La_(1-x)Li_xMnO_3体系的输运特性及EPR研究

利用固相反应法合成了掺杂锂的La1-xLixMnO3(x=0,0.10,0.15,0.20,0.25,0.30)钙钛矿氧化物．XRD测试表明，所有样品均为菱方结构．除x=0,0.3外，其它样品均随温度的降低在液氮温区可观察到从绝缘态到金属态的转变，其中x=0.15样品的转变温度最高为167K．在H=1T的磁场下，出现了负磁阻现象．EPR谱上的ｇ＝2.00信号与Mn3+和Mn4+组成的复合团簇有关

Some unusual features of highly oriented pyrolytic graphite observed by electrochemical scanning tunneling microscopy

Highly oriented pyrolytic graphite (HOPG) is the substrate often used in scanning tunneling microscopy (STM). It is well known that STM images of the basal plane of HOPG show some unusual structural patterns. In this letter, we present in situ STM images of some unusual features on HOPG in solutions, including normal or abnormal chain-like features and hexagonal or oblique superperiodic structures. These features emerge both next to and apart from the step of HOPG.

Electrochemical behavior of 3,4-dihydroxybenzoic acid in self-assembled monolayer electrode system

The self-assembled monolayer of cystamine was prepared on gold electrode and 3,4-dihydroxybenzoic acid (DHBA) was electrochemically deposited on cystamine surface as a functional group by electrostatic adsorption, namely, molecular deposition. It shows that the MD/SAM structure has a higher stability, and E-1/2 of the DBAH in MD/SAM shifts more negative than that of on naked gold electrode, The n-decanethiol was also used to fill defects in MD/SAM, it results in much better cyclic voltermmetric behavior.

Electrochemical detector at the liquid/liquid and liquid/membrane interface

Electrochemistry at the liquid/liquid and liquid/membrane interface has been developed recently. It can be used for a new kind of electrochemical detector and sensor. Some new aspects of the field in this laboratory are presented.

In situ UV-vis and CD thin-layer spectroelectrochemistry study of the electrochemical behavior of L-noradrenaline in alkaline solution

Electrochemical redox behavior of noradrenaline in alkaline solution on a glassy carbon electrode has been investigated by in situ UV-vis and CD spectroelectrochemistry by using a long optical path thin-layer cell. The experimental data were processed by using a double logarithmic method of analysis together with nonlinear regression which confirmed that the first step in both the oxidation of noradrenaline and reduction of noradrenochrome is a two-electron irreversible process governed by an EE mechanism. The kinetic parameters of the electrode reactions, i.e., charge transfer coefficient and the number of electrons transferred, alpha(1)n(1) = 0.11 and alpha(2)n(2) = 0.23, formal potentials modified with kinetics, E-1(0') = 0.65 (+/- 0.01) V and E-2(0') = 0.72V and standard rate cnstants, k(1)(0) = 7.0(+/-0.5)x10(-5) cm s(-1), for the first and second steps in the oxidation process of noradrenaline, and similarly, alpha(1)n(1) = 0.33, alpha(2)n(2) = 0.58, E-1(0') = 0.37(+/-0.01) V, E-0' = -0.25 (+/-0.01) V and k(1)(0) approximate to k(2)(0) = 1.06 (+/-0.05)x10(-4) cm s(-1) for the first and second steps in the reduction process of noradrenochrome were also determined.

Determination of sulfadiazine and sulfamethoxazole by capillary electrophoresis with end-column electrochemical detection

Capillary electrophoresis (CE) with end-column electrochemical detection (EC) of sulfadiazine (SDZ) and sulfamethoxazole (SMZ) is described. Under the optimum conditions, SDZ and SMZ were separated satisfactorily, and a highly sensitive and stable response was obtained at a potential of 1.1 V versus Ag/AgCl. Optimized end-column detection provides detection limits as low as 0.1 mu M for both compounds, which corresponds to 0.024 and 0.021 fmol with peak efficiencies of 394000 and 335000 theoretical plates for SDZ arid SMZ, respectively. The calibration graph was linear over three orders of magnitude. The relative standard deviations (n = 12) of peak currents and migration times were 2.3 and 2.7%, and 0.8 and 1.3%, respectively, for the two compounds. The proposed method was applied to the analysis of tablets and human urine samples with satisfactory results.

