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81.
Different capillary electrophoretic techniques were investigated and compared for the separation of low-molecular-mass phenolic
and neutral lignin degradation compounds. Simple capillary zone electrophoresis (CZE) was not suited for this problem. Switching
to micellar electrokinetic capillary chromatography (MEKC) by adding micelle-forming reagents to the carrier electrolyte enhanced
the separation performance considerably. Alternatively, microemulsion electrokinetic chromatography (MEEKC) was investigated.
This is a CE technique in which analytes interact with moving oil droplets present in a microemulsion buffer. Using the optimized
carrier electrolyte systems and a 60 cm×50 μm I.D. bubble cell capillary it was possible to analyse solutions of different
wood digestion procedures and to investigate differences in lignin degradation products during use of different kinds of wood
(eucalyptus, beech, scotch pine and acacia).
Received August 25, 1999. Revision April 13, 2000 相似文献
82.
Peter Nockemann Dr. Michael Pellens Kristof Van Hecke Dr. Luc Van Meervelt Prof. Dr. Johan Wouters Prof. Dr. Ben Thijs Dr. Evert Vanecht Tatjana N. Parac‐Vogt Prof. Dr. Hasan Mehdi Stijn Schaltin Jan Fransaer Prof. Dr. Stefan Zahn Barbara Kirchner Prof. Dr. Koen Binnemans Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(6):1849-1858
A series of nitrile‐functionalized ionic liquids were found to exhibit temperature‐dependent miscibility (thermomorphism) with the lower alcohols. Their coordinating abilities toward cobalt(II) ions were investigated through the dissolution process of cobalt(II) bis(trifluoromethylsulfonyl)imide and were found to depend on the donor abilities of the nitrile group. The crystal structures of the cobalt(II) solvates [Co(C1C1CNPyr)2(Tf2N)4] and [Co(C1C2CNPyr)6][Tf2N]8, which were isolated from ionic‐liquid solutions, gave an insight into the coordination chemistry of functionalized ionic liquids. Smooth layers of cobalt metal could be obtained by electrodeposition of the cobalt‐containing ionic liquids. 相似文献
83.
Tatjana M. Trtić‐Petrović Ksenija R. Kumrić Jelena S. Đorđević Goran T. Vladisavljević 《Journal of separation science》2010,33(13):2002-2009
Transport behaviour of Lu(III) across a polypropylene hollow fibre‐supported liquid membrane containing di(2‐ethylhexyl)phosphoric acid (DEHPA) in dihexyl ether as a carrier has been studied. The donor phase was LuCl3 in the buffer solution consisting of 0.2 M sodium acetate at pH 2.5–5.0. A miniaturised system with a single hollow fibre has been operated in a batch mode. The concentration of Lu(III) was determined by indirect voltammetric method using Zn–EDTA complex. The effect of pH and volume of the donor phase, DEHPA concentration in the organic (liquid membrane) phase, the time of extraction and the content of the acceptor phase on the Lu(III) extraction and stripping behaviour was investigated. The results were discussed in terms of the pertraction and removal efficiency, the memory effect and the mean flux of Lu(III). The optimal conditions for the removal of 177Lu(III) from labelled 177Lu‐radiopharmaceuticals were discussed and identified. The removal efficiency of Lu(III) greater than 99% was achieved at pH of the donor phase between 3.5 and 5.0 using DEHPA concentration in the organic phase of 0.47 M and the ratio of the donor to the acceptor phase of 182. 相似文献
84.
Ljiljana Pavlovi? Mirjana Lazi? Tatjana Aleksi? 《Discrete Applied Mathematics》2009,157(13):2938-2944
Let G be a graph and d(u) denote the degree of a vertex u in G. The zeroth-order general Randi? index 0Rα(G) of the graph G is defined as ∑u∈V(G)d(u)α, where the summation goes over all vertices of G and α is an arbitrary real number. In this paper we correct the proof of the main Theorem 3.5 of the paper by Hu et al. [Y. Hu, X. Li, Y. Shi, T. Xu, Connected (n,m)-graphs with minimum and maximum zeroth-order general Randi? index, Discrete Appl. Math. 155 (8) (2007) 1044-1054] and give a more general Theorem. We finally characterize 1 for α<0 the connected G(n,m)-graphs with maximum value 0Rα(G(n,m)), where G(n,m) is a simple connected graph with n vertices and m edges. 相似文献
85.
Victor M. Karpov Vyacheslav E. Platonov Tatjana V. Rybalova Yuri V. Gatilov Makhmut M. Shakirov 《Journal of fluorine chemistry》2006,127(7):936-942
Acetic acid-catalyzed condensation of 2-amino-3-(1-imino-2,2,2-trifluoroethyl)-1,1,4,5,6,7-hexafluoroindene (1b) with acetone and cyclopentanone gives 5,6,7,8,9,9-hexafluoro-2,2-dimethyl-4-trifluoromethyl-2,3-dihydro-1,3-diazafluorene (2a) and 5,6,7,8,9,9-hexafluoro-4-trifluoromethyl-2,3-dihydro-1,3-diazafluorene-2-spiro-1′-cyclopentane (3a) together with small amounts of 5,6,7,8,9,9-hexafluoro-2,2-dimethyl-4-trifluoromethyl-1,2-dihydro-1,3-diazafluorene (2b) and 5,6,7,8,9,9-hexafluoro-4-trifluoromethyl-1,2-dihydro-1,3-diazafluorene-2-spiro-1′-cyclopentane (3b), respectively. When acted upon by (CH3)2SO4 compounds 2, 3 were converted into corresponding fluorine-containing 1-methyl-1,2-dihydro-1,3-diazafluorenes 6, 7. 4a-Chloro-5,6,7,8,9,9-hexafluoro-2,2-dimethyl-4-trifluoromethyl-2,4a-dihydro-1,3-diazafluorene (8) has been synthesized by the interaction of compound 2 with SOCl2. Solution of compound 2 as well as 8 in CF3SO3H-CD2Cl2 generated 5,6,7,8,9,9-hexafluoro-2,2-dimethyl-4-trifluoromethyl-1,2,3,4-tetrahydro-1,3-diazafluorene-4-yl cation (2c). The structures of compounds 2, 3, 6-8 have been determined by single crystal X-ray diffraction. 相似文献
86.
