Phenothiazine–rhodamine‐based colorimetric and fluorogenic ‘turn‐on' sensor for Zn2+ and bioimaging studies in live cells

A phenothiazine–rhodamine (PTRH) fluorescent dyad was synthesized and its ability to selectively sense Zn²⁺ ions in solution and in in vitro cell lines was tested using various techniques. When compared with other competing metal ions, the PTRH probe showed the high selectivity for Zn²⁺ ions that was supported by electronic and emission spectral analyses. The emission band at 528 nm for the PTRH probe indicated the ring closed form of PTRH, as for Zn²⁺ ion binding to PTRH, the λ_em get shift to 608 nm was accompanied by a pale yellow to pink colour (under visible light) and green to pinkish red fluorescence emission (under UV light) due to ring opening of the spirolactam moiety in the PTRH ligand. Spectral overlap of the donor emission band and the absorption band of the ring opened form of the acceptor moiety contributed towards the fluorescence resonance energy transfer ON mechanism for Zn²⁺ ion detection. The PTRH sensor had the lowest detection limit for Zn²⁺, found to be 2.89 × 10^?8 M. The sensor also demonstrated good sensing application with minimum toxicity for in vitro analyses using HeLa cells.     

Exploration of highly selective fluorogenic ‘on–off' chemosensor for H2PO4− ions: ICT‐based sensing and ATPase activity profiling

Abstract In this study, the recognition contour of Chemosensor 1 was investigated using semiaqueous methanol (X_H, mole fraction = 0.31) for a range of anions and bioactive species. Host–receptor signalling based on the internal charge transfer mechanism for Chemosensor 1 was explored and reported. Structure of Chemosensor 1 and its plausible anion coordination based on hydrogen bonding is complemented with density functional theory. Consequently, we investigated the applicability of the synthesized probe in blood plasma, urine, tap water samples, and for monitoring of ATP in lysosomes by apyrase enzyme.     

A fluorescent chemosensor based on naphthol for detection of Zn2+

A simple naphthol‐based fluorescent receptor 1 was prepared and evaluated for its fluorescence response to heavy metal ions. Receptor 1 exhibits an ‘off‐on‐type’ mode with high selectivity in the presence of Zn²⁺ ion. The selectivity of 1 for Zn²⁺ is the consequence of combined effects of chelation‐enhanced fluorescence (CHEF), C = N isomerization and π–π stacking interaction between the two naphthalene rings. Copyright © 2015 John Wiley & Sons, Ltd.     

2-Amino-5-substituted-1,3,4-oxadiazole as chemosensor for Ni(II) ion detection: antifungal,antioxidant, DNA binding,and molecular docking studies

An oxadiazole derivative 2 was prepared by condensation reaction through cyclization of semicarbazone in the presence of bromine; the structural confirmation was supported by ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopy, Fourier transform-infrared spectroscopy, and liquid chromatography-mass spectrometry. Its sensing ability towards Ni²⁺ ion was examined showing a binding constant of 1.04 × 10⁵ compared with other suitable metal cations (Ca²⁺, Co²⁺, Cr³⁺, Ag⁺, Pb²⁺, Fe³⁺, Mg²⁺, and K⁺) using ultraviolet–visible (UV–vis) and fluorescence spectroscopic studies. The minimum concentration of Ni²⁺ ions and limit of detection was found to be 9.4 μM. A job's plot gave the binding stoichiometry ratio of oxadiazole derivative 2 vs Ni²⁺ ions as 2:1. Furthermore, the intercalative binding mode of oxadiazole derivative 2 with calf thymus DNA was supported by ultraviolet–visible (UV–vis) and fluorescent light, viscosity, cyclic voltammetry, time-resolved fluorescence, and circular dichroism measurements. The molecular docking result gave the binding score for oxadiazole derivative 2 as −6.5 kcal/mol, which further confirmed the intercalative interaction. In addition, the antifungal activity of oxadiazole derivative 2 was also screened against several fungal strains (C. albicans, C. glabrata, and C. tropicalis) by broth dilution and disc diffusion methods. In antioxidant studies, the oxadiazole derivative 2 showed potential scavenging activity against 2,2-diphenyl-1-picrylhydrazyl and H₂O₂ free radicals.     

