RELAXOMETRY AND MAGNETOMETRY OF FERRITIN

By combining nuclear magnetic relaxometry on 39 ferritin samples with different iron loading with magnetometry, results were obtained that s uggest a new interpretation of the core structure and magnetic propert ies of ferritin. These studies provide evidence that, contrary to most earlier reports, the ferritin core is antiferromagnetic (AFM) even at body temperature and possesses a superparamagnetic (SPM) moment due t o incomplete cancellation of antiparallel sublattices, as predicted by Neel's theory. This moment also provides a likely explanation for the anomalous T-2 shortening in ferritin solution. However, the number of SPM moments derived from this model is less than the number of ferrit in molecules determined chemically, and a similar discrepancy was foun d by retrospectively fitting previously published magnetometry data. I n other words, only a fraction of the ferritin molecules seem to be SP M. The studies also provide evidence for paramagnetic (PM) Curie-Weiss iron ions at the core surface, where the local Neel temperature is lo wer; these ions are apparently responsible for the weaker T-1 shorteni ng. In fact, the conversion of uncompensated AFM lattice ions to PM io ns could explain the small number of SPM particles. The apparent Curie Law behavior of ferritin thus appears to be a coincidental result of different temperature dependences of the PM and SPM components.