Imprinting of an ion-pair in presence of mutually compatible anion and cation host monomers leads to polymers showing enhanced ion uptake in competitive high ionic strength buffers.
The use of polymerizable
hosts in anion imprinting has led to powerful
receptors with high oxyanion affinity and specificity in both aqueous
and non-aqueous environments. As demonstrated in previous reports,
a carefully tuned combination of orthogonally interacting binding
groups, for example, positively charged and neutral hydrogen bonding
monomers, allows receptors to be constructed for use in either organic
or aqueous environments, in spite of the polymer being prepared in
non-competitive solvent systems. We here report on a detailed experimental
design of phenylphosphonic and benzoic acid-imprinted polymer libraries
prepared using either urea- or thiourea-based host monomers in the
presence or absence of cationic comonomers for charge-assisted anion
recognition. A comparison of hydrophobic and hydrophilic crosslinking
monomers allowed optimum conditions to be identified for oxyanion
binding in non-aqueous, fully aqueous, or high-salt media. This showed
that recognition improved with the water content for thiourea-based
molecularly imprinted polymers (MIPs) based on hydrophobic EGDMA with
an opposite behavior shown by the polymers prepared using the more
hydrophilic crosslinker PETA. While the affinity of thiourea-based
MIPs increased with the water content, the opposite was observed for
the oxourea counterparts. Binding to the latter could however be enhanced
by raising the pH or by the introduction of cationic amine- or Na
+
-complexing crown ether-based comonomers. Use of high-salt
media as expected suppressed the amine-based charge assistance, whereas
it enhanced the effect of the crown ether function. Use of the optimized
receptors for removing the ubiquitous pesticide glyphosate from urine
finally demonstrated their practical utility.
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