Comments on the use of a dichromophoric circular dichroism assay for the identification of β‐turns in peptides

Use of the dichromophoric CD assay for β‐turn formation in peptide sequences has been investigated. The assay involves the observation of Cotton effects in CD spectra, originating from the approach of N‐ and C‐terminal aromatic chromophores in tetrapeptides. The approach of the chromophores was believed to be brought about by a beta;‐turn in the peptide structure. Our investigations were paralleled by NMR studies which revealed the presence of a previously unreported hydrogen bond in the β‐turn conformers, which appears to play a role in the generation of the observed Cotton effects. This suggests caution in the use of the CD technique alone as an assay for β‐turn conformers in peptides.