Distribution by Scientific Domains
Distribution within Chemistry

Kinds of Tert

  • methyl tert
  • potassium tert

  • Selected Abstracts

    Genetic variation, nucleotide diversity, and linkage disequilibrium in seven telomere stability genes suggest that these genes may be under constraint,,

    HUMAN MUTATION, Issue 4 2005
    Sharon A. Savage
    Abstract To maintain chromosomal integrity and to protect the ends of chromosomes against recognition as damaged DNA, end-to-end fusion, or recombination, a coordinated set of genes is required to stabilize the telomere. We surveyed common genetic variation in seven genes that are vital to telomere stability (TERT, POT1, TNKS, TERF1, TINF2, TERF2, and TERF2IP) and validated single nucleotide polymorphisms (SNPs) in four different ethnic groups (n=118 total). Overall, our data show limited degrees of nucleotide diversity in comparison with data from other gene families. We observed that these genes are highly conserved in sequence between species, and that for nearly all of the coding SNPs the most common allele is ancestral (i.e., it is observed in primate sequences). Our findings support the hypothesis that genetic variation in a pathway that is critical for telomere stability may be under constraint. These data establish a foundation for further investigation of these genes in population-genetics, evolution, and disease-association studies. Hum Mutat 26(4), 343,350, 2005. Published 2005, Wiley-Liss, Inc. [source]

    A new multiparameter assay to assess HPV 16/18, viral load and physical status together with gain of telomerase genes in HPV-related cancers

    Wendy Theelen
    Abstract Oncogenic human papillomavirus (HPV) is the most important risk factor for cancer of the uterine cervix and a subgroup of head and neck cancers. Viral load has been associated with persistence of infection, whereas integration of HPV into the host cell genome is associated with transition to invasive disease. Viral integration is frequently correlated with loss of viral E2 and gain of the telomerase-related genes TERC and TERT. The objective of this study was to develop a rapid and sensitive multiplex ligation-dependent probe amplification (MLPA) assay for the simultaneous analysis of viral load, integration and copy number gain of TERC and TERT in HPV16/18-associated lesions. The performance of the assay was tested for HPV vs. human gene copy number ratios ranging from 0.1 to 100 and for percentages of integration ranging from 0 to 100%. The model systems used include plasmid mixtures and the HPV-positive cell lines SiHa, HeLa and CaSki described to contain a range of 2,600 viral copies per cell. In samples with low-viral load, viral integration can be reliably determined when more than 30% of the virus is integrated. Gain of the telomerase-related genes in the cell lines as determined by our MLPA assay was in accordance with data reported in the literature. Our study demonstrates that within a single MLPA-reaction viral type, load, integration and gain of TERC and TERT can be reliably determined, which will improve risk assessment for patients suspected for HPV infection. [source]

    Telomerase reverse transcriptase haploinsufficiency and telomere length in individuals with 5p, syndrome

    AGING CELL, Issue 5 2007
    Hong-Yan Du
    Summary Telomerase, which maintains the ends of chromosomes, consists of two core components, the telomerase reverse transcriptase (TERT) and the telomerase RNA (TERC). Haploinsufficiency for TERC or TERT leads to progressive telomere shortening and autosomal dominant dyskeratosis congenita (DC). The clinical manifestations of autosomal dominant DC are thought to occur when telomeres become critically short, but the rate of telomere shortening in this condition is unknown. Here, we investigated the consequences of de novo TERT gene deletions in a large cohort of individuals with 5p, syndrome. The study group included 41 individuals in which the chromosome deletion resulted in loss of one copy of the TERT gene at 5p15.33. Telomere length in peripheral blood cells from these individuals, although within the normal range, was on average shorter than in normal controls. The shortening was more significant in older individuals suggesting an accelerated age-dependent shortening. In contrast, individuals with autosomal dominant DC due to an inherited TERC gene deletion had very short telomeres, and the telomeres were equally short regardless of the age. Although some individuals with 5p, syndrome showed clinical features that were reminiscent of autosomal dominant DC, these features did not correlate with telomere length, suggesting that these were not caused by critically short telomeres. We conclude that a TERT gene deletion leads to slightly shorter telomeres within one generation. However, our results suggest that several generations of TERT haploinsufficiency are needed to produce the very short telomeres seen in patients with DC. [source]

    Frequent high telomerase reverse transcriptase expression in primary oral squamous cell carcinoma

    Kolja Freier
    Background:, Gene copy number gain of chromosomal arm 5p is frequently found in oral squamous cell carcinoma (OSCC) suggesting the activation of proto-oncogenes. TERT is a candidate gene encoding for human telomerase reverse transcriptase (hTERT). The aim of the present study was to elucidate the relevance of TERT copy number gain and high hTERT expression in OSCC. Methods:, Fluorescence in situ hybridization (FISH) for TERT and immunohistochemistry (IHC) for hTERT were performed to analyze TERT copy numbers and hTERT expression, respectively, on tissue microarray (TMA) sections including n = 247 OSCC and n = 105 pharyngeal and laryngeal squamous cell carcinomas (PSCC/LSCC). Results:, Increased hTERT protein expression was more frequently found in OSCC (71.1%, 155/218) than in PSCC/LSCC (36.0%, 35/89) (P < 0.001). By contrast, specific TERT amplifications were less common in OSCC (2.1%, 4/191) compared with PSCC/LSCC (9.9%, 8/81) (P = 0.047). Conclusions:, High hTERT expression is a frequent finding in OSCC. It might be a promising target for the development of specific anti-neoplastic therapy approaches. [source]

