Electronic state of Fe used as Mössbauer probe in the perovskites LaMO3 (M=Ni and Cu)

For the first time a comparative study of rhombohedral LaNiO₃ and LaCuO₃ oxides, using ⁵⁷Fe Mössbauer probe spectroscopy (1% atomic rate), has been carried out. In spite of the fact that both oxides are characterized by similar crystal structure and metallic properties, the behavior of ⁵⁷Fe probe atoms in such lattices appears essentially different. In the case of LaNi_0.99Fe_0.01O₃, the observed isomer shift (δ) value corresponds to Fe³⁺ (3d⁵) cations in high-spin state located in an oxygen octahedral surrounding. In contrast, for the LaCu_0.99Fe_0.01O₃, the obtained δ value is comparable to that characterizing the formally tetravalent high-spin Fe⁴⁺(3d⁴) cations in octahedral coordination within Fe(IV) perovskite-like ferrates. To explain such a difference, an approach based on the qualitative energy diagrams analysis and the calculations within the cluster configuration interaction method have been developed. It was shown that in the case of LaNi_0.99Fe_0.01O₃, electronic state of nickel is dominated by the d⁷ configuration corresponding to the formal ionic “Ni³⁺-O²⁻” state. On the other hand, in the case of LaCu_0.99Fe_0.01O₃ a large amount of charge is transferred via Cu-O bonds from the O:2p bands to the Cu:3d orbitals and the ground state is dominated by the d⁹L configuration (“Cu²⁺−O” state). The dominant d⁹L ground state for the (CuO₆) sublattice induces in the environment of the ⁵⁷Fe probe cations a charge transfer Fe³⁺+O⁻(L)→Fe⁴⁺+O²⁻, which transforms “Fe³⁺” into “Fe⁴⁺” state. The analysis of the isomer shift value for the formally “Fe⁴⁺” ions in perovskite-like oxides clearly proved a drastic influence of the 4s iron orbitals population on the Fe−O bonds character.     

A fluorescent chemosensor for Hg based on naphthalimide derivative by fluorescence enhancement in aqueous solution

Naphthalimide derivative (compound 1) containing hydrophilic hexanoic acid group was synthesized and used to recognize Hg²⁺ in aqueous solution. The fluorescence enhancement of 1 is attributed to the formation of a complex between 1 and Hg²⁺ by 1:1 complex ratio (K = 2.08 × 10⁵), which has been utilized as the basis of fabrication of the Hg²⁺-sensitive fluorescent chemosensor. The comparison of this method with some other fluorescence methods for the determination of Hg²⁺ indicated that the method can be applied in aqueous solution rather than organic solution. The analytical performance characteristics of the proposed Hg²⁺-sensitive chemosensor were investigated. The chemosensor can be applied to the quantification of Hg²⁺ with a linear range covering from 2.57 × 10⁻⁷ to 9.27 × 10⁻⁵ M and a detection limit of 4.93 × 10⁻⁸ M. The experiment results show that the response behavior of 1 toward Hg²⁺ is pH independent in medium condition (pH 4.0–8.0). Most importantly, the fluorescence changes of the chemosensor are remarkably specific for Hg²⁺ in the presence of other metal ions, which meet the selective requirements for practical application. Moreover, the response of the chemosensor toward Hg²⁺ is fast (response time less than 1 min). In addition, the chemosensor has been used for determination of Hg²⁺ in hair samples with satisfactory results, which further demonstrates its value of practical applications.     

Electrochemical behavior of hexafluoroniobate, heptafluorotungstate, and oxotetrafluorovanadate anions in N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide room temperature ionic liquid

