Evaluation of the Debye temperature for iron cores in human liver ferritin and its pharmaceutical analogue, Ferrum Lek, using Mössbauer spectroscopy

An iron-polymaltose complex, Ferrum Lek, used as antianemic drug and considered as a ferritin analogue and human liver ferritin were investigated in the temperature range of 295-90K using (57)Fe Mössbauer spectroscopy with a high velocity resolution (in 4096 channels). This study aimed to make a comparison of the Fe atom dynamics in the Ferrum Lek and ferritin iron cores by means of evaluation of the Debye temperature using the temperature dependence of the spectral center shift obtained with two different fitting procedures and the second order Doppler shift approach. The Debye temperature, evaluated as ΘD=502±24K for Ferrum Lek and ΘD=461±16K for human liver ferritin, demonstrated a very small difference in the Fe atom vibrations, reflecting a slightly smaller rigidity in the iron cores in human liver ferritin.

Unusual dynamics of Fe atoms in a chromium matrix

(57)Fe site Mössbauer spectroscopy (MS) was used to investigate the dynamics of (57)Fe atoms embedded in a chromium lattice as impurities. From the Mössbauer spectra recorded in the temperature range of 80-350 K, a temperature dependence of the Lamb-Mössbauer factor, f, was determined. The latter revealed an unusual dynamics of (57)Fe atoms, namely a harmonic mode below T≈145 K with a characteristic effective Debye temperature Θ(eff) = 190.2 K and a strongly anharmonic one above T≈145 K. The latter mode exists in two clearly defined temperature intervals with significantly different Θ(eff) values, namely (i) ∼155 K for ∼145 K ≤ T ≤ ∼240 K and the record-high anharmonic coefficient ε = -25.8 × 10(-4) K(-1), and (ii) ∼151 K for T ≥ ∼240 K with ε = -14 × 10(-4) K(-1). Based on Visscher's theory, the record-low value of the relative binding force constant for Fe atoms was determined as 0.0997 for the harmonic regime. It is suggested that the unusual dynamics observed in this study might be related to the underlying spin-, charge- and strain-density waves of chromium.

Debye temperature of disordered bcc-Fe-Cr alloys

The Debye temperature, Θ(D), of Fe(100-x)Cr(x) disordered alloys with 0 ≤ x ≤ 99.9 was determined from the temperature dependence of the centre shift of (57)Fe Mössbauer spectra recorded in the temperature range of 60-300 K. Its compositional dependence shows an interesting non-monotonous behaviour. For 0<x ≤ ∼ 45, as well as for ∼ 75 ≤ x ≤ ∼ 95, the Debye temperature is enhanced relative to its value of a metallic iron, and at x ≈ 3 there is a local maximum having a relative height of ∼ 12% compared to a pure iron. For ∼ 45 ≤ x ≤ ∼ 75 and for x ≥ ∼ 95 the Debye temperature is smaller than the one for the metallic iron, with a local minimum at x ≈ 55 at which the relative decrease of Θ(D) amounts to ∼ 12%. The first maximum coincides quite well with that found for the spin-waves stiffness coefficient, D(o), while the pretty steep decrease observed for x ≥ ∼ 95, which is indicative of a decoupling of the probe Fe atoms from the underlying chromium matrix, is likely related to the spin-density waves which constitute the magnetic structure of chromium in that interval of composition and show also anomalous dynamic behaviour. The harmonic force constant calculated from the effective Debye temperature of the least Fe-concentrated alloy (x ≥ 99.9) amounts to only 23% of the one characteristic of a pure chromium as determined from the heat capacity experiment.