Rhodamine-based probes for metal ion-induced chromo-/fluorogenic dual signaling and their selectivity towards Hg(II) ion

The new signaling probes 2-6, rhodamine-B derivatives of various receptors which contain different donor atoms for effective metal ion coordination, were synthesized and their absorption as well as fluorescence spectral responses were evaluated in the presence of various metal ions. All these probes along with the reference probe 1 have exhibited optimal metal ion-induced absorption and fluorescence enhancement with Hg(II) ion in the longer wavelength region (>500 nm) in MeCN, exploiting the spectral characteristics of metal ion-induced structural transformation of rhodamine. The selectivity and sensitivity towards Hg(II) ion were better pronounced in MeCN-H(2)O (1 : 1 v/v) medium, implying the role of the solvent molecules, water in particular, in the preferential Hg(II) coordination environment. Complexation of Hg(II) to 1-6 not only enhanced the absorption at ~560 nm, which turned the colourless solution into pink to facilitate a naked eye detection, but also amplified the fluorescence intensity simultaneously to offer high sensitivity of detection at lower concentration. The Hg(II)-induced photo-physical spectral responses of 1-6 in presence of other competitive metal ions rendered their high selectivity towards Hg(II). Further, their reversible dual channel signaling pattern under the action of counter anions, exploiting coordination tendency of anions towards Hg(II), which compete with probe-metal interaction, implied the reversibility in their Hg(II) coordination. The selectivity, sensitivity and reversibility, in principle, establishes the potential of these probes as chemosensors for Hg(II) ion detection.     

Fe(III)- and Hg(II)-selective dual channel fluorescence of a rhodamine-azacrown ether conjugate

A rhodamine-azacrown ether conjugate (1) demonstrates Fe(III)-selective green fluorescence, while showing Hg(II)-selective orange fluorescence. This is the first example of rhodamine-based fluorescent probe that shows dual channel fluorescence for two different metal cations.     

A highly selective fluorescent chemosensor for Fe (III) based on rhodamine 6G dyes derivative

A new fluorescent probe L based on the rhodamine 6G platforms for Fe³⁺ has been designed and synthesised. L showed excellent selectivity and high sensitivity for Fe³⁺ against other metal ions such as K⁺, Na⁺, Ag⁺, Cu²⁺, Co²⁺, Mg²⁺, Cd²⁺, Ni²⁺, Zn²⁺, Fe²⁺, Hg²⁺, Ce³⁺ and Y³⁺ in HEPES buffer (10 mM, pH 7.4)/CH₃CN (40:60, V/V). The distinct color change and the rapid emergence of fluorescence emission provided naked-eyes detection for Fe³⁺. The recognition mechanism of the probe toward Fe³⁺ was evaluated by Job’s plots, IR and ESI-MS. In order to further study their fluorescent properties, L + Fe³⁺ fluorescence lifetime was also measured. Moreover, the test strip results showed that these probes could act as a convenient and efficient Fe³⁺ test kit.     

Determination of Fe(II), Fe(III) and Fetotal in thermal water by ion chromatography spectrophotometry (IC-Vis)

Determination of iron speciation in water is one of the major challenges in environmental analytical chemistry. Here, we present and discuss a method for sampling and analysis of dissolved Fe(II), Fe(III), and Fe_total concentrations in natural thermal water covering a wide range of temperature, pH, chemical composition, and redox conditions. Various methods were tried in the collection, preservation, and storage of natural thermal water samples for the Fe(II) and Fe(III) determinations, yet the resultant Fe speciation determined was often found to be significantly affected by the methodology applied. Due to difficulties in preserving accurate Fe speciation in natural samples for later laboratory analysis, a field-deployed on-site method using ion-chromatography and spectrophotometry was developed and tested. The IC-Vis method takes advantage of ion chromatographic separation of Fe(II) and Fe(III), followed by post-column colour reaction and spectrophotometric detection, thus allowing analysis of Fe(II) and Fe(III) in a single 15-minute run. Additionally, Fe_total can be determined after sample oxidation. The analytical detection limits are ~2 µg L^?1 (LOD) using 200–1000 µL injection volumes and depend on the blank and reagent quality. The power of this method relies on the capability to directly determine a wide range of absolute and relative concentrations of Fe(II) and Fe(III) in the field. The field-deployed IC-Vis method was applied for the determination of Fe(II) and Fe(III) concentrations in natural thermal water with discharge temperatures ranging from 12°C to 95°C, pH between 2.46 and 9.75, and Fe_total concentrations ranging from a few μg L^?c up to 8.3 mg L^?1.     

