A Mossbauer study of the interaction of chitosan and D-glucosamine with iron and its relevance to other metalloenzymes

The interaction of iron with water-soluble polymer chitosan and monomer D-glucosamine is investigated by Mossbauer spectroscopy. The 4.2 K Mossbauer spectrum of Fe-water-soluble chitosan complex indicates the presence of a magnetic pattern and a quadrupole doublet, and analysis of the spectral data leads to the conclusion that an Fe(II) state is partially stabilized in this system. Fe-glucosamine (monomer of chitosan) complex, on the other hand, clearly stabilizes the Fe(II) state in the acidic pH range as evidenced from the isomer shift extracted from the Mossbauer spectra. The oxidation state of the metal ion in the complex is found to be pH dependent. Indirect evidence supporting the involvement of amino group in the bonding with the metal ion is discussed. From the analysis of the experimental data under varying experimental conditions, it is concluded that the metal ion in the complex is at least tetracoordinated and at most hexacoordinated with O/N ligands of the polymer or monomer and thus corroborates the bonding scheme proposed earlier.