A rhodamine appended tripodal receptor as a ratiometric probe for Hg2+ ions

A new rhodamine appended tripodal receptor 1 has been designed and synthesized. The receptor selectively recognizes Hg(2+) ions in CH(3)CN-water (4:1, v/v; 10 μM tris HCl buffer, pH 7.0) by displaying a ratiometric change in emission. Additionally, the visual detection is possible by a sharp change in color. The receptor shows in vitro detection of Hg(2+) ions in human cervical cancer (HeLa) cells.     

Recognition, encapsulation, and selective fluorescence sensing of nitrate anion by neutral C3-symmetric tripodal podands bearing amide functionality

A series of neutral C(3)-symmetric acyclic artificial receptors incorporating amide functionality has been designed, synthesized, and fully characterized. Upon protonation, these conformationally flexible N-bridged tripodal podands 1-5 form in situ cone shape conformation through hydrogen bonding and C-H···π interactions. The protonation-induced interior preorganized cavity is capable of entrapping nitrate anions through the amide N-H bonds to form discrete nitrate complexes (1a-5a), which were fully characterized by NMR, HRESI mass spectra, and single crystal structures. By incorporating suitable fluorophores at each branch of the tripod receptor, the resulting fluorescent receptor 5 selectively recognized nitrate anions by fluorescent quenching in a DMSO solution and displayed one of the highest binding affinities for nitrate anions reported so far in polar media. Receptor 5 represents a unique example of a neutral receptor for the recognition of nitrate anions in polar solvent media by its zwitterionic form. The possible mechanism of proton-induced preorganization of these flexible, acyclic receptors in a convergent cone conformation followed by nitrate complexation has been proposed to rationalize the effective nitrate recognition.     

A simple fluorescent receptor selective for Mg2+

A structurally simple fluorescent receptor (receptor 1) has been synthesized and was found to show a dramatic enhancement in its fluorescence emission upon complexation with Mg(2+). This was maybe contributed to by the inhibition of the C=N isomerization in the excited state. The experimental results show that the receptor was selective and sensitive towards Mg(2+) in the presence of competing ions, with a low detection limit of 3.5 × 10(-9) mol L(-1) (3σ).     

A ratiometric fluorescence probe for selective visual sensing of Zn2+

A simple ratiometric fluorescence probe based on vinylpyrrole end-capped bipyridine for the visual sensing of Zn2+ under aqueous physiological pH (6.8-7.4) is described. The fluorophores 3a-c showed strong emission around 537 nm in acetonitrile with a quantum yield of 0.4. In buffered (HEPES, pH 7.2) acetonitrile-water mixture (9:1 v/v), titration of transition metal salts to 3c showed strong quenching of the emission at 547 nm except in the case of Zn2+, which resulted in a red-shifted emission at 637 nm. Alkali and alkaline earth metal salts could not induce any considerable changes to the emission behavior of 3a-c. The binding of Zn2+ was highly selective in the presence of a variety of other metal ions. Though Cu2+ quenches the emission of 3c, in the presence of Zn2+, a red emission prevails, indicating the preference of 3c toward Zn2+. Job plot and Benesi-Hildebrand analysis revealed a 1:1 complexation between the probe and the metal ion. The selective visual sensing of Zn2+ with a red emission is ideally suited for the imaging of biological specimens.     

Cu2+ colorimetric sensing and fluorescence enhancement and Hg2+ fluorescence diminution in "scorpionate"-like tetrathienyl-substituted boron-dipyrrins

Four novel tetrathienyl-substituted boron-dipyrrin-type (BODIPY-type) complexes, 3-(R')-4,4-di(R')-8-R-4-bora-3a,4a-diaza-s-indacene (4a, R = 2-T, R' = 2-T; 4b, R = 3-T, R' = 2-T; 5a, R = 2-T, R' = 3-T; 5b, R = 3-T, R' = 3-T; T = thienyl) have been prepared and fully characterized to explore patterns of stoichiometric Mn+ recognition in solution. Treatment of the respective parent BF2 dipyrrin with 2- or 3-thienyllithium gave the unexpected asymmetric tetrathienyl-substituted products in 8.5-35% yield. Compounds 4a and 4b bear a neutral "scorpionate"-like [SSS] tridentate binding pocket. Extensive NMR and UV-vis spectroscopic studies were performed on 4a-5b; 5a, 4b, and 5b were structurally characterized. The PhiF values for 4a-5b all decrease compared to the BF2-containing parent molecules (0.00058, 0.012, 0.00090, and 0.0051, respectively), with lambda(abs,max) values (epsilon, M(-1) cm(-1)) of 563 (44,000), 553 (29,000), 539 (33,000), and 531 (44,000) nm, respectively, and Stokes' shifts of 25-36 nm. Upon treatment with metal ion (Ca2+, Cs+, Mn2+, Co2+, Cu2+, Ag+, Zn2+, Cd2+, Hg2+, Pb2+) perchlorate salts, the solution of 4b undergoes rapid pink-to-clear switch-off behavior upon Cu2+ addition (10 microM scale) with smaller effects seen for 4a. Further, there were 2- to 19-fold Cu2+ fluorescence enhancements for these ligands. Cu2+- and Hg2+-L (L = 4a-5b) binding was modeled, and response patterns for Mn+-L 1:1 molar solutions upon Cu2+ addition were measured. Upon treatment with Hg2+, all ligand solutions show a significant fluorescence decrease accompanied by minor absorption increases. The UV-vis spectroscopic detection limit for Cu2+ and Hg2+ is approximately 270 ppb and approximately 1.7 ppm, respectively; the naked eye detection limit for Cu2+ with 4b (1.0 x 10(-5) M) is approximately 23 microM. DFT calculations gave HOMO-LUMO gaps of 478 (4a), 462 (4b), 448 (5a), and 442 nm (5b). Molecular orbital diagrams for 4a-5b revealed that the HOMO and LUMO electron density is distributed onto the 3-position-thienyl group and to a lesser degree the B(thienyl)2 moiety.     