Electrochemical behavior of hexafluoroniobate (Nb(V)F₆⁻), heptafluorotungstate (W(VI)F₇⁻), and oxotetrafluorovanadate (V(V)OF₄⁻) anions has been investigated in N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPyrTFSA) ionic liquid at 298 K by means of cyclic voltammetry and chronoamperometry. Cyclic voltammograms at a Pt electrode showed that Nb(V)F₆⁻ anion is reduced to Nb(IV)F₆²⁻ by a one-electron reversible reaction. Electrochemical reductions of W(VI)F₇⁻ and V(V)OF₄⁻ anions at a Pt electrode are quasi-reversible and irreversible reactions, respectively, according to cyclic voltammetry. The diffusion coefficients of Nb(V)F₆⁻, W(VI)F₇⁻ and V(V)OF₄⁻ determined by chronoamperometry are 1.34 × 10⁻⁷, 7.45 × 10⁻⁸ and 2.49 × 10⁻⁷ cm² s⁻¹, respectively. The Stokes radii of Nb(V)F₆⁻, W(VI)F₇⁻, and V(V)OF₄⁻ in BMPyrTFSA have been calculated to be 0.23, 0.38, and 0.12 nm, from the diffusion coefficients and viscosities obtained.     

A ratiometric fluorescent chemosensor for Al in aqueous solution based on aggregation-induced emission and its application in live-cell imaging

A ratiometric fluorescent chemosensor 1 was developed for the detection of Al³⁺ in aqueous solution based on aggregation-induced emmision (AIE). The chemosensor showed the fluorescence of its aggregated state and Al³⁺-chelated soluble state in the absence and in the presence of Al³⁺, respectively, and resulted in a fluorescence ratio (I₄₆₁/I₅₃₇) response to Al³⁺ in neutral aqueous solution at a detection limit as low as 0.29 μmol L⁻¹. The method was also highly selective to Al³⁺ over other physiological relevant metal ions investigated in this study. Taking advantage of its AIE characteristics, the chemosensor was successfully applied on test papers for simple and rapid detection of Al³⁺. Moreover, the application of 1 for the imaging of Al³⁺ in living cells by ratiometric fluorescence changes was also achieved.     

Specific F binding to phenyl ring of aromatic polymers

Most of the hydrogels deswell more remarkably in F⁻ containing solutions than in other monovalent anion containing solutions. However, significant deswelling followed by abnormal reswelling of polymer gel in KF solutions with increasing F⁻ concentration was observed in a series of polymer gels consisted of phenyl rings, for instance, poly(styrene sulfonic acid) (PSSA), hydroxypropyl methylcellulose phthalate (HPMCP) and poly(4-vinyl phenol) (P4VPh) gel. Driving force of this phenomenon was studied to reveal the specific interactions involved in the aqueous systems of aromatic polymers. Elemental analysis and XPS results suggest that F⁻ is embedded to the gel by the physical adsorption of KF, as well as the interactions between phenyl ring and F⁻. Further theoretical calculations revealed that the interaction may be (phenyl)CH?F⁻(H₂O)_n interaction, which is stronger than (phenyl)CH?(H₂O)_n hydrogen bond. This kind of interaction decreases with the increasing water number and it is invalid when the surrounding water number is more than 5 for the phenol-F⁻(H₂O)_n system. Therefore, we conclude that F⁻ could bind to phenyl ring via such (phenyl)CH?F⁻(H₂O)_n interaction in solutions with low hydrophilicity. The strong polarization effect of F⁻ and (phenyl)CH?F⁻(H₂O)_n interaction are two important driving forces for the reswelling of gels.     

Electrically induced fluorescence Fe sensing behavior of nanostructured Tiron doped polypyrrole

Nanostructured polypyrrole (PPy) film doped with Tiron was electrodeposited from aqueous solution on the surface of transparent electrode and used for sensitive, selective and rapid electrically controlled fluorescence detection of Fe³⁺ in aqueous media. The fluorescence intensity of PPy-Tiron film decreases linearly in the presence of Fe³⁺ by applying negative potential over a concentration range from 5.0 × 10⁻⁸ to 1.0 × 10⁻⁶ mol L⁻¹, with a relatively fast response time of less than 30 s at pH 7.4. The detection is not affected by the coexistence of other competitive metal ions such as Al³⁺, Ce³⁺, Tl³⁺, La³⁺, Bi³⁺, Cr²⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺, Pb²⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺. The proposed electro-fluorescence sensor has a potential application to the determination of Fe³⁺ in environmental and biological systems. The fluorescent thin film sensor was also used as a novel probe for Fe³⁺/Fe²⁺ speciation in aqueous solution.     

