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Ab initio molecular dynamics studies of a synthetic biomimetic model of galactose oxidase
Author(s) -
Rothlisberger Ursula,
Carloni Paolo
Publication year - 1999
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/(sici)1097-461x(1999)73:2<209::aid-qua14>3.0.co;2-b
Subject(s) - chemistry , galactose oxidase , unpaired electron , molecular orbital , density functional theory , ab initio , crystallography , computational chemistry , ligand (biochemistry) , electron paramagnetic resonance , active site , chemical physics , molecule , nuclear magnetic resonance , galactose , enzyme , biochemistry , physics , receptor , organic chemistry
Very recently, highly efficient biomimetic models of the mononuclear copper enzyme galactose oxidase were synthesized which are able to reproduce the structural, spectroscopic, and functional properties of the native system exceptionally well. We have characterized an inactive and an active form of one of these biomimetic compounds using unrestricted dynamical density functional calculations. The peculiar nonsquare planar O 2 N 2 ‐coordination geometry of the copper ion in the catalytically inactive (EPR‐active) form induces a complex energy‐level diagram that cannot be related to crystal‐field models: The highest occupied orbitals are located on the π‐system of the aromatic ligands and are essentially spin‐paired while the unpaired electron is localized mainly in a lower‐lying d x 2 − y 2orbital of the copper. Using ab initio molecular dynamics simulations, we determined for the first time the structure of the active form complexed with a substrate analog. Our calculations reveal that upon substrate binding one of the phenolate ligands is pushed away from the copper center into an axial position and the electronic structure rearranges to an unusual antiferromagnetic diradical state. As in the inactive form, the unpaired α‐spin density is located in the copper d x 2 − y 2orbital. The unpaired β‐spin density, instead, is localized on the axial ligand in agreement with the ligand‐based radical mechanism that has been proposed for galactose oxidase. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 73: 209–218, 1999