Multilayer assembly of Bis-Keggin-type heteropoly compound on chemically modified glassy carbon electrode and its electrocatalysis

Through layer-by-layer assembly, the bis-Keggin-type heteropolyanion K10H3 [Nd(SiMo7W4O39)(2)] XH2O was successfully immobilized on a glassy carbon electrode surface grafted covalently by 4-aminobenzoic acid. The electrochemical behavior of the heteropolyanion was investigated. Cyclic voltammetry proved the uniform growth of the film. However, the characteristic redox peaks of the heteropolyanion in the film were deformed with increasing of the number of the multilayer film. The effect of pH on the redox behaviors of [Nd(SiMo7W4)(2)](13-) in the film was discussed. The multilayer film electrodes have excellent electrocatalytic activities to the reduction of BrO3-, HNO2 and H2O2.

Electrochemical properties of rare earth AB(3)-type alloy as negative electrode material in MH-Ni battery

Electrochemical properties of rare earth AB(3)-type hydrogen storage alloys as negative electrode material and a polymer instead of 6 M KOH aqueous solution as solid state electrolyte in MH-Ni battery have been investigated at room temperature and 28degreesC first time. The partial replacement of Ni by Al and Mn elements increases the specific capacity and cycle stability of the alloy.

Effect of configuration and conformation on the spin multiplicity in xylylene type biradicals

The singlet-triplet splitting energy gap DeltaE(S.T) = E-S - E-T is calculated for the ortho-, meta-, and para-xylylenes and their heteroatomic analogous by means of AM1-CI approach. It is shown that when the radical centers R-.(R-.=H2C.-,H2N.+- or HN.-) are twisted sufficiently Tar out of conjugation with the benzene ring, DeltaE(S.T) tends to zero or is negative, i.e, ortho-, meta-, and para-phenylenes turn into weak ferromagnetic or antiferromagnetic coupling unit, while they are strong ferromagnetic (meta-isomers) or antiferromagnetic (ortho-, para-isomers) coupling units under planar conformation. It is suggested that serious twisted conformation is not recommended candidate for the design of novel high-spin molecules with stable high-spin ground states by ortho- or para-phenylene coupling unit.

Circular dichroism and resonance Raman comparative studies of wild type cytochrome c and F82H mutant

The UV-visible, circular dichroism (CD), and resonance Raman (RR) spectra of the wild type yeast iso-1-cytochrome c (WT) and its mutant F82H in which phenylalanine-82 (Phe-82) is substituted with His are measured and compared for oxidized and reduced forms. The CD spectra in the intrinsic and Soret spectral region, as well as RR spectra in high, middle, and low frequency regions, are discussed. From the analysis of the spectra, it is determined that in the oxidized F82H the two axial ligands to the heme iron are His-18 and His-82 whereas in the reduced form the sixth ligand switches from His-82 to Met-80 providing the coordination geometry similar to that of WT. Based on the spectroscopic data, the conclusion is that the porphyrin macrocycle is less distorted in the oxidized F82H compared to the oxidized WT. Similar distortions are present in the reduced form of the proteins. Frequency shifts of Raman bands, as well as the decrease of the or-helix content in the CD spectra, indicate more open conformation of the protein around the heme. (C) 2000 John Wiley & Sons, Inc.

Ultrathin multilayer films incorporating Keggin-type heteropolyanion clusters

Two new ultrathin multiplayer films have been successfully prepared fi-om Keggin-type heteropoly acids H-4[SiW12O40] and H-3[PMo12O40] with polyelectrolytes PEI, PSS, and PAH, using the electrostatic layer-by-layer self-assembly, technique. The XR results reveal their film thickness at nanoscale (similar to 20 nm). According to the AFM images, it is believed that the surface roughness (rough degree of film surface) of the polyelectrolyte-polyoxometalate film greatly depends on the kind of polyoxometalates.

Multilayer assembly of Mn-substituted Keggin-type [ZnW11O39Mn(H2O)](8-) on chemically modified glassy carbon electrode and its electrocatalytic properties

Through layer-by-layer assembly, undecatungstozincates monosubstituted by transition metals Mn, ZnW11 Mn (H2O) O-39(8-) was successfully immobilized on a glassy carbon electrode surface grafted covalently by 4-aminobenzoic acid. The electrochemical behavior of these polyoxometalates was investigated. Cyclic voltammetry proves the uniform growth of the film. They exhibit some special electrochemical properties in the films, different from those in homogeneous aqueous solution. The effect of pH on the redox behavior of ZnW11Mn(H2O)O-39(8-) in the film was discussed in detail. The multilayer film electrodes have an excellent electrocatalytic response to the reduction of H2O2 and BrO3-, and to the oxidation of ascorbic acid.