Tuning the selectivity of two chemosensors to Fe(III) and Cr(III)

Two rhodamine-based chemosensors (1 and 2) were designed, and their sensing behavior toward metal ions was investigated by fluorescence spectroscopies. 1 and 2 achieved tuning the selectivity to Fe(III) and Cr(III) in 100% aqueous solution, whereas other ions including Cd(II), Co(II), Cu(II), Ni(II), Zn(II), Mg(II), Ba(II), Pb(II), Na(I), and K(I) induced basically no spectral change, which constituted a Fe(III)-selective and a Cr(III)-selective fluorescent chemosensor, respectively.     

Fe(III)Fe(III) and Fe(II)Fe(III) Complexes as Synthetic Analogues for the Oxidized and Reduced Forms of Purple Acid Phosphatases

Novel Fe(III)Fe(III) and Fe(II)Fe(III) complexes [Fe(2)(BBPMP)(&mgr;-OAc)(&mgr;-X)](n)() (1, X = OAc(-), n = 1+; 2, X = OH(-), n = 1+; 3, X = OAc(-), n = 0; 4, X = OH(-), n = 0), where BBPMP(3)(-) is the anion of 2,6-bis[(2-hydroxybenzyl)(2-pyridylmethyl)aminomethyl]-4-methylphenol, and OAc(-) is acetate, were prepared in order to provide models for the active site of purple acid phosphatases (PAPs). Complex 1 was obtained by the reaction of H(3)BBPMP with Fe(ClO(4))(2).6H(2)O in methanol and sodium acetate trihydrate under ambient conditions, while complex 3 was synthesized as described for 1, under an argon atmosphere with low levels of dioxygen. 2 was isolated from 1in acetonitrile by a substitution of the bridging acetate group by hydroxide, while 4 was generated in solution during a spectropotentiostatic experiment on 2, under argon. Complex 1, [Fe(III)(2)(BBPMP)(&mgr;-OAc)(2)]ClO(4).H(2)O, has been characterized by X-ray crystallography. Crystal data: monoclinic, space group P2(1)/n, a = 14.863(5) ?, b = 12.315(3) ?, c = 20.872(8) ?, beta = 90.83(3) degrees, Z = 4. IR, M?ssbauer, magnetic, electronic absorption, and electrochemical properties of 1-3 have been investigated, and some of these properties represent a contribution to the understanding of the dinuclear iron center of PAPs. Complexes 2, [Fe(III)(2)(BBPMP)(&mgr;-OAc)(&mgr;-OH)]ClO(4) (lambda(max) = 568 nm/epsilon = 4760 M(-)(1) cm(-)(1)), and 4 [Fe(II)Fe(III)(BBPMP)(&mgr;-OAc)(&mgr;-OH)] (lambda(max) = 516 nm/epsilon = 4560 M(-)(1) cm(-)(1)), constitute good synthetic analogues for the chromophoric site for the oxidized and reduced forms, respectively, of the enzyme.     

A novel ion selective membrane potentiometric sensor for direct determination of Fe(III) in the presence of Fe(II)

A new PVC membrane potentiometric sensor that is highly selective to Fe(III) ions was prepared by using 2-[(2-hydroxy-1-propenyl-buta-1,3-dienylimino)-methyl]-4-p-tolylazo-phenol [HPDTP] as a suitable carrier. The electrode exhibits a linear response for iron(III) ions over a wide concentration range (3.5 × 10⁻⁶ to 4.0 × 10⁻²) with a super Nernstian slope of 28.5 (±0.5) per decade. The electrode can be used in the pH range from 4.5 to 6.5. The proposed sensor shows fairly a good discriminating ability towards Fe³⁺ ion in comparison to some hard and soft metals such as Fe²⁺, Cd²⁺, Cu²⁺, Al³⁺ and Ca²⁺. It has a response time of <15 s and can be used for at least 2 months without any measurable divergence in response characteristics. The electrode was used in the direct determination of Fe³⁺ in aqueous samples and as an indicator electrode in potentiometric titration of Fe(III) ions.     

New fluorescent rhodamine hydrazone chemosensor for Cu(II) with high selectivity and sensitivity

[reaction: see text] A new fluorescent probe, salicylaldehyde rhodamine B hydrazone (1), was synthesized and displayed selective Cu(II)-amplified absorbance and fluorescence emission above 500 nm in neutral buffered media. Upon the addition of Cu(II), the spirolactam ring of 1 was opened and a 1:1 metal-ligand complex was formed. The detection of Cu(II) by 1 at a lower micromolar level was successful even in buffered water.     

