Action of a Fluorescent Chemosensor for Cu2+ Encapsulated in Silica Xerogel

The fluorescent chemosensor of the type Ant-NH-O-O-NH-Ant for Cu²⁺ ions has been designed by means of a supramolecular approach, as follows: two anthracene (Ant) fragments as fluorophore subunits have been linked by a noncyclic NH-O-O-NH quadridentate ligand as a receptor. The interaction of Cu²⁺ - receptor is signalled through the enhancement of the anthracene fluorescence when the receptor, i.e., the dioxodiamine chain subunit of the sensor is able to stop a photoinduced electron-transfer mechanism. The experiments with the chemosensor encapsulated in silica xerogel by the sol-gel processing are described.     

Colorimetric and fluorometric chemosensors for selective signaling toward Ca and Mg by aza-crown ether acridinedione-functionalized gold nanoparticles

The aza-crown ether acridinedione-functionalized gold nanoparticles (ACEADD-GNPs) 6 have been synthesized and investigated as a fluorescent chemosensor for metal ions. A blue shift along with an intensity enhancement of emission and color change are observed in the presence of both Ca²⁺ and Mg²⁺ ions. The enhanced fluorescence intensity is attributed to the photoinduced electron transfer (PET) suppression through space and color change of the suspension from red to blue due to shifted surface plasmon resonance (SPR) with aggregation of nanoparticles by the sandwich complexation.     

Aminoquinoline based highly sensitive fluorescent sensor for lead(II) and aluminum(III) and its application in live cell imaging

We have synthesized a new probe 5-((anthracen-9-ylmethylene) amino)quinolin-10-ol (ANQ) based on anthracene platform. The probe was tested for its sensing behavior toward heavy metal ions Hg²⁺, Pb²⁺, light metal Al³⁺ ion, alkali, alkaline earth, and transition metal ions by UV–visible and fluorescent techniques in ACN/H₂O mixture buffered with HEPES (pH 7.4). It shows high selectivity toward sensing Pb²⁺/Al³⁺ metal ions. Importantly, 10-fold and 5- fold fluorescence enhancement at 429 nm was observed for probe upon complexation with Pb²⁺ and Al³⁺ ions, respectively. This fluorescence enhancement is attributable to the prevention of photoinduced electron transfer. The photonic studies indicate that the probe can be adopted as a sensitive fluorescent chemosensor for Pb²⁺ and Al³⁺ ions.     

Optical Sensing of Cesium Using 1,3-Alternate Calix[4]-mono- and Di(anthrylmethyl)aza-crown-6

We have synthesized two derivatives of alkylanthracene covalently bonded to 1,3-alternate calix[4]aza-crown-6 at the nitrogen position to study the effect of alkali metal ion complexation on the emission properties of anthracene fluorophore. The mono- and dianthryl-substituted probes are weakly fluorescent because their emission is partially quenched by photoinduced electron transfer (PET) from the nitrogen lone pair to the excited singlet state of anthracene. Upon complexation of alkali metal ions (e.g. K⁺, Cs⁺) by the crown moiety, the nitrogen lone pair can no longer participate in the PET process causing an enhancement in the emission of anthracene fluorophore (fluorescent turn on). The maximum fluorescence enhancement observed upon complexation of cesium ions by mono- and dianthryl-substituted calix[4]aza-crown-6 relative to the uncomplexed form was 8.5- and 11.6-fold, respectively.     

Control between TICT and PET using chemical modification of N-phenyl-9-anthracenecarboxamide and its application to a crown ether type chemosensor

Both twisted intramolecular charge transfer (TICT) and photoinduced electron transfer (PET) relaxation processes of N-phenyl-9-anthrylcarboxamide derivatives can be characterized by modified substitution of the phenyl group. Introduction of a methoxy group to phenyl moiety quenched fluorescence of the anthracene using TICT or PET process, and was not retrieved even using highly viscous media. The introduction of a methylene unit induced fluorescence emissions using a solvent with both viscosity and polarity. This phenomenon demonstrates that the effects of both TICT and PET are involved in this system. Based on these data, we synthesized a novel crown ether derivative 7: its analytical usefulness as a fluorescent chemosensor for alkaline earth metal ions is reported herein.     

