Amylose-Iodine Complex. III. Potentiometric and Spectrophotometric Studies

The amylose-iodine reaction has been studied in a wider temperature range than hitherto reported by both potentiometric and spectrophotometric methods. The enthalpy change of the reaction obtained potentiometrically is −15.5 kcal. at 16°C, and appears to be independent of the chain length and the kind of parent starch of amylose. The change of the absorptions of the amylose-iodine complex with temperature has been pursued at wavelengths of 650, 288 and 350 mμ, respectively. The triiodide ion adsorbed on the surface of amylose causes an error in the spectrophotometric estimation of free iodine concentration. At the higher temperature, however, this error may be neglected, and the results obtained seem to be reliable. The enthalpy change appears to increase with increasing temperature and −20.8 kcal. has been obtained at 50°C.