Electrochemical behavior of alpha-Keggin-type nanoparticles, Co(en)(3)(PMo12O40), in polyethylene glycol

The electrochemical behavior of alpha-Keggin-type nanoparticles, Co(en)(3)(PMo12O40) (abbreviated as PMo12-Co), have been studied in poly(ethylene glycol) for four different molecular weights (PEG, average MW 400, 600, 1000, and 2000 g mol(-1)) and containing LiClO4 (O/Li=100/1) supporting electrolyte. The diffusion coefficients of the PMo12-Co nanoparticles were determined using a microelectrode by chronoamperometry for PEG of different molecular weights that were used to describe the diffusion behavior of PMo12-Co nanoparticles in different phase states. Moreover, the conductivity of the composite system increases upon addition of PMo12-Co nanoparticles, which was measured by an a.c. impedance technique. FT-IR spectra and DSC were used to follow the interactions of PEG-LiClO4-PMo12-Co, and well described the reason that the PMo12-Co nanoparticles could promote the conductivity of the PEG-LiClO4-PMo12-Co system.

Hydrothermal and solvothermal synthesis of the complex fluoride alpha '-SrAlF5

The complex fluoride alpha'-SrAlF5 has been synthesized through hydrothermal and solvothermal methods under mild conditions. The effects of the molar ratio of starting materials, temperature, reaction time and solvents on the synthesis of alpha'-SrAlF5 were discussed. The final products were characterized by XRD and SEM. The rod-like shape of alpha'-SrAlF5 is shown in SEM images.

Synthesis of 2-benzylthio-5-phenyl-3,4-disubstituted thiophenes by intramolecular condensation of alpha-oxo ketene dibenzylthioacetals

A facile route to 2-benzylthio-5-phenyl-3,4-disubstituted thiophenes was described. Catalyzed by sodium hydroxide, the title compounds were synthesized in moderate to good yields simply from the intramolecular aldol type condensation of alpha-oxo ketene dibenzylthioacetals. The chemical selectivity for this annulation reaction was studied and discussed.

Iododecarboxylation of alpha-carboxylate, alpha-cinnamoyl ketene cyclic dithioacetals

The iododecarboxylation reaction of alpha-carboxylate, alpha-cinnamoyl ketene cyclic dithioacetals 2 was successfully performed with iodine as halogenation reagent and in water insensitive media. This reaction provides a mild and efficient method for the preparation of alpha-iodo, alpha-cinnamoyl ketene cyclic dithioacetals 3 which are important kinds of potential new intermediates to be valued.

Synthesis and crystal structure of the dimeric, Ti-O-Ti bridged hydrid form polyoxoanion [alpha-1, 2-PW10Ti2O39](2)(10-)

The reaction of trivacant precursor Nag [A-PW9O34] . 19H(2)O with Ti(SO4)(2) affords the novel dimeric, di-Ti-IV-substituted tungstophosphate K4Na6[alpha-1,2-PW10Ti2O39](2) . 14H(2)O. The X-ray structural determination shows the dimeric, anhydride structure was formed by two Ti-O-Ti bonds linking two di-titanium-substituted Keggin anion [alpha-1,2-PW10Ti2O40]. It was also characterized by elemental analysis, TGA, FT-IR and U-V-vis spectroscopies.

First synthesis of single and mixed alpha-oxo ketene dithioacetals from active methenyl precursors

beta-Dioxodithioate were produced easily from active methenyl precursors, carbondisulfide and RX with potassium carbonate as base. By a selective basic assistant cleavage of a carbon-carbon bond at the beta-dicarbonyl unit of beta-dioxodithioate and the subsequent alkylation with RX/R'X in situ, single or mixed alpha-oxo ketene dithioacetals were, obtained in good yields.

Sol-gel derived carbon ceramic electrode containing methylene blue-intercalted alpha-zirconium phosphate micro particles

