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131.
Wilkie GD Elliott GI Blagg BS Wolkenberg SE Soenen DR Miller MM Pollack S Boger DL 《Journal of the American Chemical Society》2002,124(38):11292-11294
The scope of intramolecular Diels-Alder and a novel tandem Diels-Alder/1,3-dipolar cycloaddition cascade of 1,3,4-oxadiazoles is disclosed. In the cases examined, the tandem cycloadditions construct three new rings with formation of four new C-C bonds and set all six stereocenters about a central six-membered ring in a single step including three contiguous and four total quaternary centers without a trace of a second diastereomer. 相似文献
132.
Laura Marcu Javier A. Jo Pramod V. Butte William H. Yong Brian K. Pikul Keith L. Black Reid C. Thompson 《Photochemistry and photobiology》2004,80(1):98-103
Fluorescence spectroscopy of the endogenous emission of brain tumors has been researched as a potentially important method for the intraoperative localization of brain tumor margins. We investigated the use of time‐resolved, laser‐induced fluorescence spectroscopy for demarcation of primary brain tumors by studying the time‐resolved spectra of gliomas. The fluorescence of human brain samples (glioblastoma multiforme, cortex and white matter: six patients, 23 sites) was induced ex vivo with a pulsed nitrogen laser (337 nm, 3 ns). The time‐resolved spectra were detected in a 360–550 nm wavelength range using a fast digitizer and gated detection. Parameters derived from both the spectral‐ (intensities from narrow spectral bands) and the time domain (average lifetime) measured at 390 and 460 nm were used for tissue characterization. We determined that high‐grade gliomas are characterized by fluorescence lifetimes that varied with the emission wavelength (>3 ns at 390 nm, <1 ns at 460 nm) and their emission is overall longer than that of normal brain tissue. Our study demonstrates that the use of fluorescence lifetime not only improves the specificity of fluorescence measurements but also allows a more robust evaluation of data collected from brain tissue. Combined information from both the spectraland the time domain can enhance the ability of fluorescencebased techniques to diagnose and detect brain tumor margins intraoperatively. 相似文献
133.
An alternative substrate is described for enzyme immunosaasay with electrochemical detection. Alkaline phosphatase (EC.3.1.3.1) activity is determined by using p-aminophenyl phosphate as the enzyme substrate. Enzyme-generated p-aminophenol is detected amperometrically at a glassy carbon electrody by liquid chromatography with electrochemical detection. The oxidation potential obtained for the detectionof p-aminophenol is lower than that for phenol, the previously used substrate product. The detection limit for p-aminophenol is 0.20pmol. A detection limit of 30 pg ml-1 for digoxin and a 5-min incubationtime for the enzyme reaction were obtained with the new system. 相似文献
134.
The phosphorus ylids Ph3PCHR (R = Me, Et, Prn, Pri, Bun, Cl, and OMe), and the ylids Ph3AsCH2, Me2SCH2, and Me2S(O)CH2 react with [Ni(η5-C5H5)Br(PPh3)] at room temperature to give the complexes [Ni(Ph3PCHR)(η5-C5H5(PPh3)] Br, [Ni(Ph3AsCH2)(η5-C5H5)(PPh3)]Br, [Ni(Me2SCH2)(η5-C5H5)(PPh3)]Br and [Ni{Me2S(O)CH2} (η5-C5H5)(PPh3)]Br, respectively. These are readily converted into the corresponding hexafluorophosphate salts on reaction with ammonium hexafluorophosphate. Under more forcing conditions the stabilised ylid Ph3PCHCOPh gives a product believed to be the complex [Ni(Ph3PCHCOPh)2(η5-C5H5)]Br, isolated and characterised as its PF6? salt. 相似文献
135.
This paper presents the synthesis and characterization of pyridine-substituted artificial oligopeptides with an aminoethylglycine backbone of varying length, which are designed to act as scaffolds for the self-assembly of multimetallic structures. The identities and purities of the oligopeptides are confirmed with mass spectrometry, (1)H NMR, HPLC, and pH titrations. The acid dissociation constants for the oligopeptides were determined and were found to decrease with increasing pyridine units. Titrations of the oligopeptides with Cu(II) and Pt(II) complexes containing the tridentate ligands 2,2':6',2'-terpyridine and pyridine 2,6-dicarboxylic acid were monitored using UV-visible absorption spectroscopy and showed stoichiometric binding based on the number of pyridines on the peptide strand. Metal titrations performed using an analogous oligopeptide with methyl substituents (in place of the pyridine ligands) showed very weak or no binding. In the case of the oligopeptides containing bound Pt(terpyridine)(2+) complexes, cyclic voltammetry reveals two sequential one-electron reductions at formal potentials that do not vary as a function of oligopeptide length. The measured diffusion coefficients were measured with chronoamperometry and were found to decrease with increasing oliopeptide length. 相似文献
136.