    Telomerase: not just for the elongation of telomeres,

    BIOESSAYS, Issue 2 2006
    Rodrigo T. Calado
    Telomerase RNA component (TERC) and telomerase reverse transcriptase (TERT) function together to elongate telomeres and to protect chromosomal ends. Recent studies have discovered that overexpression of telomerase's TERT subunit promoted epidermal stem-cell mobilization, hair growth and stem-cell proliferation without changes in length of telomeres.1,2 This telomerase functional characteristic is TERC independent and is operated through a mechanism other than telomere elongation. These findings open new doors for future explorations to understand telomerase function and its interaction with other cell components in the regulation of cell senescence and tumorigenesis. BioEssays 28: 109,112, 2006. 2006 Wiley periodicals, Inc. [source]

    Development and functional characterization of human bone marrow mesenchymal cells immortalized by enforced expression of telomerase

    Keichiro Mihara
    Summary. To create immortal mesenchymal cell lines, we transduced primary human bone marrow mesenchymal cells with telomerase reverse transcriptase (TERT). TERT+ mesenchymal cells continued to grow for >,2 years; parallel TERT, cultures underwent senescence after 15 weeks. TERT+ mesenchymal cells did not form foci in soft agar, had a normal karyotype and could differentiate into osteoblasts and chondrocytes. Their capacity to support leukaemic lymphoblasts and normal CD34+ haematopoietic cells was equal to or greater than that of primary cells; 42 TERT+ mesenchymal cell clones varied in their supporting capacity. Immortalized mesenchymal cells offer a promising tool for identifying molecules that regulate human haematopoiesis. [source]


    David AS Parker
    SUMMARY 1The pharmacological actions of 2,6-di- tert -butyl-4-(3-hydroxy-2-spiropentylpropyl)-phenol (BSPP), a putative presynaptic GABAB receptor modulator, were examined in electrically stimulated rat neocortical brain slices preloaded with [3H]-GABA or [3H]-glutamic acid. 2At 10 mmol/L, BSPP inhibited the release of [3H]-GABA in the presence of baclofen, but not that of [3H]-glutamic acid. This effect was sensitive to the GABAB receptor antagonist (+)-(S)-5,5-dimethylmorpholinyl-2-acetic acid (Sch 50911). 3Alone, BSPP had no effect on the release of [3H]-GABA or [3H]-glutamic acid. 4It is concluded that BSPP selectively potentiates the action of baclofen at GABAB autoreceptors, but not heteroreceptors and may be a useful ligand to discriminate between presynaptic GABAB receptor subtypes. [source]

    Deposition of Niobium Nitride Thin Films from Tert -Butylamido- Tris -(Diethylamido)-Niobium by a Modified Industrial MOCVD Reactor

    Tobias B. Thiede
    Abstract Niobium nitride thin films are deposited on 2, silicon (100) wafers using a modified industrial metal-organic (MO) CVD reactor of the type AIX-200RF, starting from tert -butylamido- tris -(diethylamido)-niobium (TBTDEN) and ammonia. Films of thicknesses 50-200,nm are deposited at temperatures ranging from 400,C to 800,C under reactor pressures of 1 and 5 mbar using various ammonia flow rates, and are characterized by the use of complementary techniques, namely X-ray diffraction (XRD), scanning electron microscopy (SEM), secondary neutral mass spectrometry (SNMS), Rutherford backscattering spectrometry (RBS), X-ray photoelectron spectroscopy (XPS), and electrical measurements. Films deposited above 450,C consist of the cubic , -NbN phase, apart from the presence of Nb-O and Nb-O-N species predominantly in the outermost film regions. The lowest specific resistivities, determined by four point probe measurements, are in the range 500,600,, cm. A NbN/SiO2/p-Si gate stack is fabricated using the grown niobium nitride films. From the capacitance-voltage (C - V)-curves, flat-band voltages are extracted which, when plotted against SiO2 -insulator thickness, yield a work function of 4.72,eV for as-deposited films. [source]

    Disappearance of gender-related difference in the toxicity of benzotriazole ultraviolet absorber in juvenile rats

    Mutsuko Hirata-Koizumi
    ABSTRACT 2-(2,-hydroxy-3,,5,-di- tert -butylphenyl)benzotriazole (HDBB) is an ultraviolet absorber used in plastic resin products, such as building materials and automobile components. In oral repeated dose toxicity studies using 5- or 6-week-old rats, this chemical induced hepatic histopathological changes, such as hypertrophy accompanied with eosinophilic granular changes and focal necrosis of hepatocytes, and male rats showed nearly 25 times higher susceptibility to the toxic effects than females. Castration at approximately 4 weeks of age markedly reduced the sex-related variation in HDBB toxicity, but some difference, less than five times, remained between male and female castrated rats. Following oral HDBB administration to male and female juvenile rats from postnatal days 4,21, such gender-related difference in toxic susceptibility was not detected; therefore, it is speculated that the determinants of susceptibility to HDBB toxicity are differentiated between sexes after weaning. In young rats given HDBB, there was no gender-related difference in plasma HDBB concentration, and no metabolites were detected in the plasma of either sex. HDBB induced lauric acid 12-hydroxylase activity in the liver and this change was more pronounced in males than in females. These findings indicate that HDBB could show hepatic peroxisome proliferation activity, and the difference in the susceptibility of male and female rats to this effect might lead to marked gender-related differences in toxicity. [source]

