Compounds Pyrene Research Articles

Solvent effects on the magnetic-field-dependent reaction yields of photogenerated radical ion pairs

A pronounced solvent viscosity and polarity dependence of the magnetic field effect was found for polymethylene-linked radical ion pairs generated by photoinduced intramolecular electron transfer in compounds of the type pyrene-(CH 2) n-N,N-dimethylaniline, with n = 7–16. This is interpreted in terms of the general radical pair mechanism, i.e. the nuclear hyperfine interaction mechanism including a spin-exchange interaction, modulated by the stochastic folding motion of the linking CH 2 chain which leads to a “motional deformation” of the reaction yield spectra.

Effect of ingested benzo[ a]pyrene and cadmium on tissue accumulation, hydroxylase activity, and intestinal morphology of the black sea bass, Centropristis striata

Black sea bass, Centropristis striata, were fed shrimp containing [14C]benzo[a]pyrene (200 ppb) in the presence and absence of cadmium (10 ppm) for 10 days. Concentrations of cadmium in muscle tissue were significantly higher when both cadmium and benzo[a]pyrene were ingested simultaneously by the fish. Results indicate that selected tissue concentrations of total benzo[a]pyrene compounds (parent and metabolites) were not affected by the presence of cadmium. The bile contained the majority of benzo[a]pyrene found for all treatments. Ingestion of both contaminants had no effect on hepatic benzo[a]pyrene hydroxylase activity. Histological evidence from the feeding study demonstrated the presence of subcellular inclusions in the intestinal columnar cells and the combined effects of both contaminants appeared greater than either alone.

In vitro genotoxicity studies using complex hydrophobic mixtures: efficient delivery of a petroleum sample to cultured C3H/10T1/2 cells via lipid vesicle incorporation.

Petroleum fractions are a diverse group of extremely hydrophobic mixtures, some of which display strong carcinogenicity in animal skin painting experiments. Interpretation of in vitro genotoxicity experiments with these samples is complicated by inefficient delivery of these hydrophobic substances inside target cells. We therefore developed methods to assess and improve the efficiency of delivering a petroleum sample (Matrix, A.P.I. 81-17) to cultured C3H/10T1/2 cells for genotoxicity studies via lipid vesicle incorporation. Three radiolabeled compounds (14C-benzo(a)pyrene, 14C-decane, and 14C-naphthalene) of widely differing volatilities, broadly representative of the spectrum of compounds in petroleum samples, were separately added to Matrix. Lipid vesicles containing Matrix and radiolabeled compounds were prepared by the classical methods for preparing neutral, positive, and negatively charged multilamellar and unilamellar liposomes. Of these, the classical methods for preparing neutral unilamellar liposomes were the most successful for delivering radiolabeled compounds in Matrix to cells. Vesicles optimal for the delivery of tracers in Matrix were prepared with DSPC:cholesterol:lyso-PC (8.8:0.8:0.4, molar ratio) in a Matrix to lipid ratio of 31:69 (w/w). This new method of delivery resulted in proportional, dose-dependent, and reproducible uptake of all tracers. Further, cells treated with this preparation took up 2.5-fold more 14C-decane, 1.5-fold more 14C-BaP, and 18-fold more 14C-naphthalene added to Matrix than did cells treated with Matrix emulsified in tissue culture medium. In contrast, tracers were not taken up in a proportional or reproducible manner when emulsions were used, and in fact, uptake of 14C-naphthalene was consistently very small. Two petroleum fractions, C(2)029188 and C(3)029194, were 4- and 6-fold more cytotoxic, respectively, when delivered to C3H/10T1/2 cells by lipid vesicles than emulsions. The carcinogenic petroleum fraction C(5)0292202 induces type II transformed foci in C3H/10T1/2 cells when cells were treated with C(5)0292202 incorporated into lipid vesicles. The methods for lipid vesicle incorporation described here are effective in delivering hydrophobic petroleum fractions to cells and provide an alternative to the current inefficient and artifactual methods of emulsification currently used. With further validation and standardization, lipid vesicle incorporation of petroleum fractions and treatment of cells with these vesicles should be useful for studying the genotoxicity of complex hydrophobic mixtures in cell culture systems.

Magnetic field dependence of intramolecular exciplex formation in polymethyelene-linked A–D systems

An extremely large increase of exciplex fluorescence intensity has been observed with photoexcited compounds pyrene-(CH 2) n - DMA in acetonitrile when an external magnetic field of several hundred gauss is applied. The effect is readily explained as originating from the radical ion pair which can undergo a magnetic-field-dependent singlet-triplet conversion due to nuclear hyperfine coupling, or an association to form the exciplex. The increasing influence of the exchange interaction in the radical ion pair with decreasing chain length (CH 2) n is evident.

