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PubMed2005

Novel glassy tetra(N-alkyl-3-bromocarbazole-6-yl)silanes as building blocks for efficient and nonaggregating blue-light-emitting tetrahedral Materials.

[structure: see text] Tetrahedral precursors of tetra(N-alkyl-3-bromocarbazole-6-yl)silanes (1-3), which were amorphous with T(g) being adjustable by changing the chain length of the N-substitutent, were developed. Fluorene-conjugated glassy compound 4 and hyperbranched polymer 5 were synthesized from the precursors via Suzuki coupling reaction. 4 and 5 emitted blue light efficiently in the condensed state with high quantum efficiencies of 80 (4) and 59% (5) and small fwhm (full width at half-maximum) of 48 (4) and 55 nm (5), indicating that they did not pack into detrimental aggregates in the solid state.

Journal Article↗
PubMed2006

Facile synthesis of complicated 9,9-diarylfluorenes based on BF3.Et2O-mediated Friedel-Crafts reaction.

[reaction: see text] BF3.OEt2-mediated Friedel-Crafts reaction of 9-phenyl-fluoren-9-ol with electron-rich aromatic substrates to prepare a new family of complicated 9,9-diarylfluorenes is described. The 9,9-diarylfluorenes tethered with various functional substituents, e.g., bulky spiro units, hole-transporting moieties, and fluorescent dyes, will be promising building blocks for the construction of optoelectronic materials.

Journal Article↗
PubMed2006

Pd(OAc)(2)-catalyzed Domino reactions of 1-chloro-2-haloarenes and 2-haloaryl tosylates with hindered Grignard reagents via palladium-associated arynes.

The palladium-associated aryne generation strategy and Pd(OAc)(2)-catalyzed annulative Domino reactions of 1-chloro-2-halobenzenes and 2-haloaryl tosylates with hindered Grignard reagents via palladium-associated arynes are described. The palladium-associated aryne generation strategy described here not only allows the high yield, one-step access to potentially useful substituted fluorenes from readily available 1-chloro-2-halobenzenes and 2-haloaryl tosylates, but may also lead to the development of other tandem reactions based on these readily available ortho leaving group bearing haloarenes. [reaction: see text]

Benzene Derivatives↗
PubMed2006

Cationic dithieno[3,2-b:2',3'-d]phospholes: a new building block for luminescent, conjugated polyelectrolytes.

Cationic dithieno[3,2-b:2',3'-d]phospholes are accessible very efficiently by methylation of the phosphorus center. Further functionalization with bromo substituents in 2,6-positions affords a polymerizable monomer that can be copolymerized with a difunctionalized fluorene in a Suzuki-Miyaura-type cross-coupling protocol. The monomers as well as the resulting conjugated polyelectrolyte based on the phospholium units show very intriguing photoluminescence properties, even in the solid state. [structure: see text]

Journal Article↗
PubMedDate not supplied

A metabolically competent human cell line expressing five cDNAs encoding procarcinogen-activating enzymes: application to mutagenicity testing.

A human B-lymphoblastoid cell line, designated MCL-5, constitutively expressing human cytochrome P-450 CYP1A1 and also expressing five transfected human cDNAs encoding drug-metabolizing enzymes, has been developed. cDNAs encoding CYP1A2, CYP2A6, and microsomal epoxide hydrolase (mEH) were introduced by using a vector conferring hygromycin B resistance, and cDNAs encoding CYP2E1 and CYP3A4 were introduced by using a vector conferring resistance to 1-histidinol. MCL-5 cells stably expressed all five cDNAs and the native CYP1A1 as determined by measurement of form-specific enzyme activity levels. The mutagenicity of seven model procarcinogens to MCL-5 cells was examined at the hypoxanthine guanine phosphoribosyltransferase (hprt) and thymidine kinase (tk) loci. Exposure to benzo[a]pyrene (BP), 3-methylcholanthrene (3MC), N-nitrosodimethylamine (NDMA), N-nitrosodiethylamine (NDEA), aflatoxin B1, (AFB1), 2-(acetylamino)fluorene (AAF), or benzidine (BZD) induced a statistically significant increase in mutant frequency. Linear interpolation of the concentration of procarcinogen necessary to produce a doubling of the mutant fraction at the hprt locus in MCL-5 cells and the parent AHH-1 cell line revealed that, for each of the chemicals examined, except BZD, MCL-5 cells were significantly more sensitive than the parent AHH-1 cells. The increase in sensitivity to mutagenicity ranged from 3-fold for AAF to greater than 40,000-fold for NDMA. MCL-5 cells have great potential as a screening system for the analysis of human procarcinogen/promutagen activation.

