EFFICIENT NEW SYNTHESES OF POLYCYCLIC AROMATIC HYDROCARBON ORTHO-QUINONES AND THEIR 2′-DEOXYRIBONUCLEOSIDE ADDUCTS

Three mechanisms have been proposed to explain the carcinogenic activities of polycyclic aromatic hydrocarbons (PAHs). On the basis of the nature of the active metabolites involved, they may be termed: the diol epoxide mechanism, the quinone mechanism, and the radical-cation mechanism. In connection with studies to evaluate the relative importance of these pathways, we required practical methods for the syntheses of the active PAH metabolites involved. We now report efficient new synthesis of the o-quinones of benzo[a]pyrene (BPQ), 7,12-dimethylbenz[a]anthracene (DMBAQ), and benz[a]anthracene (BAQ). These quinones are convenient synthetic precursors of the related o-catechols, trans-dihydrodiols, and diol epoxides, as well as the stable adducts of the o-quinones with 2-deoxyadenosine and 2′-deoxyguanosine.     

SIZE DISTRIBUTIONS OF POLYCYCLIC AROMATIC HYDROCARBONS—GAS/PARTICLE PARTITIONING TO URBAN AEROSOLS

PAH size distributions were measured at Mumbai (formerly Bombay), India, to examine PAH partitioning to multimodal urban aerosols. Bimodal size distributions were obtained with a predominance of non-volatile PAH species in the fine mode and semi-volatile PAH species in the coarse mode. We develop size-resolved PAH gas/particle partition coefficients, based on adsorption and absorption theory, and analyse measurements in terms of estimated PAH size distributions in typical urban airsheds dominated by primary and secondary aerosol constituents. Adsorption explains PAH presence in the nuclei and accumulation modes where the aerosol surface area predominates (primary emissions), while absorption explains their predominance in the accumulation mode where absorbing organic matter is available (secondary aerosol constituents in a smoggy airshed). Volatilisation of semi-volatile PAH from nuclei mode aerosols, at enhanced rates (Kelvin effect), and their absorptive partitioning to accumulation mode aerosols, enhanced in a smoggy airshed, would explain previous measurements of semi-volatile PAH predominance in the accumulation mode in Los Angeles. The absence of a predominant PAH accumulation mode in Mumbai measurements is likely from the absence of significant photochemistry and aerosol organic matter. Equilibrium adsorption and absorption are unable to explain coarse particle PAH predominance which would occur by dry deposition scavenging of gaseous and nuclei-mode PAH by soil particles which undergo cyclic re-suspension and deposition in an urban airshed. Coarse particle morphology and adsorption affinity of PAH to mineral particles must be examined to better understand PAH predominance in coarse mode aerosols.     

THE SIGNIFICANCE OF POLYCYCLIC AROMATIC HYDROCARBONS AS ENVIRONMENTAL CARCINOGENS. 35 YEARS RESEARCH ON PAH—A RETROSPECTIVE

In vivo studies with laboratory animals as well as in vitro studies with bacteria and mammalian cell cultures have demonstrated that the mutagenic and/or carcinogenic properties of numerous PAHs require metabolic transformation. Metabolism of PAHs has been explored in vitro using cellular microsomal fractions, mammalian cell cultures and later genetically engineered cells expressing cytochromes P450 from several species including humans.

Balancing the carcinogenic potential of some environmental matrices (vehicle exhaust, condensate of hard coal combustion effluents, cigarette smoke condensate, used motor oil) after separation into sub-fractions evidenced that the carcinogenic effect may be attributed almost exclusively to PAH. Mixtures of well-known carcinogenic PAH in concentrations as present in these matrices, however, did not explain the total biological effect. Thus, it had been speculated that either very potent unknown carcinogens are still hidden in the PAH fraction, or that synergistic effects (enzyme induction) play a significant role.

In parallel to these carcinogenicity studies, the metabolism of various PAHs has been investigated in rat liver microsomes from untreated animals as well as from animals pre-treated with inducers of cytochrome P450. It was found that even non-carcinogenic PAHs possess a significant inducing potential. Moreover, in several mammals a highly species-specific metabolism of PAH could be observed allowing a critical view to the extrapolation from animal experiments to the human situation. This was further confirmed by experiments with mammalian cell cultures including human ones as well as by metabolic studies with genetically engineered Chinese hamster V79 cells singularly expressing various cytochrome P450 enzymes from a number of different species (human, rat, mouse, fish). With these cell lines metabolic studies were carried out with a larger number of PAHs as substrates including phenanthrene, pyrene, chrysene, benzo[a]anthracene, benzo[c]phenanthrene, benzo[a]pyrene, dibenzo[a,l]pyrene, and benzo[c]chrysene.

