Home About us Contact
|
Home About us Contact | ||
|
|
||
Linear Isomer (linear + isomer)
Selected AbstractsDisposition of perfluorinated acid isomers in sprague-dawley rats; Part 1: Single doseENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2009Jonathan P. Benskin Abstract Perfluorinated acids (PFAs) and their precursors (PFA-precursors) exist in the environment as linear and multiple branched isomers. These isomers are hypothesized to have different biological properties, but no isomer-specific data are currently available. The present study is the first in a two-part project examining PFA isomer-specific uptake, tissue distribution, and elimination in a rodent model. Seven male Sprague-Dawley rats were administered a single gavage dose of approximately 500 ,g/kg body weight perfluorooctane sulfonate (C8F17SO3,, PFOS), perfluorooctanoic acid (C7F15CO2H, PFOA), and perfluorononanoic acid (C8F17CO2H, PFNA) and 30 ,g/kg body weight perfluorohexane sulfonate (C6F13SO3,, PFHxS). Over the subsequent 38 d, urine, feces, and tail-vein blood samples were collected intermittently, while larger blood volumes and tissues were collected on days 3 and 38 for isomer analysis by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). For all PFAs, branched isomers generally had lower blood depuration half-lives than the corresponding linear isomer. The most remarkable exception was for the PFOS isomer containing an alpha-perfluoromethyl branch (1m -PFOS), which was threefold more persistent than linear PFOS, possibly due to steric shielding of the hydrophilic sulfonate moiety. For perfluoromonomethyl-branched isomers of PFOS, a structure,property relationship was observed whereby branching toward the sulfonate end of the perfluoroalkyl chain resulted in increased half-lives. For PFHxS, PFOA, and PFOS, preferential elimination of branched isomers occurred primarily via urine, whereas for PFNA preferential elimination of the isopropyl isomer occurred via both urine and feces. Changes in the blood isomer profiles over time and their inverse correlation to isomer elimination patterns in urine, feces, or both provided unequivocal evidence of significant isomer-specific biological handling. Source assignment based on PFA isomer profiles in biota must therefore be conducted with caution, because isomer profiles are unlikely to be conserved in biological samples. [source] Bent and Linear Forms of the (,-Oxo)bis[trichloroferrate(III)] Dianion: An Intermolecular Effect , Structural, Electronic and Magnetic PropertiesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 23 2003Agustí Lledós Abstract We have analyzed the great diversity of Fe,O,Fe angles, 140,180°, found in the X-ray structures of the (,-oxo)bis[trichloroferrate(III)] dianion [Cl3FeOFeCl3]2, from both experimental and theoretical points of view. Theoretical calculations show that only the linear isomer is found as a minimum on the potential energy surface. Detailed analysis of the crystal packing indicates that the angular form is due to attractive intermolecular interactions. Analysis of a selected reduced set of the 45 crystal structures retrieved from the Cambridge Structural Database allowed us to classify the bending of the [Cl3FeOFeCl3]2, dianion in three categories, depending on the balance and strength of the intermolecular O···H,X contacts. A crystal diffraction study on the bis(benzyltrimethylammonium) salt has shown both bent (144.6°) and linear (180°) forms of the (,-oxo)bis[trichloroferrate(III)] dianion. The magnetic susceptibility of this compound has been fitted by assuming two equally weighted contributions (Jang and Jlin) of the two forms, considering Jang , Jlin estimated by theoretical calculations. The obtained Jang and Jlin of ,117 and ,133 cm,1 respectively, agree well with B3LYP results. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Enantioselective Copper-Catalysed Allylic Alkylation of Cinnamyl Chlorides by Grignard Reagents using Chiral Phosphine-Phosphite LigandsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010Wibke Lölsberg Abstract The copper(I)-catalysed SN2,-type allylic substitution of E -3-aryl-allyl chlorides (cinnamyl chlorides) using Grignard reagents represents a powerful method for the synthesis of compounds carrying a benzylic stereocentre. By screening a small library of modular chiral phosphine-phosphite ligands a new copper(I)-based catalyst system was identified which allows the performance of such reactions with exceptional high degrees of regio- and enantioselectivity. Best results were obtained using TADDOL-derived ligands (3,mol%), copper(I) bromide,dimethyl sulfide (CuBr,SMe2) (2.5,mol%) and methyl tert -butyl ether (MTBE) as a solvent. Various (1-alkyl-allyl)benzene derivatives were prepared with up to 99% ee (GC) in isolated yields of up to 99%. In most cases the product contained less than 3% of the linear regioisomer (except for ortho -substituted substrates). Both electron-rich and electron-deficient cinnamyl chlorides were successfully employed. The absolute configuration of the products was assigned by comparison of experimental and calculated CD spectra. The substrates were prepared from the corresponding alcohols by reaction with thionyl chloride. Initially formed mixtures of regioisomeric allylic chlorides were homogenised by treatment with CuBr,SMe2 (2.5,mol%) in the presence of triphenyl phosphine (PPh3) (3,mol%) in MTBE at low temperature to give the pure linear isomers. In reactions with methylmagnesium bromide (MeMgBr) an ortho -diphenylphosphanyl-arylphosphite ligand with an additional phenyl substituent in ortho, -position at the aryl backbone proved to be superior. In contrast, best results were obtained in the case of higher alkyl Grignard reagents (such as ethyl-, n -butyl-, isopropyl-, and 3-butenylmagnesium bromides) with a related ligand carrying an isopropyl substituent in ortho, -position. The method was tested on a multi-mmol scale and is suited for application in natural product synthesis. [source] Simultaneous determination of parabens, triclosan and triclocarban in water by liquid chromatography/electrospray ionisation tandem mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 12 2009Iria González-Marińo A method for the determination of several household biocides in water by liquid chromatography/electrospray ionisation tandem mass spectrometry (LC/ESI-MS/MS) is presented. It permits the simultaneous determination of triclosan (TCS), triclocarban (TCC) and seven parabens, including the distinction between branched and linear isomers of propyl (i -PrP and n -PrP) and butyl parabens (i -BuP and n -BuP). Prior to LC/MS/MS, analytes are preconcentrated by solid-phase extraction (SPE) on Oasis HLB (60,mg) cartridges at natural sample pH and subsequently eluted with 4,mL of methanol. This simple SPE procedure provides extraction recoveries above 85% except for raw wastewater, where it falls to 65% for TCC. The performance of the method was tested with two triple-quadrupole LC/MS instruments from a low/mid and mid/high market range: a Varian 1200L and an API-4000. The latter system provided between 3 and 80 times lower limits of quantification (LOQs) than the first one, in the 0.08,0.44,ng/L range for surface water. Moreover, a comparison of matrix effects on both instruments showed a very different behaviour, particularly in the case of parabens. For these compounds signal suppression was observed in the 1200L instrument and signal enhancement with the 4000 instrument. As a result, different calibration approaches were chosen for them and this pointed to the need of matrix effect re-evaluation in method transfer between different LC/MS systems. The application of the method to real samples showed the ubiquity of methyl paraben (MeP) and n -PrP (at the 1,6,µg/L in raw wastewater) and the coexistence of i -BuP and n -BuP at similar levels (ca. 100,200,ng/L in raw wastewater). Copyright © 2009 John Wiley & Sons, Ltd. [source] | ||||||||||