Recognition of Hg²⁺ and Cr³⁺ in Physiological Conditions by a Rhodamine Derivative and Its Application as a Reagent for Cell-Imaging Studies

Abstract

A new rhodamine-based receptor, derivatized with an additional fluorophore (quinoline), was synthesized for selective recognition of Hg(2+) and Cr(3+) in an acetonitrile/HEPES buffer medium of pH 7.3. This reagent could be used as a dual probe and allowed detection of these two ions by monitoring changes in absorption and the fluorescence spectral pattern. In both instances, the extent of the changes was significant enough to allow visual detection. More importantly, the receptor molecule could be used as an imaging reagent for detection of Hg(2+) and Cr(3+) uptake in live human cancer cells (MCF7) using laser confocal microscopic studies. Unlike Hg(ClO(4))(2) or Hg(NO(3))(2) salts, HgCl(2) or HgI(2) failed to induce any visually detectable change in color or fluorescence upon interaction with L(1) under identical experimental conditions. Presumably, the higher covalent nature of Hg(II) in HgCl(2) or HgI(2) accounts for its lower acidity and its inability to open up the spirolactam ring of the reagent L(1). The issue has been addressed on the basis of the single-crystal X-ray structures of L(1)·HgX(2) (X(-) = Cl(-) or I(-)) and results from other spectral studies.

Hg(II)-activated emission “turn-on” chemosensors excited by up-conversion nanocrystals: Synthesis, characterization and sensing performance

“…In the presence of Hg(II) ions, the two chemosensors exhibit bright emissions peaking at 574 nm for 4 and 580 nm for 5, respectively. Here, Hg(II) ions are introduced to make the two chemosensors take the emissive xanthene structure instead of the non-emissive spirolactam one [13][14][15][16].…”

“…Upon the addition of the two chemosensors, the lifetimes slightly decrease to 184 ls for host:4 system and 187 ls for host:5 system, respectively. Here, the energy transfer between the host and the chemosensor is weak, which means that the non-emissive spirolactam structure is ineffective on adsorbing host energy [13,15,16]. In the presence of Hg(II) ions, a xanthene structure is triggered.…”

“…Given above considerations, in this work, two rhodamine derivatives are designed as potential Hg(II) sensing probes owing to their emission ''turn-on'' character activated by Hg(II) ions [13][14][15][16]. An up-conversion NaYF 4 lattice is constructed as the excitation host.…”

5-Hydroxymethylfurfural modified rhodamine B dual-function derivative: Highly sensitive and selective optical detection of pH and Cu2+

“…To the best of our knowledge, a hugely limiting factor of the above rhodamine B probes is that they can detect only the same kind of analytes using fluorescence and UV-Vis absorption spectrometry method at the same time. Furthermore, although dual-function fluorescent chemosensors designed for detecting different metal ions are plentiful [54][55][56][57][58], for pH and metal ions using different optical signals are relatively few [59].…”

A highly selective fluorescent chemosensor for Hg2+ based on a squaraine–bis(rhodamine-B) derivative: Part II

“…Without cations, these rhodamine-based chemosensors exist in a spirocyclic form that is colorless and non-fluorescent. The addition of a specific metal ion leads to opening of the spirocycle via coordination or an irreversible chemical reaction [25][26][27][28][29], which results in the appearance of a pink color or orange fluorescence. In addition, rhodamine-based compounds are ideal candidates for fluorescent sensors because of their good photophysical properties, such as absorption and emission wavelengths extended to the visible region, high fluorescence quantum yields, and large absorption coefficients [30].…”