| Abstract: | A 3-term crystal field model is used for the calculation of the magnetic properties of ferric hemoproteins. This model includes the high spin term (6A1), the low spin term (2T2) and the quartet term (4T1). The pertubation matrix between these 3 terms caused by spin orbit coupling and ligand fields of cubic, axial and rhombic symmetry are evaluated. The g-factor of the low spin cytochrome P-450 LM2 from rabbit liver are calculated using this 3-term model and the results are compared with those from the usual 1-term model. Contrary to the 1-term model, no orbital moment correction factor is necessary. That means that the orbital moment correction factor with value > 1 simulates some term interaction, predominantly with the quartet term. The g-factors of the high spin cytochrome P-450 LM4 were also calculated by means of the 3-term model and compared with a spin hamilton treatment. A good agreement between the spin hamilton parameters derived from the experimental g-factors and those calculated by the 3-term model were obtained. For hemoproteins with strongly mixed spin states the 3-term model is also useful, contrary to 1-term models or spin hamiltonians which are completely incorrect. The 3-term model is a minimal model to describe all typical magnetic properties of low spin and high spin ferric hemoproteins with the smallest number of terms. |
