Mixture Of Aromatic Compounds Research Articles

Biodegradation of mixtures of polycyclic aromatic hydrocarbons under aerobic and nitrate-reducing conditions

Contaminated sites often contain complex mixtures of aromatic compounds. This complex mixture and the system's redox condition may influence biodegradation patterns. In this study, the biodegradation of PAHs in varying mixture combinations by a pure culture of Pseudomonas putida strain KBM-1 under aerobic conditions showed that the presence of naphthalene (2-ringed PAH) stimulated phenanthrene (3-ringed PAH) degradation five-fold and pyrene (4-ringed PAH) degradation two-fold. However, the presence of phenanthrene inhibited pyrene degradation. Similar degradation patterns were observed under anaerobic, nitrate-reducing conditions; though the degradation rates were typically slower. For example, phenanthrene and pyrene degradation required 2–3 longer times to approach non-detectable levels under nitrate-reducing conditions. In contrast, the time to attain non-detectable levels using a different strain, Pseudomonas stutzeri SAG-R, was similar under both conditions. The results show the importance of improving our understanding of how to extrapolate single substrate biodegradation data obtained under aerobic conditions to multi-substrate situations in aerobic and anaerobic environments.

Metabolism of aromatic aldehydes as cosubstrates by the acetogen Clostridium formicoaceticum.

When the acetogen Clostridium formicoaceticum was cultivated on mixtures of aromatic compounds (e.g., 4-hydroxybenzaldehyde plus vanillate), the oxidation of aromatic aldehyde groups occurred more rapidly than did O-demethylation. Likewise, when fructose and 4-hydroxybenzaldehyde were simultaneously provided as growth substrates, fructose was utilized only after the aromatic aldehyde group was oxidized to the carboxyl level. Aromatic aldehyde oxidoreductase activity was constitutive (activities approximated 0. 8 U mg-1), and when pulses of 4-hydroxybenzaldehyde were added during fructose-dependent growth, the rate at which fructose was utilized decreased until 4-hydroxybenzaldehyde was consumed. Although 4-hydroxybenzaldehyde inhibited the capacity of cells to metabolize fructose, lactate or gluconate were consumed simultaneously with 4-hydroxybenzaldehyde, and lactate or aromatic compounds lacking an aldehyde group were utilized concomitantly with fructose. These results demonstrate that (1) aromatic aldehydes can be utilized as cosubstrates and have negative effects on the homoacetogenic utilization of fructose by C. formicoaceticum, and (2) the consumption of certain substrates by this acetogen is not subject to catabolite repression by fructose.

Toxicity of water‐soluble fractions derived from whole creosote and creosote‐contaminated sediments

AbstractCreosote, a complex mixture of aromatic compounds (ACs), contaminates numerous sites in the USA and elsewhere. In addition to pollution of the water column directly after a creosote spill, contaminated sediments can continue to act as source of pollution for many years, because natural and anthropogenic perturbations may redissolve or resuspend sediment‐associated contaminants. A 48‐h static renewal assay compared survival of the bay mysid, Mysidopsis bahia, exposed to water‐soluble fractions (WSFs) generated from two different sources: whole creosote and creosote‐contaminated sediment. Sediment was obtained from a Super Fund site located on the Southern Branch of the Elizabeth River in Virginia, USA. Whole creosote, contaminated sediment, and WSFs derived from these source materials were characterized. Median lethal concentrations of WSFs generated from whole creosote and sediment (expressed as total identified ACs) were 180 μg/L and 700 μg/L, respectively. The creosote‐derived WSF consisted of more than 70% low molecular weight nitrogen heterocyclics. These heterocyclics were below detectable limits in the sediment‐generated WSF, suggesting that losses of these compounds had occurred via weathering. Nitrogen heterocyclics likely contributed to the acute toxicity of the whole creosote WSF.

Nonaqueous capillary electrophoresis. Application to the separation of complex mixtures of organic acids by ion-pairing mechanism

Separation of a ten-membered model mixture of aromatic compounds possessing a carboxylic moiety along with other functional groups was investigated in the pH range 4.5–8.5. Methanol–acetonitrile (1:1) containing 10 mmol/l sodium acetate and an equal concentration of Tris was used as the background electrolyte. It was demonstrated that within the model set three categories of acids were present, namely those which moved nearby the endoosmotic flow (on the anodic side) and increased slowly their anodic mobility with the increasing apparent pH (1), those which revealed a strong increase with increasing pH and could be best discerned at apparent pH 7–7.5 in the negative operation mode (2) and those (a single member only) which possessed a strong anodic mobility even at low pH values and could be revealed within reasonable time in the negative operational mode only (3). The mobility of the latter was only slightly affected by the pH change of the background electrolyte. Further addition of hydrophobic moiety possessing ion pairing reagents (typically trimethyloctadecyl ammonium bromide) helped to refine the resolution at neutral pH. The results demonstrate clearly the wide differences in selectivity that it is possible to obtain by running electrophoretic separations in nonaqueous buffers.

