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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: Six cyclic peptides, designed to act as topological templates in the TASP (template assembled synthetic protein) approach in protein de novo design, were investigated employing a 100-ps, 900-K molecular dynamics conformational search. The peptides are composed of two Lys-X-Lys (X = Gly, Ala) tripeptides connected at its N- and C-terminal end by a Pro-Gly motif and a cystine bridge (I), two Pro-Gly units (II), naphthalene derivatives (III), and tetrahydronaphthalene derivatives of different stereochemistry (IV-VI). The molecular dynamics conformational search established that template I had β-sheet like geometry. Templates II-VI showed different preferential geometries, among them, e.g., distinct preferences for type V turns in Pro-Gly containing peptides and close spatial arrangement of hydrophobic naphthalene moieties. The orientation of the lysine side chains within preferential geometries of the individual templates is analyzed and a tentative evaluation for their potential to stabilize TASP molecules of 4-helix bundle topology is given. © 1992 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 17O-NMR signals of four true C-nitroso compounds 1-4 appear at particularly low field (1550-1265 ppm), whereas the dimers (azodioxy type) resonate at ca. 400 ppm and the ‘isonitroso compounds’ ( = quinone-oximes; 5 and 6) at ca. 250 ppm. S-Nitroso compounds ( = thionitrites; 8 and 9) show shift values of ca. 1300 ppm, not far from C - NO; the NO+ ion is much stronger shielded (474 ppm). The results, together with those for higher-shielded nitroso compounds X - NO (X = RO, R2N, Cl, O-) are discussed in terms of (a) resonance stabilization through n-donation from X(π-bond order, approximated by the known barriers of rotation around the X - N bond) and of (b) electronic excitation energies ΔE. The latter are approximated by long-wave (symmetry-forbidden) UV/VIS absorptions and confirmed, where available, by the maxima of the curves of circular dichroism (CD); the CD curve of thionitrite 9 has been measured. It is found that the δ(17O) values of X - NO depend both on bond order and on ΔE, which could not be separated. The higher shielding of NO+ compared with X - N=O is explained on the basis of anisotropy effects, which differ between sp and sp2 systems.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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