Styrene Oxidation to Benzaldehyde by Polymer Anchored Wilkinson Complex

Wilkinson complex, insolubilized by anchoring to polymeric Amberlite beads, had been used for the liquid-phase catalytic oxidation of styrene to benzaldehyde and formaldehyde in toluene medium. Styrene conversion was followed by measuring the oxygen volume in contact with the reaction mixture in a specially designed closed batch apparatus. Styrene conversion depended upon catalyst loading and distribution inside the porous beads, while temperature had little effect on it. The internal diffusional effects on the conversion process have been taken into onsideration by a mathematical model which allowed calculation of effectiveness factors for various catalyst loadings and corresponding catalyst distributions. The influence of external diffusion was separately determined by plotting initial rate versus catalyst loading. The proposed method can be readily extended to immobilized enzymes in porous matrices.

Cuprous oxide catalyzed air oxidation of thiosulfate and tetrathionate

Thiosulfate (S2O32−) and tetrathionate (S4O62−)are oxidized to sulfate by air at atmospheric pressure and 50–70°C in the presence of cuprous oxide (Cu2O) as catalyst. Sulfate is produced from S2O32− by series-parallel reaction paths involving S4O62− as an intermediate. The rate data obtained for air oxidation of S2O32− on Cu2O agree well with a pseudo-homogeneous first order kinetic scheme, yielding values of rate constants for series parallel reaction paths which have been used in modelling the catalyzed air oxidation of S2O32−. Air oxidation of S4O62− on Cu2O proceeds at a higher rate in the presence of S2O32− than in its absence. Cu2O is less active than Cu2S for the air oxidation of S2O32−, as shown by the rate constant values which for Cu2O catalyzed oxidation are an order of magnitude smaller than those for the Cu2S catalyzed oxidation.

Surface oxidation of cadmium, indium, tin and antimony by photoelectron and Auger spectroscopy

Surface oxidation of Cd, In, Sn and Sb has been investigated by employing valence bands, metal 4d levels and plasmon bands in X-ray photoelectron spectra. O(KLL), metal M4N45N45, and plasmon transitions in electron-induced Auger spectra as well as Auger transitions due to the metal (metal oxide) and plasmons in X-ray-induced Auger spectra. The surface oxides are In2O4, CdO and a mixture of SnO and SnO2 in the case of In. Cd and Sn respectively. The facility of surface oxidation is found to vary as In>Cd>Sn>Sb. Inter-atomic Auger transitions involving oxygen valence bands have been identified on oxidized surfaces of Cd and In.

XPS and XAES studies of surface segregation and oxidation of Cu-Ge alloy

Surface segregation of Ge is seen in the Cu-5at%Ge alloy with an activation enthalpy equal to 17 kJ/mol. Oxidation of the alloy in the temperature range 400 to 600 K shows the formation of Cu2O and GeO which on further heating in vacuum at 650 K converts to GeO2 with the reduction of Cu2O to Cu.

Surface segregation and oxidation studies of Cu-Sn and Cu-Pd alloys by x-ray photoelectron and auger spectroscopy

X-ray photoelectron and Auger spectroscopic techniques have been employed to study surface segregation and oxidation of Cu-1 at%Sn, Cu-9at%Pd and Cu-25at%Pd alloys. Both Cu-Pd(9%) and Cu-Pd(25%) alloys show segregation of Cu when heated above 500 K. The Pd concentration was reduced by 50% at 750 K compared to the bulk composition; the enthalpy of segregation of Cu is around - 6kJ/mol. Sn segregation is seen from 470 to 650 K in the Cu-Sn(1%) alloy, and a saturation plateau of Sn concentration above 650 K is observed. Surface oxidation of Cu-Sn(1%) and Cu-Pd(9%) alloys at 500 K showed the formation of Cu2O on the surface with total suppression of Sn or Pd on the respective alloy surfaces. On vacuum annealing the oxidised Cu-Sn alloy surface at 550 K, a displacement reaction 2Cu2O+Sn→4Cu+SnO2 was observed. However, under similar annealing of the oxidised Cu-Pd(9%) alloy surface at 500 K, oxide oxygen was totally desorbed leaving the Cu-Pd alloy surface clean. In the case of the Cu-Pd(25%) alloy, only dissociatively chemisorbed oxygen was seen at 500 K which desorbed at the same temperature. Oxygen spill-over from copper to palladium is suggested as the mechanism of oxygen desorption from the oxidised Cu-Pd alloy surfaces.

X-ray photoelectron spectra and Auger studies of the surface oxidation of cobalt

Surface oxidation of Co has been investigated at different temperatures in the 300–600 K range at oxygen exposures upto 106 L by XPES and AES techniques. In the XPES, both the valence band and core level bands have been employed to monitor the oxidation while in the AES, metal Auger intensity ratios as well as O(KLL)/Co(L23M45M45) ratios have been examined. Only CoO is formed on the surface at high oxygen exposures at and above 500 K.

