Indole-based Fluorescent Sensors for Selective Detection of Hg2+

A series of indole-based fluorescent chemosensors 1–4 were prepared and investigated characteristick features with transition metal ions. Sensors 1 and 2 were selective for Hg²⁺ ion among a series of metal ions in H₂O–DMSO with association constants of 4.60×10⁴ and 5.90×10⁴?M^?1 and detection limits of 140 and 101.6 μM, respectively.

Fluorescence Turn on Sensor for Sulfate Ion in Aqueous Medium Using Tripodal-Cu2+ Ensemble

We report the selective recognition of sulfate anion in aqueous medium at biological pH 7.2 over the other interfering anions based on naphthoic acid bearing tripodal ligand by applying fluorescence turn off-on mechanism. The carboxylic acid groups in the ligand enhance the solubility in water and enable it to form complex with copper salt. Thus formed L-Cu²⁺ ensemble quench the fluorescence of the parent ligand and in turn recognize sulfate anion via revival of fluorescence intensity. The 1:2 stoichiometry was confirmed by ESI mass spectral data and Job’s plot. The average binding constant was found to be 6.2?×?10⁸ M^?2.

Interaction Mechanism of Trp-Arg Dipeptide with Calf Thymus DNA

The interaction between Trp-Arg dipetide (WR) and calf thymus DNA (ctDNA) in pH 7.4 Tris-HCl buffer was investigated by multi-spectroscopic techniques and molecular modeling. The fluorescence spectroscopy and UV absorption spectroscopy indicated that WR interacted with ctDNA in a minor groove binding mode and the binding constant was 4.1?×?10³. The ionic strength effect and single-stranded DNA (ssDNA) quenching effect further verified the minor groove binding mode. Circular dichroism spectroscopy (CD) was employed to measure the conformation change of ctDNA in the presence of WR. The molecular modeling results illustrated that electrostatic interaction and groove binding coexisted between them and the hydrogen bond and Van der Waals were main acting forces. All the above methods can be widely used to investigate the interaction of peptide with nucleic acids, which contributes to design the structure of new and efficient drugs.

Perylene Diimide Appended with 8-Hydroxyquinoline for Ratiometric Detection of Cu2+ Ions and Metal Displacement Driven “Turn on” Cyanide Sensing

Perylene diimide (PDI) 3 and 4 appended with 8-hydroxyquinoline derivatives have been synthesized and their photophysical and spectroscopic properties have been experimentally determined. Moreover, PDIs 3 and 4 show ratiometric behavior to detect Cu²⁺ colorimetrically with visible color change from coral red to light pink, whereas 3 and 4 show “turn-off” behavior in fluorescence with lowest limit of detection 5?×?10^?7 M. The PDI 3 could be further utilized for ratiometric CN^? detection colorimetrically and as “turn-on” sensor for CN^? detection fluorometrically with lowest limit of detection 8?×?10^?6 M. The comparison of spectroscopic properties of PDI 1-4 highlights the importance of linking 8-hydroxyquinoline units on the PDI core at bay position for achieving Cu²⁺ recognition event into ratiometric signal.

Off-on Fluorescent Sensor from On-off Sensor: Exploiting Silver Nanoparticles Influence on the Organic Fluorophore Fluorescence

Turn-off fluorescence of organic fluorophore, 2-{[4-(2H-Naphtho[1,2-d][1,2,3]triazol-2-yl)-phenyl]carboxylic acid (NTPC), with metal ions (Fe³⁺, Cu²⁺, Pb²⁺) was converted into turn-on fluorescent sensor for biologically important Zn²⁺, Cu²⁺ and Fe³⁺ metal ions in aqueous solution at ppb level by exploiting strong fluorescence quenching phenomena of metal nanoparticles when organic fluorophores assembled in the vicinity of metallic surface. Amino acid attached phenolic ligands (L) were used as reducing as well as functional capping agents in the synthesis of silver nanoparticles (AgNPs). The hydrogen bonding functionality of L facilitated the assembling of NTPC in the vicinity of metallic surfaces that leads to complete quenching of NTPC fluorescence. The strong and selective coordination of L with metal ions (Zn²⁺, Cu²⁺ and Fe³⁺) separates the NTPC from the AgNPs surface that turn-on the NTPC fluorescence. HR-TEM and absorption studies confirm the metal coordination with L and separation of NTPC from the AgNPs surface. Mn²⁺ showed selective red shifting of NTPC fluorescence after 12 h with all sample. Effects of different amino acid attached phenolic ligands were explored in the metal ion sensitivity and selectivity. This approach demonstrates the multifunctional utility of metal NPs in the development of turn-on fluorescence sensor for paramagnetic heavy metal ions in aqueous solution.

