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  • Articles: DFG German National Licenses  (2)
  • Polymer and Materials Science  (2)
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  • Articles: DFG German National Licenses  (2)
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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 natural-abundance 15N-nuclear magnetic resonance (nmr) spectrum of the cyclic decapeptide gramicidin S has been measured and assigned in the solvents dimethyl sulfoxide, methanol, and 2,2,2-trifluoroethanol. Three methods have been investigated to distinguish between peptide groups which are exposed to or shielded from the solvent. The solvent dependence of the 15N chemical shift is correlated with the two types of peptide group in gramicidin S—those with the carbonyl group exposed or shielded from the solvent. The second method monitors the lability of the N—H proton (via the collapse of the reduced 15N-1H coupling) in the presence of added base used to promote intermolecular exchange - peptide protons shielded from the solvent exchange more slowly. The third method looks at the temperature dependence of the 15N chemical shifts in dimethyl sulfoxide. Here the data are not so distinctive as to allow the differentiation between solvent-exposed or shielded N—H bonds at all peptide groups.
    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 fixation of trans-(NH3)2Cl2 Pt(II) to poly(I)·poly(C) at low rb (〈 0.05) leads to the formation of two complexed species. The major species (ca. 82% of bound platinum) involves coordination of platinum to a single hypoxanthine base, while the other species involves coordination of two hypoxanthine bases, which are either far apart on the same strand or on separate poly(I) strands, to the platinum. These same two species are found after reaction with poly(I), as are two other species throughout the entire rb range studied (rb = 0-0.30). The latter two species are assigned to trans-Pt bound to two bases on a poly(I) strand with (a) one or (b) two free bases between the two bound bases. These two species, (a) and (b), account for ca. 35% of the bound platinum, although the 1:1 species remains dominant (ca. 55%). These two additional species are observed at high rb (〉0.075) after reaction with poly(I)·poly(C) but as very minor species. They are formed by reaction with melted poly(I) loops. Also at high rb, we have observed a shifted cytidine H5 resonance arising from interaction of trans-Pt with a melted loop of poly(C). Most probably, this arises from an intramolecular poly(I) to poly(C) crosslink. Results from the reaction of trans-Pt with poly(C) are presented for comparison.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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