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  • 1995-1999  (16.629)
  • 1980-1984  (16.905)
  • Polymer and Materials Science  (30.110)
  • Engineering General  (2.800)
  • Gas chromatography
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  • 1
    Digitale Medien
    Digitale Medien
    Springer
    European food research and technology 209 (1999), S. 400-406 
    ISSN: 1438-2385
    Schlagwort(e): Key words Pumpkin seed oil ; Oil adulteration ; Δ7-Phytosterols ; Sample clean-up procedure ; Gas chromatography
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Abstract  A simple and accurate method for the determination of phytosterols by capillary gas chromatography was developed for the analysis of the seeds and oil of the pumpkin Cucurbita pepo L., the naked seed variety growing in the southern Styrian parts of Austria. After extraction of the oil and saponification, the remaining unsaponifiable material was isolated and purified using silica gel columns. For greater volatility, the sterols were derivatised to trimethylsilylethers, and gas chromatography was performed on a column of high polarity, allowing separation of the Δ5-sterols from the Δ7-sterols and thus yielding a typical chromatographical pattern. Quantification of the phytosterols using 5α-cholestan or cholesterol as internal standards led to a method of high accuracy. Comparison of the chromatographic pattern of the phytosterol fraction of pumpkin seed oil with those of other vegetable oil samples permitted the use of this method to detect adulteration of pumpkin seed oil.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    International journal of legal medicine 112 (1999), S. 124-131 
    ISSN: 1437-1596
    Schlagwort(e): Key words Hydroxyproline ; D/L Aspartic acid ; N-TFA isopropyl ester derivatives ; Gas chromatography ; Collagen
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Rechtswissenschaft
    Notizen: Abstract The proportion of D- to L-enantiomers of aspartic acid in metabolically isolated proteins has been used by forensic scientists to estimate age at death. We have demonstrated the interference of a derivative of hydroxyproline (N-TFA isopropyl Hyp ester) with the N-TFA isopropyl L-Aspartic (Asp) acid ester during gas chromatography of amino acids. This has serious implications for the accurate quantification of the D- to L-Asp ratio extracted from collagenous proteins. Having demonstrated the potential for this co-elution in amino acid standards, acid-soluble dentine proteins and non-mineralised collagen, we argue that this problem can be overcome either by high resolution separation or by analysis of the (Hyp-poor) non-collagenous protein fraction.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Rechtsmedizin 9 (1999), S. 184-189 
    ISSN: 1434-5196
    Schlagwort(e): Key words Ethyl glucuronide ; Congeners of alcoholic beverages ; Alkyl glucuronide ; Gas chromatography ; Mass spectrometry ; Schlüsselwörter Ethylglucuronid ; Begleitstoffe ; Alkylglucuronid ; Gaschromatographie ; Massenspektrometrie
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Rechtswissenschaft
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Es wird die chemische Synthese von Alkylglucuroniden beschrieben, die nach Konsum von begleitstoffhaltigen Getränken als Metaboliten im Urin erscheinen. Von folgenden Alkoholen wurden die Glucuronide synthetisiert: Methanol, d5-Ethanol, Propanol, Isopropanol, Butanol, Isobutanol, R-(–)-2-Butanol, S-(+)-2-Butanol, Isopentanol, S-(–)-2-Methylbutanol. Die Retentionsindizes der Acetyl-, Pentafluorpropyl(PFP)- und Trimethylsilyl(TMS)-derivate werden mitgeteilt und der Einfluß der chemischen Struktur auf den RI-Wert diskutiert. Die Massenspektren der homologen Derivate erwiesen sich als sehr ähnlich, aber einige Fragmente sind spezifisch für die Kettenlänge der Alkylgruppe und können zur Identifizierung und Quantifizierung der Glucuronide in Urinproben herangezogen werden.
    Notizen: Abstract The chemical synthesis of alkyl glucuronides, which appear as metabolites in urine after the consumption of beverages containing congeners of ethanol, is described. Glucuronides of the following alcohols were synthesized: methanol, d5-ethanol, propanol, isopropanol, butanol, isobutanol, R-(–)-2-butanol, S-(+)-2-butanol, isopentanol and S-(–)-2-methylbutanol. The retention indices of acetyl, pentafluorpropyl (PFP) and trimethylsilyl (TMS) derivatives are given and discussed in relation to the chemical structures. Mass spectra of homologous derivatives were shown to be very similar but some fragments were specific for the chain length of the alkyl moiety and can be used for identification and a quantitative estimation of glucuronides in urine samples.
    Materialart: Digitale Medien
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  • 4
    ISSN: 1612-1112
    Schlagwort(e): Gas chromatography ; Sorptive preconcentration ; Air monitoring ; Nicotine ; Hospital air
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A novel method for the enrichment of nicotine from gaseous samples is presented. It is based on the sampling of 6 liters of air onto a cartridge packed with 100% polydimethylsiloxane (PDMS) particles. The analytes are dissolved (partitioned) into the PDMS phase which results in much better recoveries and reproducibilities compared to those obtained on common adsorbents. The PDMS tube is then placed in a thermal desorption (TD) unit connected to a CGC-NPD or CGC-MS system. The procedure was employed for routinely monitoring air in a hospital. Nicotine was typically found at levels ranging from 5 to 250 μg m−3 (ppb) depending on the location and number of smokers present. Additionally, the efficiency of nicotine filters was determined by sampling simultaneously at the filter in- and outlet and was found to be 46%.
    Materialart: Digitale Medien
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  • 5
    ISSN: 1612-1112
    Schlagwort(e): Gas chromatography ; [60] Fulleropyrrolidine polysiloxane ; High temperature stationary phase
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary In this paper, a new type of [60]fulleropyrrolidine functionalized polysiloxane in which the fullerene moieties were incorporated in the main polysiloxane chain was synthesized the first time and used as a stationary phase for capillary gas chromatography. It demonstrated high column efficiency (2600–2866 plates m−1, on a 250 μm diameter column, for naphthalenek=3.1–3.2, 120 °C), a wide operational temperature range (90–360 °C) and outstanding thermostability. It can be used at 360 °C with a baseline drift of 5∼8×10−15A. Benzene homologues, aromatic hydrocarbons, polar compounds such as alcohols, esters, ketones, anilines and phthalic diesters can be seperated well on this column.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Springer
    Chromatographia 49 (1999), S. 333-337 
    ISSN: 1612-1112
    Schlagwort(e): Supercritical fluid chromatography ; Gas chromatography ; Solvating gas chromatography ; Peak capacity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary In this paper, a general peak capacity expression was evaluated using columns containing various packing materials under solvating gas chromatography (SGC) conditions. Differing from column efficiency, peak capacity can describe both separation capability and speed when introducing the dead time into the peak capacity expression. Various factors that influence peak capacity in SGC are described, including particle pore size, chemical surface modification, particle size, column length, temperature, and pressure.
    Materialart: Digitale Medien
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  • 7
    ISSN: 1612-1112
    Schlagwort(e): Gas chromatography ; Microwave and ultrasonic extraction ; River sediment ; Dioxin-like polychlorobiphenyls ; Toxic equivalency factors
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Microwave extraction and ultrasonication of dioxin-like polychlorobiphenyls (PCBs) from sediment samples were investigated. After separation of dioxin-like PCBs from a sample matrix on an acidic-alkaline silica gel column, dioxin-like PCBs were determined by GC-ECD, using dual capillary columns. Recoveries of dioxin-like PCBs in river sediment samples exceeded 80% by both extraction techniques. Toxic equivalency factors and their use for the PCB congeners investigated were applied.
    Materialart: Digitale Medien
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  • 8
    ISSN: 1612-1112
    Schlagwort(e): Gas chromatography ; Reversed-flow gas chromatography ; Carbon monoxide oxidation ; Bimetallic Pt−Rh catalysts
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Catalytic fractional conversions of carbon monoxide to carbon dioxide over Pt−Rh alloy catalysts in the presence of excess oxygen, under steady-state or non steady-state conditions, as well as corresponding rate constants for the CO oxidation reaction were measured by using the reversed-flow gas chromatographic technique. From the variation of the conversions with temperature, maximum values of conversions were found, which depend on the catalysts nature (Pt content), while from the variation of the rate constants with temperature, activation energies for the CO oxidation reaction were determined, which also depend on the catalyst Pt content. The results suggest a synergism between Pt and Rh in the Pt−Rh bimetallic catalysts in accordance with previous works, showing that reversed-flow gas chromatography can be used with simplicity and accuracy for the kinetic study of the CO oxidation reaction, which is of technological importance for the control of air pollution.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Springer
    Chromatographia 49 (1999), S. 321-326 
    ISSN: 1612-1112
    Schlagwort(e): Gas chromatography ; Headspace analysis ; Open-tubular trap ; Very thick film column
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary An open-tubular trap with a very thick film was studied for “full on-line” headspace capillary gas chromatography, and was used as an enrichment trap for headspace sampling. The preparation of the open-tubular column with up to an 80 μm thick film, by combining both static and dynamic coating, is described in detail. The break-through volume for the open-tubular trap of different film thickness, as the loading capacity for HS sampling, does not increase linearly in proportion to the film thickness. A study of the difference between a packed adsorbent trap and an open-tubular trap shows that HS capillary GC with open-tubular trap loses less of the retention capacity, has better resolution ability and higher recovery. By independently and rapidly heating the open-tubular trap, the GC peaks may have higher resolution. Examples of successful analyses, by the opentubular trap with “full on-line” HS capillary GC, include trace aromatic hydrocarbon (1 ppm-100 ppm) in polybutadiene-styrene rubber and trace alcohol and acrylic esters (10 ppm–1000 ppm) in polyacrylate hydrous emulsion.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    Springer
    Chromatographia 49 (1999), S. 385-390 
    ISSN: 1612-1112
    Schlagwort(e): Gas chromatography ; Structure correlations ; Polycyclic aromatic hydrocarbons ; Polychlorinated biphenyls ; Polychlorinated pesticides
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A composite chromatographic retention index system has been developed for identifying polycyclic aromatic hydrocarbons, polychlorinated biphenyls and polychlorinated pesticides. When retention indices and thermodynamic data of polycyclic aromatic hydrocarbons on 5% phenylmethylsiloxane stationary phase were compared with those obtained on polydimethylsiloxane a correlation was found between retention and electronic properties. Determination and quantitation of individual contaminants in water and sediment samples from Lake Mecoacán were achieved by capillary gas chromatography with flame ionization and electrocapture detection.
    Materialart: Digitale Medien
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  • 11
    Digitale Medien
    Digitale Medien
    Springer
    Chromatographia 49 (1999), S. 268-272 
    ISSN: 1612-1112
    Schlagwort(e): Gas chromatography ; Mass spectrometry ; Analytical pyrolysis ; Chinese art objects ; Mercury analysis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A few samples of polychrome Chinese archaeological objects of art have undergone analytical pyrolysis coupled with GC-MS to evaluated the possibility of contemporary characterization of the pigments as well as the organic media used. The red pigment cinnabar (HgS) is easily media used. The red pigment cinnabar (HgS) is easily detected, whereas in the case of organic components positive results are only found where the matrices are resistant to archaeological environmental conditions.
    Materialart: Digitale Medien
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  • 12
    ISSN: 1612-1112
    Schlagwort(e): Gas chromatography ; Supercritical fluid chromatography ; Solvating gas chromatography ; Polybutadiene coated zirconia ; CO2 mobile phase
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary In this paper, practical considerations of column efficiency, separation speed, thermal stability, and column polarity of capillary columns packed with polybutadiene-coated zirconia were investigated under solvating gas chromatography (SGC) conditions using carbon dioxide as mobile phase. When compared with results obtained from conventional porous octadecyl obtained from conventional porous octadecyl bonded silica (ODS) particles, PBD-zirconia particles produced greater change in mobile phase linear velocity with pressure than conventional ODS particles under the same conditions. The maximum plate number per second (Nt) obtained with a 30 cm PBD-zirconia column was approximately 1.5 times higher than that obtained with an ODS column at 100 °C. Therefore, the PBD-zirconia phase is more suitable for fast separations than conventional ODS particles in SGC. Maximum plate numbers per meter of 76,900 and 63,300 were obtained using a 57 cm×250 μm i.d. fused silica capillary column packed with 3 μm PBD-zirconia at 50 °C and 100 °C, respectively. The PBD-zirconia phase was stable at temperatures up to 320 °C under SGC conditions using carbon dioxide as mobile phase. Polarizable aromatic compounds and low molecular weight ketones and aldehydes were eluted with symmetrical peaks from a 10 cm column packed with 3 μm PBD-zirconia. Zirconia phases with greater inertness are required for the analysis of more polar compounds by SGC.
    Materialart: Digitale Medien
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  • 13
    Digitale Medien
    Digitale Medien
    Springer
    Chromatographia 49 (1999), S. 509-512 
    ISSN: 1612-1112
    Schlagwort(e): Gas chromatography ; Homologous series ; Retention times
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary It is shown how to estimate the retention times of homologous series members in linear temperature programmed gas chromatography with the aid of a spread-sheet. Both the ease of estimation and the accuracy of the estimation depend on whether the homologue is eluted during the rising portion of the temperature program or the hold time at the end, and also on whether the homologous series is eluted from one injection or a number of injections. When all members of the series elute in the one chromatographic run the percentage standard deviation of the predicted retention times from the experimental retention times is 0.1. When members of the series elute in different chromatographic runs, the percentage standard deviation of predicted times from experimental times is 0.6, compared with an experimental percentage standard deviation for replicates of 0.5.
