Determination of hydroxyl radicals from photolysis of Fe(III)-pyruvate complexes in homogeneous aqueous solution ?

Summary Benzene was used as a probe to detect ^·OH produced by photolysis of Fe(III)-pyruvate complexes in a homogeneous system. The Fe(III)-Pyr system was found to be not catalytic. Influence of pH, temperature, as well as the concentration of Fe(III) and pyruvate (Pyr) on the ^·OH yield was investigated.     

Evidence of the hydroxyl radical formation upon the photolysis of an iron-rich clay in aqueous solutions

With the use of laser flash photolysis, the formation of hydroxyl radicals upon the photolysis of an iron-rich clay (montmorillonite KSF) was demonstrated. The ^•OH radical was shown to be formed by the photolysis of the Fe(OH)_aq ²⁺ complex that escaped from the clay into the solution bulk.     

Photokatalytische Systeme. LIX. Zur Photolyse von Oxalato-Eisen(III)-Gemischtligandkomplexen mit aromatischen α-Diiminliganden

Photocatalytic Systems. LIX. Photochemical Investigations of Iron (III) Mixed Ligand Complexes with Oxalate and Aromatic α-Diimines The photolysis of iron(III) mixed ligand complexes with oxalate and aromatic α-diimine ligands 2,2-bipyridine and 1,10-phenanthroline in aqueous/methanolic solution results in [Fe(N,N)₃]²⁺, with N,N = α-diimine and carbon dioxid as main products of the photoredox-decomposition. In dependence on the irradiation wave-length and the concentration of the complex solution quantum yields of the formation of Fe^II were determined and compared with Φ_Fe^II values of K₃[Fe(ox)₃].     

Photochemistry of iron(iii)-lactic acid complex in aqueous solutions

Photochemistry of a 1: 1 Fe^III-lactic acid complex, [Fe(Lact)]⁺, in aqueous solutions was studied by stationary photolysis, nanosecond laser flash photolysis (355 nm, 6 ns), and femtosecond pump-probe spectroscopy (400 nm, 200 fs). The quantum yield of photolysis of [Fe(Lact)]⁺ upon excitation at 355 nm is 0.4 and 0.22 in the deoxygenated and air-saturated solutions, respectively. Weak transient absorption in the range 500–750 nm was observed in the nanosecond experiments. It was assigned to a [Fe^II...-O-CH(Me)-COO^·]⁺ radical complex. The spectral properties of the ligand-to-metal charge transfer excited state and the characteristic time of formation of the radical complex (1.5 ps) were determined in the femtosecond spectroscopy experiments. A reaction mechanism was proposed, which involves inner-sphere electron transfer in the excited complex with the formation of a radical complex [Fe^II...-O-CH(Me)-COO^·]⁺ and its subsequent transformation to the end product of the photochemical reaction.     

Hydrogen photogeneration from aqueous solutions of alcohols by the Fe3+ ion

Fe(III) chlorocomplex ions are found to generate hydrogen from aqueous solutions of aliphatic alcohols on photolysis with a medium pressure Hg lamp. The reaction mechanism is believed to involve the formation of reactive intermediates Cl⁻ and H⁻, where H⁻ abstracts hydrogen from the alcohol.     

Synthesis and characterization of an iron(III) complex of glycine derivative of bis(phenol)amine ligand in relevance to catechol dioxygenase active site

A glycine derivative of bis(phenol)amine ligand (HL^Gly) was synthesized and characterized by ¹H NMR and IR spectroscopies. The iron(III) complex (L^GlyFe) of this ligand was synthesized and characterized by IR, UV-Vis, X-ray and magnetic susceptibility studies. X-ray analysis reveals that in L^GlyFe the iron(III) center has a distorted trigonal bipyramidal coordination sphere and is surrounded by an amine nitrogen, a carboxylate and two phenolate oxygen atoms. The mentioned carboxylate group acts as μ-bridging ligand for iron centers of neighbor complexes. The variable-temperature magnetic susceptibility indicates that L^GlyFe is the paramagnetic high spin iron(III) complex. It has been shown that electrochemical oxidation of this complex is ligand-centered due to the oxidation of phenolate to the phenoxyl radicals. The L^GlyFe complex also undergoes an electrochemical metal-centered reduction of ferric to ferrous ion. The oxygenation of 3,5-di-tert-butyl-catechol, with L^GlyFe in the presence of dioxygen was investigated.     

