Home  About us  Contact
 

Tetra

Distribution by Scientific Domains
Chemistry65%
Life Sciences23%
Polymers and Materials Science5%
3 Other Domains7%
Distribution within Chemistry
General & Introductory Chemistry26%
Crystallography16%
Analytical Chemistry3%
9 Other Subdomains29%

Selected Abstracts

No effect of TETRA hand portable transmission signals on human cognitive function and symptoms

BIOELECTROMAGNETICS, Issue 5 2010
Ingunn S. Riddervold
Abstract Current radio frequency radiation exposure guidelines rest on well-established thermal effects. However, recent research into analogue and digital transmission fields at levels covered by the exposure guidelines has indicated possible detrimental effects on human cognitive performance. To investigate this, we conducted a controlled climate chamber study of possible changes in cognitive performance in healthy volunteers exposed to transmission signals from TETRA hand portables (TETRA handsets). The trial deployed a balanced, randomized, double-blinded cross-over design. Performance on different paper-and-pencil, auditory and computer-based cognitive tasks was monitored in 53 male volunteers (mean age 36.41 years, SD 8.35) during 45-min exposure to a TETRA handset and sham control signals remotely controlled from a laboratory more than 100,km away. The main cognitive outcome was the Trail Making B (TMB) test. In addition, the participants completed a computer-based questionnaire measuring self-reported psychological and physical symptoms. No statistically significant differences (P,<,0.05) between the TETRA and sham conditions were found for either TMB (estimated difference 3.8%, confidence interval (CI) ,1.6% to 9.2%) or any of the remaining cognitive tasks or symptoms. In conclusion, we found no evidence that brief exposure to hand-held TETRA transmitters' affects human cognitive function or subjective symptoms. Bioelectromagnetics 31:380,390, 2010. © 2010 Wiley-Liss, Inc. [source]

Estimation of whole-body SAR from electromagnetic fields using personal exposure meters

BIOELECTROMAGNETICS, Issue 4 2010
Wout Joseph
Abstract In this article, personal electromagnetic field measurements are converted into whole-body specific absorption rates for exposure of the general public. Whole-body SAR values calculated from personal exposure meter data are compared for different human spheroid phantoms: the highest SAR values (at 950,MHz) are obtained for the 1-year-old child (99th percentile of 17.9,µW/kg for electric field strength of 0.36,V/m), followed by the 5-year-old child, 10-year-old child, average woman, and average man. For the 1-year-old child, whole-body SAR values due to 9 different radiofrequency sources (FM, DAB, TETRA, TV, GSM900 DL, GSM1800 DL, DECT, UMTS DL, WiFi) are determined for 15 different scenarios. An SAR matrix for 15 different exposure scenarios and 9 sources is provided with the personal field exposure matrix. Highest 95th percentiles of the whole-body SAR are equal to 7.9,µW/kg (0.36,V/m, GSM900 DL), 5.8,µW/kg (0.26,V/m, DAB/TV), and 7.1,µW/kg (0.41,V/m, DECT) for the 1-year-old child, with a maximal total whole-body SAR of 11.5,µW/kg (0.48,V/m) due to all 9 sources. All values are below the basic restriction of 0.08,W/kg for the general public. 95th percentiles of whole-body SAR per V/m are equal to 60.1, 87.9, and 42.7,µW/kg for GSM900, DAB/TV, and DECT sources, respectively. Functions of the SAR versus measured electric fields are provided for the different phantoms and frequencies, enabling epidemiological and dosimetric studies to make an analysis in combination with both electric field and actual whole-body SAR. Bioelectromagnetics 31:286,295, 2010. © 2009 Wiley-Liss, Inc. [source]

Synthesis and Characterization of a Series of New Luminescent NHC-Coordinated AuI,AgI Tetra- and Polymetallic Complexes Containing Benzoate-Bridged Ag2 Dimers

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 13 2009
Amit K. Ghosh
Abstract The reaction of [Au(CH3impy)2]PF6 (2), with substituted silver benzoate salts bearing different halide substituents produced a series of new mixed-metal species having two different structural motifs. One structural motif contains discrete tetrametallic Ag2Au2 diamond cores, whereas the other motif contains the same tetrametallic diamond core interconnected by benzoate-bridged silver dimers to form polymers. All the complexes are substitution-inert and stable both in the solid state as well as in solution. We also report the synthesis of oxidative addition products of [Au(CH3impy)2]PF6, which were also obtained during our attempts to oxidize the above-mentioned multimetallic assembly with bromine and iodine. Compounds 3,7 are intensely luminescent in frozen acetonitrile solution, but surprisingly no luminescence is observed at room temperature. All the complexes were completely characterized by 1H, 13C NMR, electronic absorption, emission spectroscopy, elemental analysis and X-ray crystallography. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

