectrometry, IR spectroscopy, and variable-temperature magnetic susceptibility measurements. Magnetic data analyses indicate a combination of significant intramolecular ferromagnetic and antiferromagnetic exchange interactions that give rise to an overall S(T) = 0 ground state. The sign and the magnitude of the individual couplings have been rationalized in the framework of the common magnetostructural correlations for end-to-end and end-on azido linkages, suggesting that these correlations also remain valid for the respective fragments of multiply bridging mu3-1,1,3 azido ligands. 相似文献
32.
33.
Elisabeth Seguin Michel Koch Evelyne Chenu Marcel Hayat 《Helvetica chimica acta》1980,63(5):1335-1346
Partial Synthesis and Oncostatic Properties of Pseudotubulosines, Analogues of Emetine and Tubulosine Pseudotubulosines, structural analogues of emetine and tubulosine, have been synthesized by either Pictet-Spengler or Bischler-Napieralski condensation from dihydrocorynantheal or corynantheidal. Spectral data, cytotoxic and oncostatic properties of these new alkaloids are described. 相似文献
34.
Codée JD Litjens RE den Heeten R Overkleeft HS van Boom JH van der Marel GA 《Organic letters》2003,5(9):1519-1522
Diphenylsulfoxide in combination with triflic anhydride provides a very potent thiophilic glycosylation promotor system, capable of activating disarmed thioglycosides. The usefulness of this novel thiophilic activator is illustrated in a successful chemoselective glycosylation sequence in which the donor thioglycoside in the first condensation step may be either armed or disarmed. [reaction: see text] 相似文献
35.
Ladislaus Szekeres und Elisabeth Sugár 《Fresenius' Journal of Analytical Chemistry》1960,172(1):35-38
Zusammenfassung Zur Bestimmung von Sulfit und Thiosulfat nebeneinander wird folgendes Verfahren beischrieben: In einem aliquoten Teil der zu untersuchenden Lösung wird mit elementarem Jod oxydiert, wobei die Sulfitionen zwei Äquivalente, die Thiosulfationen ein Äquivalent Jod je Mol verbrauchen. In einem zweiten aliquoten Teil der zu untersuchenden Lösung werden die Ionen mit — aus KBrO3 + KBr hergestelltem — NaOBr oxydiert; die Sulfitionen verbrauchen dabei zwei Äquivalente, die Thiosulfationen acht Äquivalente Brom je Mol. 相似文献
36.
Klaus Burger Elisabeth Windeisen Elisabeth Heistracher Torsten Lange Abdel-Aleem H. Abdel-Aleem 《Monatshefte für Chemie / Chemical Monthly》2002,2(3):41-58
The synthesis of homochiral heterocyclic α-hydroxy acids starting from (S)- and (R)-malic acid using hexafluoroacetone as protecting and activating agent is described. The new compounds are useful building
blocks for peptide and depsipeptide modification. 相似文献
37.
Dimerizable cationic detergents with a low cmc condense plasmid DNA into nanometric particles and transfect cells in culture 总被引:4,自引:0,他引:4
The size of condensed DNA particles is a key determinant for in vivo diffusion and gene delivery to cells. Gene molecules can be individually compacted by cationic thiol detergents into nanometric particles that are stabilized by oxidative conversion of the detergent into a gemini lipid. To reach the other goal, gene delivery, a series of cationic thiol detergents with various chain lengths (C(12)-C(16)) and headgroups (ornithine or spermine) was prepared, using a versatile polymer-supported synthetic strategy. Critical micelle concentrations and thiol oxidation rates of the detergents were measured. The formation and stability of complexes formed with plasmid DNA, as well as the size, xi-potential, morphology, and transfection efficiency of the particles were investigated. Using the tetradecane/ornithine detergent, a solution of 5.5 Kpb plasmid DNA molecules was converted into a homogeneous population of 35 nm particles. The same detergent, once oxidized, exhibited a typical lipid phase internal structure and was capable of effective cell transfection. The particle size did not increase with time. Surprisingly, the gel electrophoretic mobility of the DNA complexes was found to be higher than that of plasmid DNA itself. Favorable in vivo diffusion and intracellular trafficking properties may thus be expected for these complexes. 相似文献
38.
