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271.
McKeown NB Budd PM Msayib KJ Ghanem BS Kingston HJ Tattershall CE Makhseed S Reynolds KJ Fritsch D 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(9):2610-2620
Novel types of microporous material are required for chemoselective adsorptions, separations and heterogeneous catalysis. This concept article describes recent research directed towards the synthesis of polymeric materials that possess microporosity that is intrinsic to their molecular structures. These polymers (PIMs) can exhibit analogous behaviour to that of conventional microporous materials, but, in addition, may be processed into convenient forms for use as membranes. The excellent performance of these membranes for gas separation and pervaporation illustrates the unique character of PIMs and suggests immediate technological applications. 相似文献
272.
Schäfer A Winter F Saak W Haase D Pöttgen R Müller T 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(39):10979-10984
The reactivity of aryl‐substituted stannylenes, Ar2Sn ( 4 ), towards silylarenium borates, [R3SiArH][B(C6F5)4] ( 3 ), was investigated. The reaction with 2,3,4‐trimethyl‐6‐tert‐butylphenyl (mebp)‐substituted stannylene gave silyl‐substituted stannylium ions 2 a , b , which were characterized by NMR spectroscopy supported by the results of quantum‐mechanical computations of molecular structures and magnetic properties. The tri‐iso‐propylphenyl‐substituted stannylium ions 2 c , d undergo a decomposition reaction in toluene to give the dicationic tin–arene complex [Sn(C7H8)3]2+ ( 5 ) in the form of the [B(C6F5)4] salt in high yields. The 5 [B(C6F5)4]2 salt was identified by single crystal X‐ray diffraction analysis and by Mössbauer spectroscopy. The bonding situation was investigated by using natural bond orbital (NBO) and quantum theory of atoms in molecules (QTAIM) calculations. The substitution of the weakly coordinating borate anion by the carboranate [CB11H6Br6]? results in replacement of the toluene ligands and formation of tin(II) carboranate with only weak Sn2+–anion interactions as suggested by the solid‐state structure of the isolated salt. 相似文献
273.
Herein we introduce deep UV fluorescence lifetime detection in microfluidics applied for label-free detection and identification of various aromatic analytes in chip electrophoresis. For this purpose, a frequency quadrupled Nd:YAG (neodymium-doped yttrium aluminum garnet) picosecond laser at 266 nm was incorporated into an inverse fluorescence microscope setup with time-correlated single photon counting detection. This allowed recording of photon timing with sub-nanosecond precision. Thereby fluorescence decay curves are gathered on-the-fly and average lifetimes can be determined for each substance in the electropherogram. The aromatic compounds serotonin, propranolol, 3-phenoxy-1,2-propanediol and tryptophan were electrophoretically separated using a fused-silica microchip. Average lifetimes were independently determined for each compound via bi-exponential tail fitting. Time-correlated single photon counting also allows the discrimination of background fluorescence in the time domain. This results in improved signal-to-noise-ratios as demonstrated for the above model analytes. Microchip electrophoretic separations with fluorescence lifetime detection were also performed with a protein mixture containing lysozyme, trypsinogen and chymotrypsinogen emphasizing the potential for biopolymer analysis. 相似文献
274.
Ingo H. Hardt Christian Wolf Brbel Gehrcke Detlev H. Hochmuth Bernd Pfaffenberger Heinrich Hühnerfuss Wilfried A. Knig 《Journal of separation science》1994,17(12):859-864
The enantiomers of the polychlorinated polycyclic xenobiotics heptachlor, cis- and trans-chlordane, cis- and trans-heptachlorepoxide, oxychlordane, and bromocyclen have been resolved by gas chromatography with selectively substituted cyclodextrins. The order of elution of these compounds and of α-hexachlorocyclohexane (α-HCH) was determined by comparison with enantiomerically enriched reference compounds obtained by preparative enantioselective gas chromatography. A separation of the eight stereoisomers of the pyrethroid insecticide allethrin into seven peaks was achieved. Both trans-diastereomers were separated into their enantiomers and the order of elution could be determined by comparison with commercially available (S)-bioallethrin and trans-bioallethrin. Also one cis-diastereomer was separated, wheras the other cis-isomer could not be resolved. In addition 15 out of 19 stable atropisomeric polychlorinated biphenyls with 5, 6 and 7 chlorine substituents, some chiral organophosphorus pesticides, including acephate and malaoxon and the herbicide bromoacil were separated. 相似文献
275.
Detlev W. Hoffmann Ahmed Laghribi 《Transactions of the American Mathematical Society》2004,356(10):4019-4053
We study Pfister neighbors and their characterization over fields of characteristic , where we include the case of singular forms. We give a somewhat simplified proof of a theorem of Fitzgerald which provides a criterion for when a nonsingular quadratic form is similar to a Pfister form in terms of the hyperbolicity of this form over the function field of a form which is dominated by . From this, we derive an analogue in characteristic of a result by Knebusch saying that, in characteristic , a form is a Pfister neighbor if its anisotropic part over its own function field is defined over the base field. Our result includes certain cases of singular forms, but we also give examples which show that Knebusch's result generally fails in characteristic for singular forms. As an application, we characterize certain forms of height in the sense of Knebusch whose quasi-linear parts are of small dimension. We also develop some of the basics of a theory of totally singular quadratic forms. This is used to give a new interpretation of the notion of the height of a standard splitting tower as introduced by the second author in an earlier paper.
276.
The class [S] of locally compact groups G is considered, for which the algebra L1(G) is symmetric (=Hermitian). It is shown that [S] is stable under semidirect compact extensions, i.e., H ? [S] and K compact implies K ×sH? [S]. For connected solvable Lie groups inductive conditions for symmetry are given. A construction for nonsymmetric Banach algebras is given which shows that there exists exactly one connected and simply solvable Lie group of dimension ?4 which is not in [S]. This example shows that [S]. Z the center of G, in general does not imply G ?[S]. It is shown that nevertheless for discrete groups and a (possibly) stronger form of symmetry this implication holds, implying a new and shorter proof of the fact that [S] contains all discrete nilpotent groups. 相似文献
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