Given the infinitesimal generator of a -semigroup on the Banach space which satisfies the Kreiss resolvent condition, i.e., there exists an such that for all complex with positive real part, we show that for general Banach spaces this condition does not give any information on the growth of the associated -semigroup. For Hilbert spaces the situation is less dramatic. In particular, we show that the semigroup can grow at most like . Furthermore, we show that for every there exists an infinitesimal generator satisfying the Kreiss resolvent condition, but whose semigroup grows at least like . As a consequence, we find that for with the standard Euclidian norm the estimate cannot be replaced by a lower power of or .
87.
The aerial parts of Ledum palustre L. were collected near to Pudisoo River, Harju country, Estonia, in September 2007. The simultaneous distillation and extraction micro-method (SDE) was used to isolate the essential oil from the plant's samples. The capillary gas chromatographic (GC/FID) analysis was applied to the identification of oil components and determination of their content in the oil. The yield of oil from the leaves was 0.92%, from the stems, 0.24% and from the shoots, 0.78%. A total of 68 constituents, accounting for over 95% of the total oil yield, were identified in the oils. 相似文献
88.
Capillary electrophoresis based on the principles of frontal analysis (CE-FA) was used to characterize the binding of flavonoids
to human serum albumin (HSA) at near-physiological conditions: 67 mM phosphate buffer (pH 7.4), temperature 36.5 °C. The studied
flavonoids (flavone, rutin, quercitrin) displayed moderate affinities toward the human serum albumin with binding constants
in the range 103−104 M−1. The binding of the flavonoids to the protein noticeably depended on their lipophilicity and decreased in the case of glycosylation.
The corresponding thermodynamic parameters characterized the acting forces between the HSA and flavonoids as mainly hydrophobic
forces and electrostatic interactions. Based on the results of the displacement experiments, the binding of the flavonoids
took place at site I of the HSA molecule. The results demonstrated by CE-FA were similar to those obtained by fluorescence
spectroscopy. The developed method proved to be a reliable alternative to conventional methods, providing a lot of useful
parameters for characterization of ligand–protein interactions. 相似文献
89.
It is shown, that copper(I) complexes of 17-(2-iminomethyl)pyridino steroids (17-IMPY steroids) can react with molecular oxygen followed by a regio- and stereoselective γ-hydroxylation in 12β-position. After decomplexation and hydrolysis of the IMPY group 12β-hydroxy-17-ketones are available in practical useful yields. IMPY compounds are simple to prepare by condensation of oxo compounds with (2-aminomethyl)pyridine. In the cases of 17-IMPY steroids the yields in the hydroxylation procedure of an unactivated CH2 group are higher by starting with copper(II) complexes, reduction with benzoin/triethylamine in acetone and reaction with molecular oxygen in comparison to the direct reaction of copper(I) complexes with molecular oxygen in acetone. Employing the procedure in dichloromethane as solvent starting with copper(II) complexes surprisingly the 12β-chloro compound could be isolated next to the hydroxylation product. This regio- and stereoselective γ-chlorination takes place also in acetone, when triethylammonium chloride is added to the reaction mixture. Oxygen is necessary for this reaction. The mechanistic and stereochemical aspects of these new reactions are discussed. Comparison of the different yields of steroids with different A-ring [3-methoxy-estra-1,3,5(10)-triene and 3β-hydroxy-androst-5-ene] pointed out to a subtle influence of the molecular structure far from the reaction centre on these reactions. The successful hydroxylation of the IMPY derivative of 3β-hydroxy-androst-5-ene-17-one shows the tolerance of a homoallylic system against this oxidation procedure. By Oppenauer oxidation 12β-hydroxy-androst-4-ene-3,17-dione is available. The hydroxylation procedure opens a short way to 12β-hydroxy-17-oxo steroids, which are difficult to obtain by other routes. 相似文献
90.
Continuous-flow and static dialysis coupled on-line to liquid chromatography was evaluated and an automated method for determination of ciprofloxacin in biological samples developed. A trace enrichment column packed with C18 material and coupled with a continuous dialysis and reversed-phase HPLC system with fluorescence detection enabled determination of ciprofloxacin in human blood serum at the 0.1-nmol/l level. The amount of analyte preconcentrated and loaded on the HPLC system was linearly proportional to the concentration in the dialysed sample over more than 4 orders of magnitude (up to 1 x 10(-6) M). Data for linearity, repeatability and detectability for each particular set-up are given. The trace enrichment step eliminates band broadening caused by solvents different from those of the eluent and affecting retention of ciprofloxacin on the analytical column (increase in k') due to the on-column change of eluent composition. In analysis of human serum samples phthalates leached from plastic materials may interfere due to coelution with the analyte. 相似文献