Annual rates of deposition of polycyclic aromatic hydrocarbons in different forest ecosystems

Using the flux balance of the forest canopy of a beech and a spruce stand annual rates of total deposition — divided into precipitation and interception deposition — were derived for 4 polycyclic aromatic hydrocarbons (PAH). The deposition of PAH is in general higher under spruce because of higher rates of interception deposition as compared to beech. The rate of interception deposition of the various PAH compounds (3.4-Benzopyrene, Indeno (1,2,3-cd)pyrene,1.12 Benzoperylene, Fluoranthene) are significantly different. Substantial amounts of PAH are transferred to the soil by litterfall, which indicates adsorption of PAH on leaf and needle surfaces.

The order–disorder transformation in the π-molecular compound pyrene:pyromellitic dianhydride

The order–disorder transformation in the π-molecular compound pyrene:pyromellitic dianhydride

A concept to explain the variation of the triplet zero-field splitting parameters with the structure of aromatic hydrocarbons in terms of local benzenoid characteristics

The zero-field splitting (ZFS) parameters D and E of the lowest electronically excited triplet state T 1 of a series of systematically selected pyrene derivatives have been determined by ODMR techniques. With this class of compounds as an example we intended to gain some insight into the variation of the ZFS-parameters with the structure and topology of aromatic hydrocarbons. The variation of the experimental ZFS-parameters could be explained in terms of the dipole—dipole model together with criteria describing the local benzene likeness of single C 6-rings in the molecule. For these the character orders according to Polansky were calculated on an MO-basis and the local benzenoid indices according to Randić on a graph-theoretical basis. As these quantities for the local aromaticity were in accordance with Clar's qualitative sextet concept a qualitative principle could be formulated explaining the variation of the D-parameter with molecular structure. This principle correctly describes all known D-parameters of aromatic molecules measured so far. So for the first time, a clear and consistent explanation for the variation of D with molecular structure can be given. Also for the E-parameter a connection with molecular structure could be established; it could be demonstrated in which way the criteria of local aromaticity mentioned can be applied to decide on the sign of E. For the acene-analogue pyrene derivatives linear correlations could be established between the averaged local quantities and the ZFS-parameters D and E. These correlations allow a quantitative determination of the ZFS-parameters of further analogue pyrene compounds. Also for other series of aromatic hydrocarbons such correlations could be found as shown for the polyacene series as an example. For the latter also a strong similarity to the series of the acene-analogue pyrene derivatives was found. D- and E-values are given for the six molecules pentacene to decacene. These were calculated from both the correlation with the character orders and that with the Randić-indices, and the result of both methods are compared.

A Gas Liquid Chromatographic Fluorescent Procedure for the Analysis of Benzo(A)Pyrene in 24 Hour Atmospheric Particulate Samples

Abstract This paper describes a selective method for the assay of benzo(a)pyrene (BaP) in 24 hour particulate samples. Benzo(a)pyrene is partially separated from the other polynuclear aromatic hydrocarbons via gas chromatography and then is completely resolved optically from traditionally difficult to resolve compounds (benzo(e)pyrene, perylene, benzo(k)fluoranthene) by means of a gas phase fluorescent detector. Ambient air concentrations as low as 20 picograms per cubic meter of air can be assayed with this gas chromatographic - gas phase fluorescent detection system.

Über die Photoleitung flüssiger Aromaten bei Anregung des Triplett-Zustandes

Irradiation of the aromatic compounds Benzene, Naphthalene, Biphenyl, Pyrene, and Benzophenone in the liquid state with a Xenon-arc-lamp produces a photocurrent, if an external d. c. voltage is applied. This current is independent of the dark-conductivity and increases linearily with light-intensity. It does not appear, if blocking quartz electrodes are used. The spectral response curve shows one peak at the wavelength of the forbidden singlet-triplet absorption-band of the compound and another at the longwave-edge of the singlet-absorption-region. A model is proposed basing on the idea of triplet-exciton formation (T1) by direct S0—T1 transitions and by transitions from S1 to T1 states (intersystem-crossing). The triplet exciton can migrate to the electrodes and dissociate there for energetic reasons. The released electron is received by the electrode. The cation remains either in the liquid or recombines with the electron. The cation can contribute to the photocurrent only when the dissociation has happened at the anode. In agreement with the measurements, dissociation requires conducting electrodes and follows monomolecular kinetics.