Carcinogenicity Tests↗
PubMedDate not supplied

Quantitation of base substitutions and deletions induced by chemical mutagens during DNA synthesis in vitro.

An experimental system has been developed by which base substitutions and frameshift deletions can be quantitated in vitro, using two-phase 20% polyacrylamide gel electrophoresis. Oligodeoxynucleotides, modified site-specifically, were used as templates in primer extension reactions catalyzed by DNA polymerase alpha, polymerase beta, and the Klenow fragment of Escherichia coli DNA polymerase I, with and without 3'-->5' exonuclease activity. Lesions studied included 7,8-dihydro-8-oxodeoxyguanosine, 7,8-dihydro-8-oxodeoxyadenosine, O6-methyldeoxyguanosine, N-(deoxyguanosin-8-yl)-2-(acetylamino)fluorene, and N-(deoxyguanosin-8-yl)-2- aminofluorene. Products of translesional synthesis contained dC, dA, dG, or dT opposite the lesion or one- and two-base deletions and were separated using a two-phase polyacrylamide gel system. When a template containing 8-oxoguanine was used, dAMP and/or dCAMP was incorporated opposite the lesion, the relative amounts depending on the DNA polymerase used. In contrast, the nonmutagenic base, dTMP, was incorporated exclusively opposite 8-oxodA in reactions catalyzed by Klenow fragment and pol alpha. The improved resolution provided by the two-phase gel system revealed misincorporation of dGMP opposite 8-oxodA in reactions catalyzed by pol beta. dTMP and small amounts of dCMP were incorporated opposite the lesion on an O6MedG-modified template. The bulky adduct, dG-C8-AAF, principally produced deletions; in contrast, dG-C8-AF promoted incorporation of dCMP, a nonmutagenic base. This experimental system should prove useful for establishing the miscoding potential of defined lesions in DNA templates and in correlating this information with the mutagenic properties of DNA adducts observed in cells.

Alkylating Agents↗
PubMedDate not supplied

Use of silica gels and mesoporous molecular sieves as supports for the solid-phase Claisen rearrangement.

A series of silica gels and mesoporous molecular sieves differing in both the range of particle size and mean pore size were derivatized with the p-[R,S-alpha-[1-(9H-fluoren-9-yl)-methoxyformamido]-2,4-di methoxybenzyl]- phenoxyacetic acid linker and their loading capacities were measured. Loading capacities ranging between 0.4-0.6 mmol Fmoc/g were achieved. Several of these silica based materials were derivatized with the hydroxymethyl benzoic acid linker and used as supports for the solid phase Claisen rearrangement of a support bound phenyl allyl ether. Both the silica gel and mesoporous supports were heated at 225 degrees C for 3 h to effect the Claisen rearrangement. The results showed that, compared to the same reaction run homogeneously, the silica gel support achieved similar total product yields and ratios for two Claisen products. The mesoporous supports were found to selectively produce one of the Claisen products over the other. Analysis shows that the molecules bound to the mesoporous support are physically further separated from each other as compared to those bound to the silica gel support. A mechanism is presented which accounts for the selectivity of the mesoporous support in forming one Claisen product over the other. The Claisen product was further derivatized to the resulting phenyl ethyl either through a solid phase Mitsunobu reaction on the mesoporous support.

