Synthesis And Property Studies Of Dual-Responsive Probes For Metal Ions Based On Rhodamine B

Molecular/ion recognition is of great importance due to their role in biological systems and host-guest chemistry, the development of highly selective and sensitive chemosensors for metal ions are receiving considerable attention arising from their applications in biology and environment. Fluorescent and chromogenic “bare-eye” methods based on molecular chemosensors have been the most frequently used modes for ions detection attributing to their operational simplicity, high sensitivity and selectivity advantages.Rhodamine framework is an ideal mode for the construction of artificial chemosensors based on changes in the structure between spirocyclic(non-fluorescence, colorless) and open-cycle forms(fluorescence, pink color). Compared with most of the reported probes for single target, the probes for simultaneous detection of multiple targets by adjusting the pH of the system or changing the solvent are relatively rare. In this paper, based on the coordination mechanism resulting from the ring-opening process of spirolactam of probes when binding to metal ions, we designed and synthesized two dual-functional probes for metal ions based on rhodamine B.1. A dual-functional probe L1 based on rhodamine B hydroxamate derivative was synthesized. L1 gives a notable turn-on fluorescent response toward Pb2+ in pH 6.5 HEPES buffer accompanied by the solution emission color change from dark to jacinth and selectively recognizes Cu2+ by naked-eye through the visible color change from colorless to orchid in pH 7.2 HEPES buffer. Competitive experiments showed that probe L1 had high fluorescence sensitivity for Pb2+ and excellent colorimetric selectivity for Cu2+ over many environmental relevant ions. The mechanisms of L1 for sensing Pb2+ and Cu2+ were well demonstrated by a series of experiments and density functional theory calculation. Besides, membrane-permeable property of L1 was testified by microscopic imaging in living cells for the detection of Pb2+.2. A dual-functional probe L2 based on rhodamine B hydroxamate derivative with a NS2 receptor was designed and synthesized. L2 showed highly sensitive colorimetric response to Cu2+ through an obvious color change from colorless to purple in ethanol-water(pH 7.4 HEPES) of 4:1(v/v), making L2 a suitable “bare-eye” indictor for Cu2+. In pure water, L2 gave selectively turn-on fluorescent response to Hg2+(259 fold). Moreover, the response behaviors of L2 toward Cu2+ and Hg2+ were pH independent in a wide range(pH 4.0–9.0). Proof-of-concept experiment demonstrated the potential application of L2 for trace-Hg2+ detection in complicated environmental water samples. More importantly, the turn-on fluorescent probe L2 with good membrane-permeable property was successfully applied to microscopic imaging for the detection of Hg2+ in PC3 cells.