Metal-polysaccharide complexes—Part I

Many factors, including linear charge density, effective nuclear charge of the cation, basicity of the donor group, chelation, intermolecular binding of two or more donor groups by a single cation and steric fit, contribute—or possibly contribute—to the formation and stability of metal ion-polysaccharide complexes. In order to form a proper foundation for studying and interpreting metal ion-polysaccharide interactions, the author introduces into his treatise on polysaccharide complexes much current information concerning the interaction of metal ions with simple unidonor and simple multidonor ligands. For convenience of discussion, the subject of polysaccharide complexes is divided into two categories: interactions of neutral polysaccharides, such as cellulose and starch, and interactions of anionic polysaccharides, such as alginate, pectate, mucopolysaccharides and carrageenan. On the one hand, neutral polysaccharides form weak complexes with cations in neutral or non-alkaline media. Only in alkaline solution is there any great affinity between cation and donor. On the other hand, anionic polysaccharides have a strong affinity for metal counterions, even at low concentrations. Attempts are made to provide reasonable explanations for the formation of these complexes and for the often large differences in affinity between metals for a particular polysaccharide or between polysaccharides for a particular metal. In some instances, rheological behaviour of polysaccharide systems can be related to structural features of macromolecular complexes.