Lanthanide Ion Interaction with a Crown Ether Methacrylic Polymer, Poly(1,4,7,10-tetraoxacyclododecan-2-ylmethyl methacrylate), as Seen by Spectroscopic, Calorimetric, and Theoretical Studies

Abstract

The interaction between trivalent lanthanide ions and the polymer poly(1,4,7,10-tetraoxacyclododecan-2-ylmethyl methacrylate) (PCR4) containing pendant 1,4,7,10-tetraoxacyclododecane (12crown-4) groups has been studied by various spectroscopic techniques, calorimetry and theoretical calculations. Evidence for the binding of Eu(III), Tb(III), and Ce(III) ions and PCR4 in solution was obtained by the lanthanide-induced 1 H and 13 C NMR shifts and the decay of Tb(III) luminescence. From the isotope effect observed on the decay of luminescence of Tb(III) bound to PCR4 in H2O and D2O solutions, it is suggested that complexation leads to a decrease in the number of water molecules from 8 or 9 to 7. In the solid state, studies by differential scanning calorimetry (DSC) show that the interaction between Ce(III), Tb(III), and Li(I) ions and PCR4 leads to an increase in the glass transition temperature (Tg) of the polymer. Electron paramagnetic resonance (EPR) spectra of Gd(III) in the presence of the polymer are quite similar to those in aqueous solution, while Tb(III) emission is quenched by Ce(III) with nearly the same rate constants in water and aqueous PCR4 solutions, and the Ce(III) emission maxima are only very slightly shifted in the presence of the polymer, all suggesting relatively weak dynamic interaction between the cations and the crown ether. However, isotope effects on the Tb(III) luminescence lifetime confirm complexation. From the lanthanide-induced 1 H and 13 C NMR shifts the stability constants of the 1:1 complexes formed have been calculated for both Tb(III) and Eu(III), yielding values 22.5 and 1.9, respectively. The agreement between the constants calculated from 1 H and 13 C NMR shifts are very good and the low values of the calculated stability constants confirm the weak binding of the lanthanide ions by the crown ether. Results of ab initio calculations are also reported, where the interactions are modeled for 12-crown-4/La(III) complex and bond energies determined.

Stability constants: comparative study of fitting methods. Determination of second‐order complexation constants by23Na and7Li NMR chemical shift titration

“…Equations (10)(11)(12) adjust the chemical shifts in expression (6) so that they are relative to the shift of the free, uncomplexed, metal cation:…”

Interactions between Bio-Based Compounds and Cyclodextrins

“…Consequently, it is suggested that T should be chosen in such a way that its value should be of the same order of magnitude than K 1 À1 [102].…”

Colorimetric anion sensing by polyamide models containing urea-binding sites

“…The results (Table 1) show that the stability constants calculated using both proton signals are equivalent, as expected, confirming the validity of the calculation model. Therefore, gas-phase density functional theory (DFT) calculations at the B3LYP/6-31G* level of theory were performed following a previously described procedure (31,66). The interaction energies of the acetate ion with simplified models of M1, M2…”

“…In previous articles, we reported on the syntheses and characterisations of polymer materials with the following host units: crown ether (19)(20)(21), urea (22)(23)(24)(25) or pyrylium (13,18), along with their interaction with cations (26)(27)(28)(29)(30)(31), anions (13,18) or gas molecules (32). Herein, we report four model polyamide compounds (Scheme 1)…”