Na LI, Chunwei YU, Yuxiang JI, JUN ZHANG

Characterization of a Cu$^{2+}$-selective fluorescent probe derived from rhodamine B with 1,2,4-triazole as subunit and its application in cell imaging

A rhodamine B derivative containing 1,2,4-triazole as subunit was characterized as an "off-on" type Cu$^{2+}$-selective fluorescent probe. It exhibited high selectivity and sensitivity for Cu$^{2+}$ in ethanol-water solution (9:1, v:v, pH 7.0, 20 mM HEPES) and underwent ring opening. A prominent fluorescence enhancement at 570 nm was observed in the presence of Cu$^{2+}$ with the change in the absorption spectrum, and a 1:1 metal-ligand complex was formed. With the optimized experimental conditions, the probe exhibited a dynamic response range for Cu$^{2+}$ from 8.0 $\times $ 10$^{-7}$ to 7.5 $\times $ 10$^{-6}$ M with a detection limit of 2.3 $\times $ 10$^{-7}$ M in ethanol-water solution (9:1, v:v, pH 7.0, 20 mM HEPES). Its application in Cu$^{2+}$ imaging in living cells was also studied.

Anahtar Kelimeler:

Fluorescent probe, rhodamine B, triazole, Cu$^{2+}$

Characterization of a Cu2+ -selective fluorescent probe derived from rhodamine B with 1,2,4-triazole as subunit and its application in cell imaging

A rhodamine B derivative containing 1,2,4-triazole as subunit was characterized as an “off–on” type Cu 2+ - selective fluorescent probe. It exhibited high selectivity and sensitivity for Cu 2+ in ethanol–water solution (9:1, v:v, pH 7.0, 20 mM HEPES) and underwent ring opening. A prominent fluorescence enhancement at 570 nm was observed in the presence of Cu 2+ with the change in the absorption spectrum, and a 1:1 metal–ligand complex was formed. With the optimized experimental conditions, the probe exhibited a dynamic response range for Cu 2+ from 8.0 × 10 −7 to 7.5 × 10 −6 M with a detection limit of 2.3 × 10 −7 M in ethanol–water solution (9:1, v:v, pH 7.0, 20 mM HEPES). Its application in Cu 2+ imaging in living cells was also studied.

Keywords:

Fluorescent probe, rhodamine B, triazole, Cu$^{2+}$,

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In conclusion, a novel Cu2+-selective rhodamine B fluorescent probe containing 1,2,4-triazole as subunit was constructed. Cu
could induce spirolactam ring opening of the rhodamine unit and achieved an “off–on” effect. The probe P can detect as low as 2.3× 10 −7
M Cu2+. In addition, the probe P was successfully used to detect Cu2+in living cells. 3. Experimental
Reagents and instruments
All reagents and solvents are of analytical grade and used without further purification. The metal ions and anions salts employed were NaCl, KCl, CaCl2·2H2O, MgCl2·6H2O, Zn(NO3)2·6H2O, PbCl2, CdCl2, CrCl3·6H2O, CoCl·6H2O, NiCl·6H2O, HgCl2, CuCl2·2H2O, FeCl3·6H2O, and AgNO3.
Fluorescence emission spectra were conducted on a Hitachi 4600 spectrofluorometer. UV-Vis spectra were obtained on a Hitachi U-2910 spectrophotometer. Nuclear magnetic resonance (NMR) spectra were measured with a Bruker AV 400 instrument and chemical shifts are given in ppm from tetramethylsilane (TMS). Mass spectra (MS) were recorded on a Thermo TSQ Quantum Access Agilent 1100.
Synthesis of compound P
Compounds 1 and 2 were synthesized as reported.18,19
Compounds 1 (0.13 g, 1.0 mM) and 2 (0.496 g, 1.0 mM) were mixed in ethanol (40 mL). The reaction mixture was stirred at 80 ◦
C for 4 h. After the reaction was finished, the solution was removed under reduced pressure. The precipitate so obtained was filtered and purified with silica gel column chromatography (petroleum ether/acetic ether = 5:1, v:v) to afford P as yellow solid. Yields: 83.4%. MS (ES+) m/z: 609.27 [M + H]+. 1H NMR ( δ ppm, d 6-DMSO):
General spectroscopic methods
Metal ions and chemosensor P were dissolved in deionized water and DMSO to obtain 1.0 mM stock solutions, respectively. Before spectroscopic measurements, the solution was freshly prepared by diluting the high concen- tration stock solution with the corresponding solution. For all measurements, excitation/emission slit widths were 5/10 nm and excitation wavelength was 550 nm.