Chelation-enhanced Fluorescence Mechanism Research Articles

Spectral studies of synthetic symmetric syringaldehyde di-Schiff azine with β-cyclodextrin inclusion complexes as a fluorescent probe for the detection of metal ions

In the past few years, organic fluorescent probes play a crucial role in sensor fields due to their magnificent selectivity and detection ability towards various transition metals and alkali ions. Herein, A facile and profitable Schiff-based symmetrical azine derivative of 4,4′ ((1E,1′E)-hydrazine-1,2-diylidenebis(methanylylidene)) bis2,6-methoxyphenyl, dihydrazone or syringaldehyde Azine (SyA) has been synthesized which was rapidly detected dual metal ions (Cu2+ and Pb2+) in different mechanism pathway via Chelation Enhanced Fluorescence Mechanism (CHEF) and Ligand to Metal Charge Transfer (LMCT) approach in optimized physiological conditions under ACN medium. Simultaneously, the interaction mechanism between the SyA and both metals was studied with the help of Benesi-Hildebrand and 1H NMR spectroscopy. Afterward, we prepared the inclusion complex of β-cyclodextrin with SyA (β-CD:SyA) to enhance water solubility and sensing probability. The complex for the observed surprising result was that complexation not only enhanced their properties and detected the new metal ion of Al3+ (may be due to β-CD hydroxyl group interaction with metal ions) without disturbance detection of Cu2+ and Pb2+. The LOD and binding constant values of SyA and β-CD:SyA towards Cu2+, and Al2+ were calculated by absorbance and fluorescence titration profile. From an application point of view, the antibacterial activity and biological activities were evaluated.

Hierarchical Ti-MOF Microflowers for Synchronous Removal and Fluorescent Detection of Aluminum Ions.

Bifunctional luminescence metal-organic frameworks with unique nanostructures have drawn ongoing attention for simultaneous determination and elimination of metal ions in the aqueous environment, but still remain a great challenge. In this work, three-dimensional hierarchical titanium metal-organic framework (Ti-MOF) microflowers were developed by a secondary hydrothermal method for not only highly sensitive and selective detection of Al(III), but also simultaneously efficient decontamination. The resulting Ti-MOF microflowers with a diameter of 5-6 μm consisted of nanorods with a diameter of ∼200 nm and a length of 1-2 μm, which provide abundant, surface active sites for determination and elimination of Al(III) ions. Because of their substantial specific surface area and superior fluorescence characteristics, Ti-MOF microflowers are used as fluorescence probes for quantitative determination of Al(III) in the aqueous environment. Importantly, the specific FL enhancement by Al(III) via a chelation-enhanced fluorescence mechanism can be utilized for selective and quantitative determination of Al(III). The Al(III) detection has a linear range of 0.4-15 µM and a detection limit as low as 75 nM. By introducing ascorbic acid, interference of Fe(III) can be avoided to achieve selective detection of Al(III) under various co-existing cations. It is noteworthy that the Ti-MOF microflowers exhibit excellent adsorption capacity for Al(III) with a high adsorption capacity of 25.85 mg g-1. The rapid adsorption rate is consistent with a pseudo-second order kinetic model. Ti-MOF is a promising contender as an adsorbent and a fluorescent chemical sensor for simultaneous determination and elimination of Al(III) due to its exceptional water stability, high porosity, and intense luminescence.

Zn2+ion responsive fluorescent chemosensor probe of Thiophene-diocarbohydrazide derivatives

A new fluorescent probe of Thiophene- dicarbohydrazide based chemosensor synthesized for Zn2+ion detection and investigated well. It was found that the chemosensor highly emissive when its complexation with Zn2+ ion. This turn-on fluorescence recognition was premeditated in DMSO/H2O (6:4 v/v) medium. The binding constant was calculated and it found to be 1.15 × 104 M−1. The limit of detection (LOD) was calculated to be 1.51 × 10−7 M which is well below the permissible level of Zn2+ (70 μM) in drinking water. The 1:1 binding stoichiometry of the chemosensor HNTCH-Zn2+ complex was intended from Jobs’ plot. The observed fluorescent enhancement turn-on emission can be delineated by chelation enhanced fluorescence mechanism. The reversibility and INHIBIT/IMPLICATION Logic gate behaviour were performed for HNTCH-Zn2+ complex with EDTA accordingly.

Aggregation-Induced Emission-Based Sensing Platform for Selective Detection of Zn2+ : Experimental and Theoretical Investigations.

