Liting Yang

Tridentate lysine-based fluorescent sensor for Hg(II) in aqueous solution.

A novel homoplastic podand fluorescent sensor based on flexible hydrophilic lysine was prepared. Lysine with two dansyl groups-appended at both ends supplied a possibility for a tridentate binding toward Hg(II) and finally resulted in a unique selectivity to Hg(II) over other transition-metal ions with a hypersensitivity (detection limit 2.0 nM) in neutral buffered aqueous solutions. Notably, the coordination of chloride ion to the complex of sensor-Hg(II) brought forth that the trend in the NMR chemical shift for hydrogen and carbon atoms of the sensor was contrary to the findings in the former reports, which shows upfield shifts for the hydrogens and the alkane carbons but downfield shifts for the dansyl carbons, respectively.

A fluorescence reagent for the highly selective recognition and separation of lead ion (II) from aqueous solutions

A new fluorescence reagent, N,N-bi[4(1-pyrene)-butyroyl]-lysine (1) was synthesized. The new fluorescence sensor showed high sensitivity (detection limit up to 20.7 μg L(-1)) and specific selectivity for Pb(2+) over other metal ions examined in aqueous solutions. It could also be used to remove Pb(2+) from aqueous solutions by filtering the insoluble 1-Pb(2+) complex with sufficient reversibility.

Dansyl-8-aminoquinoline as a sensitive pH fluorescent probe with dual-responsive ranges in aqueous solutions

A sensitive pH fluorescent probe based on dansyl group, dansyl-8-aminoquinoline (DAQ), has been synthesized. The probe showed dual-responsive ranges to pH changes, one range from 2.00 to 7.95 and another one from 7.95 to 10.87 in aqueous solution, as it showed pKa values of 5.73 and 8.56 under acid and basic conditions, respectively. Furthermore, the pH response mechanism of the probe was explored successfully by using NMR spectra. The results indicated that the responses of DAQ to pH changes should attribute to the protonation of the nitrogen atom in the dimethylamino group and deprotonation of sulfonamide group.

Pyrene excimer-based fluorescent sensor for detection and removal of Fe(3+) and Pb(2+) from aqueous solutions.

Pyrene excimer usually serves as a chromogenic unit for developing ratiometric fluorescent sensors. But this study used excimer as a large hydrophobic group to regulate the molecular hydrophobicity, and obtained a new fluorescent sensor, N, N-bi[4(1-pyrene)-butyroyl]ornithine (1), for detection and removal of Fe3+ and Pb2+ from aqueous solutions. The coordination of 1 and Fe3+ in the aqueous solution or even pure water forms removable flocculent precipitates, accompanied by obvious fluorescent quenching of emission spectra. In aqueous solutions containing 40% (v/v) acetonitrile, the special responses exhibit a high selectivity and sensitivity to Fe3+ over other common metal ions. However, in aqueous solutions containing 40% (v/v) dimethylsulfoxide, the probe exhibits the analogous fluorescent quenching responses and the removable flocculent precipitates in the presence Fe3+ and Pb2+. These results indicate that the extremely hydrophobic 1-Fe3+/Pb2+ complexes are not only a supplement to the fluorescent sensing of Fe3+ and Pb2+, but also a requirement to the removal of Fe3+ and Pb2+ from aqueous solutions.

A medium-controlled fluorescence dual-responsive probe for Cu2+ and Hg2+ in aqueous solutions.

In this study, we report a histidine‐based fluorescence probe for Cu2+ and Hg2+, in which the amino group and imino group were modified by two common protective groups, 9‐fluorenylmethoxycarbonyl and trityl group, respectively. In a water/methanol mixed solution, the probe displayed a selective fluorescence “turn‐off” response to Cu2+ when the ratio of CH3OH/H2O was higher than 1:1. Specifically, when the solvent is changed to 1:1 methanol/water, the 304 nm fluorescence peak is enhanced, while the 317 nm peak is weakened, upon addition of either Cu2+ or Hg2+ ions. The mechanism for such distinct responses of the probe to Cu2+ and Hg2+ was further clarified by using NMR and molecular simulation. The experiment results indicated that the polarity of solvent could influence the coordination mode of 1 with Cu2+ and Hg2+, and control the fluorescence response as a “turn‐off” or ratiometric probe.