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491.
W. M. Jarman Glenn W. Johnson Corinne E. Bacon Jay A. Davis Robert W. Risebrough Robert Ramer 《Analytical and bioanalytical chemistry》1997,359(3):254-260
Levels of polychlorinated biphenyls (PCBs) were measured in water (particulate and dissolved fractions) from various locations in the San Francisco Estuary over the years 1993–1995 during six cruises. Geometric mean levels of ΣPCBs (sum of 58 congeners) in the combined dissolved and particulate fractions for the six cruises ranged from 340?ng/L to 1600?ng/L. Comparing this data to previous data from 1975 and 1980 does not reveal any significant temporal trends. The partitioning of PCBs into the dissolved/particulate fraction were correlated with total suspended solids. Using the novel chemometric technique of polytopic vector analysis (PVA) on the data from cruise 8 (April 1995), five separate PCB congener fingerprints were identified in the data. Fingerprint 1 (or end-member 1) represents a slightly degraded source of Aroclor® 1260 in the northern part of the South Bay; the end-member (EM) 2 fingerprint is related to a predominantly Aroclor® 1260 source that has been moderately-severely degraded present in the highest proportions in the Pacific Ocean sample; EM-3 is interpreted as a slightly degraded Aroclor® 1242:1254:1260 mixture in southern San Pablo Bay; end-member 4 is interpreted as a moderately degraded source of multiple Aroclors® and is present in the river samples; EM-5 is interpreted as a slightly degraded Aroclor® 1254/1260 mixture present in northern San Pablo Bay and the South Bay. 相似文献
492.
493.
The synthesis of a new linear benzo[3]phenylene-[60]fullerene dyad 1 is achieved over 10 steps in 15% overall yield by using an efficient sequence combining a double cobalt(I)-mediated cyclotrimerization with a Bingel reaction. 相似文献
494.
Corinne Chaimbault Jean Michel Leger Jean‐Jacques Bosc Christian Jarry 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(1):e29-e30
The condensation reaction of 2‐amino‐5‐tert‐butyloxymethyl‐2‐oxazoline with ethyl cyano(ethoxymethylene)acetate led to the title cycloadduct. The structure indicates a delocalization in the pyrimidine ring. 相似文献
495.
Valérie Sauvinet Laure Gabert Du Qin Corinne Louche‐Pélissier Martine Laville Michel Désage 《Rapid communications in mass spectrometry : RCM》2009,23(23):3855-3867
A reference method to accurately define kinetics in response to the ingestion of glucose in terms of total, exogenous and endogenous glucose is to use stable‐isotope‐labelled compounds such as 2H and 13C glucose followed by gas chromatography/mass spectrometry (GC/MS) and gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) analysis. The use of the usual pentaacetyl (5Ac) derivative generates difficulties in obtaining accurate and reproducible results due to the two chromatographic peaks for the syn and anti isomers, and to the isotopic effect occurring during acetylation. Therefore, the pentaacetylaldononitrile derivative (Aldo) was validated for both isotopes, and compared with the 5Ac derivative. A correction factor including carbon atom dilution (stoichiometric equation) and the kinetic isotopic effect (KIE) was determined. Analytical validation results for the 2H GC/MS and 13C GC/C/IRMS measurements produced acceptable results with both derivatives. When 2H enrichments of plasma samples were ≤1 mol % excess (MPE), the repeatability (RSDAldo Intra assay and Intra day <0.94%, RSD5Ac Intra assay and Intra day <3.29%), accuracy (Aldo <3.4%, 5Ac <29.0%), and stability of the derivatized samples were significantly better when the Aldo derivatives of the plasma samples were used (p < 0.05). When the glucose kinetics were assessed in nine human subjects, after glucose ingestion, the plasma glucose 2H enrichments were identical with both derivatives, whereas the 13C enrichments needed a correction factor to fit together. Due to KIE variation, this correction factor was not constant and had to be calculated for each batch of analyses, to obtain satisfactory results. Mean quantities of exogenous glucose exhibit marked difference (20.9 ± 1.3g (5Ac) vs. 26.7 ± 2.5g (Aldo)) when calculated with stoichiometric correction, but fit perfectly when calculated after application of the correction factor (22.1 ± 1.3g (5Ac) vs. 22.9 ± 1.9g (Aldo)). Finally, the pentaacetylaldononitrile derivative, used here in GC/C/IRMS for the first time, enables measurement of 2H and 13C enrichments in plasma glucose with a single sample preparation. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
496.
497.
Tevian Dray Jason Janesky Corinne A. Manogue 《Advances in Applied Clifford Algebras》2000,10(2):193-216
We extend previous work on the eigenvalue problem for Hermitian octonionic matrices by discussing the case where the eigenvalues
are not real, giving a complete treatment of the 2 × 2 case, and summarizing some preliminary results for the 3 × 3 case. 相似文献
498.
Moonen NN Pomerantz WC Gist R Boudon C Gisselbrecht JP Kawai T Kishioka A Gross M Irie M Diederich F 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(11):3325-3341
An extensive series of silyl-protected cyanoethynylethenes (CEEs) and N,N-dimethylanilino donor-substituted CEEs have been synthesized. More extended chromophores were constructed by selective silyl deprotection and subsequent oxidative acetylenic coupling. The strong electron-accepting nature of the CEEs was revealed by a combination of 13C NMR spectroscopic and electrochemistry measurements. Donor-substituted CEEs display strong intramolecular charge-transfer (CT) character, resulting in intense, bathochromically shifted CT bands in the UV/Vis spectrum. Their structural diversity establishes them as suitable models for the study of pi-conjugation and band gap tuning in strong charge-transfer chromophores. The extent of pi-conjugation in the donor-substituted CEEs was investigated by a combination of ground-state techniques, such as X-ray crystallography, electrochemistry, B3 LYP calculations, and NMR spectroscopy. The comparison of these ground-state results with the features observed in the UV/Vis spectra reveals that-contrary to expectations-more extensive pi-conjugation can lead to larger band gaps in molecules with strong donor and acceptor moieties. 相似文献
499.
Noël R Vanucci-Bacqué C Fargeau-Bellassoued MC Lhommet G 《The Journal of organic chemistry》2005,70(22):9044-9047
[reaction: see text] The preparation of new chiral 6-carbonyl 2,3,8,8a-tetrahydro-7H-oxazolo[3,2-a]pyridines by an efficient two-step procedure is described. 相似文献
500.