Sol/Gel Transition of Aqueous Alginate Solutions Induced by Fe2+ Cations

Novel information on the gelation mechanism of aqueous alginate solutions in the presence of iron cations is obtained by combining confocal Raman spectroscopy and viscoelastic measurements. The mechanism of gelation of alginate with iron cations is proposed to occur through a combined acid and ionotropic gelation. The low binding ability of iron cations to alginate uronate chains suggests that the formation of iron alginate hydrogels preferentially occurs through an acid gelation. This gives rise to a structure more similar to chemical gels than to physical gels in the sense that they are composed of random aggregates, in contrast to the rod-like structure exhibited by Ca-alginate gels.