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991.
A new chemiluminescence (CL) method for the selective determination of As(III) and As(V) ions in aqueous solution has been studied using a FIA system. The method is based on the increased CL intensity with the addition of As(V) ion into a solution of lucigenin and hydrogen peroxide. The addition of As(III) ion into the solution did not change the CL intensity. Total concentration of As ions was determined after pre-oxidation of As(III) to As(V) with hydrogen peroxide in basic solution. The As(III) content was estimated by subtracting the content of As(V) ion from total As concentration. The effects of concentrations of KOH and H2O2, and flow rates of reagents on CL intensity have been investigated. The calibration curve for As(V) ion was linear over the range from 1.0×10-2 to 10 μg/g, the coefficient of correlation was 0.997 and the detection limit was 5.0×10-3 μg/g under the optimal experimental conditions. 相似文献
992.
[reaction: see text] Indium-mediated allenylation of alpha,beta-unsaturated ketones in the presence of tert-butyldimethylsilyl triflate and dimethyl sulfide gives 6-siloxy-1,2,5-trienes, which undergo W(CO)(5)(L)-catalyzed 5-endo cyclization to give the corresponding cyclopentene derivatives in good yield. Furthermore, this novel W(CO)(5)(L)-catalyzed cyclization of allenyl silyl enol ethers proceeds in a 6-endo manner when 5-siloxy-1,2,5-trienes are employed as a substrate. In these reactions, effective electrophilic activation of allenyl compounds for attack by silyl enol ethers is achieved using a catalytic amount of W(CO)(6). 相似文献
993.
Tan WG Carnelley TJ Murphy P Wang H Lee J Barker S Weinfeld M Le XC 《Journal of chromatography. A》2001,924(1-2):377-386
Detection of benzo[a]pyrene diol epoxide (BPDE)-damaged DNA in a human lung carcinoma cell line (A549) has been performed using free zone affinity capillary electrophoresis with laser-induced fluorescence (LIF). Using BPDE as a model carcinogenic compound, the speed, sensitivity and specificity of this technique was demonstrated. Under free zone conditions, an antibody bound adduct was baseline-resolved from an unbound adduct in less than 2 min. The efficiencies of separation were in excess of 6 x 10(5) and 1 x 10(6) plates per meter for the antibody-bound and unbound adducts, respectively. Separation using a low ionic strength buffer permitted the use of a high electric field (830 V/cm) without the loss of resolving power. Using LIF detection, a concentration detection limit of roughly 3 x 10(-10) M was achieved for a 90-mer oligonuleotide containing a single BDPE. The use of formamide in the incubation buffer to enhance denaturing of DNA did not affect the stability of the complex between the antibody and the adducts. Using a fluorescently labeled BPDE-modified DNA adduct probe, a competitive assay was established to determine the levels of BPDE-DNA adducts in A549 cells. 相似文献
994.
We synthesized a novel colorimetric anion chemosensor bearing benzimidazole motifs as recognition sites in the pods of the receptor. The addition of tetrabutylammonium salts of F− or AcO− to the solution of receptor caused dramatic color changes from colorless to yellow, which was clearly visible to the naked eye. The receptor showed no significant changes on addition of other anions such as Cl−, Br−, I−, NO3−, and H2PO4−. 相似文献
995.
A series of new C2-symmetric 2,2′-bipyridine-contaning crown macrocycles 1-4 has been developed for enantiomeric recognition of amino acid derivatives. These new macrocycles have been showed to be strong complexing agents for primary organic ammonium salts (with K up to 4.83×105 M−1 and −ΔG0 up to 32.4 kJ mol−1) and also useful chromophores for UV-vis titration studies. These macrocyclic hosts exhibited enantioselective binding towards the (S)-enantiomer of phenylglycine methyl ester hydrochloride (Am1) with K(S)/K(R) up to 2.10 (ΔΔG0=−1.84 kJ mol−1) in CH2Cl2 with 0.25% CH3OH. The structure-binding relationship studies showed that the aromatic subunit and the ester group of the ammonium guests are both important for good enantioselectivity. In addition, the host-guest complexes have been studied using various NMR experiments. 相似文献
996.
