Fluorescence enhancement of N2O2-type dipyrrin ligand in two step responding to zinc(II) ion

Fluorescence imaging is well-suited for the live imaging of biological Zn(II), which has no facile spectroscopic or magnetic signature. The successful application of this methodology requires the development of robust Zn(II) imaging agents that display high sensitivity, selectivity and temporal fidelity. In this study, a N₂O₂-type dipyrrin based bimolecular zinc(II) complex was produced and shown to have sharper, blue-shifted and more enhanced fluorescence emission. An approximate three-fold fluorescence enhancement was achieved within the micromolar concentration range, which is an important parameter for Zn(II) detection in vivo. The increase in emission intensity was due to the dominant role of aryl-ring rotation in governing the excited state dynamics and fluorescence properties of the dipyrrin dye. Fluorescence titration showed that the ligand complex exhibited very strong zinc(II) binding affinity when compared to that in the binuclear chloro complex. The fluorescence emission changes in the dipyrrin dye to zinc(II) ion could be observed not only using instruments but also by the naked-eye (violet→sky blue).     

Optimum complexation of uranyl with amidoxime in aqueous solution under different pH levels: density functional theory calculations

This study aims to understand the complexation of uranyl with amidoxime in aqueous solution under different pH levels using density functional theory calculations. The geometries, relative stabilities of complexes, and changes in Gibbs free energies for different complexing reactions were investigated. Amidoximate ions were gradually added to the equatorial plane of uranyl to understand the complexation process. We modelled the effect of pH by varying the number of OH^? and H₂O ligands accompanying amidoximate ions in the equatorial plane of uranyl. The ?² binding motif was the most favourable form, regardless of the uranyl/amidoximate ratio and the pH level. Compared with low and high pH, neutral pH condition was more beneficial to the complexation of uranyl with amidoxime.     

A Long Wavelength Excitable Fluorophore; Chloro Phenyl Imino Propenyl Aniline (CPIPA) for Selective Sensing of Hg (II)

In this study, a very sensitive and highly selective irreversible optical chemical sensor (optode) for mercury ions was described. The sensing scheme was based on the interaction of Hg (II) with a newly synthesized fluoroionophore; chloro phenyl imino propenyl aniline (CPIPA) in plasticized PVC membrane. The sensor membranes were tested for the determination of mercury ion in aqueous solutions by batch and flow-through methods. The optodes allow determination of Hg (II) in the working range of 1.0 × 10⁻⁹–1.0 × 10⁻⁵ M with a detection limit of 4.3 ppb. The sensor exhibited excellent selectivity for Hg (II) with respect to several common alkali, alkaline earth and transition metal ions. The association constant of the 1:1 complex formation for Hg (II) was found to be K_a = 1.86 × 10⁵ M⁻¹. The CPIPA exhibited high fluorescence quantum yield, long excitation and emission wavelength and high Stokes’ shift values in the solid matrix which makes it compatible with solid state optics.     

A Novel Quinazolinone Derivative as Fluorescence Quenching Off-On Sensor for High Selectivity of Fe3+

A novel quinazolinone compound containing quinazoline-fused moiety has been synthesized as fluorescence Off-On sensor QQ. The probe exhibited highly selective and sensitive recognition toward trivalent ferric ion (Fe³⁺) over other metal ions in HEPES buffer solution (10 mM, pH?=?7.0, DMF-H₂O, 9:1, v/v). The significant quenching in the fluorescence spectral could be served as a selective fluorescence Off-On sensor. The titration study indicated the formation of 1:1 complex between QQ and Fe³⁺.     

Enhancement of uranyl fluorescence using trimesic acid: Ligand sensitization and co-fluorescence

Trimesic acid (TMA) was shown to sensitize and enhance uranyl fluorescence in aqueous medium, with the enhancement being a maximum at pH 5.0. Fluorescence spectra and lifetime data together suggest that TMA complexes with uranyl . The fluorescence of UO₂2+ in its acid complex is further enhanced by more than two orders of magnitude following the addition of Y³⁺; a process referred to as co-fluorescence, leading to the possibility of detecting uranium at sub ng/mL level. The present study demonstrates, for the first time, fluorescence enhancement of the uranyl species due to co-fluorescence.     

