Abstract
Bis(styryl) dye 1 bearing N-phenylazadithia-15-crown-5 ether receptor has been evaluated as a ratiometric fluorescent chemosensor for mercury (II) ions in living cells. In aqueous solution, probe 1 selectively responds to the presence of Hg2+ via the changes in the emission intensity as well as in the emission band shape, which is a result of formation of the complex with 1:1 metal to ligand ratio (dissociation constant 0.56 ± 0.15 µM). The sensing mechanism is based on the interplay between the RET (resonance energy transfer) and ICT (intramolecular charge transfer) interactions occurring upon the UV/Vis (380 or 405 nm) photoexcitation of both styryl chromophores in probe 1. Bio-imaging studies revealed that the yellow (500–600 nm) to red (600–730 nm) fluorescence intensity ratio decreased from 4.4 ± 0.2 to 1.43 ± 0.10 when cells were exposed to increasing concentration of mercury (II) ions enabling ratiometric quantification of intracellular Hg2+ concentration in the 37 nM–1 μM range.
Highlights
Construction of fluorescent chemosensors for heavy and transition metal cations are in the focus of current research [1,2,3]
All experiments were carried out at pH 6.0, which, on the one hand, is rather close to slightly acidic environment inside A549 cells [31], and on the other hand, excludes protonation at the azacrown ether nitrogen atom and related spectral shifts
Protonation at nitrogen atom of N-phenylazadithia-15-crown-5 ether receptor in water solution occurs at pH values lower than 4.0, as it has been shown for the previously synthesized 4-amino-N-aryl-1,8-naphthalimide [32,33], where the N-phenylazadithia-15-crown-5 ether receptor is present as an N-aryl group and not conjugated with the chromophoric part of the molecule
Summary
Construction of fluorescent chemosensors for heavy and transition metal cations are in the focus of current research [1,2,3]. Hg2+ is well-known for its high toxicity and capacity for bioaccumulation. Hg2+ ions can be released in the environment along with the effluent or as a result of atmospheric oxidation of mercury vapor [4]. Further bioaccumulation by microorganisms in water transforms Hg2+ to methylmercury, a form that can be included into the food chain [5,6]. Given that mercury and its compounds are extensively employed in industry and agriculture [8], reliable and sensitive probes for the detection of Hg2+ in biological systems are in demand
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