Chelation-enhanced Fluorescence Effect Research Articles

Aluminium(III) sensing by pyridoxal hydrazone utilising the chelation enhanced fluorescence effect

A chemosensor based on pyridoxal hydrazone was prepared in a two-step synthesis with a high yield. Chemosensor 1 exhibits high sensitivity and anti-disturbance for aluminium(III) ions among other biologically important metal ions. Aluminium(III) ion sensing was accomplished using a chelation enhanced fluorescence (CHEF) effect and photoinduced electron transfer (PET) inhibition. Chemosensor 1 shows a high association constant (1×105M−1) towards aluminium(III) ions in DMSO-H2O (9:1, v/v). The detection limit of the fluorescence response of chemosensor 1 for aluminium(III) ions is 6×10−7M.

A Highly Selective and Sensitive Fluorescent Chemosensor for Aluminum Ions Based on Schiff Base.

An efficient "off-on" type fluorescent chemosensor, (E)-N'-(4-(diethylamino)-2-hydroxybenzylidene)-2-hydroxybenzohydrazide (H 2 L), based on Schiff base for the determination of Al3+ has been designed, synthesized, and evaluated. Upon treated with Al3+, the fluorescence of H 2 L was enhanced 45-fold due to the chelation-enhanced fluorescence (CHEF) effect based on the formation of a 1:1 complex between the chemosensor and Al3+. Other metal ions, such as Na+, K+, Mg2+, Ca2+, Cu2+, Ga3+, Zn2+, Cr3+, Cd2+, Ag+, Fe3+, In3+, Mn2+, Pb2+, Co2+, and Ni2+ had little effect on the fluorescence. The results demonstrate that the chemosensor H 2 L has stronger affinity with Al3+ than other metal ions. The detection limit of H 2 L for sensing Al3+ is 3.60×10-6M in EtOH-H2O (3:7, v/v) solution. And the recognizing behavior has been investigated both experimentally and computationally.

A New Sensitive and Selective Off-On Fluorescent Zn2+ Chemosensor Based on 3,3',5,5'-Tetraphenylsubstituted Dipyrromethene.

3,3',5,5'-Tetraphenyl-2,2'-dipyrromethene was described as a highly sensitive and selective Off-on fluorescent colorimetric chemosensor for Zn2+ based on the chelation-enhanced fluorescence (CHEF) effect. The reaction of dipyrromethene ligand with Zn2+ induces the formation of the [ZnL2] complex, which exhibits the increasing fluorescence in 120 fold compared with ligand in the propanol-1/cyclohexane (1:30) binary mixture. The Zn2+ detection limit was 1.4×10-7 М. The UV-Vis and fluorescence spectroscopic studies demonstrated that the dipyrromethene sensor was highly selective toward Zn2+ cations over other metal ions (Na+, Mg2+, Co2+, Ni2+, Fe3+, Cu2+, Mn2+, Cd2+ and Pb2+), excluding Hg2+.

A Bis-Quinoline Appended Azobenzene Based Naked Eye Sensor for Selective Detection of Cd2+ Ion

A new azobenzene chromophore (AZQU), appended with a bis-quinoline unit as a turn-on chemosensor for selective detection of Cd2+ ions, has been designed and synthesized. The fluorescent receptor AZQU has an excellent selectivity and sensitivity towards Cd2+ ions over other metal ions in CH3CN:H2O (80:20, v/v) solution. AZQU is red colored and non-fluorescent in the absence of Cd2+ ions, but upon addition of Cd2+ ions it turns colorless with appreciable fluorescence. This “off–on” type signaling behavior is attributed to the CHEF (chelation-enhanced fluorescence) effect of the quinoline unit and the change in color from red to yellow occurs by an ICT process with Cd2+. The association constant for AZQU + Cd2+ was calculated to be 1.68 × 105 L·mol−1 with binding in the 1:1 stoichiometric ratio.

