Incorporation Of Oxygen Atoms Research Articles

Mechanism of the Initial Stage of the Oxidation of the Clean and Precovered with Nonmetals Iron Surface

The oxidation of the iron surface has been studied using the Auger electron spectroscopy method, particularly the intermediate state of the process proceedings between a monolayer of oxygen and an oxide layer. The oxidation of the clean iron surface has been compared to that of the iron surface precovered with carbon, sulfur, nitrogen, and phosphorus. The monolayer of carbon or nitrogen does not affect the rate of the oxidation process; however the monolayer of sulfur or phosphorus inhibits the oxidation. The mechanism of the oxidation stage between the monolayer of oxygen and the oxide layer has been elucidated taking into account the incorporation of oxygen atoms into the first iron layer. The concentration of defects in the bidimensional adsorbate layer has been taken into consideration. The number of surface defects in the 2D lattice of sulfur or phosphorus is 20 times lower than in the layer of oxygen.

The effect of surface nucleation on the evolution of crystalline microstructure during solid phase crystallization of amorphous Si films on SiO2

The effect of surface nucleation on the evolution of crystalline microstructure during the solid phase crystallization (SPC) of an amorphous Si (a-Si) film, deposited by low pressure chemical vapor deposition (LPCVD) on SiO2, has been investigated. The surface nucleation phenomenon was observed by suppressing the interface (a-Si/SiO2) nucleation by the incorporation of oxygen atoms during the initial deposition period of a-Si. It was found that the surface-nucleated polycrystalline Si (poly-Si) had equiaxial grains with the size of about 3–5 μm, while interface-nucleated one had elliptical grains with the size of about 0.3–1 μm.

Elucidation of the metabolic pathway for dibenzothiophene desulphurization by Rhodococcus sp. strain IGTS8 (ATCC 53968).

Rhodococcus sp. strain IGTS8 (ATCC 53968) is able to utilize dibenzothiophene (DBT) as a sole source of sulphur. The carbon skeleton of DBT is not metabolized and is conserved as 2-hydroxybiphenyl (HBP), which accumulates in the medium. This phenotype is due to the expression of the plasmid-encoded DBT-desulphurization (dsz) operon, which encodes three proteins, DszA, B and C. In this paper it is shown, using [35S]DBT radiolabelling studies, that sulphur is released in the form of inorganic sulphite. The pathway of DBT desulphurization is described in detail. In summary, DszC catalyses the stepwise S-oxidation of DBT, first to dibenzothiophene 5-oxide (DBTO) and then to dibenzothiophene 5,5-dioxide (DBTO2); DszA catalyses the conversion of DBTO2 to 2-(2'-hydroxyphenyl)benzene sulphinate (HBPSi-) and DszB catalyses the desulphination of HBPSi- to give HBP and sulphite. Studies with cell-free extracts show that DszA and DszC, but not DszB, require NADH for activity. 18O2-labelling studies show that each incorporated oxygen atom is derived directly from molecular oxygen. These results are consistent with the role of DszC as a mono-oxygenase, of DszA as an apparently unique enzyme which catalyses the reductive hydroxylation of DBTO2 leading to cleavage of the thiophene ring, and of DszB as an aromatic sulphinic acid hydrolase.

Channeling analysis of oxygen in oxide materials using 16O(α, α) 16O resonant backscattering

The crystalline quality of some oxide films has been investigated using 16O(α, α) 16O 3.045 MeV resonant backscattering and channeling technique. For a SiO 2 film of 5904 Å, the minimum yield ( χ min) values for Si and oxygen were both 1.0, indicating an amorphous film. However, for a TiO 2 sample, the χ min value of the resonant oxygen was twice as large as that of Ti. We discussed the difference in terms of two possibilities of imperfect incorporation of oxygen atoms and unknown effect concerning to the resonant backscattering. For other oxide films such as SrTiO 3 films, the χ min values of the resonant oxygen and other metallic elements has also been investigated.

X-ray photoelectron spectroscopic study of the oxidation of polycrystalline rhenium by exposure to O 2 and low energy O 2+ ions

X-ray photoelectron spectroscopy has been used to study the interaction of O 2 and low energy O 2 + ions with polycrystalline rhenium. The results indicate that rhenium oxides cannot be obtained at temperatures below 630 K even for very high O 2 exposures at low pressures or by low energy O 2 + implantation. It has been observed that upon exposure to oxygen the oxygen atoms incorporate into the near surface region of the metal up to 17 atom% (i.e., ReO 0.2) by a non-thermally activated process, at least for temperatures below 630 K. At higher exposures and more markedly at high temperatures a suboxide labelled as ReO forms at the surface up to coverages of ≈0.7 monolayers (ML). Bombardment with low energy O 2 + ions caused a higher incorporation of oxygen atoms up to 30 atom% (ReO 0.45), but in no case an oxidation state higher than Re 2+ was detected. In addition it is shown that the full width at half maximum (FWHM) of the Re 4f peak can be used to determine the oxygen incorporated into the Re (i.e., ReO x) during the initial steps of the oxidation process, where no appreciable chemical shifts are observed.

