Showing papers on "Aromatic hydrocarbon published in 2016"

Aerobic Degradation of Aromatic Hydrocarbons

Abstract: Aromatic hydrocarbons are widely distributed in nature. They are found as lignin components, aromatic amino acids and xenobiotic compounds, among others. Microorganisms, mostly bacteria, degrade an impressive variety of such chemical structures. The major principle of aromatic hydrocarbon biodegradation is that a broad range of peripheral reactions are transformed to a restricted range of central intermediates, which are subject to ringcleavage and funneling into the Krebs cycle. Key enzymes in aerobic aromatic degradation are oxygenases, preparing aromatics for ring-cleavage by the introduction of hydroxyl functions and catalyzing cleavage of the aromatic ring. The diverse monooxygenases and dioxygenases involved in hydroxylations, a significant proportion of them possessing relaxed substrate specificity, are discussed as well as the broad diversity of side chain processing transformations involved in the formation of ring-cleavage central intermediates. Ring cleavage dioxygenases, covering intradiol ring cleavage of ortho dihydroxylated intermediates, and a large number of diverse but mechanistically related extradiol dioxygenases participating in ring cleavage of ortho and para dihydroxylated intermediates are also discussed. Novel CoA dependent aerobic routes to allow ring-cleavage of aromatic hydrocarbons without involvement of dihydroxylated aromatic intermediates have been described in the last years and are also reviewed. The degradation of heteroarenes will not be described in this chapter.

Metabolic Pathways for Degradation of Aromatic Hydrocarbons by Bacteria

Abstract: The aim of this revision was to build an updated collection of information focused on the mechanisms and elements involved in metabolic pathways of aromatic hydrocarbons by bacteria. Enzymes as an expression of the genetic load and the type of electron acceptor available, as an environmental factor, were highlighted. In general, the review showed that both aerobic routes and anaerobic routes for the degradation of aromatic hydrocarbons are divided into two pathways. The first, named the upper pathways, from the original compound to central intermediate compounds still containing the aromatic ring but with the benzene nucleus chemically destabilized. The second, named the lower pathway, begins with ring de-aromatizacao and subsequent cleavage, resulting in metabolites that can be used by bacteria in the production of biomass. Under anaerobic conditions the five mechanisms of activation of the benzene ring described show the diversity of chemical reactions that take place. Obtaining carbon and energy from an aromatic hydrocarbon molecule is a process that exhibits the high complexity level of the metabolic apparatus of anaerobic microorganisms. The ability of these bacteria to express enzymes that catalyze reactions, known only in non-biological conditions, using final electron acceptors with a low redox potential, is a most interesting topic. The discovery of phylogenetic and functional characteristics of cultivable and non-cultivable hydrocarbon degrading bacteria has been made possible by improvements in molecular research techniques such as SIP (stable isotope probing) making trace of 13C, 15N and 18O into nucleic acids and proteins.

Tailoring ZSM-5 Zeolites for the Fast Pyrolysis of Biomass to Aromatic Hydrocarbons.

Abstract: The production of aromatic hydrocarbons from cellulose by zeolite-catalyzed fast pyrolysis involves a complex reaction network sensitive to the zeolite structure, crystallinity, elemental composition, porosity, and acidity. The interplay of these parameters under the reaction conditions represents a major roadblock that has hampered significant improvement in catalyst design for over a decade. Here, we studied commercial and laboratory-synthesized ZSM-5 zeolites and combined data from 10 complementary characterization techniques in an attempt to identify parameters common to high-performance catalysts. Crystallinity and framework aluminum site accessibility were found to be critical to achieve high aromatic yields. These findings enabled us to synthesize a ZSM-5 catalyst with enhanced activity, which offers the highest aromatic hydrocarbon yield reported to date.

