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排序方式: 共有148条查询结果,搜索用时 78 毫秒
11.
Nívia Maria Melo Coelho Edmar Isaías de Melo Hélen Cristine de Rezende Ana Graci Brito-Madurro João Marcos Madurro 《Journal of Solid State Electrochemistry》2012,16(3):945-951
In this work, carbon electrodes modified with aminophenols were developed for the production of pesticides biosensors based
on acetylcholinesterase. The polymers were potentiodynamically deposited on a graphite electrode surface by the oxidation
of monomers, 2-aminophenol, 3-aminophenol and 4-aminophenol. The electrochemical behaviour and surface analysis of the electrodes
modified by polyaminophenols non-immobilized and immobilized on acetylcholinesterase were studied by cyclic voltammetry, electrochemical
impedance spectroscopy and atomic force microscopy. Roughness values obtained for graphite electrodes modified with poly(4-aminophenol)
and poly(4-aminophenol)/acetylcholinesterase were 174 and 86 nm, respectively. The acetylcholinesterase enzyme was immobilized
on a graphite and a graphite modified with poly(4-aminophenol), and these electrodes were coupled in the flow system. Potentiometric
response due to hydrogen ions generated by an enzymatic system in the presence of acetylcholine chloride substrate was evaluated.
The results showed that the graphite/poly(4-aminhophenol) sensor presents high sensitivity to hydrogen ions when compared
with other graphite/polyaminophenols sensors. The biosensor coupled in a continuous flow system was employed for the detection
of dichlorvos. The detection and quantification limits were 0.8 and 2.4 μmol L−1 dichlorvos, respectively. This sensor reveals an efficient and promising material for biomolecules immobilization. 相似文献
12.
The reactions of 2,2,2-trichloro-1-phenylethanone with various oxygen, carbon and sulfur nucleophiles were investigated with a view of widening the use of trichloroethanones as acylating agents. 相似文献
13.
Langone Marta A. P. De Abreu Melissa E. Rezende Michelle J. C. Sant’Anna Geraldo L. 《Applied biochemistry and biotechnology》2002,98(1-9):987-996
The synthesis of monocaprin, monolaurin, and monomyristin in a solvent-free system was conducted by mixing a commercial immobilized
lipase with the organic reactants (glycerol and fatty acids) in a 20-mL batch reactor with constant stirring. The effects
of temperature, fatty acid/glycerol molar ratio, and enzyme concentration on the reaction conversion were determined. The
addition of molecular sieves in the assays of monomyristin synthesis was also evaluated. The reactions were carried out for
5 to 6 h and the nonpolar phase was analyzed by gas chromatography. The best results in terms of selectivity and conversion
(defined as the percentage of fatty acid consumed) were achieved when the stoichiometric amount of reagents (molar ratio=1)
and 9% (w/w) commercial enzyme were used and the reaction was performed at 60°C. The addition of molecular sieves did not
improve the synthesis of monomyristin. Conversions as high as 80%, with monoglycerides being the major products, were attained.
After 5 h of reaction, the concentration of monoglyceride was about twice that of diglyceride, and only trace amounts of triglyceride
were found. The results illustrate the technical possibility of producing medium chain monoglycerides in a solvent-free medium
using a simple batch reactor. 相似文献
14.
The first clear evidence for the existence of from a high resolution, far-infrared (FIR) study of the antiferromagnetic resonance (AFMR) of FeF2 is presented. The broad (4 kOe) asymmetric structure observed in transmission is shown to be a characteristic polariton effect; the linewidth ΔH at 4.2 K is only 350 Oe. The Mn impurity mode is enhanced by ~50 in agreement with a coupled equations of motion prediction. Both host and impurity resonances are broadened by superradiance. 相似文献
15.
Spectra of the N‐phenyl‐5,6‐dihydro‐2,4‐diphenylbenzo[h]quinolinium tetrafluoroborate (1) and of the N‐phenyl‐5,6,8,9‐tetrahydro‐7‐phenyldibenzo[c,h]acridinium tetrafluoroborate (2) were recorded in various solvents and temperatures. The analysis of the 1H‐NMR spectra of the tetrafluoroborate salt 1, recorded in acetone, acetonitrile, 1,1,2,2‐tetrachloroethane and chloroform, revealed the existence of an equilibrium between two conformers in solution. Tight ion‐pairing in chloroform led to a smaller barrier for interconversion between the two conformers. In more polar solvents, where the dihydrobenzoquinolinium exists as a free cation, theoretical calculations predicted larger barriers. The spectra of 1 in 1,1,2,2‐tetrachloroethane also varied with temperature, resembling at higher temperatures the spectrum in CDCl3 and at 300K spectra in more polar media. Spectra of 2 did not vary with the solvent or the temperature, in an indication of a much higher barrier to conformational interconversion, because of a greater steric hindrance between the N‐phenyl substituent and the dihydrobenzo rings. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
16.
Almodóvar I Ramírez-Rodríguez O Barriga A Rezende MC Araya-Maturana R 《Rapid communications in mass spectrometry : RCM》2011,25(2):370-378
The fragmentation patterns of nine di-, tri- and tetracyclic hydroquinones with potential antitumor activity were rationalized by invoking competing mechanisms that included sterically accelerated homolytic cleavage, Meerwein-type rearrangements and dehydrations through elimination or intramolecular nucleophilic substitution. 相似文献
17.
Castaldelli E Triboni ER Demets GJ 《Chemical communications (Cambridge, England)》2011,47(19):5581-5583
This naphthalene diimide derivative, DC18, forms highly conjugated semiconducting stacked assemblies over electrodes after electrochemical conditioning. These molecular materials are very efficient towards electrochemical photoreduction of oxygen under visible light. 相似文献
18.
A general quantitative treatment for salt effects by means of an empirical relationship between the observed rates k and the concentrations of added electrolyte is presented. The proposed equation has been successfully tested for a variety of processes in the literature. 相似文献
19.
Jorge Rezende 《Letters in Mathematical Physics》1996,38(2):117-127
In this Letter, a theorem on time-dependent linear Hamiltonian systems is recalled and its connection with the Schrödinger equation is discussed. The kernel of the evolution operator of such quantum systems is computed. Furthermore, the Lewis and Riesenfeld theory for systems with many degrees of freedom is generalized. 相似文献
20.
The radiation induced linewidth of magnetostatic modes in spheres of Yttrium Iron Garnet has been measured in microwave experiments. The linewidths of the lowest order modes (n m 0) have a ω2n+1 frequency dependence which can be explained by multipole radiation. 相似文献