A new acridine derivative as a fluorescent chemosensor for zinc ions in an 100% aqueous solution: a comparison of binding property with anthracene derivative

A new acridine derivative was synthesized as a fluorescent chemosensor for Zn²⁺ in an 100% aqueous solution. Compound 1 displayed a selective CHEF (chelation enhanced fluorescence) effect with Zn²⁺, on the other hand, a similar anthracene derivative 2 did not display any significant change with the metal ions examined.     

An NBD-based colorimetric and fluorescent chemosensor for Zn and its use for detection of intracellular zinc ions

A new 7-nitrobenz-2-oxa-1,3-diazole (NBD) based colorimetric and fluorescence chemosensor for Zn²⁺, an ion involved in many biological processes, was designed and synthesized. The NBD-probe 1 displays a red-to-yellow color change and an enhancement of fluorescent intensity in the presence of an aqueous solution of Zn²⁺ ions (pH 7.2). Internal charge transfer (ICT) and photoinduced electron transfer (PET) mechanisms are responsible for these changes. The practical use of this probe was demonstrated by its application to the biologically relevant detection of Zn²⁺ ions in pancreatic β-cells.     

Complexation and fluorescence behavior of 9,10-bis[bis(beta-hydroxyethyl)aminomethyl]anthracene

9,10-Bis[bis(beta-hydroxyethyl)aminomethyl]anthracene (1) showed weak emission, suggesting that photoinduced electron transfer (PET) from amine group to excited anthracene occur. The PET fluoroionophore (1) was found to display unique photophysical properties in the presence of the guest metal cations in H(2)OCH(3)OH (1:1, v/v). Complexation of 1 with guest metal cations increased the fluorescence intensity.     

识别过渡金属离子的1,8-萘二甲酰亚胺多胺衍生物荧光传感器的研究

A series of fluorescent chemosensors 1-3 were synthesized to detect transition metal ions. At the room temperature, fluorescence intensities of these chemosensors in acetonitrile without transition metal ions were found to be very weak, due to the process of the e±cient intramolecular photoinduced electron transfer (PET). However, after addition of the transition metal ions, the chemosensor 1-3 exhibits obvious fluorescence enhancement. Moreover, the intensity of the fluorescence emission of chemosensors increases significantly in the presence of Zn2+ and Cd2+. The fluorescent chemosensors with different polyamine as receptors show diverse a±nity abilities to the transition metal ions and signal the receptor-metal ion interaction by the intensity change of fluorescence emission.     

Highly Effective Fluorescent Sensor for Hg2+ in Aqueous Solution

A new anthracene fluorophore senses Hg²⁺ selectively in aqueous solution. Among the metal ions examined, fluorescent chemosensor 1 shows selective large CHEQ effects with Hg²⁺ and Ag⁺ at pH 7.     

Design and Synthesis of a Highly Sensitive Off–On Fluorescent Chemosensor for Zinc Ions Utilizing Internal Charge Transfer

Fluorescence imaging is a powerful tool for the visualization of biological molecules in living cells, tissue slices, and whole bodies, and is important for elucidating biological phenomena. Furthermore, zinc (Zn²⁺) is the second most abundant heavy metal ion in the human body after iron, and detection of chelatable Zn²⁺ in biological studies has attracted much attention. Herein, we present a novel, highly sensitive off–on fluorescent chemosensor for Zn²⁺ by using the internal charge transfer (ICT) mechanism. The rationale of our approach to highly sensitive sensor molecules is as follows. If fluorescence can be completely quenched in the absence of Zn²⁺, chemosensors would offer a better signal‐to‐noise ratio. However, it is difficult to quench the fluorescence completely before Zn²⁺ binding, and most sensor molecules still show very weak fluorescence in the absence of Zn²⁺. But even though the sensor shows a weak fluorescence in the absence of Zn²⁺, this fluorescence can be further suppressed by selecting an excitation wavelength that is barely absorbed by the Zn²⁺‐free sensor molecule. Focusing on careful control of ICT within the 4‐amino‐1,8‐naphthalimide dye platform, we designed and synthesized a new chemosensor ( 1 ) that shows a pronounced fluorescence enhancement with a blueshift in the absorption spectrum upon addition of Zn²⁺. The usefulness of 1 for monitoring Zn²⁺ changes was confirmed in living HeLa cells. There have been several reports on 4‐amino‐1,8‐naphthalimide‐based fluorescent sensor molecules. However, 1 is the first Zn²⁺‐sensitive off–on fluorescent sensor molecule that employs the ICT mechanism; most off–on sensor molecules for Zn²⁺ employ the photoinduced electron transfer (PeT) mechanism.     

