title: An ab initio quantum-chemical study of the blue-copper site of azurin.
abstract: The electronic structure of the blue-copper site of Pseudomonas aeruginosa azurin has been investigated by ab initio multireference determinantal configuration interaction (MRD-CI) calculations. A truncated site consisting of copper and its three equatorial ligands has been studied with emphasis on the g tensor and the nitrogen hyperfine tensors of the coordinating histidines. In the ground state the singly occupied molecular orbital (SOMO) involves a copper 3d orbital pi antibonded to the cysteine sulfur and sigma antibonded to the histidine nitrogens. A proper description of the electron-paramagnetic-resonance parameters has been achieved through the use of an effective core potential for copper up to and including the 3s electrons. Both the complete g tensor and the anisotropic hyperfine tensors at the nitrogens are essentially reproduced. Mulliken spin densities of 35 and 59% on copper and sulfur, respectively, and 2.1 and 1.7% on the respective coordinating nitrogens reflect the delocalized character of the SOMO and the inequivalence of the histidines.
authors.affiliation: Department of Molecular Physics, Huygens Laboratory, Leiden University, P.O. Box 9504, 2300 RA, Leiden, The Netherlands.
authors.forename: M
authors.initials: M
authors.lastname: van Gastel
authors.forename: J W A
authors.initials: JW
authors.lastname: Coremans
authors.forename: H
authors.initials: H
authors.lastname: Sommerdijk
authors.forename: M C
authors.initials: MC
authors.lastname: van Hemert
authors.forename: E J J
authors.initials: EJ
authors.lastname: Groenen
mesh_terms: D001400:Azurin / Q000737:chemistry*; D001665:Binding Sites; D003300:Copper / Q000737:chemistry*; D006639:Histidine / Q000737:chemistry; D008958:Models, Molecular; D011550:Pseudomonas aeruginosa / Q000737:chemistry
chemical_list: D001400:Azurin; D006639:Histidine; D003300:Copper