Analogues for the Specific Iron-binding Site in the Transferrins: Molecular Structure of a Ternary Iron(III) Model Complex and Spectroscopic, Redox, and Reactivity Properties of Related Compounds


Small-molecule analogues of the specific iron-binding site of the iron tyrosinate protein lactoferrin have been prepared and characterized. The single-crystal X-ray structure of an N-methylimidazole adduct of one of these complexes, (2-(benzimidazol-2-ylmethyl)phenolato)(2-oxo-3-methylbenzoato)bis(N- methylimidazole)iron(III), has been determined by standard procedures and refined by least-squares methods to a conventional R factor of 0.061. The purple crystals belong to the orthorhombic space group Pbca with Z = 8 and unit cell dimensions a = 17.470 (5) Å, b = 17.030 (6) Å, and c = 18.910 (7) Å. The iron(III) complex has a pseudooctahedral N3O3 donor set, utilizing bidentate ligands to provide phenolate, benzimidazole, and carboxylate coordination to mimic respectively the known tyrosinate, histidine, and aspartate protein side chains. The model complexes, which do not include any severe steric constraints, mimic several features of the transferrins: (i) tyrosinate-to-iron(III) charge-transfer band wavelength and molar absorptivity; (ii) reactivity with cyanide to produce a low-spin iron(III) adduct; and (iii) a quite negative value of E1/2. The relationship between these analogues and the active sites of the transferrins is discussed in light of these results. © 1990 American Chemical Society.



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© 1990 American Chemical Society (ACS), All rights reserved.