A comparison of the magnetic properties of polysaccharide iron complex (PIC) and ferritin

The synthetic polysaccharide iron complex (PIC) molecule has been suggested as a 'biomimic', i.e. a counterpart, to the naturally occurring biological molecule ferritin with respect to its magnetic properties based on the identification of ferrihydrite as the major mineral in both. Magnetization measurements were used to investigate the magnetic properties of PIC in relation to those of ferritin, as well as to identify differences in such properties between naturally occurring ferritin, which we designate here as FerritinI, and ferritin with an artificially high content of Fe + ions bound to its core, which is designated here as Ferritin II. The anisotropy constants K, blocking temperatures TB' magnetic moments m per particle, and number of magnetic moments 'spins' per particleNsp were found to fit the following relations for PIC and ferritin: K(Ferritin I) < K(PIC) ::s; K(Ferritin 11), TB(Ferritin I) < TB(Ferritin II) < TB(PIC), m(Ferritin II) m(Ferritin I) < m(PIC), Nsp(Ferritin II) = Nsp(Ferritin I) < Nsp(PIC). The magnetic moment per Fe ion was found to be smaller in PIC than Ferritin II due to a stronger antiferromag­ netic interaction between the Fe ions of PIC. Susceptibility measurements indicated the existence of superantiferro­ magnetism in PIC and Ferritin I and also showed that most Fe 2 + ions in Ferritin II are bound to its core surface. The enhanced values of K and TB as well as the reduced effect of superantiferromagnetism and the antiferromag­ netic interaction between the molecules at low temperatures for the Ferritin II indicates the importance of the surface magnetic moments in dominating the magnetic behavior of both PIC and femtin (Ferritin I).