Highly Sensitive and Selective Rhodamine-Based “Off–On” Reversible Chemosensor for Tin (Sn⁴⁺) and Imaging in Living Cells

A structurally characterized new oxo-chromene functionalized rhodamine derivative <b>L1</b> exhibits high selectivity toward Sn⁴⁺ by forming a 1:1 complex, among other biologically important metal ions, as studied by fluorescence, absorption, and HRMS spectroscopy. Complexing with Sn⁴⁺ triggers the formation of a highly fluorescent ring-open form which is pink in color. The sensor shows extremely high fluorescence enhancement upon complexation with Sn⁴⁺, and it can be used as a “naked-eye” sensor. DFT computational studies carried out in mimicking the formation of a 1:1 complex between <b>L1</b> and Sn⁴⁺ resulted in a nearly planar pentacoordinate Sn­(IV) complex. Studies reveal that the <i>in situ</i> prepared <b>L1</b>–Sn complex is selectively and fully reversible in presence of sulfide anions. Further, confocal microscopic studies confirmed that the receptor shows <i>in vitro</i> detection of Sn⁴⁺ ions in RAW cells

Carbazole-driven ratiometric fluorescence turn on for dual ion recognition of Zn²⁺ and Hg²⁺ by thiophene-pyridyl conjugate in HEPES buffer medium: spectroscopy, computational, microscopy and cellular studies

<p>Carbazole-based thiophene-pyridyl conjugate (<b>L</b>) was synthesised and characterised. The complexation between <b>L</b> with Zn²⁺ and Hg²⁺ was studied in HEPES buffer medium by fluorescence, absorption and visual colour change with the detection limit of ~3.7 and ~4.8 μM, respectively. The <b>L</b> detects Zn²⁺ by bringing ratiometric change in the fluorescence signals at 418 and 515 nm, but in the case of Hg²⁺, the signals are observed at 418 and 365 nm, while no new band is observed at 515 nm. The structure of <b>L</b> has been established by single-crystal XRD and that of complexes <b>[ZnL]</b> and <b>[HgL]</b> by density functional theory calculations. TDDFT calculations were performed in order to demonstrate the electronic properties of receptors and their zinc and mercury complexes. The isolated fluorescent complexes <b>[ZnL]</b> and <b>[HgL]</b> were found to be sensitive and selective towards phosphate-bearing ions and sulfide ions, respectively, among the other anions studied. The nanostructural features such as shape and size obtained using atomic force microscopy distinguish <b>L</b> from its complexes formed between <b>L</b> and Zn²⁺ from that formed with Hg²⁺. Moreover, the utility of the conjugate <b>L</b> in showing the zinc recognition in live cells has also been demonstrated using RAW cells as monitored by fluorescence imaging.</p

Installation of efficient quenching groups of a fluorescent probe for the specific detection of cysteine and homocysteine over glutathione in solution and imaging of living cells

<p>Herein, we report the synthesis and characterisation of a new fluorescent probe 4-(7-nitro-benzo[1,2,5]oxadiazol-4-yl)-benzaldehyde (<b>NBOB</b>) installed with quenching groups for highly selective and sensitive sensing of biothiols. The probe itself is non-fluorescent due to the presence of quenching groups and photoinduced electron transfer (PET) process. Thus, sensitivity of the probe towards thiols was significantly improved by quenching effects. <b>NBOB</b> has been shown to exhibit selective reactivity towards cysteine (Cys) and homocysteine (Hcy) over glutathione (GSH) under stoichiometric conditions. The response mechanism was proved by ¹H NMR, LCMS and theoretical calculation. The probe <b>NBOB</b> has been shown to react with Cys present in Vero cells by fluorescence microscopy.</p

Simple Bisthiocarbonohydrazone as a Sensitive, Selective, Colorimetric, and Ratiometric Fluorescent Chemosensor for Picric Acids

A bisthiocarbonohydrazone-based chemosensor molecule (<b>R1</b>) containing a tetrahydro-8-hydroxyquinolizine-9-carboxaldehyde moiety has been synthesized and characterized as a new ratiometric fluorescent probe for picric acid (PA). The ratiometric probe <b>R1</b> is a highly selective and sensitive colorimetric chemosensor for PA. The association between the chemosensor and PA and the ratiometric performance enabled by the key role of excited state intramolecular proton transfer in the detection process are demonstrated. Selectivity experiments proved that <b>R1</b> has excellent selectivity to PA over other nitroaromatic chemicals. Importantly, the ratiometric probe exhibited a noteworthy change in both colorimetric and emission color, and this key feature enables <b>R1</b> to be employed for detection of PA by simple visual inspection in silica-gel-coated thin-layer chromatography plates. Probe <b>R1</b> has been shown to detect PA up to 3.2 nM at pH 7.4. Microstructural features of <b>R1</b> and its PA complex have been measured by a field emission scanning electron microscope, and it clearly proves that their morphological features differ dramatically both in shape and size. Density function theory and time-dependent density function theory calculations were performed to establish the sensing mechanism and the electronic properties of probe <b>R1</b>. Furthermore, we have demonstrated the utility of probe <b>R1</b> for the detection of PA in live Vero cells for ratiometric fluorescence imaging