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  • Digitale Medien  (31)
  • Analytical Chemistry and Spectroscopy  (21)
  • Organic Chemistry  (10)
  • 1
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 14 (1987), S. 603-607 
    ISSN: 0887-6134
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Fractional dietary Ca absorption, ‘a’, is measured by determining the ratio of two stable isotopic tracers, one of them orally (44Ca @ 0.2-0.5 mg/kg) and the other intravenously (42Ca @ 0.02-0.1 mg/kg). Thermal ionization mass spectrometry (TIMS) is used to measure the perturbation of natural abundance isotope ratios (delta % excess). Typical sensitivity of the TIMS permits detection of a 2.5 delta % excess change from the natural Ca isotope ratio with relative standard deviations of about 0.5%. At sufficiently long times absorption becomes constant so that ‘a’ is determined by a product of constants and a measured ratio.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    ISSN: 0899-0042
    Schlagwort(e): receptor-operated calcium channel antagonist ; 1H NMR ; chiral HPLC ; calmodulin ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 1H nuclear magnetic resonance at 360 MHz shows that SK&F 96365 (1-{β-[3-(p-methoxyphenyl)-propyloxy]-p-methoxyphenethyl}-1H- imidazole hydrochloride), an antagonist of mammalian receptor-operated calcium channels, interacts with the calcium-binding regulatory protein calmodulin (CaM). This may be inferred by a number of chemical shift changes in the spectrum of the calcium-saturated protein induced by addition of the compound. Moreover, two well-resolved singlets corresponding to the 2-proton of the SK&F 96365 imidazolium moiety are observed in the spectrum over a wide range of protein:compound ratios. Separation of rac SK&F 96365 into its two enantiomers by high-performance liquid chromatography on a cellulose tris (4-methylbenzoate) column enabled us to show that the doubling of this NMR signal in the presence of CaM is due to a propensity of the protein to distinguish between the two optical isomers of the compound.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 6 (1994), S. 239-244 
    ISSN: 0899-0042
    Schlagwort(e): HPLC ; reverse-phase additive ; β-cyclodextrin ; methylphenobarbitone ; molecular mechanics ; complex stability ; chiral separation ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Molecular modelling of β-cyclodextrin and optimisation of its potential energy suggests that a favoured conformation is that distorted from a symmetrical torus. The inclusion of water molecules into the torus cavity simulates the increased stability in an aqueous solvent. Complexes of β-cyclodextrin with (R)- and (S)-enantiomers of methylphenobarbitone have been modelled and energetically optimised by the application of molecular mechanics. The simulations suggests that the guest molecules adopt an orientation in which the phenyl ring is projected into the torus cavity, with in each case the plane of the ring parallel to a longer axis of the distorted torus and slightly displaced from the axis through the torus cavity. It is suggested that the asymmetry in the macrocyclic ring contributes to chiral recognition as a result of additional discriminatory binding to the barbiturate ring residue of each enantiomer, which occupy different 3D geometries. The enantiomers form complexes of different minimum potential energies. The resulting difference in complex stability can be related to the behaviour of β-cyclodextrin, as a mobile phase additive in reverse-phase HPLC to effect chiral separation of rac-medthylphenobarbitone during chromatography. © 1994 Wiley-Liss, Inc.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 8 (1996), S. 58-66 
    ISSN: 0899-0042
    Schlagwort(e): molecular mechanics ; HPLC ; chiral separation ; methylphenobarbitone ; hexobarbitone ; ibuprofen ; mandelic acid ; ephedrine ; pseudoephedrine ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: β-Cyclodextrin and its derivatives have been utilised to effect chiral separation in HPLC and CZE, both as stationary phases and mobile phase additives. The basis of the method is assumed to depend upon the formation of inclusion complexes of differing stabilities between enantiomeric analytes and the cyclodextrin, resulting in a differential dynamic distribution between chromatographic phases. In this study, force field calculations have been employed to model the inclusion complexes of enantiomeric brompheniramine, ephedrine, pseudoephedrine, ibuprofen, mandelic acid, methylphenobarbitone, and hexobarbitone with β-cyclodextrin. The resulting values for Δ(ΔH), the difference in enthalpy of complex formation between enantiomeric pairs has been compared with literature chromatographic data to explain the ability of the systems to achieve enantiomeric separations. © 1996 Wiley-Liss, Inc.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 705-711 
    ISSN: 0894-3230
