Patrick P. J. Mulder

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.

Mutagenicity of cyclopenta-fused polynuclear aromatic hydrocarbons and a non-polar fraction from a fuel combustion sample in a Salmonella forward mutation assay without exogenous metabolic activation.

A series of cyclopenta-fused polynuclear aromatic hydrocarbons (PAH) were tested for mutagenicity in a bacterial forward mutation assay based on resistance to 8-azaguanine (8-AG) in Salmonella typhimurium TM677 in the absence of Aroclor-induced rat liver postmitochondrial supernatant (PMS). All of the aceanthrylenes tested were mutagenic in the absence of PMS, whereas none of the acephenanthrylenes were active. The following mutagenic potency series expressed as the minimum detectable mutagen concentration (MDMC) in nmol/ml was obtained: aceanthrylene (AA) (5.5); cyclopent[h,i]aceanthrylene (CPAA)(18.2); 6-methylaceanthrylene (6-MeAA)(112); 1,2,6,7-tetrahydrocyclopent[h,i]aceanthrylene (THCPAA) (166); 1,2-dihydroaceanthrylene (DHAA) (298). Saturation of the cyclopenta rings or methylation at the 6-position of AA reduced, but did not eliminate, mutagenicity measured in the absence of PMS. AA was unusual because it was approximately 4-fold more mutagenic in the absence of PMS than in its presence. The other aceanthrylenes tested were 1.3-10.7 times more mutagenic in the presence of PMS than in its absence to give an MDMC potency series of: CPAA (3.8); 6-MeAA (10.5); AA (19.9); THCPAA (52.9); DHAA (229). Approximately 20% of the PMS-independent mutagenicity in a combustion sample from ethylene burned under fuel-rich conditions was found in a fraction containing only non-polar, 4-7 ring PAHs, widely attributed to be mutagenic only in the presence of PMS. None of this mutagenicity could be attributed to aceanthrylenes, thus other non-polar PAHs appear to possess significant PMS-independent mutagenicity as well.

Fluorobenzo[a]pyrenes as probes of the mechanism of cytochrome P450-catalyzed oxygen transfer in aromatic oxygenations

Fluoro substitution of benzo[a]pyrene (BP) has been very useful in determining the mechanism of cytochrome P450-catalyzed oxygen transfer in the formation of 6-hydroxyBP (6-OHBP) and its resulting BP 1,6-, 3,6-, and 6,12-diones. We report here the metabolism of 1-FBP and 3-FBP, and PM3 calculations of charge densities and bond orders in the neutral molecules and radical cations of BP, 1-FBP, 3-FBP, and 6-FBP, to determine the mechanism of oxygen transfer for the formation of BP metabolites. 1-FBP and 3-FBP were metabolized by rat liver microsomes. The products were analyzed by HPLC and identified by NMR. Formation of BP 1,6-dione and BP 3,6-dione from 1-FBP and 3-FBP, respectively, can only occur by removal of the fluoro ion from C-1 and C-3, respectively, via one-electron oxidation of the substrate. The combined metabolic and theoretical studies reveal the mechanism of oxygen transfer in the P450-catalyzed formation of BP metabolites. Initial abstraction of a pi electron from BP by the [Fe(4+)=O](+)(*) of cytochrome P450 affords BP(+)(*). This is followed by oxygen transfer to the most electropositive carbon atoms, C-6, C-1, and C-3, with formation of 6-OHBP (and its quinones), 1-OHBP, and 3-OHBP, respectively, or the most electropositive 4,5-, 7,8-, and 9,10- double bonds, with formation of BP 4,5-, 7,8-, or 9,10-oxide.

CONDENSATION OF ALL-E-RETINAL

Abstract A novel base induced self condensation product of all- E -retinal is presented. The scope of the reaction is investigated with three analogous α,β-unsaturated aldehydes.

Gas phase reactions of hydroxyl radicals arenes

Abstract At elevated temperatures. OH is found to abstract H from benzene derivatives; in air, phenols are then generated via reversible addition of ArOO· to arene.

Classification of Select Aceanthrylenes, Acephenanthrylenes and Dicyclopentapyrenes as Alternant versus Nonalternant Polycyclic Aromatic Hydrocarbons on the Basis of Their Fluorescence Quenching Behavior in the Presence of Nitromethane and Cetylpyridinium Cation Selective Quenching Agents

Abstract Fluorescence behavior of dicyclopenta[cd, fg]pyrene, dicyclopenta[cd, jk]pyrene and dicyclopenta[cd, mn]pyrene is reported in the presence of nitromethane and cetylpyridinium (CPy+) cation quenching agents. Nitromethane and CPy+ are known to selectively quench fluorescence emission of alternant polycyclic aromatic hydrocarbons (PAHs). Emission intensities of nonalternant PAHs, with a few noted exceptions, are unaffected. Experimental measurements show that nitromethane and CPy+ effectively quenched fluorescence emission of the three dicyclopentapyrenes, thus suggesting that the perimeter C = C double bonds in the two cyclopenta-rings are alkenic, rather than aromatic in nature. Also reported are the fluorescence properties of 14 aceanthrylene and acephenanthrylene derivatives, as well as several structurally related compounds, to further document the cetylpyridinium cations quenching selectivity.