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991.
Synthesis and rearrangement of bicyclo(4.3.0) - 2β - hydroxy - 2α - vinyl - 1β - methyl - 8 - oxo - Δ6 - nonene was observed to yield a transannular reaction product tricycio - (6.3.0.01,8) - 2 - methyl - 8α - hydroxy - 4 - oxo - Δ2 - undecene 16. Spectral evidence supports the assigned structure. 相似文献
992.
J. P. Kennedy S. C. Feinberg S. Y. Huang 《Journal of polymer science. Part A, Polymer chemistry》1978,16(1):243-259
Block copolymers of isobutylene and styrene, PIB-b-PSt and PSt-b-PIB, have been prepared by a two-step synthesis involving (1) preparation of terminally chlorinated (telechelic) polyisobutylene or polystyrene “prepolymers” by using the H2O/BCl3 initiator system and (2) blocking from these telechelic prepolymers a second polymer segment by using an alkyaluminum, e.g., Et2AlCl coinitiator. The telechelic polyisobutylene and polystyrene contain tertiary and benzylic chlorine termini, respectively. Block copolymer characterization included detailed selective solvent extraction procedures, coupled with GPC determinations, PMR, solubility, and intrinsic viscosity studies. The synthesis of PIB-b-PSt and PSt-b-PIB provides direct chemical evidence for the presence and position of active chlorine termini in BCl3-coinitiated olefin polymerizations. 相似文献
993.
S. C. Sheu M. L. Lee H. L. Hwang H. Y. Lin M. H. Yang 《Fresenius' Journal of Analytical Chemistry》1989,334(2):143-147
Summary CuInS2 is one of the important I–III–VI2 ternary compounds which has in recent years received increasing interest in semiconductor science. In this study an electrochemical method has been developed based on a limited amount of available sample (0.5–10mg) for the precise and accurate determination of CuInS2 composition. After decomposition of the sample in concentrated HNO3 under pressure, copper and indium were sequentially determined by constant potential coulometry, and sulfur (as sulfate) by amperometric titration. Various experimental parameters which ensure high precision and accuracy of the results were carefully evaluated and calibrated. The overall errors for the determination of copper, indium and sulfur in a 10 mg sample were found to be +0.10%, –0.12% and +0.16%, respectively, which fullfills the requirement for accurate stoichiometric assessment.
Presented at the 10th International Symposium on Microchemical Techniques, August 25–29, 1986, Antwerp, Belgium 相似文献
Reproduzierbare und genaue Bestimmung der Stöchiometrie von CuInS2-Halbleitermaterial mit Hilfe elektrochemischer Verfahren
Presented at the 10th International Symposium on Microchemical Techniques, August 25–29, 1986, Antwerp, Belgium 相似文献
994.
X. Y. Li G. J. Wang J. G. Sun Y. T. Zheng B. Yan H. T. Xie X. Wang 《Chromatographia》2007,65(1-2):13-18
To support preclinical pharmacokinetic investigation of 1-[4-[2-(4-bromobenzene-sulfonaminoethyl)phenylsufonyl]-3-(trans-4-methylcyclohexyl)urea
(G004), a rapid, sensitive and specific high-performance liquid chromatography–electrospray ionization mass spectrometry (LC–ESI-MS)
method was developed and validated. Glibenclamide was employed as internal standard. After liquid–liquid extraction the analyte
was analyzed on a Kromasil C18 column (150 × 2.0 mm i.d.) with a mobile phase consisted of acetonitrile–water (0.05% acetic acid), 30:70 (v/v). The flow
rate was 0.2 mL min−1. Detection was performed on a quadrupole mass spectrometer using an electrospray ionization interface and the selected-ion
monitoring (SIM) mode. The retention time was about 3.5 and 4.2 min for Glibenclamide and G004, respectively. The assay was
linear over the concentration range of 2.0–500.0 ng mL−1. Extraction Recovery of G004 in rat plasma was more than 87%. The intra- and inter-assay precision was lower than 11.5% (CV).
This validated method was successfully applied to the pharmacokinetics of G004 in rats. 相似文献
995.
K. H. Kim J. H. Lee M. Y. Ko K. S. Shin J. S. Kang W. C. Mar J. R. Youm 《Chromatographia》2002,55(1-2):81-85
Summary A method for the assay of R-(+)- and S-(−)- metoprolol in human urine has been developed using gas chromatography-mass spectrometry.
The method involved purification by liquid-liquid extraction and derivatization with N-methyl-N-(trimethylsilyl)trifluoroacetamide
to form an O-silyl ether, followed by subsequent chiral derivatization with (−)-α-methoxy-α-(trifluoromethyl)phenylacetyl
chloride to form diastereomeric amide. The reaction was rapid and the diastereomeric derivatives were well resolved. Quantitation
was performed by selected-ion monitoring of fragment ions of the diastereomers in electron impact ionization mode. No racemization
was found during the reaction. The detection limit was 0.5 ng·mL−1. The intra-day variation ranged between 0.38 and 7.86% in relation to the measured concentration and inter-day variation
was 2.26–8.06%. The method has been applied to the determination of R-(+)-and S-(−)- metoprolol in human urine from healthy
volunteers dosed with racemic metoprolol tartrate. 相似文献
996.