Chemistry, Organic↗
PubMed2000

Combined ozonation and biodegradation for remediation of mixtures of polycyclic aromatic hydrocarbons in soil.

A study was conducted to investigate the feasibility of a combined treatment (i.e., ozonation and biodegradation) to overcome the inherent bacterial bioavailability limitation, and hence bioremediation limitation, of polycyclic aromatic hydrocarbons in soil. Ozonation was very efficient in the removal of naphthalene, fluorene, phenanthrene, and anthracene, but not for pyrene, chrysene, and benzo(a)pyrene from soil freshly spiked with the hydrocarbons. A similar result was obtained from coal tar-contaminated soil. Elimination of polycyclic aromatic hydrocarbons increased appreciably in sand containing 0.03% organic carbon, indicating the adverse effect of organic carbon on the efficiency of ozone treatment. In spiked and coal tar-contaminated soils, ozonation followed by biodegradation significantly increased the degradation of various polycyclic aromatic hydrocarbons including chrysene and benzo(a)pyrene which were not degraded by the test bacterial consortium alone. In particular, the effect of the combined treatment was more pronounced in coal tar-contaminated soil than in sterile soil spiked with hydrocarbons, probably due to the augmented biological activity of the introduced consortium. The results suggest that a combined treatment including ozonation and biodegradation may be a promising bioremediation technology in soil contaminated with mixtures of polycyclic aromatic hydrocarbons such as former manufactured gas plant sites.

Benzo(a)pyrene↗
PubMed2004

Chemical modification of hamster arylamine N-acetyltransferase 2 with isozyme-selective and nonselective N-arylbromoacetamido reagents.

Arylamine N-acetyltransferases (NATs) catalyze a variety of biotransformation reactions, including N-acetylation of arylamines and O-acetylation of arylhydroxylamines. Chemical modification of hamster recombinant NAT2 with 2-(bromoacetylamino)fluorene (Br-AAF) and bromoacetanilide revealed that Br-AAF is an affinity label for the enzyme whereas bromoacetanilide inactivates NAT2 through a bimolecular alkylation process. Electrospray ionization quadrupole time-of-flight mass spectrometry analysis of Br-AAF-treated NAT2 showed that a single molecule of 2-acetylaminofluorene had been adducted. Peptide sequencing with tandem mass spectrometry identified the catalytically essential Cys68 as the alkylated amino acid. Br-AAF exhibits similar affinity for hamster NAT1 and NAT2, but is a more effective inactivator of NAT1 because, subsequent to the formation of a reversible enzyme-Br-AAF complex, the rate of alkylation of NAT1 is greater than the rate of alkylation of NAT2. Bromoacetanilide alkylates Cys68 and, to a lesser extent, Cys237 of NAT2; it does not exhibit significant selectivity for either NAT1 or NAT2.

2-Acetylaminofluorene↗
PubMed1999

Ecology, physiology, and phylogeny of deep subsurface Sphingomonas sp.

Several new species of the genus Sphingomonas including S. aromaticivorans, S. stygia, and S. subterranea that have the capacity for degrading a broad range of aromatic compounds including toluene, naphthalene, xylenes, p-cresol, fluorene, biphenyl, and dibenzothiophene, were isolated from deeply-buried (>200 m) sediments of the US Atlantic coastal plain (ACP). In S. aromaticivorans F199, many of the genes involved in the catabolism of these aromatic compounds are encoded on a 184-kb conjugative plasmid; some of the genes involved in aromatic catabolism are plasmid-encoded in the other strains as well. Members of the genus Sphingomonas were common among aerobic heterotrophic bacteria cultured from ACP sediments and have been detected in deep subsurface environments elsewhere. The major source of organic carbon for heterotrophic metabolism in ACP deep aquifers is lignite that originated from plant material buried with the sediments. We speculate that the ability of the subsurface Sphingomonas strains to degrade a wide array of aromatic compounds represents an adaptation for utilization of sedimentary lignite. These and related subsurface Sphingomonas spp may play an important role in the transformation of sedimentary organic carbon in the aerobic and microaerobic regions of the deep aquifers of the ACP.

