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Theoretical and Experimental Study of Pb 2+ and Hg 2+ Adsorption on Biopolymers, 1. Theoretical Study
Author(s) -
Ferreira M. L.,
Gschaider M. E.
Publication year - 2001
Publication title -
macromolecular bioscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.924
H-Index - 105
eISSN - 1616-5195
pISSN - 1616-5187
DOI - 10.1002/1616-5195(20010801)1:6<233::aid-mabi233>3.0.co;2-7
Subject(s) - adsorption , chemistry , polymer science , chemical engineering , computational chemistry , chemical physics , materials science , nanotechnology , engineering
Chitosan and pectic acid have been modeled as disaccharides or oligosaccharides for Hg 2+ and Pb 2+ adsorption. Reasonable models of both biopolymers were used. Several adsorption sites of both polysaccharides were considered, mainly NH 2 in chitosan and CO 2 – in pectic acid. Hg 2+ has several points of anchorage on chitosan. The most important one is NH 2 . The Molecular Mechanic modeling permit us to compare in relative terms the different conformations of models of pectic acid and chitosan and their effect in heavy metal coordination. Using the Parameterized Model version 3 (PM3), we report the formation enthalpy of inter‐ and intramolecular compounds with Hg and Pb. The Extended Huckel method (EHM) results seem to indicate that electrostatic interaction (leading to adsorbed cation on NH 2 and on sites different to NH 2 ) could be the reason for the high uptake found for Hg 2+ using chitosan. Besides NH 2 , the OH near the amine group is the preferred site for Hg 2+ adsorption, especially if it is ionized. In the case of Pb 2+ adsorption, several sites of chitosan present no interaction with this cation. Only the NH 2 group and the ionized OH group mentioned above seem to be the preferred sites, following the EH modified (EHMO) results. The Hg‐ and Pb‐adsorption modeling on pectic acid permit us to conclude that the best site is the same for both metals: the bridge oxygen between monomers of galacturonic acid. the carbonyl group from carboxylate is the best second site for Hg 2+ , whereas the internal oxygen bridge is the best second site for Pb 2+ . Considering the Hg 2+ chemistry in aqueous solution, we evaluated the HgOH + and HgCl + or HgCl 3 – adsorption on both copolymers, using EHMO. The energetic of adsorption changed on both biopolymers for these species, comparing them with Hg 2+ .