Single peptide bonds exhibit poly(pro)II ("random coil") circular dichroism spectra

J Am Chem Soc. 2005 Jul 13;127(27):9700-1. doi: 10.1021/ja052632x.


The far-UV circular dichroism spectra of a series of amino acid derivatives containing single peptide bonds have been measured. The N-acetyl-alanine displays a polyproline (PP) II-like spectrum, but alaninamide shows a very weak positive signal. Similarly Gly-Ala shows a PPII spectrum, but Ala-Gly does not. On heating, the spectrum shows a two-state transition also shown by long PPII polypeptides. Thus the characteristic PPII negative maximum at <200 nm results from the coupling of a peptide bond N-terminal to the chiral alpha-carbon, and therefore the simplest peptide bonds have a preferred conformation that defines the spectrum of disordered proteins of any size.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Circular Dichroism*
  • Peptides / chemistry*
  • Proline / chemistry*
  • Temperature


  • Peptides
  • Proline