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71.
A new modification of existing intermediate capillary column tests for uncoated columns is presented. A short (1 m), thick film (2 μm) precolumn is coupled to the column to be tested. The use of a short precolumn results in a rapid test. This makes it attractive in terms of time to inject the test compounds separately, thus excluding mutual influences, in diluted solutions spiked with n-alkanes as references. Moreover, the short precolumn gives sharp Gaussian injection profiles on the second column. A simple versatile coupling device has been developed, which permits easy control and adjustment of pressures and carrier flows, monitoring of the effluents of the precolumn and introduction of sharp input bands on the second column. The monitor detector accurately shows the shape and time of introduction of the compounds on the second column. This permits the evaluation of peak distortion, peak shift and yield on the second column. Test compounds were selected on the basis of their physico-chemical properties (vapour pressure, acid-base properties, dipole moments, hydrogen bonding, complexation with metals, etc.). A number of differently pretreated capillaries were tested with these compounds under various external conditions. Accurate quantification and qualification of the activity of the capillary present difficulties. The test is a case of nearly ideal non-linear chromatography. When peaks of different sizes are superimposed, the tails lie on a common envelope. The k′ of the end of the tail is fixed, irrespective of the amount injected, and forms an important parameter in the evaluation. Reconstruction of the chromatogram with a k′ scale instead of a time scale eliminates the influence of carrier velocity and column length. The method is a sensitive tool for intermediate column testing and shows promises for surface characterization. 相似文献
72.
Fluorescence quenching of a thioxanthone derivative by methyl- and methoxy-substituted benzenes (MeB and MeOB, respectively) is performed in solvents of different polarity. Emissive exciplexes are observed even in polar solvents and provide kinetic and spectroscopic data over a large scale of solvent polarity. These data were subsequently analyzed by use of a new theoretical model that leads to a thermodynamic relationship between exciplex and electron-transfer driving forces Delta G(exc) and Delta G(et), respectively. The remarkable agreement found between this model and both kinetic and spectroscopic data supports its validity. Moreover, the difference observed between MeB and MeOB compounds in quenching efficiency is analyzed by this model and provides the main parameters governing exciplex features, especially the resonance integral between locally excited and charge-transfer states. 相似文献
73.
Catalysts consisting of dispersed Ni particles supported on silica and alumina, with sizes ranging from 6 to 20 nm, have been studied by ferromagnetic resonance. For the Ni on Al2O3 catalyst, a textural promotion effect is shown to be present and it is attributed to the possible presence of NiAl2O4. The FMR data confirm the epitaxial growth of Ni on SiO2 when Ni antigorite is reduced and show that some anisotropy is still present after sintering of the catalyst at about 1200K. 相似文献
74.
Top S Vessières A Leclercq G Quivy J Tang J Vaissermann J Huché M Jaouen G 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(21):5223-5236
