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Electronic Properties and Optical Activity of Oligopeptides. III. Some cyclohexapeptides with glycine, L- and D-alanine

✍ Scribed by Max Iseli; Georges Wagnière; J. Georges Brahms; Sabine Brahms

Publisher
John Wiley and Sons
Year
1979
Tongue
German
Weight
608 KB
Volume
62
Category
Article
ISSN
0018-019X

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✦ Synopsis

Abstract

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.

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