Polycyclic aromatic hydrocarbons influencing factors

Chemical carcinogenesis by polycyclic aromatic hydrocarbons (PAHs) is a multi-step process in which each of the steps must occur if a neoplasm is to develop. Thus, exposure to PAHs alone is not necessarily sufficient for the induction of a tumor. Many of these factors are summarized below and are discussed in various chapters of this volume. Considered here will be those factors influencing the reactions of the metabolically activated forms of the PAHs with DNA and the ways in which adducts may be detected and characterized. 

Another isomerization reaction of arene oxides is equilibrium with oxe-pins [5], Here, the fused six-membered carbocycle and three-membered oxirane merge to form a seven-membered heterocycle, as shown in Fig. 10.2. An extensive computational and experimental study involving 75 epoxides of monocyclic, bicyclic, and polycyclic aromatic hydrocarbons has revealed much information on the structural factors that influence the reaction rate and position of equilibrium [11], Thus, some compounds were stable as oxepins (e.g., naphthalene 2,3-oxide), while others exhibited a balanced equilibrium... 

In the pH range of 5 - 10, H20-catalyzed hydrolysis is the predominant mechanism (see Fig. 10.11, Pathway b), resulting in the formation of the (8R,9R)-dihydrodiol (10.133, Fig. 10.30). Thus, aflatoxin B1 exo-8,9-epoxide is possibly the most reactive oxirane of biological relevance. Such an extreme reactivity is mostly due to the electronic influence of 0(7), as also influenced by stereolectronic factors, i.e., the difference between the exo- and endo-epoxides. The structural and mechanistic analogies with the dihydro-diol epoxides of polycyclic aromatic hydrocarbons (Sect. 10.4.4) are worth noting. 

Pitts, J. N., Jr., H.-R. Paur, B. Zielinska, J. Arey, A. M. Winer, T. Ramdahl, and V. Mejia, Factors Influencing the Reactivity of Polycyclic Aromatic Hydrocarbons Adsorbed on Filters and Ambient POM with Ozone, Chemosphere, 15, 675-685 (1986). 

In the aromatic-ring-annelated oxepin series the resonance effect is clearly the major influence dominating other factors (e.g. temperature, solvent, etc.) which affect the oxepin-arene oxide equilibrium. It is however very difficult to exclude the presence of a minor (spectroscopically undetectable) contribution from either tautomer at equilibrium. This problem has been investigated by the synthesis of chiral arene oxides from polycyclic aromatic hydrocarbons (PAHs). The presence of oxepin (26) in equilibrium with naphthalene 1,2-oxide has been excluded by the synthesis of the optically active arene oxide which showed no evidence of racemization in solution at ambient temperature via the achiral oxepin (26) <79JCS(Pl)2437>. 

Mitra, S., Dickhut, R.M., Kuehl, S.A., and Kimbrough, K.L. (1999b) Polycyclic aromatic hydrocarbon (PAH) source, sediments deposition patterns, and particle geochemistry as factors influencing PAH distribution coefficients in sediments of the Elizabeth River, VA, USA. Mar. Chem. 66, 113-127. 

The activity (induction or inhibition) of various CYP enzymes is influenced by a variety of factors that have been identified to date. For example, genetic polymorphisms are most significant in CYP families lA, 2A6, 2C9, 2C19, 2D6, and 2E1. Nutrition effects have been documented in families lAl, 1A2, IBl, 2A6,2B6, 2C8, 2C9, 2C19, 2D6, and 3A4 (10, 11) smoking influences families lAl, 1A2, and 2E1 (12) alcohol influences family 2E1 (13) drugs influence families lAl, 1A2, 2A6,2B6,2C, 2D6, 3A3, and 3A4,5 and environmental xe nobio tics such as polycyclic aromatic hydrocarbons. 

Whereas the overall hydrophobic nature of the stationary phase is the most important factor in determining retention, bonded-phase structure can also influence k values. This effect can be observed in the separation of polycyclic aromatic hydrocarbons (PAHs). For stationary phases with a high bonding density and/or a high degree of association between adjacent bonded organic moieties, molecules that are more planar are preferentially retained. The National Institute of Standards and Technology (NIST) has developed reference mixtures to measure this effect. 

Maier M, Maier D, Lloyd BJ. 2000. Factors influencing the bobilization of polycyclic aromatic hydrocarbons (PAHS) from the coal-tar lining of water mains. Water Res 34(3) 733-786. 

Pitts, J. N. Jr., Paur, H. R., Zielinska, B., Sweetman, J. A., Winer, A. M., Ramdahl, T., and Mejia, V. (1986) Factors influencing the reactivity of polycyclic aromatic hydrocarbons adsorbed on model substrates and in ambient POM with ambient levels of ozone, Chemosphere 15, 675-685. 

Lepine FL, Milot SM, Vincent NM et al (1991) Photochemistry of higher chlorinated PCBs in cyclohexane. J Agric Food Chem 39 2053-2056 Li A, Schoonover TM, Zou Q et al (2005) Polycyclic aromatic hydrocarbons in residential air of ten Chicago area homes concentrations and influencing factors. Atmos Environ 39 3491-3501... 

The reduction process of polycycles by lithium metal converts the neutral atoms to anions. The electron transfer is best achieved in ethereal solvents. This enables the stabilization of the lithium cation by coordination to the oxygen atoms of the solvent. The hydrocarbon anion and the cation are linked together by electrostatic forces in which the solvent molecules are also involved, therefore the ion-solvation equilibrium should be considered8. The limiting cases in this equilibrium are free ions and contact ion-pairs (CIP), and in between there are several forms of solvent separated ion-pairs (SSIP)9. In reality, anionic species of aromatic hydrocarbons in ethereal solvents exist between CIP and SSIP. Four major factors influence the ion-solvation equilibrium of lithium-reduced 7T-conjugated hydrocarbons, as observed by H and 7Li NMR spectroscopies8,10. 

---