Effect of alkyl group length on the conductivity in the 2,3,7,8,12,13,17,18-octakis(alkyl-thio)tetraazaporphyrins and redox properties of the metallooctakis(hexyl-thio)tetraazaporphyrins

A series of 2,3,7,8,12,13,17,18-octakis(alkyl-thio)tetraazaporphyrins (H(2)OATTAP) with different alkyl chain lengths have been synthesized. Cyclic voltammetry and differential pulse voltammetry have been used to investigate the effect of the controlled lengths of the eight peripheral thioether tails on the redox behavior of the molecules. The electrochemical reduction of octakis(hexyl-thio)tetraazaporphyrins, MOHTTAP (where M = Cu, Ni), was studied in 1,2-dichloroethane at a platinum electrode. The Cu derivative was oxidized in one single-electron-transfer step to yield a pi-cation radical and reduced in three single-electron-transfer steps to yield a pi-anion radical, dianion and trianion, respectively. For the Ni derivative, electron transfer reactions involving both the central metal atom and the macrocyclic ring were observed. Electron transfer pathways are proposed based upon voltammetric and in situ spectroelectrochemical results.

Electrochemical study of isopoly- and heteropoly-oxometallates film modified microelectrodes .6. Preparation and redox properties of 12-molybdophosphoric acid and 12-molybdosilicic acid modified carbon fiber microelectrodes

The redox behaviours of 12-molybdophosphoric acid (12-MPA) and 12-molybdosilicic acid (12-MSA) in aqueous acid media are characterized at the carbon fiber (CF) microelectrode. The preparation of CF microelectrode modified with 12-MPA or 12-MSA monolayer and the oxidation-reduction properties of the modified electrode in aqueous acid media or 50% (v/v) water-organic media containing some inorganic acids are studied by cyclic voltammetry. 12-MPA or 12-MSA monolayer modified CF microelectrode with high stability and redox reversibility in aqueous acidic media can be prepared by simple dip coating. The cyclic voltammograms of 12-MPA and 12-MSA and their modified CF microelectrodes in aqueous acid solution exhibit three two-electron reversible waves with the same half-wave potentials, which defines that the species adsorbed on the CF electrode surface are 12-MPA and 12-MSA themselves. The acidity of electrolyte solution, the organic solvents in the electrolyte solution, and the scanning potential range strongly influence on the redox behaviours and stability of 12-MPA or 12-MSA monolayer modified electrodes. On the other hand, the catalytic effects of the 12-MPA and 12-MSA and chlorate anions in aqueous acidic solution on the electrode reaction processes of 12-MPA or 12-MSA are described.

Co-assembly of ferrocene-terminated and alkylthiophene thiols on gold and its redox chemistry modulated by surfactant adsorption

Coadsorption of ferrocene-terminated alkanethiols (FcCO(2)(CH2)(8)SH, Fc=(mu(5)-C5H5)Fe(mu(5)-C5H4)) with alkylthiophene thiols (2-mercapto-3-n-octylthiophene) yields stable, electroactive self-assembled monolayers on gold. The resulting mixed monolayer provides an energetically favorable hydrophobic surface for the adsorption of the surfactant aggregates in aqueous solution. The adsorptions have been characterized via their effect on the redox properties of ferrocenyl alkanethiols immobilized as minority components in the monolayers and on the interfacial capacitance of the electrode. Surfactant adsorption causes a decrease in the overall capacitance at the electrode and dramatically shifts the redox potential for ferrocene oxidation in a positive or negative direction depending on the identity of the surfactant employed. A structural model is proposed in which the alkane chains of the adsorbed surfactants interdigitate with those of the underlying self-assembled monolayer, leading to the formation of a hybrid bilayer membrane.

STUDIES ON SYNTHESIS, CHARACTERIZATION AND CATALYTIC PROPERTIES OF LAN+1NINO3N+1 MIXED OXIDES

A series of (AO) (ABO(3))(n)(A = La, B = Ni, n = 1 similar to 4) type mixed oxides were synthesized and characterized by means of XRD, XPS, IR, TPD, TPR. Their structure characteristics and redox properties were studied. The nonstoichiometry (lambda) of oxygen and the valence of transition metal Ni were determined by using chemical analysis method. The catalytic activities of this series of mixed oxides for complete oxidation of CO and CH4 were examined and the relationships among activity, composition and structure were discussed.