Based on the metabolism results, analytical methods have been developed to determine urinary biomarkers of human PAH exposure. Human biomonitoring studies have been performed with different occupationally exposed individuals as well as within smokers and non-smokers of the general population. Endogenous PAH exposure levels and changes in the urinary excreted metabolic profile depending on exposure level have been determined.     

GAS/PARTICLE AND SIZE DISTRIBUTIONS OF POLYCYCLIC AROMATIC HYDROCARBONS IN AMBIENT AIR IN TOKYO 2001–2002

By using an Andersen sampler equipped with a low-pressure impactor, samples of 12 size-classified (>0.13 μm to <12 μm) airborne particles and samples of gaseous components were taken from the air in Tokyo for continuous periods of 19 weeks in the summer of 2001 and 17 weeks in the winter of 2001–2. The sampling filters were changed weekly. The concentrations of eight polycyclic aromatic hydrocarbons (PAHs) in the particulate and gas-phase samples were measured by reverse-phase high performance liquid chromatography (HPLC) with fluorescence detection. Pyrene was detected in the gas phase in both summer and winter: 59% of the total pyrene detected was present in the gas phase in summer, but this fraction decreased to 40% in winter. In the particle fractions, the summer levels of benzo[k]fluoranthene (BkF), dibenz[a,h]anthracene (dBahA), and benzo[a]anthracene (BaA) peaked in particles of diameter 1.25 μm, and benzo[ghi]perylene (BghiP), benzo[a]pyrene, benzo[b]chrysene (BbC), and dibenzo[a,e]pyrene (dBaeP) peaked in particles of diameter 0.76 μm. In winter, BkF, BghiP, BaA, BbC, and dBaeP levels peaked in particles of diameter 0.52 μm, whereas dBahA peaked in particles of diameter 0.76 μm.     

THE DETECTION OF POLYCYCLIC AROMATIC COMPOUNDS IN AIR SAMPLES BY GC×GC-TOFMS

Multidimensional Gas Chromatography-Time of Flight Mass Spectrometry is a relatively new, highly versatile and productive technique that is ideally suited for the detection of PACs in environmental samples. Air samples collected in Slocan Park in Vancouver and in Langley, BC (a semi-rural site) during the PACIFIC 2001 field study and aerosol samples from St. Anicet in Quebec (a rural site) collected in 2006 were analyzed for their PAC content. In addition to the parent PAH, many alkylated-PAH, oxygen, sulphur and nitrogen heterocyclic analogues of the parent PAH were detected. Many of the PAHs observed at these sites were also found in diesel exhaust.     

PARTITIONING OF π-ELECTRONS IN RINGS OF POLYCYCLIC conjugated HYDROCARBONS. PART 1: CATACONDENSED BENZENOIDS

Recently a novel view on Kekulé valence structures (or resonance structures) was reported in which their standard geometrical representation was replaced by a numerical representation obtained by assigning π-electrons associated with CC double bonds to individual benzenoid rings. In the present article, we examine in more detail the partitioning of π-electrons to benzenoid rings for cata-condensed benzenoid hydrocarbons. For special families of cata-condensed benzenoids, we offer formulas which allow one to obtain the average π-electron ring content for individual benzenoid rings of polycyclic conjugated hydrocarbons. We also show that the average π-electron ring content for individual benzenoid rings can be calculated from Pauling bond orders without a need to examine all Kekulé resonance structures of a molecule.     

WHERE ARE THE LIMITS OF THE GAS-PHASE FLUORESCENCE ON THE POLYCYCLIC AROMATIC COMPOUND ANALYSIS?

The aim of this work has been centered on the development of a detection system which could be useful to determine polycyclic aromatic hydrocarbon (PAH) emissions in power generation processes where PAHs are released to the atmosphere in the gas phase. In this way, a suitable sensor based on gas phase fluorescence spectroscopy was designed to facilitate the PAH analysis, avoiding previous steps necessary to determine liquid samples such as extraction, concentration, and cleaning. This gas cell was applied for two experimental installations at laboratory scale. One of them was used to determine adsorption capacities and breakthrough curves of PAH binary mixtures and the other installation allowed the separation of PAH mixtures by using, previous to the gas phase fluorescence spectroscopy, a packed column.     

