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41.
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Sonia Millán Griselda Sánchez Luz Alicia Fucugauchi Janos H. Fendler 《Molecular Crystals and Liquid Crystals》2013,570(2-4):153-166
A new nematic phase in lyotropic binary liquid crystalline systems consisting of sodium dodecyl sulfate-water was detected, for the first time, in the absence of additives by utilizing positron annihilation techniques. Lyotropic and thermotropic phase transitions were also investigated by the same methods. The positron annihilation parameters have also indicated a better definition of the concentration ranges at which each phase exists in the system studied. Crossed polarized light microscopy was applied to substantiate these results. 相似文献
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Humic substances (HS) and other substance of similar nature (“building blocks” of HS, such as salicylates or phthalates) influence strongly a polarographic behaviour of europium at a mercury drop electrode. An addition of these substances into the supporting electrolyte causes an enhancement of the differential pulse polarographic (DPP) peak of Eu and an anodic shift of the maximum peak potential. It was deduced from the dependence of the peak height on the pulse time and from other experimental dependencies that an adsorption of the Eu-HS (salicylate, phthalate) complexes on the working electrode is the main mechanism responsible for the peak enhancement. Because no peak distortion or splitting were observed, the DPP determination of Eu can be realised readily in the presence of HS, e.g. in environmental samples. The sensitivity of the measurements increased in the presence of HS, whereas the limit of detection (LOD) decreased (LODs were 255 and 140 nmol/l in the absence and in the presence of HS, respectively). However, the calibration dependencies were non-linear in the presence of HS. It was found that the non-linear calibration dependencies may be approximated by the Langmuir-type equation. Special procedures, such as a method of (at least) two standard additions and numerical iterative calculations, are necessary for an evaluation of measurements. 相似文献
45.
Photocyclization of 1, 1′-Polymethylene-di-2-pyridones . Benzophenone sensitized irradiation of the four dipyridones 1-4 gave the internal photocyclization products 6 (64%, Scheme 4), 7 (60%, Scheme 5), 8 (Scheme 6), and 11 (26%, Scheme 7), respectively. The decamethylene compound 5 yielded only polymeric material. The primary [2+2] photoproduct 8 from dipyridone 3 (Scheme 6) is relatively unstable. Further irradiation or heating to 65° induced a Cope rearrangement to give compound 9 which, on heating to 137°, was converted into the isomeric compound 10 . This product, as well as the other photoproducts mentioned, are rearranged back to their respective starting materials upon direct irradiation with 254 nm light or by heating to higher temperatures. The various possibilities for cycloadditions of pyridones are discussed as well as the possible factors which are responsible for the highly regioselective photoreactions of the dipyridones 1–4 . 相似文献
46.
Janos Pless 《Helvetica chimica acta》1976,59(2):499-512
Properties and suitability of the 10,11-dihydro-5 H-dibenzo[a, d]cyclohepten-5-yl group (= 5-dibenzosuberyl group) as a new protecting group for amines, amino-acids, alcohols, thiols and carboxylic acids. The 10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5-yl group (5-dibenzosuberyl group): has been found useful for protecting amines, alcohols, thiols, and carboxylic acids. Furthermore, the investigated 5-amino compounds are extremely stable in strongly acidic media (e. g. in hydrogen bromide) and still the amino group is easily cleaved under mild conditions, such as those used for N-trityl compounds (e.g. boiling in dilute acetic acid or catalytic hydrogenation). Hence this ring system could be a valuable and adaptable protecting group, especially in peptide chemistry. 相似文献
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Toshihiko Oka Hironari Kamikubo Fumio Tokunaga Janos K. Lanyi Richard Needleman Mikio Kataoka 《Photochemistry and photobiology》1997,66(6):768-773
Abstract— The single cysteine-containing bacteriorhodopsin mutants F27C, L100C, T170C, F171C and I222C were labeled with p -chloromercuribenzoic acid, which specifically reacts with sulfhydryl groups. These cysteines should be located at the cytoplasmic ends of the transmembrane helices A, C, F or G. We determined the positions of the bound mercury atoms by X-ray diffraction of purple membrane films, with better than 1 Å accuracy. The determined mercury positions were compared with the structural model from cryoelectron microscopy (N. Grigorieff, T. A. Ceska, K. H. Downing, J. M. Baldwin and R. Henderson, J. Mol. Biol 259, 393-421, 1996). Given that the distance between the mercury and the Cα atom of the cysteine in the xy plane must be shorter than 4.5 Å and that the mercury atom is located at the δ position, the positions obtained for the mercury labels agree with their expected positions from the structural model. The present results give a rationale for detecting structural changes upon illumination as shifts occur in the mercury label position. 相似文献
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Janos P 《Electrophoresis》2003,24(12-13):1982-1992
The separation of lanthanide and actinide elements belongs to one of the most challenging tasks of the separation science, due to a great similarity in their physical and chemical properties. The electrophoretic separation can be accomplished in the presence of suitable complex-forming agents, from which alpha-hydroxyisobutyric acid (HIBA) has been used most often. In the most effective capillary electrophoretic mode--capillary zone electrophoresis (CZE)--a complete separation of lanthanide ions can be accomplished within a few minutes. Various electrophoretic methods can be relatively easily adopted for the determinations of individual lanthanide elements in certain kinds of technical materials, concentrates, precursors, etc., where the high speed and low costs of analysis characteristics of capillary electrophoresis (CE) may be advantageously exploited. Electrophoretic techniques may also be employed for speciation studies, especially for examinations of the behavior of actinides in the environment. 相似文献