A multifunctional fluorescence probe for the detection of cations in aqueous solution: the versatility of probes based on peptides.

We synthesized a tetra-functional fluorescence probe based on dansyl and peptide motif, dansyl-Gly-Trp (DGT, 1), that efficiently bound several metal ions and showed distinguishing optical properties. The probe 1 could respond to Hg(2+) with enhanced and blue-shifted fluorescence emission but to Cu(2+) with obvious fluorescence quenching. In addition, 1 was sensitive to pH ranging from 2.0 to 5.0 and precipitated in the presence of Pb(2+) at neutral conditions. The combination of these intrinsic properties with the selective responses to different chemical inputs allows this system to be implemented as an ionic switch. Furthermore, 1 could penetrate the cell membrane and accumulated well in intracellular region. The underlying mechanisms of the probe to different kind of metal ion were explored successfully by using either (1)H NMR, NOESY, electron paramagnetic resonance (EPR) or FT-IR spectra. In addition, to investigate the binding model of 1/Hg(2+) and 1/Cu(2+), simulations were also performed by using density functional theory (DFT) and reasonable binding configurations were achieved for these two complexes.