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  • 14
    Digitale Medien
    Digitale Medien
    Springer
    Chromatographia 49 (1999), S. 686-690 
    ISSN: 1612-1112
    Schlagwort(e): Gas chromatography ; Solid-phase microextraction ; Fibre coating ; Volatile organic compounds ; Semi-volatile organic compounds
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The efficiency of direct solid-phase microextraction (SPME) was determined for 27 selected volatile and semivolatile organic compounds (BTEX, chloro- and bromobenzenes, chlorinated pesticides and PCBs). The fibres used were 7μm polydimethylsiloxane (PDMS), 30μm PDMS, 100μm PDMS, 65μm PDMS-divinylbenzene, 85μm polyacrylate, 65μm Carbowax-divinylbenzene, 75μm Carboxen-PDMS and a new 65μm C8 fibre. Extraction yields for these compounds were calculated under standardised conditions: 75μm Carboxen-PDMS was found to be the most efficient fibre for compounds with low boiling points. Although 65μm C8 can be used for extraction of all compounds studied, in no one case is it the most effective coating. 100μm PDMS and the more polar coatings can be used for a broad range of compounds, whereas application of 7μm and 30μm PDMS cannot be recommended. Inter-fibre comparison revealed significant differences between three different Carboxen-PDMS fibres. The results enable suitable coatings to be chosen for each of the 27 compounds and for substances with similar properties.
    Materialart: Digitale Medien
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  • 15
    ISSN: 1612-1112
    Schlagwort(e): Gas chromatography ; Cisplatin determination ; Blood analysis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A capillary gas chromatographic method is described for the determination of cisplatin based on the complexation of platinum(II) with bis(isovalerylacetone) ethylenediimine (H2IVA2en) and extraction in chloroform. The chromatography was carried out on a BP1 or a BP5 column with an FID. Copper(II), nickel (II) and palladium(II) separated completely and did not affect the determination of platinum(II). The method was applied of the determination of cisplatin in a pharmaceutical preparation and blood samples of cancer patients after infusion of cisplatin. The amounts of cisplatin in blood were found to be within 246–283 ng mL−1 with a C.V. of 2.35–4.26%.
    Materialart: Digitale Medien
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  • 16
    Digitale Medien
    Digitale Medien
    Springer
    Chromatographia 49 (1999), S. 273-280 
    ISSN: 1612-1112
    Schlagwort(e): Gas chromatography ; Complexation stationary phases ; Bonding metal complexes ; Capillary columns
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The use of polysiloxanes with cyano or thiol groups as stationary phases for complexation gas chromatography is discussed. The polymers were obtained via polycondensation followed by polymerisation of the corresponding dichloro- or dimethoxy-silanes. Both the phases were modified by bonding transition metal chlorides with were modified by bonding transition metal chlorides with cyano (CuCl2 or CoCl2) and thiol groups (NiCl2 or CoCl2). The phases were examined in order to determine their application to the analysis of ethers, thioethers and ketones. Due to the presence of lone electron pairs on oxygen or sulphur atoms, the compounds should be capable of specific interacting with the electron-withdrawing centre of the liquid stationary phases. A number of retention parameters (retention indices, molecular retention indices and specific retention volume) were determined, which allowed characterisation of specific interactions between the bonded metal and the compound analysed. The results also enabled assessment of the influence of the structure of the compounds on their retention. The measurements were also carried out for the phases with free SH and CN groups as reference phases. The work demonstrates that the phases obtained may be useful for effective separations.
    Materialart: Digitale Medien
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  • 17
    ISSN: 1612-1112
    Schlagwort(e): Gas chromatography ; Average column pressure ; Average column flow ; Specific retention volume ; Distribution coefficient
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A systematic derivation of corresponding equations shows that averaging the pressure and the flow rate of the mobile phase in a gas chromatographic column over the column length and over the time that an unretained component resides in the column, requires the use of three different compressibility correction factors,j 2 1 ,j 3 2 , andj 4 3 . When multiplied by the adjusted retention volume,V R-VM, the Martin and James mobile phase compressibility correction factorj 3 2 , only, produces the value of specific retention volume,V g T , which is connected unambiguously with the thermodynamic phase distribution coefficient,K, of the sorbate.
    Materialart: Digitale Medien
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  • 18
    Digitale Medien
    Digitale Medien
    Springer
    Chromatographia 49 (1999), S. 513-519 
    ISSN: 1612-1112
    Schlagwort(e): Gas chromatography ; Solid phase microextraction ; Open cap vials ; Volatile compounds (BTEX) ; Water matrix
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary The testing of open cap vials in headspace solid-phase microextraction combined with capillary gas chromatography is reported. The losses of volatile analytes from such vials were analyzed theoretically and investigated experimentally. The benzene, toluene, ethylbenzene, and xylene isomers spiked in water were used as model compounds. Extraction yields and precision obtained under optimized experimental conditions as exposure time, desorption time and temperature were compared applying vials with open caps or sealed with teflon lined septa.
    Materialart: Digitale Medien
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  • 19
    Digitale Medien
    Digitale Medien
    Springer
    Chromatographia 49 (1999), S. 567-571 
    ISSN: 1612-1112
    Schlagwort(e): Gas chromatography ; Mixed stationary phase ; Calixarenes ; Crown ethers ; Cyclodextrins
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Mixed stationary phases containing of 25,27-dibutoxy-5,11,17,23-tetra-tert-butyl-26,28-diundecenyloxy calix [4]arene (C[4]B)+ω-undecylomethyl-18-crown-6 polysiloxane (PSO-11-18-C-6) and C[4]B polysiloxane (PSO-C[4]B)+permethyl-β-cyclodextrin (PM-β-CD) were investigated in capillary gas chromatography. By comparing their selectivity for positional isomers with that of the corresponding individual pure stationary phases, synergistic effects were found.
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  • 20
    ISSN: 1612-1112
    Schlagwort(e): Gas chromatography ; Electron capture detector ; Anti-picornaviral agent in dog serum ; Enteroviruses
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary A gas chromatographic assay for the determination of SCH 48973, a potent broad spectrum anti-picornaviral agent, was developed and validated in dog serum. The method involved extraction with organic solvent followed by separation on a capillary column (DB-1) with quantitation by an electron-capture detector. The method was sensitive with a limit of quantitation of 10 ng mL−1. The linearity of the method was satisfactory as indicated by correlation coefficients of 〉0.999 and visual examination of the calibration curves. The method was precise with a coefficient of variation ranging from 2.3 to 13.2% and accurate with a bias ranging from −9.1 to 7.9%. Moreover, SCH 48973 was stable in dog serum after being subjected to three freeze-thaw cycles. The assay was shown to be sensitive, specific, accurate and precise, and reliable for use in pharmacokinetic or toxicokinetic studies.
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  • 21
    Digitale Medien
    Digitale Medien
    Springer
    Chromatographia 49 (1999), S. 399-405 
    ISSN: 1612-1112
    Schlagwort(e): Gas chromatography ; Solid phase adsorption ; Supercritical fluid extraction ; Sewage ; Organic pollutants
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Summary Analytical methods have been developed for the determination of organic pollutants of intermediate polarity in sewage. Water samples are first passed through a solid phase adsorption cartridge. The analytes are then extracted from the absorbent with supercritical CO2 into a small volume of trapping solvent. Finally, the extracts are analyzed directly by capillary gas chromatography and gas chromatography-mass spectrometer. The various parameters (pressure, temperature, type and concentration of modifiers, trapping solvent, flow rate and volume of supercritical fluid and equilibrium time) influencing the efficiency of extraction were studied. Extraction efficiencies for the test compounds are 〉70%, and relative standard deviations are 〈4.6% (n=3). The methods established were applied to the analysis of sewage at the Lanzhou Wastewater Treatment Plant, China. 66 organic pollutants were detected, of which 15 compounds appeared in the list of priority pollutants suggested by the US EPA.
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  • 22
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 22 (1999), S. 24-28 
    ISSN: 0935-6304
    Schlagwort(e): Gas chromatography ; ECD ; Micro-ECD ; GC detector ; organochlorine pesticides ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---A new ECD, the HP 6890 Series Micro-ECD, was designed to address inherent deficiencies in classical electron capture detectors (ECD), especially with respect to sensitivity, linearity, dynamic range, and ruggedness. Several novel technologies were incorporated in the totally new design and were refined through practical testing and user feedback. Validation of the micro-ECD performance was accomplished through side-by-side testing of the Micro-ECD with previous ECDs following US EPA Contract Laboratory Program methods for pesticides and PCBs. In addition, extensive interviews were conducted with early users of the Micro-ECD who also had experience with other designs running a variety of ECD methods. The design and resulting performance improvements are described.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 23
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 22 (1999), S. 181-182 
    ISSN: 0935-6304
    Schlagwort(e): Gas chromatography ; microwave induced emission spectrometry ; speciation ; mercury ; SPME, headspace SPME ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---No abstract
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 24
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 22 (1999), S. 294-296 
    ISSN: 0935-6304
    Schlagwort(e): Gas chromatography ; capillary ; fused silica ; rotenone ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: No abstract
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 25
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 22 (1999), S. 303-304 
    ISSN: 0935-6304
    Schlagwort(e): Gas chromatography ; food analysis ; pesticide residues ; thiabendazole ; imazalil ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---No abstract
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 26
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 22 (1999), S. 395-402 
    ISSN: 0935-6304
    Schlagwort(e): Gas chromatography ; pulsed splitless injection ; pesticide residues ; matrix effects ; retention gap ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The applicability of pulsed splitless injection to the gas chromatographic analysis of pesticide residues in fruit and vegetables has been evaluated. 22 pesticides belonging to different chemical classes, including those known to be liable to matrix induced response enhancement, were selected for the study. The parameters of pressure pulse have been tested for optimum performance of injection. Application of the pressure pulse was found to decrease matrix effects during analyses of real samples. Further decline of matrix effects was obtained using higher sample injection volumes. The installation of a deactivated retention gap was necessary to obtain good peak shapes with injection volumes exceeding 1 μL of sample. Up to 4 μL was then injected without peak distortion and consequent loss of resolution. Using 4 μL pulsed splitless injection, matrix effects were almost completely eliminated even at very low concentration levels of analytes. The highest matrix effects observed for tested compounds at the lowest concentration level tested were in the range of 110-122%.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 27
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 22 (1999), S. 565-588 
    ISSN: 0935-6304
    Schlagwort(e): Gas chromatography ; Kovats retention index ; vapor pressure ; boiling point ; Wilson activity coefficient ; binary phase diagrams ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Non-ideal mixing in a dimethylsilicone stationary phase is modeled according to the Wilson activity coefficient. Pure liquid vapor pressures of alkylated compound series are calculated from capillary GLC retention with the functional group heat of solution in a polymer solvent. The new method uses the Kovats index, molar mass, and functional group to determine the bubble line of a compound. Boiling points at reduced and normal pressure are compared to literature values of 194 gasoline components. An unlike molecular pair interaction parameter is derived, using only bubble line data of the pure liquids. Binary phase diagrams are constructed and compared to vapor liquid equilibrium data.
    Zusätzliches Material: 22 Ill.
    Materialart: Digitale Medien
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  • 28
    Digitale Medien
    Digitale Medien
    Springer
    Journal of biomedical science 5 (1998), S. 415-420 
    ISSN: 1423-0127
    Schlagwort(e): Isoprostanes ; Oxidative stress ; Lipid peroxidation ; Gas chromatography ; Mass spectrometry ; Human disease
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract The development of a specific, reliable and noninvasive method for measuring oxidative stress in humans is essential for establishing the role of free radicals in human diseases. Currently, accurate techniques to assess oxidant injury in vivo are extremely limited although a number of approaches are being investigated. Of these, the measurement of specific products of nonenzymatic lipid peroxidation, the F2-isoprostanes (F2-IsoPs), appears to be a more accurate marker of oxidative stress in vivo in humans than other available methods. The purpose of this brief review is to acquaint the reader with the IsoPs from a biochemical perspective and to provide information regarding the utility of quantifying these compounds as indicators of oxidant stress.
    Materialart: Digitale Medien
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  • 29
    Digitale Medien
    Digitale Medien
    Springer
    Zeitschrift für Lebensmittel-Untersuchung und -Forschung 206 (1998), S. 48-51 
    ISSN: 1431-4630
    Schlagwort(e): Key words Carbohydrates ; Myo-inositol ; Orange juice quality ; Gas chromatography
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Abstract  A gas chromatographic method using a capillary column is described for the quantitative analysis of fructose, glucose, sucrose and myo-inositol in orange juice. The method is evaluated for precision and recovery using phenyl-β-glucoside as an internal standard. The results support the suitability of the method. Carbohydrates (fructose, glucose, sucrose and myo-inositol) were determined in different kinds of orange juice. The determination of carbohydrate composition and ratios of the carbohydrate constituents provide a method to assess orange juice quality, especially the myo-inositol content and myo-inositol/fructose ratio. These new indices, which were found to be lower in samples made from concentrates, provide information on the quality and genuineness of orange juice.
