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 1.1 T, 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.