The electrocatalytic oxidation of ascorbic acid on polyaniline film synthesized in the presence of camphorsulfonic acid

Polyaniline-camphorsulfonic acid (PAN-CSA) composite film on platinum electrode surface has been synthesized via the electrochemical polymerization of aniline in the presence of camphorsulfonic acid (CSA). It was found that the doping of polyaniline (PAN) with CSA extends the electroactivity of PAN in neutral and even in alkaline media. The PAN-CSA composite film coated platinum electrodes are shown to be good electrocatalytic surfaces for the oxidation of ascorbic acid (AA) in phosphate buffer solution (PBS) of pH 7.0. The anodic peak potential of AA shifts from 0.63 V at the bare platinum electrode to 0.34 V at the PAN-CSA composite modified platinum electrode with a greatly enhanced current response. A linear calibration graph is obtained over the AA concentration range of 5-50 mM using cyclic voltammetry. The kinetics of the catalytic reaction are investigated using rotating disk electrode voltammetry and chronoamperometry. The results are explained using the theory of electrocatalytic reactions at chemically modified electrodes. The PAN-CSA composite on the electrode surface shows good reproducibility and stability.

Influence of rubber content in ABS in wide range on the mechanical properties and morphology of PC/ABS blends with different composition

A series of acrylonitrile-butadiene-styrene (ABS) with different rubber content were prepared by diluting ABS grafting copolymer containing 60% rubber with a styrene-acrylonitrile copolymer. ABS prepared were blended with bisphenol-A-polycarbonate (PC) at the ratio of 70/30, 50/50, and 30/70 to prepare PC/ABS blends. Influence of rubber content in ABS on the properties of ABS and PC/ABS blends were investigated. PC/ABS blends with different compositions got good toughness when the rubber in ABS increased to the level that ABS itself got good toughness. The tensile properties and processability of PC/ABS blends decreased with the increase of the total rubber content introduced into the blends. ABS with the rubber content of 30 wt% is most suitable to be used to prepare PC/ABS blends. The rubber content in ABS affected the viscosity of ABS, and subsequently the viscosity ratio of PC to ABS. As a result, the morphology of PC/ABS blends varied. The increase of rubber content in ABS results in finer structure of PC/ABS blends.

Competition between band filling and steric effect in ordered double perovskites Sr2-xLaxMnMoO6

The ordered double perovskites, Sr2-xLaxMnMoO6, were prepared by sol-gel reaction. Structural, magnetic, and electrical properties were investigated for a series of ordered double perovskites Sr2-xLaxMnMoO6(0 <= x <= 1). The compounds have a monoclinic structure (space group P2(1)/n) and the cell volume expands monotonically with La doping. The T-C and the magnetic moment rise and the cusp-like transition temperature below which the magnetic frustration occurs shifts to high temperature as x increases. With La doping, electrical resistivity of Sr2-xLaxMnMoO6 decreases only at low doping levels (x <= 0.2); while at high doping levels (0.8 <= x <= 1), electrical resistivity tends to increase greatly. The results suggest that the competition between band filling effect and steric effect coexists in the whole doping range, and the formation of ferrimagnetic interactions is not simply at the expense of antiferromagnetic interactions.

Isothermal and nonisothermal transition kinetics of trans-1,4-polybutadiene

Analysis of the isothermal and nonisothermal transitions of hexagonal crystal formation from the melt (transition 1) and of monoclinic crystal formation from hexagonal crystals (transition 2) for trans-1,4-polybutadiene (TPBD) was carefully carried out by differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). Isothermal transitions I and 2 are described by Avrami exponents (n) of approximate to1, whereas nonisothermal transitions I and 2 are described by n approximate to 4. These different eta values indicate that different crystallization mechanisms took place for different crystallization driving forces under isothermal and nonisothermal crystallization. The Ozawa equation was also used to analyze the nonisothermal crystallization data. For transition I at lower temperature, the Ozawa equation fits the data well; however, at higher temperature, there is an inflection that shifts to lower crystallinity with increasing temperature. Inflections are also observed with the Ozawa analysis for transition 2. Furthermore, the crystallinities at the turning points are almost in the same range as those determined by Avrami analysis for nonisothermal transitions I and 2, which suggests that the Ozawa analysis inflections are due to secondary crystallization. However, TEM revealed no morphology discrepancy between the TPBD hexagonal crystals formed from melt by isothermal and nonisothermal crystallization.

