title: Understanding the interaction between trivalent lanthanide ions and stereoregular polymethacrylates through luminescence, binding isotherms, NMR, and interaction with cetylpyridinium chloride.
abstract: Complexation of isotactic, syndiotactic, and atactic poly(methacrylic acid), PMA, with trivalent lanthanide ions has been studied in water at a degree of neutralization 0.5. Metal ion binding is shown by quenching of cerium(III) fluorescence, enhancement of Tb(III) luminescence, and lanthanide-induced line broadening in the PMA (1)H NMR spectra. Comparison with lanthanide-acetate complexation suggests carboxylate binds in a bidentate fashion, while Ce(III) luminescence quenching suggests an ≈3:1 carboxylate:metal ion stoichiometry, corresponding to charge neutralization. The presence of both free and bound Ce(III) cations in PMA solutions is confirmed from luminescence decays. Studies of Tb(3+) luminescence lifetime in H2O and D2O solutions show complexation is accompanied by loss of 5-6 water molecules, indicating that each bidentate carboxylate replaces two coordinated water molecules. The behavior depends on pH and polyelectrolyte stereoregularity, and stronger binding is observed with isotactic polyelectrolyte. Binding of cetylpyridinium chloride, CPC, in these systems is studied by luminescence, NMR, and potentiometry. NMR and Tb(3+) luminescence lifetime studies show the strongest binding with the isotactic polymer. Binding of surfactant to poly(methacrylate) in the presence of lanthanides is noncooperative, i.e., it binds to the free sites; binding isotherms in the presence of lanthanides are shifted to higher free surfactant concentrations, compared with sodium ions, have lower slopes and show a clear two-step binding mechanism. While CPC readily replaces the Na(+) ions of poly(methacrylate) and binds very strongly (low critical association concentrations), exchange is much more difficult with the strongly bound trivalent lanthanide ions. Effects of tacticity are seen, with surfactant interacting most strongly with isotactic chains in the initial stages of binding, while in the final stages of binding the interaction is strongest with atactic poly(methacrylate).
authors.affiliation: Department of Chemistry and Biochemistry, Faculty of Chemistry and Chemical Technology, University of Ljubljana , Aškerčeva 5, P.O. Box 537, SI-1000 Ljubljana, Slovenia.
authors.forename: Ksenija
authors.initials: K
authors.lastname: Kogej
authors.forename: Sofia M
authors.initials: SM
authors.lastname: Fonseca
authors.forename: José
authors.initials: J
authors.lastname: Rovisco
authors.forename: M Emília
authors.initials: ME
authors.lastname: Azenha
authors.forename: M Luísa
authors.initials: ML
authors.lastname: Ramos
authors.forename: J Sérgio
authors.initials: JS
authors.lastname: Seixas de Melo
authors.forename: Hugh D
authors.initials: HD
authors.lastname: Burrows
mesh_terms: D001665:Binding Sites; D002594:Cetylpyridinium / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007477:Ions / Q000737:chemistry; D028581:Lanthanoid Series Elements / Q000737:chemistry*; D049449:Luminescence; D009682:Magnetic Resonance Spectroscopy; D011109:Polymethacrylic Acids / Q000737:chemistry*; D013237:Stereoisomerism; D013816:Thermodynamics
chemical_list: D007477:Ions; D028581:Lanthanoid Series Elements; D011109:Polymethacrylic Acids; C030613:polymethacrylic acid; D002594:Cetylpyridinium