Calculation of partition coefficients of Fe–S/Se protein models

A method permits semiquantitative estimation of partitioning of solutes between pairs of media. The organic solvent-water partition coefficients P are calculated. For Fe₄S₄Cys_n, the organic solvent–water partition coefficients for 1-octanol P_o, cyclohexane P_ch and chloroform P_cf decrease 4.46, 6.25 and 4.60 per Cys, respectively. P_o are in line with CDHI calculations, and P_ch–cf, with calculations performed with a method by Leo–Hansch. LogP_o–ch–cf mean relative errors are –17%, 25% and –17%, which represent mean and unsigned relative errors of –3% and 20%. On varying the number of Cys, the structures show hydrophobic moments indicative of amphipathic structures. For Se substitutions in Fe₄Se₄Cys_nP_o–ch–cf decrease 4.52, 6.30 and 4.66 per Cys. With the references P_o–ch–cf decrease 4.03, 4.80 and 5.76 per Cys. The similar calculated partition coefficients and hydrophobic moments for Fe₄S_4–mSe_mCys₄ suggest a role of FeSe clusters in physiological processes.