    Silver(I)-Selective PVC Membrane Potentiometric Sensor Based on a Recently Synthesized Calix[4]arene

    ELECTROANALYSIS, Issue 10 2006
    Aya Demirel
    Abstract A new PVC membrane potentiometric sensor for Ag(I) ion based on a recently synthesized calix[4]arene compound of 5,11,17,23-tetra- tert -butyl-25,27-dihydroxy-calix[4]arene-thiacrown-4 is developed. The electrode exhibits a Nernstian response for Ag(I) ions over a wide concentration range (1.010,2,1.010,6 M) with a slope of 53.81.6,mV per decade. It has a relatively fast response time (5,10,s) and can be used for at least 2 months without any considerable divergence in potentials. The proposed electrode shows high selectivity towards Ag+ ions over Pb2+, Cd2+, Co2+, Zn2+, Cu2+, Ni2+, Sr2+, Mg2+, Ca2+, Li+, K+, Na+, NH4+ ions and can be used in a pH range of 2,6. Only interference of Hg2+ is found. It is successfully used as an indicator electrode in potentiometric titration of a mixture of chloride, bromide and iodide ions. [source]

    Characterization of hydroxyaromatic compounds in vegetable oils by capillary electrophoresis with direct injection in an oil-miscible KOH/propanol/methanol medium

    ELECTROPHORESIS, Issue 17 2005
    Carla R. B. Mendona
    Abstract The separation of hydroxyaromatic compounds in vegetable oils, including synthetic antioxidants (3- tert -butyl-4-hydroxyanisol and 2,6-di- tert -butyl-4-hydroxytoluene), E-vitamers and other natural oil components, by nonaqueous capillary electrophoresis in an oil-miscible background electrolyte (BGE) was investigated. The BGE contained 40,mM KOH in a methanol/1-propanol (PrOH) mixture (15:85 v/v). The oil samples were 1:1 diluted with PrOH and directly injected in the capillary. Under negative polarity (cathode at the injection end), the anionic solutes moved faster than the electroosmotic flow, being well-resolved among them and from the triacylglycerols. Using virgin palm, extra virgin olive, wheat germ, virgin soybean and other oils, the capability of the procedure to quickly yield a characteristic profile of the biophenols present in the sample was demonstrated. The , -, (,,+,,)- (as unresolved pair) and , -tocopherols of a soybean oil sample were quantified. [source]

    Macroporous monolithic chiral stationary phases for capillary electrochromatography: New chiral monomer derived from cinchona alkaloid with enhanced enantioselectivity

    ELECTROPHORESIS, Issue 17 2003
    Michael Lmmerhofer
    Abstract A new chiral monomer derived from cinchona alkaloid, namely O -9-(tert -butylcarbamoyl)-11-[2-(methacryloyloxy)ethylthio]-10,11-dihydroquinine 1, was employed for the preparation of enantioselective monolithic capillary columns by an in situ copolymerization with 2-hydroxyethyl methacrylate 2 (HEMA), ethylene dimethacrylate 3 (EDMA) in the presence of cyclohexanol and 1-dodecanol as porogens (UV or thermal initiation of azobisisobutyronitrile (AIBN) as radical initiator). The porous properties and the electrochromatographic behavior of the new chiral monoliths were comparatively evaluated with previously described analogs obtained from O -9-[2-(methacryloyloxy)ethylcarbamoyl]-10,11-dihydroquinidine 4 as chiral monomer. Despite close structural and physicochemical similarities of the both chiral monomers, the pore distribution profiles of the resulting monoliths were shifted typically towards larger pore diameters with the new monomer 1. Once more, it was confirmed that a low cross-linking (10 wt% related to total monomers) and a pore diameter of about 1 ,m in the dry state provides the best electrochromatographic efficiency as a result of lower resistance to mass transfer (smaller C-term contribution to peak broadening) and more homogeneous flow profile (smaller A-term). Most importantly, as expected the new poly(1 - co -HEMA- co -EDMA) monoliths showed enhanced enantioselectivities and in addition faster separations as compared to poly(4 - co -HEMA- co -EDMA) analogs, which represents a significant improvement. Further, the elution order was reversed owing to the pseudoenantiomeric behavior of quinine- and quinidine-derived monomers. Fluorescence-labeled 9-fluorenylmethoxycarbonyl (FMOC), dansyl (DNS), 7-dimethylaminosulfonyl-1,3,2-benzoxadiazol-4-yl (DBD), carbazole-9-carbonyl (CC) amino acids could be separated with resolution values between 2 and 4 (with efficiencies typically between 100,000 and 200,000 plates/m) and fluorescence detection (variable wavelength fluorescence detector in-line with UV) yielding routinely a gain in detection sensitivities up to two orders of magnitude without specific optimization of the conditions with regards to fluorescence efficiency. [source]