An anthracene based bispyridinium amide receptor for selective sensing of anions

A new receptor has been designed and synthesized for selective recognition of anions through hydrogen bonding and electrostatic interactions. The recognition ability has been studied by fluorescence, UV-vis and ¹H NMR spectroscopic methods. The results demonstrate that the receptor exhibits good recognition ability towards anions and shows strong binding to AcO⁻, and F⁻.     

A benzthiazole-based simple receptor in fluorescence sensing of biotin ester and urea

A benzthiazole-based receptor 1 has been designed and synthesized for recognition of biotin ester and urea in CHCl₃ containing 1% CH₃CN. The receptor binds biotin methyl ester and urea with moderate binding constant values and shows significant increase in emission of benzthiazole motif. The emission characteristics of 1 upon complexation clearly distinguishes biotin methyl ester and urea from thiourea and N,N′-dimethylurea. Characterization and sensing properties of the receptor 1 were evaluated by ¹H NMR, UV-vis, and fluorescence spectroscopic methods.     

l-Valine-derived simple benzimidazole-based host in selective sensing of Hg(II) ions

A new and an easy-to-make simple benzimidazole-based chemosensor 1, derived from l -valine is reported. The chemosensor effectively recognises Hg²⁺ ion in the open cleft in CH₃CN containing 0.2% DMSO by exhibiting significant enhancement in fluorescence emission. In the selectivity, the steric isopropyl groups in 1 play the key role as confirmed by considering the model compound 2. The ensemble of 1.Hg²⁺, on the other hand, shows the fluorescence sensing of l -cysteine, homocysteine, and glutathione over the other amino acids with no thiol group in aq. DMSO (DMSO:H₂O = 4:1, v/v).     

Selective sensing of Zn(II) ion by a simple anthracene-based tripodal chemosensor

A new and an easy-to-make simple tripodal shaped chemosensor 1, comprising an anthracene moiety as a fluorophore and amide, alcohol functionalities as ligating groups has been designed and synthesized for Zn(II). In CH₃CN containing 0.1% DMSO, upon excitation at 370 nm, the chemosensor 1 exhibited an emission at 412 nm, which increased to a large extent upon complexation of Zn(II). Among the other metal ions examined in the study, Cd²⁺ moderately perturbed the emission of 1 under similar conditions.     

Highly selective adsorption of Hg2+ by a polypyrrole-reduced graphene oxide composite

A facile chemical route to synthesize the polypyrrole-reduced graphene oxide composite showing a highly selective Hg(2+) removal capacity is reported. The gram scale production, high adsorption capacity and recycling make this material practically useful for waste water treatment.     

Pyrenyl-appended imidazolium receptor for selective fluorescence sensing of oxalic acid

A new fluorescent imidazolium-based cholestane receptor 4 bearing a pyrene moiety was synthesized. The binding ability of 4 toward various dicarboxylic acids was examined by UV-vis and fluorescence spectroscopy. Receptor 4 showed the highest binding constant for oxalic acid among all the tested dicarboxylic acids (K_a = 5.06 × 10⁴ M⁻¹). Oxalic acid formed a complex with 4 with a 1:2 ratio in ethanol.     

A new quinoline-based chemosensor in ratiometric sensing of Hg2+ ions

A new quinoline-based chemosensor 1 has been designed and synthesised. Its metal ion-binding properties have been documented in organic and aqueous organic solvents. While chemosensor 1 recognises Hg²⁺ ions (K _a = 2.15 × 10⁴ M^? 1) by exhibiting ratiometric change in emission in CHCl₃/CH₃OH (1:1, v/v), under similar condition both Zn²⁺ and Cd²⁺ ions are sensed by significant non-ratiometric increase in emission with measurable red shift. In DMSO/H₂O (5:95, v/v), the sensor 1 exhibits a greater selectivity towards Hg²⁺ ions (K _a = 9.20 × 10³ M^? 1) over the other metal ions examined.     

