Light-dependent isomeric effects of polycyclic aromatic hydrocarbons on the predication of DNA cleavage factor efficiency

PAHs, short for polycyclic aromatic hydrocarbons, are a ubiquitous group of chemically related, environmentally persistent organic compounds having diverse structures and varied toxicity. They have been shown to cause mutagenic and carcinogenic effects on organisms and are quite immunosuppressive. Time-dependent density functional theory (TD-DFT) offers a practical means of understanding the behavior of excitation energies for PAHs. Here, we examined the performance of the long-range corrected Coulomb-attenuating functional (CAM-B3LYP) in relation to four different basis sets, determining which basis set compliments the functional better in identifying the most reactive atomic site on six isomeric PAH compounds. Condensed Fukui function indices were used to compare the performance of applied basis sets in identifying the most reactive atomic site on six isomeric PAHs compounds, assessing which basis set would be more appropriate in determining the site where free-radical formation would occur after light irradiation. Dunning’s correlation consistent triple-zeta (cc-pVTZ) basis set was determined to have the best PAH characterization performance, concluding the need for application of a higher-level basis set with the long-range corrected Coulomb-attenuating functional. Although each compound was a structural isomer of the other, the reactive atomic sites varied for each molecule with the use of an applied basis set. It was concluded that structural shape has some influence on the calculation of PAH characteristics. Lastly, in order to predict DNA single-stranded cleavage factor for the compounds proposed here, we have used the quantitative structure-activity relationship (QSAR). The cleavage factor values for the set of aromatic molecules with similar structures have been collected from the literature for a total number of 22 compounds.     

QSARs for Photoinduced Toxicity of Aromatic Compounds

Abstract

This paper reviews the results of a series of efforts to develop QSAR models for aromatic chemicals whose toxicity is enhanced by the ultraviolet radiation present in sunlight. Photoinduced toxicity of polycyclic aromatic hydrocarbons (PAHs) was found to be a result of competing factors: structural (such as molecular stability and light absorbance) and external (irradiation energy and intensity). These two factors interact, producing a complex, multilinear relationship between toxicity and electronic structure. The HOMO-LUMO gap provided a useful ground-state index to explain the persistence, light absorption, and eventually, the photoinduced toxicity of PAHs. The derived QSAR clearly distinguished phototoxic differences between pairs of structurally similar PAHs, such as phenanthrene and anthracene, benzo [a] anthracene and tetracene, et cetera. Those PAHs exhibiting photoinduced toxicity were consistently within a specific range of the electronic parameter. Further modeling revealed a significant correlation between molecular electronic structure of excited-state PAHs and toxicity. The effect of substituents on photoinduced acute toxicity of PAHs also was investigated. Some substituents such as alkyl and hydroxy moieties do not significantly reduce the HOMO-LUMO gap of parent PAHs. Nitro- and chloro- moieties cause more significant variations of the HOMO-LUMO gap. It is concluded that photoinduced toxicity of PAHs is mainly dictated by the electronic structure of the parent chemicals. Evaluation of the phototoxicity of flexible aromatic molecules (α-terthienyls), generally supported the PAH models.     

Strategies for synthesis of adducts of omicron-quinone metabolites of carcinogenic polycyclic aromatic hydrocarbons with 2'-deoxyribonucleosides