Solvent Effects on Catalytic Epoxidation of Alkenes by Tetra- n -butylammonium Periodate and (Tetraarylporphyrinato)manganese(III)

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 20 2008
Daryoush Mohajer
Abstract The epoxidation of cyclooctene and cis -stilbene was performed by tetra- n -butylammonium periodate (nBu4NIO4)in the presence of (tetraarylporphyrinato)manganese(III) [Mn(por)] and imidazole (im) in various CH2Cl2/alcohol solvents (alcohol = CH3OH, C2H5OH, n -C3H7OH, i -C3H7OH, t -C4H9OH). In accord with the coordinating abilities of the alcohols to [Mn(por)], the epoxidation yields increased from CH2Cl2/CH3OH to CH2Cl2/t -C4H9OH. In the epoxidation of cis -stilbene in the presence of (acetato)(tetraphenylporphyrinato)manganese(III) [Mn(tpp)(OAc)], the cis - to trans -stilbene oxide ratio increased consistently with the bulk of the alcohol in CH2Cl2/alcohol solvents. Also, it was found that the interaction of [Mn(tpp)(OAc)] and (acetato)(tetramesitylporphyrinato)manganese(III) [Mn(tmp)(OAc)] with nBu4NIO4 in the presence of imidazole but in the absence of alkenes yields [Mn(tpp)(O)(im)]+ and [Mn(tmp)(O)(im)]+ complexes. The formation of the Mn=O species for the small linear alcohols was faster than that for the larger ones, whereas the stability of the Mn=O complex was greater in the presence of the bulkier alcohols. Attempts were made to explain these effects.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

Chain-Like Tetra-, Penta- and Heptanuclear Cyanide-Bridged Complexes by Attachment of Organometallic Cyanides to M2, M3 and M5 Units

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 20 2003
Tianlu Sheng
Abstract Attachment of the "ligands" [Cp(dppe)Fe-CN], [Cp(PPh3)2Ru-CN], [Cp(CO)2Fe-CN] and [(CO)5M-CN],, (where M = Cr, Mo, W) to the polymetallic centres [Ru2(OAc)4]+, [Co3(dpa)4]2+ and [Ni5(tdpa)4]2+ yielded two tetra-, three penta- and five heptanuclear complexes with chain-like linear arrangements of the metal ions and the bridging cyanide ligands, as proved by the structure determination of [Ni5(tdpa)4{Cp(dppe)2Fe-CN}2](PF6)2. IR and CV data show that the Ru2, Co3 and Ni5 centres of these complexes withdraw electron density from the external organometallic units. This prevents electronic interactions between the two terminal metal ions, yet allows multistep one- and two-electron redox processes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

Tetra- tert -butyltrioxabicyclo[3.3.1]nonadienedicarboxylic Acid: Optical Resolution, Absolute Configuration and Application in Chiral Discrimination

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 19 2008
Jennifer Kremsner
Abstract The enantiopure bridged bis-dioxine 4, a dissymmetric dicarboxylic acid exhibiting axial chirality, can easily be synthesized and serve as host for separating and/or transporting chiral guest molecules. Racemic 4 gives with (R)- and (S)-1-phenylethylamine the corresponding pure diastereomeric salts 7 and 8. The absolut configuration of the diacid 4 in the diastereomeric salt 7 containing (R)-1-phenylethylamine was confirmed to be R by X-ray crystal structure analysis, which also confirmed its concave nature. Release of the acid-sensitive pure enantiomers (R)- 4 as well as (S)- 4 was achieved conveniently by use of dry flash-chromatography on silica. The CD spectrum shows a positive Cotton effect of the (S)-enantiomer at 206 nm. The enantiomeric purity was proved by 1H NMR discrimination of the diastereomeric salts with (R,R)-1,2-bis(4-methoxyphenyl)ethane-1,2-diamine as the base. The dicarboxylic acid (R)- 4 can be used as chiral auxiliary as demonstrated by the difficult resolution of racemicN,N,-di- tert -butyl-1,2-bis(4-methoxyphenyl)ethane-1,2-diamine 9.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