Use of 13C nuclear magnetic resonance to assess fossil fuel biodegradation: fate of [1-13C]acenaphthene in creosote polycyclic aromatic compound mixtures degraded by bacteria.

[1-13C]acenaphthene, a tracer compound with a nuclear magnetic resonance (NMR)-active nucleus at the C-1 position, has been employed in conjunction with a standard broad-band-decoupled 13C-NMR spectroscopy technique to study the biodegradation of acenaphthene by various bacterial cultures degrading aromatic hydrocarbons of creosote. Site-specific labeling at the benzylic position of acenaphthene allows 13C-NMR detection of chemical changes due to initial oxidations catalyzed by bacterial enzymes of aromatic hydrocarbon catabolism. Biodegradation of [1-13C]acenaphthene in the presence of naphthalene or creosote polycyclic aromatic compounds (PACs) was examined with an undefined mixed bacterial culture (established by enrichment on creosote PACs) and with isolates of individual naphthalene- and phenanthrene-degrading strains from this culture. From 13C-NMR spectra of extractable materials obtained in time course biodegradation experiments under optimized conditions, a number of signals were assigned to accumulated products such as 1-acenaphthenol, 1-acenaphthenone, acenaphthene-1,2-diol and naphthalene 1,8-dicarboxylic acid, formed by benzylic oxidation of acenaphthene and subsequent reactions. Limited degradation of acenaphthene could be attributed to its oxidation by naphthalene 1,2-dioxygenase or related dioxygenases, indicative of certain limitations of the undefined mixed culture with respect to acenaphthene catabolism. Coinoculation of the mixed culture with cells of acenaphthene-grown strain Pseudomonas sp. strain A2279 mitigated the accumulation of partial transformation products and resulted in more complete degradation of acenaphthene. This study demonstrates the value of the stable isotope labeling approach and its ability to reveal incomplete mineralization even when as little as 2 to 3% of the substrate is incompletely oxidized, yielding products of partial transformation. The approach outlined may prove useful in assessing bioremediation performance.

Bacterial community dynamics during start-up of a trickle-bed bioreactor degrading aromatic compounds.

This study was performed with a laboratory-scale fixed-bed bioreactor degrading a mixture of aromatic compounds (Solvesso100). The starter culture for the bioreactor was prepared in a fermentor with a wastewater sample of a care painting facility as the inoculum and Solvesso100 as the sole carbon source. The bacterial community dynamics in the fermentor and the bioreactor were examined by a conventional isolation procedure and in situ hybridization with fluorescently labeled rRNA-targeted oligonucleotides. Two significant shifts in the bacterial community structure could be demonstrated. The original inoculum from the wastewater of the car factory was rich in proteobacteria of the alpha and beta subclasses, while the final fermentor enrichment was dominated by bacteria closely related to Pseudomonas putida or Pseudomonas mendocina, which both belong to the gamma subclass of the class Proteobacteria. A second significant shift was observed when the fermentor culture was transferred as inoculum to the trickle-bed bioreactor. The community structure in the bioreactor gradually returned to a higher complexity, with the dominance of beta and alpha subclass proteobacteria, whereas the gamma subclass proteobacteria sharply declined. Obviously, the preceded pollutant adaptant did not lead to a significant enrichment of bacteria that finally dominated in the trickle-bed bioreactor. In the course of experiments, three new 16S as well as 23S rRNA-targeted probes for beta subclass proteobacteria were designed, probe SUBU1237 for the genera Burkholderia and Sutterella, probe ALBO34a for the genera Alcaligenes and Bordetella, and probe Bcv13b for Burkholderia cepacia and Burkholderia vietnamiensis. Bacteria hybridizing with the probe Bcv13b represented the main Solvesso100-degrading population in the reactor.

Growth performance and pathway flux determine substrate preference of Alcaligenes eutrophus during growth on acetate plus aromatic compound mixtures

During batch growth of Alcaligenes eutrophus on various aromatic compounds in the presence of acetate, several distinct behaviour patterns were observed. The utilization of substrates of the meta pathway (phenol or p-cresol) was inhibited by acetate. When the aromatic was a substrate of the p-hydroxybenzoate branch of the ortho pathway, growth was mixotrophic, i.e. both substrates were consumed simultaneously. For the substrates of the gentisate pathway or the benzoate branch of the ortho pathway, substrate preference was governed by growth performance. Aromatic compounds enabling growth rate and yields higher than those obtained on acetate alone (i.e. benzoate, benzaldehyde, m-hydroxybenzoate and gentisate) inhibited acetate utilization, while acetate was the substrate consumed preferentially in mixtures containing aromatic compounds supporting only slow growth (i.e. benzoyl formate and 4-fluorobenzoate).

