Investigation of amylose and tailored amylose matrices for scavenging iodide

Abstract

It has been known for two centuries that starch turns blue upon exposure to iodine as well as the combination of iodine and iodide. Starch contains branched-chain polysaccharides (amylopectin) and linear polysaccharides (amylose), the latter a polymer of a-D-glucose units joined by a(1à4) linkages. Amylose forms a linear helix with 6 a-D-glucose units per turn (i.e., one "amylose ring") and one iodide atom bound maximally per turn. Despite extensive work, suitable quantitative data of iodide-amylose binding seemed surprisingly scarce. To fill an apparent lacuna, examination of the intrinsic binding affinity of amylose for iodide (with measurement of "blue values" by absorption spectroscopy) via a factorial design (grid) study showed that >70% occupancy of amylose occurs with [iodide] in the range 0.05 -0.5 mM and [amylose rings] in the range 0.3 -1 mM. The required concentrations of both species set limits on possible applications. The incorporation of multiple amylose molecules into matrices was examined by reductive amination of the aldehyde terminus with an amine bearing a cross-linkable group. Subsequent cross-linking afforded molecular architectures albeit in quite low yield. A challenge in this domain concerns purification and characterization of synthetic products. The stability of amylose toward degradation by amylase enzymes was examined in the presence of amylase inhibitors. Taken together, the work establishes the foundation and prospective limits for use of amylose for scavenging iodide.