Superconductor mixed oxides La2-xSrxCuO4+/-lambda for catalytic hydroxylation of phenol in the liquid-solid phase

Superconductor mixed oxides are often used as catalysts at high temperature in gas-solid phase oxidations and considered not suitable for lower temperature reactions in the liquid-solid phase; here the catalysis of La2-xSrxCuO4+/-lambda (x = 0, 0.1, 0.7, 1) mixed oxides in phenol hydroxylation at lower temperatures are studied, and we find that the value of x has a significant effect on catalytic activity: the lower its value, the higher the catalytic activity; a mechanism is proposed to explain the experimental phenomena.

Studies on Some Simple and Zeolite-Y Encapsulated 3d-Transition Metal Complexes of Schiff Bases Derived From 2-Aminobenzothiazole

In this regard Schiff base complexes have attracted wide attention. Furthermore, such complexes are found to play important role in analytical chemistry, organic synthesis, metallurgy, refining of metals, electroplating and photography. Many Schiff base complexes are reported in literature. Their properties depend on the nature of the metal ion as well as on the nature of the ligand. By altering the ligands it is possible to obtain desired electronic environment around the metal ion. Thus there is a continuing interest in the synthesis of simple and zeolite encapsulated Schiff base complexes of metal ions. Zeolites have a number of striking structural similarities to the protein portion of natural enzymes. Zeolite based catalysts are known for their remarkable ability of mimicking the chemistry of biological systems. In view of the importance of catalysts in all the areas of modern chemical industries, an effort has been made to synthesize some simple Schiff base complexes, heterogenize them by encapsulating within the supercages of zeoliteY cavities and to study their applications. The thesis deals with studies on the synthesis and characterization of some simple and zeoliteY encapsulated Mn(II), Fe(III), Co(II), Ni(II) and Cu(II) complexes and on the catalytic activity of these complexes on some oxidation reactions. Simple complexes were prepared from the Schiff base ligands SBT derived from 2-aminobenzothiazole and salicylaldehyde and the ligand VBT derived from 2-aminobenzothiazole and vanillin (4-hydroxy-3- methoxybenzaldehyde). ZeoliteY encapsulated Mn(II), Fe(III), Co(II), Ni(II) and Cu(II) complexes of Schiff base ligands SBT and VBT and also of 2-aminobenzothiazole were synthesized. All the prepared complexes were characterized using the physico-chemical techniques such as chemical analysis (employing AAS and CHN analyses), magnetic moment studies, conductance measurements and electronic and FTIR spectra. EPR spectra of the Cu(II) complexes were also carried out to know the probable structures and nature of Cu(II) complexes. Thermogravimetric analyses were carried out to obtain the information regarding the thermal stability of various complexes. The successful encapsulations of the complexes within the cavities of zeoliteY were ascertained by XRD, surface area and pore volume analysis. Assignments of geometries of simple and zeoliteY encapsulated complexes are given in all the cases. Both simple and zeoliteY encapsulated complexes were screened for catalytic activity towards oxidation reactions such as decomposition of hydrogen peroxide, oxidation of benzaldehyde, benzyl alcohol, 1-propanol, 2-propanol and cyclohexanol.

Effect of different bleaching systems on the ultrastructure of bovine dentin

The aim of this study was to evaluate in vitro the effect of different in-office bleaching systems on the surface morphology of bovine dentin. Thirty tooth fragments measuring 4 x 4mm, containing enamel and dentin, were obtained from the crowns of extracted bovine incisors. Samples were subjected to simulated intracoronal bleaching techniques using conventional (Opalescence Endo (R) and Whiteness Super Endo (R)) and light-activated systems (Opalescence Xtra (R) and Whiteness HP Maxx (R)). Controls were treated with either sodium perborate mixed with 10% hydrogen peroxide or no bleaching agent. The samples were observed under SEM and the recorded images were evaluated for topographic alterations. The ultrastructural alterations of dentin observed in this study varied greatly between groups according to the products used. Higher pH products (Whiteness HP Maxx (R) and Opalescence Xtra (R)) associated with in-office techniques yielded better maintenance of dentin ultrastructure. Apparently, both low pH and hydrogen peroxide oxidation play a role in altering the ultrastructure of dentin during internal dental bleaching. The use of alkaline products with reduced time of application (in-office techniques) may decrease such morphological alterations.

Interference of inorganic ions on phenol degradation by the Fenton reaction

The addition of Cu2+ ions to the classical Fenton reaction (Fe2+ plus H2O2 at pH 3) is found to accelerate the degradation of organic compounds. This synergic effect causes an approximately 15 % additional reduction of the total organic carbon (TOC), representing an overall improvement of the efficiency of the mineralization of phenol. Although Fe2+ exhibits a high initial rate of degradation, the degradation is not complete due to the formation of compounds refractory to the hydroxyl radical. The interference of copper ions on the degradation of phenol by the Fenton reaction was investigated. In the presence of Cu2+, the degradation is slower, but results in a greater reduction of TOC at the end of the reaction (t = 120 min). In the final stages of the reaction, when the Fe3+ in the solution is complexed in the form of ferrioxalate, the copper ions assume the role of the main catalyst of the degradation.

