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31.
Poly(ethylene glycol)-modified glucose oxidase was immobilized in a poly(vinyl alcohol) cryogel membrane, obtained by a freezing-thawing cyclic process, to obtain a suitable amperometric glucose sensor. The covalent linkage between PEG and GOD molecule improved the physical immobilization of enzyme in the polymeric matrix, by decreasing its loss in time. Sensor behaviour was evaluated electrochemically with a hydrogen peroxide electrode. The glucose content in standard solutions was determined and linear calibration curves in the 5x10(-5)-5x10(-3) mol l(-1) range were obtained. The kinetic parameters in the immobilized system were evaluated and analytical characteristics of sensor, including stability and influence of pH and temperature, were determined. 相似文献
32.
To avoid the toxic effects of both essential and nonessential metal ions, cells elaborate a variety of metal ion trafficking proteins that regulate metal ion mobility. While structures of several trafficking proteins have been determined, kinetic characterization of metal ion transfer between cognate protein partners and the factors controlling transfer has lagged behind, in part due to a limitation on methods to monitor the rapid transfer. In this Communication we report studies on the kinetics of Hg2+ transfer between separately expressed components of the flavoenzyme mercuric ion reductase (MerA) that take advantage of the sensitivity of the flavin fluorescence to the charge state of a cysteine thiol in the Hg2+ binding pathway. The thiolate form of C558 in the Tn501 MerA partially quenches the fluorescence of the oxidized enzyme. Protonation or binding of Hg2+ to the thiolate increases the fluorescence, providing a sensitive probe for kinetic analysis of the Hg2+ binding reaction. The kinetics of Hg2+ transfer in both directions between the cysteine pair of the separately expressed N-terminal domain and the C-terminal cysteines (C558, C559) of the catalytic core are presented, along with a model describing the overall process. 相似文献
33.
Michael J. Beam Jeannette Schulz Anvita Sinha Pamela Collins Susan Hallenbeck Michael Kustin 《Journal of heterocyclic chemistry》1989,26(2):521-524
Notwithstanding its tendency toward air oxidation in solution, 2-hydrazinobenzothiazole I reacted with aromatic aldehydes in ethanol to give the corresponding hydrazones III-XV in high yields and analytical purity. In related examples, acylation took place under similar conditions to produce hydrazides XVI-XX . The near-infrared bands of the absorption spectra of the araldehyde hydrazones have been associated with charge transfer and appeared to correlate with structural elements of the compounds in a way suggesting that the charge transfer was intermolecular. 相似文献
34.
For a model of the multidimensional universe we take a smooth manifold S which under the action of a compact Lie group G fibres into orbits of the same type G/H acquiring the structure of a fibre bundle with typical fibre G/H and base-the orbit space S/G (identified with the four-dimensional spacetime). The notion of a connection form on the fibre bundle SS/G is defined and its role for some geometrical structures on S is considered. In the framework of a theory of G-invariant tensor-type fields on S, it is shown that -being itself a field of this type-determines a dimensional reduction of the objects on S to objects on S/G. 相似文献
35.
Koumi P Green HE Hartley S Jordan D Lahec S Livett RJ Tsang KW Ward DM 《Electrophoresis》2004,25(14):2227-2241
The demand for high-throughput DNA profiling has increased with the introduction of national DNA databases and has led to the development of automated methods of short tandem repeat (STR) profile production; however, a potential bottleneck still exists at the gel electrophoresis stage. Capillary electrophoresis sequencers capable of processing 96 samples with considerably reduced manual intervention are now available. In this paper, we compare the ABI Prism 377 slab-gel sequencer currently used by the Forensic Science Service with three leading capillary array electrophoresis instruments: the ABI Prism 3700, the Amersham MegaBACE 1000 and the 16-capillary ABI Prism 3100. We describe the experiments used to evaluate and validate these platforms for forensic use with the STR multiplex Ampf/STR SGMplus [1, 2], along with comparative data from the ABI Prism 377 sequencer. 相似文献
36.
