COMPLEXATION PROPERTIES OF NATURAL AND SYNTHETIC-POLYMERS OF ENVIRONMENTAL AND BIOLOGICAL INTEREST IN PRESENCE OF COPPER(II) AT NEUTRAL PH

Scatchard and differential equilibrium function (DEF) models were appl ied in parallel (for comparison) to potentiometric titration data (25 degrees C, pH 6.5 and ionic strength 0.1 mol l(-1)) of natural or synt hetic polymers: starch, cellulose, amylopectin, chitin, Chelex-100, Ch elamine and Bio-Rex-70, and humic acids (the last for comparison). Cop per(II) was used as titrant. To demonstrate exactly the meaning and qu ality of the results, identical studies were carried out on: (i) real and well known systems with simple ligands (succinate and proline); an d (ii) simulated systems including ligands with one, two, three or 10 different types of coordination sites (simulated titration curves). Th e aim of the work was the determination of: (a) conditional stability constants of copper complexes; and (b) copper(II) complexation capacit y of the polymers. The relative affinity for copper(II) of the differe nt polymers (given by the differential equilibrium function, K-DEF), d ecreased in the following order at pH 6.5: Chelamine > Chelex-100 simi lar or equal to humic acids > Bio-Rex-70 similar or equal to cellulose > amylopectin similar or equal to chitin greater than or equal to sta rch. In the range of copper(II)to-polymer concentrations embraced, the binding strength of the Chelex-100 was ca one order of magnitude lowe r than that of Chelamine, and similar to that found for the humic acid s. The complexation capacity of the polymers decreased in the followin g order: Bio-Rex-70 > Chelex-100 > Chelamine, chitin much greater than starch > cellulose > amylopectin. All polymers, including the synthet ic resins whose sorption sites are chemically homogeneous, behaved as heterogeneous ligands, like humic acids (i.e. the magnitude of the mic roscopic stability constants decreased when the fraction of all sites occupied by metal ions increased) probably due to both electrostatic a nd steric effects, and limitations of the methods of analysis and calc ulation. (C) 1997 Elsevier Science Ltd. All rights reserved.