New Application of a Known Molecule: Rhodamine B 8-hydroxy-2-quinolinecarboxaldehyde Schiff Base as a Colorimetric and Fluorescent “Off-On” Probe for Copper (II)

Rhodamine B 8-hydroxy-2-quinolinecarboxaldehyde Schiff base (1) has been investigated as a colorimetric and fluorescent “off-on” probe for the recognition of Cu²⁺ in aqueous solution. Probe 1 was synthesized by condensation of rhodamine B hydrazide and 8-hydroxy-2-quinolinecarboxaldehyde, which exhibited good selectivity for Cu²⁺ among a range of biologically and environmentally important metal ions. The Cu²⁺ recognition event undergoes a Cu²⁺ promoted hydrolysis of probe 1 to release rhodamine B and the recognition process is barely interfered by other coexisting metal ions.

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.

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.

A Novel Series Colorimetric and Off–On Fluorescent Chemosensors for Fe3+ Based on Rhodamine B Derivative

A novel series colorimetric and off–on fluorescent chemosensors (2a, 2b, 2c) were designed and synthesized, which showed reversible and highly selective and sensitive recognition toward Fe³⁺ over other examined metal ions. Upon addition of Fe³⁺, sensors (2a, 2b) exhibit remarkably and 2c exhibits moderate enhanced absorbance intensity and color change from colorless to pink in CH₃OH–H₂O(1:1, v/v). The three compounds (2a, 2b, 2c) may therefore be applicable as rhodamine-based turn-on type fluorescent chemosensors.     

Selective Fluorescent Detection of Aspartic Acid and Glutamic Acid Employing Dansyl Hydrazine Dextran Conjugate

Highly water soluble polymer (DD) was prepared and evaluated for its fluorescence response towards various amino acids. The polymer consists of dansyl hydrazine unit conjugated into dextran template. The conjugation enhances higher water solubility of dansyl hydrazine moiety. Of screened amino acids, DD exhibited selective fluorescence quenching in the presence of aspartic acid (Asp) and glutamic acid (Glu). A plot of fluorescence intensity change of DD against the concentration of corresponding amino acids gave a good linear relationship in the range of 1?×?10^?4 M to 25?×?10^?3 M. This establishes DD as a potential polymeric sensor for selective sensing of Asp and Glu.

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’.     

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.

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.

A Novel Ratiometric Fluorescent Mercury Probe Based on Deprotonation-ICT Mechanism

A new NBD-rhodamine dye (1) was developed as a colorimetric and ratiometric fluorescent chemosensor for Hg²⁺ with good selectivity in aqueous ethanol solutions under neutral to basic conditions. Sensor 1 showed absorption at 468 nm and a weak emission at 529 nm (? _F ?=?0.063) in ethanol/aqueous tris buffer (9:1, v/v) of pH 9.17 solution. Bathochromic shifts in both absorption (492 nm) and fluorescence spectra (569 nm, ? _F ?=?0.129), respectively upon addition of 2 equiv. of Hg²⁺ were observed. The ring-opening reaction of the spirolactam form to the corresponding xanthene form was not found. The interaction of Hg²⁺ with chemosensor 1 resulted in the deprotonation of the secondary amine conjugated to the NBD component so that the electron-donating ability of the N atom was enhanced. Deprotonation-ICT mechanism of secondary amines was suggested for the ratiometric fluorescent chemosensing for Hg²⁺.     

Bis(2-Hydroxy-3-Isopropyl-6-Methyl-Benzaldehyde)Ethylenediamine: A Novel Cation Sensor

Novel substituted phenol-based new symmetrical bis(2-hydroxy-3-isopropyl-6-methyl-benzaldehyde)ethylenediamine (1) has been designed and synthesized. The compound 1 fluorometrically recognized Cu²⁺ ion in CH₃OH/H₂O (90:10, v/v) by exhibiting an increase in emission upon complexation. In addition, Cu²⁺ gave rise to a change in colour of the solution of compound 1, which was clearly visible to the naked eye under UV irradiation. The association constant (K) of compound 1 with Cu²⁺ ion was computed with the Benesi-Hildebrand plot and Scatchard plot at 43,000 M^?1 and 43,011 M^?1 respectively.     