EXCESS GIBBS ENERGY FOR THE BINARY MIXTURES OF NITROBENZENE WITH SOME HYDROCARBONS AT 94.95 KPA

Bubble point temperatures at 94.95 kPa, over the entire composition range, are measured for the binary mixtures of nitrobenzene with: cyclohexane, n-hexane, n-heptane, n-decane, and o-, m-, and p-xylenes, using a Swietoslawski-type ebulliometer. Liquid phase composition versus bubble point temperature measurements are well represented by the Wilson model. Computed values of the excess Gibbs energy are presented and discussed.     

ANALYSIS OF THE REMOVAL OF H_2S WITH IMPREGNATED ACTIVATED CARBON

A general mathematical model with its governing equations in dimensionless forms has beendeveloped to describe the removal of hydrogen sulfide with impregnated activated carbon.Anapproximate relationship between the sulfur capacity and the reaction time in a single carbon pellet isobtained,and criterion to ascertain the rate controlling step of the process can then be deduced.Inthe meantime,the choice of the appropriate oxygen concentration and the principle to be followedare also described.     

CATALYTICALLY ACTIVE COMPONENTS OF Fe_2O_3-Sb_2O_4 MIXED OXIDE CATALYSTS AND THEIR ROLE IN AMMOXIDATION OF PROPYLENE

The catalytically active components of a series of Fe_2O_3-Sb_2O_4 mixed oxide catalysts with differentSb/Fe ratio,calcined at elevated temperature,as well as with or without support,have been investigated byX-ray diffraction analysis,Mossauer spectroscopy and XPS in order to elucidate their catalytic behavior inammoxidation of propylene.Correlations of acrylonitrile yield with Fe~2 and Fe~3 respectively showed that,FeSbO_4 seems to bethe basic active component of catalyst,upon which the formation of new phase containing Fe~3 is responsiblefor a good selective oxidation.     

PHOTOCHARGEABLE BEHAVIOR OF HYDROGEN STORAGE ALLOY ELECTRODE MODIFIED WITH TiO_2 NANOPARTICLES

Photochargeable behavior of hydrogen storage alloy electrode modified with TiO_2 nanoparticles(MH/TiO_2) was investigated by measuring its photocharge-discharge characteristics. The results showed the MH/TiO_2 electrode could store light energy photoelectrochemically when it was illuminated. The potential of the MH/TiO_2 electrode could be charged to 0.843 V.The discharge time of the MH/TiO_2 electrode increased with increasing the illuminating time, The mechanism of photochargeable behavior of the MH/TiO_2 electrode was discussed. When a UV photon was absorbed by TiO_2, a photoelectrochemical reaction would occur at the electrode/electrolyte interface. An electron/hole pair was generated and the electron could deoxidize the hydrogen alloy to metal hydride.     

STUDIES ON KINETICS OF DESORPTION OF CO_2 FROM HOT CARBONATED POTASH SOLUTION WITH DETA (DIETHYLENETRIAMINE) AS A CATALYST

Under atmosphe()e press()ne, rates of deseption of CO() from unmod()ed carbonated potash solutior (27 wt%)and modified carbonated potash solution(27 wt%) containing DETA as a catalyst, have been measured in a laboratory stirred reactor. Experiments were carried out with concentrations of DETA from 0—40g/L and temperatures from 90—104℃The results, show that the desorption of CO_2 from hot carbonated solutions with and without the addition of DETA, may be considered a pseudo-first order reversible reaction, and that the desorption of CO_2 from carbonated potash solution calalysed by DEIA is in agreement with the mechanism of simultancous reactions of CO_2 with amine molecules and with hydroxyl ions in solution. Mathematical models for desorptions rate cocflicient have been cstablished, and optimum concentration of DETA is proposed.     

IN SITU SEPARATION OF ETHANOL DURING BATCH FERMENTATION WITH CO_2 STRIPPING AND ACTIVATED CARBON ADSORPTION

In situ separation of ethanol during batch fermentation with CO_2 stripping and activated carbon adsorption was studied. The higher initial glucose concentration and fermentation rate were reached due to the elimination of ethanol inhibition on the cell growth by means of CO_2 stripping. The stripped ethanol vapor was selectively adsorbed by an activated carbon column. The conde(?)sate desorbed from the adsorption column can be higher than 50% by weight. Ar unstructured model was used to simulate the experimental data satisfactorily.