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PubMed2005

Tunable metallization by assembly of metal nanoparticles in polymer thin films by photo- or electron beam lithography.

The technique of patterning of surfaces with metal-rich structures on micro- or nanoscales was developed by assembling metal nanoparticles into a thin film of polymer in a controllable way. Palladium (Pd) nanoparticles were incorporated into a thin film of poly(methyl methacrylate) (PMMA) using palladium (II) bis(acetylacetonato), Pd(acac)(2), as a precursor vaporized in a nitrogen atmosphere. Depending upon its dose, the irradiation of a PMMA film by UV light or an electron beam (EB) enhances its reducing capability against Pd(acac)(2). This dependency on dose can be used to control the formation and assembly of Pd nanoparticles. Using this technique, binary patterns consisting of metal-rich and metal-poor regions in the polymer film can be created simply by irradiating the surface of the polymer through a binary photomask. Besides the creation of binary patterns, it is also possible to create grayscale patterns where the density of Pd nanoparticles can be tuned to provide shades of gray by the use of light with continuously modulated intensity. Because the electron beam also enhances the reducing power of PMMA against Pd(acac)(2), it is thus possible to obtain highly metallized films with nanoscale pattern features. The PMMA film can be selectively removed by oxygen plasma treatment or by pyrolysis. Thus, highly metallized surfaces with binary or grayscale patterns can be obtained by selective removal of the PMMA films. The metallized regions possess relatively high resistivity against CF(4) plasma compared to the bare silicon surface; therefore, the metallized surface patterns can be transferred onto the underlying silicon substrate by CF(4) plasma treatment. Because of the nanosize effect of metal nanoparticles, the thermal treatment at 900 degrees C, which is significantly lower than the melting temperature of the bulk Pd, yields continuous metallic features by binding the assembled nanoparticles.

Journal Article↗
PubMed2006

Conical tungsten tips as substrates for the preparation of ultramicroelectrodes.

Here we describe a simple method to prepare voltammetric microelectrodes using tungsten wires as a substrate. Tungsten wires have a high tensile modulus and enable the fabrication of electrodes that have small dimensions overall while retaining rigidity. In this work, 125 microm tungsten wires with a conical tip were employed. For the preparation of gold or platinum ultramicroelectrodes, commercial tungsten microelectrodes, completely insulated except at the tip, were used as substrates. Following removal of oxides from the exposed tungsten, platinum or gold was electroplated, yielding surfaces with an electroactive area of between 1 x 10-6 and 2 x 10-6 cm2. Carbon surfaces on the etched tip of tungsten microwires were prepared by coating with photoresist followed by pyrolysis. The entire electrode was then insulated with Epoxylite except the tip, yielding an exposed carbon surface with an area of around 4 x 10-6 to 6 x 10-6 cm2. All three types of ultramicroelectrodes fabricated on the tungsten wire had similar electrochemical behavior to electrodes fabricated from wires or fibers insulated with glass tubes.

Carbon↗
PubMed2006

Nanostructure PtRu/MWNTs as anode catalysts prepared in a vacuum for direct methanol oxidation.

Platinum and ruthenium nanoparticles that are uniformly dispersed on multiwalled carbon nanotubes (MWNTs) were synthesized by vacuum pyrolysis using Pt(acac)2 and Ru(acac)3 as the metal precursors. The resulting nanocomposites were characterized by transmission electron microscopy and X-ray diffraction. The Pt, Pt45Ru55, and Ru nanoparticles had mean diameters of 3.0 +/- 0.6, 2.7 +/- 0.6, and 2.5 +/- 0.4 nm and the same mole number as their metal precursors at 500 degrees C. The electrocatalytic activity of the Pt/MWNTs and PtRu/MWNTs was investigated at room temperature by cyclic voltammetry and chronoamperometry. All of the electrochemical results showed that the PtRu/MWNTs exhibited a high level of catalytic activity for methanol oxidation as a result of the large surface area of the supporting carbon nanotubes and the wide dispersion of the Pt and Ru nanoparticles. Compared with the Pt/MWNTs, the onset potential for methanol oxidation of the PtRu/MWNTs was significantly lower, and the ratio of the forward anodic peak current to the reverse anodic peak current during methanol oxidation was somewhat higher. The Pt45Ru55/MWNTs displayed the best electrocatalytic activity of all of the carbon-nanotube-supported Pt and PtRu catalysts.