Polycyclic aromatic hydrocarbons (PAHs) are major environmental carcinogens produced in the combustion of fossil fuels, tobacco, and other organic matter. Current evidence indicates that PAHs are transformed enzymatically to active metabolites that react with DNA to form adducts that result in mutations. Three activation pathways have been proposed: the diol epoxide path, the radical-cation path, and the quinone path. The latter involves aldo-keto reductase mediated oxidation of PAH dihydrodiol metabolites to catechols that enter into redox cycles with quinones. This results in generation of reactive oxygen species (ROS) that attack DNA, and the PAH quinones also react with DNA to form adducts. Several strategies for synthesis of the stable adducts formed by the o-quinone metabolites of carcinogenic PAHs with 2'-deoxyribonucleosides were investigated and compared. The PAH quinones studied were benz[a]anthracene-3,4-dione and its 7-methyl- and 7,12-dimethyl- derivatives. The parent PAHs represent a range of carcinogenicity from inactive to highly potent. Two synthetic methods were devised that differ in the catalyst employed, Pd(OAc)(2) or CuI. The Pd-mediated method involved coupling a protected amino-catechol PAH derivative with a halo-2'-deoxyribonucleoside. The copper-mediated method entailed reaction of a halo-PAH catechol derivative with a 2'-deoxyribonucleoside. Adducts of benz[a]anthracene-3,4-dione (and its 7-methyl- and 7,12-dimethyl- derivatives) with 2'-deoxyadenosine and 2'-deoxyguanosine were prepared by these methods. Availability of adducts of these types through synthesis makes possible for the first time biological studies to determine the role of these adducts in tumorigenesis. The copper-mediated method offers advantages of economy, adaptability to large-scale preparation, utility for synthesis of (13)C- or (15)N-labeled analogues, and nonformation of bis-adducts as secondary products.     

Development of an improved analytical method for the determination of carcinogenic polycyclic aromatic hydrocarbons in transformer oil

Polynuclear aromatic hydrocarbons (PAHs) are natural constituents of transformer oils and are essential in prolonging transformer in-service lifetime. Issues concerning PAH carcinogenicity demand methods that provide qualitative and quantitative information on the PAH composition of new and in-service oils to allow informed operational decisions to be made. However, current analytical methods focus on PAH fingerprinting, as opposed to quantitative analysis and are also cumbersome, relying on the use of large (>100 ml) volumes of organic solvents, some of which are hazardous. This paper reports a method for the improved quantification of carcinogenic PAHs in transformer oils that is both simple and repeatable. The method uses commercially available solid-phase extraction columns and millilitre volumes of relatively non-hazardous solvents. Extraction efficiencies of > or =74% were obtained for the Environmental Protection Agency priority PAHs. The method has potential for automation and high-throughput analysis and thus is of interest to industries that use transformer oils.     

Dissociation and multiple ionization energies for five polycyclic aromatic hydrocarbon molecules

We have performed density functional theory calculations for a range of neutral, singly, and multiply charged polycyclic aromatic hydrocarbons (PAHs), and their fragmentation products for H-, H(+)-, C(2)H(2)-, and C(2)H(2)(+)-emissions. The adiabatic and vertical ionization energies follow linear dependencies as functions of charge state for all five intact PAHs (naphthalene, biphenylene, anthracene, pyrene, and coronene). First estimates of the total ionization and fragmentation cross sections in ion-PAH collisions display markedly different size dependencies for pericondensed and catacondensed PAH species, reflecting differences in their first ionization energies. The dissociation energies show that the PAH(q+)-molecules are thermodynamically stable for q ≤?2 (naphthalene, biphenylene, and anthracene), q?≤?3 (pyrene), and q?≤?4 (coronene). PAHs in charge states above these limits may also survive experimental time scales due to the presence of reaction barriers as deduced from explorations of the potential energy surface regions for H(+)-emissions from all five PAHs and for C(2)H(2)(+)-emission from naphthalene--the smallest PAH.     

Optimization and validation of HPLC-UV-DAD and HPLC-APCI-MS methodologies for the determination of selected PAHs in water samples

Polycyclic aromatic hydrocarbons (PAHs) are environmental contaminants resulting from emissions of a variety of sources including industrial combustion, discharge of fossil fuels, and residential heating. Because of their mutagenic and carcinogenic properties, the study of PAHs in environmental matrices is of great importance. In this work, the extraction of 9 out of the 16 PAH priority pollutants according to the U.S. Environmental Protection Agency is carried out through liquid-liquid extraction (LLE) and solid-phase extraction (SPE). The determination of PAHs is made by high-performance liquid chromatography with diode-array detection and liquid chromatography-atmospheric pressure chemical ionization mass spectrometry. Between the extraction techniques used, LLE is revealed to be efficient in the extraction of the higher molecular weight PAHs, though SPE is adequate for the extraction of all PAHs. In the real water samples analyzed, no PAH is detected under the analysis conditions used.     

