Natural organic matter is quite rich in carboxylic groups that act as binding sites for cations over a wide pH range. As regards most physical and chemical properties, humic substances can be regarded as high molecular weight polyelectrolytes. Many classes of polyelectrolytes were studied as model molecules of more complicated natural macromolecules; in particular, high molecular weight polycarboxylates represent a very good model for acid-base properties and for interacting capabilities with almost all cations. GantrezTM ligands are synthetic copolymers derivatives of the methyl-vinyl-ether and maleic anhydride or acid, widely employed in different industrial fields, in waste treatment, in pharmaceutical and medical purposes. Some applications are as base polymer for making polymer salts used as bioadhesives. Some GantrezTM ligands are effective in delivery and retention of active ingredients including antimicrobials, flavors, coolants and medicants in toothpaste and mouthwash applications. These copolymers have also a main rule in the production of nanoparticles, since biocompatible and able to increase the bioavailability of some active molecules and the important capacity to control the release of the loaded drugs. Owing to the absence of thermodynamic data in aqueous solution, a systematic speciation study on the behavior of three GantrezTM copolymers of different molecular weights (AN169, S97 and S95) was carried out, determining the critical micelle concentration, the acid-base properties and the ability to form weak complexes with the alkaline cations (Na+ and K+) at different ionic strengths and temperatures. The complexing abilities towards different metal cations (Ca2+, Mg2+, Sn2+, Zn2+, Al3+) in NaCl aqueous solutions at different ionic strengths and temperatures were studied by potentiometric technique. The stability trend of the species was: Sn2+ > Al3+ >> Zn2+ > Ca2+  Mg2+. The interactions with Zn2+ and Sn2+ were also investigated in a solution containing different amounts of fluoride, in order to investigate the formation of mixed metal-ligand’-ligand’’ species. The dependence of the stability constants on ionic strength and temperature was modeled by means of modified Debye-Hückel equations. From the gradient of the stability constants with respect to the temperature, rough enthalpy and entropy change values for the formation of the species were calculated, and results that the entropic contribution is the driving force of reactions. The sequestering ability of the three Gantrez ligands towards the metal ions taken here in into account was evaluated by means of the pL0.5 parameter. This allowed us to highlight a different ability of Gantrez ligands to sequester the metal ions, with differences in some cases of ~3-4 orders of magnitude, promoting these copolymers as chelating agent of metals in natural waters and biological fluids.

USE OF GANTREZ COPOLYMERS AS POTENTIAL CHELATING AGENTS FOR THE SELECTIVE SEQUESTRATION OF METAL IONS

Francesco Crea
2018-01-01

Abstract

Natural organic matter is quite rich in carboxylic groups that act as binding sites for cations over a wide pH range. As regards most physical and chemical properties, humic substances can be regarded as high molecular weight polyelectrolytes. Many classes of polyelectrolytes were studied as model molecules of more complicated natural macromolecules; in particular, high molecular weight polycarboxylates represent a very good model for acid-base properties and for interacting capabilities with almost all cations. GantrezTM ligands are synthetic copolymers derivatives of the methyl-vinyl-ether and maleic anhydride or acid, widely employed in different industrial fields, in waste treatment, in pharmaceutical and medical purposes. Some applications are as base polymer for making polymer salts used as bioadhesives. Some GantrezTM ligands are effective in delivery and retention of active ingredients including antimicrobials, flavors, coolants and medicants in toothpaste and mouthwash applications. These copolymers have also a main rule in the production of nanoparticles, since biocompatible and able to increase the bioavailability of some active molecules and the important capacity to control the release of the loaded drugs. Owing to the absence of thermodynamic data in aqueous solution, a systematic speciation study on the behavior of three GantrezTM copolymers of different molecular weights (AN169, S97 and S95) was carried out, determining the critical micelle concentration, the acid-base properties and the ability to form weak complexes with the alkaline cations (Na+ and K+) at different ionic strengths and temperatures. The complexing abilities towards different metal cations (Ca2+, Mg2+, Sn2+, Zn2+, Al3+) in NaCl aqueous solutions at different ionic strengths and temperatures were studied by potentiometric technique. The stability trend of the species was: Sn2+ > Al3+ >> Zn2+ > Ca2+  Mg2+. The interactions with Zn2+ and Sn2+ were also investigated in a solution containing different amounts of fluoride, in order to investigate the formation of mixed metal-ligand’-ligand’’ species. The dependence of the stability constants on ionic strength and temperature was modeled by means of modified Debye-Hückel equations. From the gradient of the stability constants with respect to the temperature, rough enthalpy and entropy change values for the formation of the species were calculated, and results that the entropic contribution is the driving force of reactions. The sequestering ability of the three Gantrez ligands towards the metal ions taken here in into account was evaluated by means of the pL0.5 parameter. This allowed us to highlight a different ability of Gantrez ligands to sequester the metal ions, with differences in some cases of ~3-4 orders of magnitude, promoting these copolymers as chelating agent of metals in natural waters and biological fluids.
2018
978-88-94952-04-9
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11570/3132127
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