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71.
Ning H Kita R Kriegs H Luettmer-Strathmann J Wiegand S 《The journal of physical chemistry. B》2006,110(22):10746-10756
We studied the thermal diffusion behavior of hexaethylene glycol monododecyl ether (C12E6) in water by means of thermal diffusion forced Rayleigh scattering (TDFRS) and determined Soret coefficients, thermal diffusion coefficients, and diffusion constants at different temperatures and concentrations. At low surfactant concentrations, the measured Soret coefficient is positive, which implies that surfactant micelles move toward the cold region in a temperature gradient. For C12E6/water at a high surfactant concentration of w1 = 90 wt % and a temperature of T = 25 degrees C, however, a negative Soret coefficient S(T) was observed. Because the concentration part of the TDFRS diffraction signal for binary systems is expected to consist of a single mode, we were surprised to find a second, slow mode for C12E6/water system in a certain temperature and concentration range. To clarify the origin of this second mode, we investigated also, tetraethylene glycol monohexyl ether (C6E4), tetraethylene glycol monooctyl ether (C8E4), pentaethylene glycol monododecyl ether (C12E5), and octaethylene glycol monohexadecyl ether (C16E8) and compared the results with the previous results for octaethylene glycol monodecyl ether (C10E8). Except for C6E4 and C10E8, a second slow mode was observed in all systems usually for state points close to the phase boundary. The diffusion coefficient and Soret coefficient derived from the fast mode can be identified as the typical mutual diffusion and Soret coefficients of the micellar solutions and compare well with the independently determined diffusion coefficients in a dynamic light scattering experiment. Experiments with added salt show that the slow mode is suppressed by the addition of w(NaCl) = 0.02 mol/L sodium chloride. This suggests that the slow mode is related to the small amount of absorbing ionic dye, less than 10(-5) by weight, which is added in TDFRS experiments to create a temperature grating. The origin of the slow mode of the TDFRS signal will be tentatively interpreted in terms of a ternary mixture of neutral micelles, dye-charged micelles, and water. 相似文献
72.
Eichler J 《Combinatorial chemistry & high throughput screening》2005,8(2):135-143
Synthetic peptides have a long tradition as molecular tools in biomedical research and drug discovery. The introduction of high-throughput synthesis and screening technologies for synthetic peptides, such as arrays and combinatorial libraries, enabled the large-scale and detailed exploration of protein-ligand interactions, as well as the discovery of novel biologically active peptides. This review summarizes currently available synthetic peptide array and library technologies, in particular mixture-based peptide libraries, which are illustrated by numerous applications in various fields of biomedical research. 相似文献
73.
Baldur Föhlisch Robert Flogaus Jutta Oexle Angelika Schädel 《Tetrahedron letters》1984,25(17):1773-1776
1,1-Dichloro- and 1,3-dichloro-2-alkanones react with 2-methylfuran in the presence of lithium perchlorate/triethylamine to form 2-chloro-1-methyl-8-oxabicyclo [3.2.1]oct-6-ene-3-ones predominantly. 相似文献
74.
Lintelmann J Fischer K Karg E Schröppel A 《Analytical and bioanalytical chemistry》2005,381(2):508-519
Fine and ultrafine particles are probably responsible for numerous health effects, but it is still unclear whether and to what extent the particle itself or organic compounds adsorbed or condensed on the particle are responsible for the effects observed. One important class of particle-bound substances are the polycyclic aromatic hydrocarbons (PAH) and their oxygenated derivatives. To improve the tools used for chemical characterization of particulate matter analytical methods for the determination of PAH and oxygenated PAH in aerosol samples of different origin have been developed and optimized. PAH on high-volume filters and on soot aerosols were analyzed by using accelerated solvent extraction for extraction and high-performance liquid chromatography with fluorescence detection for separation and quantification. Total PAH concentrations were in the range 0.3–9.3 ng m–3. For analysis of selected oxygenated PAH on high-volume filters a liquid chromatography–tandem mass spectrometric method was developed and optimized. Preliminary investigations showed that oxygenated PAH at pg m–3 concentrations can be determined. 相似文献
75.
