Search results for "alkane"
showing 10 items of 162 documents
The solubilisation behaviour of some dichloroalkanes in aqueous solutions of PEO-PPO-PEO triblock copolymers: a dynamic light scattering, fluorescenc…
2006
The aggregation behaviour of PEO-PPO-PEO triblock copolymers in water and in water + chlorinated additive mixtures was studied by means of fluorescence spectroscopy, dynamic light scattering (DLS), and small-angle neutron scattering (SANS). The copolymers were chosen such as to investigate the effects of molecular architecture (L35 and 10R5) and molecular weight by keeping constant the hydrophilic/hydrophobic balance (F88 and F108). 1,2-Dichloroethane was used as a prototype of water basins contaminants. The hydrodynamic radius of the block copolymer aggregates (R(h,M)) and the intensity ratio of pyrene of the first and the third vibrational band (I(1)/I(3)) were determined as a function of…
[3.3]Metacyclophane mit anti ‐Konformation
1992
[3.3]Metacyclophanes with anti Conformation The [3.3]metacyclophanes 5 and 9 with prevailing anti conformation were prepared by using different cyclisation techniques. 1H-NMR studies and X-ray structure analyses of both phanes 5 and 9 prove their unprecedented conformations.
Degrees of freedom effect on fragmentation in tandem mass spectrometry of singly charged supramolecular aggregates of sodium sulfonates
2012
The characteristic collision energy (CCE) to obtain 50% fragmentation of positively and negatively single charged noncovalent clusters has been measured. CCE was found to increase linearly with the degrees of freedom (DoF) of the precursor ion, analogously to that observed for synthetic polymers. This suggests that fragmentation behavior (e.g. energy randomization) in covalent molecules and clusters are similar. Analysis of the slope of CCE with molecular size (DoF) indicates that activation energy of fragmentation of these clusters (loss of a monomer unit) is similar to that of the lowest energy fragmentation of protonated leucine-enkephalin. Positively and negatively charged aggregates be…
A microcalorimetric comparison of the effect ofn-alkane preadsorption on the adsorption of argon and nitrogen on Silicalite-I
1994
Then-alkanes of different lengths were preadsorbed to selectively block part of the micropores of a MFI-type zeolite, Silicalite-I. The porosity available to argon and nitrogen was then studied by quasi-equilibrium adsorption microcalorimetry and volumetry at 77K and compared to what was found for the bare zeolite. Indeed, although partial adsorption ofn-alkanes does not alter the value of the differential enthalpies of adsorption for both argon and nitrogen, then-butane preadsorption diminishes the adsorption capacity by inducing inaccessible volumes in the micropore network. Moreover, the microcalorimetric experiments clearly show thatn-butane is not evenly distributed in the zeolite chan…
Short-term occupations at high elevation during the Middle Paleolithic at Kalavan 2 (Republic of Armenia).
2021
The Armenian highlands encompasses rugged and environmentally diverse landscapes and is characterized by a mosaic of distinct ecological niches and large temperature gradients. Strong seasonal fluctuations in resource availability along topographic gradients likely prompted Pleistocene hominin groups to adapt by adjusting their mobility strategies. However, the role that elevated landscapes played in hunter-gatherer settlement systems during the Late Pleistocene (Middle Palaeolithic [MP]) remains poorly understood. At 1640 m above sea level, the MP site of Kalavan 2 (Armenia) is ideally positioned for testing hypotheses involving elevation-dependent seasonal mobility and subsistence strateg…
Stereoselective Total Synthesis and Absolute Configuration of the Natural Decanolides (−)-Microcarpalide and (+)-Lethaloxin. Identity of (+)-Lethalox…
2005
[reaction: see text] Convergent, stereoselective syntheses of the pharmacologically active, naturally occurring lactones (-)-microcarpalide and (+)-lethaloxin have been achieved from the commercially available, chiral reagents (R)-glycidol, (S,S)-tartaric acid, and d-ribose as the starting materials. These syntheses have further served to establish the hitherto unknown absolute configuration of (+)-lethaloxin and to show its identity with (+)-pinolidoxin.
Evaluation of acyl coenzyme A oxidase (Aox) isozyme function in the n- alkane-assimilating yeast Yarrowia lipolytica
1999
ABSTRACT We have identified five acyl coenzyme A (CoA) oxidase isozymes (Aox1 through Aox5) in the n -alkane-assimilating yeast Yarrowia lipolytica , encoded by the POX1 through POX5 genes. The physiological function of these oxidases has been investigated by gene disruption. Single, double, triple, and quadruple disruptants were constructed. Global Aox activity was determined as a function of time after induction and of substrate chain length. Single null mutations did not affect growth but affected the chain length preference of acyl-CoA oxidase activity, as evidenced by a chain length specificity for Aox2 and Aox3. Aox2 was shown to be a long-chain acyl-CoA oxidase and Aox3 was found to …
Prenatal exposure to perfluoroalkyl substances and birth outcomes in a Spanish birth cohort
2017
BACKGROUND: Prenatal perfluorooctanoate (PFOA) exposure has been associated with reduced birth weight but maternal glomerular filtration rate (GFR) may attenuate this association. Further, this association remains unclear for other perfluoroalkyl substances (PFAS), such as perfluorooctane sulfonate (PFOS), perfluorohexane sulfonate (PFHxS), and perfluorononanoate (PFNA). We estimated associations between prenatal PFAS exposure and birth outcomes, and the influence of GFR, in a Spanish birth cohort. METHODS: We measured PFHxS, PFOS, PFOA, and PFNA in 1st-trimester maternal plasma (years: 2003-2008) in 1202 mother-child pairs. Continuous birth outcomes included standardized weight, length, he…
Prenatal perfluoroalkyl substance exposure and neuropsychological development throughout childhood: The INMA Project.
2021
Abstract Background Perfluoroalkyl substances (PFASs) have been related to neurodevelopmental toxicity in animals. However, human studies are inconclusive. Objectives To evaluate the association between prenatal PFAS exposure and neuropsychological development during childhood. Methods 1240 mother–child pairs from the Spanish INMA Project were analyzed. Perfluorohexanesulfonic acid (PFHxS), perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS), and perfluorononanoic acid (PFNA) were measured in first-trimester maternal plasma. Neuropsychological development was assessed at 14 months, 4–5 and 7 years covering four domains: general cognitive, general motor, attention, and working me…
Early Life Exposure to Perfluoroalkyl Substances (PFAS) and ADHD: A Meta-Analysis of Nine European Population-Based Studies
2020
Introduction: To date, the evidence for an association between perfluoroalkyl substances (PFAS) exposure and attention deficit and hyperactivity disorder (ADHD) is inconclusive. Objective: We investigated the association between early life exposure to perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA), and ADHD in a collaborative study including nine European population-based studies, encompassing 4,826 mother-child pairs. Methods: Concentrations of PFOS and PFOA were measured in maternal serum/plasma during pregnancy, or in breast milk, with different timing of sample collection in each cohort. We used a validated pharmacokinetic model of pregnancy and lactation to estimate…