J AliaMatysik C Soede-Huijbregts M Baldus J Raap J Lugtenburg P Gast H J van Gorkom A J Hoff H J de Groot 《Journal of the American Chemical Society》2001,123(20):4803-4809
Low-temperature 15N and 13C CP/MAS (cross-polarization/magic angle spinning) NMR has been used to analyze BChl-histidine interactions and the electronic structure of histidine residues in the light-harvesting complex II (LH2) of Rhodopseudomonas acidophila. The histidines were selectively labeled at both or one of the two nitrogen sites of the imidazole ring. The resonances of histidine nitrogens that are interacting with B850 BChl a have been assigned. Specific 15N labeling confirmed that it is the tau-nitrogen of histidines which is ligated to Mg2+ of B850 BChl molecules (beta-His30, alpha-His31). The pi-nitrogens of these Mg2+-bound histidines were found to be protonated and may be involved in hydrogen bond interactions. Comparison of the 2-D MAS NMR homonuclear (13C-13C) dipolar correlation spectrum of [13C6,15N3]-histidines in the LH2 complex with model systems in the solid state reveals two different classes of electronic structures from the histidines in the LH2. In terms of the 13C isotropic shifts, one corresponds to the neutral form of histidine and the other resembles a positively charged histidine species. 15N-13C double-CP/MAS NMR data provide evidence that the electronic structure of the histidines in the neutral BChl a/His complexes resembles the positive charge character form. While the Mg...15N isotropic shift confirms a partial positive charge transfer, its anisotropy is essentially of the lone pair type. This provides evidence that the hybridization structure corresponding to the neutral form of the imidazole is capable of "buffering" a significant amount of positive charge. 相似文献
997.
A sensitive and rapid method is presented for the determination of vanadium at ng to sub-ng ml(-1) levels in natural waters, in which in-line preconcentration/separation is directly coupled with catalytic detection of vanadium in a flow-injection system. Vanadium was adsorbed on a small column packed with Sephadex G-25 gel and desorbed with a small volume of 0.010 M HCl. The catalytic action of vanadium on the oxidation of chromotropic acid (1,8-dihydroxy-3,6-naphthalenedisulphonic acid) by bromate in pH 3.8 buffered media was used in the sensitive determination of vanadium. Effective preconcentration/separation of trace vanadium can be achieved from Fe(III), Cu(II) and a large excess of sodium chloride in seawater sample. A linear calibration using a 5 m sample loop was obtained for vanadium in the range 0-2.5 ng ml(-1). The limit of detection was 0.02 ng ml(-1) and the relative standard deviation was 1.2% for 1.0 ng ml(-1) vanadium (n=5). The present FIA system is rapid and sensitive and can be readily applied to river water and coastal seawater samples. 相似文献
998.
An absorption intracavity laser spectrometer with two types of sample vaporization systems (graphite furnace electrothermal atomizer or laser sampler) is described that can be used for the determination of trace amounts of metals (Al, Cr, Fe and Mn) in liquid samples and at the surface of solid targets. The limits of detection for the elements tested are lower than those obtained by modern conventional spectrometers. The examined technique provides a wide dynamic range of linear standard calibration curves. 相似文献
999.
1000.
C. G. Overberger Y. Kawakami 《Journal of polymer science. Part A, Polymer chemistry》1978,16(6):1237-1248
The water-soluble monomers, 1-methyl-4-vinylimidazole, 1-methyl-5-vinylimidazole, 1-ethyl-5-vinylimidazole, and 1-propyl-5-vinylimidazole have been synthesized, polymerized, and copolymerized with 4(5)-vinylimidazole. The copolymers were characterized by 14C-labeling, NMR, pKa determination and viscosity measurements. The monomer reactivity ratios determined by 14C counting are r1 = 1.04; r2 = 0.94 [M1 = 4(5)-vinylimidazole, M2 = 1-methyl-4-vinylimidazole] and r1 = 1.01; r2 = 0.86 [M1 = 4(5)-vinylimidazole, M2 = 1-methyl-5-vinylimidazole]. The esterolytic activity of the copolymers for the hydrolysis of p-nitrophenyl acetate (PNPA) at pH 7–8 in 28.5% ethanol–water was higher than that of the mixtures of homopolymers. At pH 5–6 the esterolytic activities of the copolymers and the mixtures were similar. The most efficient esterolytic activity for PNPA hydrolysis at pH 7.11 in 28.5% ethanol–water occurred for copolymers containing 75 mole % 4(5)-vinylimidazole and for copolymers containing 1-methyl-4-vinylimidazole rather than 1-methyl-5-vinylimidazole. 相似文献