Design and molecular mechanics calculations of new iron chelates

Abstract

Empirical force field calculations are described with new ligands APn, having two carboxylic acids and two pyrocatechol functions and forming octahedral chelates with ferric ion. The design of the ligands is described with reference to other siderophores. New parameters for treating Fe^III are derived from spectroscopic data and are used to complement Allinger MM2 parameters. The calculated strain energies in the series APn show optimum stability of the chelate with a length of the polymethylene spacer corresponding to n= 4. Distortions in the octahedron are consistent with similar variations in X-ray structure. The threo configuration of one of the four geometrical isomers is preferred for the AP4 iron chelates.