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  • Articles  (48)
  • Gas chromatography  (30)
  • NMR  (18)
  • Springer  (48)
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  • Articles  (48)
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  • Springer  (48)
  • American Chemical Society
  • American Institute of Physics
  • American Meteorological Society
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  • 1995-1999  (48)
  • 1990-1994
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  • 1
    Electronic Resource
    Electronic Resource
    Synthesis and characterization of alternating silane copolymers: (Me2Si−R2Si−Me2Si) n (1995)
    Springer
    Journal of inorganic and organometallic polymers and materials 5 (1995), S. 217-236 
    Details
    ISSN: 1572-8870
    Keywords: Polysilane ; NMR ; pyrolysis ; randomization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Bimodal molecular weight distributions of alternating copolymers of the type (Me2Si−R2Si−SiMe2) n , where R=hexyl and butyl, were obtained by polymerization of BrSiMe2−R2Si−Me2SiBr, using the Wurtz coupling method. Analysis of the samples by pyrolysis GC MS and solution29Si NMR indicated that some randomization occurred, due to cleavage of the original Si−Si bonds in the monomer. The extent of randomization was significantly greater in the high molecular weight fractions. Based on the nature of the rings from the py MGC/MS traces and the number on nonads found in the29Si spectra, two types of randomization processes have been proposed, involving backbiting followed by (1) ring expulsion or (2) redistribution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01057894
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  • 2
    Electronic Resource
    Electronic Resource
    Direct hydrogen-1, carbon-13, and nitrogen-15 NMR study of magnesium(II)-isothiocyanate complexing (1995)
    Springer
    Journal of solution chemistry 24 (1995), S. 1249-1263 
    Details
    ISSN: 1572-8927
    Keywords: Hydrogen-1 ; carbon-13 ; nitrogen-15 ; NMR ; magnesiumisothiocyanate complexes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A hydrogen-1, carbon-13, and nitrogen-15 NMR study of magnesium(II)-isothiocyanate complexation in aqueous mixtures has been completed. At temperatures low enough to slow proton and ligand exchange, separate1H,13C, and15N NMR signals are observed for coordinated and bulk water molecules and anions. The1H NMR spectra reveal signals for the hexahydrate and the mono-through triisothiocyanato complexes, as well as two small signals attributed to [Mg(H2O)5(OH)]1+ and [Mg(H2O)4(OH)(NCS)]. Accurate hydration numbers were obtained from signal area integrations at each NCS− concentration. In the15N NMR spectra, signals also were observed for the mono-through triisothiocyanato complexes, and a small signal believed to be due to [Mg(H2O)4(OH)(NCS)]. Coordination number contributions for NCS− were measured from these spectra and when combined with the hydration numbers they totalled essentially six at each anion concentration. Signals for [Mg(H2O)5(NCS)]1+ through [Mg(H2O)3(NCS)3]1− also were observed in the13C NMR spectra and the area evaluations were comparable to the15N NMR results. An analysis of the magnitude and sign of the coordinated NCS− chemical shifts identified the nitrogen atom as the anion binding site. All spectra indicated [Mg(H2O)5(NCS)]1+ and [Mg(H2O)4(NCS)2] were the dominat isothiocyanato complexes over the entire range of anion concentrations. The inability to detect evidence for complexes higher than the triisothiocyanato reflects the competitive binding ability of water molecules and perhaps the decreased electrostatic interaction between NCS− and negatively charged higher complexes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00972831
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  • 3
    Electronic Resource
    Electronic Resource
    The steric structure of multiflorine methylation products (1995)
    Springer
    Monatshefte für Chemie 126 (1995), S. 233-239 
    Details
    ISSN: 1434-4475
    Keywords: Enaminoketones ; Lupin alkaloid ; Multiflorine ; NMR ; Nucleophilic methylation ; Stereospecificity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Multiflorin (1), ein Lupin-Nebenalkaloid, ergibt bei Umsetzung mit Methyllithium oder Methylmagnesiumiodid 4S-4-Hydroxy-4-methyl-2,3-didehydrospartein (2) und 2S-2-Methyl-4-oxospartein (3) als Hauptprodukte. Ihre NMR-spektroskopisch (1H und13C) aufgeklärte räumliche Struktur weist auf eine Stereoselektivität der erwähnten Reaktionen hin. Die beobachteten nucleophilen 1,2- und 1,4-Additionen zeigen, daß sich die Regiospezifität der Einwirkung von MeLi oder MeMgl auf Multiflorin von jener bis jetzt bekannter Alkylierungen von Enaminoketonen unterscheidet.
    Notes: Summary Multiflorine (1) — a minor lupine alkaloid — treated by methyl lithium or methyl magnesium iodide affords 4S-4-hydroxy-4-methyl-2,3-didehydrosparteine (2) and 2S-2-methyl-4-oxosparteine (3), respectively, as the dominating products. Their steric structure, determined by1H and13C NMR techniques, points to stereospecific preferences of these reactions. The observed nucleophilic 1,2- and 1,4-additions indicate that regiospecificity of the action of MeLi or MeMgI on multiflorine is different from that of the so far known similar alkylation of other enamino ketones.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00812252
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  • 4
    Electronic Resource
    Electronic Resource
    Synthesis and stereochemistry of 8-methyl-5-nitro-1-octalones (1995)
    Springer
    Monatshefte für Chemie 126 (1995), S. 1011-1019 
    Details
    ISSN: 1434-4475
    Keywords: Precursors of strigol analogues ; Michael reaction ; NMR ; Molecular modelling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung BasenkatalysierteMichael-Addition von 5-Nitropentan-2-on-ethylenketal (1) und Cyclohex-2-enon (2), anschließende Entfernung der Schutzgruppe und darauffolgende Aldolkondensation liefert isomer 8-Methyl-5-nitro-1-octalone (5a,b). Struktur, relative Konfiguration und Konformation von5a und5b wurden mittels1H- und13C-NMR-Spektroskopie aufgeklärt.
