A Kinetic Study of the Reaction Between Glutathione and Iron(III) in the pH Range from 1 to 3

Anaerobic reactions of iron(III) with glutathione (GSH) have been studied kinetically using stopped-flow spectrophotometry. One mixing reduced GSH with iron(III) a very rapid increase in absorbance with a broad peak centred at 620 nm was recorded. The rapid formation of the blue complex was followed by a decomposition step at a slower rate, yielding a colourless product. GSH reduces iron(III) readily in aqueous solution to yield the iron(II) GSH complex.     

Iron(II) and iron(III) complexes containing ethynyl thiophene fragments

The synthesis of the new complexes Cp*(dppe)FeCC2,5-C₄H₂SR (Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl; dppe = 1,2-bis(diphenylphosphino)ethane; 2a, R = CCH; 2b, R = CCSi(CH₃)₃; 2c, R = CCSi(CH(CH₃)₂)₃; 3a, R = CC2,5-C₄H₂SCCH; 3c, R = CC2,5-C₄H₂SCCSi(CH(CH₃)₂)₃) is described. The ¹³C NMR and FTIR spectroscopic data indicate that the π-back donation from the metal to the carbon rich ligand increases with the size of the organic π-electron systems. The new complexes were also analyzed by CV and the chemical oxidation of 2a and 3c was carried out using 1 equiv of [Cp₂Fe][PF₆]. The corresponding complexes 2a[PF₆] and 3c[PF₆] are thermally stable, but 2a[PF₆] was too reactive to be isolated as a pure compound. The spectroscopic data revealed that the coordination of large organic π-electron systems to the iron nucleus produces only a weak increase of the carbon character of the SOMO for these new organoiron(III) derivatives.     

Improved Protocol for Mononitration of Phenols with Bismuth(III) and Iron(III) Nitrates

A simple and efficient multigram procedure was developed for the selective mononitration of various activated phenols. The reaction proceeded smoothly with 0.5 equivalents of Bi(NO₃)₃ · 5H₂O or Fe(NO₃)₃ · 9H₂O in acetone at ambient temperature or at reflux. The desired products were isolated in 62–93% total yield and essentially no overnitrated compounds were detected.     

New Indicator for the Titration of Iron(III) with EDTA

Abstract

New metal indicators, 7 -(2-hydroxy-1-naphthylazo)-8-hydroxy-quinoline-5-sulfonic acids were synthesized. Among them 7-(6-nitro-4-sulfo-2-hydroxy-1-naphthylazo)-8-hydrqxyquinoline-5-sulfonic acid(NH-SNAZOXS) is recommended as an indicator for the titration of iron(III) with EDTA. The sharp color change at the equivalence point from yellow to violet is obtained at pH 2.0 to 3.0 at 50°.     

Simultaneous Polarographic Determination of Iron (II) and Iron (III) in Coal Mine Waste Water

Abstract

Polarography with a sodium carbonate-oxalic acid supporting electrolyte was used to determine both Fe(II) and Fe(III) simultaneously in actual coal mine water samples. The average relative percent error was 2.2% for Fe(II) and 2.1% for Fe(III) over a range of 10 to 500 ppm. In actual mine water the Fe(II) content was highest where the mine water emerged. As the water moved down stream from the source of pollution Fe(II) decreased and Fe(III) concentration increased as Fe(II) was oxidized to Fe(III) by oxygen. This was accompanied by a decrease in pH. Further down the stream Fe(III) started to precipitate and then its concentration steadily decreased.     

Simple and Selective Spectrophotometric Method for the Determination of Iron (III) and Total Iron Content, Based on the Reaction of Fe(III) with 1,2-Dihydroxy-3,4-Diketocyclo-Butene (Squaric Acid)

