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PubMed2005

Influence of molecular weight on the phase behavior and structure formation of branched side-chain hairy-rod polyfluorene in bulk phase.

We report on an experimental study of the self-organization and phase behavior of hairy-rod pi -conjugated branched side-chain polyfluorene, poly[9,9-bis(2-ethylhexyl)-fluorene-2,7-diyl]-i.e., poly[2,7-(9,9-bis(2-ethylhexyl)fluorene] (PF2/6) -as a function of molecular weight (M(n)) . The results have been compared to those of phenomenological theory. Samples for which M(n) =3-147 kg/mol were used. First, the stiffness of PF2/6 , the assumption of the theory, has been probed by small-angle neutron scattering in solution. Thermogravimetry has been used to show that PF2/6 is thermally stable over the conditions studied. Second, the existence of nematic and hexagonal phases has been phenomenologically identified for lower and higher M(n) (LMW, M(n) < M(*)(n) and HMW, M(n) > M(*)(n) ) regimes, respectively, based on free-energy argument of nematic and hexagonal hairy rods and found to correspond to the experimental x-ray diffraction (XRD) results for PF2/6 . By using the lattice parameters of PF2/6 as an experimental input, the nematic-hexagonal transition has been predicted in the vicinity of glassification temperature (T(g)) of PF2/6 . Then, by taking the orientation parts of the free energies into account the nematic-hexagonal transition has been calculated as a function of temperature and M(n) and a phase diagram has been formed. Below T(g) of 80 degrees C only (frozen) nematic phase is observed for M(n)< M(*)(n) = 10(4) g/mol and crystalline hexagonal phase for M(n) > M(*)(n) . The nematic-hexagonal transition upon heating is observed for the HMW regime depending weakly on M(n) , being at 140-165 degrees C for M(n) > M(*)(n). Third, the phase behavior and structure formation as a function of M(n) have been probed using powder and fiber XRD and differential scanning calorimetry and reasonable semiquantitative agreement with theory has been found for M(n) >or=3 kg/mol. Fourth, structural characteristics are widely discussed. The nematic phase of LMW materials has been observed to be denser than high-temperature nematic phase of HMW compounds. The hexagonal phase has been found to be paracrystalline in the (ab0) plane but a genuine crystal meridionally. We also find that all these materials including the shortest 10-mer possess the formerly observed rigid five-helix hairy-rod molecular structure.

Journal Article↗
PubMed2001

1,1-Di(9-fluorenyl)ethanol, a by-product from the acetylation of 9-fluorenyllithium.

Treatment of 9-fluorenyllithium with acetyl chloride produces 9-acetylfluorene, (I), and several by-products. Among them is a compound unequivocally identified for the first time as the addition product of (I) with 9-fluorenyllithium, 1,1-di(9-fluorenyl)ethanol, C(28)H(22)O, (II). The two fluorene-ring planes of (II) are essentially perpendicular [89.90 (9) degrees ]. A number of intermolecular non-bonding distances are well within or close to the sum of their respective van der Waals radii and may be responsible for the rarely observed large bowing of one of the fluorene rings. This bowing apparently arises from two molecules impinging on the convex face of the bowed ring, augmented by hydrogen bonding between the peripheral pi electrons of the concave face and the hydroxyl H atom of another molecule adjacent to that face.

Journal Article↗
PubMed2001

Cocrystals of 2-(2,4,5,7-tetranitrofluoren-9-ylidene)propanedinitrile and 2,4,5,7-tetranitrofluoren-9-one with chlorobenzene.

Crystallization of 2,4,5,7-tetranitro-9-(dicyanomethylene)fluorene [DTeF; systematic name: 2-(2,4,5,7-tetranitrofluorene-9-ylidene)propanedinitrile] and 2,4,5,7-tetranitrofluoren-9-one (TeNF) from chlorobenzene in the presence of pi-donor compounds yielded the chlorobenzene solvate, C(16)H(4)N(6)O(8) x C(6)H(5)Cl, and the bis(chlorobenzene) solvate, C(13)H(4)N(4)O(9) x 2C(6)H(5)Cl, respectively. Both structures comprise mixed stacks of twisted fluorene moieties interspersed with nearly parallel chlorobenzene molecules. Solvent-free crystals of DTeF and TeNF were obtained from pure chlorobenzene.

Journal Article↗
PubMed1996

Oxidation of naphthenoaromatic and methyl-substituted aromatic compounds by naphthalene 1,2-dioxygenase.

