Proton NMR and susceptibility measurements on the magnetic core of ferritin

Abstract

We report an investigation of the magnetic core of the biomolecule ferritin by means of proton nuclear magnetic resonance (NMR) and relaxation, magnetic susceptibility and scanning electron microscope (SEM) measurements. SEM images show that the outer protein shell is taken out completely by an appropriate chemical treatment and indicate particle sizes ranging from 10' -to 104 nm. Susceptibility measurements show a maximum in the zero-field-cooled data which is strongly field-dependent and can be ascribed to superparamagnetic behavior, whereas the hysteresis curve is different from normal ferritin. Proton NMR and spin-lattice relaxation data as a function of temperature at 4.7 T suggest the presence of an antiferromagnetic transition around 100 K.Ferritin is a biomolecule of interest in the problem of iron storage in living organisms. It is commonly reported [1-4] that ferritin becomes antiferromagnetic (AF), although the evidence is largely indirect and the Nèel temperature reported varies widely in the range 50 K < TN < 240 K. Moreover, for T < 30 K, magnetization measurements give evidence of superparamagnetic relaxation and of spin freezing of the total magnetic moment associated with the uncompensated spins at the boundary of the cluster of iron ions [5]. Recently, interest in the magnetic behavior of ferritin has been revived by the confirmation [6,7] of an early report [8] of the occurrence of macroscopic quantum coherence phenomena at low temperature. The main purpose of the present paper is to investigate the spin dynamics of the Fei+ magnetic moments in the ferritin core by means of proton nuclear magnetic resonance (NMR) and relaxation measurements. Since in the naturally occurring ferritin biomolecule the largest number of protons is contained Permanent address:

In-depth magnetometry and EPR analysis of the spin structure of human-liver ferritin: from DC to 9 GHz

“…As such, the magnetism of the protein influences the contrast of R2 and R2*-weighted MRI images. [7][8][9] In the past decades, 'bulk' magnetometry techniques have been used to characterize the magnetic and mineral state of ferritin, 10,11 along with spectroscopy techniques such as Mo ¨ssbauer spectroscopy, 11,12 electron paramagnetic resonance (EPR), 13,14 nuclear magnetic resonance (NMR), [15][16][17] as well as electron and X-ray microscopy techniques, 18,19 and diamondbased quantum spin relaxometry to study the ferritin room temperature magnetic properties. 20 Electron paramagnetic resonance (EPR), sometimes also referred to by the more general term electron magnetic resonance (EMR), has also been applied to ferritin, 13,14,[21][22][23][24][25] in spite of intrinsic challenges related to extreme spectral broadening.…”

Human-brain ferritin studied by muon spin rotation: a pilot study

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