Oligonucleotide-based label-free Hg2+ assay with a monomer-excimer fluorescence switch

A novel fluorescent Hg(2+) sensor was developed based on the T-Hg(2+)-T structure and a thioflavine T monomer-excimer fluorescent switch. Under optimum conditions, the selectivity is remarkably high, and Hg(2+) can be quantified over the dynamic range of 0.1 to 1.2 μM, with a limit of detection (LOD) of ~20 nM and a linear correlation coefficient of 0.995.     

A simple chemosensor for Hg2+ and Cu2+ that works as a molecular keypad lock

A new chemosensor which can detect Hg(2+) in water and Hg(2+)/Cu(2+) in acetonitrile and its application as a molecular keypad lock using Cu(2+) and F(-) as ionic inputs are demonstrated.     

Selective sensing of Hg2+ by a proton-ionizable calix[4]arene fluoroionophore

A fluorogenic derivative of a calix[4]arene with two proton-ionizable N-(phenyl)sulfonyl carboxamide-containing side arms in the 1,3-positions on the lower rim is employed for the selective sensing of Hg²⁺ at low concentration levels in water/MeCN (1:1, v/v) solutions containing Pb²⁺ and Cd²⁺. All three metal ions quench the fluorescence of the ligand in pure MeCN. However, in water/MeCN mixed solvent, the recognition of such cations occurs differently as only Hg²⁺ complexation quenches the fluorescence of the calixarene. Experiments carried out in the presence of an acid and a bulky non-complexing cation shows that the quenching of the calixarene fluorescence upon Hg²⁺ addition is likely due to proton displacement from the proton-ionizable side arms of the ligand. The system may be employed as a simple tool for the selective and efficient mercury sensing in mixed water/organic solvent.     

A quinoline based bis-urea receptor for anions: a selective receptor for hydrogen sulfate

A dipodal bis-urea receptor has been synthesized from the reaction of 8-amino quinoline and 1,4-phenylene diisocyanate in dichloromethane, and the anion binding ability of the receptor has been studied using fluoride, chloride, bromide, iodide, perchlorate, nitrate, dihydrogen phosphate and hydrogen sulfate by UV-Vis titrations in DMSO. The results show that the receptor binds each of the anions with a 1:1 stoichiometry, showing high affinity and moderate selectivity for hydrogen sulfate among the anions studied. Ab initio calculations based on density functional theory (DFT) suggest that an anion (X(-)) is bonded within the cleft formed by the two arms of the receptor through two NH...X(-) and two aromatic CH...X(-) interactions. The results from solution and theoretical studies suggest that binding is predominantly influenced by hydrogen bonding interactions and the basicity of anions.     

Highly selective sensing of cyanide by a benzochromene-based ratiometric fluorescence probe

Enone-functionalized benzochromene chemodosimeter (1) was prepared through the Baylis-Hillman condensation reaction and was utilized as a ratiometric fluorescence probe for cyanide anions in aqueous buffer. The probe has shown a selective and sensitive response to cyanides over other various anions through the Michael addition and a subsequent [1,3]-sigmatropic rearrangement reaction. When cyanide anions were added, a prominent ratiometric fluorescence change of 1 was observed thus allowing to detect the micromolar concentration of cyanides by the naked eye.     

A medium-controlled fluorescence dual-responsive probe for Cu2+ and Hg2+ in aqueous solutions

In this study, we report a histidine-based fluorescence probe for Cu(2+) and Hg(2+), in which the amino group and imino group were modified by two common protective groups, 9-fluorenylmethoxycarbonyl and trityl group, respectively. In a water/methanol mixed solution, the probe displayed a selective fluorescence "turn-off" response to Cu(2+) when the ratio of CH(3)OH/H(2)O was higher than 1:1. Specifically, when the solvent is changed to 1:1 methanol/water, the 304 nm fluorescence peak is enhanced, while the 317 nm peak is weakened, upon addition of either Cu(2+) or Hg(2+) ions. The mechanism for such distinct responses of the probe to Cu(2+) and Hg(2+) was further clarified by using NMR and molecular simulation. The experiment results indicated that the polarity of solvent could influence the coordination mode of 1 with Cu(2+) and Hg(2+), and control the fluorescence response as a "turn-off" or ratiometric probe.     

A novel Hg2+ fluorescence sensor TPE-TSC based on aggregation-induced emission

Abstract

A fluorescent sensor TPE-TSC with aggregation induced emission (AIE) characteristic is synthesized for detecting Hg²⁺ by attaching thiosemicarbazide (TSC) unit into tetraphenylethylene (TPE) group. TPE-TSC exhibits intense green emission in DMSO/H₂O (V:V?=?1:9) solution with the formation of the aggregation. TPE-TSC shows outstanding fluorescence quenching toward Hg²⁺ over other metal ions due to the formation of complex TPE-TSC/Hg²⁺ with a 2:1 binding ratio. The detection limit of TPE-TSC for Hg²⁺ is 1?×?10^?5 mol·L^?1.