A ‘turn-on’ fluorescent chemosensor based on rhodamine-N-(3-aminopropyl)-imidazole for detection of Al ions

A novel N-(3-aminopropyl)-imidazole-appended rhodamine-based fluorescent chemosensor was synthesized. The sensing behavior and selectivity of the synthesized chemosensor toward metal cations were studied by UV/vis and fluorescence spectroscopy. The chemosensor recognized Al³⁺ ions by a significantly enhanced fluorescence and a visible color change due to opening of the spirolactam ring triggered by the addition of Al³⁺ ions.     

Colorimetric and fluorescent chemosensor for citrate based on a rhodamine and Pb complex in aqueous solution

In this paper we unveil a novel rhodamine compound based fluorescent chemosensor (1-Pb²⁺) for colormetric and fluorescent detection of citrate in aqueous solution. This is the first fluorescent chemosensor for citrate based on rhodamine compound. The comparison of this method with some other fluorescence methods for citrate indicates that the method can detect citrate in aqueous solution by both color changes and fluorescent changes with long emission wavelength. In the new developed sensing system, 1-Pb²⁺ is fluorescent due to Pb²⁺-induced fluorescence enhancement of 1. However, the addition of citrate may release 1 into the solution with quenching of fluorescence. The chemosensor can be applied to the quantification of citrate with a linear range covering from 1.0 × 10⁻⁷ to 5.0 × 10⁻⁵ M and a detection limit of 2.5 × 10⁻⁸ M. The experiment results show that the response behavior of 1-Pb²⁺ towards citrate is pH independent in medium condition (pH 6.0–8.0). Most importantly, the fluorescence changes of the chemosensor are remarkably specific for citrate in the presence of other anions (even those that exist in high concentration), which meet the selective requirements for practical application. Moreover, the response of the chemosensor toward citrate is fast (response time less than 1 min). In addition, the chemosensor has been used for determination of citrate in urine samples with satisfactory results.     

Fluorescent oligomer as a chemosensor for the label-free detection of Fe and dopamine with selectivity and sensitivity

In this article, a sensitive and selective turn-off fluorescence chemosensor, Tyloxapol (one kind of water soluble oligomer), was developed for the label-free detection of Fe³⁺ ions in aqueous solution. Fluorescence (FL) experiments demonstrated that Tyloxapol was a sensitive and selective fluorescence sensor for the detection of Fe³⁺ directly in water over a wide range of metal cations including Na⁺, K⁺, Ag⁺, Hg²⁺, Cd²⁺, Co²⁺, Cu²⁺, Cr³⁺, Mn²⁺, Ba²⁺, Zn²⁺, Ni²⁺, Mg²⁺, Ca²⁺, and Pb²⁺. Moreover, the fluorescence intensity of Tyloxapol has shown a linear response to Fe³⁺ in the concentration range of 0–100 μmol L⁻¹ with a detection limit of 2.2 μmol L⁻¹ in aqueous solution. Next, based on a competition mechanism, another turn-on sensing application of the Tyloxapol/Fe³⁺ platform to probe dopamine (DA) against various other biological molecules such as other neurotransmitters or amino acids (norepinephrine bitartrate, acetylcholine chloride, alanine, valine, phenylalanine, tyrosine, leucine, glycine, histidine) were also investigated. It is expected that our strategy may offer a new approach for developing simple, cost-effective, rapid and sensitive sensors in biological and environmental applications.     