    Notes: Summary Base catalyzedMichael addition of 5-nitropentan-2-one ethylene ketal (1) and cyclohex-2-enone (2), subsequent deprotection, and intramolecular aldol condensation yields the 8-methyl-5-nitro-1-octalone isomers (5a,b). The structure, relative configuration, and conformation of5a and5b were elucidated utilizing the results of1H and13C NMR investigations
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00811021
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  • 5
    Electronic Resource
    Electronic Resource
    Synthesis of aluminum rich MCM-41 (1995)
    Springer
    Catalysis letters 31 (1995), S. 267-272 
    Details
    ISSN: 1572-879X
    Keywords: MCM-41 synthesis ; NMR ; FTIR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The synthesis of MCM-41 mesoporous compounds with Si/Al ratios as low as 2 without observing the presence of octahedral Al in27AlMAS NMR is reported. FTIR spectra of chemisorbed pyridine indicated that MCM-41 materials in their protonated form exhibit both Brønsted and Lewis acid sites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00808839
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  • 6
    Electronic Resource
    Electronic Resource
    MBOHO calculations of phosphorus-carbon nuclear spin-spin coupling constants (1995)
    Springer
    Theoretical chemistry accounts 92 (1995), S. 61-65 
    Details
    ISSN: 1432-2234
    Keywords: NMR ; Nuclear spin coupling constant ; Maximum bond order hybrid orbital ; Phosphorus-carbon coupling ; Net atomic charge
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The novel generalized correlation of the nuclear spin-spin coupling constants with the atomic hybrids and net charges is employed to give a new relationship for calculating the directly bonded phosphorus-carbon coupling constants by use of the maximum bond order hybrid orbital procedure together with the extended Hückel molecular orbital calculation. The calculated coupling constants of phosphorus-carbon are all in good agreement with the experimental data, which shows that the new relationship obtained in the present paper is quite satisfactory for calculation of the phosphorus-carbon coupling constants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01134204
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  • 7
    Electronic Resource
    Electronic Resource
    Determination of the structure of fusaproliferin by1H-NMR and distance geometry (1995)
    Springer
    Structural chemistry 6 (1995), S. 183-189 
    Details
    ISSN: 1572-9001
    Keywords: NMR ; distance geometry ; cluster analysis ; absolute configuration ; fusaproliferin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The absolute configuration of fusaproliferin, a toxic metabolite produced byFusarium proliferation, was determined by the combined use of1H NMR and distance geometry. The configuration of double bonds has been determined in agreement with NOESY buildup data. An R configuration for C10 was determined using Mosher's method. Processing the constraints obtained from NOESY experiments with a distance geometry program, a limited number (80) of possible structures was derived. An agglomerative nonhierarchical method of clustering was used in order to place these structures into classes suggested by the data, and not previously defined in any way. This statistical method showed that indeed the structures could be grouped in four classes. One of these classes is represented by a single structure, with the highest sum of violations and was discarded. All other structures have the same chirality; respectively S for C14 and R for C15. In solution the overall conformation is quite well defined in the region of the five-member ring and the planes of double bonds C2–C3 and C11–C12, while near to C8 and C9 internal flexibility appears evident.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02286446
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  • 8
    Electronic Resource
    Electronic Resource
    NMR study of the selective inhibition of water permeability of rat erythrocyte membrane (1995)
    Springer
    Bioscience reports 15 (1995), S. 55-63 
    Details
    ISSN: 1573-4935
    Keywords: water transport mechanisms ; NMR ; rat erythrocytes ; tritium effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The inhibition of water diffusion across the rat erythrocyte membrane was studied by NMR using two basically different types of inhibitory agents: PCMB andin vivo irradiation. The contribution of lipid and protein to water permeability revealed the inhibitory effect of each pathway. Internal contamination with tritium (25–115 mGy) reduces water permeability due to protein modifications; for doses higher than 100 mGy the lipid mediated mechanism seems also to be impaired. The same procedure enables one to assess the extent to which the higher water permeability of rat, compared to human, erythrocyte is due to one of the two pathways.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01200215
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  • 9
    Electronic Resource
    Electronic Resource
    Chemical and rheological investigations of the sol-gel transition in organically-modified siloxanes (1995)
    Springer
    Journal of sol gel science and technology 4 (1995), S. 151-162 
    Details
    ISSN: 1573-4846
    Keywords: sol-gel transition ; rheology ; siloxane ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Ormosils are well-known organic-inorganic sol-gel derived materials also called heteropolysiloxanes. This paper presents two basic heteropolysiloxane structures where the organic part is either a short organic chain bridging two silicon atoms for the first material or an organic polymer backbone for the second. Their synthesis is detailed and a variety of experimental techniques (IR, 13C and 29Si NMR and CP-MAS NMR, GPC) have been employed to investigate the chemical structure of these new materials. Their mechanical properties, more precisely their viscoelastic behaviour, have been evaluated using dynamic rheological techniques. The storage and loss moduli have been followed during the sol-gel transition at fixed and variable oscillation frequencies. The results have been correlated to the 29Si CP-MAS NMR informations concerning the network polycondensation and compared to a pure inorganic sol-gel material prepared from tetraethoxysilane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00491681
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  • 10
    Electronic Resource
    Electronic Resource
    15N resonance assignments of oxidized and reducedChromatium vinosum high-potential iron protein (1995)
    Springer
    The protein journal 14 (1995), S. 115-126 
    Details
    ISSN: 1573-4943
    Keywords: NMR ; high-potential iron protein ; 15N assignment ; heteronuclear correlation ; paramagnetic
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The15N resonances in reduced and oxidizedChromatium vinosum high-potential iron protein have been assigned by use of1H-1H COSY spectra and1H-15N HMQC, HMQC-COSY, and HMQC-NOESY spectra. Unambiguous assignment of 70 of 85 backbone15N resonances in the reduced protein and 62 of 85 resonances in the oxidized protein are made, as are 12 of 21 side-chain15N resonances.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01980323
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  • 11
    Electronic Resource
    Electronic Resource
    Correlations between gas chromatographic retention data of polycyclic aromatic hydrocarbons and several molecular descriptors (1995)
    Springer
    Chromatographia 40 (1995), S. 532-538 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Retention-structure correlation ; Molecular descriptors ; Polycyclic aromatics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Statistical and factor analysis have been used to test the ability of several molecular descriptors to predict the retention indexes (I) of polycyclic aromatic hydrocarbons determined on SPB-5 and SPB-20 stationary phases. Regression analysis with both columns showed that linear regression with connectivity index and bending energy of the molecules as independent variables gave the best correlation coefficients. ΔI 20–5, considered to be a measure of the polar forces in retention, gave a good correlation with the van der Waals radii of the molecules, or strain, and bending energy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02290264
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  • 12