    Materialart: Digitale Medien
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  • 30
    Digitale Medien
    Digitale Medien
    Springer
    Zeitschrift für Lebensmittel-Untersuchung und -Forschung 206 (1998), S. 77-82 
    ISSN: 1431-4630
    Schlagwort(e): Key words Anticarcinogen ; CLA ; Conjugated linoleic acid ; Daily intake ; Foods ; Gas chromatography ; Lipids
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Abstract  The quantities of the biologically active isomer of conjugated linoleic acid (CLA) – C18:2 c9t11 – in 139 German foods were analysed by capillary gas chromatography (results are given as a % of all identified fatty acid methyl esters). The CLA content ranged from 0.40% (Gouda) to 1.70% (Jurassic cheese, Old Emmentaler) in dairy products, from 0.11% (rabbit) to 1.20% (lamb) in meat, and from 0.01% (pike-perch) to 0.09% (carp) in fish. CLA could be detected in neither vegetable fats or oils nor in margarines (CLA 〈0.01%). Crisps, chocolates, cakes and pastries, and other foods have only a negligible CLA content. The average estimated CLA intake in Germany was calculated to be 0.35g CLA/day for women and 0.43g CLA/day for men.
    Materialart: Digitale Medien
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  • 31
    Digitale Medien
    Digitale Medien
    Springer
    Zeitschrift für Lebensmittel-Untersuchung und -Forschung 206 (1998), S. 213-216 
    ISSN: 1431-4630
    Schlagwort(e): Key words Milk fat ; Mixed fat ; Milk fat content ; Butyric acid ; Gas chromatography
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Abstract  The analysis of butyric acid (C4) is of importance for the determination of the proportion of milk fat in mixed fats. Three gas chromatographic methods were compared with regard to their precision for the measurement of C4, i.e. analysis of butyric acid methyl ester after trans-esterification of fat by sodium methylate (method A) or trimethyl sulphonium hydroxide (method B), as well as analysis of free butyric acid (method C), using an internal standard with each method. The examination of 30 milk fats which varied greatly in terms of their C4 content, using methods A, B and C, resulted in mean values of C4 of 3.42 g/100 g fat, 3.71 g/100 g fat and 3.06 g/100 g fat, respectively. The value determined using method B seemed too high, and this may have been due to the presence of co-eluting artefacts, whereas the value determined using method C was clearly too low, and can probably be attributed to losses during sample preparation. The standard deviation (SD) of 0.015 obtained from repeated analyses using method A was quite good. Results obtained using methods B and C had SDs of 0.029 and 0.074, respectively. Different levels of free fatty acids did not affect the results obtained using method A. When method A was checked by analysis of the reference fat, CRM 164, the C4 level determined was found to deviate from the certified C4 content of 3.49 (± 0.06) g/100 g fat by only 0.05 g C4/fat 100 g. Thus method A proved the most suitable for the determination of the proportion of milk fat in mixed fats by analysis of butyric acid.
    Materialart: Digitale Medien
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  • 32
    Digitale Medien
    Digitale Medien
    Springer
    Zeitschrift für Lebensmittel-Untersuchung und -Forschung 207 (1998), S. 180-181 
    ISSN: 1431-4630
    Schlagwort(e): Key words UHT milk ; Storage ; Monosaccharides ; Gas chromatography
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Abstract  Changes in the free monosaccharide fraction and non-casein nitrogen during the 3-month storage of five batches of commercial UHT milk were studied. Batches with high residual proteolytic activity showed a considerable increase in galactose, N–acetyl glucosamine and N–acetyl galactosamine levels during the storage period, whereas their glucose and myo-inositol contents remained unaltered. In batches with slight or negligible proteolytic activity no changes in the free monosaccharide fraction were observed.
    Materialart: Digitale Medien
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  • 33
    Digitale Medien
    Digitale Medien
    Springer
    Intensive care medicine 24 (1998), S. 415-421 
    ISSN: 1432-1238
    Schlagwort(e): Key words Acetone ; Gas chromatography ; Isoprene ; Lipid peroxidation ; Microwave desorption ; N-pentane
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Abstract Objective: Application of a new method for analysis of exhaled gas in critically ill patients. Design: Open study. Setting: Surgical intensive care unit of an university hospital. Patients: Thirty-seven consecutive, critically ill, mechanically ventilated patients. Interventions: None. Measurements and results: Chemical analysis of the patient's exhaled gas was based upon substance adsorption and concentration onto activated charcoal, microwave desorption and gas chromatographic separation. Patients with acute respiratory distress syndrome (ARDS) exhaled less isoprene than those without ARDS [9.8 (8.2–21.6) vs 21.8 (13.9–41.4) nmol/m2 per min [median (95 % confidence interval)], p = 0.04]. In patients who developed pulmonary infection, pentane elimination increased from 0.4 (0.0–5.4) to 2.7 (0.6–6.1, p = 0.05) nmol/m2 per min and isoprene elimination decreased from 5.2 (0–33) to 5.0 (0–17, p = 0.05) nmol/m2 per min, resulting in a significant increase in pentane/isoprene ratio from 0.1 (0–0.3) to 0.4 (0–15, p = 0.007) when compared to patients without pulmonary infection. Conclusions: The new method allows quantitative analysis of human gas samples with low substance concentrations and is well suited for clinical studies which involve the investigation of metabolic processes in the lung and the body.
    Materialart: Digitale Medien
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  • 34
    Digitale Medien
    Digitale Medien
    Springer
    Space science reviews 84 (1998), S. 199-206 
    ISSN: 1572-9672
    Schlagwort(e): Nuclear reactions ; Nucleosynthesis ; Abundances ; Stars:Evolution ; Interior ; Rotation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We first recall the observational and theoretical facts that constitute the so-called 3He problem. We then review the chemical anomalies that could be related to the destruction of 3He in red giants stars. We show how a simple consistent mechanism can lead to the destruction of 3He in low mass stars and simultaneously account for the low 12C/13C ratios and low lithium abundances observed in giant stars of different populations. This process should both naturally account for the recent measurements of 3He/H in galactic HII regions and allow for high values of 3He observed in some planetary nebulae. We propose a simple statistical estimation of the fraction of stars that may be affected by this process.
    Materialart: Digitale Medien
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  • 35
    ISSN: 0006-3525
    Schlagwort(e): folding type-specific secondary structure propensities ; amino acids ; α-helical proteins ; β sheet proteins ; α/β proteins ; α+β proteins ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Folding type-specific secondary structure propensities of 20 naturally occurring amino acids have been derived from α-helical, β-sheet, α/β, and α+β proteins of known structures. These data show that each residue type of amino acids has intrinsic propensities in different regions of secondary structures for different folding types of proteins. Each of the folding types shows markedly different rank ordering, indicating folding type-specific effects on the secondary structure propensities of amino acids. Rigorous statistical tests have been made to validate the folding type-specific effects. It should be noted that α and β proteins have relatively small α-helices and β-strands forming propensities respectively compared with those of α+β and α/β proteins. This may suggest that, with more complex architectures than α and β proteins, α+β and α/β proteins require larger propensities to distinguish from interacting α-helices and β-strands. Our finding of folding type-specific secondary structure propensities suggests that sequence space accessible to each folding type may have differing features. Differing sequence space features might be constrained by topological requirement for each of the folding types. Almost all strong β-sheet forming residues are hydrophobic in character regardless of folding types, thus suggesting the hydrophobicities of side chains as a key determinant of β-sheet structures. In contrast, conformational entropy of side chains is a major determinant of the helical propensities of amino acids, although other interactions such as hydrophobicities and charged interactions cannot be neglected. These results will be helpful to protein design, class-based secondary structure prediction, and protein folding. © 1998 John Wiley & Sons, Inc. Biopoly 45: 35-49, 1998
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 36
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 69-83 
    ISSN: 0006-3525
    Schlagwort(e): DNA branched junctions ; branch migration ; superhelical torque ; control of DNA structure ; endonuclease VII ; nanomechanical device ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: DNA branched junctions are analogues of Holliday junction recombination intermediates. Partially mobile junctions contain a limited amount of homology flanking the branch point. A partially mobile DNA branched junction has been incorporated into a synthetic double-stranded circular DNA molecule. The junction is flanked by four homologous nucleotide pairs, so that there are five possible locations for the branch point. Two opposite arms of the branched junction are joined to form the circular molecule, which contains 262 nucleotides to the base of the junction. This molecule represents a system whereby torque applied to the circular molecule can have an impact on the junction, by relocating its branch point. Ligation of the molecule produces two topoisomers; about 87% of the product is a relaxed molecule, and the rest is a molecule with one positive supercoil. The position of the branch point is assayed by cleaving the molecule with endonuclease VII. We find that the major site of the branch point in the relaxed topoisomer is at the maximally extruded position in the relaxed molecule. Upon the addition of ethidium, the major site of the branch point migrates to the minimally extruded position. © 1998 John Wiley & Sons, Inc. Biopoly 45: 69-83, 1998
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 37
    ISSN: 0006-3525
    Schlagwort(e): conformation ; aggregation ; κ-carrageenan ; flow field-flow fractionation ; multiangle light scattering ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The relatively novel combination of flow field-flow fractionation (FFF) and multiangle light scattering (MALS) was employed to study a nondegraded κ-carrageenan in different 0.1M salt solutions. The applicability of the technique was tested, and the effects of salt type and salt composition on the molar mass and radius of gyration were studied. A conformational ordering was induced at room temperature by switching the solvent from 0.1M NaCl (coil form) to 0.1M NaI (helix form). An approximate doubling of the average molar mass and an increase in radius of gyration was then observed, in agreement with results obtained previously using size exclusion chromatography-MALS. This increase in size was attributed to conformational ordering and to the formation of double helices. Severe aggregation was observed above 40% CsI in the 0.1M mixed salt solution of CsI and NaI. This was ascribed to the association of helices into large aggregates. For these large associates, having molar masses of several millions, a reversal of the elution order in flow FFF was detected. © 1998 John Wiley & Sons, Inc. Biopoly 45: 85-96 1998
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 38
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 119-133 
    ISSN: 0006-3525
    Schlagwort(e): conformations of D-alanyl-D-alanine ; β-lactam ; structural overlay ; AMBER force field ; AM1 ; ab initio ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: In this article a conformational analysis of the D-alanyl-D-alanine dipeptide, both charged and neutral, has been carried out. The preferred conformations were determined by means of ab initio and semiempirical quantum, together with empirical force field calculations. The AMBER* force field and the 6-31 + G** and 6-31G** ab initio levels give rise to a coincident minimum energy structure, which, on the other hand, differs from that determined by AM1, 3-21 + G, and 3-21G. The solvent effect on the different charged and neutral conformations have been considered through the AMSOL semiempirical method. A quantification regarding the structural similarities between the different dipeptide conformations and the ampicillin has been performed. The results show that the best overlay is attained by the minimum structure energy obtained by using the 6-31 + G** methodology, which presents a planar amidic nitrogen. © 1998 John Wiley & Sons, Inc. Biopoly 45: 119-133, 1998
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 39
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 157-163 
    ISSN: 0006-3525
    Schlagwort(e): chemical oxidation ; cellulose ; conformational transition ; capillary viscosity ; microcalorimetry ; calcium ions ; gels ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The conformational behavior of different molecular weight fractions of a synthetic C6-oxidized derivative of cellulose were investigated by means of capillary viscometry, CD, and microcalorimetric measurements. Experiments were carried out in the presence of either monovalent or divalent counterions.The experimental data indicated that C6-oxidized cellulose can assume an ordered extended conformation at low ionic strength, induced by the intrachain repulsions of negative charges. This conformation was suggested to be very similar to the fully extended structure of cellulose. In addition to this, upon increasing the ionic strength, a conformational transition of the order-to-disorder type occurred. In fact, the screening of the electrostatic repulsions introduced a number of conformational kinks into the cellulosic backbone, which enabled the polymer to assume a more coiled conformation hence producing less viscous aqueous solutions. © 1998 John Wiley & Sons, Inc. Biopoly 45: 157-163, 1998
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 40
    ISSN: 0006-3525