Selective extraction, separation and speciation of iron in different samples using 4-acetyl-5-methyl-1-phenyl-1H-pyrazole-3-carboxylic acid

A method for speciation, preconcentration and separation of Fe(II) and Fe(III) in different matrices was developed using solvent extraction and flame atomic absorption spectrometry. 4-Acetyl-5-methyl-1-phenyl-1H-pyrazole-3-carboxylic acid (AMPC) was used as a new complexing reagent for Fe(III). The Fe(III)-AMPC complex was extracted into methyl isobutyl ketone (MIBK) phase in the pH range 1.0-2.5, and Fe(II) ion remained in aqueous phase at all pH. The chemical composition of the Fe(III)-AMPC complex was determined by the Job's method. The optimum conditions for quantitative recovery of Fe(III) were determined as pH 1.5, shaking time of 2 min, 1.64 × 10⁻⁴ mol L⁻¹ AMPC reagent and 10 mL of MIBK. Furthermore, the influences of diverse metal ions were investigated. The level of Fe(II) was calculated by difference of total iron and Fe(III) concentrations. The detection limit based on the 3σ criterion was found to be 0.24 μg L⁻¹ for Fe(III). The recoveries were higher than 95% and relative standard deviation was less than 2.1% (N = 8). The validation of the procedure was performed by the analysis of two certified standard reference materials. The presented method was applied to the determination of Fe(II) and Fe(III) in tap water, lake water, river water, sea water, fruit juice, cola, and molasses samples with satisfactory results.     

31P NMR assessment of the phosvitin-iron complex in mayonnaise

Lipid oxidation is the main reason for the limited shelf life of mayonnaise. One of the main catalysts of this process is iron, which is introduced in its ferric (Fe(III)) form via phosvitin, an egg yolk phosphoprotein rich in phosphoserines. The binding of Fe(III) to phosvitin and its ability to establish a redox couple with Fe(II) is believed to determine the oxidation rate of unsaturated lipids. In this work, a ³¹P NMR based method was developed to quantify loading of phosvitin with Fe(III) and its reductive release. Both features could be quantified in model phosvitin solutions by exploiting the paramagnetic broadening of ³¹P NMR signal of phosphoserine residues by Fe(III). This method was then successfully applied to quantify the phosvitin-Fe(III) loading in mayonnaise water phase by liquid NMR, whereas ³¹P NMR MAS could only provide a qualitative measure. The ³¹P NMR method showed a direct relation between loading of the Fe(III)-phosvitin complex and lipid oxidation.     

Preconcentration extractive separation, speciation and spectrometric determination of iron(III) in environmental samples

Preconcentration, speciation and separation with solvent extraction of Fe(III) from samples of different origin, using methyl isobutyl ketone (MIBK) as a solvent and the sodium salt of 2-carboethoxy-1,3-indandione (CEIDNa) as a complexing agent for Fe(III), were studied. CEIDNa reacts with Fe(III) in the pH range 1.5–3.5 to produce a red colored complex of Fe(III)–CEIDNa (1:3 molar ratio) soluble in MIBK. The investigation includes a study of the characteristics that are essential for solvent extraction, spectrophotometric and flame atomic absorption spectrometric determination (AAS) of iron. A highly sensitive, selective and rapid spectrometric method is described for the trace analysis of iron(III) by CEIDNa. The complex formed obeys Beer's law from 0.06 to 1.8 mg l⁻¹ with an optimum range. A single step extraction was efficiently used with a distribution ratio (D)=10^3.6. The extracted red colored (1:3) Fe–CEIDNa was measured spectrophotometrically at 500 nm with a molar absorptivity of 1.2×10⁴ l mol⁻¹ cm⁻¹. In addition, the organic phase was directly aspirated to the flame for AAS determination and the signals related to Fe(III) concentration were recorded at 243.3 nm. The complexation of iron(III) with CEIDNa allows the separation of the analyte from alkali, alkaline earth and other elements, which are not complexed. The proposed preconcentration procedure was applied successfully to the determination of trace Fe(III) in soil, milk and natural water samples.     