A fluorescent carboxamide ligand, having combined ionophore/fluorophore moieties, exhibiting “On-Off” switching toward Zn2+ ion

A carboxamide ligand (N-(quinolin-8-yl)quinoline-2-carboxamide) (Hqcq) has been synthesized by a highly efficient procedure using the ionic liquid TBAB as an environmentally benign reaction medium. Selective “On-Off” switching behavior of the fluorescent ligand (Hqcq) in acetonitrile has been studied for Zn(II) ion. The Hqcq was weakly emissive in the absence of metal ions, but fluorescence intensity was increased significantly upon addition of two equivalent of Zn(II) ion. This enhancement was correlated to Zn(II) coordination of the qcq−, producing an efficient chelation-enhanced fluorescence (CHEF) effect. Other interfering elements such as Cd(II) and Hg(II), show either no or slight change in the fluorescence intensity under similar experimental conditions.

Novel Turn-On Fluorescent Sensors with Mega Stokes Shifts for Dual Detection of Al3+and Zn2+

A series of bishydrazide compounds have been developed for selective turn-on detection of Al3+ cation, based on metal chelation-enhanced fluorescence (CHEF) effects that inhibit the nonradiative PET and ESIPT processes. In aqueous solution, Al3+ selectively induces strong fluorescence of these compounds with large Stokes shifts up to ∼133 nm and emission colors varying from blue to orange. In the solid phase, both Al3+ and Zn2+ give apparent fluorescence which is simultaneously detected based on chromatographic separation.

A Chromone-Derived Schiff-Base Ligand as Al(3+) "Turn on" Fluorescent Sensor: Synthesis and Spectroscopic Properties.

In this study, a novel chromone-derived Schiff-base ligand called 6-Hydroxy-3-formylchromone (2'-furan formyl) hydrazone (HCFH) has been designed and synthesized as a "turn on" fluorescent sensor for Al(3+). This sensor HCFH showed high selectivity and sensitivity towards Al(3+) over other metal ions investigated, and most metal ions had nearly no influences on the fluorescence response of HCFH to Al(3+). Additionally, the significant enhancement by about 171-fold in fluorescence emission intensity at 502 nm was observed in the presence of Al(3+) in ethanol, and it was due to the chelation-enhanced fluorescence (CHEF) effect upon complexation of HCFH with Al(3+) which inhibited the photoinduced electron transfer (PET) phenomenon from the Schiff-base nitrogen atom to chromone group. Moreover, this sensor formed a 1 : 1 complex with Al(3+) and the fluorescence response of HCFH to Al(3+) was nearly completed within 1 min. Thus, this sensor HCFH could be used to detect and recognize Al(3+) for real-time detection.

A triazole Schiff base-based selective and sensitive fluorescent probe for Zn2 +: A combined experimental and theoretical study

A triazole-Schiff base, 4-(5-Chloro-2-hydroxybenzylideneamino)-1H-1,2,4-triazole-5(4H)-thione (HL), exhibits the high selectivity and sensitivity for Zn2+ in the fluorescence spectrometry over other common metal ions, especially Cd2+ in DMSO:H2O (1:9, v/v) solution. A 1:1 binding ratio of Zn2+/L for the complex has been obtained by Uv–Vis titration experiments and Job's plot with the detection limit of 51nmol/L. The coordination mode of the complex in solution was further confirmed by density functional theory (DFT) calculations. Time-dependent density functional theory (TD-DFT) calculations indicate that a chelation-enhanced fluorescence (CHEF) effect occurs in the process of detecting Zn ion.