Preparation and properties of a selenium-containing catalytic antibody as type I deiodinase mimic

Conversion of thyroxine (T-4) to 3,5,3'-triiodothyronine is an essential first step in controlling thyroid hormone action. Type I deiodinase (DI) can catalyze the conversion to produce the bulk of serum 3,5,3'-triiodothyronine. Acting as a mimic of DI, a selenium-containing catalytic antibody (Se-4C5) prepared by converting the serine residues of monoclonal antibody 4C5 raised against T4 into selenocysteines, can catalyze the deiodination of T4 with dithiothreitol (DTT) as cosubstrate. The mimic enzyme Se-4C5 exhibited a much greater deiodinase activity than model compound ebselen and another selenium-containing antibody Se-Hp4 against GSH. The coupling of selenocysteine with the combining pocket of antibody 4C5 endowed Se-4C5 with enzymatic activity. To probe the catalytic mechanism of the catalytic antibody, detailed kinetic studies were carried out in this paper. Investigations into the deiodinative reaction revealed the relationship between the initial velocity and substrate concentration. The characteristic parallel Dalziel plots demonstrated that Se-4C5-catalyzed reaction mechanism was ping-pong one, involving at least one covalent enzyme intermediate. The kinetic properties of the catalytic antibody were similar to those of DI, with K-m values for T-4 and DTT of approximately 0.8 muM and 1.8 muM, respectively, and a V-m value of 270 pmol per mg of protein per min. The activity could be sensitively inhibited by 6-propyl-2-thiouracil (PTU) with a K-i value of similar to 120 muM at 2.0 muM T-4 concentration. The PTU inhibition was progressively alleviated with the increasing concentration of added DTT, revealing that PTU was a competitive inhibitor for DTT.

Preparation, characterization and luminescent properties of MCM-41 type materials impregnated with rare earth complex

Hybrid materials incorporating Eu-(TTA)(3). 2H(2)O (7hereafter designated as Eu-TTA, with TTA: thenoyltrifluoroacetone) in unmodified or modified MCM-41 by 3-aminopropyl-triethoxysilane (APTES) were prepared by impregnation method. The obtained materials were characterized using X-ray diffraction (XRD), IR and diffuse reflectance spectroscopy and luminescence spectra. All the hybrid samples exhibited the characteristic emission bands of EU3+ under UV light excitation at room temperature, and the excitation spectra showed significant blue-shifts compared to the pure rare-earth complex. Although the red emission intensity in the modified hybrid was almost the half of the red emission intensity in the pure Eu-TTA complex at room temperature, the hybrid showed a much higher thermal stability due to the shielding character of the MCM-41 host.

A selenium-containing catalytic antibody with type I deiodinase activity

Acting as a mimic of type I deiodinase (DI), a selenium-containing catalytic antibody (Se-4C5) prepared by converting the serine residues of monoclonal antibody 4C5 raised against thyroxine (T-4) into selenocysteines, can catalyze the deiodination of T-4 to 3,5,3'-triiodothyronine (T-3) with dithiothreitol (DTT) as cosubstrate. Investigations into the deiodinative reaction by Se-4C5 revealed the relationship between the initial velocity and substrate concentration was subjected to Michaelis-Menten equation and the reaction mechanism was ping-pong one. The kinetic properties of the catalytic antibody were a little similar to those of DI, with K-m values for T-4 and DTT of approximately 0.8 muM and 1.8 mM, respectively, and V-m value of 270 pmol per mg protein per min. The activity could be sensitively inhibited by PTU with a K-i value of approximately 120 muM at 2.0 muM of T-4 concentration, revealing that PTU was a competitive inhibitor for DTT, (C) 2001 Academic Press.

