排序方式: 共有17条查询结果,搜索用时 15 毫秒
1.
Klemens Schachl Hailemichael Alemu K. Kalcher Helmut Moderegger Ivan Svancara Karel Vytras 《Analytical and bioanalytical chemistry》1998,362(2):194-200
A carbon thick film electrode modified with an MnO2-film is investigated as an amperometric detector for hydrogen peroxide in flow-injection analysis (FIA). At an operating potential of +0.48 V vs. Ag/AgCl catalytic oxidation of the analyte is exploited for amperometric monitoring. Experimental parameters, such as pH of the carrier, working potential, flow rate and injection volume, are optimized. The amperometric signals are linearly proportional to the concentration of H2O2 in the range from 0.005 to 10 mg/L, showing a detection limit (3σ) of 2.3 μg/L. The method is applied to the determination of H2O2 in rain water and to a simple assay to quantify glucose in human plasma. 相似文献
2.
A homogeneous assay, based on electrospray mass spectrometry, is described for identifying compounds in a combinatorial library that covalently modify a protein and thereby enhance its solubility. The technique is based on measuring the distribution of modified proteins in the supernatant versus aggregate. Compounds having the greatest anti-aggregatory activity are those with the highest supernatant/aggregate ratio. Mass is used as a marker to identify which covalent modifier in the library is involved. An exploratory study is presented which demonstrates that the antisickling activity of a family of isothiocyanates, as measured by the standard C(sat) assay, correlates well (r(2) = 0.98) with the mass spectrometry analysis of the supernatant/aggregate distribution. The technique has potential for screening libraries capable of covalently modifying other proteins of clinical interest, e.g., Alzheimer's, Huntington's, and various prion related diseases. 相似文献
3.
A technique of ultrasound-assisted low density solvent based dispersive liquid-liquid microextraction was developed for the determination of four phthalate esters, including dimethyl phthalate(DMP), diethyl phthalate(DEP), di-n-butyl phthalate(DnBP) and di(2-ethylhexyl) phthalate(DEHP) in bottled water samples. A low density solvent, toluene, was selected as extraction solvent. In the extraction process, a mixture of 15 μL of toluene(extraction solvent) and 100 μL of methanol(disperser solvent) was rapidly injected into 1.0 mL of water samples. A cloudy solution was formed after ultrasounded for 5 min, and then centrifuged at 5000 r/min for 5 min. The enriched analytes in the floating phase were determined by means of gas chromatograph. Under the optimum conditions, the enrichment factors were found to be in a range of 29-67, and the recoveries were ranged from 81.2% to 103.9%. The limits of the detection were in a range of 3.8-5.6 μg/L. The proposed method was applied to the extraction and determination of phthalate esters in bottled water samples, and the concentrations of phthalate esters found in the water samples were below the allowable levels. 相似文献
4.
Kode Nageswara Rao Kinfe K. Redda Folakemi Y. Onayemi Hailemichael Melles Jongoh Choi 《Journal of heterocyclic chemistry》1995,32(1):307-315
1,2,3,6-Tetrahydropyridines are known to possess analgesic, anti-inflammatory, hyperglycemic and hypoglycemic activities. Substituted 2,4-dinitrophenylpyridinium chlorides 3 were formed by reacting 1-chloro-2,4-dinitrobenzene with hydroxypropyl, hydroxymethyl and benzyl substituted pyridines 2 . Attack of the pyridinium chlorides 3 with pyridylcarbonyl hydrazides or benzoyl hydrazides 4 gave the isolable 2,4-dinitroanilino derivative 5 which underwent hydrolysis when refluxed in water:p-dioxane mixture (1:4 v/v) to afford the pyridinium ylides 6 . Sodium borohydride reduction of 6 in absolute ethanol at 0° for 4–6 hours resulted in the isolation of the 1,2,3,6-tetrahydropyridines 7 in good yields. 相似文献
5.
Kinfe K. Redda Hailemichael Melles Kode Nageswara Rao 《Journal of heterocyclic chemistry》1990,27(4):1041-1046
Alkyl substituted 2,4-dinitrophenylpyridinium chlorides 3 are formed by the nucleophilic substitution of 1-chloro-2,4-dinitrobenzene with alkyl pyridines. Reaction of pyridyl acid hydrazides or benzoyl hydrazides 4 with the pyridinium chlorides 3 furnish the isolable 2,4-dinitroanilino derivatives 5 which undergo hydrolysis when refluxed in water:p-dioxane mixture (1:4 v/v) to yield the pyridinium ylides 6 . Sodium borohydride reduction of 6 in absolute ethanol at 0° for 4 hours result the formation of the title compounds 7 in moderate to excellent yields. 相似文献
6.