    Electroenzymatic Synthesis of Chiral Sulfoxides

    C. Kohlmann
    Abstract Chloroperoxidase (CPO) from Caldariomyces fumago (E.C., is able to enantioselectively oxidize various sulfides to the corresponding (R)-enantiomer of the sulfoxides. For these oxidations the enzyme requires an oxidant. Most commonly, tert -butyl hydroperoxide (TBHP) and hydrogen peroxide are used. As it is known that these oxidants inactivate the enzyme, the enzymatic reaction was combined with the electrochemical in situ generation of hydrogen peroxide. As substrates for this combination of an enzymatic and an electrochemical reaction methyl p-tolyl sulfide, 1-methoxy-4-(methylthio)benzene and N-MOC- L -methionine methyl ester were used to carry out batch experiments. [source]

    Selection and identification of bacterial strains with methyl- tert -butyl ether, ethyl- tert -butyl ether, and tert -amyl methyl ether degrading capacities

    Jessica Purswani
    Abstract Nine bacterial strains isolated from two hydrocarbon-contaminated soils were selected because of their capacity for growth in culture media amended with 200 mg/L of one of the following gasoline oxygenates: Methyl- tert -butyl ether (MTBE), ethyl- tert -butyl ether (ETBE), and tert -amyl methyl ether (TAME). These strains were identified by amplification of their 16S rRNA gene, using fD1 and rD1 primers, and were tested for their capacity to grow and biotransform these oxygenates in both mineral and cometabolic media. The isolates were classified as Bacillus simplex, Bacillus drentensis, Arthrobacter sp., Acinetobacter calcoaceticus, Acinetobacter sp., Gordonia amicalis (two strains), Nocardioides sp., and Rhodococcus ruber. Arthrobacter sp. (strain MG) and A. calcoaceticus (strain M10) consumed 100 (cometabolic medium) and 82 mg/L (mineral medium) of oxygenate TAME in 21 d, respectively, under aerobic conditions. Rhodococcus ruber (strain E10) was observed to use MTBE and ETBE as the sole carbon and energy source, whereas G. amicalis (strain T3) used TAME as the sole carbon and energy source for growth. All the bacterial strains transformed oxygenates better in the presence of an alternative carbon source (ethanol) with the exception of A. calcoaceticus (strain M10). The capacity of the selected strains to remove MTBE, ETBE, and TAME looks promising for application in bioremediation technologies. [source]

    Fate of estrogens and xenoestrogens in four sewage treatment plants with different technologies,

    Guang-Guo Ying
    Abstract The fate and removal of the estrogens 17,-estradiol (E2), estrone (E1), and 17,-ethynylestradiol (EE2) and of the xenoestrogens bisphenol A (BPA), 4- tert -octylphenol (4- t -OP), 4-nonylphenol (4-NP), and nonylphenol mono- and diethoxylate (NPEO1 and NPEO2, respectively) were investigated in four South Australian sewage treatment plants (STPs; plants A,D) with different treatment technologies. The concentrations in the effluent from the two-year survey were similar to those reported in other studies. In the effluent, 4-NP, NPEO1, and NPEO2 had total concentrations up to 8 ,g/L, which were much higher than those of BPA and 4-t-OP. Estrone had the highest concentrations among the three estrogens, ranging between 13.3 and 39.3 ng/L, whereas the concentrations for E2 and EE2 varied between 1.0 and 4.2 ng/L and between 0.1 and 1.3 ng/L, respectively. The removal rates for the estrogens and xenoestrogens were variable but consistent with the plant performance parameters (biochemical oxygen demand, suspended solids, and ammonia). Considering all the estrogenic compounds analyzed in the present study, plant D, with a series of anaerobic and aerobic lagoons, was the least efficient of the four STPs in the removal of these compounds. The removal rates for 4-NP, NPEO1, and NPEO2 within the plants were 92% for plant A, with conventional activated sludge treatment; 80% for plant B, with two oxidation ditches; 70% for plant C, with three bioreactors; and 64% for plant D, with 10 lagoons in series. Comparatively, the removal of estrogens was lower, with rates ranging between 47 and 68% for E2 at the four plants. Both E1 and EE2 were more persistent during treatment, especially in plants C and D. [source]

    Methyl- tert -hexyl ether and methyl- tert -octyl ether as gasoline oxygenates: Anticipating widespread risks to community water supply wells,

    Jeff Snelling
    Abstract The widespread contamination of groundwater resources associated with methyl- tert -butyl ether (MtBE) use has prompted a search for replacement oxygenates in gasoline. Among the alternatives currently under development are higher methyl- tert -alkyl ethers, notably methyl- tert -hexyl ether (MtHxE) and methyl- tert -octyl ether (MtOcE). As was the case with MtBE, the introduction of these ethers into fuel supplies guarantees their migration into groundwater resources. In the present study, a screening-level risk assessment compared predicted well water concentrations of these ethers to concentrations that might cause adverse effects. A physicochemical model which has been successfully applied to the prediction of MtBE concentrations in community water supply wells (CSWs) was used to predict well water concentrations of MtHxE and MtOcE. The results indicate that these ethers are likely to contaminate water supply wells at slightly lower levels than MtBE as a result of migrating from leaking underground fuel tanks to CSWs. Because very little data is available on the physicochemical and environmental properties of MtHxE and MtOcE, estimation methods were employed in conjunction with the model to predict well water concentrations. Model calculations indicated that MtHxE and MtOcE will be present in many CSWs at concentrations approaching the concentrations that have caused widespread public health concern for MtBE. Based on these results and the possibility that MtHxE and MtOcE are potential carcinogens, testing of the toxicological properties of these ethers is recommended before they are used to replace MtBE in gasoline. [source]