Vanadate inhibits mevalonate synthesis and activates NADH oxidation in microsomes

Abstract is not available.

Oxidation Of Sodium Sulfide In A Foam Bed Contactor

Oxidation of sodium sulphide to sodium thiosulphate has been experimentally investigated in a foam bed contactor using air as oxidizing medium. The var.

Oxidation of alkaline earth sulfides to sulfates: Thermodynamic aspects

The emf of the galvanic cell, Pt, Ni + NiO/(CaO) ZrO2/MS + MSO4, Ir, Pt, where M is calcium, strontium, or barium, has been measured in the temperature range 850 to 1100 K. From these measurements the Gibbs’ energy changes for the oxidation of sulfides of alkaline earth metals to their respective sulfates have been calculated. The results are compared with available thermodynamic data in the literature. The agreement varies from ±2 kJ for the strontium system to ±20 kJ in the case of barium. Trends in the stabilities of alkaline earth sulfates are discussed in relation to the properties of the cationic species involved.

Effect of iodine doping on surface and optical properties of polyterpenol thin films

This study presents the effect of iodine doping on optical and surface properties of polyterpenol thin films deposited from non-synthetic precursor by means of plasma polymerisation. Spectroscopic ellipsometry studies showed iodine doping reduced the optical band gap from 2.82 eV to 1.50 eV for pristine and doped samples respectively. Higher levels of doping notably reduced the transparency of films, an issue if material is considered for applications that require high transparency. Contact angle studies demonstrated higher hydrophilicity for films deposited at increased doping levels, results confirmed by XPS Spectroscopy and FTIR. Doping had no significant effect on the surface profile or roughness of the film.

Fabrication and characterization of plasma polymer thin films from monoterpene alcohols for applications in organic electronics and biotechnology

After more than twenty years of basic and applied research, the use of nanotechnology in the design and manufacture of nanoscale materials is rapidly increasing, particularly in commercial applications that span from electronics across renewable energy areas, and biomedical devices. Novel polymers are attracting significant attention for they promise to provide a low−cost high−performance alternative to existing materials. Furthermore, these polymers have the potential to overcome limitations imposed by currently available materials thus enabling the development of new technologies and applications that are currently beyond our reach. This work focuses on the development of a range of new low−cost environmentally−friendly polymer materials for applications in areas of organic (flexible) electronics, optics, and biomaterials. The choice of the monomer reflects the environmentally−conscious focus of this project. Terpinen−4−ol is a major constituent of Australian grown Melaleuca alternifolia (tea tree) oil, attributed with the oil's antimicrobial and anti−inflammatory properties. Plasma polymerisation was chosen as a deposition technique for it requires minimal use of harmful chemicals and produces no hazardous by−products. Polymer thin films were fabricated under varied process conditions to attain materials with distinct physico−chemical, optoelectrical, biological and degradation characteristics. The resultant materials, named polyterpenol, were extensively characterised using a number of well−accepted and novel techniques, and their fundamental properties were defined. Polyterpenol films were demonstrated to be hydrocarbon rich, with variable content of oxygen moieties, primarily in the form of hydroxyl and carboxyl functionalities. The level of preservation of original monomer functionality was shown to be strongly dependent on the deposition energy, with higher applied power increasing the molecular fragmentation and substrate temperature. Polyterpenol water contact angle contact angle increased from 62.7° for the 10 W samples to 76.3° for the films deposited at 100 W. Polymers were determined to resist solubilisation by water, due to the extensive intermolecular and intramolecular hydrogen bonds present, and other solvents commonly employed in electronics and biomedical processing. Independent of deposition power, the surface topography of the polymers was shown to be smooth (Rq <0.5 nm), uniform and defect free. Hardness of polyterpenol coatings increased from 0.33 GPa for 10 W to 0.51 GPa for 100 W (at 500 μN load). Coatings deposited at higher input RF powers showed less mechanical deformation during nanoscratch testing, with no considerable damage, cracking or delamination observed. Independent of the substrate, the quality of film adhesion improved with RF power, suggesting these coatings are likely to be more stable and less susceptible to wear. Independent of fabrication conditions, polyterpenol thin films were optically transparent, with refractive index approximating that of glass. Refractive index increased slightly with deposition power, from 1.54 (10 W) to 1.56 (100 W) at 500 nm. The optical band gap values declined with increasing power, from 2.95 eV to 2.64 eV, placing the material within the range for semiconductors. Introduction of iodine impurity reduced the band gap of polyterpenol, from 2.8 eV to 1.64 eV, by extending the density of states more into the visible region of the electromagnetic spectrum. Doping decreased the transparency and increased the refractive index from 1.54 to 1.70 (at 500 nm). At optical frequencies, the real part of permittivity (k) was determined to be between 2.34 and 2.65, indicating a potential low-k material. These permittivity values were confirmed at microwave frequencies, where permittivity increased with input RF energy – from 2.32 to 2.53 (at 10 GHz ) and from 2.65 to 2.83 (at 20 GHz). At low frequencies, the dielectric constant was determined from current−voltage characteristics of Al−polyterpenol−Al devices. At frequencies below 100 kHz, the dielectric constant varied with RF power, from 3.86 to 4.42 at 1 kHz. For all samples, the resistivity was in order of 10⁸−10⁹ _m (at 6 V), confirming the insulating nature of polyterpenol material. In situ iodine doping was demonstrated to increase the conductivity of polyterpenol, from 5.05 × 10⁻⁸ S/cm to 1.20 × 10⁻⁶ S/cm (at 20 V). Exposed to ambient conditions over extended period of time, polyterpenol thin films were demonstrated to be optically, physically and chemically stable. The bulk of ageing occurred within first 150 h after deposition and was attributed to oxidation and volumetric relaxation. Thermal ageing studies indicated thermal stability increased for the films manufactured at higher RF powers, with degradation onset temperature associated with weight loss shifting from 150 ºC to 205 ºC for 10 W and 100 W polyterpenol, respectively. Annealing the films to 405 °C resulted in full dissociation of the polymer, with minimal residue. Given the outcomes of the fundamental characterisation, a number of potential applications for polyterpenol have been identified. Flexibility, tunable permittivity and loss tangent properties of polyterpenol suggest the material can be used as an insulating layer in plastic electronics. Implementation of polyterpenol as a surface modification of the gate insulator in pentacene-based Field Effect Transistor resulted in significant improvements, shifting the threshold voltage from + 20 V to –3 V, enhancing the effective mobility from 0.012 to 0.021 cm²/Vs, and improving the switching property of the device from 10⁷ to 10⁴. Polyterpenol was demonstrated to have a hole transport electron blocking property, with potential applications in many organic devices, such as organic light emitting diodes. Encapsulation of biomedical devices is also proposed, given that under favourable conditions, the original chemical and biological functionality of terpinen−4−ol molecule can be preserved. Films deposited at low RF power were shown to successfully prevent adhesion and retention of several important human pathogens, including P. aeruginosa, S. aureus, and S. epidermidis, whereas films deposited at higher RF power promoted bacterial cell adhesion and biofilm formation. Preliminary investigations into in vitro biocompatibility of polyterpenol demonstrated the coating to be non−toxic for several types of eukaryotic cells, including Balb/c mice macrophage and human monocyte type (HTP−1 non-adherent) cells. Applied to magnesium substrates, polyterpenol encapsulating layer significantly slowed down in vitro biodegradation of the metal, thus increasing the viability and growth of HTP−1 cells. Recently, applied to varied nanostructured titanium surfaces, polyterpenol thin films successfully reduced attachment, growth, and viability of P. aeruginosa and S. aureus.

