Urea-Based Imprinted Polymer Hosts with Switchable Anion Preference.

The design of artificial oxyanion receptors with switchable ion preference is a challenging goal in host-guest chemistry. We here report on molecularly imprinted polymers (MIPs) with an external phospho-sulpho switch driven by small molecule modifiers. The polymers were prepared by hydrogen bond-mediated imprinting of the mono- or dianions of phenyl phosphonic acid (PPA), phenyl sulfonic acid (PSA), and benzoic acid (BA) using N-3,5-bis-(trifluoromethyl)-phenyl-Ń-4-vinylphenyl urea (1) as the functional host monomer. The interaction mode between the functional monomer and the monoanions was elucidated by 1H NMR titrations and 1H-1H NMR NOESY supported by molecular dynamic simulation, which confirmed the presence of high-order complexes. PPA imprinted polymers bound PPA with an equilibrium constant Keq = 1.8 × 105 M-1 in acetonitrile (0.1% 1,2,2,6,6-pentamethylpiperidine) and inorganic HPO42- and SO42- with Keq = 2.9 × 103 M-1 and 4.5 × 103 M-1, respectively, in aqueous buffer. Moreover, the chromatographic retentivity of phosphonate versus sulfonate was shown to be completely switched on this polymer when changing from a basic to an acidic modifier. Mechanistic insights into this system were obtained from kinetic investigations and DSC-, MALDI-TOF-MS-, 1H NMR-studies of linear polymers prepared in the presence of template. The results suggest the formation of template induced 1-1 diad repeats in the polymer main chain shedding unique light on the relative contributions of configurational and conformational imprinting.