    Effects of 4-nonylphenol and 4- tert -octylphenol on sex differentiation and vitellogenin induction in medaka (Oryzias latipes)

    Masanori Seki
    Abstract Medaka (Oryzias latipes) were continuously exposed to various concentrations of two alkylphenols, 4-nonylphenol (NP) and 4- tert -octylphenol (OP), from fertilized eggs to 60 d posthatch. The effects on sexual differentiation and hepatic vitellogenin (VTG) induction in medaka were assessed to elucidate the lowest-observed-effect concentrations (LOECs) of NP and OP for these events during early life stages. The LOECs of NP and OP for these events were 11.6 and 11.4 ,g/L, respectively. These results suggest that NP and OP may have adverse effects at similar concentrations during early life stage in medaka. Additionally, we investigated whether the abnormal sex differentiation induced by these alkylphenols would be permanent or reversible once the medaka were returned to clean water. The appearance of the secondary sex characteristics reverted from female to male when fish were returned to clean water. However, gonadal histology showed that intersex gonads still existed, even after the fish were transferred to clean water for two months. These results suggest that the induced feminization of secondary sex characteristics in medaka exposed to alkylphenols during the stage of sexual differentiation may not always be permanent, but the gonadal alteration (testisova) may continue much longer. [source]

    Development of a fish reporter gene system for the assessment of estrogenic compounds and sewage treatment plant effluents

    Gabriele E. Ackermann
    Abstract This study reports on the development and application of a fish-specific estrogen-responsive reporter gene assay. The assay is based on the rainbow trout (Oncorhynchus mykiss) gonad cell line RTG-2 in which an acute estrogenic response is created by cotransfecting cultures with an expression vector containing rainbow trout estrogen receptor a complementary DNA (rtER, cDNA) in the presence of an estrogen-dependent reporter plasmid and an estrogen receptor (ER) agonist. In a further approach, RTG-2 cells were stably transfected with the rtER, cDNA expression vector, and clones responsive to 17,-estradiol (E2) were selected. The estrogenic activity of E2, 17,-ethinylestradiol, 4-nonylphenol, nonylphenoxy acetic acid, 4- tert -octylphenol, bisphenol A, o,p,-DDT, p,p,-DDT, o,p,-2,2-bis(chlorophenyl)-1,1-dichloroethylene (o,p,-DDE), p,p,-DDE, o,p,-2,2-bis(chlorophenyl)-1,1-di-chloroethane (o,p,-DDD), p,p,-DDD, and p,p,-2,2-bis(chlorophenyl)acetic acid (p,p,-DDA) was assessed at increasing concentrations. All compounds except o,p,-DDT, p,p,-DDE, and p,p,-DDA showed logistic dose-response curves, which allowed the calculation of lowest-observed-effect concentrations and the concentrations at which half-maximal reporter gene activities were reached. To check whether estrogen-responsive RTG-2 cells may be used to detect the estrogenic activity of environmental samples, an extract from a sewage treatment plant (STP) effluent was assessed and found to have estrogenic activity corresponding to the transcriptional activity elicited by 0.05 nM of E2. Dose-response curves of nonylphenol, octylphenol, bisphenol A, and o,p,-DDD revealed that the RTG-2 reporter gene assay is more sensitive for these compounds when compared to transfection systems recombinant for mammalian ERs. These differences may have an effect on the calculation of E2 equivalents when estrogenic mixtures of known constitution, or environmental samples, such as STP effluents, are assessed. [source]

    Utility of a juvenile fathead minnow screening assay for detecting (anti-)estrogenic substances

    Grace H. Panter
    Abstract The European Chemical Industry's aquatic research program for endocrine disrupters includes the development of an in vivo juvenile fathead minnow (Pimephales promelas) screening assay.Working within the Organization for Economic Cooperation and Development's (OECD, Paris, France) tiered approach to endocrine disrupter evaluation in fish, the juvenile fish screening protocol was adapted from the OECD test guideline 204. Six chemicals, with different (anti-)estrogenic potencies, were used to develop the in vivo juvenile fish screening protocol: diethylstilbestrol, 17,-ethynylestradiol, genistein, methoxychlor, 4- tert -pentylphenol, and ZM189,154 (a novel pharmaceutical antiestrogen). Mixed-sex juvenile fathead minnows were exposed to individual chemicals (with chemical analyzes) and sampled after 4, 7, 14, and 21 d of exposure. Wet weight, total length, condition factor, and whole-body homogenate concentrations of vitellogenin (VTG) were determined. Estrogens and antiestrogens were detected in this screen by virtue of the VTG response (an elevation or suppression, respectively) after 14 d. The study showed that the use of VTG concentrations in mixed-sex juvenile fish provides a sensitive and robust assay for the detection of both estrogenic and antiestrogenic chemicals, with widely divergent potencies. [source]

    Measurement of Henry's law constant for methyl tert -butyl ether using solid-phase microextraction