    Schlagwort(e): conformational stability ; biological polyelectrolytes ; enthalpy ; entropy ; conformational transitions ; carrageenan ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A new method is proposed for the determination of the enthalpy and entropy changes of nonionic origin upon conformational transition of linear biopolyelectrolytes in solution. For all transition midpoints, defined by given temperature and ionic strength, the total free energy change of the system is zero, which means that the nonionic contribution to the free energy change is equal in value and opposite in sign to the polyelectrolytic one. The counterion condensation theory of linear polyelectrolytes provides for the appropriate analytical expression to be used in such calculations. Linear plots of the proper functions of the calculated free energy changes vs the proper functions of temperature allows for the determination of the enthalpic and entropic terms of the nonionic free energy change of transition.The method has been applied to the extensive available data of the ion-induced conformational change of κ-carrageenan, a linear sulfated galactan extracted from seaweeds. The method has proved very successful, with the results showing a remarkable convergency of the enthalpy values for different monovalent counterions. On the other hand, the above approach has made it possible to explain the known effect of counterion specificity on the transition by a small difference in the nonionic entropic contributions. © 1998 John Wiley & Sons, Inc. Biopoly 45: 203-216, 1998
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 41
    ISSN: 0006-3525
    Schlagwort(e): uv resonance Raman spectroscopy ; Raman cross section ; hypochromism ; DNA ; deoxynucleoside ; protein ; aromatic amino acid ; virus assembly ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Ultraviolet resonance Raman (UVRR) spectra of H2O and D2O solutions of the nucleoside (dA, dG, dC, dT) and aromatic amino acid (Phe, Trp, Tyr) constituents of DNA viruses have been obtained with laser excitation wavelengths of 257, 244, 238, and 229 nm. Using the 981 cm-1 marker of Na2SO4 as an internal standard, Raman frequencies and scattering cross sections were evaluated for all prominent UVRR bands at each excitation wavelength. The results show that UVRR cross sections of both the nucleosides and amino acids are strongly dependent on excitation wavelength and constitute sensitive and selective probes of the residues. The results provide a library of UVRR marker bands for structural analysis of DNA viruses and other nucleoprotein assemblies. © 1998 John Wiley & Sons, Inc. Biopoly 45: 247-256, 1998
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 42
    ISSN: 0006-3525
    Schlagwort(e): hemoglobin ; hexagonal bilayer ; Lumbricus ; electron microscopy ; three-dimensional reconstruction ; small-angle x-ray scattering ; three-dimensional models ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The quaternary structure of Lumbricus terrestris hemoglobin was investigated by small-angle x-ray scattering (SAXS). Based on the SAXS data from several independent experiments, a three-dimensional (3D) consensus model was established to simulate the solution structure of this complex protein at low resolution (about 3 nm) and to yield the particle dimensions. The model is built up from a large number of small spheres of different weights, a result of the two-step procedure used to calculate the SAXS model. It accounts for the arrangement of 12 subunits in a hexagonal bilayer structure and for an additional central unit of cylinder-like shape. This model provides an excellent fit of the experimental scattering curve of the protein up to h = 1 nm-1 and a nearly perfect fit of the experimental distance distribution function p(r) in the whole range. Scattering curves and p(r) functions were also calculated for low-resolution models based on 3D reconstructions obtained by cryoelectron microscopy (EM). The calculated functions of these models also provide a very good fit of the experimental scattering curve (even at h 〉 1 nm-1) and p(r) function, if hydration is taken into account and the original model coordinates are slightly rescaled. The comparison of models reveals that both the SAXS-based and the EM-based model lead to a similar simulation of the protein structure and to similar particle dimensions. The essential differences between the models concern the hexagonal bilayer arrangement (eclipsed in the SAXS model, one layer slightly rotated in the EM model), and the mass distribution, mainly on the surface and in the central part of the protein complex. © John Wiley & Sons, Inc. Biopoly 45: 289-298, 1998
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 43
    ISSN: 0006-3525
    Schlagwort(e): conformational changes ; vicinal glycosylation ; branched α-l-Rhap(1-2)[β-d-Galp(1-3)]-β-d-Glc1-OMe trisaccharide ; parent disaccharides ; hydrogen bond ; isotope effect ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Conformations of the α-l-Rhap(1-2)-β-d-Glc1-OMe and β-d-Galp(1-3)-β-d-Glc1-OMe disaccharides and the branched title trisaccharide were examined in DMSO-d6 solution by 1H-nmr. The distance mapping procedure was based on rotating frame nuclear Overhauser effect (NOE) constraints involving C- and O-linked protons, and hydrogen-bond constraints manifested by the splitting of the OH nmr signals for partially deuteriated samples. An “isotopomer-selected NOE” method for the unequivocal identification of mutually hydrogen-bonded hydroxyl groups was suggested. The length of hydrogen bonds thus detected is considered the only one motionally nonaveraged nmr-derived constraint. Molecular mechanics and molecular dynamics methods were used to model the conformational properties of the studied oligosaccharides. Complex conformational search, relying on a regular Φ,Ψ-grid based scanning of the conformational space of the selected glycosidic linkage, combined with simultaneous modeling of different allowed orientations of the pendant groups and the third, neighboring sugar residue, has been carried out. Energy minimizations were performed for each member of the Φ,Ψ grid generated set of conformations. Conformational clustering has been done to group the minimized conformations into families with similar values of glycosidic torsion angles. Several stable syn and anti conformations were found for the 1→2 and 1→3 bonds in the studied disaccharides. Vicinal glycosylation affected strongly the occupancy of conformational states in both branches of the title trisaccharide. The preferred conformational family of the trisaccharide (with average Φ,Ψ values of 38°, 17° for the 1→2 and 48°, 1° for the 1→3 bond, respectively) was shown by nmr to be stabilized by intramolecular hydrogen bonding between the nonbonded Rha and Gal residues. © 1998 John Wiley & Sons, Inc. Biopoly 46: 417-432, 1998
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
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  • 44
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 489-492 
    ISSN: 0006-3525
    Schlagwort(e): refractive index increment ; proteins ; solvent ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The refractive index increment of a protein solution is a property not only of the protein, but also of the solvent. This is demonstrated theoretically and confirmed experimentally using analytical interferometry. © 1998 John Wiley & Sons, Inc. Biopoly 46: 489-492, 1998
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 45
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 47 (1998), S. 1-1 
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: No abstract.
    Materialart: Digitale Medien
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  • 46
    ISSN: 0006-3525
    Schlagwort(e): hepatitis A ; synthetic peptides ; CD ; liposomes ; computational study ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The present study was undertaken to examine the structural features that may be important to explain the immunogenicity of the (110-121) peptide sequence (FWRGDLVFDFQV) of VP3 capsid protein of hepatitis A virus. A conformational analysis of the preferred conformations by CD and molecular mechanics was carried out. Present results suggest that the interaction with liposomes as biomembrane model induces and stabilizes the amphipathic β-structure of the peptide.To study the contribution of amino acid replacements at the RGD tripeptide as well as the influence of the peptide chain length on peptide conformation, solid-phase peptide synthesis of several peptide analogs was carried out and the peptide conformation was studied using CD spectroscopy. The results show that the RGD sequence is necessary to induce the β-structure in the presence of liposomes. © 1998 John Wiley & Sons, Inc. Biopoly 45: 479-492, 1998
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 47
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 31-37 
    ISSN: 0006-3525
    Schlagwort(e): DNA liquid crystals ; DNA fragments ; screened Coulomb interactions ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The critical volume fractions pertaining to the formation of DNA liquid crystals were obtained from polarization microscopy, 31P-nmr, and phase separation experiments. The DNA length (approximately one to two times the persistence length 50 nm), ionic strength, and counterion variety dependencies are reported. The cholesteric-isotropic transition is interpreted in terms of the coexistence equations, which are derived from the solution free energy including orientational entropy and excluded volume effects. With the wormlike chain as reference system, the electrostatic contribution to the free energy is evaluated as a thermodynamic perturbation in the second virial approximation with a Debye-Hückel potential of mean force. The hard core contribution has been evaluated with scaled particle theory and/or a simple generalization of the Carnahan-Starling equation of state for hard spheres. For sufficiently high ionic strengths, the agreement is almost quantitative. At lower amounts of added salt deviations are observed, which are tentatively attributed to counterion screening effects. The contour length dependence agrees with a DNA persistence length 50 nm. © 1998 John Wiley & Sons, Inc. Biopoly 46: 31-37, 1998
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  • 48
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 245-252 
    ISSN: 0006-3525
    Schlagwort(e): gelatin ; gelation ; atomic force microscopy ; interfacial rheology ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Gelation of gelatin under various conditions has been followed by atomic force microscopy (AFM) with the objective of understanding more fully the structure formed during the gelation process. AFM images were obtained of the structures formed from both the bulk sol and in surface films during the onset of gelation. While gelation occurred in the bulk sol, the extent of helix formation was monitored by measurements of optical rotation, and the molecular aggregation was imaged by AFM. Interfacial gelatin films formed at the air-water interface were also studied. Measurements of surface tension and surface rheology were made periodically and Langmuir-Blodgett films were drawn from the interface to allow AFM imaging of the structure of the interfacial layer as a function of time. Structural studies reveal that at low levels of helical content the gelatin molecules assemble into aggregates containing short segments of dimensions comparable to those expected for gelatin triple helices. With time larger fibrous structures appear whose dimensions suggest that they are bundles of triple helices. As gelation proceeds, the number density of fibers increases at the expense of the smaller aggregates, eventually assembling into a fibrous network. The gel structure appears to be sensitive to the thermal history, and this is particularly important in determining the structure and properties of the interfacial films. © 1998 John Wiley & Sons, Inc. Biopoly 46: 245-252, 1998
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 49
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 48 (1998), S. 65-81 
    ISSN: 0006-3525
    Schlagwort(e): nucleotide analogue interference mapping ; phosphorothioate ; group I intron ; interference suppression ; RNA ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: In this review I will outline several chemogenetic approaches used to determine the chemical basis of large ribozyme function and structure. The term chemogenetics was first used to describe site-specific functional group modification experiments in the analysis of DNA-protein interactions. Within the past few years equivalent experiments have been performed on large catalytic RNAs using both single-site substitution and interference mapping techniques with nucleotide analogues. While functional group mutagenesis is an important aspect of a chemogenetic approach, chemical correlates to genetic revertants and suppressors must also be realized for the genetic analogy to be intellectually valid and experimentally useful. Several examples of functional group revertants and suppressors have now been obtained within the Tetrahymena group I ribozyme. These experiments define an ensemble of tertiary hydrogen bonds that have made it possible to construct a detailed model of the ribozyme catalytic core. The model includes a functionally important monovalent metal ion binding site, a wobble-wobble receptor motif for helix-helix packing interactions, and a minor groove triple helix. © 1998 John Wiley & Sons, Inc. Biopoly 48: 65-81, 1998
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 50
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 48 (1998), S. 83-96 
    ISSN: 0006-3525
    Schlagwort(e): nucleic acid ; disulfide cross-link ; structure ; dynamics ; stability ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: In this review I discuss straightforward and general methods to modify nucleic acid structure with disulfide cross-links. A motivating factor in developing this chemistry was the notion that disulfide bonds would be excellent tools to probe the structure, dynamics, thermodynamics, folding, and function of DNA and RNA, much in the way that cystine cross-links have been used to study proteins. The chemistry described has been used to synthesize disulfide cross-linked hairpins and duplexes, higher order structures like triplexes, nonground-state conformations, and tRNAs. Since the cross-links form quantitatively by mild air oxidation and do not perturb either secondary or tertiary structure, this modification should prove quite useful for the study of nucleic acids. © 1998 John Wiley & Sons, Inc. Biopoly 48: 83-96, 1998
    Zusätzliches Material: 9 Ill.