The copolymerizations of ethylene with 1-hexene or 1-octene by using TiCl4 /MgCl2 /THF catalysts modified with different metal halide additives(ZnCl2, SiCl4, and the combined ZnCl2-SiCl4) were investigated based on catalytic activity and copolymer properties. It was found that the catalyst modified with mixed ZnCl2-SiCl4 revealed the highest activities for both ethylene/1-hexene and ethylene/1-octene copolymerization. The increase in activities was due to the formation of acidic sites by modifying the catalysts with Lewis acids. Based on the FTIR measurements, the characteristic C―O―C peaks of the catalysts modified with metal halide additives were slightly shifted to lower wavenumber when compared to the unmodified catalyst. This showed that the modified catalysts could generate more acid sites in the TiCl4 /MgCl2 /THF catalytic system leading to an increase in activities as well as comonomer insertion(as proven by13C-NMR). However, Lewis acidmodifications did not affect the microstructure of the copolymers obtained. By comparison on the properties of copolymers prepared with the unmodified catalyst, it was found that polymers with ZnCl2 and/or SiCl4 modification exhibited a slight decrease in melting temperature, crystallinity and density. It is suggested that these results were obtained based on the different amount of α-olefins insertion, regardless of the types of Lewis acids and comonomer. 相似文献
7.
Chlorination has been widely used as a disinfection method for control of pathogens in drinking water and wastewater treatment plants. Chlorination disinfection byproducts (DBPs) are formed when organic matter is present in water, and they are harmful to human health. The main groups of compounds formed are trihalomethanes (THMs), haloacetic acids (HAAs) and haloacetonitriles (HANs). Analysis of THMs, HAAs and HANs in water samples has been reported. This paper reviews the various sample preparation methods in use for analysis of THMs, HAAs and HANs in water samples.
相似文献8.
Modelling of the impedimetric responses of an aflatoxin B1 immunosensor prepared on an electrosynthetic polyaniline platform 总被引:1,自引:0,他引:1
Owino JH Ignaszak A Al-Ahmed A Baker PG Alemu H Ngila JC Iwuoha EI 《Analytical and bioanalytical chemistry》2007,388(5-6):1069-1074
Aflatoxins are a group of mycotoxins that have deleterious effects on humans and are produced during fungal infection of plants
or plant products. An electrochemical immunosensor for the determination of aflatoxin B1 (AFB1) was developed with AFB1antibody (AFB1-Ab) immobilized on Pt electrodes modified with polyaniline (PANi) and polystyrene sulphonic acid (PSSA). Impedimetric analysis
shows that the electron transfer resistances of the Pt/PANi–PSSA electrode, the Pt/PANi–PSSA/AFB1-Ab immunosensor and Pt/PANi–PSSA/AFB1-Ab incubated in bovine serum albumin (BSA) were 0.458, 720 and 1,066 kΩ, respectively. These results indicate that electrochemical
impedance spectroscopy (EIS) is a suitable method for monitoring the change in electron transfer resistance associated with
the immobilization of the antibody. Modelling of EIS data gave equivalent circuits which showed that the electron transfer
resistance increased from 0.458 kΩ for the Pt/PANi–PSSA electrode to 1,066 kΩ for the Pt/PANi–PSSA/AFB1-Ab immunosensor, indicating that immobilization of the antibody and incubation in BSA introduced an electron transfer barrier.
The AFB1 immunosensor had a detection limit of 0.1 mg/L and a sensitivity of 869.6 kΩ L/mg. 相似文献
9.
Bhaskarchand Gautam Hailemichael Ayalew Udesh Dhawan Jayakrishnan Aerathupalathu Janardhanan Hsiao-hua Yu 《中国化学会会志》2020,67(9):1602-1610
Poly(3,4-ethylenedioxythiophene (PEDOT) derivatives display a multitude of attractive properties such as high conductivity, biocompatibility, ease of functionalization, and high thermal stability. As a result, they show promise for applications in materials and biomedical engineering. In order to increase their applications in the practical domain, trivial fabrication techniques are required. Here, we present a simple layer-by-layer dip methodology to assemble water-soluble PEDOT derivatives that can then be disassembled via electrical stimulation. As a result, a dynamic PEDOT layered system is fabricated and could be applied as responsive materials for bioengineering. PEDOT-SO3 and PEDOT-NMe3 are synthesized via direct C-H arylation polymerization and chemical polymerization, respectively. The electrostatic interactions between oppositely charged SO3− and NMe3+ enabled the stacking of PEDOT derivatives. The layer-by-layer assemblies are confirmed by ultraviolet–visible spectroscopy and profilometer. Morphological analyses are performed using scanning electron microscopy and atomic force microscopy, which revealed that the polymer coatings are uniform without any cracks. In situ material assembly is studied using quartz crystal microbalance, and we also demonstrate that these PEDOT-derivative assemblies can be disintegrated by electrical stimulation. Cyclic voltammetry shows a proportional increase in stored charge density with the increase in bilayer thickness, confirming stable electroactivity of these assemblies. Using this approach, we can assemble conductive bio interface on both conductive and nonconductive surfaces, expanding the capability to fabricate bioelectronic electrodes. 相似文献
10.
Propargylic and acetylenic silyl groups on propyne control the C-glycosidation products depending on the trimethylsilyl and triisopropylsilyl groups used. Some mechanistic discussions are included. [reaction: see text] 相似文献