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the oxidation state of the metal, its coordination number, the nature of the macrocyclic ligand, and indeed the finer details of its geometry. In molecular orbital terms the reasons for such behavior lie first with the presence of low-lying (usually -type) orbitals in the macrocycles and second with relatively deep-lying metal d orbitals at this end of the periodic table. (For gallium, two elements further along in the periodic table, we seldom consider the 3d orbitals when looking at its chemistry: they are usually considered to be buried in the core.)It is interesting to speculate that this internal electron-transfer process, which may be tailored by adjustment of the variables, we have just mentioned plays an important role in the molecular mechanism for electron transport in copper-containing proteins. Unfortunately at present there is no detailed description of the role of the copper site available to examine this idea further.Acknowledgment. This work was initiated during conversations with R. R. Gagne, to whom we are grateful for access to unpublished data on these systems. We thank the Dreyfus Foundation for a Summer Fellowship (P.D.W.). AppendixOur calculations were carried out on molecule 12 with the dimensions given. It differs from the ligand used in the experimental work by replacement of some terminal alkyl groups by H atoms. The parameters of the extended Hiickel calcu-lations17 are given in Table III. The calculations are of course rather crude ones, and the position of the x2 -y2 orbital will (17) R. Hoffmann, J. Chem. Phys., 39, 1397 (1963. F F 1.38\ / be sensitive to the actual choice of exponents and coefficients as in any calculation. Use of an arbitrary single-f radial 3d function gave an orbital description qualitatively similar to that described in the paper. The x2 -y2 6orbital dropped in energy as the (single) exponent increased in these calculations. The Richardson et al. double-f functions,18 with which we obtained the results described, needed to be employed to distinguish quantitatively, for example, between isoelectronic Ni1 and Cu!I. Values of the metal 4s and 4p orbital exponents and s, p, and d VSIP's are those used by Hoffmann and Mehrota.9 Bond lengths for the other molecules studied were similar to those of 12. In the carbonyl adducts M-CO = 1.78 Á and C-0 = 1.12 A.

Das Elektrodenpotential für den makrocyclischen Peptidkomplex (I) wurde bestimmt.

Der l4‐gliedrige makrocyclische Titelligand reagiert mit Cu(II) unter Bildung des Komplexes (I), in dem das Metallatom durch vier deprotonierte Peptid‐N‐Atome in quadratisch‐planarer Geometrie chelatisiert ist.