A multi-channel sensor based on 8-hydroxyquinoline ferrocenoate for probing Hg(II) ion

A new sensing molecule 8-hydroxyquinoline ferrocenoate (Fc-Q) which combines ferrocene and 8-hydroxyquinoline moieties was synthesized and applied as a multi-channel sensor for the detection of Hg²⁺ ion. Fc-Q can coordinate with Hg²⁺ to give colorimetric, fluorescent and electrochemical responses. Upon complexation with Hg²⁺ ion, the characteristic absorption peak is red-shifted (Δλ = 45 nm), the fluorescent intensity is quenched at 303 nm, and the oxidation peak is cathodic shifted (ΔE_1/2 = −149 mV). Quantitatively analyzed Hg²⁺ ions at the range of ppb level could be achieved by electrochemical response. For the practical application of sensing Hg²⁺ in real world water, Fc-Q modified screen-printed carbon electrodes were obtained for facile, sensitive, and on-site analysis of Hg²⁺.     

Sensing of Fe(III) ion via turn-on fluorescence by fluorescence probes derived from 1-naphthylamine

Fluorescence probes NA1 and NA2 derived from 1-naphthylamine (NA) as fluorophore have been synthesized and characterized by different spectroscopic studies. Identification behaviour of these probes towards various metal ions has been investigated. Both the fluorescent probes are selective as well as sensitive towards Fe(III) ion. Novel fluorescence probe NA2 afforded turn-on fluorescence behaviour for Fe(III) ion over other metal ions such as Ca(II), Mg(II), Mn(II), Fe(II), Co(II), Fe(III), Ni(II), Cu(II), Zn(II) and Hg(II).     

Twisting (conformational changes)-based selective 2D chalcogeno podand fluorescent probes for Cr(III) and Fe(II)

The fluorenoazomethine containing chalcogeno podand fluorescent probes having N, O/S/Se coordinating donor unit show donor specific 'turn-on' recognition property towards metals (Cr(III), Fe(II) and Cu(II)), where the fluorescence signals are controlled by the conformational change of the ligand framework on binding with the metal ion.     

Fe(III)-pyruvate and Fe(III)-citrate induced photodegradation of glyphosate in aqueous solutions

The photolysis of Fe(III)-pyruvate and Fe(III)-citrate complexes in water produces hydroxyl radicals in the presence of dissolved oxygen, and can promote the oxidation of organic compounds. The photodegradation of glyphosate with Fe(III)-pyruvate and Fe(III)-citrate complexes was investigated under irradiation at λ?≥?365?nm. The effect of initial concentration of glyphosate, the initial pH value, and the Fe(III)/carboxylate ratio were examined. Upon irradiation of glyphosate aqueous solution with the complexes in the acidic range of natural waters, the bioavailable orthophosphate could be released from degradation of glyphosate. The amount of orthophosphate increased with increasing Fe(III)/carboxylate ratio.     

Polarographic analytical determination of Hg(II), Cu(II), Cd(II), As(III), Sb(III), Ti(IV) and U(VI) in the presence of Fe(III)

The analytical determination of Hg(II), Cu(II), Cd(II), As(III), Sb(III), Ti(IV) and U(VI) in the presence of Fe(III) and 1 M H₂SO₄ are investigated using the polarographic technique. The wave corresponding to the reduction of Fe(III) to Fe(II) was found to be completely suppressed by the addition of 1% pyrogallol. Thus, different mixtures of these elements, viz. Hg(II), Cu(II), Cd(II), As(III) and Fe(III)-mixture (A), Cu(II), Cd(II), Sb(III), As(III) and Fe(III)-mixture (B), and Cu(II), Cd(II), Ti(IV), U(VI) and Fe(III)-mixture (C), were quantitatively determined using 1% pyrogallol and 1 M H₂SO₄ as supporting electrolyte. The i₁/c results give excellent correlations in each case, as indicated from the results of leastsquares regression analysis.     

Water-activity and double-layer effects on the Fe(II)/Fe(Hg) reaction

The title subject is studied by electrode-kinetic measurements in acetate buffered potassium chloride and magnesium sulphate solutions of varied concentration at 25°C, using literature data for activity and double-layer properties. The results indicate that the Fe(II)/Fe(Hg) reaction occurs by an essentially symmetric (α near 1/2) ferrous-ion transfer (n=2), that this transfer is second order in water-activity dependence, and that it exhibits a smaller than classically expected double-layer effect. No specific interaction appears for any of the ions of the supporting salts. An e.c. reaction scheme is proposed for the Fe(Hg)/Fe(II) electrode in non-complexing aqueous solution.     