    Britta G. Bierwagen
    Abstract Increasing groundwater contamination with methyl tert -butyl ether (MTBE) requires more efficient remediation technologies. Accurate measurement of MTBE's air,water partitioning coefficient (Henry's law constant, H) is important for the design and optimization of removal efficiency for many treatment systems as well as for predicting its fate and transport. Previously published data for MTBE appear to have some unusual nonlinearity at lower temperatures (15,30C), and a wide range of values exists for dimensionless H at 25C, from 0.0216 to 0.1226 in the published literature. We measured H for MTBE using headspace solid-phase microextraction (SPME) and a static method that considers equilibrium partitioning in a closed system, for temperatures between 15 and 40C. To validate our methods, we measured H for benzene, toluene, and trichloroethylene and compared our results to previously published values, with excellent agreement. The Arrhenius plot for MTBE indicates that ln(HMBTE) = 6.85,2,900 T,1, with T in K. At 25C, HMBTE = 0.0555 0.0122. [source]

    Developmental toxicity of estrogenic alkylphenols in killifish (Fundulus heteroclitus)

    Sue A. Kelly
    Abstract Estrogenic alkylphenols have been identified in the aquatic environment, and concern has arisen over the ability of these compounds to interact with and potentially disrupt vertebrate endocrine systems. Here we report that waterborne nonylphenol (NP) and 4- tert -octylphenol (4- t -OP) are toxic to the embryos and larvae of Fundulus heteroclitus, an estuarine teleost, causing both lethal and sublethal developmental abnormalities. Hatch success in surviving embryos is also adversely affected by alkylphenol exposure. Correlation analysis has indicated that decreased hatch success is strongly correlated to deformities in the torso/abdomen and tail of embryos. Larval exposure to the alkylphenols demonstrates that NP and 4- t -OP are lethal at concentrations an order of magnitude less than those lethal to embryos (NP larval 96-h LC50 = 0.95 ,M [204 ,g/L]; NP embryo 96-h LC50 = 24 ,M [5 mg/L]). In evaluating the role of estrogenicity in developmental toxicity of the alkylphenols, we have found that tamoxifen, an estrogen receptor antagonist, can prevent embryo-lethality for NP and 4- t -OP While these embryos survive, some sublethal abnormalities are still evident, particularly in the torso and tail. The results of these studies suggest that the alkylphenols have the potential to cause developmental toxicity in aquatic organisms and that this may occur through disruption of estrogen-based signals. [source]

    Nonylphenols in sediments and effluents associated with diverse wastewater outfalls,

    Robert C. Hale
    Abstract Nonylphenols (NPs) have been reported to disrupt endocrine function and sexual development in aquatic organisms at low concentrations. Environmental NP burdens are predominantly derived from degradation of nonylphenol polyethoxylate surfactants. We detected NPs in discharge-associated riverine sediments adjacent to 11 of 20 active sewage treatment plants (STPs) at concentrations up to 12,400 ,g/kg. While most previous studies have focused on STPs, nonylphenols were observed in association with a variety of outfall types. The highest sediment burden, 14,100 ,g/kg, was detected near a federal facility's stormwater discharge. Of 75 sediments examined from 67 sites, 45% contained NP concentrations >5 ,g/kg; median concentration in these NP-positive sediments was 369 ,g/kg. Other surfactant-derived alkylphenolic compounds, specifically 4- tert -octylphenol and 4-cumylphenol, were observed in two sediments at 8,220 and 70,000 ,g/kg, respectively. The maximum NP concentration detected in an effluent, 6,300 ,g/L, was from a shipyard oil/water separator. Nonylphenols were detected (> 1.0 ,g/L) in 20% of the 59 effluents examined; 10% exceeded 10 ,g/L. Sediments sampled near a STP that had ceased treatment operations 20 years prior contained 54,000 ,g/kg, indicative of long-term NP residence. Results indicate that NPs may be released from diverse sources, concentrate in associated sediments, and persist therein for extended periods. [source]

    Synthesis and Electrochemical Study of an Original Copper(II)-Capped Salen,Cyclodextrin Complex

    Elise Deunf
    Abstract A new metallocapped cyclodextrin (CD) was synthesized by the regioselective debenzylation, induced by diisobutylaluminium hydride (DIBAL-H), of perbenzylated cyclodextrins. This reaction allowed for the efficient preparation of an unprecedented CD,salen type copper(II) complex. The electrochemical behavior of both the bound and unbound CD,salen compounds was investigated by cyclic voltammetry. Notably, it was shown that the presence of tert -butyl groups at the ortho - and para -positions of the salen aromatic rings stabilized the copper(II) phenoxyl radical species that was generated upon the one-electron oxidation of the starting compound. Importantly, this stabilization remained effective when the salen-type ligand was covalently attached to the CD. This allowed for investigations of the reactivity of the copper(II) phenoxyl radical complex towards a primary alcohol to be performed by cyclic voltammetry. This reaction can be considered as mimicking the behavior of galactose oxidase. However, under these conditions, no reactivity was observed in the presence of benzyl alcohol. This may be due to distortion, either of the initially square planar salen ligand after its grafting to the CD primary face, and/or of the CD itself. On the other hand, the electrochemical reduction of the un-grafted copper(II) salen-type ligand led to a transient anionic species that exhibited significant stability on the time-scale of the slow cyclic voltammetry measurement in the absence of the CD, but was unstable in the presence of the CD. In the latter case, it was demonstrated that the anionic species was protonated by the CD. Importantly, this protonation was not fast enough to prevent catalytic activation of iodomethane by the electro-generated copper(I)-capped salen CD complex. [source]

