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Electronic Properties and Optical Activity of Oligopeptides. III. Some cyclohexapeptides with glycine, L ‐ and D ‐alanine
Author(s) -
Iseli Max,
Wagnière Georges,
Brahms J. Georges,
Brahms Sabine
Publication year - 1979
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19790620402
Subject(s) - chemistry , alanine , residue (chemistry) , spectral line , stereochemistry , molecule , crystallography , glycine , ring (chemistry) , amide , amino acid , organic chemistry , physics , biochemistry , astronomy
The wavelength range of the CD. spectra of some cyclohexapeptides containing different sequences of glycine, L ‐ and D ‐alanine is extended down to 170 nm. This allows a relatively complete recording of the (n − π*) and (π° − π*) Cotton effects. Some striking spectral changes are observed on going from one molecule to another. The relative influence of L ‐ and D ‐alanyl residues is discussed: Some spectra may be qualitatively related to each other by considering the effect of an L ‐residue at position q in the ring to cancel partially with the effect of a D ‐residue at position q ± 3. Assuming these cyclopeptides to occur in a hydrogen‐bonded pleated sheet structure, certain dominant changes in the spectra are interpreted as reflecting a transition of the overall backbone conformation from one which is closer to the (optically inactive) symmetry C i to another which is closer to the (optically active) symmetry C 2 . An attempt is made to relate the influence of L ‐ and D ‐substituents within hairpin bends of the pleated sheet structure to an amide sector rule.