类钙钛矿化合物Ca(Mn2 Cu1)Mn4 O12的磁性与磁电阻效应

利用固相反应法制备了名义成分为Ca(Mn2 Cu1 )Mn4 O1 2 的类钙钛矿锰氧化物 .x射线衍射表明 ,为了获得较为致密的样品和减小杂相含量 ,可以采用高温烧结再在 10 73K长时间空气中退火的制备方法 .样品在低温下同时存在铁磁相和反铁磁相 ,由于反铁磁相的存在导致样品在 4 5K时的磁化强度显著降低 ,并在 8T的高磁场下仍未达到饱和 .样品呈半导体导电性质 ,在 85K和 6T磁场下磁电阻比的最大值可达 - 4 6 % .     

Electromagnetic form factors of the baryon octet in the perturbative chiral quark model

We apply the perturbative chiral quark model at one loop to analyze the electromagnetic form factors of the baryon octet. The analytic expressions for baryon form factors, which are given in terms of fundamental parameters of low-energy pion-nucleon physics (weak pion decay constant, axial nucleon coupling, strong pion-nucleon form factor), and the numerical results for baryon magnetic moments, charge and magnetic radii are presented. Our results are in good agreement with experimental data.Received: 7 January 2003, Revised: 4 November 2003, Published online: 15 April 2004PACS: 12.39.Ki Relativistic quark model - 13.40.Gp Electromagnetic form factors - 14.20.Dh Protons and neutrons - 14.20.Jn Hyperons     

Visible light photodegradation of dyes over mesoporous titania prepared by using chrome azurol S as template

Mesoporous TiO₂ with anatase crystalline structure (MTiO₂/CAS) has been synthesized by using chrome azurol S (CAS, 2″,6″-dichloro-3,3′-dimethyl-4′-hydroxy-3″-sulfofuchson-5,5′-dicarboxylic acid) as template. It was characterized by X-ray diffraction, nitrogen adsorption/desorption, diffuse reflectance UV–visible and FT-IR spectrometry, and transmission electron microscopy. It was found that MTiO₂/CAS had substantial photocatalytic activity in the degradation of methylthionine chloride, rhodamine B, gentian violet, safranin T, methyl violet, and fuchsine basic whereas Degussa P25 (P25) had negligible photodegradation yield (<6%) under visible light irradiation.     

Retention Behavior of Proteins on Glutamic Acid-Boned Silica Stationary Phase

A glutamic acid-bonded silica (Glu-silica) stationary phase with cation-exchange properties was synthesized using l-glutamic acid as ligand and silica gel as matrix. The effects of solution pH value, salt concentration and metal ion on the retention of proteins were examined. The standard protein mixture was separated with a prepared chromatographic column and an iminodiacetic acid column, and compared. The influence of the binding capacity of an immobilized metal ion on the complexation of metal chelate column was studied. The results indicate that the obtained column displays cation-exchange characteristic and better separation ability for proteins. As fixing metal ion on the Glu-silica column, retention of proteins on the column is a cooperative interaction of metal chelate and cation-exchange. The stationary phase shows the typical metal chelate properties with the increase of the sorption capacity of immobilized metal ion.     

In situ synthesis of di-n-butyl l-tartrate–boric acid complex chiral selector and its application in chiral microemulsion electrokinetic chromatography

A novel procedure for in situ assembling a complex chiral selector, di-n-butyl l-tartrate–boric acid complex, by the reaction of di-n-butyl l-tartrate with boric acid in a running buffer was reported and its application in the enantioseparation of β-blockers and structural related compounds by chiral microemulsion electrokinetic chromatography (MEEKC) has been demonstrated. In order to achieve a good enantioseparation, the effect of dibutyl l-tartrate and sodium tetraborate concentration, surfactant identity and concentration, cosurfactant, buffer pH and composition, organic modifiers, as well as applied voltage and capillary length were investigated. Ten pairs of enantiomers that could not be separated with only dibutyl l-tartrate, obtained good chiral separation using the complex chiral selector; among them, seven pairs could be baseline resolved under optimized experimental conditions. The fixation of chiral centers by the formation of five-membered rings, and being oppositely charged with basic analytes were thought to be the key factors giving the complex chiral selector a superior chiral recognition capability. The effect of the molecular structure of analytes on enantioseparation was discussed in terms of molecular interaction.     

