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PubMed1996

Differential scanning calorimetric and X-ray study of the binding of the water of primary hydration to calf-thymus DNA.

Differential scanning calorimetry has been used to study the thermal properties of hydrated films of calf-thymus Na-, K- and CsDNA between 20 and 320 degrees C. A broad endothermic transition near 75 degrees C and a sharp exothermic transition near 240 degrees C are observed. The broad transition is due to the dehydration of the DNA, while the exothermic transition is due to pyrolysis of the sample. the peak temperatures of both transitions increase as the scan rate is increased. Based on a Kissinger analysis, the net activation energy for the desorption of the primary water of hydration is about 0.6 eV while that for the pyrolysis is about 1.9 eV. X-ray diffraction patterns suggest that heating the DNA films to 180 degrees C once does not, but thrice does, destroy their structural ordering.

Calorimetry, Differential Scanning↗

PubMedDate not supplied

Pyrolytic fate of piperidinocyclohexanecarbonitrile, a contaminant of phencyclidine, during smoking.

The pyrolysis products of 1-(1-piperidino)cyclo-hexanecarbonitrile (PCC), the major contaminant of illicit phencyclidine (PCP), have not been previously reported. In order to quantify PCC in mainstream smoke as well as to identify the pyrolysis products, [3H]piperidino-[14C]cyano-PCC was synthesized. Marijuana placebo cigarettes were impregnated with this double-labeled PCC and burned with an apparatus that simulated smoking. The mainstream smoke was passed through a series of traps containing glass wool, H2SO4, or NaOH. Approximately 75% of the 3H was collected in these traps, and 46, 11, and 5% of the 14C was found in the glass wool, H2SO4, and NaOH traps, respectively. Contents of the traps were analyzed by GC/MS. The glass wool trap contained 1-(1-piperidino)-1-cyclo-hexene, PCC, piperidine, and N-acetylpiperidine, and cyanide ion was detected in all three traps. Approximately 47% of the PCC was found intact in mainstream smoke. Approximately 58% was cleaved to form cyanide and 1-(1-piperidino)-1-cyclohexene. The latter was further broken down to cyclohexanone (which represented 21% of the starting material), piperidine (29%), and N-acetylpiperidine (7%), and about 2% remained intact.

Drug Contamination↗

PubMed1983

Mass spectrometric monitoring of solid phase phosphate triester synthesis of DNA fragments.

A new and convenient pyrolysis mass spectrometric approach for monitoring solid phase phosphate triester synthesis of oligodeoxyribonucleotides in 5'-3' direction has been developed. The base-typical fragment ions produced by pyrolysis at 280 degrees C of the polymer-bound oligonucleotide triesters in the mass spectrometer permit the analytical monitoring of DNA chain growth, using simple mathematical operations. The base composition can be determined directly from the polymer. In addition, minor nucleosides can easily be detected.

Base Sequence↗

PubMed1997

Biodiversity of bradyrhizobia nodulating Lupinus spp.

The genetic structure of Bradyrhizobium isolates recovered from three Lupinus species (Lupinus campestris, Lupinus montanus, and Lupinus exaltatus) grown in Mexico was examined. Among 41 Bradyrhizobium isolates, 18 electrophoretic types (ETs) were distinguished by multilocus enzyme electrophoresis of five metabolic enzymes. The mean genetic diversity, 0.64, indicated that there was great genetic diversity in the population sampled. Most isolates (63%) fell into two closely related clusters (clusters I and II) and were the types most frequently isolated from the root nodules of L. montanus and L. campestris. ET cluster III isolates were frequent nodule occupants of L. exaltatus. The isolates also were assigned to three main groups by using Curie point pyrolysis mass spectrometry. In general, the multilocus enzyme electrophoretic data and pyrolysis mass spectrometric data agreed. We determined the 16S rRNA sequences of representative Lupinus isolates and of Bradyrhizobium japonicum USDA 6T and found that the lupine isolates were highly related to the B. japonicum type strain, although not all B. japonicum type strains (subcultures maintained in different bacterial collections) had identical small-subunit rRNA.