    Electronic Resource
    Electronic Resource
    Relations between pneumatic parameters of ideal gas in a column with uniform permeability (1995)
    Springer
    Chromatographia 41 (1995), S. 15-22 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Average velocity of carrier gas ; Compressibility of carrier gas ; Pneumatic parameters of carrier gas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary This report was conceived as a source for the relations between five pneumatic parameters of carrier gas-inlet and outlet pressure, inlet and outlet velocity, and average velocity. Any pair of these parameters can be independent while the remaining three can be expressed as functions of the independent pair. As the total number of the independent pairs is ten, thirty different functions describing relations between arbitrary independent pairs and dependent parameters can be identified. All thirty were derived below together with the complete set of bounds for variations of independent parameters. To derive some relations, a third order rational equation had to be solved. Some properties of that solution are discussed. A simple case of vacuum operations with zero outlet pressure has also been considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02274189
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  • 13
    Electronic Resource
    Electronic Resource
    Simulation of column efficiency in temperature programmed gas-liquid chromatography (1995)
    Springer
    Chromatographia 41 (1995), S. 37-42 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Temperature programming ; Isothermal measurements ; Column efficiency ; Dead time
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary If the dependence of HETP on temperature is specified under isothermal conditions, it is possible to predict the HETP for programmed temperature elution and subsequently peak width at half-height. This requires knowledge of isothermal retention time at retention temperature, which is computed by means of a model including the variation with temperature of dead time estimated from 3 homologs with carbon number: n, (n+j), (n+jk), where n, j and k are any integers. Predicted and measured peak widths corresponded within 4–9%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02274193
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  • 14
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    Electronic Resource
    Solid phase microextraction using fused silica fibers coated with graphitized carbon black (1995)
    Springer
    Chromatographia 41 (1995), S. 678-684 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Solid phase micro extraction ; Graphitized carbon black ; Volatile organic compounds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary This paper presents the results obtained using fused-silica fibers coated with graphitized carbon black (Carbograph-Alltech) for solid-phase microextraction (SPME). The extraction and calibration curves relative to organic micro-pollutants present in gaseous and aqueous samples are reported. Examples of applications of this extraction procedure to GC and GC-MS analysis of organic micro-pollutants in actual samples are also reported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02267804
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  • 15
    Electronic Resource
    Electronic Resource
    Preparation and gas chromatographic characterisation of 3-bromo-4-(4-methylbenzyloxy)azobenzene stationary phase (1995)
    Springer
    Chromatographia 41 (1995), S. 697-701 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; New stationary phase ; Packed columns ; Specific retention volumes ; Activity coefficients
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The synthesis of 3-bromo-4-(4-methylbenzyloxy)azobenzene (BMBOA) and its use as a stationary phase in packed columns are described. Chromatographic characteristics such as column efficiency, polarity (McReynolds constants) and operating temperature range were studied. Retention factors, specific retention volumes and activity coefficients for alcohols, esters, ketones, aromatic hydrocarbons andn-alkanes were determined. Phenols and 2,3, and 4-chlorobenzyl chlorides were separated on the new phase. Based on experimental data some assumptions were made on the possible types of intermolecular forces between solute and solvent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02267807
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  • 16
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    Electronic Resource
    Utilization of Rohrschneider's concept and Tekler equation in linear temperature programmed GC. Precalculation of retention data (1995)
    Springer
    Chromatographia 40 (1995), S. 28-32 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Linear temperature programming ; Tekler-equation extension ; Retention index precalculation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An extension of Rohrschneider's concept to the field of the linear temperature programmed gas liquid chromatography, is proposed, which is based on Antoine's equation for the temperature dependence of the reduction index of Takács et al. and Tekler. The new method presented in this paper, applied to retention data of two stationary phases of low polarity, PS-255 and OV-105, gives a new possibility of precalculating retention data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02274603
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  • 17
    Electronic Resource
    Electronic Resource
    Analysis of short chain fatty acids from different intestinal samples by capillary gas chromatography (1995)
    Springer
    Chromatographia 40 (1995), S. 550-556 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Open tubular columns ; Short chain fatty acids ; Intestinal fluids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A capillary gas-liquid chromatography method for the analysis of free short chain fatty acids in intestinal samples was developed. Analytical results obtained with intestinal samples are influenced not only by high molecular mass matrix constituents but also by matrix components with a molecular weight smaller than 5000 daltons. To achieve a faithful transfer of SCFA into the chromatographic system it was important to avoid accumulation of involatile deposits on the surface of the inlet liner. Cleaning of the inlet linear lead to a significant weakening of matrix effects. The method described, using an Innowax column, is more effective, particularly with respect to precision and sensitivity, and is clearly superior to packed columns. The capillary is the column of choice for the separation of short fatty acids in samples from the small intestine and stomach.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02290267
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  • 18
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    Electronic Resource
    The correlation equations describing retention index data on OV-101, OV-275 and PEG 20M.n-Alkanes andn-alkynes (1995)
    Springer
    Chromatographia 41 (1995), S. 726-727 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Retention indices ; Correlation equations ; n-Alkenes ; n-Alkynes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The correlation equations between Kovats retention indices ofn-alkenes andn-alkynes, column temperature and number of carbon atoms in molecules of these compounds on OV-101, OV-225 and PEG 20M capillary columns have been calculated. The two variable equationI=A+B·n+C/T give a good fit and are the simplest for prctical use.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02267812
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  • 19
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    Invertomers at nitrogen in aziridine carboxylates by mltltinuclear (1H,13C,17O, and15N) NMR study (1995)
    Springer
    Chemistry of heterocyclic compounds 31 (1995), S. 1071-1078 
    Details
    ISSN: 1573-8353
    Keywords: NMR ; 1H NMR ; 13C NMR ; 17O NMR ; 15N NMR ; aziridine-carboxylates ; configurational analysis ; conformational analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A confrgurational and conformational study of NH, N-acetyl- and N-sulfonylaziridine carboxylates is performed by1H ,13C,17O, and15N NMR spectroscopy. The presence of acetyl and su fonyl groups on the ring nitrogen atom seems to reduce greatly the configurational stability at nitrogen.
