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Bandela A.K.,Bioinorganic Laboratory | Hinge V.K.,Indian Institute of Technology Bombay | Rao C.P.,Bioinorganic Laboratory | Rao C.P.,Indian Institute of Technology Bombay
ACS Applied Materials and Interfaces | Year: 2013

A new benzimidazole-functionalized calix[4]arene receptor (R) was synthesized and characterized. The receptor R shows better selectivity toward trinitrotoluene (TNT) compared to the other nitro explosives in solution, which also retains its effectiveness for solid-phase detection. The chemical interactions of the molecule with different nitro explosive analytes were studied by fluorescence spectroscopy and by a molecular dynamics approach. The molecular dynamics studies show a 1:3 complex between R and TNT, and hence high sensitivity was imparted by fluorescence studies. The detection of explosive vapors in ambient conditions was tested by using a sensitive coating layer of R on an SU-8/CB-based piezoresistive cantilever surface. The developed device showed large sensitivity toward TNT compared to cyclotrimethylenetrinitramine (RDX) and pentaerythritol tetranitrate (PETN) in the solid state at their respective vapor pressures at room temperature. The detection sensitivity of the device was estimated to be 35 mV for TNT at ambient conditions. Moreover, the sensor does not show a response when exposed to humidity. These results demonstrate that R can be used as one of the coating materials for a cantilever for the detection of TNT using piezoresistivity measurement. R can also detect the explosives in solution with high sensitivity and selectivity by fluorescence spectroscopy. © 2013 American Chemical Society.

Areti S.,Bioinorganic Laboratory | Areti S.,Indian Institute of Technology Bombay | Verma S.K.,Bioinorganic Laboratory | Verma S.K.,Indian Institute of Technology Bombay | And 4 more authors.
Analytical Chemistry | Year: 2016

A dansyl derivatized triazole linked glucopyranosyl conjugate (NO2L) has been synthesized and characterized and was used in the present study. The conjugate NO2L releases a fluorescent product upon reaction by Cys-SeH in aqueous PBS buffer by exhibiting a ∼210-fold fluorescence enhancement even in the presence of 20 other amino acids with a minimum detection limit of (1.5 ± 0.2) × 10-7 M. The selectivity of the Cys-SeH to NO2L was further proven by extending the fluorescence study to different other selenium compounds. The role of para-nitrobenzenesulfonyl (pNBS) center in NO2L in the selective recognition of Cys-SeH was confirmed when the fluorescence emission studies were carried out using five different derivatizations possessing two NO2, five fluoro, two fluoro, one fluoro, and no fluoro groups. The nucleophilic substitution reaction of Cys-SeH on NO2L has been clearly demonstrated on the basis of 1H NMR, ESI-MS, and absorption spectroscopy, and the heat changes were monitored by isothermal titration calorimetry. The application potential of NO2L has been demonstrated by studying its selectivity toward Cys-SeH in aqueous PBS buffer, in bovine serum, and on the silica gel surface that lead to minimum detection limits of (25 ± 2), (80 ± 5), and (168 ± 16) ppb, respectively. The biological applicability of NO2L for Cys-SeH was further demonstrated in HepG2 cells by fluorescence microscopy. Thus, NO2L is aqueous soluble and a biologically acceptable probe for Cys-SeH. © 2016 American Chemical Society.

Pathak R.K.,Bioinorganic Laboratory | Hinge V.K.,Indian Institute of Technology Bombay | Mahesh K.,Bioinorganic Laboratory | Rai A.,Indian Institute of Technology Bombay | And 3 more authors.
Analytical Chemistry | Year: 2012

An N,N-Dimethylamine ethylimino-appended triazole-linked calix[4]arene conjugate, L, has been synthesized and characterized, and its Cd 2+ complex has been isolated and characterized. The structure of [CdL] was established by computational calculation using B3LYP/LANL2DZ. Time-dependent density functional theory calculations were performed to demonstrate the electronic properties of [CdL]. This highly fluorescing [CdL] has been used to recognize Cys selectively among the 20 naturally occurring amino acids. [CdL] exhibits a minimum detection limit of 58 ppb for Cys, with reusability and reversibility being imparted to the system during sensing. Thus, the sensing of Cys was well demonstrated using various techniques, viz., fluorescence, absorption, visual color change, electrospray ionization MS, 1H NMR, and live cell imaging experiments. © 2012 American Chemical Society.

Pathak R.K.,Bioinorganic Laboratory | Tabbasum K.,Bioinorganic Laboratory | Rai A.,Indian Institute of Technology Bombay | Panda D.,Indian Institute of Technology Bombay | And 2 more authors.
Analytical Chemistry | Year: 2012

An in situ prepared Zn2+ complex of triazole linked imino-thiophenyl conjugate of calix[4]arene, [ZnL], was demonstrated to be highly fluorescent in HEPES buffer solution. [ZnL] has been used as a chemo-sensing ensemble for the recognition of phosphates in general and pyrophosphates in particular among the eighteen different anions studied. The chemo-sensing behavior of the [ZnL] has been demonstrated through fluorescence, absorption, visual fluorescent color changes, ESI MS, and 1H NMR titrations. Variations in the microstructural features of L, its zinc complex and the complex upon addition of PPi have been demonstrated through atomic force microscopy and transmission electron microscopy. Such studies have been extended to see the permeability of the conjugate into the HeLa cells by fluorescence microscopy. In accession, a reversible "write-read-erase- read" logic gate property of L has been demonstrated through a feedback loop in the presence of Zn2+ and PPi. © 2012 American Chemical Society.

Kumar Pathak R.,Bioinorganic Laboratory | Kumar Hinge V.,Indian Institute of Technology Bombay | Rai A.,Indian Institute of Technology Bombay | Panda D.,Indian Institute of Technology Bombay | And 2 more authors.
Inorganic Chemistry | Year: 2012

Pyridyl-based triazole-linked calix[4]arene conjugates, viz. L 1 and L 2, were synthesized and characterized. These two conjugates were shown to be selective and sensitive for Zn 2+ among the 12 metal ions studied in HEPES buffer medium by fluorescence, absorption, and visual color change with the detection limit of ∼31 and ∼112 ppb, respectively, by L 1 and L 2. Moreover, the utility of the conjugates L 1 and L 2 in showing the zinc recognition in live cells has also been demonstrated using HeLa cells as monitored by fluorescence imaging. The zinc complexes of L 1 and L 2 were isolated, and the structure of [ZnL 1] has been established by single-crystal XRD and that of [ZnL 2] by DFT calculations. TDDFT calculations were performed in order to demonstrate the electronic properties of receptors and their zinc complexes. The isolated zinc complexes, viz. [ZnL 1] and [ZnL 2], have been used as molecular tools for the recognition of anions on the basis of their binding affinities toward Zn 2+. [ZnL 2] was found to be sensitive and selective toward phosphate-bearing ions and molecules and in particular to pyrophosphate (PPi) and ATP among the other 18 anions studied; however, [ZnL 1] was not sensitive toward any of the 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 Zn 2+ from [ZnL 2] by PPi. Thus, [ZnL 2] has been shown to detect PPi up to 278 ± 10 ppb at pH 7.4 in aqueous methanolic (1/2 v/v) HEPES buffer. © 2012 American Chemical Society.

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