A COMPARISON OF THE MAGNETIC-PROPERTIES OF POLYSACCHARIDE IRON COMPLEX (PIC) AND FERRITIN

The synthetic polysaccharide iron complex (PIC) molecule has been sugg ested as a 'biomimic', i.e. a counterpart, to the naturally occurring biological molecule ferritin with respect to its magnetic properties b ased on the identification of ferrihydrite as the major mineral in bot h. Magnetization measurements were used to investigate the magnetic pr operties of PIC in relation to those of ferritin, as well as to identi fy differences in such properties between naturally occurring ferritin , which we designate here as Ferritin I, and ferritin with an artifici ally high content of Fe2+ ions bound to its core, which is designated here as Ferritin II. The anisotropy constants K, blocking temperatures T(B), magnetic moments m per particle, and number of magnetic moments 'spins' per particle N(sp) were found to fit the following relations for PIC and ferritin: K(Ferritin I) < K(PIC) less-than-or-equal-to K(F erritin II), T(B)(Ferritin I) < T(B)(Ferritin II) < T(B)(PIC), m(Ferri tin II) - m(Ferritin I) < m(PIC), N(sp)(Ferritin II) = N(sp)(Ferritin I) < N(sp)(PIC). The magnetic moment per Fe ion was found to be smalle r in PIC than Ferritin II due to a stronger antiferromagnetic interact ion between the Fe ions of PIC. Susceptibility measurements indicated the existence of superantiferromagnetism in PIC and Ferritin I and als o showed that most Fe2+ ions in Ferritin II are bound to its core surf ace. The enhanced values of K and T(B) as well as the reduced effect o f superantiferromagnetism and the antiferromagnetic interaction betwee n 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 ferritin (Ferritin I).