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  • 51
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 48 (1998), S. 113-135 
    ISSN: 0006-3525
    Schlagwort(e): divalent cations ; magnesium ; RNA ; ion binding ; RNA folding ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Divalent cations, like magnesium, are crucial for the structural integrity and biological activity of RNA. In this article, we present a picture of how magnesium stabilizes a particular folded form of RNA. The overall stabilization of RNA by Mg2+ is given by the free energy of transferring RNA from a reference univalent salt solution to a mixed salt solution. This term has favorable energetic contributions from two distinct modes of binding: diffuse binding and site binding. In diffuse binding, fully hydrated Mg ions interact with the RNA via nonspecific long-range electrostatic interactions. In site binding, dehydrated Mg2+ interacts with anionic ligands specifically arranged by the RNA fold to act as coordinating ligands for the metal ion. Each of these modes has a strong coulombic contribution to binding; however, site binding is also characterized by substantial changes in ion solvation and other nonelectrostatic contributions. We will show how these energetic differences can be exploited to experimentally distinguish between these two classes of ions using analyses of binding polynomials. We survey a number of specific systems in which Mg2+-RNA interactions have been studied. In well-characterized systems such as certain tRNAs and some rRNA fragments these studies show that site-bound ions can play an important role in RNA stability. However, the crucial role of diffusely bound ions is also evident. We emphasize that diffuse binding can only be described rigorously by a model that accounts for long-range electrostatic forces. To fully understand the role of magnesium ions in RNA stability, theoretical models describing electrostatic forces in systems with complicated structures must be developed. © 1999 John Wiley & Sons, Inc. Biopoly 48: 113-135, 1998
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 52
    ISSN: 0006-3525
    Schlagwort(e): 1H-nmr ; molecular modeling ; peptaibol ; peptide-lipid interaction ; sodium dodecyl sulfate micelles ; trichorzianin TA VII ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Trichorzianin TA VII, Ac0 U1 A2 A3 U4 J5 Q6 U7 U8 U9 S10 L11 U12 P13 V14 U15 I16 Q17 Q18 Fol19, is a nonadecapeptide member of the peptaibol antibiotics biosynthesized by Trichoderma soil fungi, which is characterized by a high proportion of the α,α-dialkylated amino acids, α-aminoisobutyric acid (Aib, U) and isovaline (Iva, J), an acetylated N-terminus and a C-terminal phenylalaninol (Pheol, Fol). The main interest in such peptides stems from their ability to interact with phospholipid bilayers and form voltage-dependent transmembrane channels in planar lipid bilayers. In order to provide insights into the lipid-peptide interaction promoting the voltage gating, the conformational study of TA VII in the presence of perdeuterated sodium dodecyl sulfate (SDS-d25) micelles has been carried out. 1H sequential assignments have been performed with the use of two-dimensional homo- and -heteronuclear nmr techniques including double quantum filtered correlated spectroscopy, homonuclear Hartmann-Hahn, nuclear Overhauser effect spectroscopy, 1H-13C heteronuclear single quantum correlation, and heteronuclear multiple bond correlation. Conformational parameters, such as 3JNHCαH coupling constants, temperature coefficients of amide protons (Δδ/ΔTNH) and quantitative nuclear Overhauser enhancement data, lead to detailed structural information. Ninety-eight three-dimensional structures consistent with the nmr data were generated from 231 interproton distances and six Φ dihedral angle restraints, using restrained molecular dynamics and energy minimization calculations. The average rms deviation between the 98 refined structures and the energy-minimized average structure is 0.59 Å for the backbone atoms. The structure of trichorzianin TA VII associated with SDS micelles, as determined by these methods, is characterized by two right-handed helical segments involving residues 1-8 and 11-19, linked by a β-turn that leads to an angle about 90°-100° between the two helix axes; residues 18 and 19 at the end of the C-terminal helix exhibit multiple conformations. © 1998 John Wiley & Sons, Inc. Biopoly 46: 75-88, 1998
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 53
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 127-143 
    ISSN: 0006-3525
    Schlagwort(e): 9-hydroxyellipticine ; DNA ; CD ; linear dichroism ; resonance light scattering ; intercalation ; drug-drug interactions ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The binding of 9-hydroxyellipticine to calf thymus DNA, poly[d(A-T)]2, and poly-[d(G-C)]2 has been studied in detail by means of CD, linear dichroism, resonance light scattering, and molecular dynamics. The transition moment polarizations of 9-hydroxyelliptiycine were determined in polyvinyl alcohol stretched film. Spectroscopic solution studies of the DNA/drug complex are combined with theoretical CD calculations using the final 50 ps of a series of molecular dynamics simulations as input. The spectroscopic data shows 9-hydroxyellipticine to adopt two main binding modes, one intercalative and the other a stacked binding mode involving the formation of drug oligomers in the DNA major groove. Analysis of the intercalated binding mode in poly[d(A-T)]2 suggests the 9-hydroxyellipticine hydroxyl group lies in the minor groove and hydrogen bonds to water with the pyridine ring protruding into the major groove. The stacked binding mode was examined using resonance light scattering and it was concluded that the drug was forming small oligomer stacks rather than extended aggregates. Reduced linear dichroism measurements suggested a binding geometry that precluded a minor groove binding mode where the plane of the drug makes a 45° angle with the plane of the bases. Thus it was concluded that the drug stacks in the major groove. No obvious differences in the mode of binding of 9-hydroxyellipticine were observed between different DNA sequences; however, the stacked binding mode appeared to be more favorable for calf thymus DNA and poly[d(G-C)]2 than for poly[d(A-T)]2, an observation that could be explained by the slightly greater steric hindrance of the poly[d(A-T)]2 major groove. A strong concentration dependence was observed for the two binding modes where intercalation is favored at very low drug load, with stacking interactions becoming more prominent as the drug concentration is increased. Even at DNA : drug mixing ratios of 70:1 the stacked binding mode was still important for GC-rich DNAs. © 1998 John Wiley & Sons, Inc. Biopoly 46: 127-143, 1998
    Zusätzliches Material: 11 Ill.
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  • 54
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 169-179 
    ISSN: 0006-3525
    Schlagwort(e): macromolecular carriers ; drug targeting and delivery ; branched chain synthetic polypeptides ; membrane-synthetic polypeptide interaction ; lipid monolayers/bilayers ; polymer therapeutics ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The surface properties at the air/water interface and the interaction of branched chain polymeric polypeptides with a general formula poly[Lys-(DL-Alam-X1)], where X = Π (AK), Ser (SAK), or Glu (EAK), with phospholipids were investigated. Polylysine derivatives with polycationic (SAK, AK) or amphoteric (EAK) were capable to spread and form stable monomolecular layers. The stability of monolayers at the air/water interface was dependent on the side-chain terminal amino acid residue of polymers and can be described by SAK 〈 AK 〈 EAK order. The area per amino acid residue values calculated from compression isotherms were in the same range as compared to those of linear poly-α-amino acids and proteins. Moreover, these polymers interact with phospholipid monomolecular layers composed of dipalmitoyl phosphatidyl choline (DPPC) or DPPC/PG (PG: phosphatidyl glycerol; 95/5, mol/mol). Data obtained from compression isotherms of phospholipids spread on aqueous polymer solutions at different initial surface pressure indicated that insertion into lipid monolayers for SAK or AK is more pronounced than for EAK. The interaction between branched polypeptides and phospholipid membranes was further investigated using lipid bilayers with DPPC/PG and fluorescent probes located either at the polar surface [1-(4-trimethylammonium-phenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH) sodium anilino naphthalene sulfonate (ANS)] or within the hydrophobic core (DPH) of the liposome. Changes in fluorescence intensity and in polarization were observed when TMA-DPH or ANS, but not DPH were used. Comparative data also indicate that all three polymers interact only with the outer surface of the bilayer, but even the most marked penetration of polycationic polypeptide (SAK) did not result in alteration of the ordered state of the alkyl chains in the bilayer. Taken together, data obtained from mono- or bilayer experiments suggest that the interaction between branched polymers and phospholipids are highly dependent on the charge properties (Ser vs Glu) and on the identity (Ser vs Ala) of side-chain terminating amino acids. The binding of polymers to the model membranes could be mainly driven by electrostatic forces, but the significant role of hydrophilic properties in case of SAK cannot be excluded. © 1998 John Wiley & Sons, Inc. Biopoly 46: 169-179, 1998
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 55
    ISSN: 0006-3525
    Schlagwort(e): Cα,α-dialkylated glycines ; molecular dynamics ; geometry and conformation ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The relationship between the local backbone conformation and bond angles at Cα of symmetrically substituted Cα,α-dialkylated glycines (Cα,α-dimethylglycine or α-aminoisobutyric acid, Aib; Cα,α-diethylglycine, Deg; Cα,α-di-n-propylglycine, Dpg) has been investigated by molecular dynamics (MD) simulation adopting flat bottom harmonic potentials, instead of the usual harmonic restraints, for the Cα bond angles. The MD simulations show that the Cα bond angles are related to the local backbone conformation, irrespectively of the side-chain length of Aib, Deg, and Dpg residues. Moreover, the N-Cα-C′ (τ) angle is the most sensitive conformational parameter and, in the folded form, is always larger and more flexible than in the extended one. © 1998 John Wiley & Sons, Inc. Biopoly 46: 239-244, 1998
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 56
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 319-327 
    ISSN: 0006-3525
    Schlagwort(e): methionine ligation ; parathyroid hormones ; biomimetic ligation ; S-methylation ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: In biological systems, both proteolysis and aminolysis of amide bonds produce activated intermediates through acyl transfer reactions either inter- or intramolecularly. Protein splicing is an illustrative example that proceeds through a series of catalyzed acyl transfer reactions and culminates at an O- or S-acyl intermediate. This intermediate leads to an uncatalyzed acyl migration to form an amide bond in the spliced product. A ligation method mimicking the uncatalyzed final steps in protein splicing has been developed utilizing the acyl transfer amide-bond feature for the blockwise coupling of unprotected, free peptide segments at methionine (Met). The latent thiol moiety of Met can be exploited using homocysteine at the α-amino terminal position of a free peptide for transthioesterification with another free peptide containing an α-thioester to give an S-acyl intermediate. A subsequent, proximity-driven S- to N-acyl migration of this acyl intermediate spontaneously rearranges to form a homocysteinyl amide bond. S-methylation with excess p-nitrobenezensulfonate yields Met at the ligation site. The methionine ligation is selective and orthogonal, and is usually completed within 4 h when performed at slightly basic pH and under strongly reductive conditions. No side reactions due to acylation were observed with any other α-amines of both peptide segments as seen in the synthesis of parathyroid hormone peptides. Furthermore, cyclic peptide can also be obtained through the same strategy by placing both homocysteine at the amino terminus and the thioester at the carboxyl terminus in an unprotected peptide precursor. These biomimetic ligation strategies hold promise for engineering novel peptides and proteins. © 1998 John Wiley & Sons, Inc. Biopoly 46: 319-327, 1998
    Zusätzliches Material: 5 Ill.
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  • 57
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 359-373 
    ISSN: 0006-3525
    Schlagwort(e): boundary element method ; DNA electrophoresis ; electrophoretic mobility of DNA ; free solution electrophoretic mobility of DNA ; ion relaxation, DNA electrophoresis ; modeling electrophoresis of polyions ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Boundary element methods are used to model the free solution electrophoretic mobility of short DNA fragments. The Stern surfaces of the DNA fragments are modeled as plated cylinders that reproduce translational and rotational diffusion constants. The solvent-accessible and ion-accessible surfaces are taken to be coincident with the Stern surface. The mobilities are computed by solving simultaneously the coupled Navier-Stokes, Poisson, and ion-transport equations. The equilibrium electrostatics are treated at the level of the full Poisson-Boltzmann equation and ion relaxation is included. For polyions as highly charged as short DNA fragments, ion relaxation is substantial. At .11 M KCl, the simulated mobilities of a 20 base pair DNA fragment are in excellent agreement with experiment. At .04 M Tris acetate, pH = 8.0, the simulated mobilities are about 10-15% higher than experimental values and this discrepancy is attributed to the relatively large size of the Tris counterion. The length dependence of the mobility at .11 M KCl is also investigated. Earlier mobility studies on lysozyme are reexamined in view of the present findings. In addition to electrophoretic mobilities, the effective polyion charge measured in steady state electrophoresis and its relationship to the preferential interaction parameter γgG is briefly considered. © 1998 John Wiley & Sons, Inc. Biopoly 46: 359-373, 1998
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 58
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 341-346 
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: No abstract.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 59
    ISSN: 0006-3525
    Schlagwort(e): diffusional encounter ; Brownian dynamics ; average Boltzmann factor ; acetylcholinesterase ; Poisson-Boltzmann ; electrostatics ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The utility of the average Boltzmann factor around the active site of an enzyme as the predictor of the electrostatic enhancement of the substrate binding rate is tested on a set of data on wild-type acetylcholinesterase and 18 charge mutants recently obtained by Brownian dynamics simulations. A good correlation between the average Boltzmann factors and the substrate binding rate constants is found. The effects of single charge mutations on both the Boltzmann factor and the substrate binding rate constant are modest, i.e., 〈5 fold increase or decrease. This is consistent with the experimental results of Shafferman et al. but does not support their suggestion that the overall rate of the catalytic reaction is not limited by the diffusional encounter of acetylcholinesterase and its substrate. © 1998 John Wiley & Sons, Inc. Biopoly 45: 355-360, 1998
    Zusätzliches Material: 2 Ill.
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  • 60
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 469-478 
    ISSN: 0006-3525
    Schlagwort(e): molecular dynamics ; hydrated proteins ; crystal structures ; density distributions ; globular proteins ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Using molecular dynamics simulations of fully hydrated proteins and analysis of crystal structures contained in the Protein Data Bank, we develop a transferable set of perpendicular radial distribution functions for water molecules around globular proteins. These universal functions may be used to reconstruct the unique three-dimensional solvent density distribution around every individual protein with a modest error. We discuss potential applications of this solvent treatment in protein x-ray crystallographic refinements and in theoretical modeling. We also present a fast, grid-based algorithm for construction of the perpendicular solvent density distributions. © 1998 John Wiley & Sons, Inc. Biopoly 45: 469-478, 1998
    Zusätzliches Material: 6 Ill.
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  • 61
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 47 (1998), S. 23-29 
    ISSN: 0006-3525
    Schlagwort(e): independently folded polypeptide motifs ; miniproteins ; natural target domains ; BBA motif ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: In this paper we present a redesign strategy for the development of uniquely folded polypeptide motifs of less than 40 residues. These mini proteins are based on natural target domains, including the zinc finger domains (BBA motif) Nomenclature corresponds to the defined elements of secondary structure, beginning at the N-terminus of the peptide. Roman lettering refers to a specific motif while Greek characters correspond to the elements of secondary structure within that motif. and the disulfide-rich snake and scorpion toxins (BBB motif). These motifs are designed to act as the molecular framework for the construction of novel functional polypeptides. We will explore the structural determinants of the folded BBA motif, inspired by the zinc finger peptides, in relation to the redesign process. © 1998 John Wiley & Sons, Inc. Biopoly 47: 23-29, 1998
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 62
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 47 (1998), S. 75-81 
    ISSN: 0006-3525
    Schlagwort(e): ion channel ; synthetic peptide ; de novo design ; template-assembled synthetic proteins ; supramolecular assembly ; membrane protein ; planer lipid bilayers ; amphiphilic peptide ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: To create ion channel function by synthetic peptides is a challenge in the de novo design of artificial membrane proteins. Amphiphilic α-helical motifs of ∼ 20 amino acid residues to span lipid bilayers are most often used for the creation of peptide ion channels. Template molecules to tether helical peptides have been employed to obtain more organized pore structures. Approaches to form molecular assembly of peptides in the membranes by hydrogen bonding have been also investigated. We have developed approaches to assemble helices with individual amino acid sequences to construct artificial helical proteins. Using one of these approaches, four helices corresponding to the voltage sensor segments (S4 in repeat I-IV) of the sodium channel were assembled on a peptide template to give a protein having ion channel activity with rectification. © 1998 John Wiley & Sons, Inc. Biopoly 47: 75-81, 1998
    Zusätzliches Material: 5 Ill.
