Saikat Kumar Manna

Color response of tri-armed azo host colorimetric sensors and test kit for fluoride.

Five new chromogenic tripodal receptors (2a-e) containing electron withdrawing and donating groups appended to the azophenol moiety were synthesized, characterized, and their chromogenic behaviors toward various anions were investigated. These tripodal receptors showed a distinct color change only when treated with fluoride ions in CH(3)CN solution. Yet, other anions such as Cl(-), Br(-), I(-), NO(3)(-), ClO(4)(-), AcO(-), HSO(4)(-), and H(2)PO(4)(-) could not cause any color change. Thus, the receptors 2a-e can be used as a colorimetric chemosensor for the determination of fluoride ion. In addition, (1)H NMR experiments were carried out to explore the nature of interaction between tripodal receptors and fluoride. Finally, analytical application and the use of test strip of the receptor 2b to detect fluoride was also reported.

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.

Unique Fluorogenic Ratiometric Fluorescent Chemodosimeter for Rapid Sensing of CN− in Water

A new benzimidazole-spiropyran conjugate chemosensor molecule (BISP) has been synthesized and characterized by (1)H NMR spectroscopy, mass spectrometry (ESI-MS), and elemental analysis. The two isomeric forms (BISP↔BIMC) were shown to be highly selective and sensitive to CN(-) among the ten anions studied in aqueous HEPES buffer, as shown by fluorescence and absorption spectroscopy and even by visual color changes, with a detection limit of 1.7 μM for BIMC. The reaction of CN(-) with BIMC was monitored by (1)H NMR spectroscopy, high-resolution mass spectrometry (HRMS), UV/Vis measurements, and fluorescence spectroscopy in HEPES buffer of pH 7.4. TDDFT calculations were performed in order to correlate the electronic properties of the chemosensor with its cyanide complex. Further, titration against thiophilic metal ions like Au(3+), Cu(2+), Ag(+), and Hg(2+) with [BIMC-CN] in situ showed that it acts as a secondary recognition ensemble toward Au(3+) and Cu(2+) by switch-on fluorescence. In addition, a reversible logic-gate property of BIMC has been demonstrated through a feedback loop in the presence of CN(-) and Au(3+) ions, respectively. Furthermore, the use of BIMC to detect CN(-) in live cells by fluorescence imaging has also been demonstrated. Notably, test strips based on BIMC were fabricated, which could serve as convenient and efficient CN(-) test kits.

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.

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.

Imino–phenolic–azodye appended rhodamine as a primary fluorescence “off–on” chemosensor for tin (Sn 4+) in solution and in RAW cells and the recognition of sulphide by [AR–Sn]

A new azo-rhodamine based species, AR was developed to act as an ‘off–on’ reversible luminescent probe for Sn4+ detection. The chemosensing behavior of the AR has been demonstrated through fluorescence, absorption, visual fluorescence color changes, ESI MS and 1H NMR titrations. This chemosensor AR shows a significant visible color change and displays a remarkable luminescent switch on (>2300 fold) in the presence of Sn4+ ions. The chemosensor can be used as a ‘naked eye’ sensor. The roles of the fluorophore–photochrome (azodye) dyad platform as well as the iminophenolic binding core in ARs selective recognition of tin have been demonstrated by studying appropriate control molecules. Importantly, AR can selectively recognize Sn4+ in organo-aqueous media in the presence of other cations. The biological applications of AR were evaluated in RAW cells and it was found to exhibit low cytotoxicity and good membrane permeability for the detection of Sn4+. The development of practically viable colorimetric test strips of the chemosensor AR to detect Sn4+ was also reported. It has been possible to build an INHIBIT logic gate for two binary inputs viz., Sn4+ and S2− by monitoring the fluorescence emission band at 582 nm as output.

In Situ Generated AgII-Catalyzed Selective Oxo-Esterification of Alkyne with Alcohol to α-Ketoester: Photophysical Study

An expert and easy one-step catalytic method for the multi O-C coupling of alkyne is developed for the synthesis of valuable α-ketoesters and their chiral analogues, in contrast to the generation of esters by a noncatalytic method. The in situ generated powerful Ag(II) catalyst from AgOTf is the workhorse in the oxidative grafting of alkyne with PhIO and alcohol. The radical mechanism is confirmed in our controlled experiments and UV-vis study.

A pyrene thiazole conjugate as a ratiometric chemosensor with high selectivity and sensitivity for tin (Sn4+) and its application in imaging live cells

A new pyrene thiazole conjugate (PTC) amine fluoroionophore was synthesized and characterized. The single crystal XRD structure of PTC has been established. The fluoroionophore PTC showed selectivity toward Sn4+ by switch on ratiometric fluorescence among the 16 metal ions studied in HEPES buffer medium with a detection limit of 6.93 μM. The interaction of Sn4+ with PTC has been further supported by absorption studies, and the stoichiometry of the complex formed (2 : 1) has been established on the basis of fluorescence and ESI-MS. Competitive ion titrations carried out reveal that the Sn4+ can be detected even in the presence of other metal ions of bio-importance. Moreover, the utility of the fluoroionophore PTC in showing the tin recognition in live cells has also been demonstrated using Vero 76 cells as monitored by fluorescence imaging. The tin complex of PTC was isolated, and the structure and electronic properties of [PTC–Sn] has been established by DFT and TDDFT calculations. The isolated tin complex [PTC–Sn] has been used as a molecular tool for the recognition of anions on the basis of their binding affinities toward Sn4+. [PTC–Sn] was found to be sensitive and selective toward sulphide ions among the other 12 anions studied. The selectivity has been shown on the basis of the changes observed in the emission and absorption spectral studies through the removal of Sn4+ from [PTC–Sn] by S2−.

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.