Turns in small cyclic peptides - can infrared spectroscopy detect and discriminate amongst them?

R. A. Shaw, A. Perczel, H. H. Mantsch, G. D. Fasman

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24 Citations (Scopus)


Infrared spectra are reported in the amide I absorption region for some cyclic peptides of the general formula cyclo[ε{lunate}-Aca-Pro-Xxx] (ε{lunate}-Aca = ε{lunate}-aminocaproyl; Xxx = Ala, ThrOBz) and the corresponding "dimers" cyclo[ε{lunate}-Aca-Pro-Xxx-ε{lunate}-Aca-Pro-Xxx] dissolved in D2O and acetonitrile. The acetonitrile solution spectra are very different from those measured in D2O. In particular, the D2O solution spectra exhibit amide I absorptions at exceptionally low frequencies (1595-1600 cm-1). The infrared spectra are interpreted as indicating an unusual D2O solution structure involving three-centered hydrogen bonding to the Aca carbonyl group, two amide protons interacting with the CO group to simultaneously close both a γ-turn and a β-turn. The acetonitrile solution spectra are interpreted as reflecting hydrogen-bonding characteristics of a β-turn, with certain compounds also showing absorptions that suggest the presence of other hydrogen-bonded (γ-turn) conformers.

Original languageEnglish
Pages (from-to)143-150
Number of pages8
JournalJournal of Molecular Structure
Issue number1-2
Publication statusPublished - Jul 28 1994


  • δ-Ava = δ-aminovaleric acid, CPA = cyclo[ε{lunate}-aminocaproyl-l-prolyl-l-alanine], CPT = cyclo[ε{lunate}-aminocaproyl-l-prolyl-l-threonine], (CPA)
  • ε{lunate}-Aca = ε{lunate}-aminocaproic acid

ASJC Scopus subject areas

  • Analytical Chemistry
  • Spectroscopy
  • Organic Chemistry
  • Inorganic Chemistry

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