Inorg. Chem. 1986, 25, 2160-2165
2760
the blood have been nicely discussed by Harris et aLga Acknowledgment. We thank Barbara Viglione, Susan Swope, and Barbara McCarty, who were involved in the preliminary stages of this work, Prof. George Bates for suggesting the presence of a reductant in commercial transferrin, Joan Perrault, Director
of the Chemistry Laboratory at Wentworth-Douglas Hospital, for providing serum samples, and the National Institutes of Health for financial support through Grant GM20194. Registry No. V 0 2 + , 20644-97-7; V(IV), 22541-76-0; V(V), 2253731-1.
Contribution from the Laboratoire de Chimie de Coordination, CNRS, 31400 Toulouse, France, and Research Institute, The Hospital for Sick Children, and Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada M5G 1 x 8
Complexation of Copper(I1) with a Macrocyclic Peptide Containing Histidyl Residues: Novel Observation of NMR Spectra of Paramagnetic Copper(I1) Compounds Jean-Pierre Laussac,? Anne Robert,t Raymond Haran,t and Bibudhendra Sarkar*t Received November 6. 1985
Interaction of Cu(I1) and cyclb-(Gly-His-Gly-His-Gly-His-Gly), a synthetic macrocyclic peptide, was investigated by electronic absorption, EPR, and ‘H and 13CN M R spectroscopy. These experiments have been conducted in aqueous solution as a function of pH and for different ligand:Cu(II) ratios. The results indicate the presence of two species. The species found under neutral conditions is described as one involving the three N ( 1 ) nitrogens of imidazole residues, while under basic conditions, the complexation occurs via four GlyNH deprotonated peptide nitrogens. Both systems are found to be in slow exchange over the wide pH range, with dissociation constants of 1.25 X lo’s-’ and