Photoinduced Electron Transfer Reactions of Ruthenium(II)-Complexes Containing Amino Acid with Quinones

With the aim of mimicking, at basic level the photoinduced electron transfer process in the reaction center of photosystem II, ruthenium(II)-polypyridyl complexes, carrying amino acids were synthesized and studied their photoinduced electron transfer reactions with quinones by steady state and time resolved measurements. The reaction of quinones with excited state of ruthenium(II)-complexes, I–V in acetonitrile has been studied by luminescence quenching technique and the rate constant, k_q, values are close to the diffusion controlled rate. The detection of the semiquinone anion radical in this system using time-resolved transient absorption spectroscopy confirms the electron transfer nature of the reaction. The semiclassical theory of electron transfer has been successfully applied to the photoluminescence quenching of Ru(II)-complexes with quinones.

Urea Based Dipodal Fluorescence Receptor for Sensing of Fe3+ Ion in Semi-Aqueous Medium

Urea based fluorescent chemosensor 1 was synthesized. Receptor 1 shows unique selectivity for the Fe³⁺ion and no such significant response was noticed with other metal ions (Cr³⁺, Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺, Pb²⁺ and Bi³⁺) in DMSO/H₂O (50:50,v/v) semi-aqueous solution. The binding features have been established by absorption and fluorescence spectroscopic methods. The binding constant (K) values obtained from Benesi-Hildebrand, Scatchard and Connor plot for receptor 1 is (8.3?±?0.3) × 10³ M^?1 and has good detection limit 0.7?μM. The stoichiometry of 1.Fe³⁺ complex was confirmed by mass spectroscopy and Job’s plot.

A New Thiophenyl Pyrazoline Fluorescent Probe for Cu2+ in Aqueous Solution and Imaging in Live Cell

A new thiophenyl pyrazoline probe for Cu²⁺ in aqueous solution was synthesized and characterized by IR, NMR, HRMS and X-ray analysis. The probe displays remarkably high selectivity and sensitivity for Cu²⁺ with a detection limit of 1.919?×?10^?7 M in aqueous solution (EtOH:HEPES = 1:1, v/v, 0.02 M, pH?=?7.2). In addition, the probe is further successfully used to image Cu²⁺ in living cells and the probe possesses good reversibility.

A Novel Colorimetric and Fluorescent “Off-On” Chemosensor for Cu2+ Based on a Rhodamine Derivative Bearing Naphthyridine Group

A new rhodamine-based derivative bearing a naphthyridine group (compound 1) was synthesized as a colorimetric and fluorescent “off-on” chemosensor for Cu²⁺ in aqueous solutions. The sensing behaviors of 1 toward various metal ions in neutral aqueous solutions were investigated by absorption and fluorescence spectroscopies. Compound 1 is found to exhibit a significant increase in absorbance at 561 nm and an amplified fluorescence at 590 nm toward Cu²⁺ in a selective, sensitive and rapid manner. The quantification of Cu²⁺ by 1 using an absorption spectroscopy method was satisfactory in the linear working range 0.9–10 μM, with a detection limit of 5.4?×?10^?8?M for Cu²⁺ and good tolerance of other metal ions. Upon addition of Cu²⁺, the spirolactam ring (colorless and nonfluorescent) of 1 was opened to ring-opened amide (red color and fluorescent) and a 1:1 stoichiochemetry for the 1-Cu²⁺ complex was formed with an association constant of 1.57?×?10⁴?M^?1.     

A Schiff-Based Colorimetric Fluorescent Sensor with the Potential for Detection of Fluoride Ions

A simple Schiff-based colorimetric fluorescent receptor 1 was prepared. It exhibits a “turn-on-type” mode with high sensitivity in the presence of F^?. The change in color is very easily observed by the naked eye in the presence of F^?, whereas other anions do not induce such a change. Job plot indicated a 1:2 complexation stoichiometry between receptor 1 and F^?. The association constant for 1-F^? in CH₃CN was determined as 1.32*10⁵ M^?2 by a Hill plot.