Oxidation of acenaphthene, acenaphthylene, and fluorene was examined with recombinant strain Pseudomonas aeruginosa PAO1(pRE695) expressing naphthalene dioxygenase genes cloned from plasmid NAH7. Acenaphthene underwent monooxygenation to 1-acenaphthenol with subsequent conversion to 1-acenaphthenone and cis- and trans-acenaphthene-1,2-diols, while acenaphthylene was dioxygenated to give cis-acenaphthene-1,2-diol. Nonspecific dehydrogenase activities present in the host strain led to the conversion of both of the acenaphthene-1,2-diols to 1,2-acenaphthoquinone. The latter was oxidized spontaneously to naphthalene-1,8-dicarboxylic acid. No aromatic ring dioxygenation products were detected from acenaphthene and acenaphthylene. Mixed monooxygenase and dioxygenase actions of naphthalene dioxygenase on fluorene yielded products of benzylic 9-monooxygenation, aromatic ring dioxygenation, or both. The action of naphthalene dioxygenase on a variety of methyl-substituted aromatic compounds, including 1,2,4-trimethylbenzene and isomers of dimethylnaphthalene, resulted in the formation of benzylic alcohols, i.e., methyl group monooxygenation products, which were subsequently converted to the corresponding carboxylic acids by dehydrogenase(s) in the host strain. Benzylic monooxygenation of methyl groups was strongly predominant over aromatic ring dioxygenation and essentially nonspecific with respect to the substitution pattern of the aromatic substrates. In addition to monooxygenating benzylic methyl and methylene groups, naphthalene dioxygenase behaved as a sulfoxygenase, catalyzing monooxygenation of the sulfur heteroatom of 3-methylbenzothiophene.

Journal Article↗
PubMed2001

Engineering cytochrome P450 BM-3 for oxidation of polycyclic aromatic hydrocarbons.

Cytochrome P450 BM-3, a self-sufficient P450 enzyme from Bacillus megaterium that catalyzes the subterminal hydroxylation of long-chain fatty acids, has been engineered into a catalyst for the oxidation of polycyclic aromatic hydrocarbons. The activities of a triplet mutant (A74G/F87V/L188Q) towards naphthalene, fluorene, acenaphthene, acenaphthylene, and 9-methylanthracene were 160, 53, 109, 287, and 22/min, respectively. Compared with the activities of the wild type towards these polycyclic aromatic hydrocarbons, those of the mutant were improved by up to 4 orders of magnitude. The coupling efficiencies of the mutant towards naphthalene, fluorene, acenaphthene, acenaphthylene, and 9-methylanthracene were 11, 26, 5.4, 15, and 3.2%, respectively, which were also improved several to hundreds fold. The high activities of the mutant towards polycyclic aromatic hydrocarbons indicate the potential of engineering P450 BM-3 for the biodegradation of these compounds in the environment.

Bacillus megaterium↗
PubMed2003

Degradation of polycyclic aromatic hydrocarbons at low temperature under aerobic and nitrate-reducing conditions in enrichment cultures from northern soils.

The potential for biodegradation of polycyclic aromatic hydrocarbons (PAHs)at low temperature and under anaerobic conditions is not well understood, but such biodegradation would be very useful for remediation of polluted sites. Biodegradation of a mixture of 11 different PAHs with two to five aromatic rings, each at a concentration of 10 micro g/ml, was studied in enrichment cultures inoculated with samples of four northern soils. Under aerobic conditions, low temperature severely limited PAH biodegradation. After 90 days, aerobic cultures at 20 degrees C removed 52 to 88% of the PAHs. The most extensive PAH degradation under aerobic conditions at 7 degrees C,53% removal, occurred in a culture from creosote-contaminated soil. Low temperature did not substantially limit PAH biodegradation under nitrate-reducing conditions. Under nitrate-reducing conditions,naphthalene, 2-methylnaphthalene, fluorene, and phenanthrene were degraded. The most extensive PAH degradation under nitrate-reducing conditions at 7 degrees C, 39% removal, occurred in a culture from fuel-contaminated Arctic soil. In separate transfer cultures from the above Arctic soil, incubated anaerobically at 7 degrees C, removal of 2-methylnaphthalene and fluorene was stoichiometrically coupled to nitrate removal. Ribosomal intergenic spacer analysis suggested that enrichment resulted in a few predominant bacterial populations,including members of the genera Acidovorax,Bordetella, Pseudomonas, Sphingomonas, and Variovorax. Predominant populations from different soils often included phylotypes with nearly identical partial 16S rRNA gene sequences (i.e., same genus) but never included phylotypes with identical ribosomal intergenic spacers (i.e., different species or subspecies). The composition of the enriched communities appeared to be more affected by presence of oxygen, than by temperature or source of the inoculum.