Uwe Klingebiel Jutta Neemann Prof. Dr. Anton Meller 《Monatshefte für Chemie / Chemical Monthly》1977,108(5):1099-1104
The reaction of fluorosilanes with lithium salts of bulky amines like tetramethyl-piperidine and di-tert. butylamine leads to stable aminofluorosilanes of the type R-SiF2-NRR [R=F, C(CH3)3, C6H5, C6H4N(CH3)2]. Lithium salts of silylamines react analogously: R2Si(NR-SiF2R)2 (R=R= =CH3, R=C6H5). An eight membered Si–N-ring is obtained in the reaction of a disubstituted silylaminofluorosilane with the dilithium salt of a silylamine. The mass-,1H-, and19F-NMR spectra of the above mentioned compounds are reported. 相似文献
76.
Reactions of dilithio-nitroalkanes and dilithio-allynitroalkanes with carbonyl compounds Primary nitro compounds can by acylated via dilithium derivatives 5 with carbonic-acid derivatives to give α-nitro esters 6a – i and with carboxylic-acid esters and anhydrides to give α-nitroketones 6j – q . In the reaction of 1-nitro-1-buten with two mol-equiv. of butyllithium, the dilithium compound 10 is formed by successive Michael-addition and nitronate deprotonation. Dilithium derivatives 5 also react with ketones and benzaldehyde (→ 18a – g ); the nitro aldols 25 and 26 are likewise formed by addition of doubly deprotonated allylic nitro compounds. Some of the products have been further transformed by reduction or by Nef-reactions to the hydrochloride of the α-amino-acid 26 , to 2-amino-alcohols 28a and 28b , to α-hydroxyamino-acid esters 27a – c , to α-hydroxyimino esters 35 and 36 , to α-hydroxyimino ketones 31 and 33 , to the α-diketone 34 , and to the α-keto ester 37 . 相似文献
77.
Jutta Begerow Erich Jermann Türkan Keles L. Dunemann 《Fresenius' Journal of Analytical Chemistry》1999,363(4):399-403
Two types of passive samplers differing in their geometry (OVM 3500 by 3M, ORSA 5 by Dr?ger) were compared with respect to
their suitability for typical environmental indoor and outdoor VOC concentrations. Benzene, toluene, o-, m-, p-xylene, ethylbenzene,
tetrachloroethene, trichloroethene, nonane and ethyl acetate were representatively analyzed by dual-column capillary gas chromatography
with tandem ECD-FID detection. There was a good correlation between the results obtained with OVM 3500 and ORSA 5 monitors
indicating that both monitors can be used for this kind of application. The ratio between the results for indoor air sampling
with OVM 3500 and ORSA 5 monitors was between 0.89 and 1.14 showing no systematic variation. For outdoor air sampling the
ratio was between 1.06 and 1.26 indicating that the results obtained with OVM 3500 monitors were slightly higher. Reproducibility
was slightly better when using ORSA 5 monitors. But, due to the higher sampling rates which are a result of the larger cross-sectional
area, signal-to-noise ratios obtained with OVM 3500 monitors were between six to nine times higher than those of ORSA 5 samplers.
Blank values of the unexposed samplers were comparable for both sampler types. As a consequence, detection limits were by
a factor of 1.5 to 4 better for OVM 3500 monitors.
Received: 18 August 1998 / Revised: 6 October 1998 / Accepted: 15 October 1998 相似文献
78.
α-Functionalized 2-Methyl Phenylphosphines, 2-(HE? CH2)? C6H4? PH2 (E = O, NR, PH) II. Coordination Behaviour with Metal Carbonyles of Cr, Mo, W The preparation of different carbonyl substituted coordination compounds (M: Cr, Mo, W) of the phosphines 2-(HE? CH2)C6H4? PH2 (E = O, NPh, PH) is described. In one case, after deprotonation of a PH2 group a phosphine/phosphide migration of a W(CO)5 fragment is detected. 相似文献
79.
We present results of theoretical and experimental studies of the structural and electronic properties of Ta(1 1 2) and W(1 1 2) surfaces. Atomic geometries of these surfaces and their electronic structures have been obtained from the first-principles pseudo-potential calculations based on the density functional theory and the use of the plane wave basis set. In the experimental part of our studies we have performed measurements of the photofield emission spectroscopy. The calculated density-of-states distributions are compared and discussed with energy distributions of electrons extracted from photofield emission characteristics. The photofield emission spectra measured for the surface regions of considered systems present very dense structures of features, while the corresponding dependences obtained for the bulk have much more smooth shape. Experimental results correspond very well with calculated density-of-states distributions. 相似文献
80.