Synthesis, transition temperatures, some physical properties and the influence of linkages, outboard dipoles and double bonds on smectic C formation in cyclohexylphenylpyrimidines

A trans-1,4-disubstituted cyclohexane ring has been introduced into known two-ring phenylpyrimidines to produce a wide variety of new three-ring Cyclohexylphenylpyrimidines. The length and type of the terminal chains and linking units have been varied systematically. The effect of introducing a carbon–carbon double bond of defined configuration into various positions of both terminal chains has also been investigated. The influence of lateral dipoles (i.e. oxygen and carboxyl groups) in different positions (central and terminal) in the molecular core of a model system on the smectic C (Sc) transition temperature has been studied and related in a simple empirical way to standard theories for Sc phase formation. Isolated, non-conjugated outboard dipoles (i.e. in cyclohexyl ethers and esters) have been found to destabilise the Sc and nematic (N) phases. Conjugated outboard dipoles (i.e. in phenyl ethers and esters) lead to substantial increases in the Sc transition temperature and usually to a widening of the Sc temperature range. Most of the new Cyclohexylphenylpyrimidines exhibit a variety of smectic phases as well as Sc and N phases. Several homologous series of the most interesting Cyclohexylphenylpyrimidines incorporating oxygen atoms or carboxy groups and/or a carbon–carbon double bond were synthesized and found to exhibit a relatively wide-range Sc phase at elevated temperatures. In admixture with a chiral smectic C (Sc* base mixture, some of the new three-ring cyclohexylphenylpyrimidines can induce a substantial increase in the Sc* and N transition temperatures without increasing the viscosity (and thus response times) excessively.

ChemInform Abstract: Ligand Design and Metal‐Ion Recognition. The Interaction of Copper(II) with a Range of 16‐ to 19‐Membered Macrocycles Incorporating Oxygen, Nitrogen and Sulfur Donor Atoms.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Pulsed Plasma Discharge Polymer Coatings

The authors have developed methods to enhance albumin binding to modified silicone rubber (SR) films. An intermediate bifunctional coupling agent, polyvinylmethyl siloxane-comethyl-1-ethanol siloxane (PVMS-CO-MES), is prepared from a cyclic tetramer, vinyl-methyl siloxane, by an oxymercuration-demercuration reaction, and cross-linked to silicone rubber under mild peroxide catalytic conditions. Free mercury on the surface was obtained under many reaction conditions and is shown to materially enhance 125I-labeled albumin binding. The mechanism most likely occurs via disulfide bond breakage, protein denaturation, and aggregation. The possible role of iodine-mercury bonds, an artefactual source, is ruled out with the aid of total internal reflectance-fluorescence measurements of the albumin adsorption rate constant. Although in situ albumin aggregation via disulfide bond breakage is a potentially attractive method for biocompatible protein gel formation, the toxicity of mercury makes the current method unfit for clinical practice.

Oxygen-induced restructuring of Ag(111)

Interaction of oxygen with Ag(111) surfaces at atmospheric pressure and at a temperature > 800 K leads to the activated formation of a new phase with long-rangeorder exhibiting periodicities of about 70 Å in the [112] direction and 40 Å in the [1 1 0] direction and a slight rotation by about 2° with respect to the substrate lattice, as probed by means of scanning tunneling microscopy (STM), reflection electron microscopy (REM), and reflection high energy electron diffraction (RHEED). The incorporation of oxygen atoms in subsurface sites causes a slight expansion of the topmost layer by about 3% which accounts for the formation of the observed moiré pattern. The superstructure is readily removed by reducing agents.

Oxygen-induced restructuring of Ag(111)

Abstract Interaction of oxygen with Ag(111) surfaces at atmospheric pressure and at a temperature > 800 K leads to the activated formation of a new phase with long-rangeorder exhibiting periodicities of about 70 A in the [112] direction and 40 A in the [1 1 0] direction and a slight rotation by about 2° with respect to the substrate lattice, as probed by means of scanning tunneling microscopy (STM), reflection electron microscopy (REM), and reflection high energy electron diffraction (RHEED). The incorporation of oxygen atoms in subsurface sites causes a slight expansion of the topmost layer by about 3% which accounts for the formation of the observed moire pattern. The superstructure is readily removed by reducing agents.

