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PubMed2001

Tissue-specific patterns of lignification are disturbed in the brown midrib2 mutant of maize (Zea mays L.).

Despite recent progress, several aspects of lignin biosynthesis, including variation in lignin composition between species and between tissues within a given species, are still poorly understood. The analysis of mutants affected in cell wall biosynthesis may help increase the understanding of these processes. We have analyzed the maize brown midrib2 (bm2) mutant, one of the four bm mutants of maize, using pyrolysis-mass spectrometry (Py-MS) and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS). Vascular tissues from the leaf blade and leaf sheath from different parts of the plant were investigated and compared to the corresponding samples from a wild-type plant of the same genetic background (inbred line A619). Multivariate analysis revealed that the bm2 mutant had reduced amounts of di- and trimeric lignin derivatives, notably species with m/z 272 and m/z 330, and that the ratio of guaiacyl residues to polysaccharides was reduced in the bm2 mutant. In addition, differences in cell wall composition between different parts of the plant (blade versus sheath, young versus old tissue) were much less pronounced in the bm2 mutant. These changes suggest that the functional Bm2 gene is important for the establishment of tissue-specific cell wall composition.

Cell Wall↗

PubMed2003

Chemical and spectroscopic analysis of lignin in isolated flax fibers.

The chemistry of pure flax fibers, free of contaminating nonfiber components, has not been determined. Fibers from the center sections of the stem of seed and fiber flax (Linum usitatissium L.), which had been retted after soaking in water and removal of the epidermis by hand, underwent chemical and spectroscopic analysis. Wet chemical analysis showed only trace indications of aromatics and no long chain fatty acids or alcohols in fibers. Pyrolysis mass spectroscopy (PyMS) and pyrolysis gas chromatography mass spectrometry (PyGCMS) showed only trace amounts of aromatic constituents that could be attributed to the presence of lignin. Mid-infrared (Mid-IR) and Raman spectroscopy of these fibers showed no aromatic compounds present. This study suggests that earlier work reporting the presence of lignin ranging from 1 to 4% may be the result of residual shive or epidermis/cuticle material remaining after the retting process which may be responsible for the favorable properties desired by the composites industry.

Flax↗

PubMed2005

Sorption-desorption of alachlor and linuron in a semiarid soil as influenced by organic matter properties after 16 years of periodic inputs.

The effect of management practices on soil potential for regulating the residual concentration of pesticides was examined in samples from a Calcic Haploxeralf in Toledo (central Spain). Sorption-desorption of alachlor and linuron was found to depend on inputs of lignocelullosic wastes or cattle manure for the past 16 years. For a given herbicide, the soil sorption capacity (K(f)) follows the order control < crop residues < manure, which is consistent with the organic C content in the soil samples. Some structural characteristics of the soil humic acid as revealed by visible and infrared spectroscopies and analytical pyrolysis were useful to forecast the sorption-desorption intensity. Simple and multiple linear correlation analyses illustrate enhanced sorption of alachlor and linuron in soil plots where slightly altered soil organic matter accumulated (positive correlations with the intensity of infrared lignin signature band and with the methoxyphenol yields after pyrolysis of the humic acids and negative correlation with the aromaticity as pointed out by the optical density at 465 nm). Linuron showed a preference for soils with humic acids of low molecular weight and low degree of internal cross-linking, as inferred from the positive correlation with the ratio between optical densities at 465 and 665 nm. Under the conditions of the present experiment, agricultural practices including organic amendments seem to have a beneficial effect in the control of leaching and sorption of pesticides.

Acetamides↗

PubMed2004

Origin and mechanistic pathways of formation of the parent furan--a food toxicant.