Design of a highly sensitive and selective bulk optode based on fluorescence enhancement of N,N′-bis-(1-hydroxyphenylimine)2,2′-pyridil Schiff base: Monitoring of zinc(II) ion in real samples and DFT calculation

A novel highly sensitive and selective optical chemical sensor (optode) was fabricated for the determination of Zn2+ ion. The optical sensor was prepared by incorporating recently synthesized ionophore, HPP: N,N′-bis-(1-hydroxyphenylimine)2,2′-pyridil, sodium tetraphenylborate (NaTPB) as an anionic additive, dibutyl phthalate (DBP) as a plasticizer in a poly(vinylchloride) membrane. The novel ionophore was synthesized by conventional condensation reaction between 2,2′-pyridil and 2-aminophenol and characterized using different spectroscopic techniques. The response of the sensor is based on the strong fluorescent emission enhancement of ionophore HPP upon binding to Zn2+ ions. This can be correlated to the efficient Zn2+ binding of HPP which promotes a good chelation-enhanced fluorescence (CHEF) effect and prevents the photoinduced electron transfer (PET) effect. The effect of several parameters in determining Zn2+ were studied and optimized. Under the optimum conditions, a good linear relationship between the fluorescence response and concentration of Zn2+ was achieved with high sensitivity within a wide range from 1.0×10−10 to 1.0×10−2M and a limit of detection (LOD) 6.3×10−11M. Furthermore, the present probe exhibited a high selectivity for Zn2+ over other metal ions and was successfully assessed for determination of Zn2+ ions in real samples including some food and biological samples with satisfactory results. Theoretical calculations were employed to support the sensing mechanism of the sensor toward Zn2+.

New “on–off” optical probe based on Schiff base responding to Al3+ ions: Logic gate application

Two extremely sensitive spectrophotometric receptors namely as N,N′-bis(o-hydroxyacetophenone)-m-phenylenediamine (P) and N-(o-hydroxyacetophenone)-o-phenylenediamine (Q), based on imine-hydroxy moieties as a binding and signalling unit, have been synthesized and characterized by means of various spectroscopic techniques. The receptors show an instantaneous response towards Al3+ ions through selective fluorescent enhancement, attributed to chelation enhanced fluorescence effects. The spectrophotometric behavior of the receptors in the presence of Al3+ ions was significantly compared with those of other metal cations tested. The synthesized receptors worked effectively in the physiological pH range. Further, the integrated logic gate nature based on Al3+ and EDTA titration, through the emission mode has also been described. Thus, these receptors offer a novel turn-on fluorescent approach for the selective detection of Al3+ ions qualitative as well as quantitative in biological and environmental samples.

A α-cyanostilbene-modified Schiff base as efficient turn-on fluorescent chemosensor for Zn 2 +

A novel Schiff base derivative (Z)-3-(4-(hexyloxy)phenyl)-2-(4-((E)-2-hydroxybenzylidene amino)phenyl)acrylonitrile (L) was designed, synthesized and characterized. L was used as a Zn2+ selective, turn-on, fluorescent chemosensor with a detection limit of 0.1 μM in DMF. 1:1 stoichiometric complex formation of L wih Zn2+ was confirmed through fluorescent titration experiments and Job’s plot. The enhancement of fluorescence intensity of L with addition of Zn2+ is the consequence of the inhibited isomerization of the C=N bond, namely chelation-enhanced fluorescence (CHEF) effect. α-Cyanostilbene-modified Schiff L was designed as a highly selective and sensitive zinc chemosensor. The complexation of L with Zn2+ enhanced the fluorescence intensity. This chemosensor could distinguish clearly Zn2+ from Cd2+, a frequently encountered trouble in the design for the Zn2+ fluorescent probes.

A water-soluble carboxylic-functionalized chemosensor for detecting Al(3+) in aqueous media and living cells: Experimental and theoretical studies.

A new water-soluble carboxylic-functionalized chemosensor 1 was designed and synthesized. 1 exhibited the selective fluorescence enhancement toward aluminum ions with a 1:1 complexation stoichiometry in aqueous solution. The detection limit (24nM) of 1 for Al(3+) is about two order lower than the WHO guideline (7.41μM) for the drinking water. 1 was successfully applied to living cells and real samples for detecting Al(3+). Moreover, the sensing mechanism originated from the inhibited excited-state intramolecular proton transfer (ESIPT) process and the chelation-enhanced fluorescence (CHEF) effect, as supported by theoretical calculations.

