Showing papers on "Platinum published in 1991"

Anodic oxidation of phenol for waste water treatment

Abstract: The electrochemical oxidation of phenol for waste water treatment was studied at a platinum anode. Analysis of reaction intermediates and a carbon balance has shown that the reaction occurs by two parallel pathways; chemical oxidation with electrogenerated hydroxyl radicals and direct combustion of adsorbed phenol or/and its aromatic intermediates to CO2.

Platinum and Other Metal Coordination Compounds in Cancer Chemotherapy

Abstract: By Vilhelm A. Bohr, Eddie Reed*) and Wei ping Zhen Laboratory of Molecular Pharmacology and *)Medicine Branch, National Cancer Institute, Bldg. 37 Rm 5C-25, NIH, Bethesda, MD 20892 We have developed techniques to study the DNA damage formation and repair of cisplatin lesions in individual genes. The frequency of intrastrand adducts and interstrand crosslinks can be determined in restriction fragments within genes or in non-transcribed gene regions. In hamster cells, intrastrand adducts are repaired faster from the essential dihydrofolate reductase (DHFR) gene than from an inactive region. In contrast, interstrand crosslinks are repaired at a similar rate from the active and inactive genomic regions. In an attempt to study the role of DNA repair in drug resistance, we have examined the repair of these lesions in certain important genes in cisplatin sensitive and resistant human ovarian cancer cells. The resistant cells repair interstrand crosslinks more efficiently than the sensitive ones from the DHFR gene, the multidrug resistance gene and from the inactive oglobin gene. However, these ovarian cancer cell lines do not differ in their ability to repair cisplatin intrastrand adducts from these genes.

Electrochemical waste water treatment using high overvoltage anodes Part II: Anode performance and applications

Abstract: The performance of highly doped SnO2 anodes for the oxidative treatment of biologically refractory waste water was compared with PbO2 and Pt. The oxidation of a wide range of organic compounds proceeds with an efficiency which is about 5 times higher than with platinum anodes. The oxidation efficiency was found to be independent of the pH of the water. In chloride containing media, SnO2 anodes produce less chlorine gas than platinum anodes and hence show less potential to form hazardous chlorinated organic by-products. The design of a simple plate-and-frame reactor with undivided cells for waste water treatment using SnO2 anodes was based on two experimental findings: (a) no interference of the cathode with the oxidation has been found: (b) the rate of oxidation is not limited by mass transfer, indicating the participation of homogeneous reactions in the overall oxidation. The new anode material reduces the specific energy requirement of electrochemical oxidation of organics in waste water to 30 to 50 kWh kg−1 of COD removed. This makes the process an interesting alternative to chemical oxidation using oxidants such as ozone and hydrogen peroxide, or wet oxidation using oxygen at elevated temperature and pressure.

Electrochemical reduction and oxidation of C60 films

Abstract: We describe the first electrochemical study of films of C 60 on platinum electrodes. The cyclic voltammetry (CV) of such films in tetra-n-butylammonium [(TBA)AsF 6 ]/MeCN, showing an unusual hysteresis, differs from the CV of dissolved C 60 and suggests that large structural or resistive changes occur on reduction

Penetration of carboplatin and cisplatin into rat peritoneal tumor nodules after intraperitoneal chemotherapy

Abstract: Platinum distribution was studied in rat peritoneal tumors after i.p. treatment with equimolar doses of carboplatin and cisplatin. Low platinum concentrations (4 ppm) were detected in the periphery of the tumor after carboplatin treatment, whereas no platinum was detected 0.5 mm in from the periphery. In contrast, after cisplatin treatment, high platinum concentrations (29 ppm) were measured in the periphery of the tumor and moderate concentrations (14 ppm) were measured in the center. Only following increased carboplatin doses were low platinum concentrations detectable in the tumor. The total platinum concentration in the tumors was determined after equimolar administration of both drugs. In all, 7 times more platinum was detected after cisplatin treatment than after carboplatin treatment, and 10 times more carboplatin than cisplatin had to be injected to obtain comparable platinum concentrations in the tumors. When single cells were incubated with equimolar concentrations of carboplatin and cisplatin, 6-7 times more platinum was found in cells treated with cisplatin. However, pharmacokinetic studies favored i.p. administration of carboplatin because the clearance of this compound from the peritoneal cavity, expressed as t1/2 beta, was lower than that of cisplatin (239 vs 78 min), resulting in an AUC in the peritoneal cavity for both total and ultrafiltered drug that was almost 3 times higher for carboplatin than cisplatin. The AUC for ultrafiltered carboplatin in plasma was 2-fold that for cisplatin (2,801 +/- 210 vs 1,334 +/- 431 microM m). The present study demonstrated that in spite of the pharmacological advantages of carboplatin, its capacity to penetrate into peritoneal tumors and tumor cells is far lower than that of cisplatin.