 Squaric acid (1,2-dihydroxy-3,4-diketo-cyclobutene) is used in a specific reaction with Fe(III) for the spectrophotometric determination of Fe(III) and total iron content. The optimization of the experimental parameters leads to the establishment of a simple, fast and accurate analytical method. The analytical procedure includes mixing ammonium squarate (40 mM), prepared in a phthalate buffer solution of pH 2.7, with the sample and measuring the absorbance at 515 nm. The molar absorptivity of the colored product is 3.95×10³ L·mol⁻¹·cm⁻¹, at 515 nm. Calibration graphs for Fe(III) are rectilinear for 0.5–20 mgL⁻¹, with a detection limit of 0.3 mgL⁻¹ and r.s.d. not exceeding 2.5%, for five replicates of a 3.0 mgL⁻¹ standard solution. The method has been successfully applied to the determination of iron (III) and the total iron content after quantitative oxidation of iron (II). The results for several analyzed samples when compared with those acquired by using the FAAS technique, were found to be in satisfactory agreement. Author for correspondence: University of Ioannina, Department of Chemistry, Laboratory of Analytical Chemistry, Ioannina 451 10, Greece. E-mail: panavelt@cc.uoi.gr Received July 27, 2002; accepted December 20, 2002 Published online April 11, 2003     

Solution Characteristics for Adsorption of Copper Ion with Iron(III) Hydroxide from Aqueous Ammonia Solution

The distribution of copper ion species in aqueous ammonia solution is evaluated as a function of pH by a numerical approach. Adsorption of copper on colloidal iron(III) hydroxide in solutions of total ammonia (0.14-1.2 M) are performed at various values of pH. The maximum efficiency of adsorption occurs when the sum of the fractions of the species Cu(NH₃)²⁺, Cu(NH₃)₂²⁺ and Cu(NH₃)₃²⁺ in the solution reaches its maximum. With varied solution pH, the distribution of copper species is the determining factor for maximum adsorption, whereas the surface properties of the adsorbing particles show smaller effects under the test conditions.     

Catalytic Kinetic Determination of Trace Amounts of Iron(III) With Polarographic Detection

Abstract

This method is based on the catalytic effect of Fe³⁺ on the oxidation reaction between Acid Chrome Blue K and potassium bromate in sulfuric acid medium at 100deg;C, and in 0.08 mol/L NH₄OH - 0.01 mol/L (NH₄)₂ SO₄ supporting electrolyte, Acid Chrome Blue K exhibits a sensitive polarographic wave at -0.55V vs. SCE, and change of concentration is traced by a polarographic detection technique. The linear range of Fe³⁺ is 10–100ng/mL. This new catalytic method has been applied to the determination of iron in natural water and food with satisfactory results.     

Iron(III) chloride and its coordination chemistry

Abstract

The coordination chemistry of FeCl₃ is distinctly different to that of the other 3d metal halides. It has a distinct preference for O-donor ligands. Although it primarily forms six-coordinate complexes, it has some distinctive features that set it apart from metals like Mn(II), Co(II), and Ni(II), such as the self-ionized complexes [FeL₄Cl₂]⁺ [FeCl₄]^?. There are a number of examples where very small changes in the coordination sphere tilt the balance between isomeric structures. Chloride has a significant steric effect in the coordination sphere as well as a greater trans-influence than water.     

Iron(III)‐Complexes Engaged in the Biochemical Processes in Seawater. II. Voltammetry of Fe(III)‐Malate Complexes in Model Aqueous Solution

Characteristics of iron(III) complexes with malic acid in 0.55 mol L^?1 NaCl were investigated by voltammetric techniques. Three iron(III)‐malate redox processes were detected in the pH range from 4.5 to 11: first one at ?0.11 V, second at ?0.35 V and third at ?0.60 V. First process was reversible, so stability constants of iron(III) and iron(II) complexes were calculated: log K₁(Fe^III(mal))=12.66±0.33, log β₂(Fe^III(mal)₂)=15.21±0.25, log K₁(Fe^II(mal))=2.25±0.36, and log β₂(Fe^II(mal)₂)=3.18±0.32. In the case of second and third reduction process, conditional cumulative stability constants of the involved complexes were determined using the competition method: log β(Fe(mal)₂(OH)_x)=15.28±0.10 and log β(Fe(mal)₂(OH)_y)=27.20±0.09.     