Spehar AM Koster S Linder V Kulmala S de Rooij NF Verpoorte E Sigrist H Thormann W 《Electrophoresis》2003,24(21):3674-3678
This paper characterizes the basic electrokinetic phenomena occurring within native poly(dimethylsiloxane) (PDMS) microchannels. Using simple buffers and current measurements, current density and electroosmosis data were determined in trapezoidal, reversibly sealed PDMS/PDMS and hybrid PDMS/glass channels with a cross-sectional area of 1035.5 microm(2) and about 6 cm length. This data was then compared to that obtained in an air-thermostated 50 microm inner diameter (1963.5 microm(2) cross-sectional area) fused-silica (FS) capillary of 70 cm length. Having a pH 7.8 buffer with an ionic strength (I) of 90 mM, Ohms's law was observed in the microchannels with electric field strengths of up to about 420 V/cm, which is about twice as high as for the FS capillary. The electroosmotic mobility (micro(EO)) in PDMS and FS is shown to exhibit the same general dependences on I and pH. For all configurations tested, the experimentally determined micro(EO) values were found to correlate well with the relationship micro(EO) = a + b log(I), where a and b are coefficients that are determined via nonlinear regression analysis. Electroosmotic fluid pumping in native PDMS also follows a pH dependence that can be estimated with a model based upon the ionization of silanol. Compared to FS, however, the magnitude of the electroosmotic flow in native PDMS is 50-70% smaller over the entire pH range and is difficult to maintain at acidic pH values. Thus, the origin of the negative charge at the inner wall of PDMS, glass, and FS appears to be similar but the density is lower for PDMS than for glass and FS. 相似文献
39.
Elisabeth Bakács-Polgár 《Fresenius' Journal of Analytical Chemistry》1962,190(4):373-376
Zusammenfassung Im Rahmen der Untersuchungen über die Verwendung von Metallindicatoren bei Fällungsmaßanalysen wird gezeigt, daß man Phosphationen mit 0,1 m Wismutnitratlösung bzw. Wismutionen mit 0,1 m Phosphatmaßlösung in salpetersaurer Lösung unter Zugabe von Xylenolorange-Methylenblau oder Methylthymolblau-Methylenblau als Indicatoren bestimmen kann. Der Äquivalenzpunkt wird besonders leicht und sicher erfaßt, wenn man die zu titrierende Lösung mit dem gleichen Volumen Chloroform versetzt, nach jedem Zusatz der Maßlösung durchschüttelt und nach der rasch erfolgten Phasentrennung die überstehende klare Lösung beobachtet. Die Titrationen erfordern wenig Zeit und geben zuverlässige, genaue Resultate. 相似文献
40.
Dupont A Eastoe J Martin L Steytler DC Heenan RK Guittard F Taffin de Givenchy E 《Langmuir : the ACS journal of surfaces and colloids》2004,20(23):9960-9967
Hybrid fluorocarbon-hydrocarbon (F-H) sulfate surfactants are shown to be efficient stabilizers in water-in-CO2 (w/c) microemulsions. The chain structure and F-H ratio affect the regions of P-T phase stability and aggregation structure in these w/c phases. High-pressure near-infrared spectroscopy and small-angle neutron scattering measurements of microemulsified water provide evidence for the stabilization of w/c microemulsion droplets. The relative lengths of the two chains were found to influence the favored aggregation structure: for symmetric chain surfactants (F8H8, F7H7) spherical reverse micelles are present, but for asymmetric chain surfactants (F7H4, F8H4) extended cylinder aggregates form. These changes in aggregation are consistent with different surfactant packing parameters owing to the controlled variations in molecular structure. Furthermore, the general order of w/c phase transition pressures (F8H8 < F7H7 and F8H4 < F7H4) is in line with estimations of surfactant fractional free volume, as proposed by Johnston et al. (J. Phys. Chem. B 2004, 108, 1962-1966). Studies of adsorption at the poly(dimethylsiloxane)-water interface are shown to be valuable for assessing the CO2-philicity of new surfactants. All in all, the symmetric F8H8 and F7H7 analogues are seen to be the most efficient compounds from this class for applications in CO2. 相似文献