Showing papers on "Molybdenum published in 1978"

Auger Electron Spectroscopic and Electrochemical Analysis of the Effect of Alloying Elements on the Passivation Behavior of Stainless Steels

Abstract: This investigation is concerned with the effect of chromium and molybdenum on the formation of the passive film of stainless steels, and its corrosion resistance to the chloride ion. The corrosion resistance to the chloride ion was estimated by the potential decay method and the measurement of the anodic polarization curve. The composition analysis of the passive film was performed by Auger Electron Spectroscopic Analysis. The following conclusions were obtained from the test results: (1) The passive film was more resistant in the environment containing chloride ions as the chromium content in the passive film increased, and (2) molybdenum was observed on AES analysis to have an effect on the increment of the chromium content in the passive film and to promote the passive film formation of stainless steels, probably adsorbing on the active metal surface in the form of molybdate.

Comparison of the molybdenum centres of native and desulpho xanthine oxidase. The nature of the cyanide-labile sulphur atom and the nature of the proton-accepting group.

Abstract: The non-functional form of xanthine oxidase known as the desulpho enzyme was compared with the functional enzyme in various ways, to obtain information on the structure of the molybdenum centre and the mechanism of the catalytic reaction. The desulpho enzyme, like the functional one, possesses a site for the binding of anions, presumably as ligands of molybdenum. Evidence is presented that in the Mo(V) e.p.r. signal from the desulpho-enzyme, as in that from the functional enzyme, a weakly coupled proton, in addition to a strongly coupled proton, interacts with the metal. Measurements were carried out by e.p.r. on the rate at which the proton strongly coupled to molybdenum exchanged, on diluting enzyme samples with 2H2O. For the desulpho enzyme the exchange rate constant was 0.40s-1, at pH 8.2 and 12 degrees C, and for the functional enzyme it was 85 s-1. It is shown that the great majority of reported differences between the enzyme forms are consistent with functional enzyme containing an (Enzyme)-Mo=S grouping, replaced in the desulpho form by (Enzyme)-Mo=O. Protonation of these groups, with pK values of about 8 and 10 respectively, would give (Enzyme)-Mo-SH and (Enzyme)-Mo-OH, these being the forms observed by e.p.r. The accepting group in the functional enzyme, for the proton transferred from the substrate while molybdenum is reduced in the catalytic reaction [Gutteridge, Tanner & Bray (1978) Biochem J. 175 869-878], is thus taken to be Mo=S.

Organo molybdenum friction-reducing antiwear additives

Abstract: Hydrocarbon-soluble organo molybdenum complexes obtained as the reaction product of a hydrocarbyl substituted hydroxy alkylated amine e.g. N,N',N'-tris(2-hydroxy ethyl)-n-tallow-1,3-diaminopropane, with about one molar equivalent of a molybdenum compound, e.g. ammonium molybdate, are useful hydrocarbon additives particularly in combination with an oil-soluble sulfur donor, e.g. a metal dialkyl dithiophosphate to provide an additive combination for lubricating oils since the lubricating compositions comprising these co-additives exhibit improved anti-friction and anti-wear properties.

Electron-paramagnetic-resonance studies on nitrate reductase from Escherichia coli K12

Abstract: Nitrate reductase was purified from anaerobically grown Escherichia coli K12 by a method based on the Triton X-100 extraction procedure of Clegg[(1976) Biochem. J.153, 533-541], but hydrophobic interaction chromatography was used in the final stage. E.p.r. spectra obtained from the enzyme under a variety of conditions are well resolved and were interpreted with the help of the computer-simulation procedures of Lowe [(1978) Biochem. J.171, 649-651]. Parameters for five molybdenum(V) species from the enzyme are given. The low-pH species (g(av.) 1.9827) is in pH-dependent equilibrium with the high-pH species (g(av.) 1.9762), the pK for interconversion of the species being 8.26. Of a variety of anions tested, only nitrate and nitrite formed complexes with the enzyme (in the low-pH form), giving modified molybdenum(V) e.p.r. spectra. These complexes, as well as the low-pH form of the free enzyme, showed interaction of molybdenum with a single exchangeable proton. The fifth molybdenum(V) species, sometimes detected in small amounts, appears not to be due to functional nitrate reductase. After full reduction of the enzyme with dithionite, addition of nitrate caused reoxidation of molybdenum to the quinquivalent state, in a time less than the enzyme turnover. Activity of the enzyme in the pH range 6-10 is controlled by a pK of 8.2. It is suggested that the low-pH signal-giving species is the form of the enzyme involved in the catalytic cycle. Iron-sulphur and other e.p.r. signals from the enzyme are briefly described and the enzymic reaction mechanism is discussed.