Quantitative immunoassay for determining polyaromatic hydrocarbons in electrical insulating oils

The development and application of a combined sample extraction and immunoassay protocol for the quantification of polyaromatic hydrocarbons (PAHs) in transformer oils is reported. Tests were performed on 12 different used transformer oils from three major manufacturers. The removal of matrix interferents was achieved by loading oil fractions onto silica solid phase extraction cartridges and eluting with non-polar solvent prior to evaporation and reconstitution in a more polar medium. Extracts were immunoassayed using two commercially available PAH test kits either having broad specificity towards priority PAHs or enhanced binding specificity toward more carcinogenic PAHs. The total and carcinogenic PAH test kits yielded PAH levels in the oil extracts 5.86-fold and 126-fold lower than the industry-standard IP346 method. The latter method, widely used by the industry, since it correlates with biological carcinogenicity tests, grossly over-estimates PAH levels in oils since it is a non-specific gravimetric solvent extraction approach. The assay was found to be unaffected by the extract sample matrix and was capable of determining PAHs at the nanogram per millilitre level. The assay protocol was simple, low-cost and rapid (<2 h) and equally amenable to operation at remote sites or high-throughput sample screening. The binding specificity of the total anti-PAH antibody was examined by preparing and loading an anti-PAH immunosorbent with oil, prior to solvent displacement of antibody-bound compounds and by gas chromatography (GC)–mass spectrometry (MS) analysis.     

Sur une tentative d'unification des théaories quantiques de la cancérisation par les polyacènes. II: Le rôle de la rèagion K dans le processus d'activation metabolique conduisant au cancérogène ultime. Théorie des régions M,L, et BK

This study is a unified approach to quantum theories of polyacen carcinogenesis. Part II is on the role of the K-region in metabolic activation process leading to ultimate carcinogen and discusses the M, L, and BK theory. The saturation of the polyacen K-region, or the transformation into a quinoid one, deactivates the carcinogenic process going through a diol epoxyde, which results in Bay-region carbocation. K and B regions must be considered as two interdependent parts of the same structural entity, which may be termed the BK-region. The M, L, and BK theory achieves a complete unification of the Pullman and Jerina and other theories.     

Highly sensitive routine method for urinary 3-hydroxybenzo[a]pyrene quantitation using liquid chromatography-fluorescence detection and automated off-line solid phase extraction

Many workers and also the general population are exposed to polycyclic aromatic hydrocarbons (PAHs), and benzo[a]pyrene (BaP) was recently classified as carcinogenic for humans (group 1) by the International Agency for Research on Cancer. Biomonitoring of PAHs exposure is usually performed by urinary 1-hydroxypyrene (1-OHP) analysis. 1-OHP is a metabolite of pyrene, a non-carcinogenic PAH. In this work, we developed a very simple but highly sensitive analytical method of quantifying one urinary metabolite of BaP, 3-hydroxybenzo[a]pyrene (3-OHBaP), to evaluate carcinogenic PAHs exposure. After hydrolysis of 10 mL urine for two hours and concentration by automated off-line solid phase extraction, the sample was injected in a column-switching high-performance liquid chromatography fluorescence detection system. The limit of quantification was 0.2 pmol L(-1) (0.05 ng L(-1)) and the limit of detection was estimated at 0.07 pmol L(-1) (0.02 ng L(-1)). Linearity was established for 3-OHBaP concentrations ranging from 0.4 to 74.5 pmol L(-1) (0.1 to 20 ng L(-1)). Relative within-day standard deviation was less than 3% and relative between-day standard deviation was less than 4%. In non-occupationally exposed subjects, median concentrations for smokers compared with non-smokers were 3.5 times higher for 1-OHP (p<0.001) and 2 times higher for 3-OHBaP (p<0.05). The two urinary biomarkers were correlated in smokers (ρ=0.636; p<0.05; n=10) but not in non-smokers (ρ=0.09; p>0.05; n=21).     

