Helical peptide segments that change their conformation due to external stimuli have often been employed in peptide-based molecular devices and materials. Using helices containing a pair of the iminodiacetic acid derivatives of lysine (Ida), we show that metal-induced helix destabilization is a promising approach to functional switching, especially for helices that are intrinsically stable. By i and i + 2 positioning of the Ida residues in a 17-residue model peptide, a significant decrease in the helical content was observed by the addition of Fe(III), whereas Fe(II) had no influence on the stability of the helix. The possibility of redox control of the helical structure was exemplified by the reduction of Fe(III) to Fe(II) using Na2S2O4 followed by the subsequent reoxidation. Mutual recognition of the transcription factor Jun-derived leucine-zipper peptide segment with the Fos leucine-zipper segment containing Ida residues was also modulated in the presence of Fe(III).