Fabrication of nanometer-sized electrodes and tips for scanning electrochemical microscopy

A novel method for fabrication of nanometer-sized electrodes and tips suitable for scanning electrochemical microscopy (SECM) is reported. A fine etched Pt wire is coated with polyimide, which was produced by polymerization on the Pt surface initiated by heat. This method can prepare electrodes with effective radii varying from a few to hundreds of nanometers. Scanning electron microscopy, cyclic voltammetry, and SECM were used to characterize these electrodes. Well-defined steady-state voltammograms could be obtained in aqueous or in 1,2-dichloroethane solutions. Ibis method produced the nanoelectrodes with exposed Pit on the apex, and they can also be employed as the nanotips for SECM investigations. Different sizes of Pt nanotips made by this method were employed to evaluate the kinetics of the redox reaction of Ru(NH3)6(3+) on the surface of a large Pt electrode by SECM, and the standard rate constant kappa (o) of this system was calculated from the best fit of the SECM approach curve. This result is similar to the values obtained by analysis of the obtained voltammetric data.

Studies of the ortho effect in fragmentations of acetyl ion adducts of disubstituted benzenes

The ion-molecule reactions of disubstituted benzenes under chemical ionization conditions with acetyl chloride as reagent gas were examined, and the fragmentation reactions of the adduct ions (mostly proton and acetyl ion adducts) were studied by collision-induced dissociation. Electron-releasing substituents favored the adduct reactions, and electron-withdrawing groups did not. The position and properties of substituting groups had an effect on the relative abundances of the adduct ions. Several examples of the ortho effect were observed. The fragmentation reaction of the adduct ions formed by ortho-benzenediamine with the acetyl ion was similar to the reductive alkylation reaction of amines in the condensed phase. Copyright (C) 2001 John Wiley & Sons, Ltd.

Synthesis and characterization of polynuclear half-sandwich lanthanoid complexes [Na(THF)(6)](2)[(Cp6Sm6Se13)-Sm-t] and [Li(LHF4](2)[Cp6Nd6Se13]

The half-sandwich tert-butyl cyclopentadienyl lanthanoid complexes {[Cp ' Ln(THF)](2)(mu (2)-Cl)(2)(mu (3)-Cl)(3)Na(THF)}(n) [Cp ' = eta (5)-' BuC5H4; Ln = Nd (1a), Sm (1b), Gd (1c), Yb (1d)] are prepared by the reaction of anhydrous lanthanoid trichloride, LnCl(3), with NaCp ' in THF solution. Complex 1b reacts with Na2Se5 to give hexanuclear samarium polyselenide complexes [Na(THF)(6)](2)[Cp-6' SM6(mu (6)-Se)(mu -Se-2)(6)] (2). An analogous cyclopentadienyl neodymium polyselenide complex [Li(THF)(4)](2)[Cp6Nd6(mu (6)-Se)(mu -Se-2)(6)] (3) is synthesized by the reaction of [CpNdCl2. 2LiCl . 5THF] with Na2Se5 in THF solution. The molecular structures of 1a and 2 were determined by X-ray crystal structure analysis. Complex 2 contains an interstitial selenium atom which is coordinated with six samarium atoms. (C) 2001 Elsevier Science BN. All rights reserved.

Reactive reinforcement of the interface of high performance polymer blends by PMR-POI

The effect of PMR-polyimide(POI) as the interfacial agent on the interface characteristics, morphology features and crystallization of poly (ether sulfone) /poly (phenylene sulfide) (PES/PPS) and poly(ether ether ketone)/poly (ether sulfone) (PEEK/PES) partly miscible blends were investigated by means of the scanning electron microscopy, WAXD and XPS surface analysis. It is found that the interfacial adhesion was enhanced remarkably, the size of the dispersed phase particles was reduced significantly and the miscibility was improved by the addition of POI. During melt blending cross-link and/or grafting reaction of POI with PES, PEEK and PPS homopolymers was detected, however the reaction activity of POI with PPS was much higher than that of PES and PEEK. It was also found that POI was an effective nucleation agent of the crystallization of PPS.

Formation of mesophase mono-domains and micro-structures in thin films of a series of copolyethers containing both odd-numbered methylene units

The structural and morphological evolution of mono-domains in thin films has been investigated for a series of liquid crystalline (LC) copolyethers. The copolyethers studied were synthesized by the reaction of 1-(4-hydroxy-4 ' -biphenylyl)-2-(4-hydroxyl-phenyl)propane (TPP) with 1,7-dibromoheptane and 1,11-undecane at different compositions (coTPPs-7/11). In contrast to the solution-cast thin films without annealing, which exhibit the isotropic homogeneous molecular orientation, mono-domains with a homeotropic alignment were found in coTPP-7/11(5/5) after the thin films were annealed in the high-temperature columnar phase (Phi '). Similar to the nucleation process in polymer crystallization, transmission electron microscopic observations show that small mono-domains appear in the initial stage of annealing, where molecules form a uniaxial in-plane chain orientation. With increasing annealing time, the molecular orientation gradually became tilted with respect to the substrate surface, and finally, a uniaxial homeotropic molecular orientation was achieved after a prolonged annealing time. The lateral size of mono-domains was found to increase continuously with annealing time and grew into a circular shape, indicating an isotropic lateral growth scheme which implies a hexagonal molecular packing proved by the electron diffraction experiments.