Role of Glu318 at the putative distal site in the catalytic function of cytochrome P450d.

Most microsomal P450s have a conserved "threonine cluster" composed of three Thrs (Thr319, Thr321, Thr322 for P450d) at a putative distal site. An ionic amino acid at 318 is also well conserved as Glu or Asp for most P450s. To understand the role of these conserved polar amino acids at the putative distal site in the catalytic function of microsomal P450, we studied how mutations at this site of P450d influence the activation of molecular oxygen in the reconstituted system. Catalytic activity (0.02 min-1) toward 7-ethoxycoumarin of the Glu318Ala mutant of P450d was just 6% of that (0.33 min-1) of the wild type, while those of Glu318Asp, Thr319Ala, and Thr322Ala were comparable to or even higher than that of the wild type. Consumption rates of O2 and formation rates of H2O2 of those mutants varied in accord with the catalytic activities. Especially, the efficiency (0.5%) of incorporated oxygen atom to the substrate versus produced H2O2 for the Glu318Ala mutant was much lower than that (3.7%) of the wild type, while that (58.8%) for the mutant Glu318Asp was 16-fold higher than that of the wild type. In addition, the autoxidation [Fe(II)---- Fe(III)] rate (0.074 s-1) of the Glu318Ala mutant was much lower than those (0.374-0.803 s-1) of the wild type and other mutants. Thus, we strongly suggest that Glu318 plays an important role in the catalytic function toward 7-ethoxycoumarin of microsomal P450d.

Dyeing property of wool treated with low temperature plasma.

Merino wool top was treated with low temperature plasmas of oxygen, tetrafluoromethane, and methane. Then the fibers were dyed with leveling and milling type acid dyes. Whereas the oxygen plasma treatment incorporated oxygen atoms on the fiber and led to hydrophilic surface, tetrafluoromethane plasma treatment took up a lot of fluorine atoms and produced hydrophobic surface. However, the rates of dyeing for both plasma treated fibers were much larger than that for a untreated fiber, regardless of the surface wettability. On the other hand, methane plasma treatment decreased dye exhaustion because hydrocarbon polymer was produced by the treatment and covered the fiber surface. Time of half-dyeing was reduced not only by oxygen plasma but also by tetrafluoromethane plasma treatments. Barrier effect in dyeing of the wool was diminished by both plasma treatments. Therefore, there is no relationship between wettability to water and rate of dyeing of the plasma-treated wool. It is considered that both plasma pretreatments relax the adhesive filler in interscale of the wool fiber and accelerate dye penetration into the fiber.

On the effect of an oxygen beam in sputter depth profiling

Experiments of depth resolution measurements on silicon with secondary ion mass spectrometry reveal that oxygen primary particles provide always a smaller decay length (better depth resolution) compared with other primary particles for the same penetration depth of the particle. This deviation from the classical collisional mixing model can be explained by a model which does take the incorporation of the primary particle during sputtering into account. For oxygen particles the incorporation is so high that it leads to a different matrix composition at the surface compared with the bulk of the Si sample and it results in a target swelling at the surface. It is now important to realize that the displacements of the atoms are only important relative to the position of the Si atoms in the expanded lattice and that movements with respect to the incorporated oxygen atoms does not matter. The model presented quantifies this effect and gives an accurate estimate of the reduction of the decay lengths. The model predicts a similar behavior for all primary particles with low matrix sputter yield and high incorporation of the primary particle.

Annealing behaviour of clean and oxygen covered polycrystalline palladium films: A work function and electrical resistance study

The annealing behaviour of clean and oxygen-precovered thin polycrystalline palladium films has been studied by means of work function (WF) studies, electrical resistance measurements, X-ray diffraction (XRD) and Auger electron spectroscopy, and in some instances also using scanning electron microscopy. The film morphology was varied and stabilized by annealing in the range 77–473 K. XRD studies on films annealed at 373–473 K indicate a strong (111) texture with the axis perpendicular to the surface. In spite of this texture, the WF of well-annealed films is lower than that reported for Pd(111) surfaces, suggesting a surface roughness which could not be resolved by a scanning electron microscope operated with a resolution of 10 μm. O 2 adsorption causes a WF increase which saturates at about 0.74±0.02 eV, independently of the annealing temperature of the clean film. After O 2 precoverage at 77 K the annealing behaviour is strongly affected, suggesting incorporation of oxygen atoms in the surface and, above 400 K, even into a subsurface region. Stacks of ten films, each precovered with oxygen-atoms and H 2O molecules before annealing, revealed upon XRD the crystal planes (110) and (002) of PdO. The annealing behaviour of overlayers is markedly affected by contamination of the substrate.