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    URL: http://dx.doi.org/10.1007/BF01165053
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  • 20
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    Hydrolysis of the Prodrug, 2′, 3′, 5′ -Triacetyl-6-azauridine (1995)
    Springer
    Pharmaceutical research 12 (1995), S. 1361-1370 
    Details
    ISSN: 1573-904X
    Keywords: 2′,3′,5′-triacetyl-6-azauridine ; prodrug ; hydrolysis ; pH-profile ; arrhenius plots ; CI-MS ; NMR ; liquid chromatography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Purpose. The purposes were to study the kinetics of hydrolysis of 2′,3′,5′-triacetyl-6-azauridine ( 1 ) in aqueous solution (µ = 0.5) and to identify the main intermediates and products of the reaction. Methods. A stability indicating isocratic LC assay was used to study the rate of degradation of 1 A gradient LC assay was used to study the time courses of the degradants. The products of hydrolysis were isolated by preparative liquid chromatography and identified by 1H-NMR and CI-MS. The pKa value was obtained by potentiometric titration. Results. At 36.8°C, the pH-rate profile of 1 in water was adequately described by a four-term rate equation. The intermediates were identified as the primary and secondary di-acetates, and the primary and secondary mono-acetates. The final product was 6-azauridine. Conclusions. A simplified kinetic scheme could be used to describe the concentration-time profiles of 1, the intermediates and the final product.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1016238110533
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  • 21
    Electronic Resource
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    Chromatographic determination of phosphine (PH3) and hydrogen sulfide (H2S) in the headspace of anaerobic bacterial enrichments using flame photometric detection (1995)
    Springer
    Chromatographia 40 (1995), S. 399-403 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Phosphine ; Flame photometric detection ; Anaerobic bacteria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A gas chromatographic method is presented which distinguishes phosphine from hydrogen sulfide and other possible headspace gases of anaerobic microbial cultures. In anaerobic cultures spiked with phosphine, this gas is recovered in the liquid and gaseous phase down to 10 pg per ml of gas or liquid. No biogenically produced phosphine was found. Phosphine in amounts as small as 30 ng per 1 can be stored for several days in glass bottles covered with rubber septa, filled with nitrogen, in the presence or absence of water or of an anaerobic bacterial culture. Due to the selectivity of the detector and the retention characteristics of the porous layer open tubular polymer column alkanes, alkenes and organosulfur compounds routinely found in anaerobic bacterial headspaces do not interfere with the analytical quantification of phosphine.
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    URL: http://dx.doi.org/10.1007/BF02269902
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  • 22
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    Investigation of thermal and analytical properties of two nematic liquid crystals by gas chromatography (1995)
    Springer
    Chromatographia 40 (1995), S. 581-586 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Liquid crystals ; Internal and external NO2 compounds ; Transition temperature ; Analytical properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Thermal and analytical properties of two liquid crystals containing internal [2-nitro, 3-methyl 4-(4-heptylbenzoyloxy) 4′-methylazobenzene] and external NO2 [2,3-dimethyl 4-(4-heptylbenzoyloxy) 4′-nitroazobenzene] have been investigated by gas chromatography. Transitions temperatures are determined by inverse gas chromatography using standard columns. Good agreement with values determined by differential scanning calorimetry are found. Analytical capabilities of the two liquid crystals are shown in glass capillary columns. Compared to examples in the literature, the crystals used separated different kinds of solutes. In addition, high molecular mass solutes were eluted at relatively low temperatures. Typical separations are observed for hydrocarbon positional isomers, aromatic hydrocarbons, geometric isomers, and volatile aroma compounds. Comparison between the performance of internal and external, NO2-liquid crystals is made.
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    URL: http://dx.doi.org/10.1007/BF02290272
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    Determination of volatiles in spirits using combined stationary phases in capillary GC (1995)
    Springer
    Chromatographia 41 (1995), S. 722-725 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Mixed stationary phases ; Distilled beverages ; Direct analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The analysis of spirits with a single stationary phase is still an unsolved problem; the two amyl alcohols, ethyl acetate and acetal are not separated on a polar column, methanol and acetaldehyde coelute from an apolar column. Trials with coupled columns of different polarities showed that optimum results were obtained with a 40 m capillary column, comprising 6 m of Carbowax 20 M, 12 m of 1∶1 Carbowax 20M:OV1 mixture and 30 m of PS 264. Best results were achieved when a 1 m retention gap was used, injecting a small amount of sample and using a 7 cm syringe needle.
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    URL: http://dx.doi.org/10.1007/BF02267811
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    Quantitative determination of toxic mono- and non-ortho polychlorinated biphenyls in cod liver oil after selective liquid chromatographic separation (1995)
    Springer
    Chromatographia 41 (1995), S. 585-593 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Column liquid chromatography ; Polychlorinated biphenyls ; Cod liver oil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary By application of a chromatographic column filled with Supelclean ENVI-Carb/Celite and elution with three solvents of different polarity three PCB fractions were obtained. Fraction A contained poly-ortho PCBs, Fraction B mono-ortho PCBs, and Fraction C non-ortho PCBs. The Supelclean ENVI-Carb/Celite column was used in combination with a sample preparation procedure for pre-cleaning of acid-stable chlorinated hydrocarbons such as DDT and its metabolites, HCH isomers, and regulation-relevant PCB congeners. The method was optimized using standard solutions of 55 PCB congeners, 8 chlorinated pesticides and contaminated cod liver oil samples. The influence of traces of remaining matrix on the elution profile of the organochlorine compounds on Supelclean ENVI-Carb/Celite was observed. Quantitation was carried out by GC-ECD with fused silica capillary columns of different polarity.