A real-time fluorescent sensor specific to Mg2+: crystallographic evidence, DFT calculation and its use for quantitative determination of magnesium in drinking water.

An "off-the-shelf" fluorescence "turn-on" Mg(2+) chemosensor 3,5-dichlorosalicylaldehyde (BCSA) was rationally designed and developed. This proposed sensor works based on Mg(2+)-induced formation of the 2 : 1 BCSA-Mg(2+) complex. The coordination of BSCA to Mg(2+) increases its structural rigidity generating a chelation-enhanced fluorescence (CHEF) effect which was confirmed by single crystal XRD studies of the BSCA-Mg(2+) complex and TD/DFT calculations. This sensor exhibits high sensitivity and selectivity for the quantitative monitoring of Mg(2+) with a wide detection range (0-40 μM), a low detection limit (2.89 × 10(-7) mol L(-1)) and a short response time (<0.5 s). It can also resist the interference from the other co-existing metal ions, especially Ca(2+). Consequently, this fluorescent sensor can be utilized to monitor Mg(2+) in real time within actual samples from drinking water.

A new fluorescent chemosensor for Al3+ ion based on schiff base naphthalene derivatives

A new naphthalene derivative receptor (H2L) was synthesized. The chemosensor (H2L) exhibited a strong fluorescence enhancement in the presence of trace amounts of Al3+, attributable to chelation-enhanced fluorescence (CHEF) effect, which also displayed high selectivity over a series of other metal cations (Na+, K+, Cs+, Mg2+, Ba2+, Pb2+, Cr3+, Mn2+, Fe3+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Hg2+ and Ag+) in ethanol.

A simple coumarin as a turn-on fluorescence sensor for Al(iii) ions

A simple Al(3+) sensor, 8-acetyl-7-hydroxy-4-methylcoumarin (AHMC), was synthesized. It can display an excellent fluorescence "turn-on" response to Al(3+) over other common metal ions in methanol-water media. Theoretical calculations have also been carried out to understand the configuration of the AHMC-Al complex and rationalize experimental absorption data.

A novel fluorescent ‘off-on-off’ probe for relay recognition of Zn2+ and Cu2+ derived from N,N-bis(2-pyridylmethyl)amine

A metal-to-metal relay recognition was discovered with sequence specificity via a fluorescence 'off-on-off' phenomenon. We present here the synthesis of a new N,N-bis(2-pyridylmethyl)amine-based fluorescent sensor termed NBPA and its application as a selective relay probe for sensing of free trace zinc and copper ions. The addition of Zn(2+) to NBPA causes a drastic enhancement of fluorescent intensity by the formation of a 1 : 1 NBPA-Zn(2+) complex whereas other cations have no response. Moreover, Cu(2+) can induce fluorescence quenching in the NBPA-Zn(2+) system by the formation of a 1 : 1 NBPA-Cu(2+) complex confirmed by Job's Plot. The signal change of the sensor is based on the chelation-enhanced fluorescence (CHEF) effect of NBPA-Zn(2+) with the inhibition of the photoinduced electron transfer (PET) effect and the paramagnetic nature of Cu(2+) to the NBPA-Zn(2+) system. Under optimized conditions, the fluorescence intensity is linear to the concentration of Zn(2+) and Cu(2+) separately, exhibiting good linearities from 1.0 × 10(-6) M to 8.0 × 10(-6) M and 1.0 × 10(-6) M to 1.0 × 10(-5) M (R(2) = 0.9996 and R(2) = 0.9914) with detection limits of 7.89 × 10(-7) M and 1.27 × 10(-7) M, respectively. Furthermore, the rapid, selective feature enables the proposed sensor to be promising in monitoring Zn(2+) and Cu(2+) in biological and environmental research with good accuracy and precision.