Studies performed on model systems using pyrolysis-GC-MS analysis and (13)C-labeled sugars and amino acids in addition to ascorbic acid have indicated that certain amino acids such as serine and cysteine can degrade and produce acetaldehyde and glycolaldehyde that can undergo aldol condensation to produce furan after cyclization and dehydration steps. Other amino acids such as aspartic acid, threonine, and alpha-alanine can degrade and produce only acetaldehyde and thus need sugars as a source of glycolaldehyde to generate furan. On the other hand, monosaccharides are also known to undergo degradation to produce both acetaldehyde and glycolaldehyde; however, (13)C-labeling studies have revealed that hexoses in general will mainly degrade into the following aldotetrose derivatives to produce the parent furan-aldotetrose itself, incorporating the C3-C4-C5-C6 carbon chain of glucose (70%); 2-deoxy-3-ketoaldotetrose; incorporating the C1-C2-C3-C4 carbon chain of glucose (15%); and 2-deoxyaldotetrose, incorporating the C2-C3-C4-C5 carbon chain of glucose (15%). Furthermore, it was also proposed that under nonoxidative conditions of pyrolysis, ascorbic acid can generate the 2-deoxyaldotetrose moiety, a direct precursor of the parent furan. In addition, 4-hydroxy-2-butenal-a known decomposition product of lipid peroxidation-was proposed as a precursor of furan originating from polyunsaturated fatty acids. Among the model systems studied, ascorbic acid had the highest potential to produce furan, followed by glycolaldehyde/alanine > erythrose > ribose/serine > sucrose/serine > fructose/serine > glucose/cysteine.

Acetaldehyde↗

PubMed2005

Mechanism of formation of redox-active hydroxylated benzenes and pyrazine in 13C-labeled glycine/D-glucose model systems.

To extend the analytical capabilities of the pyrolysis-gas chromatograph-mass spectrometry system that has been successfully utilized in the past as an integrated reaction, separation, and identification system to study label incorporation patterns in Maillard reaction products, a novel methodology was developed to analyze the composition of nonvolatile residues of the initial reaction products. This was achieved through a postpyrolytic in-situ derivatization technique using trimethylsilyldiethylamine. Application of this technique to the investigation of the nonvolatile products formed during pyrolysis of glucose alone and in the presence of glycine has indicated the formation of several redox-active hydroxylated benzene derivatives such as 1,2,3-trihydroxybenzene (pyrogallol), 1,4-dihydroxybenzene (hydroquinone), 1,2-dihydroxybenzene (catechol), and 2,5-dihydroxypyrazine. Labeling studies have indicated that the intact glucose carbon backbone was involved in the construction of the benzene ring of the hydroxylated benzene derivatives and that dimerization of glycine alone can lead to the formation of 2,5-dihydroxypyrazine.

Benzene↗

PubMed2006

Chemical composition of abaca (Musa textilis) leaf fibers used for manufacturing of high quality paper pulps.

The chemical composition of leaf fibers of abaca (Musa textilis), which are commonly used for high-quality paper pulp production, was thoroughly studied. The results revealed that the lignin content was 13.2% of the total fiber. The analysis of abaca fibers by pyrolysis coupled to gas chromatography-mass spectrometry (Py-GC/MS) released predominantly compounds arising from lignin and p-hydroxycinnamic acids, with high amounts of 4-vinylphenol. The latter compound was demonstrated to arise from p-coumaric acid by pyrolysis of abaca fibers in the presence of tetramethylammonium hydroxide, which released high amounts of p-coumaric acid (as the methyl derivative). Products from p-hydroxyphenyl (H), guaiacyl (G), and syringyl (S) propanoid units, with a predominance of the latter (H:G:S molar ratio of 1.5:1:4.9), were also released after Py-GC/MS of abaca fibers. Sinapyl and coniferyl acetates, which are thought to be lignin monomer precursors, were also found in abaca. The extractives content of the abaca fiber (0.4%) was low, and the most predominant compounds were free sterols (24% of total extract) and fatty acids (24% of total extract). Additionally, significant amounts of steroid ketones (10%), triglycerides (6%), omega-hydroxyfatty acids (6%), monoglycerides (4%), fatty alcohols (4%), and a series of p-hydroxycinnamyl (p-coumaric and ferulic acids) esterified with long chain alcohols and omega-hydroxyfatty acids were also found, together with minor amounts of steroid hydrocarbons, diglycerides, alpha-hydroxyfatty acids, sterol esters, and sterol glycosides.

Gas Chromatography-Mass Spectrometry↗

PubMed2002

Synthesis of 2,5-disubstituted thienosultines and their thermal reactions with dienophiles and nucleophiles.