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    URL: http://dx.doi.org/10.1007/BF02269724
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    High temperature capillary GC analysis of phytopreparations of “espinheira santa” (Maytenus ilicifolia M. andMaytenus aquifolium M. — Celastraceae), a Brazilian antiulcer plant (1995)
    Springer
    Chromatographia 40 (1995), S. 341-344 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Pentacyclic triterpenes ; Maytenus aquifolium Martius ; Maytenus ilicifolia Martius ; Phytopharmaceuticals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary We report a method for the analysis of triterpenes in aqueous alcoholic extracts ofM. ilicifolia orM. aquifolium leaves, using high temperature capillary gas chromatography in polar columns (OV-17-OH). These species are popularly known in Brazil as “espinheira santa” and have proven antiulcer properties. The method consists of the pre-concentration of the triterpenes from the aqueous alcoholic extract, followed by GC analysis, which permits the determination of the presence of friedelan-3-ol and friedelin. Direct comparison with several triterpenol standards that are usually found in falsified “espinheira santa” samples but are absent in the authentic drug, showed that GC analysis clearly allows detection of the presence of friedelan-3-ol and friedelin and, therefore, permits distinguishing between authentic and false “espinheira santa” aqueous alcoholic extracts.
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    URL: http://dx.doi.org/10.1007/BF02290367
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    Rapid multiresidue screening method for organophosphate pesticides in vegetables (1995)
    Springer
    Chromatographia 40 (1995), S. 417-420 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Organophosphate pesticides ; Vegetables ; Pesticide residue analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A rapid and efficient multiresidue extraction procedure using ethyl acetate and sodium sulfate has been applied to the analysis of diazinon, methamidophos, chlorpyrifos, malathion, parathion, parathion-methyl, dimethoate and monocrotophos residues in many different kinds of vegetables. No cleanup step was required Concentrated extracts were analysed by gas chromatography with flame photometric detection in phosphorus mode. Recovery studies were performed in six kinds of matrices at two fortification levels. Recoveries were in the range 80–115%. The limit of quantification of the analytical method has been estimated as 0.01 ppm for diazinon, methamidophos and malathion, 0.03 ppm for chlorpyrifos, parathion, parathion-methyl and dimethoate and 0.1 ppm for monocrotophos. Experiments showed that potentially it should be possible to develop a rapid and universally applicable method for organophosphate pesticide residues in different matrices.
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    URL: http://dx.doi.org/10.1007/BF02269905
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    A gas chromatographic flow method for preconcentration and determination of vitamins D2 and D3 in pharmaceutical preparations (1995)
    Springer
    Chromatographia 40 (1995), S. 425-431 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Continuous preconcentration method ; Vitamins D2 and D3 ; Pharmaceutical preparations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A continuous-flow method that combines on-line preconcentration and isolation with gas chromatography for the direct determination of vitamins D2 and D3 in oily solutions is reported. A silica gel column permits preconcentration and isolation of analytes from the vitamin D matrix, although some triglyceride (ca. 25%) is also retained. To overcome problems associated with the low volatility of triglycerides, their retained fraction is further transesterified with potassium methylate to fatty acid methyl esters after elution. The proposed method was applied to the determination of vitamin D in pharmaceutical preparations.
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    URL: http://dx.doi.org/10.1007/BF02269907
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    Determination of cholesterol in milk fat by gas chromatography with direct injection and sample saponification (1995)
    Springer
    Chromatographia 41 (1995), S. 23-28 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Cholesterol ; Direct injection ; Saponification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A rapid and direct gas chromatographic (GC) method for determining free cholesterol in milk fat using a capillary column and programmed-temperature vaporizerinjector was assayed. It was compared with other procedures involving saponification of fat, solvent extraction of unsaponifiable matter—with and without fractionation by thin-layer chromatography—and transformation of sterols into silyl derivatives prior to GC analysis. This paper proposes an alternative to other published procedures. Repeatability of the method was assessed and the coefficient of variation determined as 2.1%. The alternative saponification method exhibited comparable accuracy (coefficient of variation=1.8%). Recovery ranged from 99.1% to 105.6%.
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    URL: http://dx.doi.org/10.1007/BF02274190
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    Specific interactions of n-donor adsorbates with N-benzoylthiourea-copper(II) complexes chemically bonded to silica supports (1995)
    Springer
    Chromatographia 41 (1995), S. 107-111 
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    ISSN: 1612-1112
    Keywords: Gas chromatography ; Metal complex stationary phases ; Specific interactions ; N-benzoylthiourea groups
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Silica was modified with γ-aminopropyltriethoxylsilane, and then the amino group was converted into an N-benzoylthiourea compound. Treatment with anhydrous CuCl2 solution, gave a copper(II) complex on the surface. In order to estimate the ability of the complex to interact specifically with electron donors, a number of retention parameters were determined for three groups of compounds showing electron-donor properties: ketones, ethers and nitroalkanes. On the basis of the results, the effect of adsorbate structure on the strength of specific interactions was established. The packings studied may be useful for the analysis of the mixtures of ketones, ethers, and nitroalkanes.
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    URL: http://dx.doi.org/10.1007/BF02274203
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    Analysis of pesticide residues in fruit and vegetables by matrix solid phase dispersion (MSPD) and different gas chromatography element-selective detectors (1995)
    Springer
    Chromatographia 41 (1995), S. 685-692 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Matrix solid phase dispersion (MSPD) ; Fruit and vegetables ; Pesticide residues ; Selective detectors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A comparison between different element selective detectors for the determination of organophosphorus and organochlorine pesticide residues, from fruit and vegetables, was performed by capillary GC with electron capture detector (ECD), nitrogen phosphorus detector (NPD), flame photometric detector (FPD) in the sulphur and phosphorus modes, and mass spectrometry detector (MSD) in selected ion monitoring (SIM) mode. Pesticides were extracted from the different foodstuffs by Matrix Solid Phase Dispersion (MSPD). Recoveries of 41–108 % with relative standard deviation of 2–14 % in the concentration range 0.5–10 μg L−1 were obtained in oranges, lemons, grapefruit, pears, plums, lettuces and tomatoes. The results demonstrated that the extracts of all the samples can be analyzed by the detectors used since no interfering co-extracted compounds were detected.