Aging effect in CaLaBa{Cu1???xFex}3O7???�� with 0 �� x �� 0.07 studied by M?ssbauer spectroscopy

In this work, we study the long-term aging effect caused by Fe atoms in the superconductor CaLaBa{Cu_1???xFe_x}₃O_7????? with 0 ?? x ?? 0.07. XRD confirms that this system has a YBCO-like structure. The critical temperature (T_c) is strongly affected by aging and depends on the amount of Fe in the structure. Room temperature Mössbauer spectroscopy reveals the presence of the typical species A, B?CB ??, C and new species E ?? and F. Interestingly; A, which corresponds to the Fe^3?+? atom located in the Cu(1) of the chains with spin S _z = 3/2, shows a drastic reduction which means migration to the species B, B ?? and C. Species B and B ?? correspond to the Fe^3?+? in the Cu(2) site forming planar quasi-octahedral and planar square pyramidal, while the C specie is a square pyramidal with O(5) respectively (spin S_z = 3/2 in all these cases). Aging causes loss of superconductivity in the samples with 5 and 7% of iron content.     

The First Bifluoride Sensor Based on Fluorescent Enhancement

The first fluorescent sensor for HF₂ ^? anion, N¹, N³-di(naphthalene-1-yl)isophthalamide (L) has been derived from α-Napthylamine and isopthaloyl chloride. In 1:1 (v/v) DMSO:H₂O, L exhibits high selectivity towards HF₂ ^? anion with a 4-fold enhancement in fluorescent intensity. Very little enhancement in fluorescence intensity is observed for F^?, Cl^?, Br^?, I^?, SCN^?, PO₄ ^3?, SO₄ ^2?, and CH₃COO^? anions. The stoichiometry interaction between L and HF₂ ^? is found to be 1:1 from fluorescence and UV/Visible spectral data. DFT calculation shows that binding between HF₂ ^? and L is 1:1 and increases the relative planarity between the two naphthyl rings causing fluorescence enhancement. A shift of 0.080 V in oxidation potential of L is observed on interaction with HF₂ ^? by cyclic voltammetry and square wave voltammetry.     

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 Sensitive Schiff-Base Fluorescent Chemosensor for the Selective Detection of Zn2+

A Schiff-base fluorescent probe – N, N^/-bis(salicylidene) trans 1, 2 – diaminocyclohexane (H ₂ L) was synthesized and evaluated as a chemoselective Zn²⁺ sensor. Upon treatment with Zn²⁺, the complexation of H ₂ L with Zn²⁺ resulted in a bathochromic shift with a pronounced enhancement in the fluorescence intensity in ethanol solution. Moreover, other common alkali, alkaline earth and transition metal ions failed to induce response or minimal spectral changes. Notably, this chemosensor could distinguish clearly Zn²⁺ from Cd²⁺. The stoichiometric ratio and association constant were evaluated using Benesi – Hildebrand relation giving 1:1 stoichiometry. This further corroborated 1:1 complex formation based on Job’s plot analyses.     

A Pyrene-based Highly Selective Turn-on Fluorescent Chemosensor for Iron(III) Ions and its Application in Living Cell Imaging

A new pyrene-based chemosensor (1) exhibits excellent selectivity for Fe³⁺ ions over a wide range of tested metal ions Ag⁺, Ca²⁺, Cd²⁺, Co²⁺, Cu²⁺, Fe²⁺, Hg²⁺, K⁺, Mg²⁺, Mn²⁺, Ni²⁺, Pb²⁺, and Zn²⁺. The binding of Fe³⁺ to chemosensor 1 produces an emission band at 507 nm due to the formation of a Py-Py* excimer that is induced by Fe³⁺-binding. The binding ratio of 1-Fe³⁺ was determined to be 1:1 from a Job plot. The association constant of 1-Fe³⁺ complexes was found to be 1.27?×?10⁴ M^?1 from a Benesi-Hildebrand plot. In addition, fluorescence microscopy experiments show that 1 can be used as a fluorescent probe for detecting Fe³⁺ in living cells.     

Bis-Benzimidazolyl Diamide Based Fluorescent Probe for Copper(II): Synthesis, Structural and Fluorescence Studies

