Molecular products and radicals from pyrolysis of lignin.

Thermal degradation of lignin under two reaction regimes (pyrolysis in N(2) and oxidative pyrolysis in 4% O(2) in N(2)) has been investigated in a tubular, isothermal, flow-reactor over the temperature range 200-900 °C at a residence time of 0.2 s. Two experimental protocols were adopted: (1) Partial pyrolysis in which the same lignin sample was continuously pyrolyzed at each temperature and (2) conventional pyrolysis, in which new lignin samples were pyrolyzed at each pyrolysis temperature. The results identified common relationships between the two modes of experiments, as well as some differences. The majority of products from partial pyrolysis peaked between 300 and 500 °C, whereas for conventional pyrolysis reaction products peaked between 400 and 500 °C. The principal products were syringol (2,6-dimethoxy phenol), guaiacol (2-methoxy phenol), phenol, and catechol. Of the classes of compounds analyzed, the phenolic compounds were the most abundant, contributing over 40% of the total compounds detected. Benzene, styrene, and p-xylene were formed in significant amounts throughout the entire temperature range. Interestingly, six ringed polycyclic aromatic hydrocarbons were formed during partial pyrolysis. Oxidative pyrolysis did not result in large differences from pyrolysis; the main products still were syringol, guaiacol, phenol, the only significant difference being the product distribution peaked between 200 and 400 °C. For the first time, low temperature matrix isolation electron paramagnetic resonance was successfully interfaced with the pyrolysis reactor to elucidate the structures of the labile reaction intermediates. The EPR results suggested the presence of methoxyl, phenoxy, and substituted phenoxy radicals as precursors for formation of major products; syringol, guaiacol, phenols, and substituted phenols.

Molecular modeling studies of the reactions of phenoxy radical dimers: pathways to dibenzofurans.

The B3LYP hybrid density functional computational technique was applied to describe the sequence of phenoxy radicals coupling reactions leading to the formation of dibenzofurans. Reaction kinetic parameters were estimated for key reactions. Aromatization of bis-keto dimers of phenoxy radicals followed by intermediate dehydration or dehydroxylation was demonstrated to be a strongly stereoselective process. While the S,S-diastereomer of the ortho-C//ortho-C keto dimer forms (o,o')-dihydroxybiphenyl, a known dibenzofuran intermediate, via inter-ring hydrogen transfer reaction, the less stable R,S-stereoisomer can easily be transformed into another 5-hydroxyl-4,5-cyclohexadiene-2,3-benzofuran intermediate that provides an energetically more favorable pathway for formation of dibenzofuran. The possible channels of radical-chain processes that convert these intermediates to dibenzofuran and polychlorinated dibenzofurans are discussed.

Development of supported iron oxide catalyst for destruction of PCDD/F.

Studies on the development of supported iron oxide catalysts for PCDD/F decomposition using 2-monochlorophenol as a surrogate test compound are presented. Iron oxide catalysts supported on titania were prepared by two methods: impregnation and the sol-gel method. The latter preparation method resulted in better dispersion of iron oxide on the surface and the formation of gamma-Fe2O3. This is in contrast to the impregnated samples where alpha-Fe2O3 crystallites were formed. Formation of gamma-Fe2O3 resulted in improved reducibility of the active phase that favorably affected the catalytic oxidation properties of the catalyst, i.e., the light-off curves for the sol-gel samples were shifted toward lower temperature. Addition of calcium oxide to iron oxide catalyst further improved the performance of the system through stabilization and increase in the concentration of gamma-Fe2O3 in the sol-gel prepared samples. Addition of calcium oxide has a dual effect on the performance of the catalyst. First, it creates oxygen vacancies in the reduction-resistant Fe2O3 octahedral structures, thereby improving the reducibility of the active phase. Second, iron oxide can transform during decomposition of chlorinated hydrocarbons into iron chloride. Calcium oxide improved the chlorine transfer from the surface iron oxide species, thereby providing a relatively fresh surface for further catalytic oxidation. Comparison of TPR profiles with the position of light-off curves in 2-monochlorophenol decomposition led to the conclusion that Fe3O4 species are the active phase under conditions that facilitate redox cycling between Fe3+ and Fe2+ ions.

Neuropathological examination suggests impaired brain iron acquisition in restless legs syndrome.