Methylene blue-intercalated a-zirconium phosphate (MBZrP) micro particles in deionized water were deposited onto the surface of graphite powder to prepare graphite powder-supported MBZrP, which was subsequently dispersed into methyltrimethoxysilane-derived gels to yield a conductive composite. The composite was used as electrode material to fabricate a surface-renewable, rigid, leak-free carbon ceramic composite electrode, bulk-modified with methylene blue (MB). In the configuration, alpha-zirconium phosphate was employed as a solid host for MB, which acted as a catalyst. Graphite powder ensured conductivity by percolation, the silicate provided a rigid porous backbone and the methyl groups endowed hydrophobicity and thus limited the wetting section of the modified electrode. Peak currents of the MBZrP-modified electrode were surface-confined at low scan rates but diffusion-controlled at high scan rates. Square-wave voltammetric study revealed that MBZrP immobilized in carbon ceramic matrix presented a two-electron, three-proton redox process in acidic aqueous solution with pH ranged from 0.44 to 2.94. In addition, the chemically modified electrode showed an electrocatalytic activity toward nitrite reduction at +0.15 V (vs. Ag/AgCl) in acidic aqueous solution (pH=0.44). The linear range and detection limit are 1 x 10(-6)-4 x 10(-3) mol L-1 and 1.5 x 10(-7) mol L-1, respectively.

Studies on enzymological properties of antibody elicited by meso-tetra(alpha, alpha, alpha, alpha-O-phenylacetyl benzene)porphyrin

meso-Tetra (alpha, alpha, alpha, alpha-O-phenylacetyl benzene) porphyrin was used as a complete antigen to elicit monoclonal antibody 1F2 through the immunization and cell fusion techniques. McAb 1F2 obtained was demonstrated very pure by HPLC and MALDI/TOFMS. The retention time of McAb 1F2 was 2. 63 min. The subtype of McAb 1F2 was IgG2a. The relative molecular weight was 156 678. 8. When the McAb 1F2-porphyrin was formed, the maximal absorption of the porphyrin soret region had a redshift from 408 to 416 nm and hyperchromical effect, showing that the antigen-antibody combination was rigid and intense, and the abzyme constancy was high. But compared with HRP, the activity of the abzyme was only 4. 687 5 U/mg and 1. 899 % of that of HRP. Its K-m was 20. 29 mmol/L, k(cat) 396. 82 min(-1), k(cat)/K-m. 1. 955 7 X 10(4) L . mol(-1) . min(-1).

Polydispersity of ethylene sequence length in metallocene ethylene/alpha-olefin copolymers. I. Characterized by thermal-fractionation technique

In this article, the polydispersity of the ethylene sequence length (ESL) in ethylene/alpha-olefin copolymers was studied by atomic force microscopy (AFM) and the thermal-fractionation technique. The crystal morphology observation by AFM showed that morphology changed gradually with decreasing average ESL from complete lamellae over shorter and more curved lamellae to a granular-like morphology, and the mixed morphology was observed after stepwise crystallization from phase-separated melt. This result indicated that the ethylene sequence with different lengths crystallized into a crystalline phase with a different size and stability at the copolymer systems. The thermal-fractionation technique was used to characterize the polydispersity of ESL. Three of the following statistical terms were introduced to describe the distribution of ESL and the lamellar thickness: the arithmetic mean (L) over bar (n), the weight mean (L) over bar (w), and the broadness index I = (L) over bar (w)/(L) over bar (n). It was concluded that the polydispersity of ESL could be quantitatively characterized by the thermal-fractionation technique. The effects of temperature range, temperature-dependent specific heat capacity C-p of copolymer, and the molecular weight on the results of thermal fractionation were discussed,

Polydispersity of ethylene sequence length in metallocene ethylene/alpha-olefin copolymers. II. Influence on crystallization and melting behavior

In this work, crystallization and melting behavior of metallocene ethylene/alpha-olefin copolymers were investigated by differential scanning calorimetry (DSC) and atomic force microscopy (AFM). The results indicated that the crystallization and melting temperatures for all the samples were directly related to the long ethylene sequences instead of the average sequence length (ASL), whereas the crystallization enthalpy and crystallinity were directly related to ASL, that is, both parameters decreased with a decreasing ASL. Multiple melting peaks were analyzed by thermal analysis. Three phenomena contributed to the multiple melting behaviors after isothermal crystallization, that is, the melting of crystals formed during quenching, the melting-recrystallization process, and the coexistence of different crystal morphologies. Two types of crystal morphologies could coexist in samples having a high comonomer content after isothermal crystallization. They were the chain-folded lamellae formed by long ethylene sequences and the bundlelike crystals formed by short ethylene sequences. The coexistence phenomenon was further proved by the AFM morphological observation.

