Iodine binding by amylopectin and stability of the amylopectin–iodine complex

The iodine binding capacity (IBC) of amylopectin (AP, from potatoes) is determined to be around 0.38% (w/w) of the total AP in the solution. The mass of iodine bound comprises about 13.6% of the mass of AP involved with the complex, suggesting that with every four iodine atoms bound there are 23 anhydroglucose residues (AGU). Since our previous study indicates that four iodine atoms within the helix of 11 AGUs form a chromophore unit in the API complex, only 48% of the AGUs (11 out of 23) in the AP molecule are directly involved with the iodine. The heat of reaction for the API complex formation is determined to be around −47 kJ/mol of I–I units bound and is significantly lower in magnitude than that of the amylose-iodine (AI) complex [Biopolymers, 31, 57 (1991)]. A possible mechanism has been proposed for the formation of AI and API complexes with fixed compositions. © 1994 John Wiley & Sons, Inc.