The 2,5-disubstituted thienosultines (5,7-disubstituted 1,4-dihydro-1H-3lambda(4)-thieno[3,4-d][2,3]oxathiin-3-oxides) 5a-d were prepared from the corresponding dichlorides 4a-d with the commercially available Rongalite (sodium formaldehyde sulfoxylate) in 17-60% yields. When heated in the presence of electron-poor dienophiles, sultines 5a-d underwent elimination of SO(2), and the resulting non-Kekulé biradicals 7a-d were intercepted as the 1:1 adducts 8-12 in good to excellent yields. The pyrolysis of sultines and sulfolenes with different concentrations of dienophiles revealed that either a preequilibrium between starting reagents and biradical species or Diels-Alder and retro-Diels-Alder reaction mechanisms may be involved; however, more work is necessary to establish the proposed mechanisms. Reaction of sultine 5b with nBuLi was found to undergo a nucleophilic ring-opening reaction to give sulfinyl alcohol 17 after H(2)O workup. When sultine 5a was heated in benzene in a sealed tube in the presence of methanol, methanol-d(4), or 2-mercaptoethanol, the respective 1:1 trapping adducts 19-21 as well as the rearranged sulfolene 6a were isolated in similar amounts. The isolation of adducts 19-21 may be explained by the involvement of either biradical or ionic intermediates during the pyrolysis.

Journal Article↗

PubMed1997

Chemoselectivity in the Reactions of Acetylketene and Acetimidoylketene: Confirmation of Theoretical Predictions.

Acetylketene (1) was generated by flash pyrolysis of 2,2,6-trimethyl-4H-1,3-dioxin-4-one (6). The selectivities of 1 toward a number of representative functional groups were measured for the first time in a series of competitive trapping reactions. The trend in reactivities toward 1 follows the general order amines > alcohols >> aldehydes approximately ketones and can be rationalized by considering both the nucleophilicity and the electrophilicity of the reacting species. Alcohols show significant selectivity based on steric hindrance, with MeOH approximately 1 degrees > 2 degrees > 3 degrees. These selectivities are consistent with the activation energies and the pseudopericyclic transition structure previously calculated for the addition of water to formylketene. The results, presented here, of ab initio transition structure calculations for the addition of ammonia to formylketene are qualitatively consistent with the experimental trends as well. N-Propylacetacetimidoylketene (2) was generated by the solution pyrolysis of tert-butyl N-propyl-3-amino-2-butenoate (9a) and showed similar selectivity toward alcohols as opposed to ketones and similar steric discrimination toward alcohols. This is again in agreement with previous ab initio calculations. Taken together, these experimental trends in the reactivities of both 1 and 2 toward a variety of reagents provide strong, although indirect support for the planar, pseudopericyclic transition structures for these reactions which are predicted by ab initio calculations.

Journal Article↗

PubMed2005

Photoelectrochemical oxidation of water at transparent ferric oxide film electrodes.

The fabrication of thin-film Fe(2)O(3) photoanodes from the spray pyrolysis of Fe(III)-containing solutions is reported along with their structural characterization and application to the photoelectrolysis of water. These films combine good performance, measured in terms of photocurrent density, with excellent mechanical stability. A full investigation into the effects that modifications of the spray-pyrolysis method, such as the addition of dopants or structure-directing agents and changes in precursor species or carrier solvent, have on the performance of the photoanodes has been realized. The largest photocurrents were obtained from photoanodes prepared from ferric chloride precursor solutions, simultaneously doped with Ti(4+) (5%) and Al(3+) (1%). Doping with Zn(2+) also shows promise, cathodically shifting the onset potential by approximately 0.22 V.

Journal Article↗

PubMed2004

Surface properties of porous carbon obtained from polystyrene sulfonic acid-based organic salts.

Pyrolysis ofpolysterene sulfonic acid-co-maleic acid salts at 800 degrees C resulted in formation of new materials consisting of porous carbon and metal species dispersed on the surface. After hydrochloric acid treatment, the metal oxides/salts were removed. Obtained materials were characterized using adsorption of nitrogen, thermogravimetric analysis, Raman spectroscopy, and scanning electron microscopy with energy dispersive analysis of X-rays. The results showed highly developed porous structures in the range of micro- and mesopores. The porous features of new materials resemble those characteristics for carbon foams. The differences in the porous structure are linked to the type of transition metal used for the modification of the initial polymer and the chelation process. Macro- and mesopores are spherical/cylindrical in shape, and they are likely formed when release of pyrolysis gases, such as CO2, NO2, SO2, H2S, and CxHy, occurs. Moreover, reduction of metal, its migration to the surface, and agglomeration contribute to development of porosity. Depending on the reactivity of the metal used for cation exchange (Fe, Co, or Ni) either sulfides (nickel and cobalt) or oxides (cobalt and iron) are formed on the carbon surface.

