Towards an understanding of the electron paramagnetic resonance spectra of the ferritin core

Abstract

A technique that can be used in the study of the magnetic properties of ferritin is electron paramagnetic resonance (EPR), which is sensitive to the magnetic moments of unpaired electrons.

The magnetic properties of human liver ferritin were studied using 9 GHz EPR, with which temperature dependent spectra were acquired in the following range: 5-150 K. A novel approach, typically used in magnetic resonance spectroscopy, was employed to pre-process the baseline-corrected spectra and remove features for which it was unlikely to originate from the ferritin core. This allowed for the isolation and preservation of the general lineshape of the signal belonging to the ferritin core.
The spectra were further analysed using both a phenomenological approach and by employing the Spin Hamiltonian.
The phenomenological analysis showed that in the 20-70 K temperature range, the amplitude peak-to-peak of the ferritin-core signal decreases linearly with decreasing temperature, while its lineshape changes from Lorentzian to Gaussian between 150 and 70 K. The blocking temperature was suggested to occur between 10 and 20 K, where the signal amplitude was lost.
Whether and how the lineshape of the ferritin core signal shifts or broadens below 70 K could not be determined due to a six-line signal contamination, most likely caused by manganese impurities, obscuring the ferritin-core signal in the field range where its resonance field is positioned.
In order to study the magnetic properties of the ferritin core, and therefore gain insight on the magnetic and electronic structure of the ferritin core, a Spin Hamiltonian approach was employed. The simplified Giant Spin Hamiltonian model featured a single spin system with total spin S = 10. This analysis suggests that the ferritin-core signal is centred at g’=2.0154, hinting at a core composition of magnetite or maghemite, rather than of ferrihydrite.

An almost fully automated procedure to pre-process a set of human liver ferritin EPR spectra obtained at different temperatures is described in this thesis.