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  • 63
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 47 (1998), S. 127-142 
    ISSN: 0006-3525
    Schlagwort(e): collagen mimetics ; triple helix ; peptoid ; template ; biophysics ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Collagen peptidomimetics have been synthesized as an alternative to natural collagen. The incorporation of unnatural residues such as peptoids in the collagen sequences can demonstrate potent and specific biological activity and enhance the biostability against enzymatic degradation. Furthermore, the use of achiral peptoids simplifies synthetic strategies by reducing racemization problems. The peptoid residue N-isobutylglycine (Nleu) has been successfully incorporated into a series of collagen mimetics composed of Gly-Pro-Nleu, Gly-Nleu-Pro, and Gly-Nleu-Nleu. The discovery of template-assembled collagen mimetics and metal binding ability has laid the foundation for new opportunities in the design of novel collagen mimetic complexes. This review summarizes the synthesis and integrated biophysical analyses of the structures of these collagen mimetics. Solid phase segment condensation techniques have been utilized for the synthesis of the single chain and template-assembled analogues. The characterization of the collagen-like structures has been established by temperature-dependent optical rotation measurements, CD, NMR spectroscopy, and molecular modelling simulations. © 1998 John Wiley & Sons, Inc. Biopoly 47: 127-142, 1998
    Zusätzliches Material: 20 Ill.
    Materialart: Digitale Medien
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  • 64
    ISSN: 0006-3525
    Schlagwort(e): non-natural amino acid ; peptide ; squarylium dye ; thin film ; poly(3-methylthiophene) ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: We designed a polypeptide that behaves as a photodevice by using a non-natural amino acid with replacement of an α-hydrogen by a squarylium dye and succeeded in syntheses of the non-natural amino acid derivative containing a squarylium and its peptide with trialanine Ala-Ala-Ala. Strong dye-dye interactions were confirmed by absorption and CD spectra for the peptide in 2,2,2-trifluoroethanol solution and in water suspension. The non-natural amino acid derivative could be deposited onto a PMeT/Au electrode by the micelle disruption method. © 1998 John Wiley & Sons, Inc. Biopoly 47: 179-183, 1998
    Zusätzliches Material: 5 Ill.
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  • 65
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 47 (1998), S. 263-263 
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: No abstract.
    Materialart: Digitale Medien
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  • 66
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 117-126 
    ISSN: 0006-3525
    Schlagwort(e): electrostatically driven Monte Carlo method ; cluster analysis ; global energy minimum ; perturbed conformations ; conformational space ; lowest energy conformations ; polypeptide chain ; melittin, membrane-bound portion ; Empirical Conformational Energy Program for Peptides 3 ; annealing methods ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The electrostatically driven Monte Carlo (EDMC) method has been greatly improved by adding a series of new features, including a procedure for cluster analysis of the accepted conformations. This information is used to guide the search for the global energy minimum. Alternative procedures for generating perturbed conformations to sample the conformational space were also included. These procedures enhance the efficiency of the method by generating a larger number of low-energy conformations.The improved EDMC method has been used to explore the conformational space of a 20-residue polypeptide chain whose sequence corresponds to the membrane-bound portion of melittin. The ECEPP/3 (Empirical Conformational Energy Program for Peptides) algorithm was used to describe the conformational energy of the chain. After an exhaustive search involving 14 independent runs, the lowest energy conformation (LEC) (-91.0 kcal/mol) of the entire study was encountered in four of the runs, while conformations higher in energy by no more than 1.8 kcal/mol were found in the remaining runs with the exception of one of them (run 8). The LEC is identical to the conformation found recently by J. Lee, H.A. Scheraga, and S. Rackovsky [(1998) “Conformational Analysis of the 20-Residue Membrane-Bound Portion of Melittin by Conformational Space Annealing,” Biopolymers, Vol. 46, pp. 103-115] as the lowest energy conformation obtained in their study using the conformational space annealing method. These results suggest that this conformation corresponds to the global energy minimum of the ECEPP/3 potential function for this specific sequence; it also appears to be the conformation of lowest free energy. © 1998 John Wiley & Sons, Inc. Biopoly 46: 117-126, 1998
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  • 67
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 195-200 
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: No abstract.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 68
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 201-214 
    ISSN: 0006-3525
    Schlagwort(e): band broadening ; dispersion ; DNA ; gels ; electrophoresis ; fluorescence recovery ; photobleaching ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: We determined quantitatively the band broadening effect during gel electrophoresis by measuring the longitudinal dispersion coefficient Dx, with a fluorescence recovery after photobleaching setup, coupled to an electrophoretic cell. We carried out measurements as a function of the electric field, the average pore size, and the molecular length of DNA fragments. Our results are in good agreement with the predictions of the biased reptation model with fluctuations described by T. A. Duke et al. [(1992) Physics Review Letters, vol. 69, pp. 3260-3263]. This agreement is observed on single-stranded DNA [persistence length ≅ 4 nm; B. Tinland et al. (1997) Macromolecules, vol. 30, pp. 5763-5765] in polyacrylamide gels and on double-stranded DNA (persistence length ≅ 50 nm) in agarose gels, two systems where the ratio between the average pore size and the Kuhn length is larger than 1. © 1998 John Wiley & Sons, Inc. Biopoly 46: 201-214, 1998
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
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  • 69
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 403-415 
    ISSN: 0006-3525
    Schlagwort(e): molecular dynamics ; DNA curvature ; DNA flexibility ; TATA box functionality ; TATA box binding protein (TBP) ; TBP recognition ; TBP binding ; TBP transcriptional activation ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Four 1.5 ns molecular dynamics (MD) simulations were performed on the d(GCTATAAAAGGG) · d(CCCTTTTATAGC) double helix dodecamer bearing the Adenovirus major late promoter TATA element and three iso-composition mutants for which physical and biochemical data are available from the same laboratory. Three of these DNA sequences experimentally induce tight binding with the TATA box binding protein (TBP) and induce high transcription rates; the other DNA sequence induces much lower TBP binding and transcription. The x-ray crystal structures have previously shown that the duplex DNA in DNA-TBP complexes are highly bent. We performed and analyzed MD simulations for these four DNAs, whose experimental structures are not available, in order to address the issue of whether inherent DNA structure and flexibility play a role in establishing these observed preferences. A comparison of the experimental and simulated results demonstrated that DNA duplex sequence-dependent curvature and flexibility play a significant role in TBP recognition, binding, and transcriptional activation. © 1998 John Wiley & Sons, Inc. Biopoly 46: 403-415, 1998
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 70
    ISSN: 0006-3525
    Schlagwort(e): vibrational CD ; solution conformation ; alanine oligopeptides ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The solution conformation of a number of small, linear alanine oligomers was investigated via ir (or vibrational) CD (VCD). We find that these oligopeptides assume distinct solution conformations that depend primarily on chain lengths, and to a lesser degree on temperature, ionic strength, and pH. As expected, the longer chain oligomers exhibit more distinct VCD features and, presumably, more stable solution structures. At the level of the hexamer, however, aggregation of the peptide occurs. The fast time scale of VCD allows solution structures to be detected that may not be observable using slower techniques such as various forms of nmr spectroscopy. The VCD results reported here confirm that it is generally possible to obtain conformational information for small, linear homo- and heterooligopeptides via VCD spectroscopy. In this respect, the sensitivity of VCD is similar to that of electronic CD. Furthermore, the temperature dependence of the VCD results indicate that at elevated temperatures, the increasing number of conformational states results in a loss of discernible conformers, and consequently, a broadening and weakening of the VCD features. © 1998 John Wiley & Sons, Inc. Biopoly 46: 455-463, 1998
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 71
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 47 (1998), S. 5-22 
    ISSN: 0006-3525
    Schlagwort(e): hemoproteins ; model systems ; miniaturized proteins ; mimochromes ; helix structures ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The present paper highlights and reviews current research in the field of hemoprotein models. Hemoproteins have been extensively studied in order to understand structure-function relationships, and to design new molecules with desired functions. A wide number of synthetic analogues have been developed, using quite different approaches. They differ in molecular structures, ranging from simple meso-substituted tetraaryl-metalloporphyrins and peptide-porphyrin conjugates.In this paper we summarize the state of the art on peptide based hemoprotein models. We also report here the approach used by us to develop a new class of molecules, named mimochromes. They can be regarded as miniaturized hemoproteins, because mimochromes are low molecular weight compounds with some structural and functional properties common to those of the parent high molecular weight protein. The basic structure of mimochromes is a deuteroporphyrin ring covalently linked to two helical peptide chains. Two molecules of this series have been fully characterized. All the information derived from their structural analysis has been applied to the design of new analogues with additional functions. © 1998 John Wiley & Sons, Inc. Biopoly 47: 5-22, 1998
    Zusätzliches Material: 15 Ill.