Separation of Iron(III) with Ammonium Thiocyanate‐H2O‐n‐Propyl Alcohol Extraction System in the Presence of Sodium Chloride

The behavior and conditions of liquid‐liquid extraction‐separation of Fe(III) by ammonium thiocyanate‐H₂O‐n‐propyl alcohol system in the presence of NaCl were studied, and the possible reactive mechanism of extraction of Fe(III) was deduced. The study showed that, in the presence of a given amount of NaCl, phases were separated thoroughly between n‐propyl alcohol and water. In the process of phase separation, the complex [Fe(SCN)_n]^(3‐n) formed by NH₄SCN and Fe(III) was quantitatively extracted into the n‐propyl alcohol phase. The extracted Fe(III) exists in the n‐propyl alcohol phase mainly as the forms of Fe(SCN)₂⁺ and Fe(SCN)₃. Also, the relationship between extraction yield of Fe(III) and the amount of NH₄SCN agreed well with the quadratic equation E = 0.54 + 58.14x ? 8.39x² (E and x represent the recovery rate of Fe(III) and the volume (mL) of 0.1 M NH₄SCN respectively). The quadratic R‐Square is 0.9990. With this method, Fe(III) can be completely separated from Co(II), Ni(II), Mn(II), Al(III), Bi(III) and Cd(II) at pH 1.0?2.0. The present method was applied in determining Fe(III) in samples with satisfactory results such as relative standard deviation from 2.06% to 2.89% and recovery rate in the range of 98.4?101.4%.     

Acyl and CO Ligands in the [Fe]-Hydrogenase Cofactor Scramble upon Photolysis

[Fe]-hydrogenase harbors the iron-guanylylpyridinol (FeGP) cofactor, in which the Fe(II) complex contains acyl-carbon, pyridinol-nitrogen, cysteine-thiolate and two CO as ligands. Irradiation with UV-A/blue light decomposes the FeGP cofactor to a 6-carboxymethyl-4-guanylyl-2-pyridone (GP) and other components. Previous in vitro biosynthesis experiments indicated that the acyl- and CO-ligands in the FeGP cofactor can scramble, but whether scrambling occurred during biosynthesis or photolysis was unclear. Here, we demonstrate that the [¹⁸O₁-carboxy]-group of GP is incorporated into the FeGP cofactor by in vitro biosynthesis. MS/MS analysis of the ¹⁸O-labeled FeGP cofactor revealed that the produced [¹⁸O₁]-acyl group is not exchanged with a CO ligand of the cofactor, indicating that the acyl and CO ligands are scrambled during photolysis rather than biosynthesis, which ruled out any biosynthesis mechanisms allowing acyl/CO ligands scrambling. Time-resolved infrared spectroscopy indicated that an acyl-Fe(CO)₃ intermediate is formed during photolysis, in which scrambling of the CO and acyl ligands can occur. This finding also suggests that the light-excited FeGP cofactor has a higher affinity for external CO. These results contribute to our understanding of the biosynthesis and photosensitive properties of this unique H₂-activating natural complex.     

Studies on the effect of non-ionic surfactant micelles on color reactions: III. The effect of micelles on metal ion reactivity in the Fe(III)-PAN-Triton X-100 system

Fe(III) and PAN form Fe(PAN),OH complex in CHCl₃ extract which shows absorption maxima at 550 nm and 775 nm (log ε₅₅₀,= 4.06, log ε₇₇₅ = 4.08). In the Fc(III)-PAN-Triton X-100 system, two complex species Fe(PAN)₂⁺ and/or Fe(PAN)₂OH may be formed. Fe(PAN)₂⁺ possesses a strongly absorbing peak at 550 nm (log ε₅₅₀ = 4.36). In this paper the effect of Triton X-100 micelles on the Fe(III)-PAN color reaction has been investigated in detail. We consider that the high density of ether linkages in Triton X-100 micelles concentrate hydrous Fe(III) ions and change their existing state. Moreover, the micelles not only raise the reactivity of Fe(III), but also enhance the rate of the color reaction.     

