Synthesis and photophysical investigation of Schiff base as a Mg2+ and Zn2+ fluorescent chemosensor and its application

In view of the fluorescent switching properties and anti-fatigue properties of diarylethene, a diarylethene fluorescent chemosensor for the immediate detection of zinc ion (Zn²⁺ ) and magnesium ion (Mg²⁺ ) in acetonitrile was synthesized in this article. The structure of 1o was determined by performing spectroscopy and elemental analysis. The presence of Zn²⁺ or Mg²⁺ made the chemosensor 1o show an obvious "turn-on" fluorescent signal (bright yellow-green for Mg²⁺ and bright cyan for Zn²⁺ ). The fluorescent change caused by the 1:1 binding of 1o and Zn²⁺ or Mg²⁺ might be due to hindering the excited-state intramolecular proton transfer (ESIPT) process, which were bolstered by Benesi-Hildebrand analysis, Job's plot curves, proton nuclear magnetic resonance (¹ H-NMR) titration and mass spectrometry. The limits of detection were acquired from the standard curve plots for Mg²⁺ at 44.6 nM and for Zn²⁺ at 14 nM. Based on the fluorescent behaviors, a logic gate was constructed with the emission intensity at 528/518 nm as output signal, the ultraviolet-visible (UV-vis) lights, Mg²⁺ /Zn²⁺ and EDTA as input signals. Exogenous Zn²⁺ and Mg²⁺ fluorescent bioimaging were performed on Hela cells with 1o, indicating its potential application in biodiagnostic analysis. In particular, 1o was manufactured into test paper, and Zn²⁺ or Mg²⁺ can be conveniently, efficiently and qualitatively identified by the fluorescent color variation of the test strips.

ESIPT-AIE active Schiff base based on 2-(2'-hydroxyphenyl)benzo-thiazole applied as multi-functional fluorescent chemosensors

Three AIE (aggregation-induced emission)-ESIPT (excited-state intramolecular proton transfer) active 2-(2-hydroxyphenyl)benzothiazole derivatives, HL¹, HL² and HL³ with one, two and three rotatable phenyl groups, were obtained and characterized. Their AIE properties in THF/HEPES solution were investigated in detail. HL² shows the best AIE performance with 71-fold fluorescence enhancement, while HL³ only shows a 9-fold enhancement. With the AIE property, HL¹ and HL² could act as fluorescence chemosensors to detect Cu²⁺ ions via the "turn off" mode in THF/HEPES media. With the ESIPT property, HL¹ and HL² could also detect Zn²⁺ ions via the "turn on" mode in EtOH/HEPES media. During the detection process, both demonstrate rapid response and high contrast before and after the addition of metal ions. The species formed in the detection system were investigated. The results of X-ray single-crystal diffraction confirm that Zn²⁺ is coordinated with the oxygen atom and Schiff base nitrogen atom instead of the benzothiazole nitrogen atom in the tetrahedron geometry. Moreover, the chemosensors were successfully constructed into handy fluorescence test papers for Cu²⁺ and Zn²⁺ detection.

Acenaphtoquinoxaline as a selective fluorescent sensor for Hg (II) detection: experimental and theoretical studies

A new fluorescent chemosensor based on quinoxaline was successfully synthesized through a facile and green catalytic reaction of ortho-phenylenediamine (O-PDA) and acenaphthylene-1,2-dione in the presence of SBA-Pr-SO3H. Prepared a "switch-off" quinoxaline-based receptor to recognized Hg2+ ion in high selectively and, without any interference from other metal ions, was developed. The photophysical behavior of this fluorophore was studied in acetonitrile by using fluorescence spectra. The fluorescence properties of several cations to acenaphtoquinoxaline were investigated in acetonitrile, and the competition test displayed that the probe fluorescence changes were specific for Hg2+ ion. The obtained results have shown high selectivity and sensitivity only for Hg2+. Also, the detection limit was as low as 42 ppb, and a top linear trend was observed between the concentration of Hg2+ ions and fluorescence intensity. The binding stoichiometry between chemosensor L and Hg2+ was found to be 1:1. Moreover, a computational study was performed to obtain an electronic description of the fluorescence emission and quenching mechanisms. The optimized structures and binding mechanisms were supported with a high correlation and agreement by spectroscopy and DFT calculations.