Spectrophotometric Investigation of Iron(III)-N-Phenylcin-namohydroxamic Acid System

Abstract

N-Phenylcinnamohydroxamic acid, PCHA, was found to react with iron (III) to form complex species of different colour depending upon the reaction environment. The reaction conditions for the formation of the complex species were studied in aqueous-ethanolic medium. The general spectral properties of the species were investigated. The absorption curves were found to have two isobestic points. The number and composition of the complexes were determined and found to have composition 1:1, 1:2, 1:3 (Fe: PCHA). The wavelengths of the maximum absorbances were figured out to be 535, 495, and 445 nm for the I, II, and III complex species, respectively. It was verified that the Beer's law holds for these complexes at all wavelengths, and for the mixtures at the wavelengths of the isobestic points in a wide range of pH. The stepwise stability constants have been determined by the method of isobestic point and found to be log K₁ = 11.55, log K₂ = 10.11, and log Kg₃ = 7.44 for the I, II, and III complex species, respectively. The distribution diagrams (nomograms) of the complex species as a function of pH were constructed and the molar extinction coefficients of the three consecutive complexes have also been determined.     

A voltammetric identification of complex species inDMF solutions of Iron(III) complexes with salicylaldehydeS-methylthiosemicarbazone

The complex species existing under voltammetric conditions (0.1 mol dm^–3 LiCl) inDMF solutions of several iron(III) complexes with salicylaldehydeS-methylthiosemicarbazone (H₂ L) have been identified by adding [FeCl₄]^– and H⁺ and recording voltammograms at a glassy carbon electrode, both in stationary and rotating mode. By the action of Cl^–, a ligand release occurs, and the bis(ligand) cation [Fe(HL)₂]⁺ is transformed into [Fe(HL)Cl₃]^–. The same species is obtained in the reaction of [FeL ₂]^– with [FeCl₄]^–. Besides, the possibility has been demonstrated to obtain some complexes (and finally [FeCl₄]^–) starting from a more basic type, by a careful addition of H⁺ generatedin situ from a Pd/H electrode. A practical application of the latter procedure could be the determination of the iron(III) content in such and similar compounds.

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Die voltammetrische Identifizierung der Komplex-Spezies in DMF Lösungen von Eisen(III) Komplexen mit Salicylaldehyd-S-methylthiosemicarbazon

Zusammenfassung Die Spezies, die unter voltammetrischen Bedingungen (0.1 mol dm^–3 LiCl) inDMF Lösungen einiger Eisen(III)-Komplexe mit Salizylaldehyd-S-methylthiosemicarbazon (H₂ L) vorhanden sind, wurden durch Zusatz von [FeCl₄]^– und H⁺ und Aufnahme von Voltammogrammen an der stationären und rotierenden Glaskohlenstoffelektrode identifiziert. Unter der Wirkung von Cl^–-Ionen kommt es zu einem Ligandenaustausch, wobei das bis(Ligand)-Kation [Fe(HL)₂]⁺ in [Fe(HL)Cl₃]^– übergeht. Die gleiche Substanz erhält man bei der Reaktion von [FeL ₂]^– mit [FeCl₄]^–. Ferner wird die Möglichkeit der Gewinnung einiger Komplexe (schließlich von [FeCl₄]^–) ausgehend von der basischen Form durch stufenweise Zugabe von H⁺-Ionen, diein situ mit Hilfe einer Pd/H-Elektrode gebildet werden, beschrieben. Eine praktische Anwendung des letztgenannten Prozesses wäre die Bestimmung des Gehalts von Fe(III) in Lösungen der genannten und ähnlichen Komplexverbindungen.

     

X-Ray Diffraction Analysis and Luminescent Study of the Structure of the Tb2(CF3COO)6(H2O)6 Dimer Obtained from Terbium(III) Carbonate

The molecular and crystal structure of the terbium(III) trifluoroacetate trihydrate dimer synthesized from terbium(III) carbonate was studied by X-ray diffraction (XRD) analysis. Luminescent data unambiguously show that the compound is one of the isomers of Tb₂(CF₃COO)₆(H₂O)₆ composition. Evidence has been found for the presence of another isomer in the terbium(III) dimer obtained from terbium(III) hydroxide.     

Voltammetric Determination of Iron(III) in Water

A square wave voltammetric procedure for the determination of trace amounts of Fe(III) was developed at an unmodified edge plane pyrolytic graphite (EPPG) electrode and a screen printed electrode (SPE). This simple procedure was applied to real samples of commercially bottled mineral water. Sensitive results in the micromolar region could be achieved without modification of the electrode. Using the WHO guideline limits for the Fe(III) concentration in drinking water, recovery percentages at an EPPG gave 103 % and 107 %, and 98.6 % and 95.0 % at a SPE for the 5.36 µM (0.3 mg L^?1) and 53.6 µM (3.0 mg L^?1) additions of Fe(III), respectively.     