Thermal stability of supersaturated oxygen-doped silicon epitaxial films

Medium-energy ion scattering (MEIS) is used to study the crystallinity and thermal stability of thin (≈ 7 nm) oxygen-doped silicon epitaxial films (OXSEF's). The films were grown by evaporating silicon on a Si(111) substrate in the presence of 1 x 10 -6 Torr oxygen and at a substrate temperature of 600° C. Ion scattering shows that the crystallinity of the grown supersaturated (≈ 13 at% oxygen) layers is imperfect, which is largely due to the incorporated oxygen atoms. The films are stable against thermal annealing up to ≈ 750° C, but at 800° C oxygen diffuses out nonuniformly in lateral direction. Prolonged annealing at the same temperature results in an oxygen concentration in the film below the detection limit of MEIS (2 x 10 14 O atoms/cm 2). The observed lateral inhomogeneity associated with the loss of oxygen indicates that grain boundaries play an important role in the mechanism of oxygen outdiffusion.

Microbial Metabolism of Quinoline and Related Compounds. VII. Quinoline Oxidoreductase fromPseudomonas putida: a Molybdenum-Containing Enzyme

The quinoline oxidoreductase from Pseudomonas putida was purified 50-fold to homogeneity with 21% recovery, using ammonium sulfate precipitation, hydrophobic interaction-, anion exchange-, and gel chromatography. The Mr of the native enzyme was calculated to be 300,000 by gel filtration. SDS-polyacrylamide gel electrophoresis of the enzyme revealed three protein bands corresponding to Mr 85,000, 30,000 and 20,000. The enzyme contained 8 atoms of iron, 8 atoms of acid-labile sulfide, 2 molecules of FAD, and the molybdenum cofactor, molybdopterin. Besides quinoline, the quinoline oxidoreductase also catalysed the conversion of 5-, 6-, 7- and 8-hydroxyquinoline and 8-chloroquinoline to the corresponding 2-oxo compounds. The incorporated oxygen atom was derived from water. Cyanide and methanol were effective inhibitors.

A mass spectral study of the acid‐catalysed oxygen exchange in laevulinic acid

AbstractThe sequence, i.e. site selectivity of the acid‐catalysed 16O/18O exchange in laevulinic acid (1) is studied by mass spectrometry, ion kinetic energy spectroscopy and accurate mass measurements on 1 and its 13C(1)‐labelled congener. In the fragmentation pathways all ions of interest in the spectrum of 1 originate from the molecular ion, which may exist in six tautomeric or isomeric forms (1a–1d). The mechanism of gas‐phase cyclization of 1a is rationalized in terms of three different pathways. Formation of the most prominent fragment ions and the sequence of 16O/18O exchange at the carbonyl and carboxy group are discussed. The results indicate the ions of m/z 56, m/z 61 and m/z 98 to be the only three which have incorporated oxygen atoms originating from the carboxy group in 1 and could thus be used in further elucidadon of the rearrangement mechanism of 5‐hydroxymethylfuran (2) or 5‐hydroxymethylfuran‐2‐carbaldehyde (3) into laevulinic acid (1).

Darstellung und reaktivität von zweikernigen pentamethylcyclopentadienyloxomolybdänsulfiden

Reaction of Cp * 2Mo 2S 4 (Cp *  η 5C 5Me 5) with oxygen yields two isomers of Cp * 2Mo 2OS 3 and Cp * 2Mo 2O 2S 2, the constitution of which is determined by means of IR, 1H and 95Mo NMR spectroscopy as well as by X-ray diffraction analysis. The sulfur liberated in this reaction is oxidized and incorporated into an unusually coordinated μ,η 1-thiosulfate ligand of the compound [Cp * 2Mo 2(μ,η 2-S 2)(μ-S)(υ,η 1-S 2O 3)]. The reaction of all of these compounds with (CO) 5Cr(THF) and (CH 3CN) 3Cr(CO) 3, respectively, gives clusters either containing a trigonal-bipyramidal Mo 2CrS 2 or a cubane-like Mo 2Cr 2O n S 4- n skeleton ( n = 1,2) with five metal-metal bonds. This reaction enables the straightforward incorporation of oxygen atoms into 62- e heterocubane clusters and thus the investigation of 95Mo chemical shifts of mixed oxo/thio-heterocubanes by means of NMR spectroscopy.

