HEMOPROTEIN MODELS BASED ON A COVALENT HELIX-HEME-HELIX SANDWICH - 4 - DISCRIMINATION OF PARAMAGNETIC FE(III)-MIMOCHROME-I DELTA-ISOMER ANDLAMBDA-ISOMER BY NMR-SPECTROSCOPY

A H-1 NMR study of the paramagnetic Fe(III)-Mimochrome I, a porphyrin peptide compound based on a covalent helix-porphyrin-helix sandwich, p rototype of a new class of heme-protein models, is reported. The study demonstrates that Fe(III)-Mimochrome I exists, in d(7)-DMF solution a t millimolar concentration, as two hexacoordinated Delta and Lambda is omers. It represents the first observation of two isomeric forms of a bis-histidine Fe(III)-porphyrin peptide adduct. H-1 NMR studies in d(7 )-DMF solution of the paramagnetic Fe(III) deuteroporphyrin dimethyles ter (DPDME), either as acetate (Ac) or chloride salts, are also report ed for comparison. In the acetate form this compound gives detectable different mixed-ligand isomers by imidazole addition, while the chlori de form gives preferentially the bis-imidazole complex. (C) 1998 Elsev ier Science S.A. All rights reserved.