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    URL: http://dx.doi.org/10.1007/BF02267805
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    Modelling of GC and HPLC separations of simazin and atrazin by Experimental Design methodology (1995)
    Springer
    Chromatographia 41 (1995), S. 553-560 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Gas chromatography ; Experimental design ; Modelling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Experimental Design methodology allows the modelling and optimization of the chromatographic separation of similar pesticides (triazine family) by GC and HPLC. The GC separation of simazin and atrazin is well modelled by a first degree equation, involving injected volume, carrier gas pressure and rising oven temperature. The LC is modelled by a second degree equation, depending on injected volume, eluent flow and composition. These calculated models allow easy optimization of the separations, using isoresponse curves.
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    URL: http://dx.doi.org/10.1007/BF02269719
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    A comparison of the critical parameters of some adsorbents employed in trapping and thermal desorption of organic pollutants (1995)
    Springer
    Chromatographia 41 (1995), S. 599-604 
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    ISSN: 1612-1112
    Keywords: Gas chromatography ; Organic volatile pollutants ; Adsorbents ; Breakthrough volumes ; Thermal desorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A comparison of some adsorbents, commonly used for trapping trace volatile organic pollutants followed by thermal desorption, is presented. The evaluation has been performed on 12 compounds representative of the main classes of organic substances. Breakthrough volumes and desorption recoveries have been measured. Every adsorbent gave good results for a range of compounds, but none were able to cover all the compounds examined. Thus, a multilayer trap utilising the best features of each adsorbent was introduced with very good results.
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    URL: http://dx.doi.org/10.1007/BF02269726
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    Backbone modification of Chirasil-Val: Effect of nonpolar side chains on enantiomer separation in gas chromatography (1995)
    Springer
    Chromatographia 40 (1995), S. 718-723 
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    ISSN: 1612-1112
    Keywords: Gas chromatography ; Enantiomer separation ; Chiral polysiloxane ; Amino acids ; Physicochemical properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The polysiloxane backbone of the gas chromatography phase Chirasil-Val has been modified by replacing one methyl group per dialkylsiloxy unit by pentyl and hexyl groups, respectively. The new phases offer the advantage of reduced polarities and softening points, while the separation factors (α) of enantiomeric pairs of N,O-trifluoroacetyl amino acid propyl esters show small but intriguing deviations from those determined on Chirasil-Val.
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    URL: http://dx.doi.org/10.1007/BF02315143
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    On-line coupling of solid-phase extraction and gas chromatography with atomic emission detection for analysis of trace pollutants in aqueous samples (1995)
    Springer
    Chromatographia 40 (1995), S. 119-124 
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    ISSN: 1612-1112
    Keywords: Gas chromatography ; Atomic emission detection ; Aqueous samples ; Solid-phase extraction ; Organophosphorus pesticides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An on-line, solid-phase extraction gas chromatography atomic-emission detection (SPE-GC-AED) system has been set up using an on-column interface to transfer 100 μl of desorbing solvent to the GC part of the system. Analytical characteristics such as recovery, precision and linearity of calibration plots were comparable with those of the off-line combination of SPE-GC-AED using organophosphorus pesticides as test compounds. The fully on-line set-up causes a marked improvement in detection because of the quantitative transfer of the analytes from the SPE module to the GC: detection limits are as low as 5–20 ng l−1 for the analysis of 10 ml raw and spiked surface water samples using the phosphorus channel. Detection levels can be further enhanced by processing up to 100 ml samples. The integrated analytical system is robust. The potential of the on-line set up has been demonstrated for the analysis of surface water and waste water.
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    URL: http://dx.doi.org/10.1007/BF02272157
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    Reversed-phase liquid chromatography coupled on-line with capillary gas chromatography use of an anion-exchange membrane to remove an ion-pair reagent from the eluent (1995)
    Springer
    Chromatographia 40 (1995), S. 267-271 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Column liquid chromatography ; On-line coupling ; Ion-exchange membrane ; Ion-pair reagent
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary In order to enable the coupling of reversed-phase liquid chromatography (RPLC) with capillary gas chromatography (GC), the performance of an anion-exchange micromembrane device has been studied to remove the ion-pair reagent methanesulphonic acid from an acetonitrile/water LC eluent. The regenerant in the membrane was tetrabutylammonium hydroxide dissolved in acetonitrile/water, which effects an anion-exchange of methanesulphonate ions for regenerant hydroxide ions. The efficiency of the exchange process was found to be 99.9%. This enabled the direct introduction of the LC eluent, free of ions and with the proper acetonitrile/water ratio, into the GC. The applicability of the on-line LC-micromembrane-GC system has been illustrated for the potential drug eltoprazine, which is quantitatively recovered with a coefficient of variation for standard solutions of 3% at the 150 μg/ml analyte level.
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    URL: http://dx.doi.org/10.1007/BF02290356
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    On-line automated sample preparation-capillary gas chromatography for the analysis of plasma samples (1995)
    Springer
    Chromatographia 40 (1995), S. 500-506 
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    ISSN: 1612-1112
    Keywords: Gas chromatography ; ASPEC ; Trazodone in plasma ; Method automation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An automated sample preparation module, (the automated sample preparation with extraction columns, ASPEC), was interfaced with a capillary gas chromatograph (GC) by means of an on-column interface. The system was optimised for the determination of the antidepressant trazodone in plasma. The clean-up of untreated plasma was carried out with disposable C18 cartridges, using several washing steps. The analyte was desorbed with methanol, the extract was diluted on-line with buffer and preconcentrated on a PLRP-S trapping column. The trapping column was dried by purging with nitrogen gas. Desorption (phase switching) of the trapping column was carried out with ethyl acetate which was introduced into a retention gap using partially concurrent solvent evaporation conditions. Trazodone was determined by GC with flame ionisation detection (FID). With a 1 ml sample, this resulted in a detection limit for trazodone in plasma of 3 ng/ml. The system showed good linearity and repeatability in the range 0.01–1 μg/ml, thus covering the range of pharmacokinetic/dynamic-to-therapeutic concentrations of trazodone in plasma. Preliminary results for benzodiazepines are promising. They indicate that the use of a selective detector such as the nitrogen/phosphorus detector, is to be recommended.
