Synthesis, Spectroscopic, and Analyte-Responsive Behavior of a Polymerizable Naphthalimide-Based Carboxylate Probe and Molecularly Imprinted Polymers Prepared Thereof

Abstract

A naphthalimide-based fluorescent indicator monomer <b>1</b> for the integration into chromo- and fluorogenic molecularly imprinted polymers (MIPs) was synthesized and characterized. The monomer was equipped with a urea binding site to respond to carboxylate-containing guests with absorption and fluorescence changes, namely a bathochromic shift in absorption and fluorescence quenching. Detailed spectroscopic analyses of the title compound and various models revealed the signaling mechanism. Titration studies employing benzoate and Z-l-phenylalanine (Z-l-Phe) suggest that indicator monomers such as the title compound undergo a mixture of deprotonation and complex formation in the presence of benzoate but yield hydrogen-bonded complexes, which are desirable for the molecular imprinting process, with weakly basic guests like Z-l-Phe. Compound <b>1</b> could be successfully employed in the synthesis of monolithic and thin-film MIPs against Z-l-Phe, Z-l-glutamic acid, and penicillin G. Chromatographic assessment of the selectivity features of the monoliths revealed enantioselective discrimination and clear imprinting effects. Immobilized on glass coverslips, the thin-film MIPs of <b>1</b> displayed a clear signaling behavior with a pronounced enantioselective fluorescence quenching dependence and a promising discrimination against cross-analytes