Fluorescent chemosensors with aggregation induced emission enhancement (AIEE) emerge as promising tools in the field of sensing materials. Herein, we report the design, synthesis and applicability of a Schiff base chemosensor 1-(benzo[1,3]dioxol-4-ylmethylene-hydrazonomethyl)-naphthalen-2-ol (Hbdhn) of AIE characteristics that exhibits highly effective and selective response towards Zn2+ . The sensing effect of Hbdhn was evaluated by means of absorption/emission spectra and corresponding underlying photophysical mechanisms were proposed based on extensive quantum-chemical (TD)DFT calculations. The aggregated states in different DMSO/H2 O ratios and in a presence of Zn2+ were examined by fluorescence lifetime measurements, dynamic light scattering and scanning electron microscopy studies. The bioimaging abilities of Hbdhn were evaluated for Zn2+ in HepG2 cancer cells. The results demonstrate instant, stable in time and reproducible, colorimetric turn-on response with superb selectivity and sensitivity of Hbdhn towards Zn2+ , based on chelation enhanced fluorescence mechanism. AIEE improves further Hbdhn properties, leading to strong, long-lived fluorescence, with appearance of rod-like particles, in 90 % of water in DMSO and only 10 % of water in DMSO in the presence of Zn2+ . All these features combined with successful biomaging studies make Hbdhn one of the most promising candidate for practical applications among recently proposed related systems.

AIE active salicylaldehyde-based hydrazone: A novel single-molecule multianalyte (Al3+ or Cu2+) sensor in different solvents.

A simple asymmetric hydrazone 1 based on salicylaldehyde was designed and prepared, and exhibited an evident aggregation-induced emission (AIE) at a long wavelength of 570 nm in aqueous medium. Probe 1 can selectively sense Al3+ in CH3OH solution through the chelation-enhanced fluorescence mechanism and also recognize Cu2+ via fluorescence quenching in H2O solution through the Cu2+-induced assembly of aggregates. In addition, the probe can be applied for detecting Cu2+ in biological samples.

Facile green synthesis of carbon dots from Pyrus pyrifolia fruit for assaying of Al3+ ion via chelation enhanced fluorescence mechanism

In this work, we synthesized fluorescent carbon dots (CDs) using Pyrus pyrifolia (pear) fruit via hydrothermal method at 180 °C for 6 h without using any further treatment or surface passivating agents. The synthesized CDs possess intense blue fluorescence under UV lamp at 365 nm and exhibit emission peak at 471 nm when excited at 390 nm. Because of specific surface functional groups, the synthesized CDs showed high selectivity to detect Al3+ ion through chelation enhanced fluorescence (CHEF) mechanism. The emission peak intensity of CDs at 471 nm was gradually enhanced with increasing concentration of Al3+ ion, thereby Al3+ ion was quantified by plotting calibration curve over the range of 0.005–50 μM with a detection limit of 0.0025 μM (2.5 nM). The nanoprobe was subsequently evaluated by assaying Al3+ ion from spiked water samples, signifying the utility of nanoprobe for assaying of Al3+ ion real samples. Furthermore, we also demonstrate that the bioimaging ability of CDs for imaging of Bacillus subtilis bacterial cell, suggesting that the nanoprobe can be used for cell imaging applications.

Benzidine based fluorescent probe for the sensitive detection of heavy metal ions via chelation enhanced fluorescence mechanism—A multiplexed sensing platform

Herein, a novel benzidine based fluorescent chemosensor was developed to detect two important heavy metal ions viz. Sn2+ and Pb2+ in microheterogenous medium (DMSO-water,1:9 v/v). Benzidine based fluorescent coordination compound (BCc) was found to be an excellent receptor for the aforementioned ions via significant fluorescent enhancement which may be attributed to the inhibition of charge transfer process and an efficient chelation enhanced fluorescence (CHEF) effect. A good linear relationship between fluorescence intensity and concentrations of Sn2+ and Pb2+ ions was obtained in the range of 0–120 µM with the detection limit of 0.37 µM and 0.32 µM respectively. Interestingly, no interference was observed for 18 other tested metal ions making it highly selective probe for the detection of Sn2+ and Pb2+ ions. The multiplexed sensing ability coupled with prompt metal ion recognizing power, make this sensor specifically attractive for environmental toxicology and biomedical applications.