Sensing of Zn2+ion by N-Furfurylsalicylaldimine Based on CHEF Process†

The recognition ability of N-Furfurylsalicylaldimine (HL) toward various cations (Pb²⁺, Hg²⁺, Ba²⁺, Cd²⁺, Ag⁺, Zn²⁺, Cu²⁺, Ni²⁺, Co²⁺, K⁺, Sr²⁺, and Na⁺) has been studied by UV–Vis and fluorescence spectroscopy. The compound showed highly selective fluorescence signaling behaviour for Zn²⁺ ions in methanol-water medium based on CHEF process and is capable of distinguishing Zn²⁺ from Cd²⁺ ion. From single crystal X-ray analysis it is revealed that a Zn²⁺ ion binds two ligand molecules through imine nitrogen and phenolate oxygen atom.

Calix Receptor Edifice; Scrupulous Turn Off Fluorescent Sensor for Fe(III), Co(II) and Cu(II)

Novel Supramolecular fluorescence receptor derived from calix-system i.e. calix[4]resorcinarene bearing dansylchloride as fluorophore was designed and synthesized. The compound was purified by column chromatography and characterized by elemental analysis, NMR and Mass spectroscopy. Tetradansylated calix[4] resorcinarene (TDCR) shows a boat conformation with C₂v symmetry. The complexation behaviour of metal cations [Ag(I), Cd(II), Co(II), Fe(III), Hg(II), Cu(II), Pb(II), Zn(II), U(VI) (1?×?10^-4?M)] with tetra dansylated calix[4]resorcinarene (1?×?10^-6?M) was studied by spectophotometry and spectrofluorometry. Red shift in the absorption spectra led us to conclude that there is strong complexation Fe(III), Co(II) and Cu(II) with TDCR. These metal cations also produce quenching with red shifts in the emission spectra. The maximum quenching in emission intensity was observed in the case of Fe(III) and its binding constant was also found to be significantly higher than that of Co(II) and Cu(II). Quantum yield of metal complexes of Fe(III) was found to be lower in comparison with Co(II) and Cu(II) complexes. Stern Volmer analysis indicates that the mechanism of fluorescence quenching is either purely dynamic, or purely static.     

Study on the Selectivity of Anion Receptors Based on Similar (thio)urea Fragments

Three new selective anion receptors containing the (thio)urea binding sites were developed, Indole-3-formaldehyde phenyl-semithiocarbazone, Indole-3-formaldehyde nitrophenyl-semithiocarbazone, and Indole-3-formaldehyde nitrophenyl-semicarbazone, nominated as receptors 1, 2 and 3, respectively. Receptor 1 shows high selective recognition for F^? only, while both receptor 2 and receptor 3 containing a p-nitro group show high selective recognition for AcO^?. The high selective recognition of these receptors to anions is further investigated by X-ray crystallography diffraction, UV-vis, fluorescence analyses and ¹H NMR. Furthermore, receptor 2 changes from yellow to orange, and receptor 3 darkens when acetate is added, providing a way of detection by ‘naked-eye’.     

9, 10-Bis(8-Quinolinoxymethyl)Anthracene—A Fluorescent Sensor for Nanomolar Detection of Cu2+ with Unusual Acid Stability of Cu2+-Complex

In this work, the dipod 9,10-bis(8-quinolinoxymethyl)anthracene (1) and for comparison, monopod 9-(8-quinolinoxymethyl)anthracene (2) have been synthesized. The fluoroionophore 1 in pH 7.1 HEPES buffered CH₃CN:H₂O (4:1 v/v) solution shows quenching only with Cu²⁺ with lowest limit of detection 150 nM, amongst various metal ions. Fluoroionophore 1 could also be applied to sense Co²⁺ with lowest limit of detection 600 nM. By modulating the pH of the solution and concentration of Cu²⁺, 1 shows respective “On-Off-On” and “On-Off” fluorescent switching. The self-assembly of two Cu²⁺ ions and two molecules of fluoroionophore 1 to form closed structure [Cu₂(L)₂]⁴⁺ seems to be responsible for nanomolar sensitivity towards Cu²⁺. The combination of delayed second protonation of 1 (pK_a2?=?2.6) and stepwise protonation of [Cu₂ L ₂]⁴⁺ causes unusual stability of [Cu(LH)₂]⁴⁺ even at pH?<?2.