1-(2-Methyl-5H-chromeno[2,3-b]pyridin-5-ylidene) hydrazone as fluorescent probes for selective zinc sensing in DMSO

Two methyl-chromeno-pyridinylidene hydrazone derivatives L1, a cyclen derivative, and L2 were studied as potential fluorescent OFF–ON sensors towards Zn2+ in DMSO. Upon addition of one equivalent of Zn2+, L1 fluorescence was quenched, but addition of a second equivalent of Zn2+ restored partially the signal. Therefore ZnL1 behaved as a OFF–ON sensor for zinc. By comparison, L2 behaved as a very sensitive probe for zinc. ZnL1 and L2 sensor efficiencies were correlated to Zn2+ coordination via the hydrazone moiety of the fluorophore, which prevented a photoinduced electron transfer (PET), and allowed an efficient CHelation-Enhanced Fluorescence (CHEF) effect.

ChemInform Abstract: The Pyridyl Group in Ligand Design for Selective Metal Ion Complexation and Sensing

AbstractReview: 173 refs.

A turn-on chemosensor based on naphthol–triazole for Al(III) and its application in bioimaging

Abstract A new Schiff base 1-[(1H-1,2,4-triazole-3-ylimino)-methyl]-naphthalene-2-ol (H 2 L) exhibiting high selectivity for Al 3+ ion over other metal ions, such as Li + , Na + , K + , Ca 2+ , Mg 2+ , Cu 2+ , Co 2+ , Mn 2+ , Ni 2+ , Zn 2+ , Cd 2+ , Pb 2+ , Fe 3+ , and Cr 3+ was prepared, and it is sensitive for Al 3+ with the detection limit reaching 0.69 μM in DMF. Upon addition of Al 3+ , the significant enhancement (32-fold) of fluorescence intensity for H 2 L at 466 nm is ascribed to the formation of a 1:1 complex between Al 3+ and H 2 L, which is denoted as the chelation-enhanced fluorescence (CHEF) effect. The confocal fluorescence microscopy experiments demonstrate that H 2 L could be used as a fluorescent probe for Al 3+ in living cells.

The pyridyl group in ligand design for selective metal ion complexation and sensing

Factors in polypyridyl ligands that control their thermodynamic metal ion selectivity in aqueous solution, and their use in selective fluorescent sensing, are examined. Preorganization of polypyridyl ligands ranging from bidentate to tetradentate by bridging benzo groups, as are present in 1,10-phenanthroline (phen) compared to 2,2'-bipyridyl (bpy), is discussed. The role of solvation is considered in relation to the relative affinity of ligands containing pyridyl groups for divalent and trivalent metal ions in aqueous solution. The effects of steric clashes between H atoms on polypyridyl ligands in decreasing complex stability are evaluated, as well as the effect of chelate ring size on metal ion selectivity. Phen ligands with other donor groups present at the 2 and 9 positions, such as alcohols, amides, carboxylates, and oximes are discussed. The design of pyridyl-based ligands for the separation of Am(III) from lanthanide(III) ions is considered, as well as ligands for the removal of metal ions such as Cu(II) or Zn(II) in neurological diseases such as Alzheimer's. The design of pyridyl-based fluorescent sensors for selective sensing of metal ions is examined in terms of the role of spin-orbit coupling constants (ζ), paramagnetism, and steric effects in the development of selective fluorescent sensors that operate via chelation enhanced fluorescence (CHEF). It is concluded that for lighter metal ions with smaller ζ values such as Zn(II) and Ca(II), and to a lesser extent Cd(II), that the CHEF effect can be achieved with pyridyl-containing fluorophores that coordinate directly to the metal ion. The way in which steric effects can be used to decrease the CHEF effect in Zn(II) relative to Cd(II) to enable selective sensing of the latter is analyzed. For heavier metal ions such as Hg(II) and Pb(II), because of their large ζ values which quench fluorescence, it is concluded that the fluorophore should be tethered to the metal-binding part of the sensor, and prevented from binding to the metal ion by steric and electronic factors. How Hg(II) can quench the CHEF effect by π-contact with fluorophores such as the anthracenyl group, which at first sight might not seem able to bond with metal ions, is examined.