Natural Polycyclic Aromatic Hydrocarbons Research Articles

The mechanism of anthracene degradation by tryptophan −2,3-dioxygenase (T23D) in Comamonas testosteroni

It is well known that anthracene is a persistent organic pollutant. Among the four natural polycyclic aromatic hydrocarbons (PAHs) degrading strains, Comamonas testosterone (CT1) was selected as the strain with the highest degradation efficiency. In the present study, prokaryotic transcriptome analysis of CT1 revealed an increase in a gene that encodes tryptophane-2,3-dioxygenase (T23D) in the anthracene and erythromycin groups compared to CK. Compared to the wild-type CT1 strain, anthracene degradation by the CtT23D knockout mutant (CT-M1) was significantly reduced. Compared to Escherichia coli (DH5α), CtT23D transformed DH5α (EC-M1) had a higher degradation efficiency for anthracene. The recombinant protein rT23D oxidized tryptophan at pH 7.0 and 37 °C with an enzyme activity of 2.42 ± 0.06 μmol min−1·mg−1 protein. In addition, gas chromatography-mass (GC-MS) analysis of anthracene degradation by EC-M1 and the purified rT23D revealed that 2-methyl-1-benzofuran-3-carbaldehyde is an anthracene metabolite, suggesting that it is a new pathway.

Asphaltenes as novel thermal conductivity enhancers for liquid paraffin: Insight from in silico modeling

The practical use of paraffin and other organic phase-change materials for heat storage is largely limited by their low thermal conductivity. In this paper we employed 60 microsecond-long atomic-scale computer simulations to explore for the first time whether the asphaltenes, natural polycyclic aromatic hydrocarbons, can be used as thermal conductivity enhancers for paraffin. We focused on a simple model molecule of asphaltene (a polycyclic aromatic core decorated with the peripheral alkane chains) and showed that the asphaltenes of such molecular architecture are not able to improve the thermal conductivity of paraffin. This is most likely due to the steric constraints imposed by the peripheral alkane groups, which prevent formation of the extended ordered asphaltene aggregates. To overcome this, we proposed a possible chemical modification of the asphaltene molecules through removing the peripheral alkane groups from their aromatic cores; this could be achieved e.g. by thermal cracking (dealkylation) of asphaltenes. It turns out that such a chemical modification drastically changes the situation: the modified asphaltenes form extended columnar aggregates which can serve as thermal conduction paths, considerably enhancing the thermal conductivity of a liquid composite sample. This effect, however, vanishes upon cooling because the columnar extended stacks of chemically modified asphaltenes transform into the helical twisted structures, which reduces the overlap of adjacent asphaltenes in aggregates. Importantly, all the simulations have been carried out with two different all-atom force fields. We have demonstrated that both computational models give qualitatively similar results. Overall, our findings clearly show that chemically modified asphaltene molecules can be considered as promising carbon-based thermal conductivity enhancers for liquid paraffin; this result can be used for optimizing the paraffin-based thermal energy storage systems.

Spatial Patterns of Natural Polycyclic Aromatic Hydrocarbons in Sediment in the Lower Athabasca River

The Athabasca Oil Sands is one of the four natural oil sands deposits in Northern Alberta, Canada, and are by far the largest oil sand deposit in North America, covering an area of 46,000 km2. Sediment samples were collected from the bed and bank of several tributaries that have naturally occurring exposures of oil sand material. Oil sand deposited along the lower Athabasca River, more than 100 km downstream of naturally occurring oil sand exposures, were also sampled. The levels of alkylated polycyclic aromatic hydrocarbons (PAHs) in samples collected from these various locations ranged from not detected to almost 50 ppm. Using dibenzothiophene/chrysene (C2/D2 vs. C3/D3) double ratio plots, it is possible to approximate the relative degree of degradation or weathering of the PAHs from these various sediment deposits along the lower Athabasca River and its tributaries. Similarly a plot of dibenzothiophene/phenanthrene (D2/P2 vs. D3/P3) indicate the possible origins of the oil. A combination of these plots, D3/P3 vs. D3/C3, was particularly useful in identifying weathering characteristics of different sources of the oil. Comparison of alkylated PAH distributions between the lower Athabasca River and the tributaries show slight differences consistent with different petrogenic sources and/or different weathering patterns.

Fluxes and transport of anthropogenic and natural polycyclic aromatic hydrocarbons in the western Mediterranean Sea

Surface sediments were collected in the Gulf of Lions and in the Rhône delta and analyzed for composition of polycyclic aromatic hydrocarbons (PAH). After isolation of lipids, the hydrocarbons were separated into fractions by high-performance liquid chromatography (HPLC) and fractions were analyzed by gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS). Annual PAH fluxes were calculated for the northwestern Mediterranean basin. The fluxes of open-sea sediments varied from 164 μg m −2 year −1, for a station located far from the coast and influenced by atmospheric deposition, up to 1420 μg m −2 year −1 for stations directly influenced by the Rhône river inputs, whereas stations located in the Rhône delta were characterized by higher fluxes, up to 12 250 μg m −2 year −1. PAH concentrations decreased significantly with distance from the river mouth. Detailed analysis of PAH revealed the presence of anthropogenic compounds, pyrolytic and petrogenic, and naturally derived compounds. The distribution and ratios of specific compounds of PAH are discussed as a function of morphological and sedimentological features to evaluate and characterize the respective importance of atmospheric and Rhône-derived river inputs. Pyrolytic inputs from anthropogenic combustion processes were predominant at all studied stations. Compounds of natural origin were quantified, such as retene and related abietic acid precursors, and pentacyclic triterpenes derived from α- and β-amyrins. Anthropogenic PAH fluxes, determined for an open-sea sediment corresponding to the end of the nineteenth century (∼ 100 years ago), were three to four times less than the current flux; however, the retene flux was equal to or higher than that of today.