Relaxometry and magnetometry of ferritin

Area of Science:

• Biophysics
• Materials Science
• Biochemistry

Background:

• Ferritin's iron core structure and magnetic properties are crucial for its biological function.
• Previous studies proposed different models for ferritin's magnetic behavior.
• Understanding ferritin's magnetism is key to explaining its role in iron storage and cellular processes.

Purpose of the Study:

• To investigate the magnetic properties and core structure of ferritin.
• To reconcile discrepancies between theoretical predictions and experimental observations of ferritin's magnetism.
• To provide a new interpretation of ferritin's magnetic behavior at physiological temperatures.

Main Methods:

• Nuclear magnetic relaxometry on 39 ferritin samples with varying iron loading.
• Magnetometry measurements.
• Analysis of magnetic data in conjunction with chemical quantification of ferritin molecules.

Main Results:

• Ferritin cores exhibit antiferromagnetic (AFM) properties even at body temperature.
• A superparamagnetic (SPM) moment arises from incomplete sublattice cancellation, explaining T2 shortening.
• Paramagnetic (PM) Curie-Weiss iron ions on the core surface contribute to T1 shortening.

Conclusions:

• Ferritin's magnetic behavior is a complex interplay of AFM, SPM, and PM components.
• Only a fraction of ferritin molecules display SPM behavior, contrary to some prior assumptions.
• The observed Curie Law behavior is likely an artifact of combined temperature-dependent magnetic contributions.