Carbon ceramic electrodes modified with sub-micron particles of new methylene blue (NMB) intercalated alpha-zirconium phosphate

New methylene blue-intercalated a-zirconium phosphate (NMBZrP) was synthesized in the presence of n-butylamine and characterized by powder XRD, FTIR, TEM and elemental analysis. Sub-micron particles of NMBZrP in deionized water were apt to deposit onto the surface of graphite powder to yield graphite powder-supported NMBZrP, which was subsequently dispersed into methyltrimethoxysilane-derived gels to fabricate surface-renewable, stable, rigid carbon ceramic electrodes containing new methylene blue. Cyclic voltammetric studies revealed that peak currents of the NMBZrP-modified electrode were surface-confined at low scan rates but diffusion-controlled. at high scan rates. In addition, NMBZrP immobilized in a carbon ceramic matrix presented a two-electron, three-proton redox process in acidic aqueous solution in the pH range from 0.52 to 3.95.

The polydispersity of ethylene sequence in metallocene ethylene/alpha-olefin copolymers III: crystallization and melting behavior of short ethylene sequence

Crystallization and melting behavior of short ethylene sequence of metallocene ethylene/alpha -olefin copolymer with high comonomer content have been studied by standard DSC and modulated-temperature differential scanning calorimetry (M-TDSC) technique. In addition to high temperature endotherm around 120 degreesC, a low temperature endotherm is observed at lower temperatures (40-80 degreesC), depending on time and temperature of isothermal crystallization. The peak position of the low temperature endotherm T-m(low) varies linearly with the logarithm of crystallization time and the slope, D, decreases with increasing crystallization temperature T-c. The T-m(low) also depends on the thermal history before the crystallization at T-c, and an extrapolation of T-m(low) (30.6 degreesC) to a few seconds has been obtained after two step isothermal crystallization before the crystallization at 30 degreesC. The T-m(low) is nearly equal to T-c, and it indicates that the initial crystallization at low temperature is nearly reversible. Direct evidence of conformational. entropy change of secondary crystallization has been obtained by using M-TDSC technique. Both the M-TDSC result and the activation energy analysis of temperature dependence suggest that crystal perfection process and conformational entropy decreasing in residual amorphous co-exist during secondary crystallization.

Improved thermal fractionation technique for chain structure analysis of ethylene/alpha-olefin copolymers

In this report, we describe an improved thermal fractionation technique used to characterize the polydispersity of crystalline ethylene sequence length (CESL) of ethylene/alpha -olefin copolymers. After stepwise isothermal crystallization, the crystalline ethylene sequences are sorted into groups by their lengths. The CESLs are estimated using melting points of known hydrocarbons. The content of each group is determined using the calibrated peak area. The statistical terms: the arithmetic mean (L) over bar (n), the weighted mean (L) over bar (w) and the broadness index I = (L) over bar (w)/(L) over bar (n) are used to describe the distribution of CESL. Results show that improved thermal fractionation technique can quantitatively characterize the polydispersity of CESL with a high degree of accuracy.

Sol-gel-derived alpha(2)-K7P2W17VO62/graphite/organoceramic composite as the electrode material for a renewable amperometric hydrogen peroxide sensor

The conductive alpha (2)-K7P2W17VO62/graphite/organoceramic composite was prepared by dispersing alpha (2)-K7P2W17VO62 and graphite powder in a propyltrimethoxysilane-based sol-gel solution; it was used as the electrode material for an amperometric hydrogen peroxide sensor. The modified electrode had a homogeneous mirror-like surface and showed well defined cyclic voltammograms. Square-wave voltammetry was employed to study the pH-dependent electrochemical behavior of c alpha (2)-K7P2W17VO62 doped in the graphite organoceramic matrix, and the experiment showed that both protons and sodium cations participated in the odor process. A hydrodynamic voltammetric experiment was performed to characterize the electrode as an amperometric sensor for the determination of hydrogen peroxide. The sensor can be renewed easily in a repeatable manner by a mechanical polishing step and has a long operational lifetime. (C) 2000 Elsevier Science B.V. All rights reserved.

Preparation, structure, and properties of three-dimensional ordered alpha-Fe2O3 nanoparticulate film

alpha-Fe2O3 nanoparticulate films could be formed on the surface of alpha-Fe2O3 hydrosol after aging of the hydrosol or by compressing of the nanoparticles on the sol surface, in. which a three-dimensional ordered structure was constructed by the Langmuir-Blodgett; technique and colloid chemical methods. The structure of the LB film was characterized by AFM, TEM, XPS, and UV-vis spectra and small-angle X-ray diffraction. Gas-sensing measurement shows that the LB film has good sensitivity to alcohols at room temperature,