Catalyst composition containing segregated platinum and rhodium components

Abstract: A catalyst composition suitable for three-way conversion of internal combustion engine, eg, automobile gasoline engine, exhaust gases includes a catalytic material disposed in two discrete coats on a carrier The first coat includes a stabilized alumina support on which a first platinum catalytic component is dispersed and bulk ceria, and may also include bulk iron oxide, a metal oxide (such as bulk nickel oxide) which is effective for the suppression of hydrogen sulfide emissions, and one or both of baria and zirconia dispersed throughout the first coat as a thermal stabilizer The second coat, which may comprise a top coat overlying the first coat, contains a co-formed (eg, co-precipitated) rare earth oxide-zirconia support on which a first rhodium catalytic component is dispersed, and a second activated alumina support having a second platinum catalytic component dispersed thereon The second coat may also include a second rhodium catalytic component, and optionally, a third platinum catalytic component, dispersed as an activated alumina support The present invention also provides a method for treating engine exhaust gases by contacting the gases under conversion conditions with the catalyst composition

Effect of silver deposits on the photocatalytic activity of titanium dioxide samples for the dehydrogenation or oxidation of 2-propanol

Abstract: Until now, the effect of the deposition of metal particles onto a powdered semiconductor oxide on its photocatalytic activity has been determined for group VIII transition metals only. In this study, AGTiO2 samples were prepared by photodeposition, characterized by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) and tested, under band-gap illumination, using the oxidation of 2-propanol (neat liquid phase or mixed with water) in the absence or presence of molecular oxygen. The silver deposits were found to be metallic both before and after use, but the size of the particles and their distribution on the support were markedly influenced by the type of TiO2 sample. A small amount of silver caused the catalytic oxygen-free oxidation of 2-propanol, although the rate was much lower than that with platinum which possesses dehydrogenating properties. This effect is thought to be due to the electron-attracting role of the metal particles. For oxidation of 2-propanol by molecular oxygen, an optimum silver content was observed (corresponding to a rate improvement of approximately 50%). This was interpreted to be due to the beneficial effects of silver on the trapping of electrons and/or the reduction of oxygen. At higher than optimum silver contents there was a detrimental increase in the probability of recombination of charges at the numerous silver particles. The optimum was shifted to lower values in the presence of water, which is tentatively explained by competitive hole trapping by 2-propanol, water and silver.

Correlation between CO frequency and Pt coordination number. A DRIFT study on supported Pt catalysts

Abstract: The infrared stretching frequencies of linear-bonded carbon monoxide on face, edge and corner atoms have been identified with four platinum catalysts. The metal particles were supported on different absorbentia and each having a different average particle size, ranging from about 10 to 200 A. The $$\tilde v_{CO}$$ values of the various absorption bands correlate linearly with the number of nearest neighbours of the different surface sites (n in C n ). Effects of an interaction between Pt clusters and support on the linear-CO stretching frequency have not been observed. This empirical correlation between $$\tilde v_{CO}$$ and Cn, and the advantages ofin situ Diffuse Reflectance Fourier transform Infrared Spectroscopy in combination with derivative spectrometry opens the possibility to monitor the dispersity of supported platinum in a simple and relatively quick way.

