The CD spectra of tri-μ 3-oxo-triaquohexakis(L-amino acid)triiron(III) perchlorates

Abstract

Circular dichroic spectra of tri-μ 3-oxo triaquohexakis(L-amino acid)triiron(III) complexes, containing the [Fe 3O] 7+ unit, proposed as models for ferritin iron core, are described. The circular dichromism of these iron(III)-L-amino acid complexes is mainly due to the interaction of the charge transfer manifold with the asymmetric carbon atom of L-amino acids. Although it is possible to correlate the optical extrema with the electronic spectra of the complexes, it is not possible to correlate the sign of the extrema in the CD spectra of the complexes with specific features of their molecular structure. Extrema for complexes derived from five L-amino acids with aliphatic R group occur at the same wavelenghts in each case: 218(+), 245(−), 267(+), 311(+), 345(+), 378(−), 475(+), 538(+), and 620(+). Complexes using D-amino acids exhibit spectra which are the antipodes of these. Maximum spectra are observed when perchlorate is used as the counterion.