Journal Article↗

PubMed1987

Gas chromatographic instrumentation for the analysis of aerosols and gases in Titan's atmosphere.

During the next decade or so, NASA, in conjunction with the European Space Agency, plans to send a spacecraft to the Saturnian system so that local studies of Saturn and its satellite, Titan, can be made. In order to study the atmosphere of Titan, analysis of both aerosols and gases will have to be made. To accomplish this, gas chromatographic instrumentation for the collection and analysis of organic gases and aerosols in Titan's atmosphere is being developed. The aerosols will be collected and then subjected to pyrolysis-gas chromatography. Results using a simple pyrolysis-GC system and tholin, made by subjecting a nominal Titan mixture (96.8% N2, 3% CH4, 0.2% H2) to laser-supported shocks, show that many compounds, including hydrocarbons and simple nitriles, can be identified by this technique. Atmospheric gases will be collected using large volume (>10 cm3) sample loops and then analyzed by gas chromatography. Large volume samples are required because the ambient pressures, where the probe instruments are first deployed, will be low (<10 mbar). Preliminary studies using a 20 cm3 sampling system and a very sensitive meta-stable ionization detector show that hydrocarbon components at the 10 ppb level can be detected. Work will continue to improve GC sensitivity, minimize analysis time, and develop interfaces with suitable sample collectors for analysis of atmospheres by future spacecraft.

Aerosols↗

PubMed1995

Constraints on the origins of hydrocarbon gas from compositions of gases at their site of origin

It is widely accepted that natural gas is formed from thermal decomposition of both oil in reservoirs and, to a lesser extent, the organic matter in shales from which the oil was derived. But laboratory pyrolysis experiments on shales do not reproduce the methane-rich composition typical of most gas reservoirs, leading to suggestions that other mechanisms, such as transition-metal catalysis, may be important. The discrepancy might, however, instead arise because gas (and oil) deposits have migrated from their source rocks, so that the reservoir composition might not be representative of the composition in the source rocks where the hydrocarbons were generated. To address this question, we have analysed gas samples coproduced with oils directly from a source rock (the Bakken shales, North Dakota, USA) where the local geology has prevented significant hydrocarbon migration. The methane contents of these Bakken-shale gases are much lower than that of conventional gas reservoirs, but are consistent with that from pyrolysis experiments on these shales. Thus, because these Bakken gases form with (rather than from) oils, we argue that compositional differences between gases from source rocks and conventional gas deposits result from fractionation processes occurring after hydrocarbon expulsion from the source rock.

Fossil Fuels↗

PubMed1995

Determination of cadmium in whole blood and urine electrothermal atomic absorption spectrometry using palladium-based modifiers and in situ decontamination.

The determination of Cd in whole blood and urine by electrothermal atomic absorption spectrometry using Pd-based modifiers and in situ decontamination was studied. The performance of Pd, Pd + NH4NO3, and Pd + Mg(NO3)2 as modifiers were compared with respect to maximum pyrolysis and atomization temperatures, background attenuation, linear calibration range and matrix interference. Samples were diluted (1 + 4) with 0.1% Triton X-100 (blood) or 0.2% HNO3 (urine), and introduced onto the graphite tube platform already containing the in situ dried and decontaminated modifier. The influence of modifier volume and concentration, as well as that of the dilution ratio was investigated. The proposed procedure involves the use of Pd(NO3)2 + (Mg(NO3)2 as modifier, a pyrolysis temperature of 700 degree C and an in situ decontamination step of 1200 degrees C. The atomization temperature was 1700 degrees C. The detection limit (n = 10, k = 3) was 0.22 micrograms l-1 for both samples. Typical relative standard deviation values (n = 3) were below 3%. Using matrix-matched standards, good agreement was observed between experimental and reference values in the analysis of certified reference materials. Interlaboratory comparison data have confirmed the validity of the proposed analytical procedure.

Cadmium↗

PubMed2003

The effect of the reinforcing carbon on the microstructure of pitch-based granular composites.