Aerobiosis↗
PubMed1984

Carcinogen induced unscheduled DNA synthesis in mouse hepatocytes.

Mouse primary liver cell cultures were examined for evidence of unscheduled DNA synthesis (UDS) following treatment with the carcinogens; dimethylnitrosamine (DMNA), diethylnitrosamine (DENA), 2-acetylaminofluorene (2-AAF), N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), benzo(a)pyrene (BP), dimethylbenzanthracene (DMBA), 1,1,-bis(p-chlorophenyl)-2,2,2-trichloroethane (DDT), safrole, diethylstilbestrol (DES), aflatoxin B1 (AFB1), and dieldrin and the noncarcinogens; dimethylformamide (DMF), fluorene, and pyrene. Mouse hepatocyte cultures were simultaneously treated with three concentrations of each compound and 3H-thymidine. After 24 hrs, cells were fixed and processed for autoradiography. 3H-thymidine incorporation in both experimental and control cell nuclei, as evidenced by autoradiographic grains, was quantitated microscopically. DMNA, DENA, 2-AAF, MNNG, BP, AFB1 and DMBA significantly increased UDS over untreated cells at all concentrations studied. DDT, DMF, fluorene, pyrene, safrole, DES, and dieldrin were negative for UDS in all concentrations examined. DMNA, 2-AAF and MNNG were also studied for UDS induction in 2 hr old, 1 day old and 4 day old cultures. A progressive decrease in UDS with increased time after plating was found in DMNA and 2-AAF treated cultures. After 4 days DMNA and 2-AAF induced UDS only at the highest concentrations examined (10(-3) M and 10(-4) M respectively). MNNG induced UDS at all time periods and concentrations sampled. An attempt to enhance the sensitivity of the UDS assay by inducing the mixed function oxidative enzyme activity in the hepatocytes with phenobarbital administered in vivo resulted in no statistically significant increase in UDS with DMNA, 2-AAF, MNNG, DDT, and dieldrin when compared with cells from non-induced animals.

Animals↗
PubMed2006

Toxic effects and oxidative stress in higher plants exposed to polycyclic aromatic hydrocarbons and their N-heterocyclic derivatives.

N-heterocyclic derivatives of polycyclic aromatic hydrocarbons (NPAHs) are widespread concomitantly with their parent analogues and have been detected in air, water, sediments, and soil. Although they were shown to be highly toxic to some organisms, our understanding of their occurrence, environmental fate, biological metabolism, and effects is limited. This study evaluated toxic effects of three homocyclic aromatic hydrocarbons (PAHs-phenanthrene, anthracene, fluorene) and their seven N-heterocyclic derivates on higher terrestrial plants Sinapis alba, Triticum aestivum, and Phaseolus vulgaris. Germinability, morphological endpoints, parameters of detoxification, and antioxidant components of plant metabolism as well as lipid peroxidation were studied in acute phytotoxicity tests. Phytotoxicity of NPAHs was generally more pronounced than the effects of parent PAHs, and it significantly differed with respect to the structure of individual NPAHs. Sinapis alba and T. aestivum were more sensitive plant species than P. vulgaris. Chemicals with the strongest inhibition effect on germination and growth of plants were phenanthridine, acridine, benzo[h]quinoline, and 1,10- and 1,7-phenanthroline. All tested chemicals significantly induced activities of detoxification and antioxidant enzymes (glutathione reductase, glutathione peroxidase, and glutathione-S-transferase) at nanomolar to low micromolar concentrations. Levels of reduced glutathione were induced by all tested chemicals except 1,10- and 4,7-phenanthroline. Furthermore, fluorene, carbazole, acridine, phenanthrene, phenanthridine, benzo[h]quinoline, and 1,7-phenanthroline significantly increased lipid peroxidation. The results of our study newly demonstrate significant toxicity of NPAHs to plants and demonstrate suitability of multiple biomarker assessment to characterize mechanisms of oxidative stress and to serve as an early warning of phytotoxicity in vivo.

Biomass↗
PubMed2006

Polycyclic aromatic hydrocarbons in fresh and cold-smoked Atlantic salmon fillets.