A new sensitive and selective detection of Ga3+ by thiophene-based ‘turn-on’ fluorescent chemosensor

We designed a thiophene-based fluorescent chemosensor DHTC ((E)-2-([3,5-dichloro-2-hydroxybenzylidene]amino)thiophene-3-carboxamide) for detecting gallium (Ga³⁺). DHTC could probe Ga³⁺ using fluorescence enhancement. The limit of detection for Ga³⁺ by DHTC was 0.39 μM. The binding mode of DHTC to Ga³⁺ was determined as a 1:1 ratio from analysis by Job’s plot and electrospray ionization-mass spectrometry (ESI-MS). In addition, DHTC could selectively detect Ga³⁺ using test kits. The sensing process of Ga³⁺ by DHTC was presented using ultraviolet–visible light titration, Job’s plot, ESI-MS, ¹H nuclear magnetic resonance titration, and density functional theory calculation.     

A colorimetric chiral sensor based on chiral crown ether for the recognition of the two enantiomers of primary amino alcohols and amines

A new colorimetric chiral sensor material consisting of three different functional sites such as chromophore (2,4-dinitrophenylazophenol dye), binding site (crown ether), and chiral barrier (3,3'-diphenyl-1,1'-binaphthyl group) was prepared and applied to the recognition of the two enantiomers of primary amino alcohols and amines. Among five primary amino alcohols and two primary amines tested, the two enantiomers of phenylalaninol show the highest difference in the absorption maximum wavelength (Δλ(max)=43.5 nm) and in the association constants (K(S)/K(R)=2.51) upon complexation with the colorimetric chiral sensor material and, consequently, the two enantiomers of phenylalaninol were clearly distinguished from each other by the color difference.     

Selective fluorescence sensing and quantification of uric acid by naphthyridine-based receptor in biological sample

Naphthyridine-based fluorescent probe H1 was synthesized and characterized for the quantification and selective detection of Uric Acid (UA) in live cell. In presence of UA, H1 forms the specific host-guest complex mainly through intermolecular hydrogen bonding and aromatic stacking which produces “turn-off” fluorescence. The probe and UA is found to be 1:1 stoichiometry on the basis of absorption and fluorescence titrations. The probe H1 has been shown to detect UA up to 0.6 µM at pH 7.4. DFT-TDDFT calculations were performed in order to demonstrate the sensing mechanism and the electronic properties of the receptor-donor complex. The selectivity was evaluated in Vero cells in the presence of UA with other purine derivatives, structurally similar to UA. It was found to exhibit no cytotoxicity effect in tested concentration of H1 and good membrane permeability for the detection of UA in living cell system. The unknown concentration of UA in serum and urine can be measured easily using the fluorescence property of probe H1.     

A new fluorescent chemosensor for cadmium(II) based on a pyrene‐appended piperidone derivative and its β‐cyclodextrin complex

We report, in this article, a piperidin‐4‐one derivative carrying pyrenyl fluorescent reporter groups which acts as a Cd²⁺ ion sensor. The compound is synthesized and characterized using IR and NMR spectral techniques. The compound forms an inclusion complex with β‐cyclodextrin. It selectively binds to Cd²⁺ ions in water and aqueous β‐cyclodextrin media. The stoichiometry of the host–guest complex of the compound with β‐cyclodextrin is 1:2. The ligand–metal ion binding stoichiometry is 1:1 both in water and in β‐cyclodextrin. The linear concentration range of detection of the metal ion is reported. Cyclodextrin complex formation does not affect the metal ion selectivity of the compound.     

Colorimetric detection of oxalate in aqueous solution by a pyrogallol red‐based Cu2+ complex

The pyrogallol red (PR)‐based Cu²⁺ complex was proven to be an effective and selective colorimetric chemosensing ensemble for recognition of oxalate over other anions in a perfect aqueous solution. The addition of oxalate to the PR–Cu²⁺ complex resulted in a colour change from purple to orange colour due to the regeneration of PR by the chelation of oxalate with Cu²⁺, while other anions did not induce any significant colour change. Moreover, it was revealed that no obvious interference was observed during the titrations with oxalate into each other anion. Therefore, the PR–Cu²⁺ complex can be used as a simple and practical colorimetric chemosensor for detecting oxalate.     

A novel chromone Schiff base as Zn2+ turn-on fluorescent chemosensor in a mixed solution

In this study, a novel fluorescent chemosensor 1 based on chromone-3-carboxaldehyde Schiff base was synthesized and featured through nuclear magnetic resonance (NMR) and mass spectra. Spectroscopic investigation indicated that the fluorescent sensor showed high selectivity toward Zn²⁺ over other metal ions and that the detection limit of 1 could reach 10⁻⁷ M. These indicated that 1 acted as a highly selective and sensitive fluorescence chemosensor for Zn²⁺.