Synthesis and crystal structure of [Nd(eta(6)-1,3,5-C6H3Me3)(AlCl4)(3)]( C6H6) and structural comparison of Ln(eta(6)-arene)(AlCl4)(3)

Reaction of NdCl3, with AlCl3 and mesitylene in benzene gives complex [Nd(eta (6)-1,3,5-C6H3Me3) (AlCl4)(3)] (C6H6) (1) which was characterized by elemental analysis, IR spectra, MS and X-lay diffractions. The X-ray determination indicates that 1 has a distorted pentagonal bipyramidal geometry and crystallizes in the monoclinic, space group P2(1)/n with a = 0.9586(2), b = 1.1717(5), c = 2.8966(7) nm, beta = 90.85 (2)degrees, V = 3.2529(6) nm(3), D-c = 1.573 g/cm(3), Z = 4. A comparison of bond parameters for all the reported Ln(eta (6)-Ar) (AlCl4)(3) complexes indicates that the bond distance of Ln-C is shortened with the increasing of methyl group on benzene and with the decreasing of radius of lanthanide ions.

Study on a series of main-chain liquid-crystalline ionomers containing sulfonate groups

A series of main-chain Liquid-crystalline ionomers containing sulfonate groups pendant on the polymer backbone were synthesized by an interfacial condensation reaction of 4,4'-dihydroxy-alpha,alpha'-dimethyl benzalazine, a mesogenic monomer, with brilliant yellow (BY), a sulfonate-containing monomer, and a 1/9 mixture of terephthaloyl and sebacoyl dichloride. The structures of the polymers were characterized by LR and UV spectroscopies. DSC and thermogravimetric analysis were used to measure the thermal properties of those polymers, and the mesogenic properties were characterized by a polarized optical microscope, DSC, and wide-angle X-ray diffraction. The ionomers were thermally stable to about 310 degreesC. They were thermotropic liquid-crystalline polymers (LCPs) with high mesomorphic-phase transition temperatures and exhibited broad nematic mesogenic regions of 160-170 degreesC, and they were lyotropic LCPs with willowy leaf-shaped textures in sulfuric acid. However, the thermotropic liquid-crystalline properties were somewhat weakened because the concentration of BY was more than 8%. The inherent viscosity in N-methyl-2-pyrrolidone suggested that intramolecular associations of sulfonate groups occurred at low concentration, and intermolecular associations predominated at higher concentration. (C) 2001 John Wiley & Sons, Inc.

Synthesis and structure of a novel mononuclear tungsten (VI) citrato complex, (NH4)(3)[Li(H2O)(3)WO3(C6H4O7)]

The first mononuclear tungsten-citrato complex, (NH4)(3)[Li(H2O)(3)WO3(C6H4O7)] (1) has been prepared by the reaction of ammonium tetrathio tungstate and lithium citrate in CH3OH - H2O solution at pH 8.2. There are two crystallographically independent anions in the asymmetric crystallographic unit. The crystal structure of the title compound (triclinic, space group P (1) over bar, a = 6.901(1), b = 15.136(3), c = 16.107(3) Angstrom, alpha = 75.85(3), beta = 89.89(3), gamma = 89.97(3), V = 1631.4(6) Angstrom (3), R = 0.068, R-w = 0.1674 for 3878 reflections with I > 2 sigma (1)), reveals that in the compound a tungsten atom is coordinated to a fully deprotonated citrate as a tridentate ligand and three terminal oxygen atoms to form a distorted coordination octahedron.

Synthesis, crystal structure and reactivity of (2,4-C7H11)(2)Yb center dot DME

(2,4-C7H11)(2)Yb . DME was synthesized by the reaction of YbCl3 with K(2,4-C7H11)(2,4-dimethylpentadienyl potassium), and the single crystal X-ray diffraction showed that the complex exists in a cis- staggered conformation. Thf crystal of the compound belongs to the monoclinic space group P2(1)/n with a = 0.675 2 (1) nm, b = 1.490 6 (1) nm, c = 1.529 3 (2) nm, beta = 97.55 (2)degrees, V = 1.977 79 (4) nm(3), Z = 4, F(000) = 735.8 e, mu = 49.49 cm(-1), R = 0.033 and R-w = 0.032. The title complex can be used as a catalyst for the polymerization of methyl methacrylate (MMA).