An efficient and selective flourescent chemical sensor based on 5-(8-hydroxy-2-quinolinylmethyl)-2,8-dithia-5-aza-2,6-pyridinophane as a new fluoroionophore for determination of iron(III) ions. A novel probe for iron speciation

A novel fluorescent chemical sensor for the highly sensitive and selective determination of Fe³⁺ ions in aqueous solutions is prepared. The iron sensing system was prepared by incorporating 5-(8-hydroxy-2-quinolinylmethyl)-2,8-dithia-5-aza-2,6-pyridinophane (L) as a neutral Fe³⁺-selective fluoroionophore in the plasticized PVC membrane containing sodium tetraphenylborate as a liphophilic anionic additive. The response of the sensor is based on the strong fluorescence quenching of L by Fe³⁺ ions. At pH 5.5, the proposed sensor displays a calibration curve over a wide concentration range from 6.0 × 10⁻⁴ to 1.0 × 10⁻⁷ M, with a relatively fast response time of less than 2 min. In addition to a high stability and reproducibility, the sensor shows a unique selectivity toward Fe³⁺ ion with respect to common coexisting cations. The proposed fluorescence optode was applied to the determination of iron(III) content of straw of rice, spinach and different water samples. The fluorescent sensor was also used as a novel probe for Fe³⁺/Fe²⁺ speciation in aqueous solution.     

Perylene diimide based ‘turn-on’ fluorescence sensor for detection of Pd in mixed aqueous media

A perylene diimide (PDI) based fluorescence chemosensor (PDI-1) for Pd²⁺ was prepared. PDI-1 showed a remarkable fluorescence enhancement (over 120-fold) in the presence of Pd²⁺ in mixed aqueous media with high selectivity and sensitivity. Moreover, the dramatically ‘off–on’ fluorescence response concomitantly induced the obvious color change from dark purple to brilliant pink, which could also be identified by naked eyes easily. The low limit for Pd²⁺ detection was found to be as small as 10⁻⁹ mol/L. Hence, PDI-1 is a highly promising fluorescent chemosensor for the direct determination of residual Pd²⁺ in chemical medicines and environment samples.     

Syntheses, crystal structures and Raman spectra of Ba(BF4)(PF6), Ba(BF4)(AsF6) and Ba2(BF4)2(AsF6)(H3F4); the first examples of metal salts containing simultaneously tetrahedral BF4 and octahedral AF6 anions

In the system BaF₂/BF₃/PF₅/anhydrous hydrogen fluoride (aHF) a compound Ba(BF₄)(PF₆) was isolated and characterized by Raman spectroscopy and X-ray diffraction on the single crystal. Ba(BF₄)(PF₆) crystallizes in a hexagonal space group with a=10.2251(4) Å, c=6.1535(4) Å, V=557.17(5) Å³ at 200 K, and Z=3. Both crystallographically independent Ba atoms possess coordination polyhedra in the shape of tri-capped trigonal prisms, which include F atoms from BF₄⁻ and PF₆⁻ anions. In the analogous system with AsF₅ instead of PF₅ the compound Ba(BF₄)(AsF₆) was isolated and characterized. It crystallizes in an orthorhombic Pnma space group with a=10.415(2) Å, b=6.325(3) Å, c=11.8297(17) Å, V=779.3(4) Å³ at 200 K, and Z=4. The coordination around Ba atom is in the shape of slightly distorted tri-capped trigonal prism which includes five F atoms from AsF₆⁻ and four F atoms from BF₄⁻ anions. When the system BaF₂/BF₃/AsF₅/aHF is made basic with an extra addition of BaF₂, the compound Ba₂(BF₄)₂(AsF₆)(H₃F₄) was obtained. It crystallizes in a hexagonal P6₃/mmc space group with a=6.8709(9) Å, c=17.327(8) Å, V=708.4(4) Å³ at 200 K, and Z=2. The barium environment in the shape of tetra-capped distorted trigonal prism involves 10 F atoms from four BF₄⁻, three AsF₆⁻ and three H₃F₄⁻ anions. All F atoms, except the central atom in H₃F₄ moiety, act as μ₂-bridges yielding a complex 3-D structural network.     