    Schlagwort(e): Organic Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: An infrared spectroscopic study of the 1 : 1 hydrogen-bond association of amidates with both methanol and 4-fluorophenol showed that the site of complexation is the oxygen of the amidate function. However the formamidate HCON2Me3 forms a second 1 : 1 complex on the nitrogen of the amidate. The formation constants of the hydrogen-bond complexes of the amidates with the reference hydrogen-bond donor 4-FC6H4OH indicate that the amidates are stronger hydrogen-bond bases than are amides and amide vinylogues. As such, the amidates constitute the strongest carbonyl bases hitherto investigated on the hydrogen-bond basicity scale.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 8 (1994), S. 876-880 
    ISSN: 0951-4198
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Physik
    Notizen: The electron ionization mass spectra of fourteen 4-substituted (4-X) camphors have been recorded and analyzed using metastable ion analysis and exact mass measurement. With respect to camphor, alkyl substituents changed the relative importance of different fragmentation pathways, though they did not induce new fragmentations. Substituents X connected to the camphor framework through an atom having a lone pair of electrons were generally lost as HX. Overall the fragmentation behaviour was essentially independent of the inductive substituent constant. Under chemical ionization conditions, only methane of the reagent gases produced extensive fragmentations of these compounds; isobutane, acetone and ammonia were ineffective. The nature of the fragmentations was independent of both the inductive substituent constant of the substituent X and the proton affinity and heat of formation of the corresponding neutral compound HX.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 7
    ISSN: 1040-7685
    Schlagwort(e): chiral ; separation ; micellar ; capillary ; electrophoresis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: This article describes the synthesis of a novel chiral surfactant based on (R,R)-tartaric acid. (R,R)-Tartaric acid is acetylated while simultaneously forming a cyclic anhydride, which is then reacted with n-decylamine forming a chiral, long chain carboxylic acid. This carboxylic acid is then further reacted with the achiral amino acid taurine forming the required surfactant which has a sulfonic acid headgroup. Evidence for its surface activity and an estimate of its critical micelle concentration (cmc) have been obtained using surface tension measurements and conductivity. The surfactant has then been used as the additive in micellar electrokinetic capillary chromatography (MECC) to achieve chiral separations of compounds with multiple aromatic functionality. These separations are compared with those achieved with previously reported tartaric acid based surfactants which show a difference in selectivity. © 1995 John Wiley & Sons, Inc.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 8
    Digitale Medien
    Digitale Medien
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 22 (1993), S. 181-183 
    ISSN: 1052-9306
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: In 10 mM sodium phosphate, pH 7.6, containing 0.1 mM ethylenediaminetetraacetic acid, ions corresponding to the non-covalent, four-stranded oligonucleotide, d(CGCG4GCG)4, were detected by negative ion electrospray ionization (ESI) mass spectrometry at a low nozzle-skimmer (ΔNS) bias (-150 V), but not at a higher ΔNS bias (〉 -250 V). In contrast, when the sample was desalted and analyzed by ESI mass spectrometry at a low ΔNS bias only ions for the single-stranded d(CGCG4GCG) species were observed. These data agree with spectroscopic evidence which showed that oligonucleotides with the sequence motif 5′d(CGCGnGCG)3′, where n = 2-5, formed stable four-stranded complexes in the presence of monatomic cations, like K+, Ca2+, Na+ and Li+, but not in their absence.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 15 (1992), S. 696-697 
    ISSN: 0935-6304
    Schlagwort(e): Capillary GC ; Impurities ; 11-Bromoundecyl methacrylate ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 10
    ISSN: 0894-3230
    Schlagwort(e): Organic Chemistry ; Physical Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: An IR spectroscopic study of the hydrogen bonding of Bu3N+N-C≡N with 4-fluorophenol showed that the site of complexation is the nitrogen of the nitrile function. THe formation constant of the 1:1 complex in CCl4 indicates that this cyanamidate is a stronger hydrogen-bond base than is any nitrile, amine or pyridine. The Bu3N+-N- group increases the basicity of the nitrile group very efficiently because of the conjugation of two lone pairs on the anionic nitrogen with the π systems of the cyano group. This conjugation is also exemplified by the very low ν(C≡N) wavenumber (2104 cm-1).
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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