Journal Article↗
PubMed2000

Phenyl migrations in dehydroaromatic compounds. A new mechanistic link between alternant and nonalternant hydrocarbons at high temperatures

Flash vacuum pyrolysis of benzo[b]biphenylene, an alternant polycyclic aromatic hydrocarbon (PAH), gives fluoranthene, a nonalternant PAH, as the major product at 1100 degrees C in the gas phase. The most reasonable mechanism to explain this isomerization involves equilibrating diradicals of 2-phenylnaphthalene that rearrange by the net migration of a phenyl group to give equilibrating diradicals of 1-phenylnaphthalene, one isomer of which then cyclizes to fluoranthene.

Journal Article↗
PubMed2005

A new chiral anthracene for the asymmetric Diels-Alder/retro-Diels-Alder sequence.

(-)-(R)-9-(1,2-Dimethoxyethyl)anthracene (8) is successfully employed as a chiral template in the Diels-Alder/retro-Diels-Alder sequence for the preparation of alpha,beta-unsaturated lactams. The cycloadditions proceed with complete diastereoselectivity, and regioselectivity in subsequent transformations of the carbonyl groups is also excellent. Flash vacuum pyrolysis accomplishes the cycloreversion.

Journal Article↗
PubMed2004

Diradical-promoted (N + 2 - 1) ring expansion: an efficient reaction for the synthesis of macrocyclic ketones.

[reaction: see text] A diradical-promoted (n + 2 - 1) ring expansion reaction based on vinyl side chain insertion (+2C) and decarbonylation (-1C) has been developed. Flash vacuum pyrolysis (FVP) of medium- and large-ring 2-trimethylsilyloxy-2-vinyl-cycloalkanones at 500-600 degrees C affords the one-carbon ring-expanded cycloalkanones in good yields. Methyl groups on the vinyl moiety are transformed regiospecifically as corresponding alpha- and beta-substituents, respectively. 2-Ethynyl precursor analogues react in a manner similar to give alpha,beta-unsaturated cyclic ketones.

Journal Article↗
PubMed2004

Three-carbon ring expansion by cyclopropane insertion: macrocyclic musks from readily available C-12 starting materials.

A thermal three-carbon ring expansion based on side chain ring insertion of a cyclopropane moiety is described. Flash vacuum pyrolysis (FVP) of 1-cyclopropyl-cycloalk-3-enol derivatives leads to the three-carbon ring expanded enones with clean retention of double bond geometry. Substrates bearing methyl groups on the cyclopropane ring undergo regioselective bond cleavage, allowing for the systematic preparation of selectively substituted macrocyclic musks from low-priced C-12 starting compounds.

Journal Article↗
PubMedDate not supplied

Selection of biomarkers by a multivariate statistical processing of composite metabonomic data sets using multiple factor analysis.

We introduce a statistical approach for integrating data from several analytical platforms. We illustrate this approach using (1)H-(13)C Heteronuclear Multiple Bond Connectivity nuclear magnetic resonance spectroscopy ((1)H-(13)C HMBC NMR) and Pyrolysis Metastable Atom Bombardment Time-of-Flight mass spectrometry (Py-MAB-TOF-MS) to perform metabolic fingerprinting on cattle treated with anabolic steroids. Multiple factor analysis (MFA) integrates complementary aspects from NMR and MS data into a unique metabolic signature describing the biomarkers related to the dose-response. This work also indicates that, from a practical point of view, metabonomics and other "-omics" biotechnologies can benefit significantly from a generalized multi-platform integrative approach using multiple factor analysis.

Animals↗
PubMedDate not supplied

Chemical, physical, and toxicological characterization of fumes produced by heating tetrafluoroethene homopolymer and its copolymers with hexafluoropropene and perfluoro(propyl vinyl ether).

Submicrometer solid-particle (fume) aerosols with up to about 10(8) particles/cm3 are formed when dilute vapors of low molecular weight (MW) (ca. 5000-10,000) perfluoro polymers condense in air. The aerosol (e.g., 0.2 mg/m3) formed from these vapors is highly toxic to laboratory rats by inhalation (30-min exposure) when fresh but loses toxicity in minutes, apparently owing to coagulation. These fumes may result from (a) pyrolysis of tetrafluoroethene homopolymer or tetrafluoroethene-hexafluoropropene copolymer or (b) evaporation, at 200-320 degrees C, of isolated low MW polymer or low MW polymer present in perfluoro polymer resins. Some perfluoro polymer fume aerosols contain reactive functional groups, but others without detectable reactive groups are at least as toxic.