Adsorption of fluoride on synthetic siderite from aqueous solution

The study has investigated the feasibility of using synthetic siderite for F⁻ removal from aqueous solution. Batch experiments were performed to test effects of adsorbent dosage, contact time, initial F⁻ concentration, temperature, solution pH, and coexisting anions on F⁻ removal. Results show that the kinetic rate of F⁻ adsorption was high in the first 2 h, and thereafter significantly decreased. The kinetic data was better fitted to the pseudo-second order kinetic model than the pseudo-first order kinetic model. In comparison with Langmuir isotherm, both Freundlich and Redlich-Peterson isotherms better described the adsorption process, which indicates that the multilayer adsorption should be involved in the process of F⁻ removal. Thermodynamic study manifests that F⁻ adsorption on synthetic siderite was spontaneous and exothermic in nature. The synthetic siderite had high adsorption capacity for F⁻ removal, which was up to 1.775 mg/g in the batch with an adsorbent dosage of 5 g/L and an initial F⁻ concentration of 20 mg/L at 25 °C. The adsorption was relatively independent on solution pH between 4 and 9. The presence of Cl⁻ and NO₃⁻ had less impact on F⁻ adsorption, while PO₄³⁻ significantly affected F⁻ removal from aqueous solution. Results of X-ray diffraction (XRD) and scanning electron microscopy (SEM) suggest that the high adsorption capacity possibly arose from both coprecipitation of ferric hydroxide with F⁻ and adsorption of F⁻ on the fresh goethite.     

Hydrolysis of ammonium oxofluorotungstates: A F, O and W NMR study

Fluorine-19 and natural abundance ¹⁷O and ¹⁸³W NMR spectroscopy were employed for the characterization of aqueous solutions of (NH₄)₂WO₂F₄ and (NH₄)₃WO₃F₃. Dissolution of the (NH₄)₂WO₂F₄ complex is accompanied by its partial acid hydrolysis to give the trans(mer)-dimer, [W₂O₅F₆]⁴⁻, and unreacted cis-[WO₂F₄]²⁻. The cis(fac)-[W₂O₅F₆]⁴⁻ anion is the major soluble product resulting from the alkaline hydrolysis of (NH₄)₂WO₂F₄ along with the isolation of the solid (NH₄)₂WO₃F₂. In addition, the edge-bridging dimer, [W₂O₆F₄]⁴⁻, and the cyclic trimer, [W₃O₉F₆]⁶⁻, are also suggested as hydrolysis products. Decomposition of (NH₄)₃WO₃F₃ occurs in aqueous solution to give NH₄WO₃F.     

An ultra-sensitive and colorimetric sensor for copper and iron based on glutathione-functionalized gold nanoclusters

Here, we report an ultra-sensitive and colorimetric sensor for the detection of Fe³⁺ or Cu²⁺ successively using glutathione-functionalized Au nanoclusters (GSH-AuNCs). For GSH-AuNCs can catalytically oxidize peroxidase substrates, such as 3, 3′, 5, 5′-tetramethylbenzidine (TMB), colored products are formed in the presence of H₂O₂. While upon the addition of Fe³⁺ or Cu²⁺ into the GSH-AuNCs-TMB-H₂O₂ system, diverse color and absorbance of the system was obtained due to the self oxidation of Fe³⁺ and the inhibition of peroxidase-like activity of GSH-AuNCs. With the introduction of ethylene diamine tetraacetic acid (EDTA) or ammonium fluoride (NH₄F) to GSH-AuNCs-TMB-H₂O₂+Cu²⁺ system or GSH-AuNCs-TMB-H₂O₂+Fe³⁺ system respectively, a restoration of color and absorbance of system was realized. On the basis of above phenomenon, a colorimetric and quantitative approach for detecting Fe³⁺ and Cu²⁺ was developed with detection limit of 1.25 × 10⁻⁹ M and 1.25 × 10⁻¹⁰ M respectively. Moreover, the concentration of Fe³⁺ and Cu²⁺ in human serums was also accurate quantified by this method. So this design strategy realized the simple and simultaneous detection of Fe³⁺ and Cu²⁺, suggesting significant potential in clinical diagnosis.     