Iodine speciation at time series station DYFAMED

Iodine speciation analysis was carried out upon seawater samples collected in July 1993 at the DYFAMED station (43 °25?N, 7 °52?E) located in the northwestern Mediterranean Sea. Dissolved iodate and iodide were directly determined by differential pulse polarography and cathodic stripping square wave voltammetry, respectively, and organically bound iodine was estimated by wet-chemical oxidation with sodium hypochlorite. Iodate is the predominant species ranging from 416 nM in surface waters to 480 nM in bottom waters. Iodide is present in significant concentrations up to 60 nM in surface waters, undetectable between 500 and 1000 m depth and present in very low but measurable concentrations (about 6 nM) in deep waters. The vertical profile of total free iodine demonstrates observable removal from surface waters, slight enrichment at about 200 m depth and constant there below. Up to 40 nM of organically bound iodine has been estimated between 20 to 30 m. Factorial analysis of different iodine species with biologically relevant parameters provided strong evidence for iodine biophilic features.

Generation of hydrogen peroxide on oxidation of NADH by hepatic plasma membranes

The oxidation of NADH by mouse liver plasma membranes was shown to be accompanied by the formation of H2O2. The rate of H2O2 formation was less than one-tenth the rate of oxygen uptake and much slower than the rate of reduction of artificial electron acceptors. The optimum pH for this reaction was 7.0 and theK m value for NADH was found to be 3×10–6 M. The H2O2-generating system of plasma membranes was inhibited by quinacrine and azide, thus distinguishing it from similar activities in endoplasmic reticulum and mitochondria. Both NADH and NADPH served as substrates for plasma membrane H2O2 generation. Superoxide dismutase and adriamycin inhibited the reaction. Vanadate, known to stimulate the oxidation of NADH by plasma membranes, did not increase the formation of H2O2. In view of the growing evidence that H2O2 can be involved in metabolic control, the formation of H2O2 by a plasma membrane NAD(P)H oxidase system may be pertinent to control sites at the plasma membrane.

Vanadate stimulates oxidation of NADH to generate hydrogen peroxide

Vanadate in the polymeric form of decavanadate, but not other forms, stimulated oxidation of NADH to NAD+ NADPH was also oxidized with comparable rates. This oxidation of NADH was accompanied by uptake of oxygen and generated hydrogen peroxide with the following stoichiometry: NADH + H+ + O2 → NAD+ + H2O2. The reaction followed second-order kinetics. The rate was dependent on the concentration of both NADH and vanadate and increased with decreasing pH. The reaction had an obligatory requirement for phosphate ions. Esr studies in the presence of the spin trap dimethyl pyrroline N oxide indicated the involvement of Superoxide anion as an intermediate. The reaction was sensitive to Superoxide dismutase and other scavengers of superoxide anions.

Oxidation of aromatic substrates with hydrogen peroxide and hydrochloric acid

Chloroquinones are prepared conveniently from phenol, naphthols and aromatic amines.

A Modified Fluorimetric Method for Determination of Hydrogen Peroxide Using Homovanillic Acid Oxidation Principle

Hydrogen peroxide (H2O2) level in biological samples is used as an important index in various studies. Quantification of H2O2 level in tissue fractions in presence of H2O2 metabolizing enzymes may always provide an incorrect result. A modification is proposed for the spectrofluorimetric determination of H2O2 in homovanillic acid (HVA) oxidation method. The modification was included to precipitate biological samples with cold trichloroacetic acid (TCA, 5% w/v) followed by its neutralization with K2HPO4 before the fluorimetric estimation of H2O2 is performed. TCA was used to precipitate the protein portions contained in the tissue fractions. After employing the above modification, it was observed that H2O2 content in tissue samples was >= 2 fold higher than the content observed in unmodified method. Minimum 2 h incubation of samples in reaction mixture was required for completion of the reaction. The stability of the HVA dimer as reaction product was found to be > 12 h. The method was validated by using known concentrations of H2O2 and catalase enzyme that quenches H2O2 as substrate. This method can be used efficiently to determine more accurate tissue H2O2 level without using internal standard and multiple samples can be processed at a time with additional low cost reagents such as TCA and K2HPO4.

Wet Oxidation of AlxGa1-xAs/GaAs Distributed Bragg Reflectors

The wet oxidation of AlGaAs with high Al content in a distributed Bragg reflectors （DBR） is studied by scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. Some voids distribute along the oxide/GaAs interfaces due to the stress induced by the wet oxidation of the AlGaAs layers. These voids decrease the shrinkage of the Al2O3 layers to 8% instead of the theoretical 20% when compared to the unoxidized AlGaAs layers. With the extension of oxidation time, the reactants are more completely transported to the front interface and the products are more completely transported out along the porous interfaces. As a result,the oxide quality is better.

Selective oxidation of cyclohexane with hydrogen peroxide in the presence of copper pyrophosphate

Liquid phase oxidation of cyclohexane was carried out under mild reaction condition over copper pyrophosphate catalyst in CH3CN using hydrogen peroxide as an oxidant at the temperature between 25 and 80 degrees C. The copper pyrophosphate catalyst was characterized by means of XRD, FT-IR and water contact angle measurement. It was found that appropriate surface hydrophobicity is the key factor for the excellent performance of the catalyst. In addition, a significant improvement for the cyclohexane conversion in the presence of organic acid was observed.

Direct oxidation of benzene to phenol on manganese pyrophosphate with hydrogen peroxide

A solid catalyst manganese pyrophosphate based on non-sieves to oxidize benzene to phenol with oxidant hydrogen peroxide has shown good conversion with good selectivity in CH3CN at 65 degrees C investigating water contact angle data of three manganese salts, it is found manganese pyrophosphate has certain repulsive water character. It is further to be confirmed by benzene and phenol adsorption experiments onto catalyst surface by GC. With benzene/H2O2 ratio of 1, the benzene conversion of 13.8% with phenol selectivity of 85.0% was achieved. It is noteworthy that no any products are obtained using manganese pyrophosphate as catalyst in the oxidation of phenol in CH3CN solvent.