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441.
The analysis of ethyl glucuronide (EtG), a marker of recent alcohol consumption, in serum with an optimized CZE assay is reported. The method uses a 0.1-mm id fused-silica capillary of 50 cm effective length that is coated with linear polyacrylamide, a pH 4.4 nicotinic acid/epsilon-aminocaproic acid (EACA) BGE, reversed polarity and indirect analyte detection. The assay is based on a 1:1 dilution of serum with deionized water and has LODs for EtG, lactate and acetate of 3.8 x 10(-7) M, 2.60 x 10(-6 )M and 2.18 x 10(-6 )M, respectively. Separation of EtG from endogenous macro- and microcomponents (anionic serum components of high and low concentration, respectively) and its quantification are shown to be possible for a wide range of lactate (stacker) and acetate (destacker) concentrations, macrocomponents that have an impact on the CZE behavior of EtG and that change after intake of ethanol. The assay has been successfully applied to the analysis of EtG, lactate and acetate in (i) sera of volunteers that ingested known amounts of alcohol and (ii) samples of patients that were classified (teetotalers and social drinkers vs. alcohol abusers) via analysis of carbohydrate-deficient transferrin. 相似文献
442.
Budny A Novak F Plumeré N Schetter B Speiser B Straub D Mayer HA Reginek M 《Langmuir : the ACS journal of surfaces and colloids》2006,22(25):10605-10611
Nonporous spherical silica nanoparticles resulting from a controlled St?ber process are covalently surface modified with redox-active molecules. Ferrocene, a ruthenium(II) complex with an N2P2Cl2 ligand set, and a sterically hindered biphenylamine are used as modifiers. The resulting materials are characterized by physical, spectroscopic, electrochemical, and chemical methods. The cyclic voltammetric behavior is studied in detail and reveals effects of charge transport by electron hopping along the surface of particles adsorbed on a Pt electrode. The ruthenium(II) complex remains catalytically active with respect to hydrogenation upon immobilization on the particles. Thus, the respective material provides a heterogenized homogeneous hydrogenation catalyst on a solid support. 相似文献
443.
A method for isotachophoretic determination of sweeteners of different character in candies and chewing gums was developed. A capillary of 0.8 mm ID and 90 mm effective length made of fluorinated ethylene-propylene copolymer is filled with an electrolyte system consisting of 10 mM HCl + 14 mM Tris, pH 7.7 (leading electrolyte) and 5 mM L-histidine + 5 mM Tris, pH 8.3 (terminating electrolyte). The analysis is performed at a driving current of 200 microA and for detection current is decreased to 100 microA. Boric acid is added to the aqueous sample solution to form borate complexes with substances of polyhydroxyl nature and make them migrate isotachophoretically. Using conductivity detection, the calibration curves in the tested concentration range up to 2.5 mM were linear for all components of interest: acesulfame K, saccharine, aspartame, cyclamate, sorbitol, mannitol, lactitol, and xylitol. The concentration detection limits ranged between 0.024 and 0.081 mM. Good precision of the ITP method is evidenced by favorable RSD values ranging from 0.8 to 2.8% obtained at the analyte concentration of 1.0 mM (n = 6). The analysis time was about 20 min. Simplicity, accuracy, and low cost of analyses make ITP an alternative procedure to methods used so far for the determination of ionizable sweeteners. 相似文献
444.
Martín-Matute B Edin M Bäckvall JE 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(23):6053-6061
Highly efficient synthesis of enantiopure diacetates of 2,4-pentanediol and 2,5-hexanediol starting from commercially available mixtures of the diols (dl/meso approximately 1:1) has been realized by combining a fast ruthenium-catalyzed epimerization with an enzymatic transesterification. The in situ coupling of these two processes produces the diacetates in high yield in >99 % enantiomeric excess. 相似文献
445.