Synthesis and crystal structure of a novel amino-acid-containing polyoxometalate: K-6[Cu (Ala)(2) (H2O)(2)](2)[ CU4 (H2O)(2) (AsW9O34)(2)] center dot 16H(2)O

The novel amino-acid-containing polyoxometalate Ka(6) [Cu(Ala)(2) (H2O)(2)](2) [Cu-4 (H2O)(2) . (AsW9O34)(2)] . 16H(2)O was synthesized from the reaction of K-10[Cu-4(H2O)(2)(AsW9O34)(2)] . 20H(2)O with beta -alanine, Its structure has been determined by single crystal X-ray diffraction. It crystallizes in the triclinic space group P (1) over bar, with a=1. 196 3(2) nm, b=1. 536 5(3) nm, c=1. 591 4(3) nm, alpha =93. 97(3)degrees, beta= 110. 88(3)degrees, gamma =101. 07(3)degrees, V=2. 651 8(9) nm(3) and Z=1. Least-squares refinement of the structure leads to R and R-w factors of 0. 067 3 and 0. 162 8, respectively. An unusual structural feature of the compound is that the polyanion [Cu-4(H2O)(2) (AsW9O34)](10-) is linked with the amino-acid complex of Cu2+ by a mu -oxygen atom.

The electrochemically induced conformational transition of disulfides in bovine serum albumin studied by thin layer circular dichroism spectroelectrochemistry

The conformational transition of disulfides in bovine serum albumin (BSA) induced by electrochemical redox reaction of disulfides were monitored by in-situ circular dichroism (CD) spectroelectrochemistry, with a long optical path thin layer cell and analyzed by a singular value decomposition least square (SVDLS) method. Electrochemical reduction of disulfides drives the left-handed conformation of disulfides changed into the right-handed. At open circuit, eight of the 17 disulfides were of left-handed conformation. Four of the 17 disulfides took part in the electrochemical reduction with an EC mechanism. Only one-fourth of the reduced disulfides returned to left-handed conformation in the re-oxidation process. Some parameters of the electrochemical reduction process, i.e. the number of electrons transferred and electron transfer coefficient, n=8, alphan=0.15, apparent formal potential, E-1(0') = -0.65(+/-0.01) V, standard heterogeneous electron transfer rate constant, k(1)(0) = (2.84 +/- 0.14)x 10(-5) cm s(-1) and chemical reaction equilibrium constant, K-c=(5.13 +/- 0.12) x 10(-2), were also obtained by double logarithmic analysis based on the near-UV absorption spectra with applied potentials. (C) 2001 Elsevier Science B.V. All rights reserved.

Syntheses and crystal structures of novel di- and trinuclear rhodium complexes bridged by pyrazine

Never di- and trinuclear Rh complexes, [Rh-2(PPh3)(4)(H)(4)(Me2CO)(2)(mu -pyz)](ClO4)(2). EtOH and [Rh-3(PPh3),(mu -pyz)(3)](ClO4)(3). EtOH were selectively isolated from the reaction of [Rh(PPh3)(2)(H)(2)(Me2Co)(EtOH)]ClO4 with pyrazine (pyz) in Me2CO and THF, respectively. Their structures were crystallographically characterized.

Efforts to decrease crosslinking extent of polyethylene in a reactive extrusion grafting process

Grafting of acrylic acid and glycidyl methacrylate onto low density polyethylene (LDPE) was performed by using a corotating twin-screw extruder. The effects of residence time and concentration of initiator and monomers on degree of grafting and gel content of grafting LDPE were studied systematically. Paraffin, styrene, p-benzoquinone, triphenyl phosphite, tetrachloromethane, and oleic acid were added to try to decrease the extent of crosslinking of LDPE. 4-hydroxyl-2,2,6,6-tetramethyl-1-piperidinyloxy (4-hydroxyl-TEMPO) and dipentamethylenethiuram tetrasulfide were also tried to inhibit crosslinking reaction of LDPE during its extruding grafting process. It was found that p-benzoquinone, triphenyl phosphite and tetrachloromethane were good inhibitors for crosslinking of LDPE. (C) 2000 John Wiley & Sons, Inc.

Fragmentation reactions of adduct ions [M+CH3CO](+) of isomeric phenylenediamines

The dissociation routes of the adduct ions [M+CH3CO](+) formed by ion-molecule reaction of isomeric phenylenediamines with acetyl ion from acetone under chemical ionization condition were investigated by using collision-induced dissociation (CID) technique performed at ion kinetic energies of 40eV. The adduct ions are intermediate ion-neutral complexes.

Catalytic reduction of NO, by CO on hydrotalcites-derived mixed oxides CoAlM and MgAlM (M = Cr, Mn, Fe, Co, Ni, Cu)

Two series of mixed oxides, CoAlM and MgAlM (M = Cr, Mn, Fe, Co, Ni, Cu), were prepared by calcining their corresponding hydrotalcite-like compounds (HTLc). The ratio of Mg: Al: M (or Co: Al: hi) was 3:1:1. The catalytic activity of all samples for the reaction of NO + CO was investigated. The results showed that the activity of CoAlM was much higher than that of MgAlM. The structure and the property of redox were characterized by XRD and H-2-TPR. The results indicated that only MgO phase was observed after calcining MgAlM hydrotalcites, and the transition metals became more stable. The spinel-like phase appeared in all of CoAlM samples after the calcination, and the transition metals were changed to be more active, and easily reduced. The activities of three series of mixed oxides CoAlCu obtained from different preparation methods, different ratio of Co:Al: Cu and at different calcination temperatures, were studied in detail for proposing the mechanism of reaction. The ability of adsorption of NO and CO were investigated respectively for supporting the mechanism.