The Solution Conformation of the Ferrichromes.

Ferrichrome, ferricrocin and ferrichrysin are ferric cyclohexapeptides whose general primary composition is represented by Res3‐Res2‐Gly1‐Orn3‐Orn2‐Orn1, where the Res2,3 sites are occupied by glycyl or l‐seryl residues and Orn1,2,3 stands for δ‐N‐acetyl‐δ‐N‐hydroxy‐l‐ornithyl. The 220 MHz proton magnetic resonance spectra of deferriferricrocin and deferriferrichrysin in aqueous and in deuterodimethyl sulfoxide solutions are reported and discussed in terms of the molecular conformations. In (CD3)2SO the chemical shift temperature dependences of the amide proton resonances suggest two‐fold symmetric structures containing two intramolecular hydrogen bonds. Such hydrogen‐bonding, and other features of the data, are consistent with antiparallel β‐pleated sheet structures, as in the Schwyzer model for cyclohexapeptides. In terms of sites paired by the hydrogen bonds, however, the β‐fold differs. In water a random conformation is suggested for these peptides.