A new rhodamine-based dual chemosensor for Al and Cu

A new rhodamine B derivative bearing a hydrazone group has been designed and prepared. The synthesized colorimetric and fluorescent molecular chemosensor can be used as a dual probe, selectively detecting Al³⁺ and Cu²⁺ in acetonitrile solution by monitoring changes in the absorption and fluorescence spectral patterns. The results show that Al³⁺ ions can induce a greater fluorescence enhancement, while the addition of Cu²⁺ ions induces a strong UV–vis absorption enhancement with weak fluorescence. The limits of detection of Cu²⁺ and Al³⁺ were estimated to be 2.9 × 10⁻⁷ M and 8.3 × 10⁻⁹ M, respectively.     

Eu luminescence—a structural probe in BiCa4(PO4)3O, an apatite related phosphate

Eu³⁺ luminescence is studied in apatite-related phosphate BiCa₄(PO₄)₃O. Compositions of the formula Bi_1−xEu_xCa₄(PO₄)₃O [x=0.05, 0.1, 0.3, 0.5, 0.8 and 1.0] are synthesized and they are isostructural with parent BiCa₄(PO₄)₃O. Room temperature photoluminescence shows the various transitions ⁵D₀→⁷F_J(=0,1,2) of Eu³⁺. The emission results of compositions with different Eu³⁺ content show the difference in site occupancy of Eu³⁺ in Bi_1−xEu_xCa₄(PO₄)₃O. The intense ⁵D₀-⁷F₀ line at 574 nm for higher Eu³⁺ content is attributed to the presence of strongly covalent Eu-O bond that is possible by substituting Bi³⁺ in the Ca(2) site. This shows the preferential occupancy of Bi³⁺ in Ca(2) site and this has been attributed to the 6s² lone pair electrons of Bi³⁺. This is further confirmed by comparing the emission results with La_0.95Eu_0.05Ca₄(PO₄)₃O.     

FRET based selective and ratiometric ‘naked-eye’ detection of CN in aqueous solution on fluorescein–Zn–naphthalene ensemble platform

We have developed a FRET-based ratiometric fluorescent probe for the detection of CN⁻ using a fluorescein–Zn–naphthalene ensemble (NFH·Zn²⁺). The sensing mechanism was ascribed by displacement approach. The chemosensor exhibits high selectivity and sensibility for CN⁻. The speculation was supported by fluorescence emission spectra, UV–vis spectrum, ¹H NMR titration experiments, and mass spectra. The interconversion of probe NFH and NFH·Zn²⁺ via the complexation/decomplexation by the modulation of Zn²⁺/CN⁻ mimics INHIBIT gate. In addition, it also shows an excellent performance in ‘dip stick’ method.     

Terphenyl based fluorescent chemosensor for Cu and F ions employing excited state intramolecular proton transfer

A new terphenyl based bifunctional fluorescent chemosensor 3a has been synthesized, which demonstrates selective optical recognition of Cu²⁺ and F⁻ ions in two contrasting modes. The compound shows highly selective ‘On-Off’ switchable behavior toward Cu²⁺ ions and ‘On-Off-On’ behavior toward F⁻ ions among various cations and anions tested. The detection limits of chemosensor for Cu²⁺ and F⁻ ions are found to be 100 nM and 10 nM, respectively.     

An acyclic,dansyl based colorimetric and fluorescent chemosensor for Hg(II) via twisted intramolecular charge transfer (TICT)

An efficient fluorescent chemosensor for Hg²⁺ ion, based on 5-(dimethylamino)-N-(2-mercaptophenyl)naphthalene-1-sulfonamide, has been developed. It exhibits Hg²⁺-selective on–off fluorescence quenching behavior via twisted intramolecular charge transfer (TICT) mechanism, which is rationalized by time dependent density functional theory (TD-DFT) calculations. The system exhibits visible color change from colorless to gray upon Hg²⁺ binding with very high selectivity and sensitivity (as low as 5.0 × 10⁻¹⁰ mol L⁻¹) over other metal ions such as K⁺, Na⁺, Ag⁺, Mn²⁺, Ca²⁺, Ba²⁺, Fe²⁺, Zn²⁺, Pb²⁺, Cu²⁺, Sn²⁺, Cd²⁺, Ni²⁺ and Co²⁺. The present sensing system is also successfully applied for the detection of Hg²⁺ ion in real samples.