Turn‐On Fluorogenic and Chromogenic Detection of Small Aromatic Hydrocarbon Vapors by a Porous Supramolecular Host

Abstract: Benzene, toluene, ethylbenzene, the isomers of xylene, and trimethylbenzene are harmful volatile organic compounds and pose risks to human health and the environment. However, there are currently no effective chemosensors for vapors of these compounds. A porous supramolecular host for turn-on fluorogenic and chromogenic detection of the vapors of small aromatic hydrocarbons is presented. The host was constructed from a naphthalenediimide derivative that was supramolecularly connected to tris(pentafluorophenyl)borane. The amorphous powder form of the host allowed for effective accommodation of vapors of small aromatic hydrocarbons, resulting in a guest-dependent fluorescence emission. Increases in the fluorescence yield of 76-, 46-, and 37-fold were observed with toluene, benzene, and m-xylene, respectively. Negligible responses were obtained with common organic solvents. This simple supramolecular host could be applied as a useful sensor of small aromatic hydrocarbon vapors.

Impact of molecular structure on secondary organic aerosol formation fromaromatic hydrocarbon photooxidation under low-NO x conditions

Abstract: . The molecular structure of volatile organic compounds determines their oxidation pathway, directly impacting secondary organic aerosol (SOA) formation. This study comprehensively investigates the impact of molecular structure on SOA formation from the photooxidation of 12 different eight- to nine-carbon aromatic hydrocarbons under low-NOx conditions. The effects of the alkyl substitute number, location, carbon chain length and branching structure on the photooxidation of aromatic hydrocarbons are demonstrated by analyzing SOA yield, chemical composition and physical properties. Aromatic hydrocarbons, categorized into five groups, show a yield order of ortho (o-xylene and o-ethyltoluene) > one substitute (ethylbenzene, propylbenzene and isopropylbenzene) > meta (m-xylene and m-ethyltoluene) > three substitute (trimethylbenzenes) > para (p-xylene and p-ethyltoluene). SOA yields of aromatic hydrocarbon photooxidation do not monotonically decrease when increasing alkyl substitute number. The ortho position promotes SOA formation while the para position suppresses aromatic oxidation and SOA formation. Observed SOA chemical composition and volatility confirm that higher yield is associated with further oxidation. SOA chemical composition also suggests that aromatic oxidation increases with increasing alkyl substitute chain length and branching structure. Further, carbon dilution conjecture developed by Li et al. (2016) is extended in this study to serve as a standard method to determine the extent of oxidation of an alkyl-substituted aromatic hydrocarbon.

Modular Synthesis of Aromatic Hydrocarbon Macrocycles for Simplified, Single-Layer Organic Light-Emitting Devices

Abstract: A method for the modular synthesis of aromatic hydrocarbon macrocycles has been developed for base materials in single-layer organic light-emitting devices. The method with Ir-catalyzed direct C–H borylation and Suzuki–Miyaura coupling was concise and scalable, which allowed for a gram-scale preparation of aromatic hydrocarbon macrocycles that have bulky substituents at the periphery. The new arylated hydrocarbon macrocycles enabled a quantitative electro-optical conversion in organic light-emitting devices with a phosphorescent emitter, which is, notably, in a single-layer architecture consisting of two regions of doped and undoped materials. The highest external quantum efficiencies reached 24.8%, surpassing those of previous hydrocarbon base materials.

Role of methyl group number on SOA formation from monocyclic aromatic hydrocarbons photooxidation under low-NO x conditions

Abstract: . Substitution of methyl groups onto the aromatic ring determines the secondary organic aerosol (SOA) formation from the monocyclic aromatic hydrocarbon precursor (SOA yield and chemical composition). This study links the number of methyl groups on the aromatic ring to SOA formation from monocyclic aromatic hydrocarbons photooxidation under low-NOx conditions (HC/NO > 10 ppbC : ppb). Monocyclic aromatic hydrocarbons with increasing numbers of methyl groups are systematically studied. SOA formation from pentamethylbenzene and hexamethylbenzene are reported for the first time. A decreasing SOA yield with increasing number of methyl groups is observed. Linear trends are found in both f44 vs. f43 and O / C vs. H / C for SOA from monocyclic aromatic hydrocarbons with zero to six methyl groups. An SOA oxidation state predictive method based on benzene is used to examine the effect of added methyl groups on aromatic oxidation under low-NOx conditions. Further, the impact of methyl group number on density and volatility of SOA from monocyclic aromatic hydrocarbons is explored. Finally, a mechanism for methyl group impact on SOA formation is suggested. Overall, this work suggests that, as more methyl groups are attached on the aromatic ring, SOA products from these monocyclic aromatic hydrocarbons become less oxidized per mass/carbon on the basis of SOA yield or chemical composition.

