J. Cornelisse

Bacterial and human cell mutagenicity study of some C18H10 cyclopenta-fused polycyclic aromatic hydrocarbons associated with fossil fuels combustion.

A number of isomeric C18H10 polycyclic aromatic hydrocarbons (PAHs), thought to be primarily cyclopenta-fused PAHs, are produced during the combustion and pyrolysis of fossil fuels. To determine the importance of their contributions to the total mutagenic activity of combustion and pyrolysis samples in which they are found, we characterized reference quantities of four C18H10 CP-PAHs: benzo[ghi]fluoranthene (BF), cyclopenta[cd]pyrene (CPP), cyclopent[hi]acephenanthrylene (CPAP), and cyclopent[hi]aceanthrylene (CPAA). Synthesis of CPAA and CPAP is described. The availability of reference samples of these isomers also proved to be an essential aid in the identification of the C18H10 species often found in combustion and pyrolysis samples. Chemical analysis of selected combustion and pyrolysis samples showed that CPP was generally the most abundant C18H10 isomer, followed by CPAP and BF. CPAA was detected only in pyrolysis products from pure PAHs. We tested the four C18H10 PAHs for mutagenicity in a forward mutation assay using S. typhimurium. CPP, BF, and CPAA were roughly twice as mutagenic as benzo[a]pyrene (BaP), whereas CPAP was only slightly active. These PAHs were also tested for mutagenic activity in human cells. In this assay, CPP and CPAA were strongly mutagenic but less active than BaP, whereas CPAP and BF were inactive at the dose levels tested. Also, the bacterial and human cell mutagenicity of CPAA and CPAP were compared with the mutagenicity of their monocyclopenta-fused analogs, aceanthrylene and acephenanthyrlene. Although the mutagenicities of CPAP and acephenanthrylene are similar, the mutagenic activity of CPAA is an order of magnitude greater than that of aceanthyrlene.

Photoreactions of aromatic compounds—XXXV1: Nucleophilic photosubstitution of methoxy substituted aromatic compounds. Monophotonic ionization of the triplet

Abstract Methoxy groups exert an activating and ortho/para directing influence in light induced nucleophilic substitution reactions (cyanation, hydroxylation, etc) of aromatic compounds in aqueous media. The first chemical step in these processes is monophotonic ionization of the aromatic compound in its lowest triplet state, followed by reaction of the radical cation with the nucleophile Quantum yields of photocyanation of 4-fluoro- and 4-chloroanisole indicate that in 99% (mole fraction) water virtually all triplets formed undergo electron ejection. This hypothesis is in agreement with the results of charge density calculations for the radical cations. It is directly supported by the similarity of the product composition of these photochemical substitutions with that of anodic substitutions, where the intermediacy of an aromatic cation is generally accepted. The presence of an oxidizing agent (oxygen, or persulphate) is required only when a hydrogen is replaced. The nucleophilic photosubstitution at electron rich aromatic systems in solvents as water can therefore be classified as an S r + n 1(3Ar*) process.

Nucleophilic Aromatic Photosubstitution

Publisher Summary This chapter outlines the recent developments in the field of nucleophilic aromatic photosubstitution. The chapter addresses fundamental questions and discusses the suggested lines of investigation, illustrating the pathways and the intermediates of nucleophilic aromatic photosubstitution, the mechanism of the reaction steps, and the factors governing product composition and quantum yields. The photohydrolyses are often very clean reactions with good quantum yields. The reaction may follow a different course with different nucleophiles. Experiments with 18 O-labelling have shown that m- nitrophenyl phosphate, upon illumination, undergoes hydrolytic attack by water at the phosphorus atom, whereas with hydroxide ion and methylamine genuine aromatic substitution through attack at the ring carbon atom takes place. The reaction is first order in light intensity and zero order in the light absorbing aromatic reaction partner. The results obtained by conventional flash photolysis and with laser photolysis are discussed in the chapter.

The meta photocycloaddition of anisole to oxa- and dioxa-cyclopentenes and to ethyl vinyl ether

Abstract The meta photocycloaddition of anisole to 2,3- and 2,5-dihydrofuran, 1,3-dioxole and ethyl vinyl ether is described. The NMR data of the adducts are presented. The reaction yields mixtures of endo and exo adducts. The endo/exo ratio is strongly influenced by the presence of one or two oxygen atoms next to the double bond of the alkene. A mechanism is presented in which a zwitterionic intermediate is formed from the excited anisole and the alkene.

