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51.
The CGC analysis of 25 organophosphorus and organonitrogen pesticides was optimized on two different stationary phases, namely a 5% diphenyl dimethyl silicone (SE-54 type) and a 50% diphenyl dimethyl silicone (OV-17 type) by selecting the best temperature program conditions, using computer simulation. 相似文献
52.
Izquierdo S Rúa F Sbai A Parella T Alvarez-Larena A Branchadell V Ortuño RM 《The Journal of organic chemistry》2005,70(20):7963-7971
[Chemical reaction: See text] Several derivatives of (+)- and (-)-2-aminocyclobutane-1-carboxylic acid, 1, have been prepared through enantiodivergent synthetic sequences. The stereoselective synthesis of free amino acid (+)-1 has been achieved, and this product has been fully characterized for the first time. Stereocontrolled alternative synthetic methodologies have been developed for the preparation of bis(cyclobutane) beta-dipeptides in high yields. Among them, enantio and diastereomers have been synthesized. beta,beta- and beta,delta-Dimers resulting from the coupling of a cyclobutane residue and a linear amino acid have also been prepared. The ability of the cyclobutane ring as a structure-promoting unit both in the monomers and in the dimers has been manifested. The NMR structural study and DFT theoretical calculations evidence the formation of strong intramolecular hydrogen bonds giving rise to cis-fused [4.2.0]octane structural units that confer high rigidity on these molecules both in solution and in the gas phase. The contribution of a cis-trans conformational equilibrium derived from the rotation around the carbamate N-C(O) bond has also been observed, the trans form being the major conformer. In the solid state, this equilibrium does not exist, and moreover, intermolecular hydrogen bonds are present. 相似文献
53.
Chemosensors for the marine toxin saxitoxin 总被引:1,自引:0,他引:1
Gawley RE Pinet S Cardona CM Datta PK Ren T Guida WC Nydick J Leblanc RM 《Journal of the American Chemical Society》2002,124(45):13448-13453
Eleven anthracylmethyl crown ethers have been synthesized and evaluated as fluorescence sensors for the marine toxin saxitoxin. Fluorescence enhancement data are consistent with a 1:1 binding complex for all crowns. The binding constants are in the range of 10(4) M(-)(1) in ammonium phosphate buffer (pH 7.1) in 80% ethanol solvent. Selectivity for sensing saxitoxin versus several organic analytes has been demonstrated for the first time. Possible modes of binding are presented, and relevance to saxitoxin monitoring programs are discussed. 相似文献
54.
Applications performed by capillary electrochromatography (CEC) in all its modes, namely packed column CEC (packed-CEC), open tubular CEC (OT-CEC) and pressure-assisted CEC (pseudo-CEC), and published by June 1999 are reviewed. The review is divided into (i) separation of neutral, acidic and basic analytes with the main goal of evaluating column and system performance, (ii) separation according to field of application and/or chemical class, and (iii) separation of chiral analytes. 相似文献
55.
Chambers C Smith F Williams C Marcos S Liu ZH Hayter P Ciaramella G Keighley W Gribbon P Sewing A 《Combinatorial chemistry & high throughput screening》2003,6(4):355-362
The measurement of intracellular calcium fluxes in real time is widely applied within the pharmaceutical industry to measure the activation of G-protein coupled receptors (GPCRhyp;s), either for pharmacological characterisation or to screen for new surrogate ligands. Initially restricted to G(q) coupled GPCRs, the introduction of promiscuous and chimeric G-proteins has further widened the application of these assays. The development of new calcium sensitive dyes and assays has provided sensitive, homogeneous assays which can be readily applied to high throughput screening (HTS). In this paper we describe the full automation of this assay type using a fluorometric imaging plate reader (FLIPR ) integrated into a Beckman/Sagian system to establish a simple robotic system that is well suited for the current medium throughput screening in this area of lead discovery. Using a recently completed HTS we discuss important determinants for FLIPR based screening, highlight some limitations of the current approach, and look at the requirements for future automated systems capable of keeping up with expanding compound files. 相似文献
56.
Lee KJ Mao S Sun C Gao C Blixt O Arrues S Hom LG Kaufmann GF Hoffman TZ Coyle AR Paulson J Felding-Habermann B Janda KD 《Journal of the American Chemical Society》2002,124(42):12439-12446
Overexpression of the cell-surface glycosphingolipid G(M3) is associated with a number of different cancers, including those of the skin, colon, breast, and lung. Antibodies against the G(M3) epitope have potential application as therapeutic agents in the treatment of these cancers. We describe the chemoenzymatic synthesis of two G(M3)-derived reagents and their use in the panning of a phage-displayed human single-chain Fv (scFv) antibody library derived from the blood of cancer patients. Three scFv-phage clones, GM3A6, GM3A8, and GM3A15, were selected for recombinant expression and were characterized using BIAcore and flow cytometry. BIAcore measurements using the purified, soluble scFvs yielded dissociation constants (K(d)) ranging from 4.2 x 10(-7) to 2.1 x 10(-5) M. Flow cytometry was used to evaluate the ability of each scFv to discriminate between normal human cells (human dermal fibroblast, HDFa), melanoma cells (HMV-1, M21, and C-8161), and breast cancer cells (BCM-1, BCM-2, and BMS). GM3A6 displayed cross-reactivity with normal cells, as well as tumor cells, and GM3A15 possessed little or no binding activity toward any of the cell lines tested. However, GM3A8 bound to five of the six tumor cell lines and showed no measurable reactivity against the HDFa cells. Hence, we have demonstrated that a synthetic G(M3) panning reagent can be used to isolate a fully human scFv that is highly specific for native G(M3) on the surface of tumor cells. The result is a significant step toward effective immunotherapies for the treatment of cancer. 相似文献
57.