Enantioselective separation of chiral vicinal diols in capillary electrophoresis using a mono‐6A‐aminoethylamino‐β‐cyclodextrin as a chiral selector

This paper describes an improved access to mono‐6^A‐aminoethylamino‐β‐CD (β‐CDen), a very efficient cationic chiral selector for CZE in the separation of eight chiral aromatic vicinal diols. The β‐CDen concentration has a strong influence on the efficiency of enantioseparation. The effects of the pH and concentration of the BGE, the capillary temperature, and the applied voltage on the resolution and separation selectivity have been studied. Excellent chiral resolution was achieved under the optimal conditions of β‐CDen 10 mM, pH 10, 200 mM borate buffer at 15 kV and 20°C within 20 min. Moreover, the developed method was successfully applied to the determination of the enantiomeric purity of the catalytic asymmetric dihydroxylation (AD) reaction products.     

A Novel Spectrophotometric Method for the Determination of Levodopa with the Detection System of Potassium Ferricyanide‐Fe(III)

In this paper, a novel method has been established to determine levodopa with the detection system of potassium ferricyanide‐Fe(III). In the presence of potassium ferricyanide, it has been demonstrated that Fe(III) is reduced to Fe(II) by levodopa at pH 4.0. In addition, the in situ formed Fe(II) reacts with potassium ferricyanide to form soluble prussian blue (KFe^III[Fe^II(CN)₆]). Beer's law is obeyed in the range of levodopa concentrations of 0.01–4.00 μg mL^?1 at the maximal absorption wavelength of 735 nm. The linear regression equation is A = 0.0082 + 0.61365 C (μg mL^?1) with a correlation coefficient of 0.9996. The detection limit (3σ/k) is 9 ng mL^?1, and R.S.D. is 0.73% (n = 11). Moreover, the apparent molar absorption coefficient of indirect determination of levodopa is 1.2 × 10⁵ Lmol^?1cm^?1. The parameters with regard to determination are optimized, and the reaction mechanism is discussed. This method has been successfully applied to determine levodopa in pharmaceutical, serum and urine samples. Analytical results obtained with this novel assay are satisfactory.     

Synthesis of new 2-aryl-6-styryl-2,3-dihydropyridin-4(1H)-one derivatives from curcuminoids

Series of new 2-aryl-6-styryl-2,3-dihydropyridin-4(1H)-one derivatives were synthesized in acceptable to good yields by treatment of the curcuminoids with aqueous ammonia,the mechanism was proposed.By modification of the primary products,total 13 new compounds were obtained.The structures of all products were elucidated by spectroscopy analysis including HR-MS,~1H NMR and ~(13)C NMR.     

On a way to new types of the polyfunctional and polytopic systems based on cage metal complexes: Cadmium-promoted nucleophilic substitution with low-active nucleophilic agents

The nucleophilic substitution of the reactive halogen atoms of clathrochelate precursors with soft nucleophilic agents was promoted by cadmium(II) ion using various types of cadmium-containing compounds. Cadmium(II) activates the C–Hal bond both by the coordination of halogen substituents to this ion and the formation of anionic forms of a nucleophilic agent with cadmium amides, that increase the electron density on a reactive site of this agent. The cadmium-promoted substitution reactions of the reactive chlorine ribbed substituents in the di- and hexachlorine-containing clathrochelate precursors afforded the clathrochelate ribbed-functionalized derivatives of soft nucleophiles [alcohols (including fluorinated ones) and aromatic amines (including the nucleophiles with electron-withdrawing substituents)] by efficient one-pot procedures in high yields under mild conditions with generated in situ low-basic cadmium(II) alcoholates and amides. The complexes obtained were characterized using elemental analysis, MALDI-TOF mass spectrometry, IR, UV–Vis, ⁵⁷Fe Mössbauer, and NMR spectroscopies, and X-ray crystallography. The potential of cadmium-promoted reactions for synthesis of different types of organic and coordination compounds is discussed.     

Colorimetric and electrochemical Pb~(2+) detection by imine-bridged tetrathiafulvalene-pyridine derivatives

Imine-bridged TTF-π-pyridine derivatives, 2NTTF, 3NTTF and 4NTTF, were synthesized and the cation-binding study was performed. It is noted that with the addition of the micromolar concentration of Pb2+ to the solution, these compounds display remarkable changes in solution color, 1H NMR spectra and electrochemical properties. The nitrogen atom of the imine-bridge in 2NTTF not only serves as a π-conjugated spacer but also participates in the sensing and coordinating properties.