Bacterial Proteins↗

PubMed1993

A simple chemical test to distinguish mycobacteria from other mycolic-acid-containing actinomycetes.

Two hundred and fifty-two representatives of the general Corynebacterium, Gordona, Mycobacterium, Nocardia, Rhodococcus and Tsukamurella were degraded by alkaline hydrolysis and their mycolic acids extracted as methyl esters following phase-transfer-catalysed esterification. When the mycolic acid methyl esters were treated with a mixture of acetonitrile and toluene all mycobacterial mycolates formed copious white precipitates whereas all but 5 out of the 106 non-mycobacterial mycolates remained in solution. The precipitated methyl mycolates and the dried soluble mycolates were compared by pyrolysis gas chromatography and silica gel thin-layer chromatography. On pyrolysis, the precipitated methyl mycolates from mycobacteria yielded fatty acid methyl esters with 20 to 26 carbon atoms whereas those from the remaining taxa produced shorter-chain esters. Mycobacteria and Tsukamurella paurometabola gave multispot mycolic acid patterns on thin-layer chromatography of their methyl esters whereas those from the remaining strains gave single spots. Our results indicate that Rhodococcus chlorophenolicus strains contain mycolic acids atypical of mycobacteria. It can be concluded that the mycolic acid precipitation test provides a simple and reliable way of distinguishing mycobacteria from all other prokaryotes, notably from other mycolic-acid-containing taxa.

Actinomycetales↗

PubMed1995

A numerical taxonomic study of the gram-positive anaerobic cocci.

Clinical (101) and collection (26) strains of gram-positive anaerobic cocci were examined in conventional tests and pyrolysis mass spectrometry (PMS). Numerical classifications based upon conventional test reaction patterns (CTRPs) and PMS showed 27 and 22 clusters, respectively. Cross-tabulation of cluster membership in the two classifications showed excellent correlation, with the combined classifications showing clear groups corresponding to the currently recognised species Peptostreptococcus anaerobius, P. heliotrinreducens, P. hydrogenalis, P. indolicus, P. lactolyticus, P. magnus, P. micros and Peptococcus niger. Strains of P. prevotii and P. tetradius clustered together in a heterogeneous group of saccharolytic organisms. However, strains previously identified as P. asaccharolyticus were divided into three distinct groups in PMS, two of which differed only in indole-associated pyrolysis products. A further four groups and several single-member clusters were distinct from these species. PMS data supported the validity of identification by pre-formed enzyme profiles and confirmed that Hare group III is synonymous with P. hydrogenalis, Hare group IV with P. magnus, and the "ADH group" with P. vaginalis. There is clearly a need for a taxonomic revision of the genus Peptostreptococcus, which probably encompasses several generic groups.

Bacteria, Anaerobic↗

PubMed1997

Reduced Lignin Content and Altered Lignin Composition in Transgenic Tobacco Down-Regulated in Expression of L-Phenylalanine Ammonia-Lyase or Cinnamate 4-Hydroxylase.

We analyzed lignin content and composition in transgenic tobacco (Nicotiana tabacum) lines altered in the expression of the early phenylpropanoid biosynthetic enzymes L-phenylalanine ammonia-lyase and cinnamate 4-hydroxylase (C4H). The reduction of C4H activity by antisense expression or sense suppression resulted in reduced levels of Klason lignin, accompanied by a decreased syringyl/guaiacyl monomer ratio as determined by pyrolysis gas chromatography/mass spectrometry Similar reduction of lignin levels by down -regulation of L-phenylalanine ammonia-lyase, the enzyme preceding C4H in the central phenylpropanoid pathway, did not result in a decreased syringyl/guaiacyl ratio. Rather, analysis of lignin methoxyl content and pyrolysis suggested an increased syringyl/guaiacyl ratio. One possible explanation of these results is that monolignol biosynthesis from L-phenylalanine might occur by more than one route, even at the early stages of the core phenylpropanoid pathway, prior to the formation of specific monolignol precursors.

Journal Article↗

PubMed1995

Distribution of C22-, C24- and C26-alpha-unit-containing mycolic acid homologues in mycobacteria.