Fluorescence Detection of the Ornamental Fish Cardinal Tetra (Paracheirodon axelrodi)

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2009
Richard P. Brinn
The fluorescence spectra of the tropical fish, Cardinal Tetra (Paracheirodon axelrodi), originating in the Amazon region of Brazil, were determined. These spectra were then treated using factor analysis, generating two contributing spectra and separating out the noise. Time-resolved fluorescence results indicated that the fluorescent system in the epidermis undergoes excited state reaction. Excited state proton transfer is suggested as being present. Both intentionally stressed and nonstressed individuals were used and some small differences were noted in the contributions of the two calculated contributing spectra to the experimental spectra, presumably as a function of stress. The results are compared with those obtained by the standard determination of cortisol level using the whole body extraction method and it is suggested that the method could be tested as an improved, nondestructive way to determine stress in this species, which is a necessary step in the development of "best management practices" of methods for storage and transport of the fish. [source]

Ultrafast Energy Transfer from Bound Tetra(4- N,N,N,N -trimethylanilinium)porphyrin to Synthetic Dopa and Cysteinyldopa Melanins,

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2003
Tong Ye
ABSTRACT The binding of tetra(4- N,N,N,N -trimethylanilinium)porphyrin (TAP) to melanins quenches the porphyrin emission. Time-resolved femtosecond absorption spectroscopy reveals that the mechanism behind this quenching is ultrafast nonradiative energy transfer (,ET < 100 fs) from electronically excited TAP to melanin. Similar dynamics are observed for both dopa and cysteinyldopa melanins. Steady-state emission studies demonstrate that the emission from melanin increases upon excitation of bound TAP, thereby confirming that rapid energy transfer occurs. These results are consistent with previous photoacoustic studies, which revealed that the TAP,melanin complex behaves like a supermolecular system liberating heat as a whole. [source]

Differentiation of fluoronitroaniline isomers by negative-ion electrospray mass spectrometry

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 3 2006
ej Gierczyk
Tetra- and trifluoronitroanilines were studied by electrospray ionization mass spectrometry. These compounds gave signals only in the negative-ion mode. It was found that the so-called ,in-source' fragmentation, induced by cone voltage increase, enables differentiation of isomers. For para -nitroanilines, in contrast to ortho derivatives, the loss of NO2 was the most favored process and other fragment ions were characterized by low abundances. For trifluoro conjugates the substitution pattern of aromatic ring by fluorine atoms also affected their fragmentation patterns. For example, in 2,3,6-trifluoro-4-nitroaniline, in contrast to 2,3,5-trifluoro-4-nitroaniline, efficient NO loss, followed by HF loss, took place. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Amplifikation der Chiralität in monodispersen, enantiomerenreinen Allen-Acetylen-Oligomeren,

ANGEWANDTE CHEMIE, Issue 12 2010
Pablo Rivera-Fuentes
Die oxidative Homokupplung optisch reiner 1,3-Diethinylallene mit einem Pd-Katalysator lieferte enantiomerenreine Allen-Acetylen-Oligomere definierter Länge (Di-, Tetra-, Octa- und Hexadecamer). Die starke Amplifikation der chiroptischen Aktivität (siehe Diagramm) legt die Bildung helicaler Sekundärstrukturen nahe. Diese Annahme wird durch zeitabhängige quantenmechanische Rechnungen gestützt. [source]

Pd-PEPPSI-IPent: Low-Temperature Negishi Cross-Coupling for the Preparation of Highly Functionalized, Tetra- ortho -Substituted Biaryls,

ANGEWANDTE CHEMIE, Issue 11 2010
Selçuk Çalimsiz Dr.
Herausforderung angenommen: Komplexe gehinderter Biaryle wurden bei Temperaturen zwischen 0°C und Raumtemperatur, oder unter leichtem Erwärmen, hergestellt, wobei der Katalysator (siehe Schema) Ausgangsmaterialien mit Säureeinheiten erfolgreich kuppelt und Biarylderivate mit einem oder zwei heterocyclischen Ringen liefert. Ar1=Aryl oder Heteroaryl (gehindert), Ar2=Aryl oder Heteroaryl (nichtaktiviert). [source]