A Cu protein cavity mimicking fluorescent chemosensor for selective Cu recognition: tuning of fluorescence quenching to enhancement through spatial placement of anthracene unit

Four new fluoroionophores possessing four ligating sites (2S+2N) and an essential hydrophobic environment, as prevailing in the plastocyanin and rusticyanin proteins, have been synthesized. In these PET fluoroionophores, the position of fluorophore anthracene moiety effectively modulates the Cu²⁺ induced emission properties (quenching vs enhancement) of the fluorophore. The addition of Cu²⁺ to solution of receptor with anthracene moiety in its center caused quenching in emission intensity through photoinduced fluorophore-to-metal electron transfer mechanism and in cases where anthracene is present at terminus nitrogen, the emission intensities increased by nearly 1000% due to inhibition of the photoinduced electron transfer from receptor-to-fluorophore in the presence of Cu²⁺ ions. The hydrophobic environment created by various aromatic rings clearly manifested the stability of fluorescence of these molecules above pH 2.0 and their Cu²⁺ complexes above pH 4. The application of such fluoroionophores has been elaborated for building OR and AND logic gates.     

A ‘turn-on’ fluorescent chemosensor based on rhodamine-N-(3-aminopropyl)-imidazole for detection of Al ions

A novel N-(3-aminopropyl)-imidazole-appended rhodamine-based fluorescent chemosensor was synthesized. The sensing behavior and selectivity of the synthesized chemosensor toward metal cations were studied by UV/vis and fluorescence spectroscopy. The chemosensor recognized Al³⁺ ions by a significantly enhanced fluorescence and a visible color change due to opening of the spirolactam ring triggered by the addition of Al³⁺ ions.     

Photo-physical behavior as chemosensor properties of anthracene-anchored 1,3-di-derivatives of lower rim calix[4]arene towards divalent transition metal ions

Anthracene anchored 1,3-di-derivatives of lower rim p-tert-butyl-calix[4]arene were synthesized and characterized. These derivatives were subjected to the binding studies with the divalent metal ions, viz., Mg²⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺ using fluorescence and absorption spectra. The imine moiety that is in conjugation with the anthryl unit is responsible for quenching the fluorescence in the absence of metal ion, however, in the presence of Fe²⁺ and Cu²⁺, the spectra showed very high enhancement in fluorescence intensity indicating that the lone pair present on the imine-N is involved in the metal ion binding and as a result the photo-induced electron transfer is prevented. Based on the photo-physical studies, it has been found that the anthracene derivative that is coupled with the calix[4]arene unit through an imine bond acts as a chemosensor for Fe²⁺ and Cu²⁺. The fluorescence studies are further augmented by the absorption spectra.     

Sensitive and Selective Fluorescent Chemosensors Combining Multiple PET Processes for Ag+ Sensing

In this work, a novel fluorescent chemosensor combining multiple photoinduced electron transfer(PET) processes for the detection of Ag⁺ ion was synthesized. The PET processes were derived from the lone electron pair of the selenium donors and the tertiary nitrogen atom of the coumarin fluorophore, which have not yet been used in the fluorescent chemosensor designed for Ag⁺ ion. Interestingly, the chemosensors showed fluorescent responses to Ag⁺ ion with a fluorescence enhancement factor of 3-5-fold by blocking the intramolecular PET quenching pathways. Furthermore, the probe exhibited high selectivity and sensitivity for Ag⁺ ion over other relevant species with detection limit down to 10 nmol/L level. The chemosensors also showed excellent performances in analyzing natural water samples. The chemosensors developed herein represent a new strategy for the PET fluorescent chemosensor design for the detection of Ag⁺ ion.     

