A magnetic study of an Fe-chitosan complex and its relevance to other biomolecules

Structural and magnetic properties of an Fe-chitosan complex is investigated by Mössbauer spectroscopy. From the isomer shift deduced from the Mössbauer spectra measured at various temperatures, it is concluded that the metal ion in the complex is in the high-spin Fe(III) state and is coordinated to at least five N and/or O ligands. The 4.2 K Mössbauer spectrum is magnetic with an internal magnetic field of 441 kG, considerably smaller than the ideal theoretical value for a high-spin Fe(III), suggesting a strong covalency between the metal and its surrounding ligands. The experimental data also indicate that the system undergoes a phase transition at around 100 K as evidenced by the appearance of a quadruple doublet Mössbauer spectrum. An analysis of the temperature dependence of the isomer shift indicates the harmonic coupling between the atoms to a reasonable approximation. From the analysis of the experimental data, a scheme for the Fe-chitosan complex has been proposed.