Sandra Hübner Dirk Michalik Dr. Haijun Jiao Dr. Helfried Neumann Dr. Stefan Klaus Dirk Strübing Dr. Anke Spannenberg Dr. Matthias Beller Prof. Dr. 《化学:亚洲杂志》2007,2(6):734-746
Chiral N‐dienyl lactams are crucial building blocks for the synthesis of complex organic compounds. However, their generation is rather challenging. This paper reports the novel one‐pot reaction of (S)‐methyl pyroglutamate as the a mide component with different a ldehydes and d ienophiles (AAD reaction) to give novel chiral 1‐amido‐2‐cyclohexenes. The corresponding N‐dienyl lactams generated in situ undergo subsequent Diels–Alder reactions in good yield and diastereoselectivity. The scope and limitations of the three‐component protocol were investigated. X‐ray and NMR spectroscopic analysis of the products as well as DFT calculations of the intermediates were also performed to explain the observed stereoselectivity and structural features. 相似文献
58.
Arsenic speciation is of increasing interest to the food industry, as concerns about high total arsenic concentrations in
food can often be alleviated to a great extent if the ratio of toxic, less toxic and non-toxic arsenic compounds in the sample
is known.
The lipid matrix of fish oil is a challenge in the determination of arsenic species, as current methods for this type of analysis
require the analyte to be water-soluble. In this study, two sample preparation techniques were applied. One the one hand water-soluble
species were extracted with methanol/water, on the other, acid digestion was applied to release lipid-soluble arsenic compounds
into the aqueous phase. Ion chromatography – inductively coupled plasma mass spectrometry (IC-ICP-MS) was used for separation
and sensitive element-specific detection of arsenic compounds. Additional experiments, including alkaline hydrolysis, were
carried out to find out more about the type of lipids arsenic is bound to in fish oil.
Up to eight different arsenic species were detected and quantified in fish oil with dimethylarsinate being the major compound
both in the aqueous extract and in the acid digest. No inorganic arsenic was detected in the aqueous extract, and the maximum
concentration of arsenate determined in the acid digest was 0.05 μg g−1.
The total arsenic concentration determined by ICP-MS ranged from <0.1 to 5 μg g−1. With regard to the mass balance, approximately 1% of the total arsenic content was extractable with methanol/water, whereas
the sum of arsenic species quantified after acid digestion yielded 85–100% of the total arsenic content. It was confirmed
that the large fraction of arsenic in fish oil not extractable on an aqueous basis consists of organoarsenic compounds.
This new approach in sample preparation makes the complete characterization of the arsenic content in the sample possible
with regard to the respective species, providing necessary information required for risk assessment. 相似文献
59.
P. G. Mendoza Jr D. D. Jackson T. M. Niemczyk 《Journal of Radioanalytical and Nuclear Chemistry》1990,141(2):357-371
The uranium spectrophotometric measurement using the uranylnitrate-quaternaryamine solvent extraction method is investigated to identify factors that affect precision and accuracy of the uranium determination. The inherent spectrophotometric precision was measured with neutral density filters in the sample light path and was found to be <0.1% relative standard deviation (RSD). Under selected experimental conditions, temperature instability has a –0.02% effect on the extraction, and a –0.4% effect on the absorbance of the uranium extract in 2-nitropropane (2-NP) or methyl isobutyl ketone (MIBK) solvents. Under optimum conditions at the 10 mg uranium level, RSDs of 0.1% resulted. 相似文献
60.
Sandra Jiménez-Alonso Ana Estévez-Braun Ángel G. Ravelo Rafael Zárate Matías López 《Tetrahedron》2007,63(14):3066-3074
Several bis-pyrano-l,4-benzoquinones have been synthesized by a double domino Knoevenagel hetero Diels-Alder reaction. The synthetic approach is highly efficient allowing the construction of complex polycyclic scaffolds with six new σ-bonds. These reactions performed more efficiently and more rapidly using microwave irradiation. The resulting bis-pyrano-1,4-benzoquinones are the first examples of a double domino Knoevenagel hetero Diels-Alder reaction. Our approach represents a novel contribution to the chemistry of 2,5-dihydroxy-l,4-benzoquinones and the first general method for the synthesis of bis-pyranobenzoquinones. 相似文献