    Platinum Complexes of Aromatic Selenolates

    Amy L. Fuller
    Abstract Several synthetic methods are used to prepare naphthalene-based aromatic 1,2-diselenoles. A new one-pot synthesis starting from naphthalene is used to produce theknown compound naphtho[1,8- c,d][1,2]diselenole (Se2naph).Friedel,Crafts alkylation is used on Se2naph to substitute either one tert -butyl group to form 2- tert -butylnaphtho[1,8- c,d][1,2]diselenole (mt-Se2naph) or two tert -butyl groups to form 2,7-di- tert -butylnaphtho[1,8- c,d][1,2]diselenole (dt-Se2naph). Bromination of mt-Se2naph results in dibromination of the naphthalene ring, rather than reaction at selenium, to give 4,7-dibromo-2- tert -butylnaphtho[1,8- c,d][1,2]diselenole (mt-Se2naphBr2). Reduction of the Se,Se bond in Se2naph, mt-Se2naph, dibenzo[c,e][1,2]diselenine (dibenzSe2), or diphenyl diselenide (Se2Ph2) with LiBEt3 H, followed by in-situ addition of [PtCl2{P(OPh)3}2] yields the four-coordinate mono- and dinuclear platinum(II) bis(phosphite) complexes [Pt(Se2naph){P(OPh)3}2] (1), [Pt(mt-Se2naph){P(OPh)3}2] (2), [Pt2(dibenzSe2)2{P(OPh)3}2] (3), cis -[Pt(SePh)2{P(OPh)3}2] (4), and trans -[Pt2(SePh)4{P(OPh)3}2] (5). [source]

    Synthesis, Structures, and Magnetic Properties of N -Trialkylsilyl-8-amidoquinoline Complexes of Chromium, Manganese, Iron, and Cobalt as well as of Wheel-Like Hexanuclear Iron(II) and Manganese(II) Bis(8-amidoquinoline)

    Astrid Malassa
    Abstract The transamination of 8-(tert -butyldimethylsilylamino)quinoline with (thf)2Cr[N(SiMe3)2]2 yields monomeric bis[8-(tert -butyldimethylsilylamido)quinoline]chromium(II) (1). Similar reactions of M[N(SiMe3)2]2 (M = Mn, Fe, Co) with 8-(trialkylsilylamino)quinoline lead to the formation of monomeric bis[8-(trialkylsilylamido)quinoline]metal(II) [M = Mn, SiR3 = SiMe2tBu (2a), SiiPr3 (2b); M = Fe, SiR3 = SiMe2tBu (3a),SiiPr3 (3b); M = Co, SiR3 = SiMe2tBu (4a), SiiPr3 (4b)]. The transamination of 8-aminoquinoline with M[N(SiMe3)2]2 (M = Mn, Fe, Co) allows the isolation of the heteroleptic 1:1 and homoleptic 2:1 products. The 1:1 complexes bis[8-amidoquinoline metal(II)bis(trimethylsilyl)amide] [M = Mn (5), Fe (6), Co (7)] are dimeric with bridging 8-amidoquinoline moieties. The 2:1 complexes of Mn and Fe, bis(8-amidoquinoline)manganese(II) (8) and bis(8-amidoquinoline)iron(II) (9), form hexamers with wheel-like molecular structures consisting of metal-centered nitrogen octahedra interconnected by common NN edges. The cobalt complex, bis(8-amidoquinoline)cobalt(II) (10), precipitates as a microcrystalline powder. Investigations of the magnetic properties by DFT corroborate the experimental data for the Mn derivative 8, where an antiferomagnetic coupling is observed. By contrast, calculations on the Fe6 -wheel 9 yield very close-lying ferromagnetically and antiferromagnetically coupled states. [source]

    Synthesis, Crystal Structure, and Catalytic Properties of Novel Dioxidomolybdenum(VI) Complexes with Tridentate Schiff Base Ligands in the Biomimetic and Highly Selective Oxygenation of Alkenes and Sulfides

    Abdolreza Rezaeifard
    Abstract Four novel dioxidomolybdenum(VI) complexes [MoO2(Lx)(CH3OH)] have been synthesized, using 2[(E)-(2-hydroxy-2-phenylethylimino)methyl]phenol derivatives as tridentate ONO donor Schiff base ligands (H2Lx) and MoO2(acac)2. A monoclinic space group was determined by X-ray crystallography from single-crystal data of a sample of these new complexes. The epoxidation of alkenes by using tert -butyl hydroperoxide and oxidation of sulfides to sulfoxides by urea hydrogen peroxide were efficiently enhanced with excellent selectivity under the catalytic influence these new MoVI complexes. The high efficiency and relative stability of the catalysts have been observed by turnover numbers and UV/Vis investigations. The electron-poor and bulky ligands promoted the effectiveness of the catalysts. [source]

    Synthesis and Photophysical Properties of Copper(I) Complexes Obtained from 1,10-Phenanthroline Ligands with Increasingly Bulky 2,9-Substituents

