Measurement of dioxygen by electrocatalytic reduction on microelectrodes modified with Nafion and methyl viologen

Nafion/methyl viologen (MV) has been chemically modified on a gold disk microelectrode (GDME). The electrochemistry of the Nafion/MV modified GDME is investigated by cyclic voltammetry (CV). Linear sweep voltammetry (LSV) and differential pulse amperometry (DPA) show that the Nafion/MV modified GDME exhibits very high electrocatalytic activity toward dioxygen reduction with good reproducibility and high sensitivity. The electrocatalytic peak current is found to be linear with the dioxygen concentration in the range of 3.44x10(-7) to 2.59x10(-4) mol l(-1) (at 25 degrees C), with a correlation coefficient of 0.9978. The detection limit (signal/noise=3) is calculated to be 0.19 mumol l(-1). The response time of the microsensor for dioxygen measurement is less than 15 s. For ten parallel measurements for 8.50 mumol l(-1) dioxygen, the relative standard deviation (RSD) is found to be 2.7%. The sensitivity of the microsensor is 0.17 nA mumol(-1) l(-1). This microsensor has been successfully employed to measure the concentration of dioxygen in real samples. The quantity of dioxygen, released from the three kinds of chloroplasts of plant leaves under different illumination, is monitored by the Nafion/MV modified gold microsensor. In order to survey the dioxygen concentration in vivo, a Nafion/MV modified carbon fiber microelectrode (CFME) is fabricated by a modification procedure similar to that of the Nafion/MV GDME. As a preliminary test, the dioxygen levels in the different areas of rat brain are determined by the Nafion/MV modified carbon fiber microsensors. The mechanism of the catalytic reaction is also addressed.     

The role of rigid unit modes in negative thermal expansion

The rigid unit mode (RUM) model provides a valuable computational method to investigate correlations of transverse thermal motions of atoms important in negative thermal expansion (NTE) materials. We report here detailed RUM calculations of ten framework oxide structures that have been studied for their negative (or ultra low) thermal expansion properties. The results negate any simple and direct correlation between presence or absence of RUMs in a structure and its NTE property. All the structures considered can be viewed as networks of polyhedral connected by corners only. All evidence supports the importance the transverse motion of the atoms at the corners, but NTE does not correlate well with the presence RUMs for the polyhedra.     

DRY METHOD SYNTHESIS OF PURE SILICEOUS FORM OF ZEOLITE ZSM-35

IntroductionZeoliteZSM-35isclassifiedasfcrricritc(FER)t\pc.x'hicllalsoincludesZSM-ZI.ZSM-38andFER.Zeolitesofthist}'pcha\lcrclatit'CI}UlldiscrinlinablcXRDpattcnlswhichindicatetheirsinlilarit\'illst,u.tu,.,I11.Thehighsiliceousfonllsofthesezeolitesarcgcllcra…     

Oxidation of Styrene with Molecular Oxygen in Supercritical CO2

The oxidation of styrene with molecular oxygen catalyzed by PdCl2 CuCl2 has been investigated in supercritical CO2 with a batch reactor. The oxidative system of styrene contains four components at the beginning and seven components during the reaction. The critical temperature, critical pressure, and critical density at different conversions are determined by using a high-pressure view cell. The effect of phase behavior on the conversion and selectivity were studied. Experimental results showed that the critical parameters of the reaction mixture at fixed initial molar ratio changed with the conversion of reactant. The conversion of styrene reached maximum near the critical density of the reaction mixture. Product selectivity also varied with density of reaction mixture and could be tuned to some degree.     

