A Turn-on Fluorescent Chemosensor for Zn<Superscript>2+</Superscript> Based on Quinoline in Aqueous Media

A simple “off-on fluorescence type” chemosensor 1 3-((2-(dimethylamino)ethyl)amino)-N-(quinolin-8-yl)propanamide has been synthesized for Zn²⁺. The receptor 1 comprises the quinoline moiety as fluorophore and the N,N^′-dimethylethane-1,2-diamine as a binding site. 1 showed a remarkable fluorescence enhancement in the presence of Zn²⁺ in aqueous solution. Importantly, the chemosensor 1 could be used to detect and quantify Zn²⁺ in water samples. In particular, this chemosensor could clearly distinguish Zn²⁺ from Cd²⁺. The binding properties of 1 with Zn²⁺ ions were investigated by UV-vis, fluorescence, electrospray ionization mass spectroscopy and ¹H NMR titration.     

8-Hydroxyquinoline Functionalized Graphene Oxide: an Efficient Fluorescent Nanosensor for Zn<Superscript>2+</Superscript> in Aqueous Media

A nanosensor, based on 8-hydroxyquinoline functionalized graphene oxide, was developed for the fluorescence detection of Zn²⁺. It showed high selectivity and sensitivity for Zn²⁺ion in aqueous solution over other metal ions such as Li⁺, Na⁺, Ca²⁺, Mg²⁺, Al³⁺, Cd²⁺, Co²⁺, Cu²⁺, Hg²⁺, Ni²⁺, Pb²⁺, Fe²⁺, Fe³⁺and Cr³⁺. Due to the linearity of the emission intensity toward Zn²⁺ concentration, fluorescent technique could be used for the detection of Zn²⁺ ion even at very low concentrations.     

A New Fluorescent Chemosensor Detecting Co<Superscript>2+</Superscript> and K<Superscript>+</Superscript> in DMF Buffered Solution

A new fluorescent chemosensor 2-(2-thiophene)imidazo [4,5,f]-1,10-phenanthroline (L) was prepared and characterized. By adding univalent or divalent metal ions such as Na⁺, K⁺, Mg²⁺, Ba²⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Ag⁺, Zn²⁺, Cd²⁺ and Hg²⁺ ions into the solution of L in DMF under buffered conditions with the working pH ranging from 7.0 to 8.0, we found that L could be used to detect K⁺ ratiometricly and it could also be applied to sense Co²⁺ with the phenomenon of fluorescence quenching of L. While the response behavior of L was not discernibly affected by other examined metal ions.     

Condensation Product of Phenylalanine and Salicylaldehyde: Fluorescent Sensor for Zn<Superscript>2+</Superscript>

The condensation product of phenylalanine and salicylaldehyde (L) was synthesised and characterised which was found to be selective fluorescent “off-on” sensor for Zn²⁺ ion with the detection limit 10^?5 M. The sensor is free of interferences from metal ions - Na⁺, K⁺, Al³⁺, Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Pb²⁺, Cd²⁺ and Hg²⁺. The Fluorescence and the UV/visible spectral data reveals a 1:1 interaction between the sensor and Zn²⁺ ion with binding constant 10⁸. The DFT and TDDFT calculations confirm the structures of the sensor and the sensor-Zn²⁺ complex.     

A New bis(rhodamine)-Based Fluorescent Chemosensor for Fe<Superscript>3+</Superscript>

A new bis(rhodamine)-based fluorescent probe 4 was synthesized, and it exhibited high selectivity for Fe(3+) over other commonly coexistent metal ions in both 50% ethanol and Tris-HCl buffer. Upon the addition of Fe(3+), the spirocyclic ring of 4 was opened and a significant enhancement of visible color and fluorescence in the range of 500-600 nm was observed.     

Coumarin Based Fluorescent Probe for Colorimetric Detection of Fe<Superscript>3+</Superscript> and Fluorescence Turn On-Off Response of Zn<Superscript>2+</Superscript> and Cu<Superscript>2+</Superscript>