Tetra-,-chloro-1:2,4Cl;1:3,4Cl -bis(4,4,-di­methyl-2,2,-bi­pyridine)-2,2N,3,2N -lithium(I)­dipalladium(II) tetrakis­(penta­fluoro­phenyl)­borate di­chloro­methane 1.196-solvate

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 10 2003
Han Shen
In the crystal structure of the title compound, [LiPd2Cl4(C12H12N2)2](C24F20B)·1.196CD2Cl2 or [{(Me2bipy)PdCl2}2(,-Li)]+·B(C6F5)4,·1.196CD2Cl2 (Me2bipy is 4,4,-di­methyl-2,2,-bi­pyridine), an Li+ cation is stabilized by complexation with two (Me2bipy)PdCl2 units through weak Li,Cl interactions. This compound is thus a rare example of a complex that exhibits an arrested Cl, abstraction. [source]

Tetra-,-acetato- O:O,-bis­[(7-aza­indole- N)­copper(II)]

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2000
Yoshiyuki Kani
The title complex, [Cu2(C2H3O2)4(C7H6N2)2], shows a binuclear cage structure having an inversion centre. There are intramolecular N,H,O hydrogen bonds between the 7-aza­indole ligands and the bridging acetate O atoms. [source]

ChemInform Abstract: One-Pot Three-Component Solvent-Free Syntheses of n-Alkyl-Bridged N,N,N,,N,-Tetra(2-hydroxybenzyl)diamines (II) and N,N-Bis(2-hydroxybenzyl) Amines (VI).

CHEMINFORM, Issue 40 2010
Antti Riisioe
Abstract Isolation of the products can be a problem. [source]

ChemInform Abstract: Tetrabutylammonium Tetra(tert-Butyl Alcohol)-Coordinated Fluoride as a Facile Fluoride Source.

CHEMINFORM, Issue 6 2009
Dong Wook Kim
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

ChemInform Abstract: In Search of Covalently Bound Tetra- and Penta-Oxygen Species: A Photoelectron Spectroscopic and ab initio Investigation of MO4 - and MO5 - (M: Li, Na, K, Cs).

CHEMINFORM, Issue 36 2002
Hua-Jin Zhai
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

Remarkably Effective Phosphanes Simply with a PPh2 Moiety: Application to Pd-Catalysed Cross-Coupling Reactions for Tetra- ortho -substituted Biaryl Syntheses

CHEMISTRY - A EUROPEAN JOURNAL, Issue 27 2010
Ming So
Expanding the horizons of ArPPh2: New applications of triarylphosphane ligands are presented. The Pd,L1 and Pd,L2 complexes offer exceptionally high activity in Suzuki,Miyaura cross-couplings of aryl chlorides. The extremely congested synthesis of tetra- ortho -substituted biaryl compounds is achieved for the first time by simply using triarylphosphane ligands. [source]

The Assembly of Macrocyclic Bis- and Tetra-,-lactams with Embedded Platinum or Palladium Square-Planar Centers

CHEMISTRY - A EUROPEAN JOURNAL, Issue 28 2009
Daniel Pellico
Abstract The synthesis, isolation, and full characterization of different types of stable, metal-assembled macrocyclic ,-lactams are reported. By using adequately functionalized bis-,-lactams with defined stereochemistry as building blocks, a series of mono- and bimetallic Pd and Pt macrocycles has been prepared in good to quantitative yields. These novel structures combine the ,-lactam moiety with transition-metal fragments with cis -square-planar geometry and constitute a new class of metal-assembled cavities involving molecules with biological relevance as building blocks. By combining the adequate ligands, metallic fragments, and tuning the reaction conditions, different mono- and bimetallic macrocyclic ,-lactam cavities can be selectively obtained. Macrocycles with Pt,ethynyl groups are suitable to form host,silver triflate guest complexes in a tweezer fashion. El trabajo describe la síntesis, aislamiento y caracterización completa de una serie de Pd y Pt-metalo-,-lactamas. Estos compuestos se obtienen con excelente rendimiento a partir de bis-,-lactamas adecuadamente funcionalizadas y con estereoquímica definida, y los correspondientes complejos de Pd y Pt. Las bis y tetra-metalo-,-lactamas obtenidas constituyen un nuevo tipo de cavidades macrocíclicas, que combinan en su estructura los fragmentos ,-lactámicos con complejos metálicos de geometría cis-plano cuadrada. Combinando adecuadamente los ligandos precursores (bis-,-lactama y complejo metálico) y las condiciones de reacción, es posible controlar de forma totalmente selectiva, el tamaño del macrociclo obtenido y preparar bis y tetra-,-lactamas mono o bimetálicas. La presencia de fragmentos Pt-etinilo en la estructura permite a las compuestos macrocíclicos obtenidos la formación de complejos pinzados con sales de plata. [source]

