ELECTRON-SPIN-RESONANCE STUDIES OF STARCH WATER PROBE INTERACTIONS

Interactions between starch, water and stable nitroxide radicals were studied by electron spin resonance. The motional properties of TEMPO, 4-(2-bromoacetamido) TEMPO (BrAcTEMPO), 5-DOXYL-stearic acid and 16-DOXYL-stearic acid probes as well as a label covalently attached to amylopectin were investigated in concentrated (10-50%) starch-water systems as a function of temperature, concentration of polymer and storage period. The nitroxide label on the amylopectin exhibited a much slower mobility than the corresponding free probe as well being found to be more motionally sensitive to temperature changes; such motional behavior was interpreted as reflecting contributions from rotation of the label around the chain backbone as well as local segmental motion of the polymer chain itself. Starch gels doped with free probes or the spin labelled amylopectin displayed no change in the motion of the nitroxide group upon storage, i. e. , the tumbling rates did not follow the time-dependent conformational changes associated with the retrogradation phenomenon.