Laser irradiation induced spectral evolution of the Laser irradiation induced spectral evolution of the surface-enhanced Raman scattering(SERS)of 4-tert-butylbenzylmercaptan on gold nanoparticles assembly

The spectral evolution of the surface-enhanced Raman scattering (SERS) of 4-tert-butylbenzylmer-captan(4-tBBM)on gold nanopanlcles assembly under laser irradiation is reported.The reIative intensities of typical peaks in the spectrum of 4-tBBM gradually change with irradiation time.Comparison of the rate of spectral changes under several experimental conditions indicates that the surface plasmon resonance(SPR)induced heat in the gold nanoparticles assembly is the origin of the spectraI evolution.During the process of self-assembly,4-tBBM molecules do not form a compact ordered monolayer because of the spatial hindrance of the 4-tert-butyl end group.The heat induced by laser irradiation drives the 4-tBBM molecules to rearrange to a more stable orientation.     

Synthesis of symmetrical 1,5-bis-thio-substituted anthraquinones for cytotoxicity in cultured tumor cells and lipid peroxidation

The synthesis of a series of anthraquinone moieties bearing symmetrical sulfur-linked substituents in the 1 and 5 positions is described. These compounds were evaluated for their ability to inhibit the growth of suspended rat glioma C6 cells and human hepatoma G2 cells, respectively. In addition, the redox property of the compounds was determined based on the inhibition of lipid peroxidation in model membranes. Compounds 2a and 2h in this series compared favorably and exhibited the most potent cytotoxicity (0.02, 0.05 microM) against C6 cells in the XTT colorimetric assay. As far as redox properties are concerned, all bis-thio-anthraquinones show potential lipid peroxidation in model membranes very close to that of mitoxantrone (MX), and 2a, 2d, 2e, 2i, 2j, and 2k have more potential than that of MX. The lack of cytotoxicity of compound 2i cannot be related to lipid peroxidation, but the steric and electronic properties of the side-chain substituent maybe impair effective recognition of the cleavable complex. In contrast to MX, 2a and 2h are cytotoxic in rat glioma C6 cells and do not enhance lipid peroxidation in model membranes.     

金属铜升温熔化过程的分子动力学模拟

采用分子动力学方法模拟了金属铜的升温熔化过程.原子间作用势采用FS (Finnis-Sinclair)势，结构分析采用双体分布函数(PCF)、均方位移(MSD)等方法.计算结果表明,在连续升温过程中，金属铜在1444 K熔化，在该熔化点的扩散系数为4.31×10－9 m2•s－1.上述结论与实验值相当接近，并且比之采用EAM镶嵌原子势所作模拟得到的结果更佳，说明FS势可以用来处理象液铜这样较复杂的无序体系.本文指出了升温速率在金属熔化过程中所起的作用.     

Structure and Two-photon Excited Blue Fluorescence of an Asymmetrical Substituted Stilbene

In common fluorescence process, molecular excitation is caused by the absorption of at least a single photon with shorter wavelength. When certain laser is used as the pump source, some compounds can be excited by simultaneous absorption of at least two photons and then the emission of up-converted fluorescence may occur. This process is called two-photon excited fluorescence (TPEF)1,2. Because of several advantages of TPEF, including intrinsic high three-dimensional resolution and the p…     

A general method for the preparation of 4- and 6-azaindoles

Nitropyridines reacted with an excess of vinyl Grignard reagent to produce 4- or 6-azaindoles. Improved yields were obtained when a halogen atom was present at the position alpha to the nitrogen atom in the pyridine ring.     

242-260nm波长区CS2分子的多光子解离电离

在242－260nm波氏范围通过CS2分子的共振增强多光子电离（REMPI）获得了母体离子CS和碎片离子的分质量激发谱．在λ＜246.4nm区间，CS激发谱上呈现出来源于CS2双光子电离的弥散谱带,碎片离子激发谱的归属强烈提示多光子过程中有中性基电子态的CS和S（经由CS2的光解离）产生：（1）CS 的谱带主要来源于中性CS碎片经由单光子跃迁产生的（1＋1）共振增强电离，（2）除了部分S 的谱峰来自CS 的光解外，多数S 的锐谱峰来自中性S原子经由3p3（2D0）4p，3p3（4S0）np（n＝6，7，8）←3p43pJ（J＝2，1,0）双光子跃迁产生的（2＋1）共振增强电离．