Kinetics of toluene degradation in a biofilm system under denitrifying conditions

In this paper a variability study of the kinetics of toluene biodegradation in biofilm systems under nitrate reducing conditions is presented. A total of 10 kinetic experiments were performed: 4 with toluene as a single compound and 6 with toluene in the presence of a mixture of aromatic compounds (benzene, ethylbenzene and xylenes: BEX). When toluene was the only substrate the maximum utilization rate, kx, and the half saturation constant, Ks, ranged between 1.3 to 1.8 d−1, and 0.17 and 1.7 mg/L respectively. Based on the nitrite production, the average yield coefficient was 1.0 to 1.2 mg biomass/mg toluene degraded. Furthermore, it was shown that the presence of benzene, xylenes and ethylbenzene significantly decreased the toluene removal.

Chemical constitution of Pocahontas No. 3 coal

A new method for the definition of the larger aromatic structural elements in high-rank coals has been developed. The procedure involves the oxidative decom-position of the coal with oxygen in basic solution and the subsequent decarboxylation of the aromatic arboxylic acids to yield a mixture of aromatic compounds that can readily be analyzed by conventional methods. This approach has been tested with pure compounds and applied to Pocahontas No. 3 coal.

Mechanistic insight into the reactions of O [rad]− with aromatic compounds and the synthesis of didehydroaromatic anions in the gas phase

The gas-phase ion/molecule reactions of O − with benzene, pyridine, furan, thiophene, pyrrole, and 1,3-cyclopentadiene have been quantitatively characterized under the thermally equilibrated (298 ± 3 K) conditions attainable with the flowing afterglow technique. All atomic oxygen radical anion reactions examined were found to be fast, with reaction occurring on at least three out of four collisions. While reaction rate coefficients are the same for all aromatic compounds, the product distributions for the O − reactions are extremely sensitive to the structure and properties of the neutral. In general, four reaction channels need to be considered: H + 2 -transfer, oxide anion formation (i.e. addition of an oxygen atom and loss of a hydrogen atom), H-atom transfer (i.e. formation of HO −), and H +-transfer. Formation of the didehydroaromatic radical anion was detected for each neutral while H-atom transfer was a minor pathway and was only found for pyrrole and 1,3-cyclopentadiene. Oxide anion formation was a major pathway for the six-membered aromatic rings. For the five-membered rings, only thiophene produced the corresponding oxide anion (as a trace product) upon reaction with O − . Proton transfer was always important where thermochemically allowed (thiophene, pyrrole, and 1,3-cyclopentadiene). The observations are interpreted with the aid of a reaction coordinate diagram detailing a series of sequential steps for O − with benzene, starting with formation of an ion/neutral complex followed by partitioning into the four reaction channels. The data are supplemented by measurements made for benzene- d 6 and pyridine- d 5, as well as for HO − reacting with each of the neutrals. In addition to demonstrating the synthetic utility of didehydroaromatic radical anion generation by this method, this work suggests that O − and HO − can be complementary to each other as negative-ion chemical ionization mass spectrometric reagents for analysis of mixtures of aromatic compounds by mass spectrometry.

Biodegradation of mixtures of substituted benzenes by Pseudomonas sp. strain JS150.

Pseudomonas sp. strain JS150 was isolated as a nonencapsulated variant of Pseudomonas sp. strain JS1 that contains the genes for the degradative pathways of a wide range of substituted aromatic compounds. Pseudomonas sp. strain JS150 grew on phenol, ethylbenzene, toluene, benzene, naphthalene, benzoate, p-hydroxybenzoate, salicylate, chlorobenzene, and several 1,4-dihalogenated benzenes. We designed experiments to determine the conditions required for induction of the individual pathways and to determine whether multiple substrates could be biodegraded simultaneously. Oxygen consumption studies with whole cells and enzyme assays with cell extracts showed that the enzymes of the meta, ortho, and modified ortho cleavage pathways can be induced in strain JS150. Strain JS150 contains a nonspecific toluene dioxygenase with a substrate range similar to that found in strains of Pseudomonas putida. The presence of the dioxygenase along with multiple pathways for metabolism of substituted catechols allows facile extension of the growth range by spontaneous mutation and degradation of mixtures of substituted benzenes and phenols. Chlorobenzene-grown cells of strain JS150 degraded mixtures of chlorobenzene, benzene, toluene, naphthalene, trichloroethylene, and 1,2- and 1,4-dichlorobenzenes in continuous culture. Under similar conditions, phenol-grown cells degraded a mixture of phenol, 2-chloro-, 3-chloro, and 2,5-dichlorophenol and 2-methyl- and 3-methylphenol. These results indicate that induction of appropriate biodegradative pathways in strain JS150 permits the biodegradation of complex mixtures of aromatic compounds.