OBJECTIVE: To assess neuropathology in individuals with restless legs syndrome (RLS). METHODS: A standard neuropathologic evaluation was performed on seven brains from individuals who had been diagnosed with RLS. The substantia nigra was examined in greater detail for iron staining and with immunohistochemistry for tyrosine hydroxylase and proteins involved in iron management. Five age-matched individuals with no neurologic history served as controls. RESULTS: There were no histopathologic abnormalities unique to the RLS brains. Tyrosine hydroxylase staining in the major dopaminergic regions appeared normal in the RLS brains. Iron staining and H-ferritin staining was markedly decreased in the RLS substantia nigra. Although H-ferritin was minimally detected in the RLS brain, L-ferritin staining was strong. However, the cells staining for L-ferritin in RLS brains were morphologically distinct from those in the control brains. Transferrin receptor staining on neuromelanin-containing cells was decreased in the RLS brains compared to normal, whereas transferrin staining in these cells was increased. CONCLUSIONS: RLS may not be rooted in pathologies associated with traditional neurodegenerative processes but may be a functional disorder resulting from impaired iron acquisition by the neuromelanin cells in RLS. The underlying mechanism may be a defect in regulation of the transferrin receptors.

X-ray spectroscopic studies of the high temperature reduction of Cu(II)O by 2-chlorophenol on a simulated fly ash surface.

The reaction of 2-chlorophenol on Cu(II)O at 375 degrees C is studied using X-ray absorption near edge structure (XANES) spectroscopy. A mixture of copper(II) oxide and silica is prepared to serve as a surrogate for fly ash in combustion systems. 2-Chlorophenol is utilized as a model precursor for formation of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/F). The Cu K-edge spectra shiftto lower binding energy, reflecting the reduction of the copper. The substrate is found to form a mixture of Cu(II), Cu(I), and Cu(O), with the dominant species being Cu(I). The data are fitted well with a first-order reaction scheme, with a time constant at 375 degrees C of 76 s. This is the first application of XANES spectroscopy for studying the kinetics and mechanism of heterogeneous reactions relevant to combustion processes, and the results demonstrate the utility and desirability of such X-ray spectroscopic studies.

Quinoid redox cycling as a mechanism for sustained free radical generation by inhaled airborne particulate matter.

The health effects of airborne fine particles are the subject of government regulation and scientific debate. The aerodynamics of airborne particulate matter, the deposition patterns in the human lung, and the available experimental and epidemiological data on health effects lead us to focus on airborne particulate matter with an aerodynamic mean diameter less than 2.5 microm (PM(2.5)) as the fraction of the particles with the largest impact in health. In this article we present a novel hypothesis to explain the continuous production of reactive oxygen species produced by PM(2.5) when it is deposited in the lung. We find PM(2.5) contains abundant persistent free radicals, typically 10(16) to 10(17) unpaired spins/gram, and that these radicals are stable for several months. These radicals are consistent with the stability and electron paramagnetic resonance spectral characteristics of semiquinone radicals. Catalytic redox cycling by semiquinone radicals is well documented in the literature and we had studied in detail its role on the health effects of cigarette smoke particulate matter. We believe that we have for the first time shown that the same, or similar radicals, are not confined to cigarette smoke particulate matter but are also present in PM(2.5). We hypothesize that these semiquinone radicals undergo redox cycling, thereby reducing oxygen and generating reactive oxygen species while consuming tissue-reducing equivalents, such as NAD(P)H and ascorbate. These reactive oxygen species generated by particles cause oxidative stress at sites of deposition and produce deleterious effects observed in the lung.

Role of free radicals in the toxicity of airborne fine particulate matter.

Exposure to airborne fine particles (PM2.5) is implicated in excess of 50 000 yearly deaths in the USA as well as a number of chronic respiratory illnesses. Despite intense interest in the toxicity of PM2.5, the mechanisms by which it causes illnesses are poorly understood. Since the principal source of airborne fine particles is combustion and combustion sources generate free radicals, we suspected that PM2.5 may contain radicals. Using electron paramagnetic resonance (EPR), we examined samples of PM2.5 and found large quantities of radicals with characteristics similar to semiquinone radicals. Semiquinone radicals are known to undergo redox cycling and ultimately produce biologically damaging hydroxyl radicals. Aqueous extracts of PM2.5 samples induced damage to DNA in human cells and supercoiled phage DNA. PM2.5-mediated DNA damage was abolished by superoxide dismutase, catalase, and deferoxamine, implicating superoxide radical, hydrogen peroxide, and the hydroxyl radical in the reactions inducing DNA damage.

Hazardous air pollutants formation from reactions of raw meal organics in cement kilns.

