X-ray structure of two Schiff bases: TURN-ON sensing of Fe3+ and Al3+ in the HepG2 cell line.

The efficiency of the fluorescence sensitivity of a sensor may be tuned by the modulation of the steric and electronic parameters in the structure. In this study, the thiophenyl Schiff base (E)-N1-(phenyl(pyridin-2-yl)methyl)-N2-(thiophen-2-ylmethylene)benzene-1,2-diamine (HL') exhibited very high selectivity and a sensitive fluorescence enhancement towards Fe3+ with violet emission (λem, 385 nm; LOD, 3.8 nM). On the other hand, the naphthyl Schiff base (E)-1-(((2-((phenyl(pyridin-2-yl)methyl)amino)phenyl)imino)methyl)naphthalen-2-ol (H2L'') exhibited fluorescence sensitivity towards Al3+, showing blue emission (λem, 502 nm; LOD, 3.3 nM) in H2O (HEPES buffer, pH 7.4) medium. The emission enhancement of HL' upon binding to Fe3+ may be considered to be due to the restriction of intramolecular rotation, while the selectivity of H2L'' towards Al3+ may be due to the turn on emission through the restriction of excited state intramolecular proton transfer (ESIPT) and the introduction of chelation enhanced fluorescence (CHEF). Furthermore, DFT computation supported the sensing strategy and the probes were applied for intracellular detection of Fe3+ and Al3+ in HepG2 cell lines.

Aggregation-Induced Emission-Active Hydrazide-Based Probe: Selective Sensing of Al3+, HF2 -, and Nitro Explosives.

(E)-N'-((2-Hydroxynaphthalen-1-yl)methylene)picolinohydrazide (H-PNAP) shows aggregation-induced emission (AIE) strictly in a 90% water/MeOH (v/v) mixture at 540 nm, and the solid-state emission is blue-shifted to 509 nm upon excitation at 400 nm. The AIE activity of H-PNAP is selectively quenched by 2,4,6-trinitrophenol (TNP) and 2,4-dinitrophenol (DNP) out of different nitroaromatic compounds with a limit of detection (LOD) of 7.79 × 10-7 and 9.08 × 10-7 M, respectively. The probe is nonemissive in aqueous medium (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid, HEPES buffer, pH 7.2); however, it shows a strong emission to Al3+ (λem, 490 nm) in the presence of 17 other biological metal ions, and the LOD is 2.09 nM which is far below the WHO recommended value (7.41 mM). The emission of the [Al(PNAP)(NO3)2] complex is quenched by HF2 - (F- and PO4 3- are weak quencher), and the LOD is as low as 15 nM. The probable mechanism of the sensing feature of the probe has been authenticated by 1H nuclear magnetic resonance titration, mass spectrometry, Fourier transform infrared spectroscopy, Benesi-Hildebrand plot, and Job's plot in each case. The probe has some practical applications such as recovery of Al3+ from the drinking water sample, construction of the INHIBIT logic gate, and detection kits for Al3+ and TNP/DNP by simple paper test strips. The probe, H-PNAP, has successfully been applied to the detection of intracellular Al3+ and HF2 - ions in the human breast cancer cell, MDA-MB-468.

Selective detection of trinitrophenol by a Cd(ii)-based coordination compound.

A Cd(ii)-based coordination compound, [CdI2(4-nvp)2] (1), has been synthesized using CdI2 and monodentate N-donor ligand 4-(1-naphthylvinyl)pyridine (4-nvp). The solid-state supramolecular architecture has been characterized by X-ray crystallography. An acute thermal stability and excellent level of phase purity tempted us to use it for material applications. Interestingly, compound 1 exhibits a high selectivity towards trinitrophenol (TNP) in the presence of other nitroaromatics. Therefore, this material may be used for anti-terrorist activities in the detection of explosive materials as well as in the recognition of TNP in analytical laboratories.

An azine-based carbothioamide chemosensor for selective and sensitive turn-on-off sequential detection of Zn(II) and H2PO4-, live cell imaging and INHIBIT logic gate.

Hydrazino-carbothioamide, 1, serves as a turn-on fluorescent chemosensor to Zn2+ and the mixture shows green emission (λem 492) in presence of large number of ions with impressive limit of detection (LOD), 0.59 nM. Intense fluorescence of Zn-complex is selectively turn-off upon adding H2PO4- only to the limit of detection, 26 µM, while other anions remain silent. The sensing mechanism of 1 is established by suppressing the ESIPT of 1 and complexation with Zn2+ (CHEF) is supported by Job's plot, 1H NMR, and HR-MS data. Turn-on-off sequential detection of Zn2+ and H2PO4- also have successfully been employed for the engineering of INHIBIT molecular logic gate. The sensor is non-toxic and has been used in identifying Zn2+ in the intracellular region of African green monkey kidney cells (Vero cells).