Theory of the magnetic properties of ferric hemoproteins: development of a 4-term ligand field model.

A ligand field 4-term model is used to calculate the g-values and the magnetic moments of ferric hemoproteins. The 4-term model allows the common description of the magnetic properties of high spin and low spin hemoproteins with the same approach. The model includes the four energetic lowest cubic terms (6A1, 2T2, 4T1, 4T2) which are mixed by ligand field components of axial and rhombic symmetry and by spin-orbit coupling. Especially the g-values of the high spin cytochrome P-450 LM4 and of the low spin cytochrome P-450 LM2 were simulated and compared with the results of a 3-term model (without 4T2) earlier developed by Ristau [5, 6]. The multiterm model is also suitable to calculate the magnetic properties of spin-mixed ferric hemoproteins with ligand field strengths in the crossover region of ground states.