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    URL: http://dx.doi.org/10.1007/BF02290259
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    A simple gas chromatographic method for the analysis of oxygenates in gasoline (1995)
    Springer
    Chromatographia 40 (1995), S. 607-610 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Packed column separations ; C1−C4 alcohols ; Ethers ; Gasoline
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A number of oxygenated compounds such as C1−C4 alcohols, methyl tert-butyl ether (MTBE), and tertamyl methyl ether (TAME) are increasingly being used in gasoline as octane boosters and to reduce vehicular emissions. Monitoring of individual oxygenates in gasoline is important for quality control and regulatory purpose. Although, several analytical methods based on gas chromatography have been reported, a need was still felt to develop a simple and cost effective method of analysis. In this paper, a packed column gas chromatographic method is described for the analysis of C1−C4 alcohols, MTBE and TAME over a wide concentration range (2–20% V/V) in gasoline. The method involves determination of alcohols and ethers separately on two different columns. The alcohols are determined on a 20 ft column packed with poly(ethylene glycol) 400 as a stationary phase while the ethers are analysed on a 20 ft OPN-Poracil C column. The analysis of alcohols on poly(ethylene glycol) 400 column also provides data on aromatic components of gasoline.
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    URL: http://dx.doi.org/10.1007/BF02290276
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    Comparison of correlation equations for the prediction of gas chromatographic separation of alkylbenzenes (1995)
    Springer
    Chromatographia 41 (1995), S. 183-186 
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    ISSN: 1612-1112
    Keywords: Gas chromatography ; Correlation equation ; Alkylbenezenes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A detailed statistical analysis, comparing the validity of the best literature recommended equations for prediction of retention indices of alkylbenzenes on squalane and methylsilicone stationary phases with the unified retention index concept, is presented. A comparison with literature sources shows that the unified retention index provides the smallest residual error. Hence, it can be applied for prediction purposes.
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    URL: http://dx.doi.org/10.1007/BF02267952
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    Ring opening of cyclohexane over ZSM-zeolites followed by reversed-flow gas chromatography (1995)
    Springer
    Chromatographia 41 (1995), S. 227-235 
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    ISSN: 1612-1112
    Keywords: Gas chromatography ; Reversed-flow technique ; Catalysis ; Ring opening
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Kinetic parameters for the ring opening of cyclohexane over modified ZSM-5 zeolites can be measured simultaneously under non-steady state conditions using reversed-flow gas chromatography. At relatively low temperatures, the main product detected and measured was propene. The mathematical relations used for the calculation of adsorption-desorption rate constants, surface reaction rate constants and adsorption equilibrium constants for the reactant cyclohexane are different from previously studied catalytic reactions, owing to the different experimental arrangement for feeding the catalytic bed. The diffusion bands obtained experimentally for reactant or product are described by the sum of two or three exponential functions of time, respectively. From the exponential coefficients of time and the pre-exponential factors, all determined by simple PC programs, the above kinetic parameters are calculated.
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    URL: http://dx.doi.org/10.1007/BF02267960
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    Gas chromatography on a self-associating component of a binary phase. Retention model by formal analogy with conductance of electrolytes in dilute solution (1995)
    Springer
    Chromatographia 41 (1995), S. 221-226 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Binary stationary phase ; Self-associating phase components ; Retention model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The dependence of specific retention by a binary stationary phase in GC can be expressed as the sum of the products of the specific retention of the pure components times their respective volume fractions. In this study, however, one component has a site, which is not only mainly responsible for the selectivity, but also participates in strong self-association. This requires introduction of a concentration-dependent factor (μx) in the corresponding term of the equation correlating Vg mix x with x. In the GC resolution of N-trifluoroacetyl-amino acid isopropyl esters on a binary phase, N-lauroyl-L-amino t-butyl amide-squalane, data for the values of μx were obtained. Adapting a previously developed LC retention model to the above GC data, an equation was derived for the dependence of μx on the weight fraction (x) of the selector, namely μx=√1/x. This relationship permits calculation of retention volumes on the binary phase for a given x, as well as corresponding resolution coefficients of enantiomeric amino acid derivatives with generally excellent agreement with experiment. The chirality of the system is not relevant to application of the equation.
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    Fast headspace analysis with short microcapillary columns (1995)
    Springer
    Chromatographia 41 (1995), S. 419-423 
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    ISSN: 1612-1112
    Keywords: Gas chromatography ; Headspace analysis ; Microcapillary columns ; Short columns ; Volatile compounds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A new method of analysis using headspace gas chromatography with microcapillary columns is proposed. Small diameter (50 μm I.D.) fused-silica capillary columns with non-extractable SE-54 and PS-255 polysiloxane stationary phases were used for the analysis of low boiling organic compounds. The small diameter columns possess the usual very high efficiency so that the method can be employed for the headspace analysis of complex mixtures. The use of short microcolumns reduces the analysis times in comparison to conventional capillary columns. Good performances were obtained in the analysis of volatile compounds in some lemon essential oil, perfumes, and water samples.
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    URL: http://dx.doi.org/10.1007/BF02318616
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    Capillary gas chromatography of aromatic bicyclic and tricyclic spiro ketones (1995)
    Springer
    Chromatographia 41 (1995), S. 594-598 
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    ISSN: 1612-1112
    Keywords: Gas chromatography ; Capillary column ; Bicyclic spiro ketones ; Tricyclic spiro ketones ; Retention index at different temperatures ; Retention vs stationary phase polarity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The separation of some aromatic bicyclic and tricyclic spiro ketones on fused silica capillary columns coated with polydimethylsiloxane, cyanopropylmethylsiloxane and poly(ethylene glycol) stationary phases was investigated. Retention indices were determined at two temperatures in order to enable understanding of the compounds' chromatographic behaviour. The respective standard deviation values were 0.8, 0.5 and 0.3 index units. The influence of the polarity of the stationary phases on the chromatographic retention of these cyclic spiro ketones is discussed.
