Heisenberg model for tetrameric iron clusters in high-potential iron-sulfur proteins. II. Double exchange in distorted cluster

Abstract

The joint Heisenberg and double exchange models for the [Fe 3(III)Fe(II)] cluster of the oxidized form of the high-potential proteins are considered. The double exchange and Heisenberg interactions form the exchange-resonance states of this cluster in the case of electron migration. In the model with S 34 exchange mixing, the increase of resonance interaction leads to non-linear double exchange behavior of the levels. For the model with electron transfer between two mixed-valence iron ions in the tetramer, the parameter b ij of the electron transfer and the Heisenberg term δ 1 form one effective exchange-resonance parameter δ ± b=δ 1± b ij /(2 S 12+1)(2 s a+1), which depends on the type of the exchange-resonance multiplet. The linear double exchange splitting of the Heisenberg exchange states takes place in the case of the model with S 12 exchange mixing.