A series of ferrocene derivatives based upon the structure of the antiestrogenic drug tamoxifen or of its active metabolite hydroxytamoxifen has been prepared and named by analogy ferrocifens and hydroxyferrocifens. This series includes 1-[4-(O(CH(2))(n)NMe(2))phenyl]-1-phenyl-2-ferrocenyl-but-1-ene and 1-[4-(-O(CH(2))(n)NMe(2))phenyl]-1-(4-hydroxyphenyl)-2-ferrocenyl-but-1-ene, with n=2, 3, 5 and 8, and 1-[4-(-O(CH(2))(2)NMe(2))phenyl]-1-(4-hydroxyphenyl)-2-ferrocenylethene. Most of these molecules have been synthesised by McMurry cross-coupling of the appropriate ketones, except for the ethene complexes, which were prepared by a four-step reaction sequence starting from the ferrocenylacetic acid. All these compounds were obtained as mixtures of Z and E isomers. The isomers were separated in the cases of the ferrocenyl derivatives of tamoxifen and hydroxytamoxifen (n=2). No isomerisation of the Z and E isomers occurred in DMSO after one day, while a 50:50 mixture of the isomers was obtained within one hour in chloroform. The X-ray structure of (E)-1-[4-(-O(CH(2))(2)NMe(2))phenyl]-1-(4-hydroxyphenyl)-2-ferrocenyl-but-1-ene has been determined. The relative binding affinity (RBA) values of the hydroxyferrocifens for the estrogen receptor alpha (ERalpha) was good to moderate, with values decreasing progressively with the length of the basic chain. The RBA values found for the estrogen receptor beta (ERbeta) are equal to or slightly less than those found for the alpha form. The lipophilicity of the hydroxyferrocifens are superior to the values found for estradiol and increase with lengthening of the chain. The antiproliferative effects of the four hydroxyferrocifens with n=2, 3, 5 and 8 were studied on four breast cancer cell lines (MCF7, MDA-MB231, RTx6 and TD5) possessing different levels of ERalpha. On MCF7 cells containing high levels of ERalpha, hydroxyferrocifens behave as antiestrogens. At a molarity of 1 microM the effect is close to that of hydroxytamoxifen (used for reference) when n=2 or 5, more marked when n=3, and weaker when n=8. Ferrocene alone has no effect. For the MDA-MB231 cells, classed as a hormone-independent breast cancer cell line, on the other hand, the hydroxyferrocifens show remarkable antiproliferative behaviour while the hydroxytamoxifen is completely inactive. Hydroxyferrocifens therefore show the unique property of being active both on hormone-dependent and on hormone-independent breast cancer cell lines. The molecular modelling study provides some clues for understanding of the antagonist effect of these molecules, while an additional cytotoxic effect due to the vectorised ferrocenyl unit is revealed in some occasions. 相似文献
75.
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
76.
Paul-Henri Ducrot Albert Kollmann Adil E. Bala Amel Majira Lucien Kerhoas Robert Delorme Jacques Einhorn 《Tetrahedron letters》1998,39(52):7282-9658
Two new antifungal resveratrol dimers, cyphostemmins A-B (1–2), have isolated from the roots of Cyphostemma crotalarioides planch (Vitaceae) together with resveratrol 3 and previously known reseveratrol dimers (4–7). Structures of these new compounds have been established on the basis of their MS and 1H and 13C NMR spectroscopic data. 相似文献
77.
Addition-elimination reactions from germanium heterocycles . III. 2,2-Diethyl-2-germa-1,-3-oxazolidines (R = Et; X = O; Y = NH, NMe) . The reactions of 2,2-diethyl-2-germa-1,3-oxazolidines with heterocumulenes (PhNCO, PhNCS, CS2, CO2, CH2?C?O) and carbonyl compounds (aldehydes and ketones) are studied. Generally, monoinsertion derivatives are formed by addition of one molecule of the unsaturated compound accross the Ge? N bond. This bond is always the most reactive center of the molecule. In the case of the carbonyl compounds used, diinsertion may occur in a second step by a further addition across a Ge? O bond. Generally, this latter reaction is reversible. By thermal eliminat on of (Et2GeO)n or (Et2GeS)3 the monoaddition derivatives yield the corresponding oxazolidines and thiooxazolidines. The mechanisms of these reactions are discussed. 相似文献
78.
Muriel Lepère Ghislain Blanquet Jacques Walrand Jean-Pierre Bouanich 《Journal of Molecular Spectroscopy》1996,180(2):218-226
Infrared absolute line intensities of the ν6band of CH3F have been measured around 8.5 μm using a diode-laser spectrometer. These line strengths were obtained by the equivalent width method and, for 13 lines, by fitting a Rautian profile to the measured shape of the lines. From these results, we have deduced the vibrational band strength to beS0v= 9.66 ± 0.13 cm−2atm−1at 296 K and the first Herman–Wallis factors. 相似文献
79.
80.