Animals↗
PubMed2001

Detection of PhIP (2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine) in the milk of healthy women.

An increased risk of breast cancer has been observed in women who consume "very well-done" meats. Heterocyclic amines are mutagenic and carcinogenic pyrolysis products formed during high temperature cooking of meats. In the present study, human milk samples were analyzed for PhIP, one of the most abundant dietary heterocyclic amine. A protocol was developed with a mixed-mode cation exchange sorbent for the extraction of heterocyclic amines from milk. Milk samples were acquired from healthy Canadian women. With LC/MS analysis and the method of isotope dilution for quantification, levels of PhIP were determined in human milk samples. PhIP was detected in 9 of the 11 milk samples, at levels as high as 59 pg/mL (ppt). No PhIP was detected in the milk of the vegetarian donor. Detection of PhIP in milk indicates that ductal mammary epithelial cells are directly exposed to this carcinogen, suggesting that heterocyclic amines are possible human mammary carcinogens.

Adult↗
PubMed2002

Studies on hydrolytic and oxidative metabolic pathways of anhydroecgonine methyl ester (methylecgonidine) using microsomal preparations from rat organs.

During smoking of cocaine-base (crack), anhydroecgonine methyl ester (AEME, methylecgonidine) is formed in large amounts as a pyrolysis product of cocaine and is absorbed in the lungs. The metabolism of AEME was studied in the present investigation using microsome preparations from rat liver, lung, kidney, and brain. Potential metabolites of AEME were synthesized and used as substrate to complement the experiments. Analysis of the incubation mixtures was performed using gas chromatography-mass spectrometry and nanoelectrospray multiple-stage mass spectrometry. Screening for metabolites was focused on postulated oxidative pathways, chemical and enzymatic hydrolysis, and ethanol dependent transesterification as known from cocaine metabolism. Enzymatic hydrolysis of AEME to anhydroecgonine (AE), which was inhibited by sodium fluoride, was found in all microsomal preparations. Liver microsomes exhibited the highest activity, brain microsomes the lowest. Anhydronorecgonine methyl ester (ANEME) and anhydroecgonine methyl ester N-oxide were identified as AEME metabolites of liver and lung microsomes only. In the presence of ethanol AEME was metabolized to anhydroecgonine ethyl ester and anhydronorecgonine ethyl ester. Further metabolism of AE or ANEME was not observed. No N-hydroxy-anhydronorecgonine derivatives were found which could represent precursors of cytotoxic metabolites as known to be formed from cocaine.

Animals↗
PubMedDate not supplied

Novel rhodococci and other mycolate actinomycetes from the deep sea.

A large number of mycolate actinomycetes have been recovered from deep-sea sediments in the NW Pacific Ocean using selective isolation methods. The isolates were putatively assigned to the genus Rhodococcus on the basis of colony characteristics and mycolic acid profiles. The diversity among these isolates and their relationship to type strains of Rhodococcus and other mycolate taxa were assessed by Curie point pyrolysis mass spectrometry (PyMS). Three major (A, C, D) and two minor (B, E) groups were defined by PyMS. Cluster A was a large group of isolates recovered from sediment in the Izu Bonin Trench (2679 m); Cluster C comprised isolates from both the Izu Bonin Trench (6390 and 6499 m) and from the Japan Trench (4418, 6048 and 6455 m). These Cluster C isolates showed close similarity to Dietzia maris and this was subsequently confirmed using molecular methods. Cluster D contained isolates recovered from a sediment taken from a depth of 1168 m in Sagami Bay and were identified as members of the terrestrial species Rhodococcus luteus. Clusters B and E had close affinities with members of the genera Gordonia and Mycobacterium. The presence of Thermoactinomyces in certain of the deep-sea sediments studied was indicative of the movement of terrestrial material into the ocean depths. 16S ribosomal RNA gene sequence analyses produced excellent definition of most genera of the mycolata, and indicated that the among the deep sea isolates (1) were novel species of Corynebacterium, Gordonia and Mycobacterium, and (2) a Sea of Japan isolate the phylogenetic depth of which suggests the possibility of a new genus. Polyphasic taxonomic analysis revealed considerable diversity among the deep sea rhodococci and evidence for recently diverged species or DNA groups.

