A Theoretical Study on Redox Potential and pKa of [2Fe-2S] Cluster Model from Iron-Sulfur Proteins

Abstract

Abstract Iron-sulfur proteins are essential in several biological processes, such as electron transfers in photosystems and respiratory chains. The range of redox potentials of these proteins are so wide that many substrates can interact with them. Thus, the redox potentials of the iron-sulfur proteins are crucial to facilitate the process. This study aims to investigate the redox potential of iron-sulfur proteins with [2Fe-2S] core by using two typical exchange-correlation functionals in density functional theory (DFT), i.e., B3LYP and M06, with and without the diffuse function. Since it involves transition metals, several types of spin approximation were also explored, such as high spin (HS), low spin (LS), approximated spin projection (AP), and J coupling parameter (JC) methods. We found that the diffuse function contributes to improving the accuracy. We also found that M06 functional produced more accurate results than B3LYP. The best result is obtained for AP UM06/6-31++G(d,p) with the absolute error of 0.01 V.