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    Mammalian exocrine secretions: IX. Constituents of preorbital secretion of oribi,Ourebia, ourebi (1995)
    Springer
    Journal of chemical ecology 21 (1995), S. 1191-1215 
    Details
    ISSN: 1573-1561
    Keywords: Ourebia ourebi ; Bovidae ; mammalian semiochemicals ; mammalian pheromones ; exocrine secretion ; preorbital secretion ; dimethyl disulfide derivatization ; skipped dienes ; chemical-ionization mass spectrometry ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Using gas chromatography-mass spectrometry in conjunction with ancillary techniques such as chemical ionization with different reactant gases, determination of the position of double bonds by means of dimethyl disulfide derivatization, and finally gas chromatographic and mass spectrometric comparison with authentic synthetic material, 75 constituents were identified in the preorbital secretion of the male oribi,Ourebia ourebi. The secretion contains compounds with long-chain, unbranched structures similar to those found in many other preorbital secretions but with a finite volatility range, in contrast to the seemingly endlessly increasing chain lengths typical of other preorbital secretions.
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    URL: http://dx.doi.org/10.1007/BF02228320
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    New backbone cyclic substance P analogs (1995)
    Springer
    International journal of peptide research and therapeutics 2 (1995), S. 121-124 
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    ISSN: 1573-3904
    Keywords: Backbone cyclization ; Substance P ; NMR ; Molecular dynamics ; Conformational analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Structure-activity relationships of cyclic substance P (SP) analogs were extensively studied in our laboratories utilizing the new concept of backbone cyclization. Employing the C-terminal hexapeptide SP6–11, we examined the influence of chemical changes in peptides containing backbone-to-amino-end cyclization. These changes in the ring have significant influence on activity, and should be carefully designed in order to optimize pharmacological feature.
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    URL: http://dx.doi.org/10.1007/BF00119137
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    Production, isolation and characterization of [Leu4]- and [Ile4]surfactins from Bacillus subtilis (1995)
    Springer
    International journal of peptide research and therapeutics 2 (1995), S. 41-47 
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    ISSN: 1573-3904
    Keywords: Biosurfactant ; Lipopeptide ; NMR ; Hydrophobic substitution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Bacillus subtilis coproduces several surfactin variants that are powerful biosurfactants and have potential applications in biology and industry. A single amino acid substitution in the heptapeptide moiety of surfactins strongly modifies their properties. To better establish structure-activity relationships and to search new variants with enhanced properties, Bacillus subtilis was grown into two modified culture media. Two new variants were isolated by chromatographic methods and studied by NMR spectroscopy. As planned, modifications consisted in the substitution of the l-valine residue at the fourth position by a more hydrophobic residue, i.e., leucine or isoleucine. These [Leu4]- and [Ile4]surfactins have a higher affinity for hydrophobic solvents and a twice improved surfactant power. Structure-property correlations were confirmed by analysis of the hydrophobic residue distribution in the three-dimensional model of the structure of surfactin in solution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00122922
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  • 46
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    Electronic Resource
    Structure of Leu5-enkephalin bound to a model membrane as determined by high-resolution NMR (1995)
    Springer
    International journal of peptide research and therapeutics 2 (1995), S. 59-70 
    Details
    ISSN: 1573-3904
    Keywords: Opioid peptide ; NMR ; Enkephalins ; Micelles ; Dodecylphosphocholine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Opioid peptides are thought to interact with the cell membrane in their biological journey to the membrane-bound receptor. Both organic solvents and model membranes have been used previously to determine the stable solution conformations of peptide hormones. Leucine enkephalin has been studied in a number of different environments, but with limited resolution. Here it is shown that leucine enkephalin forms a stable type IV β-turn structure in dodecylphosphocholine micelles. We have observed a highly solvent-shielded amide proton with no evidence for a complementary hydrogen bond acceptor. The structural details of the peptide as determined by NMR spectroscopy in solution are described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00128499
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  • 47
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    Electronic Resource
    New conformationally constrained Xxx-Pro bicyclic mimetics (1995)
    Springer
    International journal of peptide research and therapeutics 2 (1995), S. 161-164 
    Details
    ISSN: 1573-3904
    Keywords: Cyclised peptide ; Dioxopiperazine ; Thiazolidine ; NMR ; Computer modelling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Conformationally constrained peptidomimetics of the Lys-Pro sequence have been obtained using a new polycyclic structure. Bicyclic compounds containing a dioxopiperazine-thiazolidine fused ring have been synthesised starting from N-lysyl-4-ethoxycarbonylthiazolidine-2-carboxylic acid. The carboxyl group in either position 2 or 4 of the thiazolidine ring was reacted with the N-terminal amino group, giving different regioisomers. NMR and computer modelling were used to study the configuration of isomers and the lysine side-chain orientation with respect to the pseudoproline ring.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00119143
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  • 48
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    Electronic Resource
    Synthesis and conformational analysis of AzAsx-containing oligopeptides (1995)
    Springer
    International journal of peptide research and therapeutics 2 (1995), S. 239-242 
    Details
    ISSN: 1573-3904
    Keywords: Pseudopeptide ; Triphosgene ; Beta-turn ; NMR ; FT-IR ; X-ray diffraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary For the sake of improving synthetic methods and evaluating the conformational perturbation induced by the substitution of AzAsx for the Asx residue in the cognate dipeptide R-CO-Asx-Pro-NHR′, we prepared the AzAsx-dipeptide sequence by making use of the crystalline triphosgene. This reagent allows, in situ and under very mild experimental conditions, both the carbonylation and the activation of the properly substituted and N-protected hydrazine before coupling with the proline partner. With regard to conformational behaviour, the azadipeptide sequence displays a β-fold, unlike the cognate dipeptide which adopts an Asx-turn.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00119162
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