There are three mycolic acid homologues with C22-, C24- and C26-alpha-units in Mycobacterium. In order to reveal the composition and distribution of these homologues in each subclass and molecular species of mycolic acids and to compare them with the composition of constitutive non-polar fatty acids (free and bound forms), we have separated non-polar fatty acids and each subclass of mycolic acids from 21 mycobacterial species by thin-layer chromatography, and analyzed non-polar fatty acid methyl esters by gas chromatography (GC) and the cleavage products of methyl mycolate by pyrolysis GC. We further performed mass chromatographic analysis of trimethylsilyl (TMS) ether derivatives of mycolic acid methyl esters by monitoring [B-29]+ ions (loss of CHO from the alpha-branched-chain structure of mycolic acids) of m/z 426, 454 and 482 which are attributed to C22-, C24- and C26-alpha-units of TMS ether derivatives of methyl mycolates, respectively, (Kaneda, K. et al, J. Clin. Microbiol. 24: 1060-1070, 1986). By pyrolysis GC, C22:0, C24:0 and C26:0 fatty acid methyl esters generated by the C2-C3 cleavage of C22-, C24- and C26-alpha-unit-containing mycolic acid methyl esters, respectively, were detected. Their proportion was almost the same among subclasses of mycolic acids in every Mycobacterium and also similar to the proportion of constitutive non-polar C22:0, C24:0 and C26:0 fatty acids. By mass chromatography, the composition and distribution of C22- and C24-alpha-unit-containing homologues were revealed to be similar between alpha- and alpha'-mycolic acids in every Mycobacterium.(ABSTRACT TRUNCATED AT 250 WORDS)

Chromatography, Thin Layer↗

PubMed1988

Tetraenoic and pentaenoic mycolic acids from Mycobacterium thamnopheos. Structure, taxonomic and biosynthetic implications.

On the basis of the analysis of mycolates, the type strain of Mycobacterium thamnopheos has been considered as a member of the genus Nocardia. In a comparative study conducted on mycobacterial species we found that M. thamnopheos synthesized two types of mycolate having the same mobilities on thin-layer chromatography as those of mycobacteria, but different from nocardomycolates. Mass spectrometry analyzes showed that the major series of both types consisted of polyunsaturated mycolic acids, ranging from C72 to C78 with four or five double bonds. On pyrolytic mass spectrometry or gas chromatography, the least polar mycolates released mainly monounsaturated C22 esters whereas the other type yielded saturated C20 and C22 esters. These results suggested that M. thamnopheos might be more related to the Aurantiaca taxon than to mycobacteria and Nocardia. The permanganate-periodate oxidation products of esters obtained by pyrolysis of the least polar mycolates showed that they contained docosen-4-oic and docosen-6-oic acids. Both types of mycolate esters yielded the same set of long-chain meroaldehydes on pyrolysis. These meroaldehydes were significantly distinct from those of mycobacterial mycolates in the location of the double bonds. After hydrogenation of the double bond located in the alkyl-branched chain, the two types of mycolates had the same mobility on thin-layer chromatography, indicating that the difference of migration was due to the additional double bond found in the least polar mycolates. Based on stereochemical data, the relative configuration of both mycolates was found to be threo, like that established for all mycolates studied so far.

Chromatography↗

PubMed1999

Ceramic fibers for matrix composites in high-temperature engine applications

High-temperature engine applications have been limited by the performance of metal alloys and carbide fiber composites at elevated temperatures. Random inorganic networks composed of silicon, boron, nitrogen, and carbon represent a novel class of ceramics with outstanding durability at elevated temperatures. SiBN(3)C was synthesized by pyrolysis of a preceramic N-methylpolyborosilazane made from the single-source precursor Cl(3)Si-NH-BCl(2). The polymer can be processed to a green fiber by melt-spinning, which then undergoes an intermediate curing step and successive pyrolysis. The ceramic fibers, which are presently produced on a semitechnical scale, combine several desired properties relevant for an application in fiber-reinforced ceramic composites: thermal stability, mechanical strength, high-temperature creep resistivity, low density, and stability against oxidation or molten silicon.