Synthesis of Silver(I) and Gold(I) Complexes with Cyclic Tetra- and Hexacarbene Ligands

CHEMISTRY - A EUROPEAN JOURNAL, Issue 35 2008
Ekkehardt Hahn Prof.
Treasure complexes: Lutidine-bridged tetraimidazolium salts form macrocyclic mono- and dinuclear silver(I) and gold(I) carbene complexes, whereas the lutidine-bridged hexakis(imidazolin-2-ylidene) ligand reacts with silver(I) to yield complex [1]+, which contains six silver(I) atoms arranged in a hexagon and sandwiched in between two hexacarbene ligands. [source]

Cyclic ,-Tetra- and Pentapeptides: Synthesis through On-Resin Cyclization and Conformational Studies by X-Ray, NMR and CD Spectroscopy and Theoretical Calculations

CHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2005
Frank Büttner Dr.
Abstract The solution-phase synthesis of the simplest cyclic ,-tetrapeptide, cyclo(,-Ala)4 (4), as well as the solid-phase syntheses through side chain anchoring and on-resin cyclization of the cyclic ,3 -tetrapeptide cyclo(-,3hPhe-,3hLeu-,3hLys-,3hGln-) (14) and the first cyclic ,3 -pentapeptide cyclo(-,3hVal-,3hPhe-,3hLeu-,3hLys-,3hLys-) (19) are reported. Extensive computational as well as spectroscopic studies, including X-ray and NMR spectroscopy, were undertaken to determine the preferred conformations of these unnatural oligomers in solution and in the solid state. cyclo(,-Ala)4 (4) with no chiral side chains is shown to exist as a mixture of rapidly interchanging conformers in solution, whereas inclusion of chiral side chains in the cyclo-,3 -tetrapeptide causes stabilization of one dominating conformer. The cyclic ,3 -pentapeptide on the other hand shows larger conformational freedom. The X-ray structure of achiral cyclo(,-Ala)4 (4) displays a Ci -symmetrical 16-membered ring with adjacent CO and N-H atoms pointing pair wise up and down with respect to the ring plane. CD spectroscopic examinations of all cyclic ,-peptides were undertaken and revealed results valuable as starting point for further structural investigations of these entities. [source]

Highly Efficient Redox Isomerization of Allylic Alcohols at Ambient Temperature Catalyzed by Novel Ruthenium,Cyclopentadienyl Complexes,New Insight into the Mechanism

CHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2005
Belén Martín-Matute Dr.
Abstract A range of ruthenium cyclopentadienyl (Cp) complexes have been prepared and used for isomerization of allylic alcohols to the corresponding saturated carbonyl compounds. Complexes bearing CO ligands show higher activity than those with PPh3 ligands. The isomerization rate is highly affected by the substituents on the Cp ring. Tetra(phenyl)methyl-substituted catalysts rapidly isomerize allylic alcohols under very mild reaction conditions (ambient temperature) with short reaction times. Substituted allylic alcohols have been isomerized by employing Ru,Cp complexes. A study of the isomerization catalyzed by [Ru(Ph5Cp)(CO)2H] (14) indicates that the isomerization catalyzed by ruthenium hydrides partly follows a different mechanism than that of ruthenium halides activated by KOtBu. Furthermore, the lack of ketone exchange when the isomerization was performed in the presence of an unsaturated ketone (1 equiv), different from that obtained by dehydrogenation of the starting allylic alcohol, supports a mechanism in which the isomerization takes place within the coordination sphere of the ruthenium catalyst. [source]

Influence of Intermolecular Interactions on the Formation of Tetra(carbomethoxy)-tetrathiafulvalene Assemblies

