Search results for "Isomerism"
showing 10 items of 747 documents
Topographical geometric factors governing the biological activities of methomyl derivatives on binding receptors of maize mitochondria
1986
Abstract The topographical study of the binding receptors of T and N mitochondria was undertaken with methomyl derivatives acting as molecular probes. The two biological activities related to topography and geometric isomerism are distinguishable from the receptor sites of T and N mitochondria.
Geometry of conjugated double bonds of CLA isomers in a commercial mixture and in their hepatic 20∶4 metabolites
1999
Rats were fed a fat-free diet for 2 wk. After this period, while maintaining the animals on the same diet, the rats were given intragastrically 180 mg per day of a mixture of conjugated linoleic acids (CLA) as triacylglycerols. Gas chromatography mass spectrometry (GC-MS) analyses of this mixture, as well as hydrazine reduction and GC-MS and GC-Fourier transform infrared analyses of the resulting monoenes, revealed the presence of two major isomers, the 9c,11t- and the 10t,12c-18:2 accompanied by smaller amounts of the 8t, 10c and the 11c, 13t-18:2 isomers. Minor quantities of cis,cis and trans,trans conjugated isomers also were detected. The total fatty acid methyl esters from the liver li…
Stereochemical features of the hydrolysis of 9,10-epoxystearic acid catalysed by plant and mammalian epoxide hydrolases
2002
cis-9,10-Epoxystearic acid was used as a tool to probe the active sites of epoxide hydrolases (EHs) of mammalian and plant origin. We have compared the stereochemical features of the hydrolysis of this substrate catalysed by soluble and membrane-bound rat liver EHs, by soluble EH (purified to apparent homogeneity) obtained from maize seedlings or celeriac roots, and by recombinant soybean EH expressed in yeast. Plant EHs were found to differ in their enantioselectivity, i.e. their ability to discriminate between the two enantiomers of 9,10-epoxystearic acid. For example, while the maize enzyme hydrated both enantiomers at the same rate, the EH from soybean exhibited very high enantioselecti…
Chiral Serum Pharmacokinetics of 4-Fluoroamphetamine after Controlled Oral Administration
2021
Abstract Over the last two decades, misuse of 4-fluoroamphetamine (4-FA) became an emerging issue in many European countries. Stimulating effects last for 4–6 hours and can impact psychomotor performance. The metabolism of amphetamine-type stimulants is stereoselective and quantification of (R)- and (S)-enantiomers has been suggested for assessing time of use. To date, no data on enantioselective pharmacokinetics is available for 4-FA in serum samples. An enantioselective liquid chromatography−tandem mass spectrometry (LC–MS-MS) method was developed using a chiral Phenomenex® Lux 3 μm AMP column. Validation of the method showed satisfactory selectivity, sensitivity, linearity (0.5–250 ng/mL…
A butterfly like motion as a clue to the photophysics of thioxanthone
2006
Abstract A theoretical, quantum-chemical study of the thioxanthone (TX) molecule has been performed at the MP2 and CASPT2 levels of theory. Geometries, absorption energies, and transition and state properties have been investigated. Two conformers have been found very close in energy with planar (P) and non-planar (NP) structures, the latter characterized by a dihedral angle θ = 173.3° representing the bend of the side benzene rings and an out-of-plane angle ϕ = 4° of the C O bond. Large changes in the relative positions and properties of the two low-lying electronic absorption bands, ππ * and nπ * , are computed when changing the conformation. As a consequence of the analysis of the TX a…
Conformational Properties of Nickel(II) Octaethylporphyrin in Solution. 2. A Low-Temperature Optical Absorption Spectroscopy Study
1996
We have measured the absorption spectrum of Ni(II) octaethylporphyrin in CH2Cl2 and in a 50% v/v isopentane/ethyl ether mixture as a function of temperature between 150 and 300 K and 40 and 300 K, respectively. The Soret band can be decomposed into two subbands whose frequencies differ by 220 cm-1. By analogy with resonance Raman results (Jentzen et al. J. Phys. Chem. 1996, 100, 14184−14191 (preceding paper)), we attribute the low-frequency subband to a conformer with a nonplanar macrocycle structure, whereas the high-frequency subband is interpreted as resulting from a planar conformer. The subbands' intensity ratios exhibit a solvent-dependent van't Hoff behavior between 300 and 160 K. Cr…
Reversed phase liquid chromatography for the enantioseparation of local anaesthetics in polysaccharide-based stationary phases. Application to biodeg…
2020
[EN] A comprehensive study on the chiral separation of bupivacaine, mepivacaine, prilocaine and propanocaine with eight commercial polysaccharide-based chiral stationary phases (CSPs) in reversed phase conditions compatible with MS detection is performed. Methanol and acetonitrile are used as organic modifiers. Retention and resolution values obtained for each compound in the different CSPs and mobile phases are compared. The polysaccharide-based CSPs tested present different enantioselectivity towards the analytes. From the results, the experimental conditions for determining the enantiomers of bupivacaine, mepivacaine, prilocaine and propanocaine in saline aqueous samples using MS detecti…
The identification of vicinally substituted cyclohexane isomers in their mixtures by 1H and 13C NMR spectroscopy.
2000
The radical addition reactions of organobromine compounds, XBr (X = CH2COOMe, PhCH2, CHBr2 and CCl3) with cyclohexene afforded mixtures of cis/trans isomer pairs of 1-X-2-Br-cyclohexanes. In addition to benzyl benzoyloxy derivatives are formed also, when benzoyl peroxide is used as an initiator. Owing to the great difficulties in separating these cis/trans isomer pairs, they are identified directly in their mixtures by NMR spectroscopy. In addition to one-dimensional (ID) 1H, proton decoupled 13C and DEPT-135, also two-dimensional (2D) 13C-13C INADEQUATE as well as 1H-13C HMQC experiments have been used in assigning the signals of each compound in their mixtures. The identification of each …
N-Heterocyclic Carbene Catalyzed [3+2] Cycloaddition of Enals with Masked Cinnamates for the Asymmetric One-Pot Synthesis of Adipic Acid Derivatives.
2017
A novel short entry to 3,4-disubstituted adipic acids has been developed by employing an asymmetric NHC-catalyzed [3+2] cycloaddition of enals with masked cinnammates in moderate to good yields and high stereoselectivities. The synthetic utility of the protocol was demonstrated by the basic conversion of the masked cyclopentanone intermediates to 3S,4S-disubstituted adipic acid precursors of pharmaceutically important gababutins.
The autoantigen La/SS-B: Analysis of the expression of alternatively spliced La mRNA isoforms
1996
The gene for the nuclear autoantigen La/SS-B encodes two La mRNA isoforms. In order to study the function and expression of both La mRNA forms, an in situ hybridization procedure was developed allowing the selective identification of either exon 1 or exon 1'. For this purpose, digoxigenin-labeled exon-specific sense and anti-sense probes were prepared by in vitro transcription from plasmids that contained the respective exon sequence. Detection of the probes was carried out by using rhodamine-conjugated anti-digoxigenin antibody and confocal laser scanning microscopy. Both La mRNAs were found in the cytoplasm of endothelial cells but not in smooth muscle cells. In addition to the in situ te…