Cyclopenta-Fused Polycyclic Aromatic Hydrocarbons (CP-PAH). Recurring Combustion Effluents and Their Biological Significance

Abstract

The convenient synthesis of a large set of (multiple) CP-PAH by Flash Vacuum Thermolysis (FVT), which have all been identified in combustion exhausts, allows their systematic assessment for mutagenicity in the bacterial mutagenicity assay (Ames-assay, TA98±S9-mix). Consequently, the physico-chemical characterization (1H and 13C NMR, cyclic voltammetry, etc.) is carried out to elucidate structure-activity relationships and to explain the high activity exhibited by some CP-PAH, on one hand, and the inactivity of others, on the other hand. To gain further insight in the mechanisms for positive mutagenicity response in the presence and in the absence of the exogenous metabolic activation mixture (± S9-mix), dihydro-CP-PAH derivatives are synthesised and assayed for mutagenic activity. Hence, the importance of the olefinic bond in the five-membered rings can be evaluated. Furthermore, the corresponding epoxides at the cyclopenta moieties are proposed as the ultimate mutagenic active forms of CP-PAH in the presence of the metabolic activation mixture. Their synthesis permits the evaluation of their contribution to the mutagenic activity or inactivity of the corresponding parent CP-PAH. In addition, FVT-pyrolysates are considered as partial mimics of combustion exhausts. Moreover, the results also demonstrate that the mutagenic activity of mixtures containing exclusively (CP)-PAH cannot be accounted for by the addition of the individual contributions of the constituents. However, in practice for general genotoxic potency screening of complex combustion mixtures, still only the 16 PAH listed by the US-EPA are generally taken into consideration and the global genotoxicity is commonly reported as equivalent to that exerted by benzo[a]pyrene (B[a]P). The results presented in this Ph.D. thesis show that the assumption of only additive processes among the combustion mixture constituents is incorrect and cannot be maintained. Moreover, other compounds that are more active that B[a]P are shown to greatly contribute to the global genotoxicity of the mixture. Semi-empirical AM1 calculations (MOPAC) of the proposed ultimate mutagenic active forms, i.e. epoxides and mono hydroxy-carbocations at the cyclopenta moieties, are employed to support the experimental results. In Chapter I a general introduction concerning the sources, environmental distribution, physico-chemical and genotoxic properties of CP-PAH is presented. The FVT method is also described. In Chapter II the bacterial mutagenicity some mono-CP-PAH is re-evaluated and compared to that exerted by their dihydro-derivatives and epoxide. The results are rationalized by semi-empirical AM1 calculations. In Chapter III, the bacterial mutagenic activity of the three isomeric dicyclopenta-fused pyrene congeners is reported. Their mutagenic potency is markedly affected by the number and the topology of the cyclopenta moieties. The order in mutagenic potency can be explained by semi-empirical AM1 calculations. Furthermore, dicyclopenta[cd,fg]- and diyclopenta[cd,mn]pyrene are identified as novel contributors to the direct-acting mutagenic activity found in the non-polar fraction of combustion exhausts. Chapter IV reports the synthesis and assessment for bacterial mutagenicity of the di-epoxides derived from the three isomeric dicyclopenta-fused pyrene congeners. All epoxides exert direct-acting mutagenicity response and high toxicity, which confirms their role as ultimate mutagenic active forms. Chapter V reports the global mutagenic activity exerted by FVT-pyrolysates of the dicyclopenta-fused pyrene congeners. In Chapter VI the bacterial mutagenic activity of the fluoranthene derivatives is determined. An FVT-pyrolysate containing all derivatives is also evaluated for mutagenic activity. In Chapter VII the experimental total 1H and 13C NMR assignments of the dicyclopenta-fused pyrene congeners are described and compared to those obtained by ab initio calculations using the CTOCD-PZ2 method. This thesis concludes with a Summary and an Outlook and Perspectives sections. Furthermore, a summary in Dutch (Samenvatting) and in Spanish (Resumen) are also provided.