Jochmann MA Blessing M Haderlein SB Schmidt TC 《Rapid communications in mass spectrometry : RCM》2006,20(24):3639-3648
Compound-specific isotope analysis (CSIA) has been established as a useful tool in the field of environmental science, in particular in the assessment of contaminated sites. What limits the use of gas chromatography/isotope ratio mass spectrometry (GC/IRMS) is the low sensitivity of the method compared with GC/MS analysis; however, the development of suitable extraction and enrichment techniques for important groundwater contaminants will extend the fields of application for GC/IRMS. So far, purge and trap (P&T) is the most effective, known preconcentration technique for on-line CSIA with the lowest reported method detection limits (MDLs in the low microg/L range). With the goal of improving the sensitivity of a fully automated GC/IRMS analysis method, a commercially available P&T system was modified. The method was evaluated for ten monoaromatic compounds (benzene, toluene, para-xylene, ethylbenzene, propylbenzene, isopropylbenzene, 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, fluorobenzene) and ten halogenated volatile organic compounds (VOCs) (dichloromethane, cis-1,2-dichloroethene, trans-1,2-dichloroethene, carbon tetrachloride, chloroform, 1,2-dichloroethane, trichloroethene, tetrachlorethene, 1,2-dibromoethane, bromoform). The influence of method parameters, including purge gas flow rates and purge times, on delta13C values of target compounds was evaluated. The P&T method showed good reproducibility, high linearity and small isotopic fractionation. MDLs were determined by consecutive calculation of the delta13C mean values. The last concentration for which the delta13C value was within this iterative interval and for which the standard deviation was lower than +/-0.5 per thousand for triplicate measurements was defined as the MDL. MDLs for monoaromatic compounds between 0.07 and 0.35 microg/L are the lowest values reported so far for continuous-flow isotope ratio measurements using an automated system. MDLs for halogenated hydrocarbons were between 0.76 and 27 microg/L. The environmental applicability of the P&T-GC/IRMS method in the low-microg/L range was demonstrated in a case study on groundwater samples from a former military air field contaminated with VOCs. 相似文献
446.
Jens Hartung Irina Kempter Thomas Gottwald Michaela Schwarz Rainer Kneuer 《Tetrahedron: Asymmetry》2009,20(18):2097-2104
Esterification of cyclic thiohydroxamic acids, for example, N-hydroxypyridine-2(1H)-thione, N-hydroxy-4-methylthiazole-2(3H)-thione, and N-hydroxy-4-(p-chlorophenyl)-thiazole-2(3H)-thione, occurred with inversion of configuration at the attacked stereocenter, as evident from the use of chiral alcohols, alkyl p-toluene sulfonates, and cyclic sulfates. Stereochemical analysis of enantiomerically pure O-alkyl thiohydroxamates was performed on the basis of CD-spectroscopy and chemical derivatization. The assignment of the relative configuration in cyclic O-esters was feasible via NMR spectroscopy, whereas chiral aliphatic glycolato monoesters required hydroxyl group derivatization with chloro-(4R,5R)-bis[(1R,2S,5R)-menth-1-yloxycarbonyl)]-1,3,2-dioxaphospholane for this purpose. 相似文献
447.
448.
Raymond Behrendt Christian Renner Michaela Schenk Fengqi Wang Josef Wachtveitl Dieter Oesterhelt Luis Moroder 《Angewandte Chemie (International ed. in English)》1999,38(18):2771-2774
The cis ⇌ trans photoisomerization of the azobenzene building block 4-(4-aminophenylazo)benzoic acid incorporated in a cyclic peptide (see scheme) facilitated a two-state transition of the peptide chain from a rigid constrained conformation in the trans isomer into the largely free conformational space of the cis isomer. 相似文献
449.
450.
Dominika Valachová Michaela Marčeková Dr. Oľga Caletková Dr. Andrej Kolarovič Dr. Pavol Jakubec 《European journal of organic chemistry》2023,26(13):e202201341
Protodenitration, a direct reduction of nitroalkanes to corresponding alkanes, already spans two centuries and is enabled by various reagents. This mini-review provides a historical development of the fundamental transformation and highlights the governing position of the Ono-Tanner reaction employing tributyltin hydride. Due to the unchallenged dominance of the toxic tributyltin hydride and environmentally unpopular solvents sharply contrasting with modern ecological trends, the current situation was dubbed “the last fortress of tin's tyranny.” 相似文献