ISOLATION AND PROPERTIES OF MOLYBDENUM SERIES OF HETEROPOLY BLUE WITH KEGGIN STRUCTURE

The present paper reports the methods for preparing and isolating 8 kinds of 1:12 molybdenum series of heteropoly blue complexes KyHzXMo12O40 . nH2O (X=Si, P, As, Ge). The products were characterized by elemental analyses, potential titration, polarograms, cyclic voltammetry, IR spectra, visible-UV spectra, X-ray powder diffraction, XPS and P-31 NMR. The single crystal structure of 4-electron molybdenum-silicon heteropoly blue was measured and the positions of reduced molybdenum atoms were determined, i.e. they were located at Mo(3), Mo(7), Mo(8) and Mo(10). The experimental results show that the heteropoly blue remains Keggin structure. ESR spectra of heteropoly blue solids were first studied, from which it was found that the delocalization extent of 2-electron heteropoly blue and 4-electron heteropoly blue is smaller than that of 1-electron heteropoly blue. The study of thermal properties shows that the thermal stability increases with the increase of the reduction extent of heteropoly blue. The study of redox properties shows that the oxidizing power order of heteropoly blue changes in different mediums, and the polarographic half-wave voltage is found to be dependent on the electronegativity of the hetero atom linearly. It is found that the phosphorus heteropoly blue and arsenic heteropoly blue show a strong anti-acid property.

The role of CeO2-ZrO2 as support in the ZnO-ZnCr2O4 catalysts for autothermal reforming of methanol

Autothermal reforming of methanol for hydrogen production was investigated over ZnO-ZnCr2O4 supported on a series of metal oxides (Al2O3, CeO2, ZrO2 and CeO2-ZrO2)CeO2-ZrO2 mixed oxides with Ce /Zr molar ratio of 4/1 was found to be the optimal support which showed significant effect on the catalytic activity and selectivity. The ZnO-ZnCr2O4/CeO2-ZrO2 and ZnO-ZnCr2O4 catalysts were characterized by XRD, TEM, H-2-TPR and XPS. The results show that CeO2-ZrO2 mixed oxides have significant effect on the catalytic performance and the supported catalyst shows more uniform temperature distribution in the catalyst bed which was mainly due to its reasonable redox properties.

Luminescent Boron-Contained Ladder-Type pi-Conjugated Compounds

Four diboron-contained ladder-type pi-conjugated compounds 1-4 were designed and synthesized. Their thermal, photophysical, electrochemical properties, as well as density functional theory calculations, were fully investigated. The single crystals of compounds 1 and 3 were grown, and their crystal structures were determined by X-ray diffraction analysis. Both compounds have a ladder-type g-conjugated framework. Compounds I and 2 possess high thermal stabilities, moderate solid-state fluorescence quantum yields, as well as stable redox properties, indicating that they are possible candidates for emitters and charge-transporting materials in electroluminescent (EL) devices. The double-layer device with the configuration of [ITO/NPB (40 nm)/1 or 2 (70 nm)/LiF (0.5 nm)/Al (200 nm)] exhibited good EL performance with the maximum brightness exceeding 8000 cd/m(2).

Effect of strontium substitution on the activity of La2-xSrxNiO4 (x=0.0-1.2) in NO decomposition

The aim of this work is to study the effect of Sr substitution on the redox properties and catalytic activity of La2-xSrxNiO4 (x = 0.0-1.2) for NO decomposition. Results suggest that the x = 0.6 sample shows the highest activity. The characterization (TPD, TPR, etc.) of samples indicates that the x = 0.6 sample possesses suitable abilities in both oxidation and reduction, which facilitates the proceeding of oxygen desorption and NO adsorption. At temperature below 700 degrees C, the oxygen desorption is difficult, and is the rate-determining step of NO decomposition. With the increase of reaction temperature (T > 700 degrees C), the oxygen desorption is favorable and, the active adsorption of NO on the active site (NO + V-o + Ni2+ -> NO--Ni3+) turns out to be the rate-determining step. The existence of oxygen vacancy is the prerequisite condition for NO decomposition, but its quantity does not relate much to the activity.

Surface-enhanced resonance Raman spectroscopic study of yeast iso-1-cytochrome c and its mutant

The structural stability and redox properties of yeast iso-1-cytochrome c and its mutant, F82H, were studied by surface-enhanced resonance Raman scattering (SERRS) spectroscopy. Phenylalanine, which exists at the position-82 in yeast iso-1-cytochrome c, is replaced by histidine in the mutant. The SERRS spectra of the proteins on the bare silver electrodes indicate that the mutant possesses a more stable global structure with regard to the adsorption-induced conformational alteration. The redox potential of the mutant negatively shifts by about 400 mV, relative to that of yeast iso-1-cytochrome c. This is ascribed to axial ligand switching and higher solvent accessibility of the heme iron in the mutant during the redox reactions.