The optical spectroscopic properties of rare earth-activated barium orthophosphate in VUV-Vis range

The optical properties of rare earth ions-activated barium orthophosphate phosphors, Ba-3(PO4)(2):RE (RE = Ce3+, Sm3+, Eu3+, Eu2+, and Tb3+), were investigated in vacuum ultraviolet (VLTV)-Vis range. A band-band transition Of PO43- in Ba-3(PO4)(2) is observed in the region of 150-170 nm. The partial reduction of Eu3+ to Eu2+ was observed and confirmed by luminescent spectra under the VUV-UV excitation. It is proposed that the electronegative defects that formed by aliovalent substitution of Eu3+ on the Ba2+ site in the host are responsible for the reduction process.

Bonding and Mossbauer isomer shifts in (Tl, Pb)-1223 cuprate

By using the clinical bond theory of dielectric description, the chemical bond parameters of (Tl.Pb) - 1223 was calculated. The results show that the Sr-O, Tl-O, and Ca-O types of bond have higher ionic character and the Cu-O types of bond have more covalent, character. Mossbauer isomer shifts of Fe-57 and Sn-119 doped in (Tl, Pb) -1223 were calculated by using the chemical environmental factor, h, defined by covalency and electronic polarizability. Four valence state tin and three valence iron sites were identified ill Fe-57, and Sn-119 doped (Tl, Pb) -1223 superconductor. We conclude that all of' the Fe atoms substitute the Cu at square planar Cu (H site, whereas Sn prefers to Substitute the square pyramidal Cu (2) site.

Investigation of covalency and spectrum shifts in 3d transition-metal compounds

By using a correction factor of d electron effects on bond, PV theory is applied to the calculation of chemical bond;parameters of d transition-metal compounds. Racah parameters and Mossbauer isomer shifts are calculated, and the results are agreement with the experimental values.

Oxidation of ascorbic acid by rutin at a glassy carbon electrode modified with lipid films

A stable film was prepared by casting dipalmitoylphosphatidylcholine (DPPC) and rutin onto the surface of a glassy carbon (GC) electrode. The electrochemistry behavior of rutin in the DPPC film was investigated. The modified electrode coated with rutin shows a quasi-reversible reduction-oxidation peak on the cyclic voltammogram in phosphate buffer (pH 7.4). This model of biological membrane was not only used to provide biological environment but also to investigate the oxidation of ascorbic acid by rutin. The DPPC-rutin modified electrode behaves as electrocatalytic oxidation to ascorbic acid. The oxidation peak current of ascorbic acid increases drastically and the peak potential of 4 x 10(-4) mol L-1 ascorbic acid shifts negatively about 100 mV compared with that obtained at a bare glassy carbon electrode. The catalytic current increased linearly with the ascorbic acid concentration in the range of 2 x 10(-4) mol L-1 and 1.4 x 10(-3) mol L-1 at a scan rate of 50 mV s(-1).

Prediction of C-13-nuclear magnetic resonance chemical shifts for aliphatic amines

Prediction of C-13-nuclear magnetic resonance chemical shifts for aliphatic amines is performed. The topological, geological and electronic descriptors are generated. To reduce the variables, the best subsets of the descriptors are obtained by using leaps-and-bounds regression analysis. The model is achieved using multiple regression with satisfactory results.