Estrogenic Activity of Mineral Oil Aromatic Hydrocarbons Used in Printing Inks

Abstract: The majority of printing inks are based on mineral oils (MOs) which contain complex mixtures of saturated and aromatic hydrocarbons. Consumer exposure to these oils occurs either through direct skin contacts or, more frequently, as a result of MO migration into the contents of food packaging that was made from recycled newspaper. Despite this ubiquitous and frequent exposure little is known about the potential toxicological effects, particularly with regard to the aromatic MO fractions. From a toxicological point of view the huge amount of alkylated and unsubstituted compounds therein is reason for concern as they can harbor genotoxicants as well as potential endocrine disruptors. The aim of this study was to assess both the genotoxic and estrogenic potential of MOs used in printing inks. Mineral oils with various aromatic hydrocarbon contents were tested using a battery of in vitro assays selected to address various endpoints such as estrogen-dependent cell proliferation, activation of estrogen receptor α or transcriptional induction of estrogenic target genes. In addition, the comet assay has been applied to test for genotoxicity. Out of 15 MOs tested, 10 were found to potentially act as xenoestrogens. For most of the oils the effects were clearly triggered by constituents of the aromatic hydrocarbon fraction. From 5 oils tested in the comet assay, 2 showed slight genotoxicity. Altogether it appears that MOs used in printing inks are potential endocrine disruptors and should thus be assessed carefully to what extent they might contribute to the total estrogenic burden in humans.

Proteogenomic Characterization of Monocyclic Aromatic Hydrocarbon Degradation Pathways in the Aniline-degrading Bacterium Burkholderia sp. K24

Abstract: Burkholderia sp. K24, formerly known as Acinetobacter lwoffii K24, is a soil bacterium capable of utilizing aniline as its sole carbon and nitrogen source. Genomic sequence analysis revealed that this bacterium possesses putative gene clusters for biodegradation of various monocyclic aromatic hydrocarbons (MAHs), including benzene, toluene, and xylene (BTX), as well as aniline. We verified the proposed MAH biodegradation pathways by dioxygenase activity assays, RT-PCR, and LC/MS-based quantitative proteomic analyses. This proteogenomic approach revealed four independent degradation pathways, all converging into the citric acid cycle. Aniline and p-hydroxybenzoate degradation pathways converged into the β-ketoadipate pathway. Benzoate and toluene were degraded through the benzoyl-CoA degradation pathway. The xylene isomers, i.e., o-, m-, and p-xylene, were degraded via the extradiol cleavage pathways. Salicylate was degraded through the gentisate degradation pathway. Our results show that Burkholderia sp. K24 possesses versatile biodegradation pathways, which may be employed for efficient bioremediation of aniline and BTX.

The C--H Stretching Features at 3.2--3.5 Micrometer of Polycyclic Aromatic Hydrocarbons with Aliphatic Sidegroups