Validation of the analysis of the 15+1 European-priority polycyclic aromatic hydrocarbons by donnor-acceptor complex chromatography and high-performance liquid chromatography-ultraviolet/fluorescence detection

The European Commission recommends to monitor the 16 polycyclic aromatic hydrocarbons (PAHs) possessing both genotoxic and carcinogenic properties. Since robust analytical methods specific for this set of European PAH are lacking, a new method for their analysis in food is proposed. The donnor-acceptor complex chromatography (DACC) is used as clean-up step and high-performance liquid chromatography-ultraviolet/fluorescence detection (HPLC-UV/FLD) is used for detection and quantification. The method has been validated for analysis of PAH in oil and in dried plants and bears very good results for all compounds.     

Development of a targeted adductomic method for the determination of polycyclic aromatic hydrocarbon DNA adducts using online column‐switching liquid chromatography/tandem mass spectrometry

Human exposure to polycyclic aromatic hydrocarbons (PAHs) from sources such as industrial or urban air pollution, tobacco smoke and cooked food is not confined to a single compound, but instead to mixtures of different PAHs. The interaction of different PAHs may lead to additive, synergistic or antagonistic effects in terms of DNA adduct formation and carcinogenic activity resulting from changes in metabolic activation to reactive intermediates and DNA repair. The development of a targeted DNA adductomic approach using liquid chromatography/tandem mass spectrometry (LC/MS/MS) incorporating software‐based peak picking and integration for the assessment of exposure to mixtures of PAHs is described. For method development PAH‐modified DNA samples were obtained by reaction of the anti‐dihydrodiol epoxide metabolites of benzo[a]pyrene, benzo[b]fluoranthene, dibenzo[a,l]pyrene (DB[a,l]P) and dibenz[a,h]anthracene with calf thymus DNA in vitro and enzymatically hydrolysed to 2′‐deoxynucleosides. Positive LC/electrospray ionisation (ESI)‐MS/MS collision‐induced dissociation product ion spectra data showed that the majority of adducts displayed a common fragmentation for the neutral loss of 116 u (2′‐deoxyribose) resulting in a major product ion derived from the adducted base. The exception was the DB[a,l]P dihydrodiol epoxide adduct of 2′‐deoxyadenosine which resulted in major product ions derived from the PAH moiety being detected. Specific detection of mixtures of PAH‐adducted 2′‐deoxynucleosides was achieved using online column‐switching LC/MS/MS in conjunction with selected reaction monitoring (SRM) of the [M+H]⁺ to [M+H–116]⁺ transition plus product ions derived from the PAH moiety for improved sensitivity of detection and a comparison was made to detection by constant neutral loss scanning. In conclusion, different PAH DNA adducts were detected by employing SRM [M+H–116]⁺ transitions or constant neutral loss scanning. However, for improved sensitivity of detection optimised SRM transitions relating to the PAH moiety product ions are required for certain PAH DNA adducts for the development of targeted DNA adductomic methods. Copyright © 2010 John Wiley & Sons, Ltd.     

Comparison of immunoassay and gas chromatography-mass spectrometry for measurement of polycyclic aromatic hydrocarbons in contaminated soil

