AMINE DEPROTONATION IN COPPER(III)-PEPTIDE COMPLEXES

Copper(III)-peptide complexes react rapidly with base, changing color from yellow to red (or to blue with a prolyl group at the amine terminal), prior to their redox decomposition. The initial Cu(III) complexes have three deprotonated peptide groups, and the proposed reaction with base is a deprotonation of the coordinated amine terminal of the peptide. Complexes in which the amine group has been N-formylated or dimethylated do not exhibit the effect and therefore it cannot be attributed to hydroxide addition to the metal. The reaction occurs only with the +3 oxidation state of copper. The pKa values determined for complexes of eight peptides and peptide amides vary from 11.3 to 12.3. © 1979, American Chemical Society. All rights reserved.