The XUV spectra of highly ionised molybdenum

Abstract: The spectra of molybdenum ions produced in Tokamaks in the wavelength range 10-200 AA have been reproduced in a plasma formed by laser beam irradiation of solid molybdenum targets. Lines from highly ionised stages of molybdenum (Mo XXX to Mo XXXII) have been distinguished by varying the laser beam intensity. Detailed analyses of the simpler ions, Mo XV (Ni-like), Mo XVI (Co-like), Mo XXXII (Na-like), and to a lesser extent Mo XXXI (Mg-like) and Mo XVII (Fe-like), have been achieved by comparison with ab initio calculations. A general interpretation of intermediate ion stages is also given but it is shown that most of these spectra are so complex, as a result of inner-subshell excitation, that detailed term-scheme analyses are nearly impossible.

Active homogeneous catalysts for the water gas shift reaction derived from the simple mononuclear carbonyls of iron, chromium, molybdenum, and tungsten

Abstract: This paper describes the homogeneous catalysis of the water gas shift reaction (CO + H/sub 2/O reversible CO/sub 2/ +H/sub 2/) using basic solutions of the mononuclear metal carbonyls Fe(CO)/sub 5/ and M(CO)/sub 6/(M = Cr, Mo and W).

Hydrogen storage material

Abstract: An economical metallic material for storage of hydrogen comprising an alloy representable by the formula ABα in which "A" comprises from 50 to under 100 atomic percent of titanium and the remainder which is at least one element selected from the group I consisting of zirconium and hafnium, B comprises from 30 to below 100 atomic percent of manganese and the remainder which is at least one element selected from the group II consisting of chromium, vanadium, niobium, tantalum, molybdenum, iron, cobalt, nickel, copper and rare earth elements, and α is a value indicating a ratio of B to A, and is in the range of 1.0 to 3.0. The materials of the invention very easily absorb large amounts of hydrogen and efficiently release it at other predetermined temperatures, pressures and electrochemical conditions, whereby it is able to store hydrogen safely, usefully and economically.

Isolation of thiomolybdate compounds from the molybdenum-iron protein of clostridial nitrogenase.

Abstract: Acid/base treatment of the molybdenum-iron protein of the nitrogenase from Clostridium pasteurianum 25 yields low-molecular-weight compounds of molybdenum, which can be separated from the protein by gel chromatography. Elementary analysis and spectral properties relate these compounds to thiomolybdate anions. It is proposed that in its native state nitrogenase contains a thio complex of molybdenum coupled to iron-sulfur clusters.

Catalyst comprising Raney nickel with adsorbed molybdenum compound

Abstract: This invention provides an improved Raney nickel catalyst characterized by having a molybdenum compound adsorbed thereon. The novel catalyst contains about 0.5-15 parts by weight of molybdenum adsorbed per 100 parts by weight of Raney nickel solids. Optionally, one or more additional metals may be included in the catalyst. The catalyst is particularly effective in the manufacture of high quality butanediol by hydrogenation of butynediol, and for selective hydrogenation of carbonyl groups, sometimes even in the presence of carbon-carbon unsaturation, e.g. for the conversion of furfural to furfuryl alcohol.

The molybdenum centre of native xanthine oxidase. Evidence for proton transfer from substrates to the centre and for existence of an anion-binding site.

Abstract: The observation by Bray & Knowles [Proc. R. Soc. London Ser. A (1968) 302, 351--353] of direct transfer, during the catalytic reaction, of hydrogen atoms from substrate molecules to the enzyme xanthine oxidase was reinvestigated. The experimental phenomenon and its basic interpretation were confirmed and extended. In the reduced functional enzyme, molybdenum(V) interacts with two enzyme-bound protons, which are exchangeable with solvent protons. One of these is coupled to the metal with AHav. 1.4mT and the other with AHav. 0.3mT. The molecule also contains a site for the binding of anions, presumably as ligands of molybdenum. This is shown by effects of nitrate ions on the e.p.r. spectra. The spectra of the nitrate and 1-methylxanthine complexes of the reduced enzyme are very similar to one another, and are designated Rapid type-1 spectra. It is concluded that, in the Michaelis complex, the substrate molecule occupies the anion site, probably being bound to molybdenum via the nitrogen in its 9-position. During the turnover process, hydrogen from the substrate C-8 position, after transfer to the enzyme, appears as the proton more strongly coupled to molybdenum. This proton then exchanges with solvent deuterium with a rate constant of 27s-1, at pH 8.2 and 12 degrees C. It has been confirmed that substrate molecules occupying the anion site do not interfere with observation of the transfer and exchange processes.