Bifunctional Calix[4]arene Sensor for Pb(II) and Cr2O7 2− Ions

A readily available chromionophore 5,11,17,23-tetra-tert-butyl-25,27-bis(hydrazidecarbonylmethoxy)-26,28-dihydroxycalix[4]arene (HCC4) was employed as a chromogenic sensing probe selective for Pb(II) and Cr₂O₇ ^2? ions among a series of various ions such as Li(I), Na(I), K(I), Rb(I), Ba(II), Sr(II), Al(III), Cd(II), Co(II), Cu(II), Hg(II), Ni(II), Pb(II) and Zn(II) as well as Cr₂O₇ ^2?, CH₃CO₂ ^?, Br^?, Cl^?, F^?, I^?, ClO₄ ^? and NO₃ ^? that have been examined by UV-visible and fluorescence spectroscopic techniques. The HCC4 in DCM-MeCN system forms 2:1 (ligand-metal) complex with Pb(II). It also shows 2:1 stoichiometry with Cr₂O₇ ^2?. The complexation phenomenon has been confirmed by FTIR spectroscopy that favors the selective nature of HCC4 with Pb(II) and Cr₂O₇ ^2?. Thermal gravimetric analysis (TGA) also supports its utility in drastic conditions.     

Synthesis, characterization and fluorescence studies of a novel europium complex based sensor

A novel europium(III) complex was synthesized using TTA (α-thenoyltrifluoroacetone) as the first ligand and H₂bpdc (2,2′-bipyridine-3,3′-dicarboxylate) as the second ligand. Elemental analysis, thermal analysis, IR and UV–vis spectrum and fluorescence spectrum of the europium(III) complex were carried out. A characteristic Eu³⁺ fluorescence emission was observed in ethanol–water (1:1) solution, indicating that the complex is stable in solution and the emission of Eu(III) ions was not influenced by the water molecules. The fluorescence emission of the complex was quenched completely by the Co²⁺ and Fe³⁺ ions, but the quenched emission was recovered in the presence of glycine. Moreover, the Eu³⁺ emission was very sensitive to pH, so the complex can be used as pH-dependent fluorescence probe or chemosensors.     

A turn-on fluorescent anion receptor based on N,N′-di-β-naphthyl-1,10-phenanthroline-2,9-diamide

A simple turn-on fluorescent anion chemosensor with amide moiety as binding sites was designed, synthesized and characterized. Binding ability of the receptor 1 with anions was evaluated through the fluorescence titration in DMSO and the ¹H NMR titration in DMSO-d₆ and coordination of anions to 1 led to a visible enhancement in fluorescence intensity. The fluorescence enhancement could be explained on the basis of two signaling transduction mechanisms: (1) inhibition of a photoinduced electronic transfer (PET) mechanism and (2) anion-induced increase of the rigidity of the host molecules. In addition, the results of ¹H NMR titrations suggested that a host-guest hydrogen-bonding complex with an association constant K_ass=7379 mol⁻¹ L was formed between 1 and F⁻ and the mode of host-guest interactions was provided.     

Novel Pyrazoline-Based Selective Fluorescent Sensor for Hg2+

This paper presents the preparation of a pyrazoline compound and the properties of its UV–Vis absorption and fluorescence emission. Moreover, this compound can be used to determine Hg²⁺ ion with selectivity and sensitivity in the EtOH:H₂O?=?9:1 (v/v) solution. This sensor forms a 1:1 complex with Hg²⁺ and shows a fluorescent enhancement with good tolerance of other metal ions. This sensor is very sensitive with fluorometric detection limit of 3.85?×?10^?10 M. In addition, the fluorescent probe has practical application in cells imaging.     

Analysis of Tb3+- and melittin-binding with the C-terminal domain of centrin in Euplotes octocarinatus