Application of evolved gas analysis to surface characterization of organically-modified inorganic materials

Evolved gas analysis has been used in the routine characterization of organically-modified oxides, silicates and phosphates. Titania and kieselguhr, both modified with a bis-amino silane, show similar characteristics. In each case, surface hydrogencarbonates yield CO 2 and H 2O, before the organic species dissociate in two steps. During modification with a mono-amino silane the surface of a borosilicate glass retains three organic layers, two of which are probably hydrogen-bonded. After treating with β-phenylalanine the structure of zirconium phosphate is comprised of pillared layers. During programmed heating the pillars collapse and reactions can occur between the gaseous products, leading to the evolution of a mixture of aromatic compounds.

Residues from biological materials after pressure decomposition with nitric acid : Part 2. Identification of the Reaction Products

During the degradation of biological materials under pressure with 69% nitric acid at 180°C the organic matrix constituents are completely mineralized, with a few exceptions. Apart from sample constituents that occur in such low concentrations that their degradation products do not make a significant contribution to the organic residue, only five substances provide residues of organic compounds that cannot be volatilized at temperatures up to 130°C. On the basis of IR and NMR spectra and results from further analytical studies, it is shown that the phenylalanine contained in the biological sample reacts to give a mixture of isomeric nitrobenzoic acids, histidine to give imidazole-4-carboxylic acid, linoleic acid to give cyclopropane-1,2-dicarboxylic acids and tryptophan to give a mixture of aromatic compounds. Methionine is oxidized to methanesulphonic acid and cystine and cysteine to sulphuric acid. The phosphorus fraction of organic matrix constituents is converted to phosphate in the course of decomposition.

Photodiode array detection in high-performance capillary electrophoresis

A photodiode array detection system was applied to high-performance capillary electrophoresis. Spectra were obtained for mixtures of aromatic compounds and water-soluble vitamins. Photodiode array detection enabled accurate characterization of separated components and was a powerful tool for the investigation of mixed zones.

Carbon deposition during the hydrogenation of a complex aromatic feedstock

Carbon formation during hydrogenation of a well-characterized, complex mixture of aromatic compounds has been studied over the range 680–800 °C at total pressures of 5 MPa. The results are in agreement with a theory of carbon formation based on chemical dimerization of the aromatic species. The following empirical equation relating the rate of carbon formation to the experimental conditions has been derived: rate of carbon formation = 10 9.34 ± 1.56 exp(− (22350 ± 3630) T )[ feed] 2[H 2] −1 gh −1 . This equation is only applicable to the experimental conditions and reaction system used in this study. Light hydrocarbons (⩽ C 3) do not produce carbon either alone or by reaction with aromatic molecules under the above conditions. Scanning electron microscopy of the carbon deposits showed the presence of spherical particles of diameter 1–4 μm. The origin of spherical carbon particles in pyrolysis and combustion has been discussed with reference to some recent studies of carbon cluster formation.

A comparison of fluorescence and GC for the determination of petroleum hydrocarbons in mussels

The suitability of fluorescence spectroscopy for the determination of aromatic concentrations in mussel tissue was investigated. A mixture of aromatic compounds, with a total emission spectrum similar to those of the samples, was found to be the most suitable standard with measurement being made at the emission maximum. Significant correlations were found between aromatic hydrocarbon concentrations obtained by fluorescence spectroscopy and both aliphatic and aromatic hydrocarbon concentrations obtained by gas chromatographic analysis (GC). Results indicate that analysis of the aliphatic fraction by GC and fluorescence analysis of the aromatic fraction provides a suitable estimation of the relative degree of contamination of mussel tissues by petroleum hydrocarbons.

Chemical of current interest--benzene.

