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  • 1
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The aggregated form of poly(L-glutamic acid) can be isolated by gel permeation chromatography, whereby it was found that in a polydispersed sample the lower molecular weight fractions precipitate preferentially and the higher fractions tend instead to aggregate. In addition, aggregation has the effect of retarding or inhibiting precipitation.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The instability of aqueous solutions of poly(α-L-glutamic acid) (PGA) at low pH is due to two distinguishable phenomena: precipitation, favored above 40°C., and aggregation, favored below 20°C. The aggregated form of PGA can be isolated by gel permeation chromatography. Both aggregation and precipitation increase with decreasing pH, i.e., with decreasing ionization of the side chain carboxyl groups. Temperature-induced aggregation and disaggregation give rise to a reproducible hysteresis loop which can be followed by optical rotation, light scattering, sedimentation, viscosity, and chromatography. Hysteresis has been observed with different PGA samples, and in several aqueous buffered or unbuffered solvents and organic-aqueous solvent mixtures and in the pH range 4.1-4.5. Aggregation manifests itself as an increase in negative optical rotation in the visible and ultraviolet spectral range. The specific relation at 233 mμ is sensitive to aggregation and also reflects the hysteresis. Measurements of optical rotatory dispersion indicate that a0 reflects the hysteresis but b0 does not, the latter revealing only reversible changes with aggregation and disaggregation. The helix-coil equilibrium is apparently unperturbed by aggregation, as is the thermal stability of the helix structure. For fully aggregated PGA it is estimated that a0 increases by about 300 degrees, which suggests that a0 may be a sensitive parameter to measure aggregation in other systems. The rate of aggregation increases with decreasing temperature. The disaggregation, upon heating, is more rapid. However, kinetics measurements have not yet been done. The temperature M at which all aggregates are disrupted increases with decreasing pH, but is independent of total PGA concentration, at constant pH. No molecular weight dependence of M was detected in the range 20-100 × 103. The shape and size of the hysteresis loop depends upon pH and molecular weight, which is interpreted as a dependence on the extent of aggregation. One branch of the loop, representing the helix-coil transition of isolated molecules, is reversible, while the others, representing the formation and disruption of the aggregates, are not. The system exhibits both ascending and descending scanning curves, which are typical of a true hysteresis.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 12 (1973), S. 2199-2209 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the present work, the synthesis of the three primary oligomers of α-L-glutamic acid is described; the general formula is the following: [I] The choice of protective groups at the both ends of the chain allows for the good solubility in the water and the liberation of free carboxyl groups on the side chain. Thus, models are obtained for the study of thermodynamic properties of solutions and especially of the interactions between polyanions and cations. The prepared products are characterized by different techniques such as mass spectrometry potentiometry, tonometry, and thin-layer chromatography. The results are in agreement and lead to the conclusions that the molecules have the general formula of [I] and are stereoregular.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 76 (1964), S. 381-382 
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 28 (1989), S. 273-283 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Analogues of alamethicin, a 20-mer amphipathic helical peptide with ionophore activity, in the sequence of which all Aib residues were substituted by Ala (A1) or Leu (L1), were synthesized by the solid phase method, purified by high performance liquid chromatography and characterized by fast atomic bombardment mass spectrometry. Infrared and CD studies showed that A1 easily underwent a transconformation to β-structure whereas L1 displayed a predominant α-helical character, thus being a potential ionophore model. Its voltage-dependent multistate activity in model membrance showed that Aib is not a requisite residue to observe an alamethicin-like behavior. However, as the lifetime of the single channels was much shorter than for alamethicin, the peptide chain was lengthened by a Leu (LL1) or a Ser (SL1) residue. The last peptide gave an increased channel lifetime, but the design of other non-Aib peptides, taking into account the hydroxyl C-terminus and side-chain interactions between helices in a barrel-stave bundle, is desirable to approach more closely the alamethicin activity.