Susan T. Weintraub R. Neal Pinckard Timothy G. Heath Douglas A. Gage 《Journal of the American Society for Mass Spectrometry》1991,2(6):476-482
Direct derivatization of the acyl analogue of platelet-activating factor (acyl-PAF) with heptafluorobutyric anhydride results in replacement of the phosphocholine moiety with a heptafluorobutyryl (HFB) group. Electron capture (EC) mass spectrometric analysis of this compound that makes use of negative ion detection along with subsequent accurate mass measurement and tandem mass spectrometry studies revealed that in addition to expected fragmentation due to losses of elements of HF, ketene, and/or acetic acid, there is a rearrangement reaction between the HFB group and the substituent on carbon-2 of the glycerol backbone. For 2-acetyl isomers, this fragmentation yields a characteristic ion at m/z 237; for 1-acetyl isomers, the analogous ion is observed at [M-135]−, along with a corresponding carboxylate anion. The use of the HFB derivative is invaluable for analysis of PAF homologues and analogues because it provides detailed structural information in combination with the high sensitivity of a gas chromatography combined with EC-mass spectrometry assay. 相似文献
37.
Clark SB Turnipseed SB Nandrea GJ Madson MR Hurlbut JA Sofos JN 《Journal of AOAC International》2002,85(5):1009-1014
A confirmatory method is described for phenylbutazone (PB) residues in bovine kidney tissue. Ground kidney tissue is diluted with water, and the mixture is made basic with 25% ammonium hydroxide in water; the lipids are extracted with ethyl and petroleum ethers. The ether layer is discarded, and the tissue is acidified with 6N HCl. PB residues are extracted with tetrahydrofuranhexane (1 + 4). The extract is passed through a silica solid-phase extraction column, and the eluate is evaporated to dryness. The residue is dissolved in acidified acetonitrile-water-acetic acid (50 + 49.4 + 0.6). A single quadrupole mass spectrometer coupled to a liquid chromatograph with an electrospray interface is used to confirm the identity of the PB residues in the kidney extract. Negative-ion detection with selected-ion monitoring of 4 ions is used. Sets of control and fortified-control kidney tissues (at 50, 100, and 200 ppb PB) and several kidney tissue field samples were analyzed for method validation. The method was tested further during the course of a survey to determine the incidence of PB residues in bovine kidney samples obtained from slaughterhouses across the country. In addition, the method was tested for use with an ion-trap mass spectrometer coupled to a liquid chromatograph, which allowed confirmation of PB at lower levels (5-10 ppb) in kidney tissue. 相似文献
38.
The metal complexes [Os(byp)(2)(pic)](+) and [Ru(byp)(2)(pic)](+) where byp is 2,2'-bipyridine and HPic is o-picolinic acid were synthesised and characterised using spectroscopic and electrochemical techniques. These complexes were then evaluated as mediators for a glucose oxidase (GOx)-based biosensor. Results demonstrate the electrocatalytic behaviour of both metal couples towards regeneration of the flavoprotein GOx (FADH(2)) group, when co-immobilised with glucose oxidase. Surface immobilisation was achieved by potential cycling in aqueous solutions of the metal complexes at a glucose oxidase (GOx)/Nafion modified electrode. This proved successful in terms of catalytic efficiency and stability of redox sites. Kinetic parameters associated with both enzymatic and mediator reactions were estimated and the stability/performance properties of the sensor were tested. 相似文献
39.
Susan D. Goff Barbara L. Jelus Edward E. Schweizer 《Journal of mass spectrometry : JMS》1977,12(1):33-36
In the 70 e V electron impact mass spectra of a series of alkyldiphenylphosphine oxides (R?2PO, R = Me, Et, n-Pr, i-Pr, n-Bu, i-Bu, t-Bu, neopentyl, n-decyl), molecular ions of low abundance are observed and [M + H]+ ions are formed to a small extent at high sample pressures. The major ions include [?2PO]+, [?2POH]+; [?2CH2PO]+ and [?2CH2POH]+ which are formed by rearrangement and cleavage processes. The chemical ionization mass spectra obtained with methane and isobutane reagents consist of [M + H]+ ions. The proton affinity of R?2PO was found to be 219 ± 2.5 kcal mol?1. 相似文献
40.
Xiaohua C. Huang Susan G. Stuart Paul F. Bente III Thomas M. Brennan 《Journal of chromatography. A》1992,600(2):289-295
Capillary gel electrophoresis has proven to be a powerful tool in biomedical research. We report our investigation of some of the critical parameters affecting separations of single-stranded DNA fragments as monitored by ultraviolet (UV) absorbance detection. Although not as sensitive as laser-induced fluorescence (LIF), UV absorbance detection allows one to calculate quite accurately, and inexpensively, the molarity of each separated DNA fragment and, moreover, the signal “fading” effect normally observed with LIF detection can be, in many cases, substituted for fluorescence to detect the many different single-stranded DNAs, as well as for detection of sequencing reactions. 相似文献