Thermally induced chlorination, condensation, and formation reactions of raw meal organic surrogates were investigated on different types of surfaces. The System for Thermal Diagnostic Studies provided a powerful tool to study these reactions under defined reaction conditions, which were related to typical conditions in the preheater zone of cement kiln. Experiments were conducted with benzene and benzene/myristic acid (C6H6/C13H27COOH) mixtures in a quartz reactor containing different chlorinating catalysts/reagents over a temperature range of 300-500 degrees C. Reaction products were trapped in-line and analyzed by GC-MS. A mixture of chlorides of calcium, potassium, aluminium and iron was highly effective for chlorination/condensation reactions of benzene and benzene/myristic acid mix at temperatures above 300 degrees C. The same behavior was observed only when calcium chloride and potassium chloride were used as chlorinating catalyst/reagent. This result showed that transition metal chlorides like FeCl3 are not necessary for chlorination/condensation of organics under post-combustion conditions. Methylene chloride was the major chlorinated product followed by chloroform and various other C1, C2 and C6 chlorinated products. Yields of chlorinated aliphatics were highest at 400 degrees C for both benzene and benzene/myristic acid mix. C6 products were mainly mono- to hexa-chlorinated benzenes with trace amounts of chlorinated phenols. The major chlorinated products observed in this study (i.e., methylene chloride, chloroform, chloroethanes and monochlorobenzene) were also present as major chlorinated hydrocarbons in the cement kiln field emission data.

Genetic modifiers of the Drosophila NSF mutant, comatose, include a temperature-sensitive paralytic allele of the calcium channel alpha1-subunit gene, cacophony.

The N-ethylmaleimide-sensitive fusion protein (NSF) has been implicated in vesicle trafficking in perhaps all eukaryotic cells. The Drosophila comatose (comt) gene encodes an NSF homolog, dNSF1. Our previous work with temperature-sensitive (TS) paralytic alleles of comt has revealed a function for dNSF1 at synapses, where it appears to prime synaptic vesicles for neurotransmitter release. To further examine the molecular basis of dNSF1 function and to broaden our analysis of synaptic transmission to other gene products, we have performed a genetic screen for mutations that interact with comt. Here we report the isolation and analysis of four mutations that modify TS paralysis in comt, including two intragenic modifiers (one enhancer and one suppressor) and two extragenic modifiers (both enhancers). The intragenic mutations will contribute to structure-function analysis of dNSF1 and the extragenic mutations identify gene products with related functions in synaptic transmission. Both extragenic enhancers result in TS behavioral phenotypes when separated from comt, and both map to loci not previously identified in screens for TS mutants. One of these mutations is a TS paralytic allele of the calcium channel alpha1-subunit gene, cacophony (cac). Analysis of synaptic function in these mutants alone and in combination will further define the in vivo functions and interactions of specific gene products in synaptic transmission.

Full-scale evaluation of the thermal stability-based hazardous organic waste incinerability ranking.

The results of a full-scale evaluation of the thermal stability-based hazardous organic waste incinerability ranking are presented. Tests were conducted for a surrogate mixture consisting of sulfur hexafluoride, chlorobenzene, toluene, tetrachloroethene, methylene chloride, 2-chloropropene and 1,1,1-trichloroethane under nominal incinerator operating conditions. Based on median surrogate DREs, the results indicated that the pyrolytic ranking was statistically significant at the 90 percent confidence level while the oxidative ranking was statistically significant at the 97.5 percent confidence level. The heat of combustion ranking failed to give a statistically significant correlation at the 90 percent confidence level. The statistical success of the thermal stability rankings and statistical failure of the heat of combustion ranking suggest that chemical reaction kinetics controlled the relative emission rates of the surrogate compounds during these tests.

Laboratory evaluations of the thermal degradation properties of toxic organic materials in sewage sludge.

Laboratory thermal decomposition studies were performed to evaluate potential emissions from sewage sludge incinerators. Precisely controlled thermal decomposition experiments were conducted on sludge spiked with mixtures of hazardous organic compounds, on mixtures of pure compounds without sludge, and on unspiked sludge. Experiments were conducted in nitrogen and air atmospheres with gas phase reaction times of 2.0 seconds over the temperature range 300 degrees C-1000 degrees C. It was found that sludge inhibited the decomposition of moderately stable spiked contaminants but accelerated the decomposition of the most stable components. This effect was attributed to radical scavengers produced by the sludge matrix at lower temperatures which then decomposed at higher temperatures. A multiple hearth simulation study suggested that most of the organic material present in the sludge matrix is vaporized within the upper hearths that are held at lower temperatures and may consequently escape from such incinerators undestroyed. A number of stable byproducts resulted from the sludge decomposition that may be of environmental concern.