Polycyclic aromatic hydrocarbons (PAHs) are frequently encountered in the environment and may pose health concerns due to their carcinogenicity. A commercial enzyme-linked immunosorbent assay (ELISA), was evaluated as a screening method for monitoring PAHs at contaminated sites. The ELISA was a carcinogenic PAH (C-PAH) RaPID assay testing kit that cross-reacts with several PAHs and utilizes benzo[a]pyrene (BaP) as a calibrator. Soil samples were extracted with 50% acetone in dichloromethane (DCM) for analysis by ELISA and gas chromatography-mass spectrometry (GC-MS). The overall method precision was within ±30% for ELISA and within ±20% for GC-MS. Recovery data for spiked soils ranged from 46 to 140% for BaP as determined by ELISA. Recoveries data of the GC-MS surrogate standards, 2-fluorobiphenyl and chrysene, were greater than 70%. The GC-MS procedure detected a total of 19 priority PAHs (2-6-ring PAHs) including seven probable human carcinogens (4-6-ring B2-PAHs). The ELISA results were compared to GC-MS summation results for the total 19 target PAHs as well as for the subset of the seven B2-PAH compounds. For all soil samples, the PAH concentrations derived from ELISA were greater than the sum of B2-PAH concentrations obtained by GC-MS. ELISA determinations were also frequently greater than the results obtained by GC-MS for the total 19 PAH compounds. This discrepancy can be expected, since the ELISA is a screening assay for the detection of several related PAHs while the GC-MS procedure detects priority PAH compounds. Thus, only a subset of PAHs (e.g. 19 PAHs) in the soil samples were measured by GC-MS while additional PAHs, including alkylated PAHs, and PAH derivatives have been demonstrated to be cross-reactive in the C-PAH ELISA. Results of paired tests show that the PAH data from ELISA and GC-MS methods are significantly different (P<0.001), but highly correlated. The ELISA data had a strong positive relationship with the GC-MS summation data for the B2-PAHs as well as for the 19 PAHs targeted by the GC-MS method. Results indicate that the ELISA may be useful as a broad screen for monitoring PAHs in environmental samples.     

Rapid method for the determination of polycyclic aromatic hydrocarbons in agricultural soils by sonication-assisted extraction in small columns

A rapid method has been developed for the determination of 16 polycyclic aromatic hydrocarbons (PAHs) in soil based on their sonication-assisted extraction in small columns (SAESC) with a low volume of ethyl acetate and subsequent quantitation and identification by GC with electron impact mass spectrometric detection in the SIM mode (GC-MS-SIM). Spiked blank soil extracts were used as standards to counteract the matrix effect observed in the chromatographic determination. PAHs were confirmed at trace level by their retention times, their qualifier and target ions, and their qualifier/target abundance ratios. Recovery studies were performed at 0.5, 1.0, 5.0, and 10 microg/kg fortification levels for each PAH, and the recoveries obtained ranged from 91.2 to 99.8% with RSDs between 0.4 and 9.3%. The detection limits of the method ranged from 0.03 to 0.3 microg/kg for the different PAHs studied. The developed method is linear over the range assayed, 1-100 microg/L with determination coefficients higher than 0.996. PAH levels were determined using this method in soil samples taken from different agricultural areas of Spain. In general, PAH concentrations were low and the most frequently occurring PAHs were naphthalene, pyrene, phenanthrene, and fluoranthene.     

Selective Formation of Indene through the Reaction of Benzyl Radicals with Acetylene

The combustion of fossil fuels forms polycyclic aromatic hydrocarbons (PAHs) composed of five‐ and six‐ membered aromatic rings, such as indene (C₉H₈), which are carcinogenic, mutagenic, and deleterious to the environment. Indene, the simplest PAH with single five‐ and six‐membered rings, has been predicted theoretically to be formed through the reaction of benzyl radicals with acetylene. Benzyl radicals are found in significant concentrations in combustion flames, owing to their highly stable aromatic and resonantly stabilized free‐radical character. We provide compelling experimental evidence that indene is synthesized through the reaction of the benzyl radical (C₇H₇) with acetylene (C₂H₂) under combustion‐like conditions at 600 K. The mechanism involves an initial addition step followed by cyclization and aromatization through atomic hydrogen loss. This reaction was found to form the indene isomer exclusively, which, in conjunction with the high concentrations of benzyl and acetylene in combustion environments, indicates that this pathway is the predominant route to synthesize the prototypical five‐ and six‐membered PAH.     

