Magnetic Control of Macromolecular Conformations in Supramolecular Anionic Polysaccharide-Iron Complexes

The anionic iota carrageenan polysaccharide is enriched with Fe-II and Fe-III by ion exchange against FeSO4 and FeCl3. With divalent iron, portions of polymer chains undergo a secondary structure transition from random coils to single helices. The single-chain macromolecular conformations can be manipulated by an external magnetic field: upon exposure to 1.1T, the helical portions exhibit 1.5-fold stiffening and 1.1-fold stretching, whereas the coil conformations respond much less as a result of lower contents of condensed iron ions. Along with the coil-helix transition, the trivalent iron triggers the formation of superstructures. The applicability of iron-enriched iota carrageenan as functional ingredient for food fortification is tested by free Fe2+ and Fe3+ contents, respectively, with the most promising iota-Fe-III yielding 53% of bound iron, which is due to the superstructures, where the ferric ions are chelated by the supramolecularly self-assembled polymer host.