Journal Article↗
PubMed2002

Sensitization of singlet oxygen via encounter complexes and via exciplexes of pipi* triplet excited sensitizers and oxygen.

Both excited singlet states, 1sigma(g)+ and 1delta(g), and the triplet ground state, 3sigma(g)-, of molecular oxygen are competitively formed during the quenching by O2 of triplet (T1) excited sensitizers of sufficient energy. The corresponding overall rate constants kT(1sigma), kT(1delta), and kT(3sigma) as well as the T1 state energies E(T) and the oxidation potentials E(ox), have been determined for a series of six fluorene derivatives. Graduated and in part strong charge transfer (CT) effects on kT(1sigma), kT(1delta), and kT(3sigma) are observed. These and literature data strongly indicate that quenching occurs in two different channels each capable of producing O2(1sigma(g)-), O2(1delta(g)), and O2(3sigma(g)-). One proceeds via internal conversion (IC) of excited 1,3(T1 x 3sigma) complexes with no CT character (nCT), which cannot be distinguished from encounter complexes, the other via IC of 1,3(T1 x 3sigma) exciplexes with partial CT character (pCT). The contributions of nCT and pCT deactivation channels to the overall formation of O2(1sigma(g)+), O2(1delta(g)). and O2(3sigma(g)-) depend on E(T) and E(ox). The rate constants of the nCT channel are controlled by the excess energies of the respective IC processes by an energy gap law. The rate constants of the pCT channel depend on the change of free energy deltaG(CET) for complete electron transfer from T1 excited sensitizer to O2. Equations are presented which show the functional form of the dependence of the oxygen quenching rate constants on E(T) and E(ox). Particular emphasis is laid on the question of whether these relations could generally be valid for pipi* triplet sensitizers.

Journal Article↗
PubMed2002

Exposure of garbage truck drivers and maintenance personnel at a waste handling centre to polycyclic aromatic hydrocarbons derived from diesel exhaust.

Exposure to diesel exhaust was evaluated in summer and winter by measuring vapour and particle phase polycyclic aromatic hydrocarbons (PAHs). Fifteen PAHs were simultaneously determined from the air samples obtained from truck drivers collecting household waste and maintenance personnel at a waste handling centre. The major compounds analysed from the personal air samples of exposed workers were naphthalene, phenanthrene and fluorene. The total PAH exposure (sum of 15 PAHs) of garbage truck drivers ranged from 71 to 2,660 ng m(-3) and from 68 to 900 ng m-3 in the maintenance work. The exposure of garbage truck drivers to benzo[a]pyrene (B[a]P) ranged from the mean of 0.03 to 0.3 ng m(-3) whereas no B[a]P in control samples or in those collected from maintenance workers was detected. A statistically significant difference in diesel-derived PAH exposure between the garbage truck drivers and the control group in both seasons (in summer p = 0.0022, degrees of freedom (df) 70.5; and in winter p < 0.0001, df = 80.4) was observed. Also, a significant difference in PAH exposure between the garbage truck drivers and the maintenance workers (in summer p < 0.0001, df = 50.1; and in winter p < 0.0001, df = 44.2) was obtained.

Adult↗
PubMed2003

Solid-phase microextraction to monitor the sonochemical degradation of polycyclic aromatic hydrocarbons in water.

