FRET induced by an ‘allosteric’ cycloaddition reaction regulated with exogenous inhibitor and effectors

A Cu(I) catalyzed Huisgen cycloaddition was engineered to afford products featuring intramolecular excimer formation (exciplex, ) or intramolecular Förster resonance energy transfer (FRET, , ). It was further demonstrated that this reaction could be silenced by ethylenediaminetetraacetic acid (EDTA), which prohibited the reduction of copper(II) sulfate to the catalytically active Cu(I) species by sodium ascorbate. Exogenous transition metal ions such as Zn2+ and Pb2+ were shown to competitively coordinate with EDTA thus releasing free Cu2+ for the subsequent reduction, and consequently restoring the reaction. The modulated catalysis showed metal ion concentration dependence and could be monitored by both HPLC and fluorescence. This study is a demonstration of a new sensing paradigm, where a catalytic organometallic reaction can be used as the signal amplifying module of a sensing application by engineering a regulatory element into the reaction process, analogous to an allosteric enzyme or an allosteric ribozyme system.