The occurrence of polycyclic aromatic hydrocarbons (PAHs) in smoked fish as a consequence of cold smoking was studied. Raw fillets of Salmo salar from Norway or the Irish Sea were sampled in a modern smokehouse and examined for PAH content. The same fillets, labeled with an identification number, were sampled immediately after the smoking process and analyzed. Among the investigated compounds, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, benz[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, and benzo[ghi]perylene were detected in both raw and smoked fillets. No significant difference (P < 0.01) was observed between raw and smoked samples in the concentrations of six PAHs, but significant differences were found for fluorene, anthracene, fluoranthene, benz[a]anthracene, and benzo[ghi]perylene. Results confirm that PAHs concentrations in smoked fish are the product of both sea pollution and the smoking process. A modern smoking plant with an external smoke generator and a mild treatment as described here will not add significantly to the concentration of PAHs, except for some compounds.

Animals↗
PubMed1999

Design and synthesis of stable, water soluble radicals as potential anti-cancer agents.

A free diazafluorenyl radical based on the Koelsch free radical was designed and synthesized with expectations of stability and water solubility. The novel radical precursors were synthesised from the parent brominated stilbene and the substituted fluorenes in an IPSO substitution, as a key synthetic step. The precursors were deprotonated and the anion was discharged by an aqueous solution of potassium cyanoferrate. The new radicals were prepared from fluorene in 6 steps with good overall yields. These radicals have shown promising anticancer activity in initial screenings on 2 different MAC cell lines.

Antineoplastic Agents↗
PubMed2001

Effects of polycyclic aromatic compounds on the drought tolerance of Folsomia fimetaria (Collembola, Isotomidae).

Drought tolerance (survival at 98.2% relative humidity and 20 degress C) was investigated for adult individuals of the springtail Folsomia fimetaria after three weeks of exposure to different polycyclic aromatic compounds (PACs). Seven PACs were investigated (acridine, dibenzofuran, carbazole, fluorene, dibenzothiophene, fluoranthene, and pyrene), with each substance used at several exposure concentrations. Sublethal concentrations of dibenzothiophene, fluorene, fluoranthene, and pyrene caused a dose-related decrease in drought tolerance in exposed adults, whereas no such relationship was found for acridine, dibenzofuran, and carbazole. The organisms used in the drought tolerance study were taken directly from standard ecotoxicity tests that had just been completed, hence the concentrations causing subsequent effects on drought tolerance and those affecting survival and reproduction in the ecotoxicity tests could be compared. Some of the tested substances significantly reduced the drought tolerance of F. fimetaria at concentrations that had little effect on survival, indicating a synergistic effect of the two stressors. However, drought tolerance was affected at concentrations below the threshold value for toxicity in standard tests (no-observed-effect concentration for reproduction) only for dibenzothiophene. In the field, soil organisms exposed to contaminants also face multiple environmental stressors such as drought and cold. Because the reduced drought tolerance is a side effect of chemical exposure, such effects should be considered when extrapolating from laboratory to field conditions.

Adaptation, Physiological↗
PubMed2003

Three-dimensional distribution of GFP-labeled Pseudomonas putida during biofilm formation on solid PAHs assessed by confocal laser scanning microscopy.

Confocal laser scanning microscopy was used to monitor the colonization pattern of the gfp-labeled derivative strain of Pseudomonas putida ATCC 17514 on fluorene and phenanthrene crystals. The in situ experiments showed that P. putida tends to grow directly on phenanthrene, forming a biofilm on accessible crystalline surfaces. On the other hand, no significant biofilm formation was observed in the presence of fluorene. The results obtained showed that substrate properties affected bacterial strategy regarding uptake.

Biofilms↗
PubMed2006

[Prediction of PAHs uptake by ryegrass with a partition-limited model].

The performance of a partition-limited model on prediction of four PAHs (acenaphthene, fluorene, phenanthrene and pyrene) uptake by ryegrass simultaneously was evaluated using a hydroponic system. Results suggest that the model has a good performance on prediction of PAHs uptake. However, the model focused on root translocation only, while excluded foliar uptake, which resulted in a poor performance on prediction of PAHs in shoots. The differences of simulated and experimented concentrations of PAHs were less than 57.4% for roots and less than 98.5% for shoots respectively. If the influence of foliar uptake on the performance of the model was taken into account, the differences for all the four PAHs would be reduced significantly. Since the influence of foliar uptake increased with the increase of the hydrophobic property of the PAHs, the differences decreased with an order of pyrene> phenanthrene> fluorene> acenaphthene, among which the maximum difference for pyrene decreased from 98.5% down to 69.4%.