Solid-phase microextraction (SPME) coupled with GC-MS has been used to monitor the degradation of polycyclic aromatic hydrocarbons (PAHs) by ultrasound treatment. Immersion SPME sampling enabled the fast and solventless extraction of target contaminants at the low microg l(-1) concentration level. The developed protocol was found to be linear in the concentration range from 0.1 to 50 microg l(-1) for most target analytes, with the limits of detection ranging between 0.01 and 0.70 microg l(-1) and the relative standard deviations between 4.31 and 27%. The developed SPME protocol was used to follow concentration profiles of aqueous solutions containing 16 PAHs, which were subject to low frequency ultrasonic irradiation. At the conditions employed in this study (80 kHz of ultrasound frequency, 130 W l(-1) of applied electric power density, 30 microg l(-1) of initial concentration for each of the 16 PAHs), sonochemical treatment was found capable of destroying the lower molecular weight PAHs (naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene and pyrene) within 120-180 min of irradiation. The higher molecular weight PAHs were more recalcitrant to ultrasound treatment.

Environmental Monitoring↗
PubMed2003

The decomposition of diazo-compounds induced by nucleophiles. The decomposition of 9-diazofluorene in the presence of hydroxide or alkoxide ions.

9-Diazofluorene, on treatment with stoichiometric or substoichiometric amounts of quaternary ammonium hydroxide or methoxide or of potassium t-butoxide in solution in aqueous or alcoholic dimethyl sulfoxide or acetonitrile at 30 degrees C, decomposes with evolution of nitrogen to yield fluorenone azine [bis(fluorenylidene)hydrazine] in almost quantitative yield. Studies are reported of the identity of the minor by-products, together with an examination of the kinetics of the reactions and additional spectroscopic experiments. The general rate equation is v = k[FIN2]3/2[Nu-]1/2, where Nu- represents the nucleophile. It is concluded that the oxyanions, most probably after nucleophilic attack on 9-diazofluorene under these basic conditions to generate a new anionic species, are capable of transferring an electron to the diazo-compound. This initiates decomposition of further diazo-molecules in a process of electron-transfer chain catalysis that bears some similarities to, but has also some differences from, that encountered using cathodic initiation. In support of this interpretation it is found that reactions can be accelerated by the introduction of carbon acids (fluorene, 9-phenylfluorene) into the reaction mixtures. The nature of the initiation, propagation and termination steps of the chain mechanism are discussed.

Journal Article↗
PubMed2004

Inclusion by a fluorenyl host with volatile guests: structures, thermal stability and kinetics.

The structures of the inclusion compounds formed by the host H = 9,9'-(biphenyl-4,4'-diyl)bis(fluoren-9-ol) with N,N-dimethylacetamide (H.2DMA and H.4DMA), 1,4-dioxane (H.3DIOX), methyl ethyl ketone (H.2MEK), as well as that of the apohost have been elucidated. The compounds were characterised by thermal analysis and solid state NMR, and the kinetics of desorption of H.4DMA, H.2DMA and H.3DIOX have been examined.

Journal Article↗
PubMed2004

Catechin and hydroxybenzhydrols as models for the environmental photochemistry of tannins and lignins.

The photochemistry of several model plant-derived compounds has been studied in aqueous solution. In particular, the reactions of catechin as a model tannin and methoxy-substituted hydroxybenzhydrols as model lignin functionalities were investigated. Tannins and lignins constitute a significant portion of the humic substances in aquatic systems, which are themselves the main component of dissolved organic matter thought to be responsible for the absorption and attenuation of light in these environments. Catechin (1) was found to undergo a reversible photoisomerization reaction to give epicatechin (2). Such a reaction is an explicit example of a photon absorbing process that enables catechin (1) and its derivatives to act as natural sunscreens by attenuating light energy through non-destructive reactions. The methoxy-substituted hydroxybenzhydrols were found to undergo photosolvolysis reactions via efficient generation of quinone methide intermediates. The intermediate quinone methides were observed to be longer lived, and thus more stable, than previously studied hydroxybenzhydrol derivatives. The meta-hydroxybenzhydrol isomer (5) was found to undergo additional chemistry leading to the production of a ring-closed fluorene from the quinone methide intermediate.

Journal Article↗