CHEMPHYSCHEM, Issue 10 2007
Núria Crivillers
Abstract We study the assemblies that tetra(carbomethoxy)tetrathiafulvalene (TCM,TTF) forms in solution and when deposited on a surface depending on intermolecular interactions and on the interactions with the substrate and the solvent. Its organization on graphite and mica substrates was studied by atomic force microscopy, and different molecular assemblies were observed depending on the prevailing interactions. The promotion of molecule,molecule interactions gave rise to the formation of molecular fibers. The investigation of the influence of the solvent,molecule interactions on TCM,TTF molecular organizations was carried out by UV/Vis spectroscopy, and a new TCM,TTF polymorph was obtained by changing the nature of the solvent. Finally, an explanation for all these phenomena, supported by computational modeling, is put forward. [source]

Selective Inclusion of Fluoboric Acid by Tetra(p-tert -butyl)-thiacalix[4]arene: Crystal Structure and Theoretical Study

CHINESE JOURNAL OF CHEMISTRY, Issue 3 2005
Hong Jin
Abstract The structure of fluoboric acid selectively embedded within the hydrophobic cavity of the tetra(p-tert -butyl)thiacalix[4]arene was determined by X-ray crystallography. Crystal data: C40H49O4S4BF4, Mr=808.88, tetragonal, space group P4/nmm, a=1.5887(2) nm, b=1.5887(2) nm, c=0.8428(0) nm, V=2.127(2) nm3, Z=2, Dc=1.263 g·cm,3, R1=0.0405, wR[I>2,(I)]=0.1218. 19F NMR confirmed the existence of fluoboric acid with a signal at , ,151.4. The noncovalent interactions in the molecular structure were characterized by Bader's theory of "atoms in molecules" (AIM). The results reveal that besides the C,H,F hydrogen bonding and cation-anion electrostatic interaction present in the fluoboric acid inclusion complex, the F,, -C,+ electrostatic interaction also exists for stabilizing the fluoboric acid embedded within the hydrophobic cavity of tetra(p-tert -butyl)thiacalix[4]arene. [source]

Predator Inspection Behaviour in a Characin Fish: an Interaction between Chemical and Visual Information?

ETHOLOGY, Issue 9 2003
Grant E. Brown
Recent evidence suggests that predator inspection behaviour by Ostariophysan prey fishes is regulated by both the chemical and visual cues of potential predators. In laboratory trials, we assessed the relative importance of chemical and visual information during inspection visits by varying both ambient light (visual cues) and predator odour (chemical cues) in a 2 × 2 experimental design. Shoals of glowlight tetras (Hemigrammus erythrozonus) were exposed to a live convict cichlid (Archocentrus nigrofasciatus) predator under low (3 lux) or high (50 lux) light levels and in the presence of the odour of a cichild fed tetras (with an alarm cue) or swordtails (Xiphophorus helleri, with an alarm cue not recognized by tetras). Tetras exhibited threat-sensitive inspection behaviour (increased latency to inspect, reduced frequency of inspection, smaller inspecting group sizes and increased minimum approach distance) towards a predator paired with a tetra-fed diet cue, regardless of light levels. Similar threat-sensitive inspection patterns were observed towards cichlids paired with a swordtail-fed diet cue only under high light conditions. Our data suggest that chemical cues in the form of prey alarm cues in the diet of the predator, are the primary source of information regarding local predation risk during inspection behaviour, and that visual cues are used when chemical information is unavailable or ambiguous. [source]

4-Aryl-2-quinolones through a Pseudo-Domino Heck/Buchwald,Hartwig Reaction in a Molten Tetrabutylammonium Acetate/ Tetrabutylammonium Bromide Mixture

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 3 2007
Gianfranco Battistuzzi
Abstract 4-Aryl-2-quinolones can be prepared from readily available o -bromocinnamamide and aryl iodides using phosphine-free palladium(II) acetate as the precatalyst and a molten tetra(n -butyl)ammonium acetate/tetra(n -butyl)ammonium bromide mixture as the reaction medium. The reaction proceeds through a pseudo-domino process involving two mechanistically independent, sequential catalytic cycles: a Heck reaction followed by an intramolecular Buchwald,Hartwig CN bond forming reaction. [source]

Novel Thorium Membrane Sensors with Anionic Response Based on Trioctylphosphine Oxide and Toluate Ionophores