A new coumarin based Schiff-base chemosensor-(E)-7-(((8-hydroxyquinolin-2-yl)methylene) amino)-4-methyl-2H-chromen-2-one (H ₁₁ L) was synthesized and evaluated as a colorimetric sensor for Fe³⁺ and fluorescence “turn on-off” response of Zn²⁺ and Cu²⁺ using absorption and fluorescence spectroscopy. Upon treatment with Fe³⁺ and Zn²⁺, the absorption intensity as well as the fluorescence emission intensity increases drastically compared to other common alkali, alkaline earth and transition metal ions, with a distinct color change which provide naked eye detection. Formation of 1:1 metal to ligand complex has been evaluated using Benesi-Hildebrand relation, Job’s plot analyses, ¹H NMR titration as well as ESI-Mass spectral analysis. The complex solution of H ₁₁ L with Zn²⁺ ion exhibited reversibility with EDTA and regenerate free ligand for further Zn²⁺ sensing. H ₁₁ L exhibits two INHIBIT logic gates with two different chemical inputs (i) Zn²⁺ (IN1) and Cu²⁺ (IN2) and (ii) Zn²⁺ (IN1) and EDTA (IN2) and the emission as output. Again, an IMPLICATION logic gate is obtained with Cu²⁺ and EDTA as chemical inputs and emission as output mode. Both free ligand as well as metal-complexes was optimized using density functional theory to interpret spectral properties. The corresponding energy difference between HOMO-LUMO energy gap for H ₁₁ L, H₁₁L-Zn²⁺ and H₁₁L-Cu²⁺ are 2.193, 1.834 and 0.172 eV, respectively.     

A Highly Sensitive and Selective Fluorescent Chemodosimeter for Hg<Superscript>2+</Superscript> in Neutral Aqueous Solution

A fluorescent assay of Hg²⁺ in neutral aqueous solution was developed using N-[p-(dimethylamino)benzamido]-N′-phenylthiourea (1). 1’s fluorogenic chemodosimetric behaviors towards various metal ions were studied and a high sensitivity as well as selectivity was achieved for Hg²⁺. It was because of a strongly fluorescent 1,3,4-oxadiazoles which was produced by the Hg²⁺ promoted desulfurization reaction. The spectra of ESI mass and IR provided evidences for this reaction. According to fluorescence titration, a good linear relationship ranging from 1.0 × 10⁻⁷ to 2.0 × 10⁻⁵ mol l⁻¹ was obtained with the limit of detection as 3.1 × 10⁻⁸ mol l⁻¹. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Highly Selective and Anions Controlled Fluorescent Sensor for Hg<Superscript>2+</Superscript> in Aqueous Environment

A highly selective PET fluorescent sensor B1 for Hg²⁺ containing a BODIPY fluorophore and a NS₂O₂ penta-chelating receptor has been synthesized and characterized. Its absorption maximum wavelength (498 nm) and emission maximum wavelength (512 nm) are both in the visible range. The fluorescence quantum yields of the B1 and Hg²⁺-bound states of BHg1 are 0.008 and 0.58 in 70% aqueous ethanol solution, respectively. The pKa of 1.97 is the lowest in metal ions PET chemo sensors reported up till now as we know. Thus, B1 can detect the Hg²⁺ in a wide pH span, which indicates that it has more potential and further practical applications for biology and toxicology. Furthermore, BHg1 also displays response to some anions such as Cl⁻(Br⁻), , SCN⁻ and CH₃COO⁻, which is attributed to the significant coordinating ability of these anions to Hg²⁺.     

A Novel Chemosensor Based on Rhodamine Derivative for Colorimetric and Fluorometric Detection of Cu<Superscript>2+</Superscript> in Aqueous Solution

A new rhodamine-based reversible chemosensor (2) was synthesized, which exhibits high sensitivity and selectivity for Cu²⁺ but no significant response toward other competitive metal ions in aqueous solution. Upon the addition of Cu²⁺, the spirolactam ring of 2 was opened and the solution color changed from colorless to red. Strangely, an unexpected fluorescence quenching was observed, which is contrary to the fluorescence turn-on of the most rhodamine-based chemosensors. The likely novel sensing mechanism has been proposed.     

A Dual-Target Fluorescent Probe with Response-Time Dependent Selectivity for Cd<Superscript>2+</Superscript> and Cu<Superscript>2+</Superscript>

A novel fluorescent probe (NT) was developed by merging 2-hydrazinylbenzothiazole with 2-hydroxy-1-naphthaldehyde for the detection of Cd²⁺ and Cu²⁺. The probe alone is almost nonfluorescent due to the isomerization of C=N in the excited state. The addition of Cd²⁺ can cause an immediate strong green fluorescence owing to the suppression of C=N isomerization by Cd²⁺-coordination. Furthermore, NT gives a delayed turn-on fluorescence response to Cu²⁺ although it is a vigorous fluorescence quencher, which was thanks to the inhibition of the electron transfer between excited fluorophore and paramagnetic Cu²⁺ by sulfur donor. Based on fluorescence spectra and ESI-MS analysis, the binding modes between NT and Cd²⁺/Cu²⁺ were proposed.     