Electrochemical study of gramicidin D forming ion-permeable channels in the bilayer lipid membranes

Gramicidin within the lipid bilayer matrix is a well-known channel-forming polypeptide, but the mechanism of the ions across the membrane induced by gramicidin is not well understood. We found that at very low concentration of gramicidin in a bilayer lipid membrane, the channel behavior was controlled by the voltage applied across the membrane. When the voltage is higher than 75 mV, the channel is closing, while lower than 75 mV, the channel is opening. But when the concentration of the gramicidin in the BLMs is high, the channel behavior is changed into voltage-independent. (C) 1998 Elsevier Science Ltd. All rights reserved.

Electrochemical probe of hydroxylation of 4-nitrophenol by cytochrome c with hydrogen peroxide

The reaction of hydrogen peroxide with cytochrome c makes them coupled to lead to the hydroxylation of 4-nitrophenol. In situ electrochemical probe was used to detect the hydroxylation of 4-nitrophenol, which can avoid the tedious extraction procedure, the loss of the active species and the interference of some colored substances in the detection of 4-nitrocatechol by spectroscopic method. The hydroxyl radical scavengers mannitol and sodium benzoate did not eliminate hydroxylation, but the inhibitory effect of uric acid on the hydroxylation lead to the formation of the ferryl species of the protein during the reaction. These studies suggest that the electrochemical probe might efficiently detect the trace 4-nitrocatechol from the onset of the hydroxylation reaction and thus provides a more sensitive tool.

The electrochemical behavior of polypyrrole from self-assembly polymerization

The electrochemical behavior and the charge transport of polypyrrole film prepared by self-assembly polymerization have been investigated. Ir is found that the microstructure of the film influences the electrochemical behavior of polypyrrole, and that the p-toluenesulfate (Tos(-)) ion plays avery important role in this system.

A novel electrochemical method for simultaneously measuring diffusion coefficient and ion transference number

This paper introduces a new method to estimate the diffusion coefficient and transference number of a salt or an electroactive ion in a solution with little or no supporting electrolyte. The above two parameters can be obtained from a single potential step experiment without previous knowledge of either one. It would appear that the method could also be used in the study of ion transport in a high viscosity solvent or a solid electrolyte. (C) 1998 Elsevier Science S.A.

The electrochemical behaviour of soluble polyimides

The electrochemical behaviour of five soluble polyimides was studied in organic solution using cyclic voltammetry. The relationship between the electrochemical behaviour and the molecular structure was discussed, It was found that the colours of polyimides can be changed due to the electrochemical redox reactions.

Electrochemical studies of a lanthanide heteropoly tungstate/molybdate complex in polypyrrole film electrode and its electrocatalytic reduction of bromate

An electrode modified with a polybasic lanthanide heteropoly tungstate/molybdate complex K10H3[Nd(SiMo7W4O39)(2)] entrapped into polypyrrole (PPy) film, denoted as Nd(SiMo7W4)(2)-PPy, exhibits three couples of two-electron redox waves in pH 1-5 buffer solutions. The redox waves are surface-controlled at lower scan rates and diffusion-controlled at higher scan rates. The effects of pH on the electrochemical behavior of Nd(SiMo7W4)(2) in PPy film were investigated in detail and compared with that of Nd(SiMo7W4)(2) in aqueous solution. The various charge states of PPy during its redox process have peculiar effects on the relationship between pH and formal potentials of Nd(SiMo7W4)(2)-PPy at different acidities. The Nd(SiMo7W4)(2)-PPy cme can remarkably catalyze the electrochemical reduction of bromate with good stability. (C) 1997 Elsevier Science Ltd.

PP-EPR-PP增容PP/EPT的研究

采用δ－ＴｉＣｌ３－Ｅｔ２ＡｌＣｌ催化合成了三元乙丙嵌段共聚物ＰＰ－ＥＰＲ－ＰＰ，作为乙丙橡胶（ＥＰＴ）增韧聚丙烯（ＰＰ）的增容剂，以改善ＰＰ的低温冲击性能。实验发现，ＰＰ－ＥＰＲ－ＰＰ中ＥＰＲ段较长，有利于提高其增容效果，ＰＰ－ＥＰＲ－ＰＰ的加入量仅为４％，就可以显著的改善ＰＰ和ＥＰＴ相容性，使ＰＰ／ＥＰＴ／ＰＰ－ＥＰＲ－ＰＰ共混物的无缺口冲击强度比相应的ＰＰ／ＥＰＴ在－２０℃时提高４０％，在－４０℃时提高了１２０％，达到较高的耐冲击等级。形态观察表明，ＰＰ－ＥＰＲ－ＰＰ同时又起到了“乳化剂”的作用，使ＥＰＴ在ＰＰ中均匀分散。还提出了ＰＰ－ＥＰＲ－ＰＰ的增容模型，完满地解释了实验结果。