ELECTROANALYSIS, Issue 19 2008

Abstract Two novel potentiometric polymeric membrane sensors for rapid and accurate determination of thorium are described. These are based on the use of trioctylphosphine oxide (TOPO) and thorium toluate (Th-TA) as ionophores dispersed in poly(vinyl chloride) matrix membranes plasticized with nitrophenyloctyl ether. In strong nitric acid medium, Th(IV) nitrate is converted into [Th(NO3)6]2, complex and sensed as anionic divalent ion which exclude most cationic effect. Validation of the assay methods using the quality assurance standards (linearity range, accuracy, precision, within-day variability, between-day-repeatability, lower detection limit and sensitivity) reveals excellent performance characteristics of both sensors. The sensors exhibit near-Nernstian response for 1.0×10,6,1.0×10,1 M Th over the pH range 2.5,4.5. Calibration slopes of ,32.3±0.3 and ,27.2±0.2,mV/decade, precision of ±0.5 and ±0.8% and accuracy of 98.8±0.9 and 97.9±0.7% are obtained with TOPO and Th-TA based sensors, respectively. Negligible interferences are caused by most interfering mono-, di-, tri-, tetra-, penta-, and hexa-valent elements commonly associated with thorium in naturally occurring minerals and ores. High concentrations of Cl,, F,, SO42,, and NO3, ions have no diverse effect. Complete removal of the effect of the interferents in complex matrices is achieved by retention of [Th(NO3)6]2, complex from 5,M nitric acid/methanol mixture (1,:,9,v/v) on a strong anion exchanger, washing out the cationic interferents followed by stripping off thorium anion complex and measurements. Both sensors are used for determining thorium in certified thorium ore samples (20,120,mg Th/kg) and some naturally occurring ores (200,600,mg Th/kg). The results obtained agree fairly well with the certified labeled values or the data obtained using X-ray fluorescence spectrometry [source]

Predicting world health organization toxic equivalency factor dioxin and dioxin-like polychlorinated biphenyl levels in farmed atlantic salmon (Salmo salar) based on known levels in feed

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2007
Marc H. G. Berntssen
Abstract Assimilation and elimination rate constant of dietary polychlorinated dibenzo- p -dioxins and dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (DLPCBs) with a World Health Organization toxic equivalency factor (WHO-TEF) were estimated in market-size Atlantic salmon (Salmo salar) using fish that were previously fed vegetable oil,based (low in PCDD/Fs and DLPCBs) or fish oil,based (high in PCDD/Fs and PCBs) diets. At the start of the kinetic trial, half the fish that were fed fish oils were fed vegetable oil feeds and inverted (cross-over design) for five months. The assimilation efficiencies of the PCDD/F congeners were more variable (3,89%) and, generally, were lower than those of the DLPCBs (70,80%). Among the PCDD/F congeners, the assimilation efficiency of the most toxic tetra- and pentachlorinated PCDD/Fs was greater than that of higher-chlorinated PCDD/Fs. Elimination rates for DLPCBs were higher than those for PCDD/Fs. Lower-chlorinated PCDDs had a lower elimination rate than the higher-chlorinated PCDDs, but no differences were observed among PCDF congeners or DLPCB congeners. Kinetic parameters were used to predict the level of WHO-TEF dioxins and DLPCBs in Atlantic salmon reared in a large-scale facility under commercial conditions. Predictions were based on preanalyzed levels of these organochlorines in feeds with three different replacement levels (0, 30, and 60%) of vegetable oil. A simple one-compartmental, first-order kinetic model was used to predict the level of sum WHO toxic equivalents for PCDD/Fs and DL-PCBs. The predicted values varied by 0 to 11% from the measured values in the commercially reared salmon. [source]

Accumulation and distribution of polychlorinated dibenzo- p -dioxin, dibenzofuran, and polychlorinated biphenyl congeners in atlantic salmon (Salmo salar)