A Highly Selective Turn-On Fluorescent Chemosensor for Zinc Ion in Aqueous Media

In the paper, a novel rhodamine6G based fluorescent chemosensor bearing 3-carbaldehyde chromone was designed and synthesized. According to the fluorescence behavior toward several metal ions, it showed highly selectivity and sensitivity to Zn(II) over other commonly coexistent metal ions (Cu(II), Cd(II), Hg(II), Mg(II), K(I), Pb(II), Fe(III) and Cr(III)) in aqueous environment (pH?=?7.4). Meanwhile the binding constant between Zn(II) and chemosensor achieved 6.21?×?10¹¹ M^?1 in aqueous media. Moreover, according to the Job plot, 1:1 stoichiometry between Zn(II) and sensor was deduced in aqueous media (pH?=?7.4). The good selectivity and sensitivity in aqueous media effectively enhanced the application value of the fluorescent chemosensor for Zn(II).     

A Rhodamine Derivative Based Chemosensor with High Selectivity and Quick Respond to Cr<Superscript>3+</Superscript> in Aqueous Solution

In this paper, a new kind of colorimetric chemsensor aiming at detecting Cr³⁺ has been synthesized, and it is based on the “Off-On” effect of a rhodamine derivative. Comparing with other metal irons (Na⁺, K⁺, Ni²⁺, Hg²⁺, Fe³⁺, Mn²⁺, Co²⁺, Cd²⁺, Cu²⁺, Pb²⁺, Zn²⁺, Mg²⁺, Ba²⁺, Ag⁺, Fe²⁺, Ce³⁺), the chemsensor has a quick and accurate response to Cr³⁺ in H₂O-EtOH solution (4/1, v/v). There is an obvious change in color, from colorless to bright pink when Cr³⁺ is detected. According to the fitting curve based on Benesi-Hildebrand equation and working curve of absorption strength in UV-vis spectrum, the binding pattern of Cr³⁺ and the rhodamine derivative follows a 1:1 stoichiometry. The chemsensor shows great potential in monitoring Cr³⁺ in the aqueous medium with high efficiency, which is supposed to complete the recognition in the minimum as 5.2?×?10^?7 mol/L within 5 min.     

A highly Sensitive Turn-on Fluorescent Sensor for Ba<Superscript>2+</Superscript> Based on G-Quadruplexes

A G-quadruplex-based fluorescent biosensor for highly sensitive detection of barium ion (Ba²⁺) was constructed for the first time. In the absence of Ba²⁺, the G-quadruplex-specific fluorescence ligand N-methyl mesoporphyrin IX (NMM) remained weakly fluorescent when coexisted with a single-stranded G-quadruplex sequence AGRO100. Upon addition of Ba²⁺, AGRO100 was folded into G-quadruplex structures with the aid of Ba²⁺, which bound with NMM by stacking forces and significantly enhanced its fluorescence. The maximum fluorescence intensity of NMM was increased by ca. 22-fold in response to 1 μM Ba²⁺. This simple method exhibites a good linear relationship in the range of 0–600 nM with the detection limit of 4 nM. The detection method is turn-on, fast, economic, high in signal-to-noise ratio and free of participation of toxic organic solvents, demonstrating its great potential for on-site and real-time Ba²⁺ detection.     

A Dansyl-Rhodamine Ratiometric Fluorescent Probe for Hg<Superscript>2+</Superscript> Based on FRET Mechanism

Based on resonance energy transfer (FRET) from dansyl to rhodamine 101, a new fluorescent probe (compound 1) containing rhodamine 101 and a dansyl unit was synthesized for detecting Hg²⁺ through ratiometric sensing in DMSO aqueous solutions. This probe shows a fast, reversible and selective response toward Hg²⁺ in a wide pH range. Hg²⁺ induced ring-opening reactions of the spirolactam rhodamine moiety of 1, leading to the formation of fluorescent derivatives that can serve as the FRET acceptors. Very large stokes shift (220 nm) was observed in this case. About 97-fold increase in fluorescence intensity ratio was observed upon its binding with Hg²⁺.     