Morphological Effect on Fluorescence Behavior of Silver Nanoparticles

Effect of Silver nanoparticles (AgNPs) morphology on their fluorescence behavior is reported. AgNPs sol stabilized by Ethylene Diamine Tetra Acetic-Acid (EDTA) was prepared by chemical reduction method. Morphology of the AgNPs was tuned through changing the Ag⁺ ion concentration and P^H of reaction mixture. Additional peaks observed in surface Plasmon resonance spectra suggest the an-isotropic nature of AgNPs. Actual morphology was judged by Transmission Electron Microscopy. Emission spectra recorded using Spectrofluoremeter suggest the fluorescent nature of AgNPs, which also influenced by morphology of AgNPs and attributed to the variation in surface structure of an-isotropic AgNPs.

Study on the Interaction between Florasulam and Bovine Serum Albumin

In this paper, the interaction between florasulam (FU, 2′,6′,8-trifluoro-5-methoxy [Kragh-Hansen U, Molecular aspects of ligand binding to serum albumin. Pharmacol Rev 33(1):17–53 1981; Carter DC and Ho JX, Structure of serum albumin. Adv Protein Chem 45:153–203 1994; He XM, and Carter DC, Atomic structure and chemistry of human serum albumin. Nature 358(6383):209–215 1992] triazolo [1,5-c]pyrimidine-2-sulfonanilide) and bovine serum albumin (BSA) was investigated by fluorescence, ultraviolet absorption (UV) and Far-UV circular dichroism (CD) spectrometries. A strong fluorescence quenching was observed and the quenching mechanism was considered as static quenching. The binding constant of FU with BSA at 299 and 309 K were obtained as 1.5?×?10⁴ and 7.1?×?10³ l mol^?1, respectively. There was one binding site between FU and BSA. The thermodynamic parameters enthalpy change (ΔH) and entropy change (ΔS) were calculated as ?57.89 kJ mol^?1 and ?113.6 J mol^?1 K^?1, respectively, which indicated that the acting force between FU and BSA was mainly hydrogen bond and Van der Waals force. According to the Förster non-radiation energy transfer theory, the average binding distance between donor (BSA) and acceptor (FU) was obtained (r?=?1.59 nm). The investigations of the UV/Vis and CD spectra of the system showed that the conformation of BSA was changed in presence of FU.     

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.

Studies on ionic solvation behavior of ionic liquid (tetrabutylphosphonium tetrafluoroborate) in some liquid media by volumetric,viscometric, and acoustic measurements

Physicochemical properties such as density (ρ), viscosity (η), ultrasonic speed (u) of ionic liquid tetrabutylphosphonium tetrafluoroborate in acetonitrile, tetrahydrofuran, 1,3-dioxolane, and their binaries have been studied over the entire range of composition at 298.15°K. Apparent molar volumes (? _V ) and viscosity B-coefficients supplemented with the data of densities and viscosities, respectively, have been interpreted in terms of ion–solvent interactions. The limiting apparent molar volumes (? _V ⁰ ), experimental slopes (S _V ^? ) derived from the Masson equation, and viscosity A and B-coefficients analyzed by the Jones–Dole equation have also been interpreted. The adiabatic compressibility (β) has been evaluated using the ultrasonic speed (u) values. Thereafter, limiting apparent molar adiabatic compressibilities (? _K ⁰  ) have been evaluated and discussed for the same.

A Colorimetric and Fluorescent Probe Based on Michael Acceptor Type Diketopyrrolopyrrole for Cyanide Detection

A new probe 1 was synthesized by incorporating an α,β-unsaturated ketone to a diketopyrrolopyrrole fluorophore. The probe exhibited a selective and sensitive response to cyanide against other anions. Addition of CN^? aqueous solution to 1 resulted in a rapid color change from pink to light yellow together with a blue shift from 518 to 421 nm, while other anions did not induce any significant color change. Furthermore, the Michael addition of cyanide to 1 elicited 98% fluorescence quenching at 608 nm, which constituted the fluorescence signature for cyanide detection. The detection limit was 0.67 μM using the fluorescence spectra changes, which was far lower than the WHO guideline of 1.9 μM. Moreover, 1-based test strips could successfully detect CN^? solutions.     

Recent Results at BESIII

The BESIII detector operating at the BEPCII e ⁺ e ^? collider collected 2.25 × 10⁸ J/ψ events, 1.06 × 10⁸ ψ(3686) events, 2.9 fb^?1 data at ${\sqrt s}$ = 3.773 GeV and 477 pb^?1 data at ${\sqrt s}$ = 4.01 GeV, respectively, by the end of 2011. We report some recent results on light hadron spectroscopy, charmonium spectroscopy and charm physics, which are obtained by analyses of these data.