    Materialart: Digitale Medien
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  • 72
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 503-516 
    ISSN: 0006-3525
    Schlagwort(e): discrete charge model of DNA ; dielectric cylinder in water ; effective dielectric constant ; salt effects ; Debye shielding factor ; potential variations in DNA surface ; Boltzmann averaged bending angles ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: We have studied electrostatic properties of DNA with a discrete charge model consisting of a cylindrical dielectric core with a radius of 8 Å and a dielectric constant Di = 4, surrounded by two helical strings of phosphate point charges at 10 Å from the axis, immersed in an aqueous medium with dielectric constant Dw = 78.54. Eliminating the dielectric core makes potentials in the phosphate surface less negative by about 0.5 kT/e. Salt effects are evaluated for the model without a dielectric core, using the shielded Coulomb potential. Smearing the phosphate charges increases their potential by about 2.5 kT/e, due mostly to the self-potential of the smeared charge. Potentials in the center of the minor and major grooves vary less than 0.02 kT/e along their helical path. The potential in the center of the minor groove is from 1.0 to 1.7 kT/e, more negative than in the center of the major groove, depending on dielectric core and salt concentration. So multivalent cations and also larger cationic ligands, such as some antibiotics, are likely to adsorb in the minor groove, in agreement with earlier computations by A. and B. Pullman. Dielectric effects on the surface potential and the local potential variations are found to be relatively small. Bending of DNA is studied by placing a multivalent cation, MZ+, in the center of the minor or major groove, curving DNA around it for a certain length, and calculating the free energy difference between the bent and the straight configuration. Boltzmann averaged bending angles, 〈β〉, are found to be maximal in 0.03M monovalent salt, for a length of about 50 or 25 Å of curved DNA when an MZ+ ion is adsorbed in the minor or the major groove, respectively. When the dielectric constant of water is used throughout the calculation, we find maximal bends of 〈β〉 = 11° for M2+ and 〈β〉 = 16° for M3+ in the minor groove, 〈β〉 = 13° for M3+ in the major groove. The absence of bends in DNA adsorbed to mica in the presence of Mg salts supports the role of Mg2+ in “ion bridging” between DNA and mica. The treatment of the effective dielectric constant between two points outside a dielectric cylinder in water is appended. © 1998 John Wiley & Sons, Inc. Biopoly 46: 503-516, 1998
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
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  • 73
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 47 (1998), S. 63-73 
    ISSN: 0006-3525
    Schlagwort(e): protein de novo design ; novel macromolecules ; topological templates ; Template Assembled Synthetic Proteins (TASP) ; biosensors ; protein folding ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The ultimate goal in protein de novo design is the creation of novel macromolecules with tailor-made receptor, sensory, and catalytic functions. Despite considerable progress in understanding basic rules of secondary structure formation and protein stability, the well-known protein folding problem is still far from being solved and, in general, only a limited number of designed proteins are folded uniquely. In this article the state-of-the-art in protein design is demonstrated on some selected examples, indicating that the construction of protein-like macromolecules mimicking some essential features of natural proteins seems to be within reach. Thus, protein design and mimicry has become an interdisciplinary challenge with most intriguing perspectives. © 1998 John Wiley & Sons, Inc. Biopoly 47: 63-73, 1998
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 74
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 47 (1998), S. 451-463 
    ISSN: 0006-3525
    Schlagwort(e): bacteria ; antibiotics ; linear amphipathic α-helical antimicrobial peptides ; peptide-lipid interactions ; membrane permeation ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The increasing resistance of bacteria to conventional antibiotics resulted in a strong effort to develop antimicrobial compounds with new mechanisms of action. Antimicrobial peptides seem to be a promising solution to this problem. Many studies aimed at understanding their mode of action were described in the past few years. The most studied group includes the linear, mostly α-helical peptides. Although the exact mechanism by which they kill bacteria is not clearly understood, it has been shown that peptide-lipid interactions leading to membrane permeation play a role in their activity. Membrane permeation by amphipathic α-helical peptides can proceed via either one of the two mechanisms: (a) transmembrane pore formation via a “barrel-stave” mechanism; and (b) membrane destruction/solubilization via a “carpet-like” mechanism. The purpose of this review is to summarize recent studies aimed at understanding the mode of action of linear α-helical antimicrobial peptides. This review, which is focused on magainins, cecropins, and dermaseptins as representatives of the amphipathic α-helical antimicrobial peptides, supports the carpet-like rather the barrel-stave mechanism. That these peptides vary with regard to their length, amino acid composition, and net positive charge, but act via a common mechanism, may imply that other linear antimicrobial peptides that share the same properties also share the same mechanism. © 1999 John Wiley & Sons, Inc. Biopoly 47: 451-463, 1998
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 75
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 48 (1998), S. 39-55 
    ISSN: 0006-3525
    Schlagwort(e): modified nucleotides ; site-specific probes ; RNA structure ; RNA function ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Modified nucleotides can be incorporated site specifically into RNA by the use of total chemical synthesis as well as by use of a variety of recombinant RNA techniques. The range of nucleotide analogues includes modifications to base, sugar, and phosphate for structure-function analysis and for cross-linking studies as well as to answer specific mechanistic questions in RNA catalysis. We describe how RNA containing site-specific modifications are prepared, concentrating in particular on routes involving chemically synthesized oligoribonucleotides, and give examples of their application in studies of the hammerhead and hairpin ribozymes. © 1998 John Wiley & Sons, Inc. Biopoly 48: 39-55, 1998
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 76
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 48 (1998), S. 29-37 
    ISSN: 0006-3525
    Schlagwort(e): amide synthase ; catalytic antibodies ; Diels-Alderase ; ideal catalyst platform ; in vitro selection ; Lewis acid ; modified uridines ; modified RNA ; ribozymes ; SELEX ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: In this manuscript the catalytic ability of RNA is examined and compared to other biopolymers. Despite having considerably fewer catalytically enabling properties when compared to proteins, the power of in vitro selection has allowed for RNA and DNA catalysts to be isolated. RNA catalysis has been expanded by incorporating modified bases to enrich the structural and functional diversity of RNA. Successful examples of new RNA chemistry using base modifications include carbon-carbon bond forming reactions and creation of highly specific active sites that are capable of recognizing small organic molecules without the need for nucleic acid templating or intercalation. In fact, the scope of functional modifications available for use in the RNA platform may eventually surpass those that are found in proteins and there are already hints that well chosen modifications allow nucleic acid catalysts to take advantage of mechanisms not available to selected protein catalysts for similar reactions. The chemical versatility of RNA is just emerging and future research directions will likely entail more creative methods for functional modification that will lead to new catalysts. © 1998 John Wiley & Sons, Inc. Biopoly 48: 29-37, 1998
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 77
    Digitale Medien
    Digitale Medien
    New York : Wiley-Blackwell
    Biopolymers 48 (1998), S. 137-153 
    ISSN: 0006-3525
    Schlagwort(e): RNA ; pseudoknot ; Turnip Yellow Mosaic Virus ; Mouse Mammary Tumor Virus ; Beet Western Yellows Virus ; Simian Retrovirus type-1 ; Hepatitis Delta Virus ; translational frameshifting ; ribozyme ; nmr ; x-ray diffraction ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Recently, several high-resolution structures of RNA pseudoknots have become available. Here we review the progress in this area. The majority of the structures obtained belong to the classical or H-type pseudoknot family. The most complicated pseudoknot structure elucidated so far is the Hepatitis Delta Virus ribozyme, which forms a nested double pseudoknot. In particular, the structure-function relationships of the H-type pseudoknots involved in translational frameshifting have received much attention. All molecules considered show interesting new structural motifs. © 1999 John Wiley & Sons, Inc. Biopoly 48: 137-153, 1998
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
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  • 78
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 737-748 
    ISSN: 0887-624X
    Schlagwort(e): inverse microemulsion polymerization ; MADQUAT ; nucleation ; photopolymerization ; molecular weights ; flocculants ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The polymerization of inverse microemulsions of 2-methacryloyl oxyethyl trimethyl ammonium chloride stabilized by a blend of nonionic emulsifiers (a sorbitan sesquioleate and a sorbitan monooleate) and initiated by UV light in the presence of Azobis(isobutyronitrile) (AIBN) was investigated. The effect of initiator concentration, light intensity, emulsifier concentration, and dispersed phase weight fraction on the polymerization rate (Rp), number of polymer particles (Np), and polymer molecular weight (Mw) was studied. The application of this process to tubular reactors is discussed. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 737-748, 1998
    Zusätzliches Material: 15 Ill.
    Materialart: Digitale Medien
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  • 79
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1217-1226 
    ISSN: 0887-624X
    Schlagwort(e): polypropylene ; pyrene ; two-solute system ; pulse radiolysis ; solute ionic species ; solute excited states ; low-temperature radiolysis ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A pulse radiolysis study of isotactic polypropylene (PP) film has been carried out with the main aims of investigating charge trapping in an undoped system and solute radical ion generation in an pyrene (Py) doped matrix. In PP, pulse radiolysis gives electron-positive hole pairs. The electron can be stabilized in the undoped system as a trapped electron, et-. The transient absorption spectrum of et- in the near-IR (up to 1800 nm) was observed in the temperature range 30-100 K. This IR absorption was not detected in the case of oxidized PP. In such a matrix electrons can be scavenged by oxidation products generating respective radical-anions (absorption in the UV RANGE, λ 〈 350 nm). In a doped matrix transient absorption bands centered at 450 and 500 nm were observed which can be assigned to the Py radical cation and anion, respectively. The recombination of these ionic species leads to monomer excited-state formation observed during and after the 17 ns pulse. Contrary to the Py-doped polyethylene no excimer emission was detected at room temperature even if Py content in PP was close to 0.02 mol dm-3. The rate of Py radical-ion decay was found to be temperature dependent. Two linear parts of the Arrhenius plot were observed which intersected at ca. 240 K, the glass transition temperature, Tg, for PP. The activation energies calculated for two parts of Arrhenius plot were equal to 111 and ca. 0.78 kJ mol-1 for T 〉 Tg and T 〈 Tg, respectively. Some preliminary results concerning the ionic processes in PP containing two solutes (Py, 3,3′-dimethyldiphenyl) were presented. The mechanism of ionic recombination in PP will be proposed and discussed. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1217-1226, 1998
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 80
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1345-1348 
    ISSN: 0887-624X
    Schlagwort(e): acid functional ; telechelic ; benzyl alcohol ; poly(ε-caprolactone) ; polymerization ; living ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 81
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 883-888 
    ISSN: 0887-624X
    Schlagwort(e): temperature sensitive ; particle ; emulsion polymerization ; morphology ; adsorption ; enzyme ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Two kinds of temperature-sensitive composite polymer particles were prepared by seeded emulsion copolymerizations of (dimethylamino)ethyl methacrylate and ethylene glycol dimethacrylate with 0.14 μm-sized polystyrene and 0.26 μm-sized poly(methylmethacrylate) seed particles. To evaluate the usefulness as a carrier for biomolecules, the enzymatic activities of trypsin adsorbed on these two composite polymer particles were measured at temperatures above and below each lower critical solution temperature (LCST). In both cases, adsorbed trypsin retained its enzymatic activity during repeated adsorption/desorption measurements. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 883-888, 1998
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 82
    ISSN: 0887-624X
    Schlagwort(e): (1→6)-2,5-anhydro-D-glucitol ; HPLC ; optical resolution ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The cyclopolymerization of 3,4-di-O-allyl-1,2 : 5,6-dianhydro-D-mannitol (1) was carried out using BF3·OEt2 and t-BuOK. The polymer obtained by the polymerization with BF3·OEt2 mainly consisted of (1→6)-bonded 3,4-di-O-allyl-2,5-anhydro-D-glucitol as the five-membered constitutional repeating unit, though it contained a small amount of other cyclic repeating units. On the other hand, during the polymerization using t-BuOK, the stereoregular polymer (1→6)-linked 3,4-di-O-allyl-2,5-anhydro-D-glucitol (2) was synthesized via a regio- and stereoselective mechanism. Cleavage of the allyl ether linkage in polymer 2 occurred to produce the polymer consisting of only 2,5-anhydro-D-glucitol units, i.e., (1→6)-2,5-anhydro-D-glucitol (3). Chromatographic enantioseparation of chloroquine and tröger base has been performed on (3,5-dimethylphenyl)carbamate and 4-methylbenzoate derivatives of 3 as a chiral stationary phase for high-performance liquid chromatography. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 901-909, 1998
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 83
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 939-947 
    ISSN: 0887-624X
    Schlagwort(e): fluorine ; perfluoropolyether ; polyester ; segmented ; thermoplastic ; interfacial synthesis ; thermal transitions ; dynamic-mechanical properties ; chemical resistance ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Linear segmented polyesters containing soft perfluoropolyether (PFPE) and hard aromatic segments are obtained by an interfacial polycondensation reaction of an acyl chloride-ended fluorinated prepolymer with various aromatic diphenols in the presence of phase transfer catalysts (PTC) as accelerators. Experimental conditions for reaching high molecular weights are discussed. The calorimetric analysis (DSC) of all the polyesters synthesized shows a typical biphasic morphology, where a very low Tg (〈 -110°C) corresponding to the segregated PFPE moiety, is always accompanied by another Tg or a higher melting temperature, depending on the nature of the hard phase. Dynamic-mechanical analysis (DMA) has been carried out confirming the DSC results and suggesting diversified mechanical behaviors at the various temperatures in line with the amorphous or semicrystalline nature of the polymer. Chemical resistance was finally tested by dipping in several solvents and chemicals. The new polyesters show high contact angles, a moderate swelling in many organic solvents and excellent stability in aggressive hydrolytic environments. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 939-947, 1998
    Zusätzliches Material: 6 Ill.
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  • 84
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1919-1928 
    ISSN: 0887-624X
    Schlagwort(e): emulsion polymerization ; vinylidene chloride ; kinetics ; sodium lauryl sulfate ; potassium persulfate ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Emulsion polymerization of vinylidene chloride was carried out at 50°C using sodium lauryl sulfate as emulsifier and potassium persulfate as initiator, respectively. Contrary to the results so far reported, the stirring rate did not affect the progress of the polymerization and such an abnormal kinetic behavior as the rate of polymerization suddenly drops in the course of polymerization was not observed. The number of polymer particles produced was proportional to the 0.7 power of the concentration of emulsifier forming micelles and to the 0.3 power of the initial initiator concentration, respectively, and was independent of the initial monomer concentration. The rate of polymerization was in proportion to the 0.3 power of the concentration of emulsifier forming micelles, to the 0.5 power of the initial initiator concentration, to the 0.2 power of the initial monomer concentration, and to the 0.45 power of the number of polymer particles, respectively. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1919-1928, 1998
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
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  • 85
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1961-1964 
    ISSN: 0887-624X
    Schlagwort(e): Poly(4,4′-phenylene-3,3′,4,4′-biphenyltetracarboxyimide) ; poly(4,4′-oxydiphenylenepyromellitimide) ; precursor solution ; aprotic polar solvent ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: No abstract.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 86
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1969-1972 
    ISSN: 0887-624X
    Schlagwort(e): hydrosilation ; polymer ; siloxane ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: No abstract.
    Zusätzliches Material: 2 Ill.
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  • 87
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    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1995-1999 
    ISSN: 0887-624X
    Schlagwort(e): poly-γ-D-glutamic acid ; biopolymer ; covalent modification ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Methods for the covalent modification in aqueous solution of poly-γ-D-glutamic acid from Bacillus licheniformis have been studied. Co-derivatization of a synthetic UV-absorbent amine and ethanolamine, using a water-soluble carbodi-imide coupling agent, yielded a water-soluble modified polymer. Derivatization of the polymer was accompanied by cleavage of the γ-linked polypeptide backbone, and a reduction in molecular mass from 170 to 10 kDa. A procedure was developed for the removal of noncovalently bound ligands by treatment with 5 M CaCl2. The polymer sidechains also reacted in aqueous solution with p-nitrophenyl acetate to form covalent linkages. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 1995-1999, 1998
    Zusätzliches Material: 4 Ill.
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  • 88
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 2037-2042 
    ISSN: 0887-624X
    Schlagwort(e): radical polymerization ; vinylcyclopropane ; vinylsilane ; desilylation ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Synthesis and radical polymerization of novel vinylcyclopropanes; 1-carboethoxy-2-trimethylsilyl-2-vinylcyclopropane (1a) and 1-carboethoxy-2-(1-trimethylsilyl)-vinylcyclopropane (1b), were examined. 1a and 1b were prepared by the coupling reaction of 2-trimethylsilylbutadiene with ethyl diazoacetate, which was prepared from glycine ethyl ester hydrochloride. The radical polymerization of 1a and 1b was carried out at 60°C in bulk for 40 h in the presence of 2,2′-azobis(isobutyronitrile) (5 mol % vs. monomer). Poly(1) consisted of a 1,5-ring-opened unit. Desilylation reaction of poly(1) proceeded quantitatively in aqueous hydrochloric acid. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2037-2042, 1998
    Zusätzliches Material: 1 Ill.