Journal Article↗

PubMed2000

Shaped ceramics with tunable magnetic properties from metal-containing polymers

A shaped, magnetic ceramic was obtained from a metal-containing polymer network, which was synthesized by thermal polymerization of a metal-containing organosilicon monomer. Pyrolysis of a cylinder, shape, or film of the metal-containing polymer precursor produced a low-density magnetic ceramic replica in high yield. The magnetic properties of the shaped ceramic could be tuned between a superparamagnetic and ferromagnetic state by controlling the pyrolysis conditions, with the particular state dependent on the size of iron nanoclusters homogeneously dispersed throughout the carbosilane-graphitic-silicon nitride matrix. These results indicate that cross-linked metal-containing polymers may be useful precursors to ceramic monoliths with tailorable magnetic properties.

Journal Article↗

PubMed1976

Cat heart acetylcholine: structural proof and distribution.

The distribution of acetylcholine (ACh) in the cat heart was investigated by a pyrolysis-gas chromatography (PGC) method. The hearts were dissected into various regions and homogenized in acetonitrile in the presence of propionylcholine, internal standard. Following extraction with toluene and hexane, the choline esters were precipitated as the enneaiodide complex. The isolated choline esters were analyzed by PGC, and the peak corresponding to ACh was quantified. The compound extracted from heart tissue that eluted with the retention time of authentic ACh was identified by mass spectrometry as dimethylaminoethylacetate, the pyrolysis product of ACh. ACh concentrations were found to be higher in the atria than the ventricles. In both the atria and the ventricles, a higher content of ACh was found in the right than the left portions: right ventricle, 5.0 compared to left ventricle, 2.0 nmol/g; and right atrium, 16.8 compared to left atrium, 11.3 nmol/g. Some cats were subjected to a bilateral cervical vagotomy 3 wk before removal and analysis of heart tissue. Hearts from vagotomized cats contained less ACh than controls in the right ventricle (-31%), right atrium (-54%), SA node (-42%), and papillary muscle (-53%), but no decreases were found in the left ventricle, left atrium, or interventricular septum.

Acetylcholine↗

PubMed1984

Alterations in the antibacterial properties of rabbit pulmonary macrophages exposed to wood smoke.

We studied the local response of the bronchoalveolar cell population after acute exposure to smoke from pyrolysis of Douglas fir wood. Cell viability experiments and function of the pulmonary macrophages were assessed, including adherence to surfaces, bacterial phagocytosis, and the intracellular bactericidal process. The smoke-exposed group (n=23) when compared with control animals (n=15) produced a significantly greater total cell yield (p less than 0.01) on bronchoalveolar lavage. There was no increase in the percentage of polymorphonuclear leukocytes. As carboxyhemoglobin levels increased, macrophage adherence to glass decreased (r = -0.79, p = 0.0001). Pulmonary macrophages from exposed animals were 33% less adherent at 120 min in vitro; however, these nonadherent smoke-exposed macrophages remained viable (55 to 78% viable by trypan blue dye exclusion). Both the phagocytic rate (361 14C cpm/unit time) and the maximal number of bacteria associated (at 60 min) with the exposed macrophages were significantly less than in the sham-exposed animals (uptake = 672 14C cpm/time, p less than 0.002 for each). The antibacterial properties of pulmonary macrophages are adversely affected by exposure to wood pyrolysis.

Animals↗

PubMed2001

Three-dimensional micropatterns of well-aligned carbon nanotubes produced by photolithography.

Three-dimensional micropatterns of well-aligned carbon nanotubes were prepared on photolithographically prepatterned substrates by pyrolysis of iron(II) phthalocyanine (FePc) under an Ar/H2 atmosphere at 800-1100 degrees C. The photopatterning was achieved by photolithographic cross-linking of a chemically amplified photoresist layer spin-cast on a quartz plate or a silicon wafer, coupled with solution development. Owing to an appropriate surface characteristic, the patterned photoresist layer was found in this case to support aligned carbon nanotube growth by pyrolysis of FePc, as were the photoresist-free substrate surfaces. The difference in chemical nature between the surface areas covered and uncovered by the photoresist film, however, caused a region-specific growth of the nanotubes with different tubular lengths and packing densities, leading to the formation of three-dimensional aligned nanotube patterns suitable for various device applications.