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 7 2004
Pirjo Isosaari
Abstract Adult Atlantic salmon (Salmo salar) were fed on four diets containing polychlorinated dibenzo- p -dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs) for 30 weeks. Lipid-normalized concentrations showed that all congeners were equally partitioned between whole-fish and fillet samples. Skinned fillet accumulated approximately 30% of the total PCDD/F and PCB content in fish. Accumulation efficiencies in whole fish were 43% for 2,3,7,8-chlorinated dibenzo- p -dioxins and dibenzofurans, 83% for dioxin-like PCBs, and 78% for other PCB congeners. Among PCDD/Fs, tetra- and pentachlorinated congeners were preferentially accumulated in salmon, whereas hepta- and octachlorinated dibenzo- p -dioxins were excreted in the feces. Substitution patterns that were associated with a preferential accumulation of PCBs in salmon included non- ortho substitution and tetrachlorination. Accumulation efficiencies and lipid-normalized biomagnification factors (BMFs) were not influenced by the PCDD/F and PCB concentrations of the diets. Biomagnification (BMF > 1) of tetra- and pentachlorinated dibenzo- p -dioxins and dibenzofurans and of all the PCBs was observed. Differences in the behavior of PCDD/F and PCB congeners resulted in a selective enrichment of the most toxic congeners in salmon. [source]

Toxicokinetics of sediment-associated polybrominated diphenylethers (flame retardants) in benthic invertebrates (Lumbriculus variegatus, oligochaeta)

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2004
Matti T. Leppänen
Abstract Polybrominated diphenylethers (PBDEs) are ubiquitous environmental contaminants showing rapid temporal increase in some sample types. The compounds are known to biomagnify in aquatic food webs and are assumed to archive into sediments and soils. Currently, no direct evidence indicates whether sediment-associated PBDEs are available for biota. The aim of the present study was to explore the uptake and elimination of two common congeners (47 and 99) in sediment-inhabiting invertebrates to shed light on possible bioavailability of sediment-associated PBDEs. Two clean lake sediments were spiked with environmentally relevant concentrations of 14C-labeled tetra- and pentabromo diphenylether, and oligochaetes (Lumbriculus variegatus) were exposed for three or four weeks to allow kinetic accumulation calculations. Subsequent depuration tests were performed after three weeks of exposure to obtain depuration rates. Both congeners were clearly bioavailable, and only slight differences in steady-state tissue concentrations were found between the four sediment-ingesting oligochaete treatments (biota sediment accumulation factors [BSAFs], 3.0,3.7). The tetrabromo diphenylether-exposed oligochaetes that did not ingest sediment had clearly lower influx rates (0.1 vs 1,3 nmol h -1) than sediment-ingesting worms. Also, the estimated BSAF (1.8) was statistically different from that of the sediment-ingesting oligochaetes. These findings support the significance of feeding behavior in bioaccumulation of very hydrophobic organic contaminants. Depuration of both congeners was biphasic, indicating two kinetically different compartments in L. variegatus. Compartment A made up 73 to 92% of total radioactivity in tissues and had relatively fast depuration rates (half-lives, 10.5,47.5 h); the smaller compartment B had very slow depuration rates. No significant biotransformation of PBDEs was evident. The present study clearly demonstrates that the sediment-associated PBDEs, like other hydrophobic organic contaminants of environmental concern, are not totally sequestered from sediment-inhabiting oligochaetes and are subject to trophic transfer. [source]

Spatial distribution of polychlorinated naphthalenes in air over the Great Lakes and air-water gas exchange in Lake Ontario

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 9 2003
Paul A. Helm
Abstract High-volume air sample were collected during research cruises of Lake Superior in August 1996 and May 1977 and of Lake Ontario (North America) in July and September 1998 and June 2000 and analyzed for polychlorinated naphthalenes (PCNs). Levels of tetra- to octachloronaphthalene (,PCN) varied spatially, with mean values (±SD) of 1.78 ± 0.74 and 1.46 ± 1.07 pg m,3 for Lake Superior in 1996 and 1997, respectively, and of 5.53 ± 2.19 and 5.60 ± 2.24 pg m,3 for Lake Ontario in 1998 and 2000, respectively. Evaporative sources were predominant, although combustion marker congeners such as tetrachloronaphthalenes 44 and 29 and pentachloronaphthalene 54 were present in most samples and were enhanced relative to technical PCN mixtures. The ,PCN concentrations were higher in Lake Ontario samples collected in the western half of the lake and when winds were from the west. Greater proportions of the population and industrial areas are located around the western part of Lake Ontario. Water-air fugacity ratios, calculated from air and water samples collected in June 2000, indicate that the trichloronaphthalenes are volatilizing from Lake Ontario, whereas the tetrachloronaphthalenes are close to equilibrium and the net deposition of tetrachloronaphthalenes can occur when the urban air plume influences levels over the lake. [source]