Jason C. White Zakia D. Parrish Martin P.N. Gent Brian D. Eitzer 《Microchemical Journal》2005,81(1):148-155
Ten plant species previously shown to accumulate inorganic elements effectively from natural solids were grown under field conditions in p,p′-dichlorodiphenyldichloroethane (p,p′-DDE) contaminated soil. The plant species, which included rye, mustard, canola, vetch, pigeonpea, clover, peanut, and 3 cultivars of white lupin, represented both monocots and dicots, as well as two major families within the dicots: the Brassicaceae and the Fabaceae. The plants varied widely in their ability to phytoextract and translocate weathered p,p′-DDE. The percentage of contaminant phytoextracted ranged from 0.06% (white lupin) to 0.22% (clover, vetch), and the translocation factors (TF; contaminant concentration ratio of stems to roots) ranged from 0.04 (clover, white lupin) to 0.37 (canola). An inverse relationship exists between the amount of contaminant in the roots as measured by the root BCF (bioconcentration factor; dry weight contaminant concentration ratio of root to soil) and the TF. Duplicate mounds of each species were periodically amended with nitrogen (N), phosphorus (P), nitrogen and phosphorus together (N/P); a minus phosphorus treatment involved the addition of AlSO4 to the soil prior to planting. The effect of nutrient regime on plant biomass, p,p′-DDE uptake and translocation, and inorganic element content varied greatly among the 10 plant species. For some species (rye, vetch, pigeonpea, clover, white lupin), reductions or non-significant changes in p,p′-DDE uptake were observed under the nutrient treatments and were not correlated with plant biomass effects. For mustard, canola, and peanut, the percentage of p,p′-DDE phytoextracted in the various treatments was more than doubled and was directly correlated with a two-fold increase in total plant biomass. Although it is generally assumed that fertilizer amendments will enhance the phytoremediation of organic and inorganic pollutants, the data here suggest that such effects are highly species specific and in some cases may actually decrease remediation potential. 相似文献
137.
Several varieties of blue ballpoint pen inks were analyzed by high performance liquid chromatography (HPLC) and infrared spectroscopy (IR). The chromatographic data extracted at four wavelengths (254, 279, 370 and 400 nm) was analyzed individually and at a combination of these wavelengths by the soft independent modeling of class analogies (SIMCA) technique using principal components analysis (PCA) to estimate the separation between the pen samples. Linear discriminant analysis (LDA) measured the probability with which an observation could be assigned to a pen class. The best resolution was obtained by HPLC using data from all four wavelengths together, differentiating 96.4% pen pairs successfully using PCA and 97.9% pen samples by LDA. PCA separated 60.7% of the pen pairs and LDA provided a correct classification of 62.5% of the pens analyzed by IR. The results of this study indicate that HPLC coupled with chemometrics provided a better discrimination of ballpoint pen inks compared to IR. The need to develop a suitable IR method for analysing blue ballpoint pen inks has been emphasized and it is hoped that the development of such a method would indeed provide a valuable tool for the non-destructive analysis of blue ballpoint pen ink samples for forensic purposes. 相似文献
138.
D. J. Newman
M. M. Curtis
《Journal of Physics and Chemistry of Solids》1969,30(12):2731-2737Crystal field parameters have been calculated, using ab initio LCAO-MO theory, for the ion pair Pr3+—F− at five metal ligand distances appropriate to Pr3+:LaF3. The parameters are found to be twice as large as in PrCl3, but with only half the distance dependence. In the absence of precise Pr3+:LaF3 experimental parameters only qualitative agreement with experiment can be recorded. However, very good numerical agreement is obtained with the experimental covalency parameters for Yb3+:CaF2, which provides a check on the methods adopted for calculating energy denominators. 相似文献
139.
R. Casalbuoni S. De Curtis D. Dominici P. Chiappetta A. Deandrea R. Gatto 《Zeitschrift fur Physik C Particles and Fields》1995,67(2):327-336
Decays and branching ratios of light neutralino production in $Z_R^0 \to \tilde \chi _i^0 \tilde \chi _j^0 $ in the left-right super-symmetric model are considered. We study in detail the signatures of one and two sided events in $Z_R^0 \to \tilde \chi _1^0 \tilde \chi _2^0 $ and $Z_R^0 \to \tilde \chi _2^0 \tilde \chi _2^0 $ respectively, and their dependence on the parameters of the light neutralino mixing matrix. 相似文献
140.
Mark Curtis Wilson 《Proceedings of the American Mathematical Society》1996,124(2):383-387
We show that a primeness criterion for enveloping algebras of Lie superalgebras discovered by Bell is applicable to the Cartan type Lie superalgebras , even. Other algebras are considered but there are no definitive answers in these cases.