Asulam in Aqueous Solutions: Fate and Removal Under Solar Irradiation

The photodegradation of the pesticide asulam (methyl[(4-aminophenyl)sulfonyl]carbamate) in aqueous solutions (1.0 2 10 m 4 mol L m 1 = 23 mg L m 1 ) has been investigated with and without Fe(III). The asulam disappearance were measured by direct photolysis at 254 nm as a function of pH and oxygen concentration. Different photoproducts have been identified, among them a blue condensation product which was only observed upon selective direct excitation of asulam. In the presence of Fe(III) and by excitation at 365 nm, we obtained the complete mineralisation of asulam, while no complete transformation of organic carbons into CO 2 was observed by direct photolysis. The continuous formation of ” OH radicals generated from the excitation of Fe(III) species allowed the total mineralisation of asulam. Information is also given about the fate of asulam in aqueous solutions under solar irradiation.     

2-Bis(carboxymethyl)-amino-5-hydroxy-terephthalsäure als ambifunktioneller Ligand in Eisen(III)-Komplexen

2-Bis(carboxymethyl)-amino-5-hydroxy-terephthalic Acid as an Ambifunctional Ligand in Iron(III) Complexes From steric reasons the anthranilic acid -N,N-diacetic acid group and the salicylic acid group of 2-bis(carboxymethyl)-amino-5-hydroxy-terephthalic acid (H₅C) cannot coordinate to the same central atom. With iron(III) H₅C forms the mononuclear complex (HC)Fe(OH)^2?, the central atom is fixed to the anthranilic acid N,N-diacetic acid group. In a weak acid medium (HC)Fe(OH)^2? is converted into the binuclear species (HC)Fe(C)Fe(OH)^4? which is of a deep red colour. In this complex the anion C^5?has the function of a bridging ligand coordinating both by the anthranilic acid-N,N-diacetic acid group and by the salicylic acid group. The complex formation in the ternary system iron(III)/nitrilo triacetic acid/5-sulfo salicylic acid may be used as model for the dimerisation of the anion (HC)Fe(OH)^2?.     

New method for simultaneous determination of Fe(II) and Fe(III) in water using flow injection technique

The method exploits the possibilities of flow injection gradient titration in a system of reversed flow with spectrophotometric detection. In the developed approach a small amount of titrant (EDTA) is injected into a stream of sample containing a mixture of indicators (sulfosalicylic acid and 1,10-phenanthroline). In acid environment sulfosalicylic acid forms a complex with Fe(III), whereas 1,10-phenanthroline forms a complex with Fe(II). Measurements are performed at wavelength λ = 530 nm when radiation is absorbed by both complexes. After injection EDTA replaces sulfosalicylic acid and forms with Fe(III) more stable colourless complex. As a result, a characteristic “cut off” peak is registered with a width corresponding to the Fe(III) concentration and with a height corresponding to the Fe(II) concentration. Calibration was performed by titration of four two-component standard solutions of the Fe(II)/Fe(III) concentrations established in accordance with 2² factorial plan. The method was tested with the use of synthetic samples and then it was applied to the analysis of water samples taken from artesian wells. Under optimized experimental conditions Fe(II) and Fe(III) were determined with precision less than 0.8 and 2.5% (RSD) and accuracy less than 3.2 and 5.1% (relative error) within the concentration ranges of 0.1-3.0 and 0.9-3.5 mg L⁻¹ of both analytes, respectively.     

