ISSN:
0947-3440
Keywords:
Helical structures
;
Circular dichroism
;
Peptides
;
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
X-Ray diffraction analyses of the fully protected peptides Boc-[(S)-Iva]n-OMe (n = 3, 4, 6) reveal two independent molecules in the asymmetric unit. The structures of these can be described as β-turns or 310 helices (depending on the length of the oligopeptide) of alternating screw sense (M and P) in a head to tail alignment. This structure is stabilized by hydrogen bonds between the N—H(1) of the (M)-helix and the O=C(ω-1) of the (P)-helix and the N—H(2) (M) and the ester carbonyl group (P). Low temperature 1H-NMR spectra of the hexamer in CD2Cl2 solution show two interchanging species in a ratio of 4:1; NOESY experiments prove that these are the two helical conformers found in the crystal (P:M, 4:1). The NOESY spectrum at -90°C indicates the pairing of (P) and (M) helices. Thermodynamic and kinetic parameters for the helix transformation P ⇌ M (unfolding/folding) are presented.
Additional Material:
12 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jlac.199719970811
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