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  • 89
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 2021-2027 
    ISSN: 0887-624X
    Schlagwort(e): 2,2′-bis(3,4-dicarboxyphenoxy)biphenyl dianhydride ; aromatic polyimides ; solubility ; thermal behavior ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A new aromatic tetracarboxylic dianhydride having a crank and twisted noncoplannar structure, 2,2′-bis(3,4-dicarboxyphenoxy)biphenyl dianhydride, was synthesized by the reaction of 4-nitrophthalonitrile with biphenyl-2,2′-diol, followed by hydrolysis and cyclodehydration. The biphenyl-2,2′-diyl-containing aromatic polyimides having inherent viscosities up to 0.66 dL/g were obtained by the conventional two-step procedure starting from the dianhydride monomer and various aromatic diamines. Most of the polyimides were readily soluble in amide-type solvents such as N,N-dimethylacetamide and N-methyl-2-pyrrolidone. The aromatic polyimides had glass transition temperatures in the range of 205-242°C, and began to lose weight around 415°C, with 10% weight loss being recorded at about 500°C in air. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2021-2027, 1998
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 90
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 2069-2079 
    ISSN: 0887-624X
    Schlagwort(e): Candida antarctica lipase ; Novozym 435® ; polyester ; enzymatic polymerization ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Preliminary enzymatic polymerization studies in the simple stoichiometric adipic acid/butane-1,4-diol system using lipase B from Candida antarctica, immobilized as Novozym 435®, suggest that in solvent-free conditions a step-growth mechanism operates involving the sequential addition of an AB synthon by esterification mode only. Conversely, in toluene as solvent there is a change to the more facile transesterification mode in line with the conventional polyesterification procedure, pointing to a change in specificity of the lipase. Evidence is drawn from qualitative studies using a series of synthetic intermediates, enabling authentication of product mixtures together with an indication of the comparative reactivity of species along the proposed reaction pathway. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2069-2080, 1998
    Zusätzliches Material: 5 Ill.
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  • 91
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 2111-2117 
    ISSN: 0887-624X
    Schlagwort(e): dendritic polymer ; blends ; coatings ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Hybrid blends of poly(amidoamine) PAMAM dendrimers with two linear high polymers, poly(vinyl chloride), PVC, and poly(vinyl acetate), PVAc, are reported. The interaction between the blend components was studied using dynamic mechanical analysis, xenon nuclear magnetic resonance (NMR) spectroscopy, and tensile property measurements. The data suggest a much higher degree of interaction between components of PVAc-containing blends compared to those containing PVC. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2111-2117, 1998
    Zusätzliches Material: 4 Ill.
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  • 92
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 2135-2146 
    ISSN: 0887-624X
    Schlagwort(e): SCLC polyurethanes ; azobenzene mesogenic group ; alkyl spacer ; bilayer smectic phases ; hydrogen bonding ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A series of side chain liquid crystal polyurethanes (CnCNPs), in which the spacer length was varied from 2 to 12 methylene units, were synthesized by the addition polymerization of α-[bis(2-hydroxyethyl)amino]-ω-(4-cyanoazobenzene-4′-oxy)alkanes (CnCN-diols) with hexamethylene diisocyanate. The liquid crystalline properties of CnCNPs were characterized by means of differential scanning calorimetry, polarizing optical microscopy, and X-ray diffraction. Polyurethanes with spacer length 4 or higher exhibited mesomophic properties. C4CNP and C5CNP exhibited an enantiotropic nematic mesophase, while C6-C12CNPs exhibited enantiotropic bilayer smectic mesophases. CnCNPs have a high tendency to crystallize; crystallization is kinetically controlled. Polyurethane's backbone crystallization is closely related to hydrogen bonding. To establish the role of hydrogen bonding in mesophase formation as well as crystallization, Fourier transform infrared spectroscopy studies of CnCNPs were carried out at different temperatures focusing on H-bonds between the N—H and C=O groups of the urethane backbone. With increasing temperature, C=O and N—H stretching bands were evenly shifted to higher wavenumbers, with two exceptions (C4CNP and C5CNP) discussed in detail in the text. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2135-2146, 1998
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 93
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 2169-2176 
    ISSN: 0887-624X
    Schlagwort(e): free radical ; initiation ; styrene ; acrylonitrile ; copolymerization ; nitroxide trapping ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The competitive reactions of cyanoisopropyl radicals with the mixed monomers styrene and acrylonitrile have been investigated using the nitroxide radical trapping technique. When the trap concentration is kept low, second, third, and even fourth generation (in terms of successive monomer addition) carbon radicals have been observed as trapped products. The ratio of rate constants for the addition of styrene and acrylonitrile to cyanoisopropyl radicals is 2.7 at 75°C and 5.3 at 105°C. These values are compared with the ratios for reactions of these two monomers with a number of other radicals and discussed in terms of the polarities of the radicals and monomers. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2169-2176, 1998
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 94
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 2193-2200 
    ISSN: 0887-624X
    Schlagwort(e): N-phenylated polyamides ; 4,4′-dianilinobiphenyl ; solubility ; thermal behavior ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: New N-phenylated aromatic-aliphatic and all aromatic polyamides were prepared by the high-temperature solution polycondensation of 4,4′-dianilinobiphenyl with both aliphatic (methylene chain lengths of 6-11) and aromatic dicarboxylic acid chlorides. All of the aromatic-aliphatic polyamides and the wholly aromatic polyamides exhibited an amorphous nature and good solubility in amide-type and chlorinated hydrocarbon solvents, except for those aromatic polyamides containing p-oriented phenylene or biphenylylene linkages in the backbone; the latter were crystalline and insoluble in organic solvents except m-cresol. The N-phenylated aromatic-aliphatic polyamides and aromatic polyamides had glass transition temperatures in the range of 79-116°C and 207-255°C, respectively, and all the polymers were thermally stable with decomposition temperatures above 400°C in air. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2193-2200, 1998
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 95
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 2237-2245 
    ISSN: 0887-624X
    Schlagwort(e): NMR ; polysiloxane, polysiloxane-block-polyimide ; solution imidization ; kinetic analysis ; structure analysis ; spin-lattice relaxation time ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A series of polysiloxane-block-polyimides were synthesized by solution imidization of the polyamic acids derived from the combination of 3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride (DSDA), 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), and diamino(polysiloxane) (PSX (Mw = 750)) in N-methyl-2-pyrrolidone (NMP). Their structures were analyzed by 1H-, 13C-, and 29Si-NMR spectra as well as by IR spectroscopy. The solid-state NMR spectrum was also measured to determine the spin-lattice relaxation time of the copolyimides. The observed relaxation times of both aromatic and polysiloxane segments were similar in the copolyimides having 10-30 wt % of PSX, while those in the copolyimide with 50 wt % of PSX was significantly different. This may be attributed to the morphology change due to the increase in PSX composition in the polymer backbone. The reduced viscosity of the copolyimides could be controlled by changing the monomer ratio in the feed or by adding an end-capping reagent such as phthalic anhydride into the polymerization system. The kinetic study of the solution imidization revealed that the imidization reaction obeyed second-order kinetics. The activation energy calculated for this imidization was 99.2 kJ/mol, being similar to that for the imidization of the DSDA-based aromatic polyimides. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2237-2245, 1998
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
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  • 96
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 2229-2235 
    ISSN: 0887-624X
    Schlagwort(e): polyarylates ; aromatic polyether ; 2,2-bis(4-hydroxyphenyl)-1,2-diphenylethanone ; solubility ; thermal behavior ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: New polyarylates having benzopinacolone units were synthesized from 2,2-bis(4-hydroxyphenyl)-1,2-diphenylethanone and aromatic dicarboxylic acid chlorides. The polymers having an inherent viscosity of 0.71-0.94 dL/g were obtained by the two-phase method using toluene as an organic solvent. The polymers were easily soluble in various organic solvents and had high glass transition temperatures in the range of 200-240°C. An aromatic polyether having benzopinacolone unit was also prepared. However, its inherent viscosity was low because of the occurrence of a side reaction. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2229-2235, 1998
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 97
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 31-38 
    ISSN: 0887-624X
    Schlagwort(e): triblock copolymers ; polycondensations ; telechelic character ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Telechelic oligo(ether-ketone)s containing two trimethylsiloxy end groups and one methyl group per repeating unit were prepared by polycondensation of 4-fluoro-2′-methyl-4′-(trimethylsiloxy)benzophenone. The telechelic character was achieved by cocondensation of a small amount of silylated bisphenol-P. The end groups of the silylated oligo(ether-ketone)s were acetylated by means of acetyl chloride. On the basis of 1H-NMR end group analyses two samples of α,ω-bis(acetoxy) oligo(ether-ketone)s with DP = 14 and DP ∼ 28 were obtained. These oligo(ether-ketone)s and a 70 or 140 fold molar amount of silylated 3,5-bis(acetoxy)benzoic acid were polycondensed at 270°C in bulk. The resulting A-B-A triblock copolymers were fractionated by dissolution in tetrahydrofuran. In three out of four experiments a small fraction of precipitated material rich in oligo(ether-ketone) was isolated. The purified triblock copolymers were characterized by inherent viscosities and NMR spectra. For those samples containing the long oligo(ether-ketone) block a low degree of crystallinity was observed after annealing. Four additional polycondensations were conducted with an initial reaction temperature of 290°C. In this way a completely soluble and amorphous triblock copolymer was obtained. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 31-38, 1998
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 98
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 21-29 
    ISSN: 0887-624X
    Schlagwort(e): liquid crystalline polymers ; epoxy resins ; thermotropic ; polymer chain extension ; catalytic polyaddition ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: This work is a continuation of the authors' earlier investigations of liquid crystalline epoxy resins prepared from diglycidyl ether of 4,4′-dihydroxybiphenyl (DGE-DHBP), which was used as a mesogenic agent, and aliphatic dicarboxylic compounds, which were used as flexible spacers. In this paper, the synthesis and characterization of liquid crystalline epoxy resins, prepared from DGE-DHBP and difunctional aromatic compounds are described. Three series of liquid crystalline epoxy resins were prepared by chain extension of DGE-DHBP with isomeric hydroxybenzoic and benzenedicarboxylic acids as well as diphenols. An isophthalic-terminated polyether was applied to decrease the temperature of phase transitions. The syntheses were carried out by catalytic polyaddition in the melt. Triphenylphosphine was applied as the catalyst. The resulting epoxy resins were investigated by DSC, polarizing microscope as well as by X-ray and IR spectroscopy. The phase transition temperatures and the type of mesophase of the resulting products depend on the character of the functional groups in the chain extender and on the position of the functional groups in the aromatic ring. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 21-29, 1998
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 99
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1987-1994 
    ISSN: 0887-624X
    Schlagwort(e): triphenylamine-based bis(o-aminophenol)s ; aromatic polybenzoxazoles ; solubility ; thermal behavior ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Two new triphenylamine-based bis (o-aminophenol) monomers, 4,4′-diamino-3,3′-dihydroxytriphenylamines, were successfully synthesized by the cesium fluoride-mediated condensation of 2-(benzyloxy)-4-fluoronitrobenzene with aniline derivatives, followed by simultaneous deprotection and reduction. Aromatic polybenzoxazoles having inherent viscosities of 0.58-1.05 dL/g were obtained by the low-temperature solution polycondensation of the bis(aminophenol)s with various aromatic dicarboxylic acid chlorides and the subsequent thermal cyclodehydration of the resultant poly(hydroxyamide)s. All the polybenzoxazoles were amorphous, and most of them were soluble in organic solvents such as m-cresol and o-chlorophenol. Flexible and tough films of polybenzoxazoles could be cast from the DMAc solutions of some aromatic poly(hydroxyamide)s, followed by thermal cyclodehydration. The glass transition temperatures and 10% weight loss temperatures of the polybenzoxazoles under nitrogen were in the range of 262-327 and 610-640°C, respectively. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1987-1994, 1998
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 100
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 2013-2019 
    ISSN: 0887-624X
    Schlagwort(e): asymmetric polymerization ; anionic polymerization ; (2-fluorophenyl)(4-fluorophenyl)(2-pyridyl) methyl methacrylate ; optically active polymer ; helix ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A novel racemic methacrylate, (2-fluorophenyl)(4-fluorophenyl)(2-pyridyl)-methyl methacrylate1 (2F4F2PyMA), was synthesized and polymerized with chiral complexes of N,N′-diphenylethylenediamine monolithium amide (DPEDA-Li) with (-)-sparteine (Sp), (2S, 3S)-(+)-2,3-dimethoxy-1,4-bis(dimethylamino)butane (DDB), and (S)-(+)-1-(2-pyrrolidinylmethyl)pyrrolidine (PMP) in toluene at -78°C. The monomer showed higher resistance against methanolysis compared with triphenylmethyl methacrylate (TrMA) and several other analogues. In the asymmetric anionic polymerization of 2F4F2PyMA, PMP was found to be a more effective chiral ligand than DDB and Sp and gave quantitatively an optically active polymer with nearly perfect isotacticity. Enantiomer selection was observed in the polymerization of racemic 2F4F2PyMA with the chiral lithium complexes. Chiral recognition ability of the optically active poly(2F4F2PyMA) was examined by an enantioselective adsorption experiment. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2013-2019, 1998
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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