The meta photocycloaddition of benzonitrile and α,α,α-trifluorotoluene to cyclopentene

Abstract The photocycloaddition of benzonitrile to cyclopentene yields four major cyano-substituted tetracyclo[6.3.0.0 2,11 .0 3,7 ]undec-9-enes, all with the cyano group at positions 9 or 11. This is in agreement with a reaction pathway involving polarized structures as are the results of the irradiation of α,α,α-trifluorotoluene in the presence of cyclopentene.

Photoreactions of aromatic compounds—XXVI : Photoinduced reactions of biphenyl and biphenyl derivatives with cyanide ion

Abstract The photoreactions of a number of biphenyl derivatives, in particular nitrobiphenyl derivatives, with cyanide ion have been investigated. Photosubstitution by cyanide ion has been found to predominate; photoreduction is not observed. In some cases (4-nitrobiphenyl, 4,4′-dinitrobiphenyl, 3-nitrobiphenyl and similar compounds) the behaviour can be rationalized on the basis of analogy to the pattern of photocyanation of biphenyl itself (preference for substitution of the 4-position). 2-Methoxy-4-nitrobiphenyl and 2-methoxy-5-nitrobiphenyl on irradiation reacted with cyanide ion following the pattern of the nitroanisoles rather than that of the nitrobiphenyls not containing a methoxy substituent. In photo-excited 2,4,6-trimethylbiphenyls the favoured position for attack by cyanide ion appears to be at the 3-position, i.e. in the methyl substituted ring.

Wavelength effect on the photochemical reactions of (Z)-2,5-dimethyl-1,3,5-hexatriene : selective excitation of rotamers

Abstract The UV absorption spectrum of Z-2,5-dimethyl-1,3,5-hexatriene 1 is typical of a cZt triene, but the long wavelength tail Indicates the presence of the (minor) cZc rotamer. The sudden change In the photoreactivity of 1 around 290 nm is in agreement with selective excitation of these rotamers. No indication is obtained for an intrinsic excitation energy dependence of the photoreactivity of the Individual rotamers.

The meta photocycloaddition of anisole and benzonitrile to 1,3-dioxol-2-one

Abstract The meta photocycloadditions of benzonitrile and anisole to 1,3-dioxol-2-one both yield two major products. In both cases the adducts are those which would be expected if some form of polar species were to develop along the reaction pathway. The absence of exo adducts in the case of benzonitrile and 1,3-dioxol-2-one is discussed.

Intramolecular meta photocycloaddition of conformationally restrained 5-phenylpent-1-enes. Part II: Steric and electronic effects caused by 4-mono- and 4-disubstitution

Abstract The meta photocycloaddition of 4-substituted 5-phenylpent-1-enes, 10–18, has been studied. The monosubstituted derivatives always prefer 2,6 addition, independent of the size of the substituent. For 2,6 addition two basic conformations are possible. Disubstituted compounds yield predominantly 1,3 addition with the sterically more demanding group exo. Except for the methoxymethyl and THF derivative the oxygen is found exo as a result of repulsion, while the monohydroxy derivative gives also endo which might be explained by hydrogen bonding. The products from compound 11 change from mainly endo-OH in cyclohexane to chiefly exo-OH in methanol. Much similarity is found with Diels-Alder cycloaddition.

Selective fluorescence quenching to discriminate between alternant and non-alternant polycyclic aromatic hydrocarbons: acephenanthrylene derivatives as exceptions to the nitromethane quenching rule

Nitromethane selectively quenches the fluorescence emission of alternant polycyclic aromatic hydrocarbons (PAHs)via an electron transfer mechanism. Emission intensities of non-alternant PAHs, for the most part, are unaffected. Results of previous measurements show that nitromethane does quench the fluorescence emission of the nine acenaphthylene solutes studied, which is completly contrary to what would be expected based on the fact that all nine solutes are non-alternant PAHs. To investigate this phenomenon further, the fluorescence behaviour of 1-, 3-, 4-, 5-, 6-, 7-, 8-, 9- and 10- methylacephenanthrylene dissolved in neat acetonitrile, acetonitrile–ethyl acetate and acetonitrile–toluene solvents was measured at different nitromethane concentrations. Experimental results support the notion that the double bond in the five-membered ring is fixed; therefore, the solutes act as alternant rather than non-alternant PAHs.