A non-porous supported-platinum catalyst for aromatization of n -hexane

Abstract: THE cyclization of C6 and C7n-alkanes to form aromatic compounds is highly desirable in the petroleum-refining industry. Platinum metal clusters incorporated into the channels of zeolite L have been found to catalyse the aromatization of hexane and heptane with high activity and selectivity1,2. The susceptibility of this catalyst to sulphur poisoning, however, means that the hydrocarbon reagents must be of high purity, free from sulphur contamination2. It has been generally believed that the pore structure of the zeolite plays an important part in the selectivity of the catalytic process. Here we describe a non-porous platinum catalyst that can convertn-hexane to benzene with an activity and selectivity comparable to that of the zeolite. The catalyst consists of platinum clusters, about 2 nm in diameter, supported on a basic, high-surface-area magnesium oxide stabilized by aluminium. The product distribution for n-hexane is almost identical to that obtained using the zeolite L catalyst. These results point to a new approach to hydrocarbon reforming based on metal species supported on highly basic, non-porous carriers.

Enantioselective Hydrogenation of Ethyl Pyruvate: Effect of Catalyst and Modifier Structure

Abstract: The effect of catalyst and modifier structure on selectivity and activity for the enantioselective hydrogenation of ethyl pyruvate with cinchona modified Pt/Al2O3 catalysts has been investigated. It has been found that the platinum dispersion and the method of catalyst preparation have a decisive influence on the catalytic performance. In order to get high optical yields, the platinum dispersion should be lower than 0.2 - 0.3. The texture of the support is less important but must be optimized with respect to pore size in order to get high enantioselectivity. Modifiers derived from cinchonidine lead to an excess of (R)-ethyl lactate while cinchonine gives preferentially the S enantiomer. Changes in the O-C9-C8-N part of the cinchona alkaloid have a decisive influence both on sign and size of the optical induction while the nature of the substituent in the quinuclidine part, R1, has only a minor effect. Partial hydrogenation of the quinoline rings results in a decreased enantioselectivity. Conclusions concerning the mode of action of the enantioselective catalyst are discussed.

In situ infrared spectroscopy at single-crystal metal electrodes : an emerging link between electrochemical and ultrahigh-vacuum surface science

Abstract: The utilization of infrared reflection-absorption spectroscopy for the in situ molecular characterization of monocrystalline metal-solution interfaces is outlined in comparison with the behavior of metal surfaces in ultrahigh vacuum (uhv) and illustrated for the adsorption of carbon monoxide on low-index platinum and rhodium surfaces in aqueous media

Reactivity of chloro- and aqua(diethylenetriamine)platinum(II) ions with glutathione, S-methylglutathione, and guanosine 5'-monophosphate in relation to the antitumor activity and toxicity of platinum complexes

Abstract: The reactivity of the two platinum(II) complexes [Pt(dien)Cl] + and [Pt(dien)(H 2 O)] 2+ with glutathione (GSH), S-methylglutathione (GS-Me), and guanosine 5'-monophosphate (5'-GMP) has been investigated and compared The reactions of GSH and GS-Me with the two platinum complexes are second order, ie with a direct nucleophilic attack by the entering ligand on the platinum

Excimer laser device

Abstract: At least the opposing surface portions of the main electrodes of an excimer laser device are covered with materials which are resistive to chemical etching than nickel. The etching resistive material may be a platinum based alloy containing rhodium, ruthenium, iridium, or osmium; a nickel based alloy containing gold, platinum, rhodium, ruthenium, iridium, or osmium; or rhodium, ruthenium, iridium, or osmium. Thus, an excimer laser device is realized by which the lives of the electrodes and the laser gas are prolonged.

Electrochemical oxidation of methanol on tin-modified platinum single-crystal surfaces