A new fluorescent probe based on a bis-benzimidazole diamide N ²,N ^2′-bis[(1-ethyl-benzimidazol-2-yl)methyl]biphenyl-2,2′-dicarboxamide ligand L ₁ with a biphenyl spacer group and a Copper(II) trinuclear metallacycle has been synthesized and characterized by X-ray single crystallography, elemental and spectral (FT-IR, ¹H & ¹³C NMR, UV-Visible) analysis. The fluorescence spectra of L ₁ in MeOH show an emission band centered at 300 nm. This band arises due to benzimidazolyl moiety in the ligating system. The diamide L ₁ in the presence of Cu²⁺ show the simultaneous ‘quenching’ of (300 nm) and ‘enhancement’ of (375 nm) emission band. Similar fluorescence behavior was found in water–methanol mixture (9:1). The new emission band at 375 nm is attributed to intra ligand π–π* transition of the biphenyl moiety. L ₁ exhibited high selectivity and sensitivity towards Cu²⁺ in both the medium over other common metal ions like Ni²⁺, Co²⁺, Mn²⁺, Mg²⁺, Zn²⁺, Pb²⁺ and Hg²⁺. The binding constant with Cu²⁺ was calculated by the Benesi-Hildebrand equation. Selective “off-on-off” behavior of L ₁ in methanol has also been studied. The fluorescent intensity of 375 nm bands in L ₁ enhances (turns-on) upon addition of Cu²⁺ and quenches (turn-off) upon addition of Na₂-EDTA.     

Some estimates for magnetic fluctuations in a turbulent medium

A new integral relationship between the fluctuations b(r, t) of a magnetic field and its mean B ₀(r, t) is derived for the steady-state magnetic field in a turbulent medium. This formula provides the estimate 〈b?curlb〉=?B ₀?curlB ₀. Simultaneously, the coefficient of amplification of the mean magnetic field α effect) is obtained: α=(η+β)B ₀? curlB ₀/B ₀ ² . The formula for α allows for a decrease in this coefficient owing to the back action of the magnetic field on the turbulent velocity field. It is shown that the Zel’dovich’s estimate 〈 b ²〉?β/η B ₀ ² for two-dimensional turbulence holds for magnetic fields at the instant the fluctuations 〈a ²〉 of the vector potential, rather than 〈b ²〉, reach a maximum. Here, η and β are the ohmic (molecular) and turbulent diffusion coefficients, respectively. This estimate is refined with allowance made for the fact that the condition for diffusion approximation itself relates the β, b, and B ₀ quantities to each other.     

Spectroscopic and Computational Study of a Naphthalene Derivative as Colorimetric and Fluorescent Sensor for Bioactive Anions

The anion recognition property of a naphthalene based receptor (L) was investigated by naked-eye, UV-Vis, fluorescence, ¹H NMR and computational methods. The receptor L showed fluoride selective naked-eye detectable colorimetric and UV-Vis spectral changes over other tested anions due to the formation of hydrogen bonding complex in 1:1 stoichiometry and/or deprotonation between fluoride and the receptor. Interestingly, the fluorescence of L was quenched by fluoride but enhanced by acetate.     

Two-dimensional representation of position, velocity and acceleration by PFG-NMR

A novel view on the presentation of pulsed field-gradient nuclear magnetic resonance experiments to encode position and translational displacements is given. A conventional diffusion or flow experiment employing two magnetic field gradients of effective areak ₁, andk ₂ separated by a time interval Δ can formally be expressed as a means to probek space in a two-dimensional way. While for most applications, a full coverage of the [k ₁,k ₂] space is not necessary, an experiment withk ₁ = ?k ₂ can be regarded as a sampling of the secondary diagonal in [k ₁,k ₂] space. Likewise, the main diagonal is represented by the conditionk ₁ =k ₂ and encodes position. Thus, the [r ₁,r ₂] space conjugate to [k ₁,k ₂], which is obtained by Fourier transformation, can be transferred into a position/displacement correlation plot simply by rotation of the coordinate system by an angle of 45°. While displacementR =r ₂ ?r ₁ corresponds to an average velocity? =R/Δ, an extension towards higher-order derivations such as acceleration is straightforward by modification of the pulse sequence. We discuss this new concept in a general way, treating both the magnetic field and the particle position by Taylor expansions with respect to space and time, respectively, and present examples for fluid flowing through capillary systems in the light of the suggested interpretation.     

Design and Synthesis of a Pyridine Based Chemosensor: Highly Selective Fluorescent Probe For Pb2+

A pyridine based imine-linked chemosensor has been synthesized and evaluated its binding affinity with library of transition metal ions. It has prominent selectivity towards Pb²⁺ among other metal ions in DMF/H₂O (9:1, v/v) solvent system. The 1:1 stoichiometric was confirmed by job’s plot and has a binding constant (K_a)?=?5.142?×?10³ M^?1 on fluorescence. A B3LYP/6-31G and B3LYP/LanL2DZ basis sets were employed for optimization of 3 and 3.Pb²⁺.