A new type of polymer-supported metallocene catalyst for ethylene polymerization

A new polymer-supported metallocene catalyst has been prepared, The polymer-supported metallocene displayed considerably high activity in ethylene polymerization, the highest being 3.62x10(7) gPE/molZr.h, the molecular weight of the polyethylene produced was Mn = 1.29x10(5). about 3-4 times those of corresponding homogeneous zirconocenes. The polymer-supported metallocene keeps the characteristics of homogeneous metallocene catalysts, and offers some features, such as adaptable to gas phase and slurry processes: easy to prepare in low cost: relatively high activity and lower MAO/Zr ratio; lower inorganic residues in the polyolefins as compared to cases of SiO2, Al2O3 or MgCl2; unitary active structure, no complex surface as with SiO2; good control of morphology of the resulting polymer.

Sol-gel-derived graphite organosilicate composite electrodes bulk-modified with Keggin-type alpha-germanomolybdic acid

A novel inorganic-organic hybrid material incorporating graphite powder and Keggin-type alpha -germanomolybdic acid (GeMo12) in methyltrimethoxysilane-based gels has been produced by the sol-gel technique and used to fabricate a chemically bulk-modified electrode. GeMo12 acts as a catalyst, graphite powder ensures conductivity by percolation, the silicate provides a rigid porous backbone, and the methyl groups endow hydrophobicity and thus limit the wetting section of the modified electrode. The GeMo12-modified graphite organosilicate composite electrode was characterized by cyclic and square-wave voltammetry. The modified electrode shows a high electrocatalytic activity toward the reduction of bromate, nitrite and hydrogen peroxide in acidic aqueous solution. In addition, the chemically-modified electrode has some distinct advantages over the traditional polyoxometalate-modified electrodes, such as long-term stability and especially repeatability of surface-renewal by simple mechanical polishing.

Ester-type precursor of polyimide and photosensitivity

In order to investigate the influence of the main chain structure and molecular weight on the sensitivity of photosensitive ester-type precursor of polyimide (photo-PAE), an improved method was used to synthesize several kinds of photo-PAEs with relatively high molecular weight. Their sensitivities (at 365 nm) were investigated, and it was found that some additives such as sensitizer and photoinitiator had the greatest influence on the sensitivity of photo-PAE, that the photo-PAE with BPDA and mPDA as the main chain structure had the best sensitivity (D-0.5: 5-10 mJ/cm(2)) among the studied photo-PAEs, and that the sensitivity did not significantly change with the change of inherent viscosity of photo-PAE. Meanwhile, the thermal imidization of these photo-PAEs was also investigated by means of TGA and IR analyses. Additionally, a discussion was made for formulation of PSPI resist. (C) 1999 Elsevier Science Ltd. All rights reserved.

An unusual electrochemically induced demetalation of iron-substituted Keggin-type undecatungstozincate ZnW11FeIII(H2O)O-39(7-)

Firstly reported for Fe-containing transition metal substituted polyoxometalates was an unusual Fe-centered demetalation process induced by the reduction of ZnW11FeIII to ZnW11FeII which resulted in a new couple of Fe-relating redox waves at positive potentials. (C) 1999 Elsevier Science S.A. All rights reserved.

Evaluation of bond covalency and bond valence in Sr-doped perovskite-type compounds

Formulas for decomposing of complex crystals to a sum of binary crystals are described and applied to the study of bond covalency in La1-xSrxFeO3 (0.0 less than or equal to x less than or equal to 0.9) and Ca1-xSrxMnO3 (0.0 less than or equal to x less than or equal to 0.5). The bond valence is treated by bond-valence sums scheme. The results indicate that, for both compounds, with the increasing doping level, the bond covalency and bond valence show the same trend, namely, larger bond covalency corresponds to higher bond valence. For La1-xSrxFeO3, with the increase of doping level, the bond covalency of La-O, Ca-O decreases in the orthorhombic (0.0 less than or equal to x less than or equal to 0.2) and rhombohedral (0.4 less than or equal to x less than or equal to 0.7) systems, then increases slightly for the cubic (0.8 less than or equal to x less than or equal to 0.9) system, but that of Fe-O increases for all crystal systems. A sharp decrease in bond covalency was observed where the crystal changes from orthorhombic to rhombohedral, while a smooth trend was seen for the rhombohedral-to-cubic transition. On the other hand, for orthorhombic Ca1-xSrxMnO3, the bond covalency of Ca-O, Sr-O, and Mn-O (4-coordinate site) decreases with the increasing doping level, that of Mn-O (2-coordinate site) increases.