Novel Fluorescent Molecular Clips: Selective Recognition Towards Fe<Superscript>3+</Superscript> in Aqueous Solution

In this paper, we report the synthesis, characterization and Fe³⁺-sensing properties of a series of new artificial fluorescent molecular clips, and structure of clip 1 is confirmed by X-ray crystallography. All these molecular clips had the ability to bind and sense Fe³⁺ selectively through decrease fluorescence responses in THF-MeOH-Water. Fluorimetric titration experiment indicated that the quenching of these compounds’ fluorescence upon Fe³⁺ probably arises from the electron/energy transfer between Fe³⁺ and the excited chemosensors. The limit of detection, linear concentration range and selectivity of the fluorescent molecular clips were evaluated in this study as well.     

Synthesis and Evaluation of a Schiff-Based Fluorescent Chemosensors for the Selective and Sensitive Detection of Cu<Superscript>2+</Superscript> in Aqueous Media with Fluorescence Off-On Responses

Copper being an essential nutrient; also pose a risk for human health in excessive amount. A simple and convenient method for the detection of trace amount of copper was employed using an optical probe R1 based on Schiff base. The probe was synthesized by Schiff base condensation of benzyl amine and 2-hydroxy-1-napthaldehyde and characterized by single X-ray diffraction, ¹H NMR and FTIR. By screening its fluorescence response in a mixture of DMSO and H₂O (20:80, v/v) R1 displayed a pronounced enhancement in fluorescence only upon treatment with copper. Other examined metal ions such as alkali, alkaline and transition had no influence. Within a wide pH range 5–12 R1 could selectively detect copper by interrupting ICT mechanism that results in CHEF. From Job’s plot analysis a 2:1 binding stoichiometry was revealed. The fluorescence response was linear in the range 1–10?×?10^?9 M with detection limit 30?×?10^?9 M. Association constant was determined as 1?×?10¹¹ M^?2 by Benesi-Hilderbrand plot. As a fast responsive probe it possesses good reproducibility and was employed for detection of copper in different water samples.     

Synthesis of Two Coumarin-Derived Schiff Bases and Investigation of theirs Selectivity for Zn<Superscript>2+</Superscript>

In this study, the coumarin-derived schiff bases (HL₁ and HL₂) have been designed and synthesized. Upon the addition of Zn²⁺, both of them show significant fluorescence enhancement owing to inhibits PET and ESIPT process respectively. However, the receptor HL₂ response toward Cd²⁺, Mg²⁺, Ba²⁺, Ca²⁺ besides Zn²⁺ and exhibits fluorescence enhancement but not enough to detection of the concentration levels of Zn²⁺.     

Neutron transition densities for the 2<Superscript> + </Superscript>-8<Superscript> + </Superscript> multiplet of states in <Superscript>90</Superscript>Zr

Neutron transition densities for the 2 ⁺ -8 ⁺ levels in ⁹⁰Zr were extracted in the process of analyzing scattering at 400 MeV. They were compared with the calculated neutron transition densities and with the experimental proton transition densities. Radial distributions of the experimental neutron and proton transition densities for each state were found to be different.Received: 9 January 2004, Revised: 4 April 2004, Published online: 14 September 2004PACS: 25.40.Ep Inelastic proton scattering - 21.10.-k Properties of nuclei; nuclear energy levels     

A Ratiometric and near-Infrared Fluorescent Probe for Imaging Cu<Superscript>2+</Superscript> in Living Cells and Animals

We have rationally constructed a novel ratiometric and near-infrared Cu²⁺ fluorescent probe based on a tricarbocyanine chromophore. The new probe NIR-Cu showed a ratiometric fluorescent response to Cu²⁺ with a large emission wavelength shift (up to 142 nm) in the far-red to near-infrared region. The probe also displayed a large variation in the fluorescence ratio (I₆₃₆/I₇₇₈) to Cu²⁺ species with high sensitivity and selectivity. Additionally, the developed probe NIR-Cu was suitable for fluorescence imaging of Cu²⁺ in living cells and mice.     

A Rhodamine-Cyclen Conjugate as Chromogenic and Fluorescent Chemosensor for Copper Ion in Aqueous Media

A novel compound 1 containing rhodamine B and macrocyclic groups has been synthesized. It was found to exhibit a reversible colorimetric response, high selectivity and sensitivity for Cu(II) ion over other commonly coexistent metal ions. The colorimetric and fluorescent response to Cu(II) can be conveniently detected even by the naked eye, which provided a facile method for visual detection of Cu(II). Approximate 71 and 53-fold enhancement in the absorbance at about 557 nm and fluorescence intensity at about 580 nm were estimated when Cu(II) ion was added to the aqueous media of compound 1. The detection limit was calculated to be 2 μM.