Topochemistry in Starch-Iodine Diffusion Reaction Systems

Starch, a naturally occurring polyglucan, primarily exists in two structural forms; amylose, a linear (unbranched) form consisting of alpha (1-4) linked glucose monomers in a 4C1 chair conformation and amylopectin, a branched form with alpha (1-4) and alpha (1-6) linked glucose. Amylose folds to form supramolecular complexes with a large variety of guest species e.g. alcohols, fatty acids and fluorescent dyes etc. The best known complex is perhaps the blue amylose-iodine complex (discovered in 1814) in which a linear polyiodide chain I5 minus inserts into the central channel of a starch helix. As part of studies on the kinetics of nucleation and growth of this nanoparticulate complex, we have discovered the possible formation of Turing structures and chaos patterns. The diffusion and reaction of I2 with starch "solutions" under an extraordinarily wide variety of conditions produced a rich series of beautiful patterns with both spatial and temporal stability. Compositional and mathematical modeling studies of the formation processes are currently being carried out.