Actinomycetales↗
PubMed2000

Rapid characterisation of deep-sea actinomycetes for biotechnology screening programmes.

A continual need in natural product discovery is dereplication, that is the ability to exclude previously tested microorganisms from screening programmes. Whole-cell fingerprinting techniques offer an ideal solution to this problem because of their rapidity and reproducibility, dependence on small samples, and automation. One such technique, Curie-point pyrolysis mass spectrometry (PyMS), has been deployed for the characterisation of a unique collection of actinomycetes recovered from Pacific Ocean sediments approximately 2000 to 6500 m below sea level. This paper addresses the question: to what extent are pyrogroups, defined on the basis of PyMS fingerprinting, related to classifications derived from more conventional microbial systematics? A collection of 44 randomly chosen deep-sea rhodococci were coded and subjected to a double-blind PyMS and numerical taxonomic (NT) analysis; the latter sorted the strains into clusters (taxospecies) using large sets of equally weighted phenotypic data. At the end of the experiment the codes were disclosed and the NT classification shown to generate 6 homogeneous clusters corresponding to different deep-sea sites. The matching of these clusters with the resulting pyrogroups was very high with an overall congruence of nearly 98%. Thus, PyMS characterisation is directly ascribable to the phenotypic variation being sought for biotechnology screens. Moreover, the exquisite discriminatory power of PyMS readily revealed infraspecific diversity in these industrially important bacteria.

Actinomycetales↗
PubMed1998

Review and latest results of laboratory investigations of Titan's aerosols.

Titan, the largest satellite of Saturn, has an atmosphere chiefly made up of N2 and CH4, and including many organics. This atmosphere also partly consists of hazes and aerosol particles which shroud the surface of this satellite, giving it a reddish appearance. The aerosols observed in Titan's atmosphere are thought to be synthesized at high altitudes (>300 km) and fall to the surface. Varying with temperature profiles, condensation phenomena take place in the lower atmosphere, about 100 km below. These solid particles, often called 'tholins', have been currently investigated for many years by laboratory scientists and physics modellers. This paper assesses past research and results in different fields (elemental composition, optical constants, pyrolysis, particle size), hightlighting interests and questions aroused by these studies. It also presents the latest results and advances, and concludes with existing problems and future pathways.

Aerosols↗
PubMed1999

Biodegradation of dicyclopentadiene in the field.

Dicyclopentadiene (DCPD) is formed during the pyrolysis of alkanes to produce olefins suitable for manufacturing synthetic polymers. DCPD has an irritating odor with a 5 ppb detection level that provides the impetus for remediation efforts. One method of destroying odors is to alter the structure of the chemical. This can be accomplished by biological oxidation using microorganisms. Field studies at two sites, where DCPD was a soil contaminant, indicated that biodegradation contributed significantly to DCPD removal. DCPD degradation was stimulated by decreasing bulk soil density and adding nitrogen and phosphorous nutrients. The presence of other easier degradable aromatic hydrocarbons may also be beneficial, suggesting that the process is cometabolic.

Biodegradation, Environmental↗
PubMed2000

Selective isolation and characterisation of members of the Streptomyces violaceusniger clade associated with the roots of Paraserianthes falcataria.

Large numbers of putatively novel streptomycetes were isolated from environmental samples collected from in and around the root system of the tropical angiosperm, Paraserianthes falcataria. Representative isolates were assigned to 37 multi-membered and 107 single membered colour groups based on their ability to form pigments on oatmeal and peptone yeast extract iron agars. The largest taxon, colour group 3, encompassed 94 isolates which had morphological properties typical of members of the Streptomyces violaceusniger clade. Twelve representatives of this taxon chosen on the basis of Curie-point pyrolysis mass spectrometric data were compared with representatives of the validly described species which constitute the Streptomyces violaceusniger clade. Six out of the twelve representative strains were readily distinguished from one another and from the marker strains using a combination of genotypic and phenotypic properties. These organisms were consequently considered to merit species status as Streptomyces asiaticus sp. nov., Streptomyces cangkringensis sp. nov., Streptomyces indonesiensis sp. nov., Streptomycesjavensis sp. nov., Streptomyces rhizosphaerius sp. nov. and Streptomyces yogyakartensis sp. nov.

Bacteriological Techniques↗