Approximately one-half of all known protein crystal structures in the protein data bank (PDB) contain metal ion cofactors, which play vital roles in charge neutralization, structure, and function.1,2 These proteins range in size from 5000-107 Da with the metal ion corresponding to only on the order of 0.1 wt % of the molecule. Yet, for a wide range of these metalloproteins, the metal ion and its environment are key to the chemistry as these comprise the active site in catalysis. It is the purpose of this review to present the information content of spectroscopic methods, which allow one to focus in on the metalloactive site (Figure 1), define its electronic structure, evaluate the role of the protein in determining geometric and electronic structure, and elucidate the contributions of electronic structure to function. Metalloproteins are simply metal complexes but with remarkably intricate and complex ligands. The metal ion, clusters of metal ions bridged by oxide or sulfide ligands or equatorially chelated by N-heterocyclic ligands (heme, corrin, etc.), are bound to the protein through one or more of the endogenous ligand lone pair donors in Table 1. Note that for most of the donor groups, this requires deprotonation, and the metal ion competition with the proton for the free base lowers the effective pKA by at least several log units from those intrinsic values listed in Table 1. It is important to emphasize that for a number of the ligands in Tables 1 and 2, in particular phenolate, thiolate, oxo and sulfido, and the N-heterocyclic chelates, the metal complex exhibits extremely intense low energy charge transfer (CT) absorption bands, which reflect highly covalent ligand-metal bonds. These make major contributions to the electronic structure of an active site and can be affected by the geometry of the metal site and the orientation of the ligand-metal bond, which in turn can be influenced by the protein matrix. * To whom correspondence should be addressed. † Department of Chemistry, Stanford University. ‡ Stanford Synchrotron Radiation Laboratory, SLAC, Stanford University. 419 Chem. Rev. 2004, 104, 419−458

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Electronic Structures of Metal Sites in Proteins and Models: Contributions to Function in Blue Copper Proteins

A complete Intermediate Neglect of Differential Overlap model suitable for the examination of transition metal complexes is described. The model is characterized by the inclusion of all the one-center exchange terms necessary for rotational invariance and accurate spectroscopic predictions, as well as an accurate description of integrals involving 3d atomic orbitals. The model is within the unrestricted Hartree-Fock formalism, and a method for spin purification is described. Problems with convergence of the self-consistent field are discussed, and a method that has been found successful in aiding the convergence is outlined. The model has been applied to many transition metal systems. In this article the results of calculations on the chlorides of Fe, Co and Cu are described. The results of these calculations are compared with experiment, and with the results of calculations by other methods.

An intermediate neglect of differential overlap theory for transition metal complexes: Fe, Co and Cu chlorides

As a consequence of the non-spherical symmetry of the copper(II) ion, d9 configuration, and of the influence of the Jahn-Teller, and pseudo Jahn-Teller effect on six-coordinate geometries, the stereochemistries of the copper(II) ion are characterized by non-rigid geometries (fluxional behaviour), and ranges of distorted geometries (Plasticity Effect) The latter may be connected by a series of Structural Pathways, which may be characterised by an ‘Electronic Criterion of Stereochemistry’ for a related series of complexes, eg the [Cu(bipy)2X] [Y] complexes

A new look at the stereochemistry and electronic properties of complexes of the copper(II) ion

Plasticity of the coordination sphere of copper(II) complexes, its manifestation and causes

Splitting of d-orbitals in square planar complexes of copper(II), nickel(II) and cobalt(II)

Crystal structures of the green and yellow thermochromic modifications of bis(N-Methylphenethylammonium) tetrachlorocuprate (II). Discrete square-planar and flattened tetrahedral tetrachlorocuprate(2-)anions

Crystal and molecular structure of bis[(+)-N,.alpha.-dimethylphenethylammonium] tetrachlorocuprate(II). Relation between the electronic spectrum and the distortion of the tetrachlorocuprate chromophore from tetrahedral symmetry

Crystal structure of N-methylphenethylammonium trichlorocuprate(II). Distorted trigonal-bipyramidal coordination

Crystal and molecular structure of bis((+)‐n,alpha‐dimethylphenethylammonium)tetrachlorocuprate(ii), relationship between the electronic spectrum and the distortion of the cucl4 chromophore from tetrahedral symmetry

Crystal structures of the green and yellow thermochromic modifications of bis(n-methylphenethylammonium) tetrachlorocuprate(ii), discrete square-planar and flattened tetrahedral cucl4(2-) anions

R. L. Harlow

Papers

Crystal structures of the green and yellow thermochromic modifications of bis(N-Methylphenethylammonium) tetrachlorocuprate (II). Discrete square-planar and flattened tetrahedral tetrachlorocuprate(2-)anions

Crystal and molecular structure of bis[(+)-N,.alpha.-dimethylphenethylammonium] tetrachlorocuprate(II). Relation between the electronic spectrum and the distortion of the tetrachlorocuprate chromophore from tetrahedral symmetry

Crystal structure of N-methylphenethylammonium trichlorocuprate(II). Distorted trigonal-bipyramidal coordination

Crystal and molecular structure of bis((+)‐n,alpha‐dimethylphenethylammonium)tetrachlorocuprate(ii), relationship between the electronic spectrum and the distortion of the cucl4 chromophore from tetrahedral symmetry

Crystal structures of the green and yellow thermochromic modifications of bis(n-methylphenethylammonium) tetrachlorocuprate(ii), discrete square-planar and flattened tetrahedral cucl4(2-) anions