Abstract: To understand the role of tin as a promoter in the electrochemical oxidation of methanol, the authors have studied the geometric and electronic effect of tin atoms in different chemical states on/in the platinum surface by using single-crystal faces of the ordered alloy Pt{sub 3}Sn and single-crystal faces of pure Pt modified by electrodeposited/adsorbed tin, i.e., the so-called adatom state. They found that none of the alloy surfaces were more effective catalysts than any of the pure platinum surfaces under the conditions of measurement employed here and that alloying platinum with tin to any extent significantly reduced the activity. As reported previously by others, they observed tin to spontaneously adsorb on platinum surfaces from dilute sulfuric acid supporting electrolyte containing Sn(II) in concentrations above ca. 5 {mu}M. At a given concentration, the coverage by tin decreased as the atomic density of the platinum surface increased. However, they did not observe any enhancement of methanol oxidation on any platinum modified by this irreversibly adsorbed tin. They did observe a diffusion-limited enhancement on Pt(111) and on Pt(100) due to Sn(II) in the electrolyte at 1 {mu}M concentration. At this concentration, tin did not appear to be adsorbed to any observable extent, andmore » the catalysis appeared to occur via the direct interaction of a dissolved tin species with the surface. They propose a mechanism of catalysis that is a hybrid homogeneous-heterogeneous sequence based on known homogeneous Pt-Sn catalysts.« less

Tumor-inhibiting bis(β-Diketonato) metal complexes. Budotitane, cis-diethoxybis(1-phenylbutane-1,3-dionato)titanium(IV)

Abstract: Cisplatin, cis-diamminedichloroplatinum(II), and carboplatin, cis-diammine(cyclobutane-1,1-dicarboxylato)platinum(II), are the first drugs from inorganic chemistry to have come under routine clinical use in medical oncology. Their antitumor activity ranges from testicular carcinomas, ovarian carcinomas, and tumors of the head and neck to bladder tumors. However, the spectrum of indication is fairly limited. There is no or only insufficient antitumor activity in tumors which account for the major share of cancer mortality today, e.g. lung tumors and gastrointestinal tumors. Direct derivatives of cisplatin such as carboplatin have only led to a limited reduction or change in drug toxicity. In most cases, the toxicity pattern has changed from nephrotoxicity to myelotoxicity. New metal complexes are now being developed which are designed to supplement the spectrum of indication of platinum complexes. Among non-platinum complexes, budotitane (INN), cis-diethoxybis(1-phenylbutane-1,3-dionato)titanium(IV), is among the most advanced. It is undergoing clinical trials today. Extensive investigations into structure-activity relations have clearly shown a dependence of the activity on the central metal and the diketonato ligand. The tumor-inhibiting effect decreases in the order titanium > zirconium > hafnium > molybdenum > tin > germanium. Antitumor activity is also highly dependent on the nature of the diketonate used. Ligands substituted with planar aromatic ring systems such as the phenyl groups in budotitane are advantageous. Most of the tumor-inhibiting bis(β-diketonato) complexes are cis-configurated. The cis-configurated compounds with an unsymmetrically substituted β-diketonate as ligand are in an equilibrium between three possible cis-isomers in solution at room temperature, due to the fact that the diketonate can rotate via a twist mechanism. The easily hydrolizable group in these complexes does not play a major role in antitumor activity, but it is important for the galenic formulation in the clinic. The ethoxy group as leaving group in budotitane hydrolizes at a slower rate than the corresponding halides.

Low temperature adsorption of ethylene and butadiene on platinum and palladium surfaces: A theoretical study of the diσ/π competition

Abstract: The different low temperature coordination modes of ethylene and butadiene on a platinum (111) face, (110) face and on a palladium (111) face are compared on the basis of extended Huckel calculations. The nature of the chemical interaction between the olefin and the surface is detailed and the electronic factors that govern the coordination mode of the hydrocarbon are underlined. The different surfaces are modelled by a 49 or a 44 atoms cluster. A correction is applied in the calculation in order to minimize the artefact introduced by this cluster representation of an extended surface. For the adsorption, the respective importance of two electrons interactions and four electrons repulsions is the key point for the determination of the preferred mode. The di-σ coordination is more stable on platinum (111) but on the platinum (110) face the π coordination yields the same adsorption energy than the di-σ one. This is roughly the same result for the palladium (111) face. The π mode is there favored by a decrease of the four electrons repulsions caused either by a smaller number of metal neighbours for the surface atom (Pt(110)) or by a reduced radial expansion of the metal orbitals (Pd(111)). This π coordination is associated with a smaller hybridization of the ethylene molecule. The results are extended to the adsorption of butadiene and this allows a qualitative explanation of the better selectivity for butadiene partial hydrogenation on palladium compared with platinum.