Cu II Ion Coordination to an Unprotected Pentadecapeptide Containing Two His Residues: Competition Between the Terminal Amino and the Side‐Chain Imidazole Nitrogen Donors

The complex‐formation equilibria of the pentadecapeptide TLEGTKKGHKLHLDY, the 114−128 protein fragment of SPARC, with the Cu II ion have been investigated, at I = 0.1 mol·dm −3 (KNO 3 ) and T = 298.2 K. Protonation and complex‐formation constants have been determined potentiometrically, and formation enthalpies measured by direct solution calorimetry; the complex‐formation model and species stoichiometry have been carefully checked by means of UV/Vis absorption, CD and EPR spectroscopy. The structure hypotheses of the complex species are also based on detailed study of the 1 H and 13 C NMR spectra of the ligand in both the absence and presence of copper ions. The involvement in complex‐formation of both the terminal amino and imidazole groups has been suggested and their specific behaviour at different pH values elucidated. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)