Structural and magnetic study of the iron cores in iron(III)-polymaltose pharmaceutical ferritin analogue Ferrifol

Iron(III)-polymaltose pharmaceutical ferritin analogue Ferrifol® was investigated by high resolution transmission electron microscopy (HRTEM), X-ray diffraction, thermogravimetry, electron magnetic resonance (EMR) spectroscopy, direct current magnetization measurements and 57Fe Mössbauer spectroscopy to get novel information about the structural arrangement of the iron core. The Ferrifol® Mössbauer spectra measured in the range from 295 K to 90 K demonstrated non-Lorentzian two-peak pattern. These spectra were better fitted using a superposition of 5 quadrupole doublets with the same line width. The obtained Mössbauer parameters were different and an unusual line broadening with temperature decrease was observed. Measurements of the Ferrifol® Mössbauer spectra from 60 K to 20 K demonstrated a slow decrease of magnetic relaxation in the iron core. Zero-field-cooled and field-cooled magnetization measurements revealed a blocking temperature at ~33 K and a paramagnetic state of the Ferrifol® iron core at higher temperatures. Isothermal magnetization measurements at 5 K show that the saturation magnetic moment is ~0.31 emu/g. X-band EMR spectroscopy measurements revealed the presence of different magnetic species in the sample. Transmission electron microscopy demonstrated that the size of the iron cores in Ferrifol® is in the range 2–6 nm. The lattice periodicity in these iron cores, measured on the HRTEM images, vary in the range 2.2–2.7 Å. This can be best understood as sets of close packed O(OH) layers in ferrihydrite cores without long range correlation. The Mössbauer spectra of iron(III)-polymaltose pharmaceutical ferritin analogue Ferrifol® (T=295–90 K) were fitted using five quadrupole doublets. The blocking temperature for the largest iron cores is 33 K. High resolution transmission electron microscopy shows the lattice periodicity in the Ferrifol® iron cores in the range 2.2–2.7 Å. [Display omitted] •Ferrifol® is an iron(III)-polymaltose pharmaceutical ferritin analogue.•Magnetization measurements of Ferrifol® demonstrate a blocking temperature at ~33 K.•The lattice periodicity in the Ferrifol® iron cores varies in the range 2.2–2.7 Å.