Synthèses photochimiques diastéréosélectives de complexes à liaison fer-métal du groupe 14

The diastereomeric Fe^*(MR₃(CO)(P^*R¹R²R³)Cp complexes (M  Si, Ge and Sn, R  aryl or methyl) are synthesized by photolysis of the prochiral Fe(MR₃(CO)₂Cp, precursors in the presence of the corresponding racemic phosphorus III ligands. Asymmetric induction at iron is observed if the phosphorus atom is bound to a group containing a specific heteroatom (nitrogen or oxygen).     

Cathodic stripping determination of iron at a platinum electrode modified by adsorption of adenosine-5'-monophosphate

Irreversible adsorption of adenosine-5'-monophosphate onto platinum yields an electrode surface which is readily plated by formation of a non-labile complex with iron(III) present initially in solution or formed by oxidation of iron(II). A negative potential scan subsequent to a 60-s deposition step produces a cathodic stripping peak, the height of which is proportional to the sum of the Pe(III) and Fe(II) concentrations in solution. Oxalate can be used to mask the response to Fe(III). The method is shown to be applicable to determinations of Fe(III) and Fe(II) in the concentration range lO^-8–lO^-6 mol l^-1.     

Characterization of metal-deferoxamine complexes by continuous variation method: A new approach using capillary zone electrophoresis

Siderophores are low molecular weight non-ribosomal peptides with extremely high affinity by iron. However, other metals present affinity for siderophores but to a smaller degree. Deferoxamine is an example of a bacterial hydroxamic siderophore, which was investigated herein. Capillary zone electrophoresis (CZE) was used as a new approach in the continuous variation method for the characterization of metal-deferoxamine complexes. A set of samples containing both metal (e.g., Fe(III), Fe(II) or Ni(II)) and siderophore with different molar ratios was prepared and analyzed by both CZE and UV-vis spectrophotometry. A phosphate buffer pH 8.0 was used as the background electrolyte in the first case due to best complex and free ligand peaks resolution. The Job's plots obtained from complex peak areas (complex concentration) versus metal molar fraction revealed complexes stoichiometries of M : L of 2 : 3, 1 : 2 and 1 : 1 for Fe(III), Fe(II) and Ni(II) complexes, respectively. Conditional formation constants could also be calculated for Fe(III) and Fe(II) complexes as K_f = 1.03 × 10¹³ and 2.47 × 10⁴, respectively. UV-visible spectrophotometric analysis confirmed the data obtained for Fe(III)-complex.     

Catalytic wave of hydrogen in systems based on iron(II) nitrosyl complexes

The electroreduction of Fe(III) at a dropping mercury electrode in an acetate buffer solution containing NO ₂ ^- and NH ₄ ⁺ ions and some hydroxy acids was studied. Based on the fact that the current depends on a number of factors, it was concluded that the wave observed was catalytic wave of hydrogen. The proposed mechanism of the process includes the electroreduction of the Fe(III) complex, the formation of a mixed-ligandFe(II) complex, and its protonation and reduction at a dropping mercury electrode with the liberation of hydrogen. Presented at the V All-Russian Conference with the Participation of CIS Countries on Electrochemical Methods of Analysis (EMA-99), Moscow, December 6–8, 1999.     

A study of the aerobic reaction between dopamine and Fe(III) in the presence of S<Subscript>2</Subscript>O<Subscript>3</Subscript><Superscript>2−</Superscript>

The reaction between Fe(III) and dopamine in aqueous solution in the presence of Na₂S₂O₃ was followed through UV–Vis spectroscopy, pH and oxy-reduction potential (Eh) measurements. The formation and quick disappearing of the complex [Fe(III)HL¹⁻]²⁺, HL¹⁻ = monoprotonated dopamine was observed with or without S₂O₃ ²⁻ at pH 3. An unexpected reaction occurs in presence of thiosulfate forming the stable anion complex [Fe(III)(L²⁻)₂]¹⁻, L²⁻ = dopacatecholate (λ = 580 nm) and the auto-increasing of the pH, from 3 to 7. It was proposed that H⁺ and molecular oxygen are consumed by free radical thiosulfate formed during the reaction.