Polyelectrolytic and Specific Interaction in Natural Polymers: Experimental And Theoretical Study Of Humic Acid In Mixed Counterion Solution.

RODOLFO D. PORASSO; MARC A. G. T. VAN DEN HOOP; SERGIO PAOLETTI; JULIO C. BENEGAS

Congreso; IV Biophysics Congress of the Southern Cone; 2000

In the analysis of the physico-chemical properties of the natural polymers, one is sometimes faced with the problem of their complex and unknown constitution. Several (bio)polymers are constituted by functional groups with different intrinsic pK° and concentration. Paoletti et al. have studied this problem in co-polymers, introducing an extension of the counterion condensation theory in order to consider polysaccharides constituted by two different functional groups. In this work we present a methodology to characterize, from the polyelectrolytic point of view, natural polymers made of different functional groups of unknown pK° and concentration. Proper use of this extension can be helpful in planning suitable experiments in order to determinates basic physico-chemical characteristics of the solution like the linear charge density, the number of different functional groups, their concentration and pK°. Our aim in this work is to study the different modes of interaction between heavy metals and polyelectrolytes found in natural environments. As an application we consider the particular case of Humic Acid in water solution with counterion of mixed valency. The humic acid average charge density was found to be 0.80. Four main functional groups have been consistently identified with their pK° and fractional abundance. Different divalent metal ions have been used in order to establish the differences in polymer/heavy metal association mechanism. Our results show an increase in chemical binding to the polymer in the order Ca < Cu ≅ Pb.