Carbon composites were prepared with four pitches (a commercial impregnating coal-tar pitch, two thermally treated pitches and an air-blown pitch) and four granular carbons (anthracite, graphite, green petroleum coke and foundry coke). Granular carbon/pitch proportions were optimized for each composite and differed in the characteristics of the single components. Interactions of the pitch with the granular carbons during pyrolysis and their subsequent effects on the microstructure of the final composite were monitored by light microscopy. The results show that the light texture of the matrix and the porosity of the composite depend not only on the chemical composition of the pitch but also on the specific granular carbon used as reinforcing material. The same pitch may generate different light textures depending on the characteristics of the carbon. Composites from thermally treated pitches and graphite show highly ordered matrices orientated in the direction of graphite planes. Graphite particles seem to exert a huge influence on mesophase development during the pyrolysis of the treated pitches, affecting not only the orientation of the mesophase, but also reducing the rate of mesophase formation. On the other hand, when green petroleum coke is used with the thermally treated pitches, matrices show a small size light texture, due to the high reactivity of the pitch in the presence of this granular carbon. The porosity of the composites is controlled by both the pitch and the granular carbon.

Carbon↗

PubMed1975

Nonprevalence of biochemical fossils in kerogen from pre-Phanerozoic sediments.

Evidence of biochemical and geochemical evolution was sought in insoluble carbonaceous matter from 30 selected pre-Phanerozoic sediments ranging in age from about 3.8 to about 0.7 x 10(9) years. The carbon isotope ratios observed were in the range of -20 to -32 per mil with reference to the Peedee belemnite standard, similar to those previously reported. No systematic trends are obvious to us. Stepwise pyrolysis-gas-chromatography showed only molecules with fewer than 8 carbon atoms at the level of sensitivity of 10(-9) g of organics in a 10 mg rock sample. Carbon, hydrogen, and nitrogen analyses showed noncarbonate carbon from less than 0.1% to more than 3%, with very small amounts of N. The H/C (atomic) ratios on HCl-leached and HF-treated samples were generally less than 0.3. Evidence of low pyrolysis yields (micro-analysis) and low H/C atomic ratios (macro-analysis) implies that the carbonaceous solids in even the least metamorphosed of these ancient sediments have evolved far toward amorphous carbon or graphite and do not yield useful "biochemical fossils."

Journal Article↗

PubMed1993

Structural biopolymer preservation in Miocene leaf fossils from the Clarkia site, northern Idaho.

The 17- to 20-million-year-old locality at Clarkia, northern Idaho, is renowned for yielding amplifiable DNA from a magnolia leaf fossil. In-source pyrolysis-mass spectrometry and pyrolysis-gas chromatography/mass spectrometry now reveal that molecular preservation of biomacromolecules is highly selective; structural polysaccharides, cutin polyesters, and proteins were not preserved in detectable quantity in the leaf tissues, whereas both lignin and an aliphatic biopolymer were detected. This study points up the need for improved understanding of the precise modes and extent of preservation of biomacromolecules in fossil materials and sediments.

Journal Article↗

PubMed1977

An experimental laboratory system to evaluate the industrial fate of toxic volatile inorganic hydrides.

This paper reports the development of a gas sampling and static reactor system for identifying potentially toxic volatile byproducts from an industrial process and for characterizing their airborne stability at trace levels. The system has been applied in an exemplary manner to the analysis and fate of diborane and phosphine. The heart of the system consists of a static reactor to which pyrolysis products or other reactants can be added from a flow reactor. The static reactor can be resampled at any time. Methods for identifying and quantifying pyrolysis products by chromatography with multiple detectors and mass spectroscopy are included.

Air Pollutants↗

PubMedDate not supplied

Intoxication by cyanide in fires: a study in monkeys using polyacrylonitrile.

It is suspected that hydrogen cyanide (HCN) may be an important factor in incapacitating fire victims, but the effects of sublethal exposures are not well characterized. Also, the incapacitating effects of fire atmospheres result from exposure to a mixture of toxic products so that the contribution from each component is difficult to determine. The mechanisms of incapacitation in monkeys exposed to the pyrolysis products of polyacrylonitrile (PAN) were compared to those resulting from low level HCN gas exposures. The physiological effects of the PAN atmospheres were almost identical to those of HCN gas alone. They consisted of hyperventilation, followed by loss of consciousness after 1-5 min, bradycardia with arrhythmias and T-wave abnormalities, and were followed by a rapid recovery after exposure. Hydrogen cyanide is considered to be the major toxic product formed by the pyrolysis of PAN. It is suggested that HCN may produce rapid incapacitation at low blood levels of cyanide in fires, while death may occur later due to carbon monoxide poisoning or other factors.

Acrylic Resins↗