Abstract: The so-called unidentified infrared emission (UIE) features at 3.3, 6.2, 7.7, 8.6, and 11.3 micrometer are ubiquitously seen in a wide variety of astrophysical regions. The UIE features are characteristic of the stretching and bending vibrations of aromatic hydrocarbon materials, e.g., polycyclic aromatic hydrocarbon (PAH) molecules. The 3.3 micrometer aromatic C--H stretching feature is often accompanied by a weaker feature at 3.4 micrometer. The latter is often thought to result from the C--H stretch of aliphatic groups attached to the aromatic systems. The ratio of the observed intensity of the 3.3 micrometer aromatic C--H feature to that of the 3.4 micrometer aliphatic C--H feature allows one to estimate the aliphatic fraction of the UIE carriers, provided that the intrinsic oscillator strengths of the 3.3 micrometer aromatic C--H stretch (A3.3) and the 3.4 micrometer aliphatic C--H stretch (A3.4) are known. While previous studies on the aliphatic fraction of the UIE carriers were mostly based on the A3.4/A3.3 ratios derived from the mono-methyl derivatives of small PAH molecules, in this work we employ density functional theory to compute the infrared vibrational spectra of several PAH molecules with a wide range of sidegroups including ethyl, propyl, butyl, and several unsaturated alkyl chains, as well as all the isomers of dimethyl-substituted pyrene. We find that, except PAHs with unsaturated alkyl chains, the corresponding A3.4/A3.3 ratios are close to that of mono-methyl PAHs. This confirms the predominantly-aromatic nature of the UIE carriers previously inferred from the A3.4/A3.3 ratio derived from mono-methyl PAHs.

Novel Approach for Evaluating Secondary Organic Aerosol from Aromatic Hydrocarbons: Unified Method for Predicting Aerosol Composition and Formation

Abstract: Innovative secondary organic aerosol (SOA) composition analysis methods normalizing aerosol yield and chemical composition on an aromatic ring basis are developed and utilized to explore aerosol formation from oxidation of aromatic hydrocarbons. SOA yield and chemical composition are revisited using 15 years of University of California, Riverside/CE-CERT environmental chamber data on 17 aromatic hydrocarbons with HC:NO ranging from 11.1 to 171 ppbC:ppb. SOA yield is redefined in this work by normalizing the molecular weight of all aromatic precursors to the molecular weight of the aromatic ring Yield′=Yieldi×MWiMWAromatic ring, where i is the aromatic hydrocarbon precursor. The yield normalization process demonstrates that the amount of aromatic rings present is a more significant driver of aerosol formation than the vapor pressure of the precursor aromatic. Yield normalization also provided a basis to evaluate isomer impacts on SOA formation. Further, SOA elemental composition is explored relative to the...

On the aliphatic versus aromatic content of the carriers of the ‘unidentified’ infrared emission features

Abstract: Although it is generally accepted that the so-called "unidentified" infrared emission (UIE) features at 3.3, 6.2, 7.7, 8.6, and 11.3 micrometer are characteristic of the stretching and bending vibrations of aromatic hydrocarbon materials, the exact nature of their carriers remains unknown: whether they are free-flying, predominantly aromatic gas-phase molecules, or amorphous solids with a mixed aromatic/aliphatic composition are being debated. Recently, the 3.3 and 3.4 micrometer features which are commonly respectively attributed to aromatic and aliphatic C-H stretches have been used to place an upper limit of ~2\% on the aliphatic fraction of the UIE carriers (i.e. the number of C atoms in aliphatic chains to that in aromatic rings). Here we further explore the aliphatic versus aromatic content of the UIE carriers by examining the ratio of the observed intensity of the 6.2 micrometer aromatic C-C feature (I6.2) to that of the 6.85 micrometer aliphatic C-H deformation feature (I6.85). To derive the intrinsic oscillator strengths of the 6.2 micrometer stretch (A6.2) and the 6.85 micrometer deformation (A6.85), we employ density functional theory to compute the vibrational spectra of seven methylated polycyclic aromatic hydrocarbon molecules and their cations. By comparing I6.85/I6.2 with A6.85/A6.2, we derive the fraction of C atoms in methyl(ene) aliphatic form to be at most ~10\%, confirming the earlier finding that the UIE emitters are predominantly aromatic. We have also computed the intrinsic strength of the 7.25 micrometer feature (A7.25), another aliphatic C-H deformation band. We find that A6.85 appreciably exceeds A7.25. This explains why the 6.85 micrometer feature is more frequently detected in space than the 7.25 micrometer feature.