Iron(III) tosylate-catalyzed deprotection of aromatic acetals in water

The deprotection of aromatic as well as conjugated acetals and ketals in water is catalyzed by iron(III) tosylate (1.0-5.0 mol %). Iron(III) tosylate is an inexpensive and readily available catalyst. The use of water, the most environmentally benign solvent, makes this procedure especially attractive for acetal deprotection.     

Kinetics and mechanism of oxidation of glycine by iron(iii)-1,10-phenanthroline complex in perchloric acid medium

Kinetics and mechanism of oxidation of glycine by iron (III)-1,10-phenanthroline complex has been studied in perchloric acid medium. The reaction is first order with respect to iron(III) and glycine. An increase in (phenanthroline) increases the rate, while increase in [H⁺] decreases the rate. Hence it can be inferred that the reactive species of the substrate is the zwitterionic form and that of the oxidant is [Fe(phen)₂(H₂O)₂]³⁺. The proposed mechanism leads to the rate law as elucidated.     

Iron(III) and nickel(II) template complexes derived from benzophenone thiosemicarbazones

New iron(III) and nickel(II) chelates were synthesized by template reaction of 2,4-dihydroxy- and 2-hydroxy-4-methoxy-benzophenone S-methylthiosemicarbazones with 2-hydroxy- and 5-bromo-2-hydroxy-benzaldehydes. The template complexes were isolated as stable solids and characterized by elemental analysis, conductivity and magnetic measurements, IR, ¹H NMR, UV–Visible, and mass spectra. The crystal structure of N ¹-(2-hydroxy-4-methoxyphenyl)(phenyl)methylene-N ⁴-(2-hydroxy-phenyl)methylene-S-methyl-thiosemicarbazidato-Fe(III) was determined by X-ray diffraction. A five-coordinate, distorted square-pyramidal geometry was established crystallographically for the iron(III) complex. Cytotoxicity and proliferation properties were determined using human erythromyeloblastoid leukemia and HL-60 mouse promyelocytic leukemia cell lines. For K 562 and HL-60 cells, compounds 1a and 2b were found to be cytotoxic at concentrations of 10 and 20 µg mL^?1.     

Determination of Total Iron in Environmental Samples by Solid Phase Extraction with Dimethyl(E)‐2‐(2‐Methoxyphenoxy)‐2‐Butenedioate

A novel solid phase extraction technique for determination of total iron in environmental water samples was developed. The method is based on sorption of Fe(III) ions on octadecyl silica membrane disk modified with a new synthetic ligand dimethyl(E)‐2‐(2‐methoxyphenoxy)‐2‐butenedioate (I). Iron(III) is quantitatively retained on the disk in the pH range of 3–7 at a flow rate of 1–7 mL min⁻¹. The Fe(III) eluted with 10 mL of 0.01 M EDTA and than was measured by flame atomic absorption spectrometry (FAAS) at 248.3 nm. The maximum capacity disk modified by 7 mg of ligand was found to be 197 ± 2 μg of iron(III). The breakthrough volume was greater than 2000 mL. The iron(III) was completely recovered (> 99%) from water with a preconcentration factor of more than 200. The limit of detection of the proposed method was 1.00 ng mL⁻¹. The various cationic and anionic interferences had no effect on the recovery of iron(III) from the binary mixtures. The proposed method was successfully applied to determination of total iron from three different water samples.     

Theoretical Study of NO Dimer Adsorption and Dissociation on the CuCr204 (100) Surface

Theoretical simulation of the adsorption and dissociation of two NO molecules at the Cu2 , Cr3 and bridge Cr3 sites (b-Cr3 ) on the normal spinel CuCr2O4 (100) surface has been carded out by density functional theory calculations. The results show that the formed N-down and O-down NO dimers are negatively charged. The formation of stable O-down dimers on the surface leads to the great elongation of N-O bond, which contributes to the NO reduction. The transition-state calculations indicate that the decomposition of O-down NO dimer at the b-Cr3~ site is most favorable and N2O is the major reduction product.