基于四丹磺酰胺杯[4]芳烃的汞离子荧光化学传感器

我们方便地合成了上沿修饰四丹磺酰胺基团的杯[4]芳烃衍生物1,发现该化合物在含50％水的乙腈中显示出对汞离子高选择性和灵敏性的识别作用,竞争实验表明多数金属离子对其检测干扰较小。机理研究结果表明荧光萃灭源于由丹磺酰胺基团到汞离子的光致电子转移过程。另外,通过研究1和1-Hg2+的荧光衰减实验,以及对比双丹磺酰胺杯[4]芳烃2和单丹磺酰胺杯[4]芳烃3对汞离子的识别作用,发现化合物1的四丹磺酰胺基团具有很好的预组织和协同作用。化合物1对汞离子的检测限为3.41×10-6 mol·L-1,这可以使1成为一个潜在的汞离子荧光化学传感器。     

A Highly Selective and Sensitive Turn-On Fluorescent Chemosensor Based on Rhodamine 6G for Iron(III)

Recently, more and more rhodamine derivatives have been used as fluorophores to construct sensors due to their excellent spectroscopic properties. A rhodamine-based fluorescent and colorimetric Fe³⁺ chemosensor 3’,6’-bis(ethylamino)-2-acetoxyl-2’,7’-dimethyl-spiro[1H-isoindole-1,9’-[9H]xanthen]-3(2H)-one (RAE) was designed and synthesized. Upon the addition of Fe³⁺, the dramatic enhancement of both fluorescence and absorbance intensity, as well as the color change of the solution, could be observed. The detection limit of RAE for Fe³⁺ was around 7.98 ppb. Common coexistent metal ions showed little or no interference in the detection of Fe³⁺. Moreover, the addition of CN⁻ could quench the fluorescence of the acetonitrile solution of RAE and Fe³⁺, indicating the regeneration of the chemosensor RAE. The robust nature of the sensor was shown by the detection of Fe³⁺ even after repeated rounds of quenching. As iron is a ubiquitous metal in cells and plays vital roles in many biological processes, this chemosensor could be developed to have applications in biological studies.     

An ‘off-on’ fluorescent chemosensor of selectivity to Cr and its application to MCF-7 cells

A ‘switching-on’ fluorescent chemosensor for the selective and sensitive signaling of intraceullar Cr³⁺ has been designed and synthesized exploiting the guest-induced prohibition of the photoinduced electron transfer process between naphthyridine moiety and 7,10-diphenylfluoranthene moiety, the system shows a Cr³⁺-selective chelation-enhanced fluorescence response not only in ethanol but in cell.     

Naphthalene-derived Al3+-selective fluorescent chemosensor based on PET and ESIPT in aqueous solution

A simple fluorescent chemosensor HL based on naphthalene with high selectivity and sensitivity towards Al³⁺ over other commonly coexisting metal cations in fully aqueous solution to enhance the potential applications of the fluorescent chemosensor was developed. HL exhibited a significant fluorescence enhancement at 475?nm in the presence of Al³⁺ over other competitive metal ions with a low detection limit of 0.43?μM due to the inhibition of the photo induced electron transfer (PET) and the excited-state intramolecular proton transfer (ESIPT). The 1:1 binding stoichiometry between HL and Al³⁺ was corroborated by the Job plot and the ESI-MS spectrum. Importantly, the reversible recognition process of HL to Al³⁺ will make HL could be used circularly and repeatedly in practical applications by addition of Na₂EDTA. In addition, the binding behavior and sensing mechanism of HL to Al³⁺ were illustrated in detail by the ¹H NMR titration experiment.