Noncovalent and covalent immobilization of oxygenase on single-walled carbon nanotube for enzymatic decomposition of aromatic hydrocarbon intermediates

Abstract: The decomposition of various aromatic hydrocarbon intermediates was examined using a recombinant oxidative enzyme immobilized on single-walled carbon nanotubes (SWCNTs). Hydroxyquinol 1,2-dioxygenase (CphA-I), which catalyzes ring cleavage of catechol and its analogues, was obtained from Arthrobacter chlorophenolicus A6 via cloning, overexpression, and subsequent purification. This recombinant enzyme was immobilized on SWCNTs by physical adsorption and covalent coupling in the absence and presence of N-hydroxysuccinimide. The immobilization yield was as high as 52.1%, and a high level of enzyme activity of up to 64.7% was preserved after immobilization. Kinetic analysis showed that the substrate utilization rates (vmax) and catalytic efficiencies (kcat/KM) of the immobilized enzyme for all substrates evaluated were similar to those of the free enzyme, indicating minimal loss of enzyme activity during immobilization. The immobilized enzyme was more stable toward extreme pH, temperature, and ionic strength conditions than the free enzyme. Thus, the oxidative enzyme immobilized on SWCNTs can be used as an effective and stable biocatalyst for the biochemical remediation process if further investigations would be carried out under field conditions.

Use of a High-Performance Poly(p-phenylene)-Based Aromatic Hydrocarbon Ionomer with Superacid Groups in Fuel Cells under Low Humidity Conditions

Abstract: Aromatic ionomers with perfluoroalkyl sulfonic acid groups for fuel cell applications have been prepared mostly by the post-functionalization method. Herein, we present a direct polymerization method using a novel monomer with a perfluorosulfonic acid group to control the amount and position of the sulfonic acid groups. A poly(p-phenylene)-based aromatic hydrocarbon ionomer bearing a pendant perfluorosulfonic acid group in a substituent at the 2-position is synthesized by Ni(0)-catalyzed coupling polymerization. The direct polymerization provides Mn values of up to 169 000 with a highly controlled molecular structure and allows the formation of thin membranes. These ionomers were found to combine the positive features of perfluorinated and aromatic hydrocarbon ionomers, and these thin membranes with a relatively high ion exchange capacity showed high proton conductivity and excellent fuel cell performance (907 mW cm–2 even at 80 °C and 30% RH) under low humidity conditions compared with other reported aro...

Conversion pathways of palm oil into jet biofuel catalyzed by mesoporous zeolites

Abstract: Three mesoporous zeolites (Ni/Meso-Y, Ni/Meso-Hbeta, and Ni/Meso-HZSM-5) were used to catalytically convert palm oil into jet biofuel through various reaction pathways. Zeolite Ni/Meso-Y exhibited the highest jet range alkane yield (30.7%) and the lowest jet range aromatic hydrocarbon yield (13%). The acid density and surface area of zeolite Ni/Meso-Y were higher than those of zeolites Meso-Hbeta and Meso-HZSM-5. Of the palm oil, 53% was converted into jet range alkane and 17% was converted into jet range aromatic hydrocarbons over Ni/Meso-Y. On one hand, palm oil was converted into C15–C18 alkanes through decarbonylation, which further cracked into C8–C14 alkanes or dehydrogenated into aromatic hydrocarbons through aromatization. On the other hand, palm oil directly cracked into C8–C14 alkanes over Ni/Meso-Y. Zeolite Ni/Meso-Y exhibited higher selectivity of jet range alkane (55.32%) and lower selectivity of jet range aromatic hydrocarbons (9.47%) than those of regenerated Ni/Meso-Y (36.18% and 22.66%, respectively).