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.

Steric Aspects Of The Oxidation Of Thioketones By Singlet Oxygen

Singlet oxygen oxidation of dialkyl thioketones yields the corresponding ketones and in some cases sulfoxides in varying amounts. Steric considerations on the reactive zwitterionic/diradical intermediates have been invoked to rationalise the product distribution.

A Novel Approach to the Study of Surface Oxidation States and Oxidation of Transition Metals by Auger Electron Spectroscopy

L$_{23}$ M$_{45}$ M$_{45}$/L$_{23}$ M$_{23}$ M$_{45}$, L$_{23}$ M$_{45}$ M$_{45}$/L$_{23}$ M$_{23}$ M$_{23}$ and L$_{23}$ M$_{23}$ M$_{45}$/L$_{23}$ M$_{23}$ M$_{23}$ Auger intensity ratios in transition metal oxides and sulphides are shown to be directly related to the number of valence electrons in the metal as well as to its oxidation state. The metal Auger intensity ratios provide a unique probe, independent of O (KLL) intensity, to study surface oxidation states of metals. These intensity ratios have been effectively employed to investigate surface oxidation of nickel, iron and copper. The oxidation studies have unravelled some interesting aspects of surface oxidation.

Oxidation of sodium sulphide in the presence of fine activated carbon particles in a foam bed contactor

The oxidation of sodium sulphide in the presence of fine activated carbon particles (4.33 μm) has been studied at 75°C in a foam bed contactor. The existing single-stage model of a foam bed reactor has been modified to take into account the effect of heterogeneous catalyst particles and the absorption in the storage section. The variables studied are catalyst loading, initial sulphide concentration and the average liquid hold-up in the foam bed. It is seen that the rates of oxidation of sodium sulphide are considerably enhanced by an increase in the loading of activated carbon particles. The rate of conversion of sodium sulphide also increases with an increase in the average liquid hold-up in the foam. The modified model predicts these effects fairly well. The contribution of reaction in the storage section is found to be less than 2% of the overall rate of conversion in the contactor.