Synthesis of the o-quinones and other oxidized metabolites of polycyclic aromatic hydrocarbons implicated in carcinogenesis

Efficient new syntheses of the o-quinone derivatives of benzo[a]pyrene (BPQ), 7,12-dimethylbenz[a]anthracene (DMBAQ), and benz[a]anthracene (BAQ), implicated as active carcinogenic metabolites of the parent polycyclic aromatic hydrocarbons (PAHs), are reported. These PAH quinones also serve as starting compounds for the synthesis of the other active metabolites of these PAHs thought to be involved in their mechanism(s) of carcinogenesis. The latter include the corresponding o-catechols, trans-dihydrodiols, and the corresponding anti- and syn-diol epoxides.     

Polyaromatic hydrocarbon profile of a mineral oil (JBO-P) by gas chromatography

The present investigation was aimed at identifying the compound(s) responsible for the carcinogenic activity of a variety of jute batching oil (known as non-FDA variety, pre-FDA variety, or JBO-P), a crude petroleum distillate substantially used in jute industries. This was initially performed by isolating from JBO-P a polyaromatic hydrocarbon (PAH) fraction containing compounds of more than three rings. This fraction was then analysed for its PAH profile by gas chromatography and individual components identified by comparing its flame ionisation detector (FID) signal with those obtained from reference PAHs. The results revealed that PAHs of more than three rings, reported to be a recognised class of chemical carcinogens, were present in the JBO-P sample at the level of 3300 mg/kg of oil (0.33%, w/w); benzo(a)pyrene and dibenz(a,h)anthracene, known to be highly potent carcinogens, constituted 129 mg/kg (0.0129%, w/w) and 29 mg/kg (0.0029%, w/w) of the total oil, respectively; and except for a few signals, the PAH profile of JBO-P was found to be somewhat similar to that reported for a sample of carcinogenic used engine oil.     

Diels–Alder Cycloaddition to the Bay Region of Perylene and Its Derivatives as an Attractive Strategy for PAH Core Expansion: Theoretical and Practical Aspects

PAHs (polycyclic aromatics hydrocarbons), the compound group that contains perylene and its derivatives, including functionalized ones, have attracted a great deal of interest in many fields of science and modern technology. This review presents all of the research devoted to modifications of PAHs that are realized via the Diels–Alder (DA) cycloaddition of various dienophiles to the bay regions of PAHs, leading to the π-extension of the starting molecule. This type of annulative π-extension (APEX) strategy has emerged as a powerful and efficient synthetic method for the construction of polycyclic aromatic hydrocarbons and their functionalized derivatives, nanographenes, and π-extended fused heteroarenes. Then, [4 + 2] cycloadditions of ethylenic dienophiles, -N=N-, i.e., diazo-dienophiles and acetylenic dienophiles, are presented. This subject is discussed from the organic synthesis point of view but supported by theoretical calculations. The possible applications of DA cycloaddition to PAH bay regions in various science and technology areas, and the prospects for the development of this synthetic method, are also discussed.     

Comparison of PAH Levels and Sources in Pine Needles from Portugal,Spain, and Greece

The main objective of this work was to assess and compare the levels, patterns, and sources of contamination of 16 polycyclic aromatic hydrocarbons (PAHs) between Portugal, Spain, and Greece (in the island of Crete). A total of 9 sampling sites were chosen (4 in urban and 5 in non-urban areas) in each country and pine needles from the Pinus pinea L. species were collected. Although the mean total PAH levels was similar in the three countries (279 ± 236 ng g^?1 for Portugal, 294 ± 258 ng g^?1 for Spain, 301 ± 253 ng g^?1 for Greece, all dry weight) and, in general, 3-ring and 4-ring PAHs were predominant (being phenanthrene consistently the most abundant), there were some visible differences in the aromatic ring patterns and possible sources between the three regions. Source apportionment was done using PAH ratios (Phen/Ant and Flt/Pyr crossplots) and reflected mixed petrogenic and pyrogenic sources. Furthermore, Principal Component Analysis (PCA) clearly separated the urban and the non-urban sites and all three countries, which reinforces that the sources of contaminations vary in each case and the suitability of pine needles for trans-boundary biomonitoring of PAHs.