In-situ FTIR study on adsorption and oxidation of native and thermally denatured calf thymus DNA at glassy carbon electrodes

In-situ Fourier transform infra-red (FTIR) spectra of native and thermally denatured calf thymus DNA (CT DNA) adsorbed and/or oxidized at a glassy carbon (GC) electrode surface are reported. The adsorption of native DNA occurs throughout the potential range (-0.2 similar to 1.3 V) studied, and the adsorbing state of DNA at electrode surface is changed from through the C=O band of bases and pyrimidine rings to through the C=O of cytosine and imidazole rings while the potential shifts negatively from 1.3 V to -0.2 V. An in-situ FTIR spectrum of native CT DNA adsorbed at GC electrode surface is similar to that of the dissolved DNA, indicating that the structure of CT DNA is not distorted while it is adsorbed at the GC electrode surface. In the potential range of -0.2 similar to 1.30 V, the temperature-denatured CT DNA is adsorbed at the electrode surface first, then undergoes electrochemical oxidation reaction and following that, diffuses away from the electrode surface. (C) 2001 Elsevier Science B.V. All rights reserved.

Isotope effect in proton-transfer and association-dissociation reactions for butylamine by ultrasonic relaxation methods

Ultrasonic absorption coefficients were measured for butylamine in heavy water (D2O) in the frequency range from 0.8 to 220 MHz and at concentrations from 0.0278 to 2.5170 mol dm(-3) at 25 degrees C; two kinds of relaxation processes were observed. One was found in relatively dilute solutions (up to 0.5 mol dm(-3)), which was attributed to the hydrolysis of butylamine. In order to compare the results, absorption measurements were also carried out in light water (H2O). The rate and thermodynamic parameters were determined from the concentration dependence of the relaxation frequency and the maximum absorption per wavelength. The isotope effects on the diffusion-controlled reaction were estimated and the stability of the intermediate of the hydrolysis was considered while comparing it with the results for propylamine in H2O and D2O. Another relaxation process was observed at concentrations greater than 1 mol dm(-3) in D2O. In order to examine the solution characteristics, proton NMR measurements for butylamine were also carried out in D2O. The chemical shifts for the gamma- and delta-proton in butylamine molecule indicate the existence of an aggregate. From profiles of the concentration dependence of the relaxation frequency and the maximum absorption per wavelength of sound absorption, the source of the relaxation was attributed to an association-dissociation reaction, perhaps, associated with a hydrophobic interaction. The aggregation number, the forward and reverse rate constants and the standard volume change of the reaction were determined. It was concluded from a comparison with the results in H2O that the hydrophobic interaction of butylamine in D2O is stronger than that in H2O. Also, the isotope effect on this reaction was interpreted in terms of the solvent structure.

PC/ABS BLENDS:COMPATIBILIZATION AND MECHANICAL-BEHAVIOR

PC/ABS(M) blends, encompassing the whole composition range between pure PC and ABS(M), were prepared by melt-mixing in a Brabender-like apparatus. Thermal, mechanical and impact tests were performed on compression moulded specimens. Inward Tg shifts were

BLENDS OF POLY[3,3-BIS(CHLOROMETHYL)OXETANE] WITH POLY(VINYL ACETATE) .1. THERMAL AND MECHANICAL-PROPERTIES

Blends of poly[3,3-bis(chloromethyl)oxetane] (Penton) with poly(vinyl acetate) were prepared. Compatibility, morphology, thermal behavior, and mechanical properties of blends with various compositions were studied using differential scanning calorimetry (DSC), dynamic mechanical measurements (DMA), tensile tests, and scanning electron microscopy (SEM). DMA study showed that the blends have two glass transition temperatures (T(g)). The T(g) of the PVAc rich phase shifts significantly to lower temperatures with increasing Penton content, suggesting that a considerable amount of Penton dissolves in the PVAc rich phase, but that the Penton rich phase contains little PVAc. The Penton/PVAc blends are partially compatible. DSC results suggest that PVAc can act as a beta-nucleator for Penton in the blend. Marked negative deviations from simple additivity were observed for the tensile strength at break over the entire composition range. The Young's modulus curve appeared to be S-shaped, implying that the blends are heterogeneous and have a two-phase structure. This was confirmed by SEM observations.

