Synthesis and characterization of cobalt(III) ethylenediamine-N,N′-diacetate complexes with azo dyes and azo amino acids

Article abstract of DOI:10.1021/ic50224a016

A series of ternary cobalt(III) complexes containing the quadridentate ligand ethylenediamine-N,N′-diacetate (EDDA) and bidentate azo ligands have been prepared and characterized as models for cobalt(III) azo protein derivatives. The azo ligands investigated are an azo naphthol dye, p-(2-hydroxy-1-naphthylazo)benzenesulfonic acid (OD-II = orange dye II), an azo phenol dye, 2-(4-carboxyphenylazo)-4,5-dimethylphenol (CDP), and azo amino acid derivatives, N-acetyl-3-(arsanilazo)-L-tyrosine (NA-MAT), N-acetyl-2-(arsanilazo)-L-histidine (NA-MAH(C-2)), N-acetyl-4-(arsanilazo)-L-histidine (NA-MAH(C-4)), and N-acetyl-2,4-bis(arsanilazo)-L-histidine (NA-BAH), which are direct analogues of the cobalt(III) azo protein derivatives. Two of the possible geometrical isomers for the OD-II and CDP complexes were separated and characterized by their ¹H NMR spectra. The visible electronic absorption spectra of the azo dyes and azo amino acids are distinctly and systematically altered upon cobalt(III) coordination, permitting the quantitative determination of cobalt(III) complexation to azo proteins. The absorption spectra vary little between isomers.