Benzene is one of the world's major commodity chemicals. It is derived from petroleum and coal and is used both as a solvent and as a starting material in chemical syntheses. The numerous industrial uses of benzene over the last century need not be recounted here, but the most recent addition to the list of uses of benzene is as a component in a mixture of aromatic compounds added to gasoline for the purpose of replacing lead compounds as anti-knock ingredients. The best known and longest recognized toxic effect of benzene is the depression of bone marrow function seen in occupationally exposed individuals. These people have been found to display anemia, leucopenia, and/or thrombocytopenia. When pancytopenia, i.e., the simultaneous depression of all three cell types, occurs and is accompanied by bone marrow necrosis, the syndrome is called aplastic anemia. In addition to observing this decrease in humans and relating it to benzene exposure, it has been possible to establish animal models which mimic the human disease. The result has been considerable scientific investigation into the mechanism of benzene toxicity. Although the association between benzene exposure and aplastic anemia has been recognized and accepted throughout most of this century, it is only recently that leukemia, particularly of the acute myelogenous type, has been related to benzene. The acceptance of benzene as an etiological agent in aplastic anemia in large measure derives from our ability to reproduce the disease in most animals treated with sufficiently high doses of benzene over the necessary time period. Unfortunately, despite extensive efforts in several laboratories, it has not been possible to establish a reproducible, reliable model for the study of benzene-induced leukemia. The recent demonstration that several animals exposed to benzene either by inhalation or in the drinking water during studies by Drs. B. Goldstein and C. Maltoni suggests that such a model may be forthcoming. Nevertheless, at this time it is not clear whether bone marrow damage of the type that leads to aplastic anemia is required for the development of leukemia. Most studies of benzene toxicity have involved dosing animals with benzene either by inhalation or by injection, using high doses to ensure a toxic response. Very few studies have concentrated on the oral route of administration and none have concentrated on administering benzene by mouth at the low doses occasionally detected in drinking water.(ABSTRACT TRUNCATED AT 400 WORDS)

Supercritical fluid chromatography using mixtures of carbon dioxide or ethane with 1,4-dioxane as eluents

In supercritical fluid chromatography (SFC), the permanent chemical modification of a silica stationary phase which occurs when eluent mixtures containing 1,4-dioxane are used leads to decreased retention with ethane and carbon dioxide as the mobile phases. Contrary to ethane, with carbon dioxide improved resolution is obtained on the dioxane-modified silica stationary phase. The chromatographic parameters capacity factor, selectivity, and mean resolution for a test mixture of aromatic compounds showed maxima as a function of temperature. The intensity of these maxima decreased with increasing pressure and increasing amount of 1,4-dioxane in mixtures with carbon dioxide or ethane. Furthermore, their positions were shifted to higher temperatures with increasing pressure and with increasing dioxane content, the latter effect being due to the much higher critical temperature of dioxane compared to carbon dioxide and ethane. The data presented can be used for optimizing SFC separations with mixed mobile phases.

Isolation and identification of mutagenic polycyclic aromatic hydrocarbons from a coal gasifier condensate

An iterative scheme of short-term bacterial mutagenesis assays and multidimensional liquid chromatographic methods was used to isolate mutagens from a neutral fraction of a complex carcinogenic tar formed as a by-product of coal gasification. Mutagens in the complementary reversed- and normal-phase liquid chromatographic fractions were identified by capillary column gas chromatography and gas chromatography-mass spectrometry. The principal mutagens included a variety of 4- to 6-ring unsubstituted polycyclic aromatic hydrocarbons, their alkylated homologs, and related methylene-bridged compounds. Most of the unsubstituted mutagens were known carcinogens that were qualitatively similar to those detected by carcinogenicity assays of fractions from other types of coal tars and cigarette smoke condensate. The chromatographic approach is generally applicable to complex mixtures and is especially well suited for fractionating mixtures of aromatic compounds and their alkyl homologs.

Supercritical fluid fractionation of petroleum- and coal-derived mixtures

A supercritical fluid chromatographic system was constructed to provide separations and fraction collection on a semipreparative scale. Columns packed with silica materials of intermediate particle size (30-70 ..mu..m) were used to allow dynamic pressure programming with minimum pressure drop of the CO/sub 2/ mobile phase along the length of the column. A variety of complex coal- and petroleum-derived polycyclic aromatic compound mixtures were fractionated according to the number of aromatic rings using columns packed with an NH/sub 2/-modified stationary phase bonded on silica particles. The CO/sub 2/ mobile phase was programmed with an alternating series of linear pressure ramps and isobaric intervals to effect even peak spacing and near base line resolution of compounds of differing ring number in a coal tar. A solvent refined coal heavy distillate and a crude oil were similarly fractionated. Effluents were monitored with an ultraviolet spectrophotometer at 254 nm and a flame ionization detector while fractions were collected in pressurized vessels for subsequent analysis by capillary gas chromatography. Sample capacities of up to 20 mg were possible with this system.