Intramolecular Ligation of Carbonyl Oxygen to Central Zinc in Synthetic Oligopeptide-Linked Zinc-Porphyrins

Oligopeptide-linked zinc-porphyrins were prepared (oligopeptide = –Phem–Alan–OMe and porphyrin = 5,15-diaryl-2,3,7,8,12,13,17,18-octaethylporphyrin). 1H NMR, IR, visible, and CD spectra of the synthetic molecule in a chlorinated methane (CDCl3 or CH2Cl2) showed that the carbonyl oxygen of the N-terminal amino acid of the linked peptide should ligate the central zinc metal in the molecule as the axial ligand to form a pentacoordinated zinc-porphyrin. The coordination of the zinc with the peptide framework changed the optical and electrical properties, indicating that such ligation might control the reactivity in biological metallotetrapyrrole–protein systems as well as the coordination to the peptide residue.