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Model peptides containing one aromatic residue were synthesized and characterized in order to investigate their interactions with polynucleotides. Chromatographically pure block oligopeptides (L-alysyl)m-(L-alanyl)n- L-tyrosyl- (L-alanyl)n, with n = 3 and m=3 or 6, were prepared by fragments condensation using the mixed anhydride method. The protected fragments were prepared by stepwise addition of amino acid residues through the dicyclohexylcarbodiimide method. The purity of the intermediate coupling product was analyzed by gradient elution chromotography on carboxylmethylcellulose. Both block oligopeptides were isolated by preparative chromatography on carboxymethylcellulose. The different features of these syntheses are discussed.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformation of chromatographically pure block oligopeptides (L-lysyl)m-(L-alanyl)n- L-tyrosyl-(L-alanyl)n-(L -lysyl)m with n = 3 and m = 6 or 3 is investigated. By circular dichroism it is shown that these peptides may exhibit a partially α-helical structure depending upon pH, ionic strength, solvent, and temprerature. An attempt is made to describe the helical content of these small peptides by utilizing the data obtained on high-molecular-weight poly(L-lysine). By measurement of the quantum yield and the decays of the peptides fluorescence, it is shown that, in aqueous solution, at neutral pH, the fluorescence of the peptides is quenched by interactions with the peptide carbonyl groups. The decays are multiexponential, which shows the presence of several conformations of the phenolic chromophore relative to the peptide chain. The addition of methanol, which induced the helix formation, decreases the quenching of the fluorescence and the multiexponential character of the decays. In presence of sodium hydroxide, which further increases the helical content of the peptides, a dynamic quenching occured that can be attributed to interactions between the phenol hydroxyl group of tyrosine (ith residue) and the ε-amino groups of the (i+4)th and (i -4)th lysyl residues.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 30 (1958), S. 149-154 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Polypeptides were prepared from racemic mixtures of the following amino acids: \documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{l} {dl{\rm - 2 - aminooctadecanoic\ acid,}} \\ \qquad \qquad \qquad \qquad {{\rm CH}_{\rm 3} - ({\rm CH}_{\rm 2} )_{15} - {\rm CHNH}_{\rm 2} - {\rm CO}_{\rm 2} {\rm H}}\\ {dl{\rm - 2 - aminotridecanedioic\ acid - 1,13 - benzylester - 13,}} \\ \qquad \qquad \qquad \qquad {{\rm C}_{\rm 7} {\rm H}_{\rm 7} {\rm CO}_{\rm 2} - ({\rm CH}_{\rm 2} )_{10} - {\rm CHNH}_{\rm 2} - {\rm CO}_{\rm 2} {\rm H}}\\ \end{array} $$\end{document} The amino acids were obtained by the action of NH3 on the corresponding brominated acids, with the exception of the following variation in the preparation of the second. The 2-carboxytridecanedioic-1,13 acid, obtained from its triethylester, was brominated and then treated with ammonia. The amino-triacid yielded, on decarboxylation, dl-2-aminotridecanedioic-1,13 acid, which was monoesterified with benzyl alcohol. From the amino acids, the corresponding Leuchs derivatives, 4-hexadecyloxazolidinedione-2,5 and 4-decamethyleneoxazolidinedione-2,5 benzyl carboxylate, were prepared by the direct action of phosgene. Dimorphism has been observed in the case of the later oxazolidimdione and of 1-bromoundecanoic acid. The oxazolidinediones were polymerized in solution with the use of alkaline initiators and fractionated by precipitation. Viscosity and light scattering studies of the poly-dl-2-aminooctadecanoic acid in benzene solutions indicated that aggregates form at higher concentrations.
    Notes: Les auteurs ont préparé des polypeptides dérivant des acides α-aminés racémiques suivants: \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l} {\rm l'acide }\ dl\hbox{- amino - 2 - octad\'e cano\"ique,} \\ \qquad \qquad \qquad \qquad {{\rm CH}_2\hbox{---}({\rm CH}_2 )_{15}\hbox{---}{\rm CHNH}_2\hbox{---}{\rm CO}_2 {\rm H}} \\ {{\rm et l'acide }\ dl\hbox{- amino - 2 - trid\'e} \hbox{cano\"i} \hbox {que oate 13 de benzyle,}} \\ \qquad \qquad \qquad \qquad {{\rm C}_7 {\rm H}_7 {\rm CO}_2\hbox{---}({\rm CH}_2 )_{10}\hbox{---}{\rm CHNH}_2\hbox{---}{\rm CO}_2 {\rm H}} \\ \end{array} $$\end{document} Les acides α-aminés sont obtenus par action de NH3 sur les acides α-bromés, le deuxième avec une variante: l'acide carbonique 2-tridécanedioique, obtenu à partir de son triester éthylique, est brcmé, puis traité par NH3; l'amino-triacide, dCcarboxylé, engendre le dl-amino-2-tridbcanedioique; celui-ci est monoestbrifib par l'alcool benzylique. A partir des acides aminbs, on passe aux dérivés de Leuchs correspondants, par l'acton directe de l'oxychlorure de carbone: hexadécyl-4 oxazolidine dione-2,5 et dbcamethyl- Bne-4 oxazolidine dione-2,5 carbonate de benzyle. Le dimorphisme a été observe sur ce dernier et sur l'acide bromo-1 1-undbcanolque. Les oxazolidines diones-2,5-polymérisent en solution sous l'influence d'initiateurs alcalins. AprBs fractionnement par precipita- tion, l'btude de la viscositb des solutions benzbniques de poly-dl-amino-2-octadbcanoique, ainsi qusla diffusion de la lumière par celles-ci suggèrent la formation d'agrégats lorsque la concentration croit.
    Additional Material: 2 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 3 (1964), S. 389-390 
    ISSN: 0570-0833
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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