Showing papers on "Platinum published in 1987"

The mechanism of action of platinum antitumor drugs

Abstract: A discussion is presented on the mechanism of action of platinum amine compounds, used as antitumor drugs. The relationship between biological acitivity and structure of the compounds is discussed, with special attention to the nature of the ligands coordinated to platinum. The primary biological target appears to be the interaction with nucleic acids, and therefore studies of the interaction of platinum amine compounds (both active and inactive ones) with nucleic acids and nucleic acid fragments are of great interest. Studies on mononucleotides have made clear that a strong preference exists for platinum binding at guanine—N7 sites. Investigations on oligonucleotides have shown that, when two neighboring guanines are present, chelation of the cis—Pt(NH3)2 unit (abbreviated cisplatin) is strongly preferred above all other possibilities. Studies on DNA ( in vivo and in vitro) have made clear that similar binding modes occur in DNA and oligonucleotides, and that after cisplatin binding — the DNA structure is distorted in the same way as double-stranded oligonucleotides.

Extending surface-enhanced Raman spectroscopy to transition-metal surfaces: carbon monoxide adsorption and electrooxidation on platinum- and palladium-coated gold electrodes

Abstract: Thin (ca. one to three monolayers) films of platinum and palladium electrodeposited on electrochemically roughened gold are observed to yield surface-enhanced Raman (SER) spectra for adsorbed carbon monoxide. The major vibrational band(s) on these surfaces are diagnosed from their frequencies as arising from C-O stretching vibrations, nu/sub CO/ bound to the transition-metal overlayers rather than to residual gold sites. The observed SFR nu/sub CO/ frequencies are closely similar to (within ca. 10 cm/sup -1/ of) those obtained for these systems from potential-difference infrared (PDIR) spectra. The major SERS and PDIR nu/sub CO/ features for the platinum and palladium surfaces appear at 2060-2090 and 1965-1985 cm/sup -1/, respectively, consistent with the presence of terminal and bridging CO on these two electrodes. The infrared as well as electrochemical properties of these systems are closely similar to those for the corresponding polycrystalline bulk electrodes. A difference between the SER- and IR-active adsorbed CO, however, is that the former undergoes electrooxidation on both surfaces at 0.2-0.3 V higher overpotentials than the latter form. Examination of the potential-dependent SERS bands for metal oxide vibrations, nu/sub PtO/, on the platinum surface shows that the electrooxidation potential for the SERS-active adsorbed CO coincides with that for themore » appearance of the nu/sub PtO/ band. Some broader implications to the utilization of SERS for examining transition-metal surfaces are pointed out.« less

Electrocatalysis of oxygen reduction by chalcogenides containing mixed transition metal clusters

Abstract: A new class of catalysts for the reduction of molecular oxygen to water in acid environment has been discovered, which show eletrocatalytical activity comparable to that of platinum. They are Chevrel type chalcogenides with the stoichiometry Mo/sub 6-x/M/sub x/X/sub 8/ (M = transition metal, X = chalcogen atom), containing octahedral mixed-metal clusters of transition-metal atoms. Experimental data obtained with rotating disk and rotating ring disk techniques, photoelectrochemical studies, photoelectron spectroscopy, and conductivity measurements are presented for the compound Mo/sub 4.2/Ru/sub 1.8/Se/sub 8/, which is a p-type semiconductor (energy gap determined to be E/sub g/ = 1.3 eV). The catalytic activity increases from samples containing nonsubstituted Mo octahedra showing metallic behavior to samples containing Ru substituted Mo octahedra showing semiconducting behavior due to an electron count close to 24. Possible mechanisms of catalysis are discussed. Important features are considered to be the capacity of the cluster to act as a reservoir for electronic charge carriers while maintaining a stable electrochemical potential, its capacity to provide neighboring binding sites for reactants and intermediates, and its ability to change its volume and bonding distances in the course of electron transfer.

Ruthenium dioxide as a hydrogen-evolving cathode

Abstract: Ruthenium dioxide was investigated as a cathode material for hydrogen evolution in acid media. In 1 N H2SO4 a Tafel slope of 40m V was obtained and an exchange current density of 6×10−5 A cm−2, which is about one order of magnitude lower than that for platinum. XPS analysis showed that only partial reduction of the oxide occurred during hydrogen evolution. RuO2 cathodes are almost insensitive to poisoning by metal ions in solution. This observation is in contrast to the behaviour of platinum and can be correlated to the underpotential deposition phenomenon which does not occur on RuO2. The performance of RuO2 cathodes in lab-scale Membrel water electrolysis cells is demonstrated and compared to that of platinum cathodes.

Process for the oxidation of di-, tri-, oligo- and polysaccharides into polyhydroxycarboxylic acids, the catalyst used and the products so obtained

Abstract: Process for the selective oxidation of di-, tri-, oligo- and polysaccharides comprising a reducing terminal function of the aldose type into polyhydroxycarboxylic acids, wherein the oxidation is carried out in an alkaline medium by means of an oxygen-containing gas, in the presence of a noble metal based catalyst selected from the group constituted by palladium, platinum, rhodium and osmium and fixed on an inert support, said catalyst being "doped" with one or several metals, or promoters, of Groups IV, V or VI of the Periodic Table.

Catalytic reforming process

Abstract: In a catalytic reforming process wherein a charge is circulated successively through a first catalyst bed and then at least one further catalyst bed, the improvement wherein the catalyst of the first bed comprises a carrier of alumina base and, by weight in proportion to the carrier, 0.05-0.6% of platinum, 0.005-3% of rhenium and 0.1-15% of at least one halogen and wherein each catalyst of the other beds contains a carrier of alumina base and, by weight with respect to the carrier, 0.05-0.6% of platinum, 0.05-3% of at least one metal promoter selected from the group consisting of tin, thallium and indium and 0.1-15% of at least one halogen, the proportion by weight of the catalyst containing platinum and rhenium ranging from 8 to 40% with respect to the total catalyst mass used in all the catalyst beds.

Digital simulation of homogeneous chemical reactions coupled to heterogeneous electron transfer and applications at platinum/mica/platinum ultramicroband electrodes

Abstract: Analytical Chemistry is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Digital simulation of homogeneous chemical reactions coupled to heterogeneous electron transfer and applications at platinum/mica/platinum ultramicroband electrodes Theresa Varco. Shea, and Allen J. Bard Anal. Chem., 1987, 59 (17), 2101-2111 • DOI: 10.1021/ac00144a021 Downloaded from http://pubs.acs.org on February 3, 2009

Effect of terraces and steps in the electrocatalysis for formic acid oxidation on platinum

Abstract: Hydrogen and oxygen adsorption was examined on 14 stepped surfaces having [100] zone axis and on 17 stepped surfaces having zone axis of [110]. The electrocatalytic activity for formic acid oxidation was also studied. It was found that there are 6 groups of hydrogen peaks and corresponding oxygen peaks which are typical for the low index planes (111), (100), (110), and for (533) and (311). The electrocatalytic activity changes with terrace width, the maximum of which is on the (111) terrace and on (210).