Biodegradation, Environmental↗
PubMed1989

Localization of DNA repair synthesis by human cell extracts to a short region at the site of a lesion.

Double-stranded bacteriophage M13 DNA molecules were constructed containing a single specifically placed 2-(acetylamino)fluorene adduct or a single 4'-hydroxymethyl-4,5',8-trimethylpsoralen monoadduct. These circular DNA molecules were used to analyze in vitro DNA repair synthesis by cell extracts from normal human lymphoid cell lines. Both types of lesions stimulate DNA repair synthesis at the site of the adduct. DNA repair synthesis induced by the 2-(acetyl-amino)fluorene adduct took place in the damaged strand and was confined to a region within a 31-base pair restriction fragment around the adduct.

2-Acetylaminofluorene↗
PubMed1998

Chemical synthesis and characterization of the sweet protein mabinlin II.

The sweet protein mabinlin II isolated from the seeds of Capparis masaikai consists of the A chain with 33 amino acid residues and the B chain composed of 72 residues. The B chain contains two intramolecular disulfide bonds and is connected to the A chain through two intermolecular disulfide bridges. The A chain was synthesized by the stepwise fluoren-9-ylmethoxycarbonyl (Fmoc) solid-phase method in a yield of 5.9%, while the B chain was synthesized by a combination of the stepwise Fmoc solid-phase method and fragment condensation in a yield of 6.0%. Disulfide formation and combination of the A and B chains followed by purification by ion-exchange high-performance liquid chromatography (HPLC) gave mabinlin II in a yield of 47.4%. The characterization of the synthetic mabinlin II by HPLC, electrospray ionization mass spectrometry, amino acid analysis, and disulfide bond determination fully supported the expected structure. A 0.1% solution of the synthetic mabinlin II had an astringent-sweet taste.

Amino Acid Sequence↗
PubMed2000

The crystal structure of Afc-containing peptides.

A systematic structural analysis of Afc (9-amino-fluorene-9-carboxylic acid) containing peptides is here reported. The crystal structures of four fully protected tripeptides containing the Afc residue in position 2: Z-X(1)-Afc(2)-Y(3)-OMe (peptide a: X = Y = Gly; peptide b: X = Aib, C(alpha, alpha)-dimethylglycine, Y = Gly; peptide c: X = Gly, Y = Aib; peptide d: X = Y = Aib) have been solved by x-ray crystallography. All the results suggest that the Afc residue has a high propensity to assume an extended conformation. In fact, the Afc residue adopts an extended conformation in three peptides examined in this paper (peptides a-c). In contrast, Afc was found in a folded conformation, in the 3(10)-helical region, only in the peptide d, in which it is both preceded and followed by the strong helix promoting Aib.

Amino Acids↗
PubMed2004

Synthesis and characterization of monodisperse oligofluorenes.

An efficient synthesis of 9,9-bis(2-ethylhexyl)fluorene oligomers up to the heptamer is reported, with repetitive Suzuki and Yamamoto coupling reactions employed in the synthesis. The key steps for preparation of the essential intermediates include Pd-catalyzed transformation of aryl bromides to aryl boronic esters (Miyaura reaction) and the application of the much higher reactivity of aryl boronic esters over aryl bromides in the Pd-catalyzed cross-coupling reaction with aryl diazonium salts. Variation of the UV/Vis absorption and photoluminescence characteristics with chain length is reported. Moreover, glass transition and liquid-crystal characteristics of the oligomers are described and compared with those of the polymer.

Cross-Linking Reagents↗
PubMed2006

Twin probes as a novel tool for the detection of single-nucleotide polymorphisms.

Single-nucleotide polymorphisms (SNPs) are the most common form of DNA sequence variation. There is a strong interest from both academy and industry to develop rapid, sensitive and cost effective methods for SNP detection. Here we report a novel structural concept for DNA detection based on fluorescence dequenching upon hybridization. The so-called "twin probe" consists of a central fluorene derivative as fluorophore to which two identical oligonucleotides are covalently attached. This probe architecture is applied in homogeneous hybridization assays with subsequent fluorescence spectroscopic analysis. The bioorganic hybrid structure is well suited for sequence specific DNA detection and even SNPs are identified with high efficiency. Additionally, the photophysical properties of the twin probe were investigated. The covalent attachment of two single stranded oligonucleotides leads to strong quenching of the central fluorescence dye induced by the nucleobases. The twin probe is characterized by supramolecular aggregate formation accompanied by red-shifted emission and broad fluorescence spectra.

Biochemistry↗