Crystallization↗

PubMed2002

Synthesis of mesoporous silica with embedded nickel nanoparticles for catalyst applications.

Here we describe a new route for the synthesis of nanometric Ni particles embedded in a mesoporous silica material with excellent potential for catalytic applications. Mesoporous silica with a surface area in the range of 202-280 m2/g, with narrow pore size distribution and Ni nanoparticles (particles in the range of 3-41 nm) were obtained in a direct process. A different approach was adopted to process such a nanocomposite. This new approach is based on the formation of a polymer with the silicon oxianion and nickel cation chelated to the macromolecule structure and on the control of the pyrolysis step. The CO/CO2 atmosphere resulting from the pyrolysis of the organic material promotes the reduction of the Ni citrate.

Bicyclic Monoterpenes↗

PubMed2003

Carbon nanotube synthesis in a flame with independently prepared laser-ablated catalyst particles.

Laser ablation has been used ex situ to create metal nanoparticles for introduction into a reactive pyrolysis flame. By prior synthesis of the metal nanoparticles, the effects of the reactive gases can be clearly separated from the pyrolysis chemistry of a solvent carrier, as when nebulized solutions are used. Moreover, varying reactivity issues associated with particle growth and size are bypassed. Our results show that Fe selectively reacts with CO to produce nanotubes, whereas Ni selectively reacts with C2H2 to produce nanofibers. These observations are interpreted through the donation and withdrawal of electron density between the adsorbate's molecular orbitals and surface atoms of the metal nanoparticle. The rate of reaction of Ni with only C2H2 is found to be greater than the rate with C2H2 and CO. This suggests that CO inhibits the Ni-catalyzed reaction.

Aerosols↗

PubMed2004

Highly ordered carbon nanotubes based on porous aluminum oxide.

Highly ordered carbon nanotubes (CNTs) are widely pursued due to their unique properties. Anodic aluminum oxide (AAO) exhibits great possibility for this purpose. Here, CNTs based on AAO templates were produced using acetylene or ethylene as the hydrocarbon sources with or without the presence of Co catalysts. CNTs grown on the Co-embedded AAO samples were normally confined within the nanopores of the AAO template. It was found that C2H4 normally requires 100 degrees C higher pyrolysis temperature than C2H2 under otherwise identical conditions. The pyrolysis temperature is greatly reduced with the presence of Co catalysts. CNTs can grow out of the nanopores if Co particles are present at the bottom of the nanopores, and if the nanopores are short in length or large in diameter. The graphitization of AAO-template grown CNTs was studied by Raman spectroscopy. CNTs produced from ethylene are generally better in graphitization than those from acetylene, and CNTs grown with the presence of Co catalysts deposited at the bottom of nanopores are better than those without Co catalysts or with Co catalysts coated on the entire inner wall of nanopores. The growth temperature is found not to play a critical role in graphitization.

Adsorption↗

PubMed2005

Highly ordered carbon nanotubes based on porous aluminum oxide: fabrication and mechanism.

Highly ordered carbon nanotubes (CNTs) are wildly pursued due to their unique properties. Anodic aluminum oxide (AAO) exhibits great possibility for this purpose. Here, CNTs based on AAO template were produced using acetylene or ethylene as the hydrocarbon sources with or without the presence of Co catalysts. CNTs grown on the Co-embedded AAO samples were normally confined within the nanopores of the AAO template. It was found that C2H4 normally requires 100 degrees C higher pyrolysis temperature than C2H2 under otherwise identical conditions. The pyrolysis temperature is greatly reduced with the presence of Co catalysts. CNTs can grow out of the nanopores, if Co particles are present at the bottom of the nanopores and if the nanopores are short in length or large in diameter. The graphitization of AAO template grown CNTs was studied by Raman spectroscopy. The CNTs produced from ethylene are generally better in graphitization than those from acetylene, and the CNTs grown with the presence of Co catalysts deposited at the bottom of nanopores are better than those without Co catalysts or with Co catalysts coated on the entire inner wall of nanopores. The growth temperature is found not to play a critical role in graphitization.

Aluminum Oxide↗