- Triazolopyridine, a New Derivative for the Structural Determination of Fatty Acids by Gas Chromatography/Mass Spectrometry
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Triazolopyridine is proposed as a new derivative for the location of branches and double bonds in fatty acids.It is compared with previously used derivatives and found to be clearly superior to the pyrrolidide and slightly superior to the β-picolinyl ester with regard to the structure-specific fragmentation pattern.It is prepared by reacting the activated acid with 2-hydrazinopyridine followed by cyclization.
- Vetter, Walter,Meister, Walter,Oesterhelt, Gottfried
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- Mass Spectrometric Studies on 17β-Estradiol-17-fatty Acid Esters: Evidence for the Formation of Anion-Dipole Intermediates
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The behaviour towards low collision energy processes (eV range) of (1-) prepared under negative ion chemical ionization (NICI) ammonia conditions from 17β-estradiol-17-fatty acid esters has been investigated.From such bifunctional compounds containing two acidic sites (i.e. phenol and ester groups), two isomeric forms (i.e. phenoxide and enolate forms) characterize the (1-) ion structures, whose distribution depends on the ion preparation mode.Here NICI (ammonia) provides both phenoxide and enolate forms as the (1-) species.This behaviour contrasts with the regioselectivity observed for proton abstraction from phenol under NICI (N2O) and fast atom bombardment conditions.Production of both phenoxide and enolate forms in NICI (ammonia) is demonstrated under NICI (ND3) conditions in which DO-labelled d - H>(1-) enolate ions are produced in a similar yield to unlabelled d - D>(1-) phenoxide ions.Collisionally activated dissociation (CAD) spectra of both isomeric deprotonated molecules differ strongly by the presence of two different pairs of complementary daughter ions, suggesting that these ionic species are unconvertible.This is due to a steric hindrance effect on the long-distance proton transfer.A mechanistic investigation on the formation of fragment ion pairs produced under CAD was performed with various deuterium-labelled molecules.From these experiments, evidence is provided for molecular isomerizations into ion-dipole complexes (prior to dissociation) which are structurally dependent on the initial charge location.Direct dissociation of these intermediates competes with the occurence of exothermic proton transfer(s) yielding the formation of other isomeric intermediate forms.The orientation of these proton transfers is dictated by the relative acidities of both moieties of the complex.
- Debrauwer, Laurent,Paris, Alain,Rao, Dinesh,Fournier, Francoise,Tabet, Jean-Claude
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p. 709 - 719
(2007/10/02)
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- DEUTERON NMR STUDY OF MOLECULAR MOBILITY IN A POLYMER MODEL MEMBRANE.
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The molecular mobility of a polymer model membrane is studied by **2H NMR. The lipid analogue consists of a quaternary ammonium ion, to which a methacryloylic moiety is attached via a spacer to the hydrophilic head group. A methylene group of the spacer, the methyl-head group and methylene groups in the 1-, 2-, and 7-position of the lipid chains are selectively deuterated. Temperature dependent **2H NMR spectra are reported for both, the monomer and the polymer membrane below and above the main phase transition. The data are quantitatively analyzed in terms of a simple motional model, in which the complex molecular dynamics is approximated by a six-site jump model describing rotations about the long axis of the molecule and conformational changes. The increasing mobility with increasing temperature is only in part due to an increase of the jump rate between different sites.
- Ebelhaeuser,Spiess
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p. 1208 - 1214
(2007/10/02)
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