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911.
Wensheng Huang Chunhai Yang Wanyun Qu Shenghui Zhang 《Russian Journal of Electrochemistry》2008,44(8):946-951
In this work, an electrochemical method for the determination of malachite green was developed on the basis of enhancement
effect of an anionic surfactant: sodium dodecyl benzene sulfonate. It is found that the oxidation peak current of malachite
green at carbon paste electrode significantly increases in the presence of low concentration of sodium dodecyl benzene sulfonate
in pH 6.5 phosphate buffer, suggesting that sodium dodecyl benzene sulfonate shows obvious enhancement effect for the determination
of malachite green. The experimental parameters, such as supporting electrolyte, kind of surfactant, concentration of sodium
dodecyl benzene sulfonate and accumulation time, were optimized, and then a sensitive and convenient electrochemical method
was proposed for the determination of malachite green. The oxidation peak current is proportional to the concentration of
malachite green over the range from 8.0 × 10−9 to 5.0 × 10−7 mol l−1, and the detection limit is 4.0 × 10−9 mol l−1 after 5 min of accumulation. Finally, this new method was successfully employed to detect malachite green in fish samples.
Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 8, pp. 1019–1024.
The text was submitted by the authors in English. 相似文献
912.
M. Dolores Fernández M. Jesús Fernández 《Journal of Thermal Analysis and Calorimetry》2008,92(3):829-837
The thermal degradation of poly(vinyl acetate) (PVA), poly(vinyl alcohol) (PVAL), vinyl acetate-vinyl alcohol (VAVAL), vinyl
acetate-vinyl-3,5-dinitrobenzoate (VAVDNB) and vinyl alcohol-3,5-dinitrobenzoate (VALVDNB) copolymers have been studied using
differential thermal analysis (DTA) and thermogravimetry (TG) under isothermal and dynamic conditions in nitrogen. Thermal
analysis indicates that PVA and PVAL are thermally more stable than VAVAL copolymers, being PVAL the most stable polymer.
The presence of small amounts of vinyl-3,5-dinitrobenzoate (VDNB) in PVA or PVAL produces a marked decrease in the thermal
stability of both homopolymers, being VALVDNB copolymers the less stable materials. The apparent activation energy of the
degradative process was determined by the Kissinger and Flynn-Wall methods which agree well. 相似文献
913.
Lidija Fras Zemljič Zdenka Peršin Per Stenius Karin Stana Kleinschek 《Cellulose (London, England)》2008,15(5):681-690
The influence of peroxide bleaching and slack-mercerization on the amount of acidic groups in regenerated fibres (viscose,
modal and lyocell) were studied. Conductometric titration was used to determine the total content of acidic carboxylic groups.
Polyelectrolyte titration was used for surface and total charge determination, and to obtain information about the charge
distribution and accessibilities of charged groups. Changes in fibre crystallinity to pre-treatment processes were characterized
using iodine sorption (Schwertassek method) and correlated to treatments and the amount of carboxylic groups. For all three
types of fibres the amount of accessible carboxyl groups was lowered by an increase in the degree of crystallinity. Bleaching
with hydrogen peroxide causes some oxidative cellulose damage and, therefore, a larger amount of carboxyl groups (presumably
formed at the end of cellulose chains). Slack-mercerization did not significantly change the total amount of acidic groups
in the fibres, but their accessibility to cationic polyelectrolytes, in particular to polymers with high molecular weight
was substantially lowered.
Lidija Fras Zemljič, Zdenka Peršin, and Karin Stana Kleinschek are the members of the European Polysaccharide Network of Excellence
(EPNOE). 相似文献
914.
Kristina Starčević Marijana Hranjec Dejana Carić Grace Karminski-Zamola 《Monatshefte für Chemie / Chemical Monthly》2008,139(8):975-983
A series of novel substituted derivatives related to furyl-phenyl-acrylates and naphthofurans, was synthesized and characterized
by UV/Vis and fluorescence spectroscopy. Acyclic compounds can undergo photochemical dehydrocyclization by visible light irradiation
in order to obtain their cyclic derivatives. The interactions of the prepared compounds with calf thymus DNA was investigated by means of electronic absorption and fluorescence spectra. It is intriguing that addition of ct-DNA induced a fluorescence increase of acyclic derivatives, exactly the opposite of the strong fluorescence quenching observed
for cyclic derivatives 10 and 12. Compound 11 showed decreasing fluorescence intensity for lower concentrations of ct-DNA, while increasing of fluorescence is observed for high excess of added ct-DNA.
Correspondence: Grace Karminski-Zamola, Department of Organic Chemistry, Faculty of Chemical Engineering and Technology, University
of Zagreb, Marulićev trg 20, HR-10000 Zagreb, Croatia. 相似文献
915.
Xu Z Yao S Wei Y Zhou J Zhang L Wang C Guo Y 《Journal of the American Society for Mass Spectrometry》2008,19(12):1849-1855
A matrix-assisted laser desorption/ionization Fourier transform mass spectrometry (MALDI-FTMS)-based assay was developed for
kinetic measurements and inhibitor screening of acetylcholinesterase. Here, FTMS coupled to MALDI was applied to quantitative
analysis of choline using the ratio of choline/acetylcholine without the use of additional internal standard, which simplified
the experiment. The Michaelis constant (K
m) of acetylcholinesterase (AChE) was determined to be 73.9 μmol L−1 by this approach. For Huperzine A, the linear mixed inhibition of AChE reflected the presence of competitive and noncompetitive
components. The half maximal inhibitory concentration (IC50) value of galantamine obtained for AChE was 2.39 μmol L−1. Inhibitory potentials of Rhizoma Coptidis extracts were identified with the present method. In light of the results the
referred extracts as a whole showed inhibitory action against AChE. The use of high-resolution FTMS largely eliminated the
interference with the determination of ACh and Ch, produced by the low-mass compounds of chemical libraries for inhibitor
screening. The excellent correlation with the reported kinetic parameters confirms that the MS-based assay is both accurate
and precise for determining kinetic constants and for identifying enzyme inhibitors. The obvious advantages were demonstrated
for quantitative analysis and also high-throughput characterization. This study offers a perspective into the utility of MALDI-FTMS
as an alternate quantitative tool for inhibitor screening of AChE. 相似文献
916.