Fluorogenic detection of Hg2+ and Ag+ ions via two mechanistically discrete signal genres: A paradigm of differentially responsive metal ion sensing

Abstract Selective and specific detection of Hg2+ and Ag+ ions has been enabled by a prudently developed new schiff base probe (L) in a differentially responsive manner of emission intensity. An exciting aspect of the devised ligand is its efficient detection ability of Hg2+ and Ag+ ions by two different fluorometric responses: a TURN-ON signal for Hg2+ and a TURN-OFF response for Ag+. The sensing aptitude of the analytes in concern in 1:1 (v/v) acetonitrile/HEPES Buffer (10 mM, pH 7.4) mixed aqueous medium further make it an encouraging prospect for practical applications. The functioning of two different mechanisms for judicious distinction and detection of the Hg2+ and Ag+ ions has also been successfully validated. Sensing of Hg2+ proceeds via conventional metal chelation enhanced fluorescence mechanism (CHEF) whereas detection of Ag+ follows from the formation of nano-sized aggregates in the working medium.

Fabrication of an acylhydrazone based fluorescence probe for Al3+

A simple acylhydrazone derivative 4-chloro-N′-(pyridin-2-ylmethylene) benzo- hydrazide (CPBH) has been designed to be a fluorescence probe for Al3+. CPBH displays a highly sensitive and selective fluorescence enhancement with Al3+ among various metal ions, due to a reduced intramolecular charge transfer and chelation enhanced fluorescence mechanism. The limit of dection for Al3+ is 0.2μM (5.4ppb), and the linear range is from 2 to 15μM (50–400ppb, c(CPBH)=20μM) in the low concentration while another linear range is from 20 to 80μM (540–2200ppb, c(CPBH)=100μM). The CPBH and Al3+ form a 2:1 coordination complex according to the ESI-MS, Job plots and spectroscopy data. The binding equilibrium constant K is about 4.69×104M−1 and 3.68×104M−1 based on the data from absorption and emission spectra, respectively. To conclude, CPBH can be used as a sensitive and selective fluorescent probe for Al3+.

α-Monoacylated and α,α′- and α,β′-Diacylated Dipyrrins as Highly Sensitive Fluorescence “Turn-on” Zn2+ Probes

With the purpose of developing readily synthesized CHEF (chelation-enhanced fluorescence) type Zn(2+) probes with relatively simple molecular structures and excellent sensing behavior, p-anisoyl chloride was used for the acylation of 5-(pentafluorophenyl)dipyrromethane. Interestingly, the α,β'-diacylated product PS2 with a unique substitution mode was obtained in high yield in addition to the normal α-substituted mono- and diacylated products PS1 and PS3. Further oxidation of PS1-PS3 afforded dipyrrins S1-S3. Crystal structure and (1)H NMR measurements of S2 demonstrate the existence of a pure tautomer, which is consistent with DFT calculations. S1-S3 show highly Zn(2+) selective "turn-on" fluorescence based on a CHEF mechanism by the formation of 2:1 (probe:metal) Zn(2+) complexes. The emission colors can be easily tuned from green to red by changing the dipyrrin substitution modes. Furthermore, these probes demonstrate fast responses and wide applicable pH ranges. Among them, S2 shows the highest Zn(2+) sensitivity, with a detection limit of 4.4 × 10(-8) M.

Reversible fluorescence sensing of Zn2+ based on pyridine-constrained bis(triazole-linked hydroxyquinoline) sensor

Zinc ion (Zn2+) is an important and a most useful biological trace nutrient responsible for the activity of several enzymes. Zn2+ concentrations in the environment as well as in the human body increase beyond permissible limits as a consequence of its mining and widespread industrial applications. Such excess Zn2+ concentrations are toxic to humans and many aquatic organisms. The magnetic inertness and spin paired electronic configuration of Zn2+ makes it hard to detect by common analytical techniques. Therefore, fluorometric detection using chemosensor is the most effective tool for the environmental and biological detection of Zn2+. We have developed a novel pyridine-constrained bis(triazole-linked hydroxyquinoline) ligand as a reversible fluorescent chemosensor for Zn2+. The symmetrical ligand is highly selective for Zn2+ and fluoresces brightly upon complexation compared with other metal ions based on chelation-enhanced fluorescence mechanism. Interestingly, free ligand can be regenerated by treating the ligand–Zn2+ complex with aqueous ammonia.

Ratiometric Zn2+ Fluorescent Sensor and New Approach for Sensing Cd2+ by Ratiometric Displacement

A fluorescent sensor QB, based on quinoline with DPA as receptor, is designed as a ratiometric sensor for Zn(2+) and CHEF (chelation enhanced fluorescence) sensor for Cd(2+). Moreover, another ratiometric signal output for Cd(2+) can be observed when the bound Zn(2+) in the QB-Zn(2+) complex is displaced by Cd(2+). These results demonstrate that QB can act not only as a ratiometirc sensor for Zn(2+) but also as a dual-mode Cd(2+)-selective sensor via the CHEF mechanism and ratiometric displacement.