Binding of Copper(II) to Pectins by Electrochemical Methods

The interaction between Cu(II) and pectin extracted from citrus fruit was studied in KNO30.10 mol dm−3at 25 °C and pH 5.5, using ion selective electrode potentiometry and voltammetry, namely differential pulse polarography and square‐wave voltammetry. Although many independent variables may affect Cu(II)‐polymer interactions such as charge density, polymer concentration and copper to polymer concentration ratio, a good fitting was observed for the model with ML and ML2complex species, when M:L total concentration (mol dm−3) ratio varies from 0.2 to 2.7 and the ligand concentration is in the range (0.2 to 1) g dm−3, i.e., (0.4 to 2)×10−3mol COO−dm−3. The complex parameters found in these conditions were log βCuL=3.5±0.1 and log βCuL2=8.0±0.2. For lower total ligand and total metal ion concentrations, used in voltammetry, the interaction Cu(II)‐pectin is affected by a cooperative mode (increase of metal ion‐ligand affinity) when the total metal ion concentration increases and by an anti‐cooperative mode when the total ligand concentration increases, possibly due to different conformations of the polymer.