A new fluorescent sensor containing glutamic acid for Fe3+ and its resulting complex as a secondary sensor for PPi in purely aqueous solution
A new fluorescence sensor L with benzimidazo[2,1-α]benz[de] isoquinoline-7-one as fluorophore and glutamic acid moiety as receptor was synthesized and characterized. In 100% aqueous buffer (tris 10 mM, pH = 7.4) solution, L showed fluorescence quenching completely in the presence of Fe3+ over other competitive metal ions. It worked based on the Fe3+-induced formation of a 1:1 L-Fe3+ complex, producing a reverse-PET mechanism effect. The quantum yield was determined to be 0.28 and 0.04 for free L and L-Fe3+ complex, respectively. The L-Fe3+ ensemble could be served as a subsequent sensor for PPi due to the strong attraction between Fe3+ and PPi by fluorescence recovery without the interference of the biological competitors including ATP, ADP and PO43-. The LOD calculated by 3σ/s methods was found to be as low as 8 × 10-7 Μ for Fe3+ and 1.53 × 10-6 Μ for PPi. The DFT and a solvent-dependent (H2O) TDDFT calculations also confirmed the proposed reverse-PET mechanism indirectly.