Chang Gon Lee 《Tetrahedron letters》2004,45(40):7409-7413
We developed an efficient synthetic method for indenoquinoline skeletons from Baylis-Hillman adducts. 4b,5,10a,11-Tetrahydroindeno[1,2-b]quinolin-10-ones and 7H-indeno[2,1-c]quinolines were prepared from Baylis-Hillman adducts in polyphosphoric acid. 相似文献
997.
A new synthesis of 6‐carbomethoxy‐1,2,3,5‐tetrahydroirnidazo[2,3‐b][1,3]benzodiazocines 13 by the intramolecular cycloaddition reaction of methyl 2‐(1‐aziridinylmethyl)‐3‐(2‐ureidophenyl)propenoates 10 under Appel's dehydration conditions is described. The latter were readily obtained from 2‐nitrobenzalde‐hyde with methyl acrylate through the Baylis‐Hillman reaction. 相似文献
998.
Chung‐Cheng Chang Kuo‐Ching Yang Jeng‐Gong Guo Leigh‐May Huang Li‐Chyung Wang Gene‐Hsiang Lee Shie‐Ming Peng 《中国化学会会志》2003,50(5):965-971
The insertion reaction of CS2 with Mg(NR2)2 (R= Et, iPr), MgR′2 (R′= Et, Ph) and R″MgBr (R″= iPr, Ph) respectively lead solid products, Mg(S2CNR2)2(THF)n ( 1 : R= Et, n=2; 2 : R= iPr, n=1), Mg(S2C′R)2(THF)2 ( 3 : ′R= Et, 4 : ′R= Ph), BrMg(S2C″R) (THF)3 ( 5 : ″R= iPr, 6 : ″R= Ph) in which the inserted carbon disulfides act as terminal chelating ligands. These compounds were characterized with 1H, 13C NMR, IR spectroscopy, mass spectrometry, elemental analyses, and X‐ray crystallography. 相似文献
999.
Molecular diodes based on conjugated diblock co-oligomers 总被引:2,自引:0,他引:2
This report describes synthesis and characterization of a molecular diode based upon a diblock conjugated oligomer system. This system consists of two conjugated blocks with opposite electronic demand. The molecular structure exhibits a built-in electronic asymmetry, much like a semiconductor p-n junction. Electrical measurements by scanning tunneling spectroscopy (STS) clearly revealed a pronounced rectifying effect. Definitive proof for the molecular nature of the rectifying effect in this conjugated diblock molecule is provided by control experiments with a structurally similar reference compound. 相似文献
1000.
Lei Liu Wes Lee Mingbin Yuan Chris Acha Michael B. Geherty Brandon Williams Osvaldo Gutierrez 《Chemical science》2020,11(12):3146
Design and implementation of the first (asymmetric) Fe-catalyzed intra- and intermolecular difunctionalization of vinyl cyclopropanes (VCPs) with alkyl halides and aryl Grignard reagents has been realized via a mechanistically driven approach. Mechanistic studies support the diffusion of alkyl radical intermediates out of the solvent cage to participate in an intra- or intermolecular radical cascade with a range of VCPs followed by re-entering the Fe radical cross-coupling cycle to undergo (stereo)selective C(sp2)–C(sp3) bond formation. This work provides a proof-of-concept of the use of vinyl cyclopropanes as synthetically useful 1,5-synthons in Fe-catalyzed conjunctive cross-couplings with alkyl halides and aryl/vinyl Grignard reagents. Overall, we provide new design principles for Fe-mediated radical processes and underscore the potential of using combined computations and experiments to accelerate the development of challenging transformations.Design and implementation of the first (asymmetric) Fe-catalyzed intra- and intermolecular difunctionalization of vinyl cyclopropanes (VCPs) with alkyl halides and aryl Grignard reagents has been realized via a mechanistically driven approach. 相似文献