Centrin is a low molecular mass (20 KDa) protein that belongs to the EF-hand superfamily. In this work, the interaction between the Tb³⁺-saturated C-terminal domain of Euplotes octocarinatus centrin (Tb₂-C-EoCen) and 2-p-toluidinylnaphthalene-6-sulfonate (TNS) was investigated using difference UV–vis spectra and the fluorescence spectra methods. In 100 mM N-2-hydroxy-ethylpiperazine-N-2-ethanesulfonic acid (Hepes) at pH 7.4, with the addition of Tb₂-C-EoCen, four new peaks were observed at 265 nm, 278 nm, 317 nm and 360 nm by absorptivity compared with blank solution of TNS. At the same time, the reaction could be measured by fluorescence spectra. The fluorescence emission of TNS was shifted from 480 nm to 445 nm in the presence of Tb₂-C-EoCen. Meanwhile, its fluorescence intensity was increased markedly. The 1:1 stoichiometric ratio of C-EoCen to TNS was confirmed by fluorescence titration curves. The conditional binding constants of TNS with C-EoCen and Tb₂-C-EoCen were calculated to be log K_{(C-EoCen-TNS)}=5.32±0.04  M^?1 and log K_{(Tb2-C-EoCen-TNS)}=5.58±0.12 M^?1, respectively. In addition, the protein of Tb₂-C-EoCen binding with melittin was also studied. Based on the fluorescence titration curves, the 1:1 stoichiometric ratio of Tb₂-C-EoCen to melittin was confirmed. And the conditional binding constant of C-EoCen with melittin was calculated to be log Ka′=6.79±0.17 M^?1.     

Acidichromism and Ionochromism of Luteolin and Apigenin,the Main Components of the Naturally Occurring Yellow Weld: A Spectrophotometric and Fluorimetric Study

Luteolin and apigenin, extracted from Reseda luteola L., were spectrophotometrically and fluorimetrically studied. The spectra were investigated as a function of pH in methanol/water solutions (1/2, v/v) in the 2–12 pH range. The absorption spectra markedly shifted to the red by increasing the pH. Three acid–base dissociation steps were detected for luteolin (pK _a = 6.9; 8.6; 10.3) and two for apigenin (pK _a = 6.6; 9.3). Fluorescence emission was very weak or undetectable (Φ _F < 10⁻⁴) in acidic solution, but increased in intensity with increasing the pH. Both molecules exhibited a great propensity towards complex formation with metal ions, with association constants on the order of 10⁵–10⁷ for the first complexation step; in the presence of excess Al³⁺ ions, multiple equilibria were detected. A marked fluorescence enhancement was observed upon complexation with Al³⁺ ions (Φ _F ∼ 1 for luteolin and ∼10⁻² for apigenin).     

The nature of the effect of Gd(III) on fluorescence of Ln(III) chelates in water solutions

The intensity of fluorescence of Eu(III) and Sm(III) ions sensitized by molecules of n-benzoyltrifluoroacetone and 1,10-phenanthroline introduced in a water solution in a ratio of 3: 1 is studied as a function of the ion concentration in the solution. The comparison of the fluorescence decay curves of Eu(III) and Sm(III) in D₂O and H₂O (pH≥7) solutions containing 10^?4 M of n-Cl-BTFA and 3×10^?5 M of 1,10-phen and the values of τ_fl of Sm(III) in themselves (51–90 μs) are indicative of an insignificant content of water molecules in the first coordination sphere of ions. The effect of other ions on I _fl and τ_fl of Eu(III) ions is studied under these conditions. The intensity of fluorescence of Eu(III) in solutions of 10^?4 M Cl-BTFA and 3×10^?5 H 1,10-phen is found to increase by 1–2 orders of magnitude in the presence of Y(III) and Gd(III) ions, and the magnitude of this effect is unaffected by deoxygenation of the solution. The introduction of a third ion Nd(III) in the solution is shown to attenuate the influence of Gd(III) on I _fl of Eu(III) for Nd(III) concentrations commensurable with the Eu(III) concentration in the solution. The strength of the influence of Gd(III) ions on I _fl of Eu(III) is found to depend on the method of preparation of the solution. The analysis of the results obtained testifies that inhomogeneities consisting of chelates of lanthanide ions displaced from the water structure appear in water. The presence of these inhomogeneities results in efficient energy transfer from ligands of Gd(III) chelates to Eu(III) chelates, which is the reason for the increasing I _fl of Eu(III). The possibility of using data on the enhancement of I _fl of Eu(III) in the presence of Gd(III) and on the reduction of τ_fl of Eu(III) in the presence of Nd(III) for estimating dimensions and structures of displaced systems is discussed.     

Optical Recognition of Anions by Ruthenium(II)-Bipyridine-Calix[4]Arene System

The two t-butylcalix[4]arene attached ruthenium(II)-bipyridine complexes (Rubc2 and Rubc3) has been synthesized and the anion recognition studies have been carried out using emission techniques. The binding of anions, which are sensed by the complexes, are studied by UV-visible and emission techniques. The complex Rubc2 recognizes the Cl^?, H₂PO₄ ^? and AcO^? anions. The complex Rubc3 recognizes the Br^? and AcO^? anions. The AcO^? quenches the emission intensity of both two complexes but the other anion increases the emission intensity of the complexes. The excited state lifetime and transient absorption studies were carried out the AcO^? facilitates non radiative pathway. The other anions stabilize the excited state and facilitate the radiative pathway.     

