title: Structural effects of soft nanoparticulate ligands on trace metal complexation thermodynamics.
abstract: Metal binding to natural soft colloids is difficult to address due to the inherent heterogeneity of their reactive polyelectrolytic volume and the modifications of their shell structure following changes in e.g. solution pH, salinity or temperature. In this work, we investigate the impacts of temperature- and salinity-mediated modifications of the shell structure of polymeric ligand nanoparticles on the thermodynamics of divalent metal ions Cd(ii)-complexation. The adopted particles consist of a glassy core decorated by a fine-tunable poly(N-isopropylacrylamide) anionic corona. According to synthesis, the charges originating from the metal binding carboxylic moieties supported by the corona chains are located preferentially either in the vicinity of the core or at the outer shell periphery (p(MA-N) and p(N-AA) particles, respectively). Stability constants (KML) of cadmium-nanoparticle complexes are measured under different temperature and salinity conditions using electroanalytical techniques. The obtained KMLis clearly impacted by the location of the carboxylic functional groups within the shell as p(MA-N) leads to stronger nanoparticulate Cd complexes than p(N-AA). The dependence of KMLon solution salinity for p(N-AA) is shown to be consistent with a binding of Cd to peripheral carboxylic groups driven by Coulombic interactions (Eigen-Fuoss mechanism for ions-pairing) or with particle electrostatic features operating at the edge of the shell Donnan volume. For p(MA-N) particulate ligands, a scenario where metal binding occurs within the intraparticulate Donnan phase correctly reproduces the experimental findings. Careful analysis of electroanalytical data further evidences that complexation of metal ions by core-shell particles significantly differ according to the location and distribution of the metal-binding sites throughout the reactive shell. This complexation heterogeneity is basically enhanced with increasing temperature i.e. upon significant increase of particle shell shrinking, which suggests that the contraction of the reactive phase volume of the particulate ligands promotes cooperative metal binding effects.
authors.affiliation: CNRS, LIEC (Laboratoire Interdisciplinaire des Environnements Continentaux), UMR 7360, Vandoeuvre-lès-Nancy F-54501, France and Université de Lorraine, LIEC, UMR 7360, Vandoeuvre-lès-Nancy F-54501, France. elise.rotureau@univ-lorraine.fr.
authors.forename: Elise
authors.identifier: http://orcid.org/0000-0003-1330-5631
authors.initials: E
authors.lastname: Rotureau
authors.affiliation: CNRS, LIEC (Laboratoire Interdisciplinaire des Environnements Continentaux), UMR 7360, Vandoeuvre-lès-Nancy F-54501, France and Université de Lorraine, LIEC, UMR 7360, Vandoeuvre-lès-Nancy F-54501, France. elise.rotureau@univ-lorraine.fr.
authors.forename: Yves
authors.initials: Y
authors.lastname: Waldvogel
authors.affiliation: CNRS, LIEC (Laboratoire Interdisciplinaire des Environnements Continentaux), UMR 7360, Vandoeuvre-lès-Nancy F-54501, France and Université de Lorraine, LIEC, UMR 7360, Vandoeuvre-lès-Nancy F-54501, France. elise.rotureau@univ-lorraine.fr.
authors.forename: José P
authors.initials: JP
authors.lastname: Pinheiro
authors.affiliation: Centro de Quimica Fisica Molecular and IN-Institute of Nanoscience and Nanotechnology, Instituto Superior Tecnico, University of Lisbon, 1049-001 Lisboa, Portugal.
authors.forename: José Paulo S
authors.identifier: http://orcid.org/0000-0002-6394-5031
authors.initials: JP
authors.lastname: Farinha
authors.affiliation: CNRS, LIEC (Laboratoire Interdisciplinaire des Environnements Continentaux), UMR 7360, Vandoeuvre-lès-Nancy F-54501, France and Université de Lorraine, LIEC, UMR 7360, Vandoeuvre-lès-Nancy F-54501, France. elise.rotureau@univ-lorraine.fr.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Bihannic
authors.affiliation: CNRS, LIEC (Laboratoire Interdisciplinaire des Environnements Continentaux), UMR 7360, Vandoeuvre-lès-Nancy F-54501, France and Université de Lorraine, LIEC, UMR 7360, Vandoeuvre-lès-Nancy F-54501, France. elise.rotureau@univ-lorraine.fr.
authors.forename: Romain M
authors.initials: RM
authors.lastname: Présent
authors.affiliation: CNRS, LIEC (Laboratoire Interdisciplinaire des Environnements Continentaux), UMR 7360, Vandoeuvre-lès-Nancy F-54501, France and Université de Lorraine, LIEC, UMR 7360, Vandoeuvre-lès-Nancy F-54501, France. elise.rotureau@univ-lorraine.fr.
authors.forename: Jérôme F L
authors.initials: JF
authors.lastname: Duval