Theoretical study on orientations of axially coordinated imidazoles in model systems of cytochromes

Abstract

The quantum chemical (DFT) calculations were performed on heme model systems with non-substituted Fe-porphyrin core for the different orientations of the axially coordinated imidazoles of [Fe-II(por)(im)(2)] and [Fe-III(por)(im)(2)](+) complexes. These calculations show that the energy difference between parallel and perpendicular orientations of imidazoles is very small for both Fe(II) and Fe(III) complexes, and that there is almost no preference for one or other orientation. (C) 2003 Elsevier Science B.V. All rights reserved.