Fluorescence enhancement of oxide fluoride glass co-doped with TbF3 and SmF3

The fluorescence property of xTbF₃-BaF₂-AlF₃-GeO₂+ySmF₃ (x=0.01-40 mol%, y=0-5 wt%) glasses were investigated. The enhancement of Sm³⁺ fluorescence was recognized in the presence of Tb³⁺. Increasing Tb³⁺ content, the emission color changed from green to orange. When the intensity of fluorescence at 540 nm originated from Tb³⁺ is compared with that at 600 nm originated from Sm³⁺, the information about the concentration quenching of Tb³⁺ and Sm³⁺ was obtained. From these results, rare earth ions were dispersed identically in the glasses. After heating to 673 K or cooling to 77 K, the emission color of 20TbF₃-20BaF₂-10AlF₃-50GeO₂/mol%+0.05 wt% SmF₃ glass was reversibly changed from orange to green. In addition, while the emission from 10TbF₃-20BaF₂-10AlF₃-60GeO₂+0.01 wt% SmF₃ glass was green, its crystallized sample, prepared by annealing at 1073 K, exhibited an orange emission due to Sm³⁺ at room temperature.     

Spectroscopic Study of Porphyrin-Caffeine Interactions

The association between water-soluble porphyrins: 4,4′,4″,4?-(21?H,23?H-porphine-5,10,15,20-tetrayl)tetrakis-(benzoic acid) (H₂TCPP), 5,10,15,20-tetrakis(4-sulfonatophenyl)-21?H,23?H-porphine (H₂TPPS₄), 5,10,15,20-tetrakis[4-(trimethylammonio)phenyl]-21?H,23?H-porphine tetra-p-tosylate (H₂TTMePP), 5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21?H,23?H-porphine tetra-p-tosylate (H₂TMePyP), the Cu(II) complexes of H₂TTMePP and H₂TMePyP, as well as chlorophyll a with caffeine (1,3,7-trimethylxanthine) has been studied analysing their absorption and emission spectra in aqueous (or acetone in case of chlorophyll a) solution. During the titration by caffeine the porphyrins absorption spectra undergo the evolution – the bathochromic effect can be observed as well as the hypochromicity of the Soret maximum. The association constants were calculated using curve-fitting procedure (K_AC of the order of magnitude of 10³?mol^-1). Whereas the emission spectra point at the presence of the fluorescence quenching effect testifying for the partial inactivation of the porphyrin molecule. The fluorescence quenching constants were calculated from Stern-Volmer plots. The results obtained show that caffeine can interact with water-soluble porphyrins and through formation of stacking complexes is able to quench their ability to emission.     

Spectra-Structure Correlations in 2,2′-Bipyridine Mercury(II) Saccharinate: Comparison With Mercury(II) Saccharinate And Chloromercury(II) Saccharinate∗

Abstract

The infrared spectrum of 1:1 complex of mercury(II) saccharinate with 2,2′-bipyridine, [Hg(C₇H₄NO₃S)₂(C₁₀H₈N₂)], was studied in the CO and SO₂stretching regions. The appearance of the spectrum in the region of the carbonyl stretching modes was correlated with the number of non-equivalent CO groups in the structure. The spectral and structural characteristics of the CO groups in the title compound were compared with the corresponding ones in the mercury(II) saccharinate and chloromercury(II) saccharinate. It was found that the frequency of the CO stretchings in the spectrum of Hg(bpy) (sac)₂ is significantly lower (1630 and 1615 cm^?1) than the frequency of the corresponding modes in the spectra of covalently bonded mercury(II) saccharinate (1705 and 1680 cm^?1) and chloromercury saccharinate (1694 cm^?1). An attempt was also made to assign the bands which are mainly due to the symmetric and the antisymmetric SO₂ stretching vibrations.

