title: Xanthan Exopolysaccharide: Cu(2+) Complexes Affected from the pH-Dependent Conformational State; Implications for Environmentally Relevant Biopolymers.
abstract: The conformational impact of environmental biopolymers on metal sorption was studied through Cu sorption on xanthan. The apparent Cu(2+) complexation constant (logK; Cu(2+) + L(-) ↔ CuL(+)) decreased from 2.9 ± 0.1 at pH 3.5 to 2.5 ± 0.1 at pH 5.5 (ionic strength I = 0.1). This behavior is in apparent contradiction with basic thermodynamics, as usually the higher the pH the more cations bind. Our combined titration, circular dichroism and dynamic light scattering study indicated that the change observed in Cu bond strength relates to a conformational change of the structure of xanthan, which generates more chelating sites at pH 3.5 than at pH 5.5. This hypothesis was validated by the fact that the Cu sorption constants on xanthan were always higher than those measured on a mixture of pyruvic and glucuronic acids (logK = 2.2), which are the two constitutive ligands present in the xanthan monomer. This study shows the role of the structural conformation of natural biopolymers in metal bond strength. This finding may help to better predict the fate of Cu and other metals in acidic environmental settings such as aquatic media affected by acid mine drainage, as well as peats and acidic soils, and to better define optimal conditions for bioremediation processes.
authors.affiliation: LEHNA/ENTPE/UCB/CNRS UMR 5023, F-69518 Lyon, France.|ISTERRE/CNRS UMR 5275/Université Grenoble Alpes/IRD, F-38058 Grenoble, France.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Causse
authors.affiliation: ISTERRE/CNRS UMR 5275/Université Grenoble Alpes/IRD, F-38058 Grenoble, France.|LTHE/CNRS UMR 5564/Université Grenoble Alpes/IRD, F-38058 Grenoble, France.
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Spadini
authors.affiliation: ISTERRE/CNRS UMR 5275/Université Grenoble Alpes/IRD, F-38058 Grenoble, France.
authors.forename: Géraldine
authors.initials: G
authors.lastname: Sarret
authors.affiliation: ISTERRE/CNRS UMR 5275/Université Grenoble Alpes/IRD, F-38058 Grenoble, France.
authors.forename: Adeline
authors.initials: A
authors.lastname: Faure
authors.affiliation: CERMAV/CNRS UPR 5301, F-38041 Grenoble, France.
authors.forename: Christophe
authors.initials: C
authors.lastname: Travelet
authors.affiliation: IBS/CNRS UMR 5075/Université Grenoble Alpes/CEA, F-38044 Grenoble, France.
authors.forename: Dominique
authors.initials: D
authors.lastname: Madern
authors.affiliation: LEHNA/ENTPE/UCB/CNRS UMR 5023, F-69518 Lyon, France.
authors.forename: Cécile
authors.initials: C
authors.lastname: Delolme
mesh_terms: D000327:Adsorption; D001704:Biopolymers / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D004777:Environment; D006863:Hydrogen-Ion Concentration; D008968:Molecular Conformation; D011135:Polysaccharides, Bacterial / Q000737:chemistry*
chemical_list: D001704:Biopolymers; D011135:Polysaccharides, Bacterial; D003300:Copper; C002563:xanthan gum