Understanding the Interaction between Trivalent Lanthanide Ions and Stereoregular Polymethacrylates through Luminescence, Binding Isotherms, NMR, and Interaction with Cetylpyridinium Chloride

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• 作者：Ksenija Kogej ; Sofia M. Fonseca ; Jos茅 Rovisco ; M. Em铆lia Azenha ; M. Lu铆sa Ramos ; J. S茅rgio Seixas de Melo ; Hugh D. Burrows
• 刊名：Langmuir
• 出版年：2013
• 出版时间：November 26, 2013
• 年：2013
• 卷：29
• 期：47
• 页码：14429-14437
• 全文大小：363K
• 年卷期：v.29,no.47(November 26, 2013)
• ISSN：1520-5827

文摘

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 ¹H NMR spectra. Comparison with lanthanide鈥揳cetate complexation suggests carboxylate binds in a bidentate fashion, while Ce(III) luminescence quenching suggests an 鈮?: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 Tb³⁺ luminescence lifetime in H₂O and D₂O solutions show complexation is accompanied by loss of 5鈥? 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 Tb³⁺ 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).