     

Quinoline-Based “On-Off” Fluorescent Sensor for Acetate: Effect of Link Mode between Binding Sites and Fluorophore on Fluorescence Changes

ABSTRACT

A novel colorimetric and fluorescence anion sensor based on 8-nitroquinolyl-2-aldehyde phenyl-thiosemicarbazone (1) was designed and synthesized according to the approach that the binding sites were covalently linked to the signaling units. In DMSO, sensor 1 exhibited a naked-eye color change from colorless to yellow upon complexation with acetate. The association constant of 1 for acetate ion was determined to be 1.20 × 10³ M^?1 by nonlinear fitting analyses of the titration curves. The strong interactions of compound 1 with acetate ion could be rationalized on basis of not only the guest basicity but also shape complementarity between 1 and acetate. In addition, the fluorescence emission of 1 was effectively quenched upon addition of acetate ions owing to the fact that the photoinduced electron transfer (PET) was enhanced.     

Salicylaldehyde Phenylhydrazone: A New Highly Selective Fluorescent Lead (II) Probe

The fluorescence intensity of salicylaldehyde phenylhydrazone (L), in 1:1 (v/v) CH₃OH:H₂O was enhanced by ca. 100 times with a blue shift in emission maximum, on interaction with Pb²⁺ ion. No enhancement in fluorescent intensity of L was observed on interaction with metal ions - Na⁺, K⁺, Ca²⁺, Cu²⁺, Ni²⁺, Zn²⁺, Cd²⁺ and Hg²⁺. This signal transduction was found to occur via photoinduced electron transfer (PET) mechanism. A 1:1 complexation between Pb²⁺ and L with log β?=?7.86 has been proved from fluorescent and UV/Visible spectroscopic data. The detection limit of Pb²⁺ was calculated to be 6.3?×?10^?7?M.     

The Smart 2-(2-Fluorobenzoyl)-N-(2-Methoxyphenyl)Hydrazinecarbothioamide Functionalized as Ni(II) Sensor in Micromolar Concentration Level and its Application in Live Cell Imaging

In recent years, fluorescent probes for the detection of environmentally and biologically important metal cations have received extensive attention for designing and development of fluorescent chemosensors. Herein, we report the photophysical results of 2-(2-fluorobenzoyl)-N-(2-methoxyphenyl) hydrazinecarbothioamide (4) functionalized as Ni (II) sensor in micromolar concentration level. Through fluorescence titration at 488 nm, we were confirmed that ligand 4 showed the remarkable emission by complexation between 4 and Ni (II) while it appeared no emission in case of the competitive ions (Cr³⁺, Fe²⁺, Co²⁺, Ba²⁺, Cu²⁺, Ca²⁺, Na⁺, K⁺, Cu⁺, Cs⁺). Furthermore, ligand 4 exhibited no toxicity with precise cell permeability toward normal living cells using L929 cell lines in bio imaging experiment investigated through confocal fluorescence microscope. The non-toxic behavior of ligand 4 (assessed by MTT assay) and its ability to track the Ni²⁺ in living cells suggest its possibility to use in biological system as nickel sensor.

Positions of the Glycans in Molluscan Hemocyanin, Determined by Fluorescence Spectroscopy

Molluscan hemocyanins are glycoproteins with different quaternary and carbohydrate structures. It was suggested that the carbohydrate chains of some Hcs are involved in their antiviral and antitumor effect, as well in the organization of the quaternary structure of the molecules. Using a well-known complex for saccharide sensing, positions and access to the carbohydrate chains in the native hemocyanins from Rapana venosa (RvH) and Helix lucorum (HlH) and also their structural subunits (RvH1, RvH2 and β_cHlH) and functional units (FUs) were analysed by fluorescence spectroscopy and circular dichroism. Almost no effect was observed in the fluorescence emission after titration of the complex with native RvH and HlH due to lack of free hydroxyl groups which are buried in the didecameric form of the molecules. Titration with the structural subunits β_cHlH and RvH2, increasing of the emission indicates the presence of free hydroxyl groups compared to the native molecules. Complex titration with the structural subunit βc-HlH of H. lucorum Hcs leads to a 2.5 fold increase in fluorescence intensity. However, the highest emission was measured after titration of the complex with FU βcHlH-g. The result was explained by the structural model of β_cHlH-g showing the putative position of the glycans on the surface of the molecule. The results of the fluorescent measurements are in good correlation with those of the circular dichroism data, applied to analyse the effect of titration on the secondary structure of the native molecules and functional units. The results also support our previously made suggestion that the N-linked oligosaccharide trees are involved in the quaternary organization of molluscan Hcs.