Deep extractive desulfurization of oil over 12-Molibdophosphoric acid encapsulated in metal-organic frameworks

Abstract: A desulfurization process for model oil and real oil was investigated based on the chemical oxidation of mixed sulfur containing compounds in the presence of nitrogen compounds (indole and quinoline) using hydrogen peroxide as oxidizing agent and dodecamolibdophosphoric acid (H3PMo12O40) encapsulated in a kind of metal-organic framework (HKUST-1) as PMo@HKUST-1. The effect of isopropanol, ethanol and acetonitrile as extractive solvent and 1-ring (toluene, xylene and mesitylene) and 2-ring (naphthalene) aromatic hydrocarbons in desulfurization of model oil was studied. The desulfurization of sulfur-containing compounds was accelerated in the presence of aro- matic hydrocarbons. In fact, a higher desulfurization efficiency of the heterogeneous catalyst could be achieved with system containing a polar solvent in contact with an aromatic hydrocarbon. Quinoline had no effect on oxidative desulfurization (ODS) reaction, whereas indole had a slightly negative effect. Presence of aromatic compounds had slightly positive effect on ODS reaction.

Catalyst for directly preparing synthesis gas into aromatic compounds and preparation method and application of catalyst

Abstract: The invention discloses a multifunctional catalyst capable of directly converting synthesis gas into aromatic hydrocarbon at one step and a preparation method and application of the multifunctional catalyst The catalyst comprises one or more oxides in Fe, Mo, Co, Zn and Ga as active components, one or more oxides in Na, K, Ca, Mg, V, Cr, Mn and Cu as assistants, and hydrogen-type ZSM-5 molecular sieve as a carrier The catalyst is cheap and easily available in raw materials, simple in preparation method and low in cost, has high catalytic activity in synthesis gas and has good industrial application prospect, CO conversion per pass can reach over 80%, and the content of aromatic components in products is not lower than 50%

Aromatic Hydrocarbon Production from Bio-Oil by a Dual-Stage Hydrogenation-Cocracking Process: Furfural as a Model Compound

Abstract: Bio-oil upgrading by catalytic cracking faces problems of low aromatic hydrocarbon yield and coking because of its hydrogen-lacking property. In this work, an improved hydrogenation-cocracking process was developed to achieve the appropriate hydrogen supply in two stages. Furfural was selected as the model compound of bio-oil, and methanol was the coreactant. The hydrogen supply in the hydrogenation stage was successfully regulated by hydrogenation catalysts, and the 5Ni-5Cu/SiO2 catalyst exhibited the best performance because of a suitable degree of hydrogenation of furfural over it, which favored the formation of aromatic hydrocarbons during cracking. With the optimum 5Ni-5Cu/SiO2 catalyst, hydrogenation cocracking was compared with single-stage cocracking, hydrogenation cracking, and direct cracking processes. The results confirmed that hydrogen supplements by hydrogenation pretreatment and methanol cocracking were both significant for the generation of aromatic hydrocarbons and the suppression of coke...

Geochemical markers and polycyclic aromatic hydrocarbons in solvent extracts from diesel engine particulate matter.

Abstract: Exhaust particulate from compression ignition (CI) engines running on engine and chassis dynamometers was studied. Particulate dichloromethane extracts were qualitatively and quantitatively analyzed for polycyclic aromatic hydrocarbons (PAHs) and biomarkers by gas chromatography with flame ionization detector (GC-FID) and gas chromatography-mass spectrometry (GC-MS). PAH group profiles were made and the PAH group shares according to the number of rings (2 or 3; 4; 5 or more) as well as diagnostic indices were calculated. Values of geochemical ratios of selected biomarkers and alkyl aromatic hydrocarbons were compared with literature values. A geochemical interpretation was carried out using these values and biomarker and alkyl aromatic hydrocarbon distributions. It has been shown that geochemical features are unequivocally connected to the emission of fossil fuels and biofuels burned in CI engines. The effect of the exothermic combustion process is limited to low-molecular-weight compounds, which shows that the applied methodology permits source identification of PAHs coexisting in the particulate emitted.