大气季节内振荡对东亚夏季风活动的影响研究

利用ERA40逐日再分析资料、NCEP/NCAR2逐日再分析资料、中国740个测站日降水资料、上海台风研究所提供的西太平洋热带气旋资料、Kaplan等重建的月平均SSTA资料、NOAA逐日长波辐射（OLR）等资料，应用离散功率谱分析、带通滤波、EOF分析等统计方法，研究了东亚夏季风(EASM）的移动特征、东亚地区季节内振荡(ISO)的基本特征、季节内振荡对东亚夏季风活动的影响、季节内振荡对东亚夏季风异常活动的影响机理。主要结论如下： （1）综合动力和热力因素定义了可动态描述东亚夏季风移动和强度的指数，并利用该指数研究了东亚夏季风的爆发和移动的季节内变化及其年际和年代际变化特征。研究发现，气候平均东亚夏季风前沿分别在28候、33候、36候、38候、40候、44候出现了明显的跳跃。东亚夏季风活动具有显著的年际变率，主要由于季风前沿在某些区域异常停滞和突然跨越北跳或南撤引起，造成中国东部旱涝灾害频繁发生。东亚夏季风的活动具有明显的年代际变化，在1965年、1980年、1994年发生了突变，造成中国东部降水由“南旱北涝”向“南涝北旱”的转变。 （2）东亚季风区季节内变化具有10~25d和30~60d两个波段的季节内振荡周期，以30-60d为主。存在三个主要低频模态，第一模态主要表征了EASM在长江中下游和华北地区活动期间的低频形势；第二模态印度洋-菲律宾由低频气旋式环流控制，主要表现了ISO在EASM爆发期间的低频形势；第三模态主要出现在EASM在华南和淮河活动期间的低频形势。第一模态和第三模态是代表东亚夏季风活动异常的主要低频形势。 （3）热带和副热带地区ISO总是沿垂直切变风的垂直方向传播。因此，在南海-菲律宾东北风垂直切变和副热带西太平洋北风垂直切变下，大气热源激发菲律宾附近交替出现的低频气旋和低频反气旋不断向西北传播，副热带西太平洋ISO以向西传播为主。中高纬度地区，乌拉尔山附近ISO以向东、向南移动或局地振荡为主；北太平洋中部ISO在某些情况下向南、向西传播。 （4）季风爆发期，伴随着热带东印度洋到菲律宾一系列低频气旋和低频反气旋， 冷空气向南输送，10~25天和30~60天季节内振荡低频气旋同时传入南海加快了南海夏季风的爆发。在气候态下，ISO活动表现的欧亚- 太平洋（EAP）以及太平洋-北美（PNA）低频波列分布特征(本文提出的EAP和PNA低频波列与传统意义上的二维定点相关得到的波列不同)。这种低频分布形式使得欧亚和太平洋中高纬度的槽、脊及太平洋副热带高压稳定、加强，东亚地区的低频波列则成为热带和中高纬度ISO相互作用影响东亚夏季风活动的纽带。不同的阶段表现不同的低频模态，30~60d低频模态的转变加快了EASM推进过程中跳跃性；30-60d低频模态的维持使得EASM前沿相对停滞。 （5）30-60d滤波场，菲律宾海域交替出现的低频气旋和低频反气旋不断向西北传播到南海-西太平洋一带。当南海-西太平洋地区低频气旋活跃时，季风槽加强、东伸，季风槽内热带气旋（TC）频数增加；当南海-西太平洋低频反气旋活跃时，季风槽减弱、西退，TC处于间歇期，生成位置不集中。 （6）在El Nino态下，大气季节内振荡偏弱，北传特征不明显，但ISO由中高纬度北太平洋中部向南和副热带西太平洋向西的传播特征显著，东亚地区ISO活动以第三模态为主，EASM集中停滞在华南和淮河流域，常伴随着持续性区域暴雨的出现，易造成华南和江淮流域洪涝灾害，长江和华北持续干旱。在La Nina态下，大气季节内振荡活跃，且具有明显的向北传播特征，PNA低频波列显著，东亚地区ISO活动以第一模态单峰为主；EASM主要停滞在长江中下游和华北地区，这些地区出现异常持续强降水，华南和淮河流域多干旱；在El Nino态向La Nina态转换期，ISO活动以第一模态双峰为主，长江中下游常常出现二度梅。