Syed Samim Ali

Ratiometric fluorescent and chromogenic chemodosimeter for cyanide detection in water and its application in bioimaging

An indole conjugated thiophene–pyridyl (ITP) sensor for cyanide has been synthesized and characterized using NMR and mass spectroscopy. The selectivity of ITP has been explored in aqueous solution, and the resulting ratiometric fluorescence response toward CN−, among 11 different anions, was studied. The complexation of ITP–CN has been addressed using HRMS, 1H-NMR, and UV-vis spectroscopy. ITP displays substantial dual changes in both its ratiometric emission and absorption spectra, exclusively in the presence of CN− in aqueous solution. This is due to the nucleophilic attack of the indolium group of ITP by CN−, which induces a ratiometric fluorescence change and consequently a large emission shift. DFT/TDDFT calculations were performed in order to demonstrate the electronic properties of ITP and the ITP–CN adduct. The resultant ITP–CN adduct was used as a secondary sensing chemo-ensemble for the detection of cyanophilic metal ion-containing molecules by removing CN− from ITP–CN and regenerating ITP with switch-on red fluorescence. For the practical application of the sensor, test strips based on ITP were made up, which could act as suitable and proficient kits for CN− testing and cell studies.

Colorimetric and ratiometric fluorescent chemodosimeter for selective sensing of fluoride and cyanide ions: tuning selectivity in proton transfer and C–Si bond cleavage

A simple innovative anthraimidazolyldione (LHSi) based colorimetric and ratiometric fluorescent chemodosimeter was designed and synthesized for fluoride and cyanide ion sensing. Upon reaction with the F− and CN− anions in THF solution, probe LHSi shows dramatic color changes from light yellow to red and remarkable ratiometric fluorescence enhancement signals. These properties are mechanistically ascribed to a fluoride/cyanide-triggered deprotonation and C–Si bond cleavage that resulted in a green to red fluorescence.

A BODIPY/pyrene-based chemodosimetric fluorescent chemosensor for selective sensing of hydrazine in the gas and aqueous solution state and its imaging in living cells

A BODIPY-based pyrenebutyrate-linked (BPB) chromogenic and fluorogenic probe was synthesized and characterized for the specific detection of hydrazine. In the presence of hydrazine, BODIPY-based pyrenebutyrate was selectively deprotected, producing switch off meso-phenoxyBODIPY along with a color change from yellow to brown, allowing colorimetric detection of hydrazine by the naked eye. Selectivity experiments proved BPB has excellent selectivity to hydrazine over other environmentally abundant ions and common amine-containing species. Probe BPB was also successfully applied in vapor hydrazine detection into a solid state over other interfering volatile analytes. Furthermore, the probe BPB coated with silica gel TLC plates could act as a visual and fluorimetric probe for hydrazine vapor detection. The probe (BPB) has been shown to detect hydrazine up to 1.87 μM at pH 7.4. DFT and TDDFT calculations were performed in order to demonstrate the sensing mechanism and the electronic properties of the probe and hydrazinolysis product. BPB can also be used for the detection of hydrazine in Vero cells without appreciable interference from other biologically abundant analytes.

A highly sensitive fluorescent probe for detection of hydrazine in gas and solution phases based on the Gabriel mechanism and its bioimaging

A new probe 2-benzo[1,2,5]thiadiazol-4-yl-isoindole-1,3-dione (BTI) based on the Gabriel reaction mechanism was synthesized and characterized for the specific detection of hydrazine with high selectivity against other amines in an organo-aqueous solution. Upon hydrazinolysis of BTI in the presence of hydrazine in a H2O–DMSO (4 : 6, v/v) solution (10 mM HEPES buffer, pH 7.4) at room temperature, the chemosensor produces fluorescent aminobenzthiadiazole with a maximum emission at 498 nm along with a color change from colorless to green, allowing selective colorimetric and fluorometric detection of hydrazine by the naked eye. Probe BTI was also successfully applied in vapor phase hydrazine detection into a solid state over other interfering volatile analytes. Furthermore, the probe BTI coated with silica gel TLC plates could act as a visual and fluorimetric probe for hydrazine vapor detection. The experimental detection limit of hydrazine is 2.9 ppb, which is well below the accepted limit (10 ppb) for hydrazine set by the U.S. Environmental Protection Agency (EPA). DFT and TDDFT calculations were performed in order to demonstrate the sensing mechanism and the electronic properties of probe and hydrazinolysis products. Additionally, probe BTI could also be applied for the imaging of hydrazine in living cells.