Chemiluminescence flow system for the determination of Fe(II) and Fe(III) in water

A novel chemiluminescence (CL) flow system has been developed for the sequential determination of Fe(II) and Fe(III) in water. Fe(II) was detected by its catalytic effect on the CL reaction between luminol immobilized on an anion exchange resin column and dissolved oxygen; Fe(III) was determined by difference measurement after on-line conversion to Fe(II) in a reducing mini-column packed with Cu plated Zn granules. For both ions, the calibration graph was linear in the range 1 × 10^–9 to 1 × 10^–6 g/mL, and the detection limit was 4 × 10^–10 g/mL. A complete analysis could be performed in 1.5 min with a relative standard deviation of less than 5%. The system could be reused for over 200 times and has been applied successfully to the determination of Fe(II) and Fe(III) in natural water samples.     

Determination of Fe(II)-Fe(III) and Fe(III)-Ni(II) by the two-component potentiometric complexometric titration

Summary The two-component complexometric potentiometric titration has been applied to the simultaneous determination of Fe(III) and Fe(II), and of Fe(III) and Ni(II) in solution. In each case the two analytes were determined by reading the end-points directly from the titration curve. The end-points are determined in a sense arbitrarily, but they are repeatable and easy to be detected precisely. However, the apparent (found) analytical results are biased. They are effectively corrected with the use of a set of two calibration equations (uncomplete second degree polynomials), which approximate the relationship between found endpoints and true concentrations of analytes in solution. The regression coefficients in the equations are determined on the basis of titration data obtained for standard solutions whose compositions correspond to a 2² factorial. Permanent address: Department of Analytical Chemistry, Jagiellonian University, Krakow     

Chemiluminescence flow system for the determination of Fe(II) and Fe(III) in water

A novel chemiluminescence (CL) flow system has been developed for the sequential determination of Fe(II) and Fe(III) in water. Fe(II) was detected by its catalytic effect on the CL reaction between luminol immobilized on an anion exchange resin column and dissolved oxygen; Fe(III) was determined by difference measurement after on-line conversion to Fe(II) in a reducing mini-column packed with Cu plated Zn granules. For both ions, the calibration graph was linear in the range 1 × 10^–9 to 1 × 10^–6 g/mL, and the detection limit was 4 × 10^–10 g/mL. A complete analysis could be performed in 1.5 min with a relative standard deviation of less than 5%. The system could be reused for over 200 times and has been applied successfully to the determination of Fe(II) and Fe(III) in natural water samples. Received: 13 March 1997 / Revised: 3 June 1997 / Accepted: 6 June 1997     

Discrete Rh(III)/Fe(II) and Rh(III)/Fe(II)/Co(III) cyanide-bridged mixed valence compounds

The heterotrinuclear complexes trans- and cis-[{cis-VI-L(15)Rh(III)(μ-NC)}{trans-III-L(14S)Co(III)(μ-NC)}Fe(II)(CN)(4)](2+) are unprecedented examples of mixed valence complexes based on ferrocyanide bearing three different metal centers. These complexes have been assembled in a stepwise manner from their {trans-III-L(14S)Co(III)}, {cis-VI-L(15)Rh(III)}, and {Fe(II)(CN)(6)} building blocks. The preparative procedure follows that found for other known discrete assemblies of mixed valence dinuclear Cr(III)/Fe(II) and polynuclear Co(III)/Fe(II) complexes of the same family. A simple slow substitution process of [Fe(II)(CN)(6)](4-) on inert cis-VI-[Rh(III)L(15)(OH)](2+) leads to the preparation of the new dinuclear mixed valence complex [{cis-VI-L(15)Rh(III)(μ-NC)}Fe(II)(CN)(5)](-) with a redox reactivity that parallels that found for dinuclear complexes from the same family. The combination of this dinuclear precursor with mononuclear trans-III-[Co(III)L(14S)Cl](2+) enables a redox-assisted substitution on the transient {L(14S)Co(II)} unit to form [{cis-VI-L(15)Rh(III)(μ-NC)}{trans-III-L(14S)Co(III)(μ-NC)}Fe(II)(CN)(4)](2+). The structure of the final cis-[{cis-VI-L(15)Rh(III)(μ-NC)}{trans-III-L(14S)Co(III)(μ-NC)}Fe(II)(CN)(4)](2+) complex has been established via X-ray diffraction and fully agrees with its solution spectroscopy and electrochemistry data. The new species [{cis-VI-L(15)Rh(III)(μ-NC)}{trans-III-L(14S)Co(III)(μ-NC)}Fe(II)(CN)(4)](2+) and [{cis-VI-L(15)Rh(III)(μ-NC)}Fe(II)(CN)(5)](-) show the expected electronic spectra and electrochemical features typical of Class II mixed valence complexes. Interestingly, in the trinuclear complex, these features appear to be a simple addition of those for the Rh(III)/Fe(II) and Co(III)/Fe(II) moieties, despite the vast differences existent in the electronic spectra and electrochemical properties of the two isolated units.