Thermotropic liquid-crystalline polymers XXVI. Synthesis of comb-like polymers with oxygen containing spacers and a study of their phase transitions

Abstract Synthesis of new liquid-crystalline comb-like polymers with oxygen-containing spacers and mesogenic cyanbiphenyl groups is described. Liquid-crystalline homo-polymers of acrylates and methacrylates, their copolymers and liquid-crystalline polysiloxane are obtained. It is shown that the incorporation of oxygen atoms in spacer leads to decrease of the clearing temperature. The mesophase types of the homopolymers and copolymers are determined.

Origin of oxygen atoms in cantharidin biosynthesized by beetles

Biosynthesis by blister beetles (Co1eoptera:Meloidae) of the defensive substance cantharidin (2), an apparent monoterpene, proceeds by unprecedented degradation of farnesol (l), a sesquiterpenoid precursor. To obtain chemical insight into this transformation, we examined the origin of the four oxygen atoms in 2. Labeling studies used adult male Epicauta pestifera that were exposed to either I80-enriched O2 or H20. Analysis of the mass spectrometric data of the resulting 2 indicated that the tetrahydrofuranyl oxygen atom and two, but not three, of the anhydride oxygen atoms are derived from 02, whereas the third anhydride oxygen atom comes from H20. Examination of maximally labeled 2 using mass spectrometry-mass spectrometry, which obviated complications owing to isotope dilution, revealed that the H20-derived oxygen atom is located in the anhydride ring in some molecules and in a carbonyl group in others, implicating intramolecular oxygen scrambling. Results indicate that 0,-derived incorporated oxygen atoms undergo no appreciable exchange with the medium. The possibility that 2 is a juvenile hormone metabolite is suggested. Insects not only are the largest and most diverse group of organisms on earth but also are evolutionarily distant from vertebrates, plants, and bacteria. For these reasons, the study of insect metabolism promises to reveal novel biological chemistry. For example, use by some insects of homomevalonate to synthesize their juvenile hormone,I a homosesquiterpenoid, is unique among all types of organisms studied. An understanding of the unique metabolic features of insects may reveal insights regarding biological chemistry and could provide the foundation for new approaches for the control of pest insects. Cantharidin (2), an apparent monoterpene that serves as a defensive substance in blister beetles,2 is formed by an unprecedented degradation of the CIS farnesyl skeleton. Following early experiment^,^ an extensive series of I4C radiolabeling studies4 by Schmid and his collaborators demonstrated that the carbon atoms in 2 are derived from farnesol (l), which itself is derived from (1) (a) Schooley, D. A,; Judy, K. J.; Bergot, B. J.; Hall, M. S.; Siddall, J. B. Proc. Natl. Acad. Sci. U.S.A. 1973, 70, 2921-2925. (b) Bergot, B. J.; Jamieson, G. C.; Ratcliff, M. A.; Schooley, D. A. Science (Washington, D. C. ) 1980, 210, 336-338. (2) Carrel, J. E.; Eisner, T . Science (Wushington, D . C.) 1974, 183, 155-751. (3) (a) Schlatter, C.; Waldner, E. E.; Schmid, H. Experientia 1968, 24, 994-995. (b) Guenther, H.; Ramstad, E.; Floss, H. G. J . Pharm. Sci. 1969, 58, 1274. (4) (a) Peter, M. G.; Waespe, H.-R.; Woggon, W.-D.; Schmid, H. Helu. Chim. Acto 1977,60, 1262-1272. (b) Woggon, W.-D.; Peter, M. G.; Schmid, H. Helu. Chim. Acta 1977.60, 2288-2294. (c) Peter, M. G.; Woggon, W.-D.; Schmid, H. Helv. Chim. Acta 1977, 60, 2756-2762. (d) Woggon, W.-D.; Hauffe, S. A,; Schmid, H. J. Chem. Soc., Chem. Commun. 1983, 212-274. mevalonate in the normal manner. Intriguingly, the two terminal methyl groups of 1 are almost completely randomized during its conversion into Z3** Tritium labeling experiments demonstrated that all of the hydrogen atoms in 2, with the exception of one attached to C-6, are derived from m e ~ a l o n a t e . ~ ~ . ~ Unfortunately, knowledge of the prigins of the carbon and hydrogen atoms in 2 fails to unveil chemical details regarding its biosynthesis beyond