Aminomethylpyrene-based imino-phenols as primary fluorescence switch-on sensors for Al3+ in solution and in Vero cells and their complexes as secondary recognition ensembles toward pyrophosphate

Three aminomethylpyrene-based salicyl-imines, viz. L1, L2 and L3 were synthesized and characterized and their recognition of biologically relevant Mn+ ions was studied. These three receptors were shown to be selective and sensitive for Al3+ among the 13 metal ions studied in a HEPES buffer medium by fluorescence, absorption, and visual emission color change with detection limits of 3.60, 2.13 and 2.16 μM, respectively, by L1, L2 and L3. The interaction of Al3+ with the three receptors (L1, L2 and L3) has been further supported by absorption studies, and the stoichiometry of the complex formed (1 : 1) has been established on the basis of emission and ESI-MS. Competitive ion titrations carried out reveal that the Al3+ can be detected even in the presence of other metal ions of bio importance. The structure of the aluminium complexes and their mode of interactions were established by DFT calculations. TDDFT calculations were performed in order to demonstrate the electronic properties of receptors. Microstructural features of L2 and its Al3+ complex have been measured by AFM. Moreover, the utility of the receptors L1, L2 and L3 in showing aluminium recognition in live cells has also been demonstrated using Vero cells as monitored by fluorescence imaging. In situ prepared [AlL1] and [AlL3] complexes were found to be sensitive and selective toward phosphate-bearing ions and molecules and in particular to pyrophosphate (PPi) among the other 15 anions studied; however, [AlL2] was not sensitive toward any of the anions studied.

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

A bisthiocarbonohydrazone-based chemosensor molecule (R1) 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 R1 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 R1 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 R1 to be employed for detection of PA by simple visual inspection in silica-gel-coated thin-layer chromatography plates. Probe R1 has been shown to detect PA up to 3.2 nM at pH 7.4. Microstructural features of R1 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 R1. Furthermore, we have demonstrated the utility of probe R1 for the detection of PA in live Vero cells for ratiometric fluorescence imaging.

Highly sensitive ratiometric fluorescence probes for nitric oxide based on dihydropyridine and potentially useful in bioimaging

Hantzsch dihydropyridine-based ratiometric fluorescent NO probes, viz. PyNO and TPANO, were synthesized and characterized. These two probes were shown to be selective and sensitive for NO among the reactive oxygen/nitrogen species (ROS/RNS) studied in HEPES buffer medium by absorption, fluorescence, and visual color change with detection limits of 2.6 μM and 0.08 μM, respectively. Nitric oxide (NO) reacts with Hantzsch dihydropyridines to give the corresponding intensely fluorescent product pyridines via aerobic oxidation and this is applied to detect nitric oxide (NO). A reaction mechanism for dihydropyridine with NO is proposed in this study. The probe shows good stability over a broad pH range (pH > 4). The structures of the PyNO and TPANO probes have been established by single-crystal XRD. DFT and TDDFT calculations were done to demonstrate the electronic properties of the probes and their aromatic products. Moreover, the utility of the PyNO and TPANO probes in detecting NO in live cells has also been demonstrated using Vero cells as monitored by fluorescence imaging. A study of the detection of endogenously generated NO was also carried out by increasing the incubation time of the probe with lipopolysaccharide (LPS) pre-treated cells and it was found that a highly fluorescent cell image could be obtained.

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

Abstract Carbazole-based thiophene-pyridyl conjugate (L) was synthesised and characterised. The complexation between L 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 L 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 L has been established by single-crystal XRD and that of complexes [ZnL] and [HgL] 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 [ZnL] and [HgL] 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 L from its complexes formed between L and Zn2+ from that formed with Hg2+. Moreover, the utility of the conjugate L in showing the zinc recognition in live cells has also been demonstrated using RAW cells as monitored by fluorescence imaging.

Phenanthroline-fluorescein molecular hybrid as a ratiometric and selective fluorescent chemosensor for Cu2+ via FRET strategy: synthesis, computational studies and in vitro applications

Abstract A FRET-based chemosensor L containing donor phenanthroline and acceptor fluorescein moiety was designed, synthesised and characterised for the ratiometric fluorescent detection of Cu2+ in organo-aqueous solution. Probe L showed high selectivity and excellent sensitivity towards Cu2+ ions by exhibiting both colorimetric and fluorometric changes due to opening of the spirolactum ring of fluorescein upon complexation with Cu2+. In presence of Cu2+ ions, probe L formed L-Cu2+ complex in 1:1 stoichiometric fashion which is established on the basis of Job’s plot and mass spectroscopy. We also performed DFT computational studies to know the binding nature and coordination feature of the complex. Furthermore, fluorescence imaging studies revealed that probe L was cell permeable and could be used to detect intracellular Cu2+ in living cells.

A Michael addition–cyclization-based switch-on fluorescent chemodosimeter for cysteine and its application in live cell imaging

Based on a conjugate addition/intramolecular cyclization sequence, we designed and synthesized a fast response fluorescent probe, BTAC (benzothiazol-azacoumarin), for the discriminative detection of cysteine (Cys). The reaction of cysteine with BTAC results in the cleavage of the acrylate moiety from BTAC, thereby producing BTAC-OH, with a remarkable fluorescence enhancement at 560 nm. The probe exhibits high sensitivity and selectivity toward cysteine over homocysteine and glutathione and the detection limit reached as low as 124 nM for cysteine. The addition of Cys resulted in the color of the solution of BTAC changing from colorless to greenish yellow under the simulation of physiological conditions and BTAC could serve as a “naked-eye” indicator. The structure of BTAC was established by computational DFT (density functional theory) calculation and time dependent density functional theory (TDDFT) calculations were performed to demonstrate the electronic properties of BTAC and its product, BTAC-O−. Finally, the probe was successfully applied for the fluorescence bioimaging of cysteine owing to its photostability and low cytotoxicity.