    Gianluca Accorsi
    Abstract In this paper, we describe the synthesis and the electronic properties of a series of [Cu(NN)2]+ systems. The NN ligands investigated are 2,9-bis[(tert -butyldimethylsilyloxy)methyl]-1,10-phenanthroline (1), 2,9-bis[(triisopropylsilyloxy)methyl]-1,10-phenanthroline (2), 2,9-bis[(tert -butyldiphenylsilylmoxy)ethyl]-1,10-phenanthroline (3), 2,9-bis[2,6-bis(benzyloxy)phenethyl]-1,10-phenanthroline (4) and 2-(1,3-diphenylpropan-2-yl)-9-phenethyl-1,10-phenanthroline (5). The electrochemical properties and the ground state electronic absorption spectra of Cu(1)2,Cu(5)2 are in line with the classical behaviour of such [Cu(NN)2]+ derivatives. Whereas all the compounds exhibit MLCT luminescence centered around 630,650 nm, the emission quantum yields and the lifetimes are dramatically different as a function of stereoelectronic effects and/or the possibility of internal exciplex quenching when oxygen-containing functional groups are attached to the phenanthroline ligands. [source]

    Synthesis, Structure, and Reactivity of Rhodium Bipyridine Compounds: Formation of a RhII Hydrido Cluster and a RhIII Peroxido Complex

    Anna Penner
    Abstract Treatment of [Rh(,-Cl)(coe)2]2 (coe = cyclooctene) with 4,4,-di- tert -butyl-2,2,-bipyridine (tbbpy) gives the bipyridine complex [Rh(Cl)(tbbpy)(coe)] (1). A subsequent reaction with dihydrogen results in the formation of the cluster [{Rh(Cl)(H)(tbbpy)}]4 (2). The reaction of [Rh(,-Cl)(coe)2]2 with tbbpy in thf followed by the addition of CNtBu affords [Rh(Cl)(tbbpy)(CNtBu)] (3). The latter reacts with O2 or 18O2 to yield the peroxido complexes [Rh(Cl)(O2)(tbbpy)(CNtBu)] (4a) and [Rh(Cl)(18O2)(tbbpy)-(CNtBu)] (4b), respectively. Complexes 1,4 were characterized by X-ray crystallography. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

    Mono(aryloxido)Titanium(IV) Complexes and Their Application in the Selective Dimerization of Ethylene

    Jean-Benoit Cazaux
    Abstract We report on the synthesis of mono(aryloxido)titanium(IV) complexes of general formula {Ti[O(o -R)Ar]X3}, with X = OiPr, ArO = 2- tert -butyl-4-methylphenoxy and R = CMe3 (2a), CMe2Ph (2b) and CH2NMe2 (2c). Attempts to reach pure mono(aryloxido) complexes when R = CH2NMe(CH2Ph) (2d) or CH2N(CH2Ph)2 (2e) were unsuccessful. When R = CH2OMe, the analogous mononuclear complex was not obtained, and instead, a dinuclear complex [(2- tert -butyl-4-methyl-6-methoxymethylphenoxy) TiCl(OiPr)(,2 -OiPr)2TiCl(OiPr)2] (3) was formed. Complexes 2b and 3 were characterized by single-crystal X-ray diffraction. The former contains a tetrahedrally coordinated TiIV centre, whereas in the latter the aryloxido ligand behaves as a chelating,bridging ligand between the two, chemically very different metal centres that form two face-sharing octahedra. Different synthetic approaches starting from [Ti(OiPr)4] or [TiCl(OiPr)3] were evaluated and are discussed. The hemilabile behaviour of the aryloxido ligand resulting from reversible coordination of its side arm was studied by variable-temperature 1H NMR spectroscopy for 2c (R = CH2NMe2). Complexes 2a,d were contacted with ethylene and AlEt3 as cocatalyst. When activated with AlEt3 (3 equiv.) at 20 bar and 60 C, complex 2c exhibits interesting activity (2100 g/gTi/h) for the selective dimerization of ethylene to 1-butene (92,% C4=; 99+% C4=1). Noticeable differences in catalyst activity were observed when the R group was modified. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

    vic -Dichlorodiphosphapropenes , Synthesis and Coordination Ability

    Raluca Septelean
    Abstract New substituted 2,3-dichloro-1-,3,2 -P,3-,3,3 -P-diphosphapropenes Mes*P=C(Cl)-P(Cl)tBu (1) (Mes* = 2,4,6-tri- tert -butylphenyl) and the oxidation compounds Mes*P=C(Cl),P(=E)(Cl)R [R = tBu, E = S (2), O (3); R = Mes, E = O (4)] are reported. From the reaction of 2 with W(CO)5(thf) the chelate compound W(CO)4[Mes*P=C(Cl),P(S)(Cl)tBu] (5) was obtained. Reaction of 1 or 2 with PdCl2(cod) led to PdCl2[cyMes*PC(H)(Cl),P(Cl)tBu] (cyMes*P = 5,7-di- tert -butyl-3,3-dimethyl-1-phosphaindane) (6) or PdCl2[cyMes*PC(H)(Cl),P(S)(Cl)tBu] (7), in which the coordination to the Pd atoms is accompanied by intramolecular addition of CH(tBu) of Mes* to the P=C bond of the dichlorodiphosphapropene. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]