Heitler-London Calculation on the Bonding of Oxygen to Hemoglobin. III. Singlet States in the Case of O–O Axis Inclined to Heme Plane

Abstract

The electronic structure of the heme-O₂ system is studied on the inclined arrangement in which the O–O axis is at 60° to the normal of the heme plane. The method of the calculation is the same as in parts I and II for the parallel arrangement. The results show that the lowest energy eigenvalue is almost equal to that of the ¹A₂ state of the parallel arrangement and that the eigenfunction of this lowest state is more complicated in the present inclined arrangement, i.e., it is composed mainly of the two basic configurations with almost equal weight, one is the triplet-triplet coupling, and the other the singlet-singlet coupling, and the contribution from some charge transfer configurations is also found. The various interpretations of the recent experimental data seem to be attributable to this complex feature of the of the binding state.