Synthesis of 1,2-disubstituted benzimidazoles using an aza-Wittig-equivalent process

Based on an aza-Wittig-equivalent process, a novel synthetic approach for 1,2-disubstituted benzimidazoles has been successfully designed, which provides mild reaction conditions and excellent yields.

Photoinduced formation of stable Ag-nanoparticles from a ternary ligand-DNA-Ag+ complex

The irradiation of a ternary complex between an intercalator crown-ether conjugate, double-stranded DNA, and Ag⁺ ions leads to the formation of stable Ag nanoparticles.

2-Aminotryptanthrin derivative with pyrene as a FRET-based fluorescent chemosensor for metal ions

1-(2-tryptanthrinylaminoacetoxy)-14-(1-pyrenecarboxy)-3,6,9,12-tetraoxatetradecane (T2NH-P5P) was synthesized as a fluorescent chemosensor for metal ions. We investigated the metal-ion recognition of T2NH-P5P by separately adding Mg(2+), Ca(2+), Ba(2+), Fe(2+), Fe(3+), Co(2+), Ni(2+), Cu(2+), Ag(+), Zn(2+), Cd(2+), Hg(2+), Al(3+), and Pb(2+) in an acetonitrile solution. When using excitation at 325 nm, which corresponds to the absorption of the pyrene unit of T2NH-P5P, emission at 600 nm, from the 2-aminotryptanthrin unit, was observed, indicating that intramolecular fluorescence resonance energy transfer (FRET) occurs in T2NH-P5P (FRET-on). However, when Fe(2+), Fe(3+), Ni(2+), Cu(2+), Cd(2+), Hg(2+), and Al(3+) were added to an acetonitrile solution of T2NH-P5P, the behavior changed from FRET-on to FRET-off, which means that the fluorescence of 2-aminotryptanthrin was quenched, whereas that of the pyrene group was revived (FRET-off). Especially, this behavior was remarkable for Fe(2+), Fe(3+), Cu(2+), and Hg(2+). T2NH-P5P is suitable for use as a fluorescent chemosensor for Fe(2+), Fe(3+), Cu(2+), and Hg(2+).

Highly sensitive, selective, and rapid fluorescence Hg2+ sensor based on DNA duplexes of poly(dT) and graphene oxide

Coupling T base with Hg(2+) to form stable T-Hg(2+)-T complexes represents a new direction in detection of Hg(2+). Here a graphene oxide (GO)-based fluorescence Hg(2+) analysis using DNA duplexes of poly(dT) that allows rapid, sensitive, and selective detection is first reported. The Hg(2+)-induced T(15)-(Hg(2+))(n)-T(15) duplexes make T(15) unable to hybridize with its complementary A(15) labelled with 6'-carboxyfluorescein (FAM-A(15)), which has low fluorescence in the presence of GO. On the contrary, when T(15) hybridizes with FAM-A(15) to form double-stranded DNA because of the absence of Hg(2+), the fluorescence largely remains in the presence of GO. A linear range from 10 nM to 2.0 μM (R(2) = 0.9963) and a detection limit of 0.5 nM for Hg(2+) were obtained under optimal experimental conditions. Other metal ions, such as Al(3+), Ag(+), Ca(2+), Ba(2+), Mg(2+), Zn(2+), Mn(2+), Co(2+), Pb(2+), Ni(2+), Cu(2+), Cd(2+), Cr(3+), Fe(2+), and Fe(3+), had no significant effect on Hg(2+) detection. Moreover, the sensing system was used for the determination of Hg(2+) in river water samples with satisfactory results.

Nano-C60 as a novel, effective fluorescent sensing platform for mercury(II) ion detection at critical sensitivity and selectivity

The present communication demonstrates the use of water-soluble nano-C(60) as a novel, effective fluorescent sensing platform for Hg(2+) detection for the first time. This sensing system achieves a detection limit as low as 500 pM and exhibits excellent selectivity.

A selective oligonucleotide-based luminescent switch-on probe for the detection of nanomolar mercury(II) ion in aqueous solution

An oligonucleotide-based luminescent platinum(II) switch-on probe has been developed for selective detection of nanomolar Hg(2+) ions.