Brugnanin (1), a neolignan dioate, was isolated from a mangrove plant Bruguiera gymnorrhiza. Based on spectroscopic interpretation of MS, IR, and NMR data, 1 was elucidated as (7R*,8S*,E)-3-hydroxy-5,5′-dimethoxy-7-O-4′,8-3′-neolignan-7′-ene-9,9′-dioic acid dioctadecyl ester. MTT assay showed that 1 had weak inhibitory activity against growth of CNE-1 nasopharyngeal carcinoma cell line.
Published in Khimiya Prirodnykh Soedinenii, No. 2, pp. 147–149, March–April, 2008. 相似文献
917.
Homogeneous hydrogenation of barbituric acid derivatives with parahydrogen yields a substantial increase of the (1)H NMR signals of the reaction products. These physiologically relevant compounds were hydrogenated at both ambient and elevated temperatures and pressures using a standard cationic rhodium catalyst. The resulting nonthermal nuclear spin polarization (hyperpolarization) is limited by the spin-lattice relaxation time T(1) of the corresponding nuclei in the products, being shorter than the time constant of the hydrogenation. The signal-to-noise ratio of the NMR spectra could be further increased upon signal averaging the antiphase PHIP signals of 25 successive scans following 30 degrees pulse experiments and a delay of 10 s. 相似文献
918.
A series of six open-chain tetrapyrroles has been synthesized and used as chromophores for the plant photoreceptor protein phytochrome. The novel chromophores vary in the size of substituents 17 and 18 at ring D. This ring undergoes maximal conformational change upon light excitation ( Z --> E photoisomerization of the 15,16-double bond). Instead of methyl and vinyl substituents (positions 17, 18) as present in the native chromophore phytochromobilin, dimethyl, methyl and isopropyl, methyl and tert-butyl, ethyl and methyl, vinyl and methyl, and isopropyl and methyl substituents have been generated. All novel chromophores assemble with the apoprotein. The obtained chromoproteins show hypsochromic shifts of the absorbance maxima by 10 nm maximally, compared to the native pigment, except for the 17-isopropyl-18-methyl-substituted compound which showed a 100 nm hypsochromic shift of selectively the P r form. The assembly kinetics were slowed down in correlation to the increasing size of the substituents, with stronger effects for modified substituents at position 17. The thermal stability of the photoinduced P fr form for the 18-isopropyl and the 18- tert butyl substituents was even greater than that of the native pigments. Those chromophores carrying substituents at position 17 larger than the methyl group (ethyl and isopropyl) showed a very low stability of the respective P fr forms. Time-resolved detection of the P r to P fr conversion (laser-induced flash photolysis) revealed a slower formation of the P fr form for those chromophores carrying larger substituents at position 18, whereas the rise and decay kinetics of the early intermediates are only moderately changed. Introduction of larger substituents at position 17 (ethyl, vinyl, and isopropyl) causes drastic changes in the kinetics; in particular the formation of the first thermally stable intermediate, I 700, is significantly slowed, making a detection of its rise possible. 相似文献
919.
Oleg A. Petrii 《Journal of Solid State Electrochemistry》2008,12(5):609-642
Three periods of Pt–Ru research are considered step-by-step: the initial period after discovery (1963–1970); observation and
classification of basic tendencies (like the effects of composition, segregation, structural features on the activity; up
to 1990); nanostructural studies and molecular level consideration of electrocatalytic phenomena in combination with advanced
applied studies of materials, mechanistic, and applied aspects (after 1990). The main idea of this review is to balance various
aspects of Pt–Ru electrochemistry related to material science and electrocatalysis as well as to remember the early basic
results being of importance for future understanding of Pt–Ru functional properties.
Dedicated to Professor Teresa Iwasita, as a token of her remarkable contribution to electrocatalysis.
相似文献
Oleg A. PetriiEmail: |
920.
The kinetics of the oxidation of sulfanilic acid (SAA) by sodium N-chloro-p-toluenesulfonamide (CAT) in the presence and absence of ruthenium(III) chloride have been investigated at 303 K in perchloric
acid medium. The reaction shows a first-order dependence on [CAT]o and a non-linear dependence on both [SAA]o and [HClO4] for both the ruthenium(III)-catalyzed and uncatalyzed reactions. The order with respect to [RuIII] is unity. The effects of added p-toluenesulfonamide, halide, ionic strength, and dielectric constant have been studied. Activation parameters have been evaluated.
The rate of the reaction increases in the D2O medium. The stoichiometry of the reaction was found to be 1:1 and the oxidation product of SAA was identified as N-hydroxyaminobenzene-4-sulfonic acid. The ruthenium(III)-catalyzed reactions are about four-fold faster than the uncatalyzed
reactions. The protonated conjugate acid (CH3C6H4SO2NH2Cl+) is postulated as the reactive oxidizing species in both the cases. 相似文献