Synthesis and electrochemical characteristics of lanthanide complexes with 2-nitro-5,10,15,20-tetraphenylporphyrin and acetylacetonate

Four lanthanide complexes with 2-nitro-5,10,15,20-tetraphenylporphyrin and acetylacetonate were prepared and characterized by elemental analyses, LR, UV-Visible,H-1 NMR, XPS and molar conductance. The redox properties of the lutetium complex with 2-nitro-5,10,15,20-tetraphenylporphyrin and acetylacetonate in dichloromethane were studied by cyclic voltammetry.

Investigations on the promoting effect of metal oxides on La-V-O catalyst in propane oxidative dehydrogenation

The addition of reducible metal oxides as promoters shows a positive effect on the catalytic behavior of lanthanum vanadate (LaVO4). A C3H6 yield increase of 6.5% is observed at 500 degreesC on molybdenum-promoted LaVO4, which can be attributed to the change of the redox properties, the blocking of the strong oxidation sites of the catalysts and to an increase of the accessibility of the labile oxygen toward the reactant. The influence of the catalyst preparation method and of the Mo loading as well as the additional promoting effect of CO2 in the gas feed was also examined.

Synergetic effect between NiO and Ni3V2O8 in propane oxidative dehydrogenation

The oxidative dehydrogenation (ODH) of propane was investigated on Ni-V-O catalysts in a wide range of vanadium contents (5-40%). The addition of a small amount of vanadium significantly increased the catalytic activity of NiO for oxidative dehydrogenation of propane to propene. The formation of propene has a good correlation with the coexistence of NiO and Ni3V2O8. This result strongly suggests that a synergetic effect exists between them in NiXV1-XOY (X = 0.95 to 0.6). The best results were obtained with a high Ni/V ratio (e.g. X = 0.95 to 0.85). The active sites and selective oxygen species are discussed. The influence of the catalyst preparation technique and the redox properties of the catalyst were also examined.

Some new observation on the formation and optical properties of CdS clusters in zeolite-Y

CdS clusters in zeolite-Y have been prepared by the exchange of Cd2+ into the zeolite following by sulfurization with Na2S in solution. Blue-shifts from the bulk caused by quantum size effect and the change of absorption upon CdS loading are observed. Two absorption bands are detected for one of the sample and are assigned to the 1s-1s band and exciton transition, respectively. The exciton feature is more pronounced in the excitation spectrum than in the absorption spectrum, and the luminescence excited at the exciton band is stronger than that at the 1s-1s band. Copyright (C) 1996 Elsevier Science Ltd

Characterization of metal-containing molecular sieves and their catalytic properties in the selective oxidation of cyclohexane

Three types of metal-containing molecular sieves with AFI, AEL and CHA structures (Me = Co, Mn, Cr and V) were synthesized hydrothermally and characterized by XRD, XRF, TG, TPR, NH3-TPD and FT-IR. It was revealed that metals were incorporated into the framework of molecular sieves and induced the presence of charge centers. Both cobalt and manganese in the framework of AIPO-5, AlPO-11 and SAPO-34 were not reducible before the structure collapse. The redox behaviours of these catalysts in cyclohexane oxidation at 403 K using O-2 as oxidant were examined. CoAPO-11 exhibited best activity and good selectivities for the monofunctional oxidation products (88.5%). Cyclohexanol was the major product over most catalysts, whereas for Cr-containing molecular sieves, high selectivity of cyclohexanone was observed. Investigation of reaction mechanism based on CoAPO-11 and CrAPO-5 catalysts indicated that the decomposition of cyclohexyl hydroperoxide (CHHP), the intermediate in cyclohexane oxidation, followed the pathway: cyclohexanone <-- CHHP --> cyclohexanol -->cyclohexanone. (C) 2004 Elsevier B.V. All rights reserved.

Robust Tris-Cyclometalated Iridium(III) Phosphors with Ligands for Effective Charge Carrier Injection/Transport: Synthesis, Redox, Photophysical, and Electrophosphorescent Behavior

With the target to design and develop new functionalized green triplet light emitters that possess distinctive electronic properties for robust and highly efficient phosphorescent organic light-emitting diodes (PHOLEDs), a series of bluish-green to yellow-green phosphorescent tris-cyclometalated homoleptic iridium(III) complexes [Ir(ppy-X)(3)] (X=SiPh3, GePh3, NPh2, POPh2, OPh, SPh, SO2Ph, Hppy=2-phenylpyridine) have been synthesized and fully characterized by spectroscopic, redox, and photophysical methods