Search results for "ISOMER"
showing 10 items of 1308 documents
Eight-Membered Rings With Two Heteroatoms 1,2
2022
The chapter titled “Eight-membered Rings with two Heteroatoms 1,2” deals with heterocine rings with two heteroatoms in a 1,2 relationship, namely 1,2-diazocine, 2H-1,2-oxazocine, 2H-1,2-thiazocine, 1,2-dioxocin, 1,2-oxathiocin and 1,2-dithiocin. This article covers the literature from 2007 to 2019 and reports the chemistry of uncondensed derivatives, heterocines fused to carbocycles and heterocycles, as well as bridged heterocines. As usual, in the case that a particular section is not mentioned, it means that no chemistry has been reported. In this article, the “Biosynthesis” paragraph was additionally introduced, since in the latest years the contribution of Nature to the synthesis of dih…
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…
Experimental and theoretical NMR and IR studies of the side‐chain orientation effects on the backbone conformation of dehydrophenylalanine residue
2011
Conformation of N‐acetyl‐(E)‐dehydrophenylalanine N′, N′‐dimethylamide (Ac‐(E)‐ΔPhe‐NMe2) in solution, a member of (E)‐α, β‐dehydroamino acids, was studied by NMR and infrared spectroscopy and the results were compared with those obtained for (Z) isomer. To support the spectroscopic interpretation, the ϕ, ψ potential energy surfaces were calculated at the MP2/6‐31 + G(d,p) level of theory in chloroform solution modeled by the self‐consistent reaction field‐polarizable continuum model method. All minima were fully optimized by the MP2 method and their relative stabilities were analyzed in terms of π‐conjugation, internal H‐bonds and dipole interactions between carbonyl groups. The obtained N…
Conformational properties of cyanomethoxy calix[4]arenes.
2005
O-Alkylation of the dinitro calix[4]arene 2, easily available by selective ipso-nitration of the di-cyanomethyl ether 1, with allylbromide (DMF/Cs2CO3) gave tetraethers 3 and 4 with anti- and syn-orientations of the two allyl ether residues. The two possible stereoisomers of 3 in the partial cone and 1,2-alternate conformation exist as an equilibrium mixture which could be quantitatively analysed by 1H NMR spectroscopy. The temperature dependence of this equilibrium leads to ΔH0 = − 7.6 to −9.7 kJ mol−1 in different solvents (tetrachloroethane, benzene, dimethylsulfoxide). Since 3(1,2-alt) could be obtained in pure form, its isomerisation to the equilibrium mixture with 3(paco) could be fol…
Substituted Dibenzothiophenes I: Synthesis, Chromatography, Mass Spectrometry and Structure Elucidation by1H NMR Spectroscopy
1992
Abstract Some polychlorinated and polymethylated dibenzothiophenes have been synthesized to serve as model compounds in environmental analysis. In order to obtain pure isomers, the synthesis mixtures have been fractionated with reversed-phase high performance liquid chromatography. In spite of a high sensitivity, mass spectrometry does not provide any reliable way to determine the precise structures of different isomers. Therefore, 1H NMR spectroscopy has been utilized as an aid in their analysis. The structures for two isomeric tetramethyldibenzothiophenes could be suggested on the basis of their 1H NMR spectra. Also some proposals for possible structures of two isomeric trimethyldibenzoth…
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…
Genomic organization and promoter characterization of the gene encoding a putative endoplasmic reticulum chaperone, ERp29
2002
Abstract ERp29 is a soluble protein localized in the endoplasmic reticulum (ER) of eukaryotic cells, which is conserved in all mammalian species. The N-terminal domain of ERp29 displays sequence and structural similarity to the protein disulfide isomerase despite the lack of the characteristic double cysteine motif. Although the exact function of ERp29 is not yet known, it was hypothesized that it may facilitate folding and/or export of secretory proteins in/from the ER. ERp29 is induced by ER stress, i.e. accumulation of unfolded proteins in the ER. To gain an insight into the mechanisms regulating ERp29 expression we have cloned and characterized the rat ERp29 gene and studied in details …
Towards large‐scale steady‐state enhanced nuclear magnetization with in situ detection
2021
Magnetic resonance in chemistry 59(12), 1208 - 1215 (2021). doi:10.1002/mrc.5161
Isomeric state of $^{80}$Y and its role in the astrophysical rp-process
2001
5 pages, 7 figures.-- PACS nrs: 21.10.Tg; 23.20.Nx; 27.50.+e.
Identification of isomeric states in the N=73 neutron-deficient nuclei 132Pr and 130La
2012
Decays from isomeric states in the neutron-deficient N=73 nuclei 132Pr and 130La have been observed for the first time. Half-lives of 486(70) ns and 2.46(4) μs were measured for two isomeric states in 132Pr. The decay from the 486ns (8 -) isomer has been interpreted as a hindered E1 transition from the bandhead state of the excited πh 11/2νg 7/2 configuration. The decay from the 2.5 μs (8 +) isomer is consistent with the Weisskopf estimate for a low-energy E2 transition. An analogous 0.74(3) μs decay from an (8 +) isomer in the neighboring isotone 130La has also been observed which similarly can be explained if the transition has E2 character. The Weisskopf interpretation for the isomer hin…