Evolution of the reaction mechanism during the MTH induction period over the 2-dimensional FER zeolite

Abstract: The methanol conversion reaction mechanism over HZSM-35, an ferrierite (FER)-type zeolite with 2-D channel intersections, was investigated during the induction period. The MTH induction period could be obviously shortened by co-feeding toluene or precoking the catalyst and the formation of tetramethylcyclopentenyl cation (tetraMCP+) during the induction period was also confirmed through 13C magic angle spinning (MAS) NMR and GC-MS experiments, suggesting the active role of aromatics. Moreover, the dual-cycle mechanism was evidently found to evolve as the induction reaction progressed. In the early stage, both the aromatic- and olefin-based routes work efficiently and pentamethylbenzene (pentaMB) was identified as the main aromatic hydrocarbon pool (HCP) species. While in the latter stage of the induction period, the olefin-based route turned out to be more dominant and pentaMB as well as hexamethylbenzene (hexaMB) became the main aromatic HCP species. Despite the limited space of the channel intersections, the reactivity of aromatics with larger molecular sizes like 1-ethyl-2,3,4,5,6-pentamethylbenzene (1-E-pentaMB) and hexaMB were much higher than lower methylbenzenes which indicates that the aromatic-based cycle can also proceed on the external acid sites of the HZSM-35 catalyst.

Method for producing aromatic hydrocarbon with oxygen-containing compound as raw material

Abstract: The invention relates to a method for producing aromatic hydrocarbon with an oxygen-containing compound as a raw material, and is used for mainly solving the technical problems in the prior art that the total aromatic yield is low and energy consumption is high when an oxygen-containing compound is used for preparing aromatic hydrocarbon. In particular, the invention relates to the method for producing the aromatic hydrocarbon with the oxygen-containing compound as the raw material. The method includes the steps I), II), III), IV, V), VI) and VII) described in the specification. The method can better solve the problems, and can be used in industrial production of preparation of the aromatic hydrocarbon with the oxygen-containing compound as the raw material.

Depolymerizing Activities of Aromatic Hydrocarbon Degrading Phyllosphere Fungi in Sri Lanka

Abstract: Application of aromatic hydrocarbon degrading fungi to bioremediate aromatic hydrocarbonic (AH) pollutants is a current trend and many research on the use of such fungi to remediate aromatic hydrocarbonic pollutants in temperate situations have been reported. Bioremediation of these hydrocarbons is through an array of lignolitic and non lignolitic extra cellular enzymes. Therefore, the present investigation attempts to assess lignolytic and non lignolytic enzyme activities of selected phyllosphere aromatic hydrocarbon degrading fungi during the aromatic hydrocarbon degradation. In a previous research aromatic hydrocarbon degrading fungi were isolated from ornamental leaf samples collected from highly urbanized and industrialized areas of Sri Lanka. These fungal species were then selected to evaluate their enzyme activities when degrading aromatic hydrocarbons. They were screened for their manganese dependent peroxidases (Mnp), Lignin peroxidases (Lip) and laccases enzyme activities. Most efficient naphthalene degrading fungi showed Mnp and Lip enzyme activities. The best naphthalene degrader, Penicillium oxalicum showed significantly higher Mnp (26 Uml-1 min-1) activity during naphthalene degradation process. However, phenanthrene degrading phyllosphere fungal strains showed higher laccase activities. Penicillium oxalicum showed significantly higher laccase activity during the phenanthrene degradation showing the same fungal species had different enzyme predominant pathways for different xenobiotics. Same fungal species performed differently for different AH substrates. Mnp was the predominantly used enzyme in the most efficient naphthalene degrading fungal species and phenanthrene degradation of them was manipulated by laccases. The promising results of the present investigation will broaden the perspective of ecofriendly practical application of the above fungal strains at environmental sites where contamination is caused by AHs especially, phenanthrene, naphthalene, toluene and xylene. Also this opens many avenues for conducting future research in the field of bioremediation and biodegradation.