Binding of the Trace Elements: Cu(II) and Fe(III) to the Native and Modified Nutritive Potato Starches Studied by EPR

The Cu(II) and Fe(III) ions have been adsorbed by four potato starches of different degrees of oxidation (different numbers of COOH groups replacing host CH$\text{}_{2}$OH groups): native (no oxidized), white (pudding) with oxidation degree of 0.04%, gelating (0.1%), and LUBOX starch (0.5%). Concentration of the ions in starches was determined from atomic absorption and EPR spectrum intensity. For small concentration of the adsorbed ions (below 4 mg/g) nearly all ions are adsorbed from the solution. EPR shows that adsorbed copper(II) ions are chemically bonded to the starch molecules (preferably) at COOH sites and uniformly dispersed in the starch structure. The complexes are typical of octahedral or square-quadratic coordination with spin-Hamiltonian parameters g$\text{}_{ǁ}$=2.373, g$\text{}_{⊥}$= 2.080, A$\text{}_{ǁ}$=12.1 mT, A$\text{}_{⊥}$=1.0 mT. For higher concentrations the Cu(II) displays a tendency to clustering. Iron(III) ions are introduced into starch in a form of clusters mainly, even for the smallest concentration. The highest concentrations of both Cu(II) and Fe(III) were observed in LUBOX starch having the highest degree of oxidation.