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Calculation of partition coefficients of Fe–S/Se protein models
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1  Institut Universitari de Ciència Molecular, Universitat de València, Edifici d'Instituts de Paterna, P. O. Box 22085, E-46071 València, Spain

Abstract: A method permits semiquantitative estimation of partitioning of solutes between pairs of media. The organic solvent-water partition coefficients P are calculated. For Fe4S4Cysn, the organic solvent–water partition coefficients for 1-octanol Po, cyclohexane Pch and chloroform Pcf decrease 4.46, 6.25 and 4.60 per Cys, respectively. Po are in line with CDHI calculations, and Pch–cf, with calculations performed with a method by Leo–Hansch. LogPo–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 Fe4Se4CysnPo–ch–cf decrease 4.52, 6.30 and 4.66 per Cys. With the references Po–ch–cf decrease 4.03, 4.80 and 5.76 per Cys. The similar calculated partition coefficients and hydrophobic moments for Fe4S4–mSemCys4 suggest a role of FeSe clusters in physiological processes.
Keywords: Solvation parameter model, Partition coefficient, Hydrophobic moment, Iron-sulphur protein, Iron-selenium protein, Mixed-valence non-integer oxidation number, Cysteine ligand