Simultaneous kinetic determination of Fe(III) and Fe(II) by H-point standard addition method

The H-point standard addition method (HPSAM) was applied to kinetic data for simultaneous determination of Fe(III) and Fe(II) or selective determination of Fe(III) in the presence of Fe(II). The method is based on the difference in the rate of two processes; reduction of Fe(III) with Co(II) and subsequent complex formation of resulted Fe(II) with 1,10-phenanthroline, and direct complex formation between Fe(II) and 1,10-phenanthroline in pH 3 and cetyl trimethyl ammonium bromide, CTAB, micellar media. Fe(III) can be determined in the range of 0.75-5.13 mug ml(-1)with satisfactory accuracy and precision in the presence of excess Fe(II) under working conditions. The proposed method was successfully applied to the simultaneous determination of Fe(III) and Fe(II) and also to the selective determination of Fe(III) in the presence of Fe(II) in several synthetic mixtures containing different concentration ratios of Fe(III) to Fe(II).     

Rapid and simple method for determination of Nepsilon-(carboxymethyl)lysine and Nepsilon-(carboxyethyl)lysine in urine using gas chromatography/mass spectrometry

A new procedure was developed to determine in urine the concentrations of N(epsilon)-(carboxymethyl)lysine (CML) and N(epsilon)-(carboxyethyl)lysine (CEL), the major products of oxidative modification of glycated proteins, to assess levels of oxidative stress in physiological systems. The urine samples were acetonitrile-deproteinized, then derivatized by ethylchloroformate, and N(O,S)-ethoxycarbonyl ethyl esters of amino acids were analysed by isotope dilution gas chromatography/mass spectrometry. Recovery averaged 89%. Linearity was excellent (r = 0.998-0.999) in the 0.5-25 micromol/L range for CML and CEL. The limit of detection of this assay was 0.1 micromol/L (corresponding to 0.20 pmol of CML or CEL on column). Intra-day and inter-day precisions were likewise excellent, with relative standard deviations <4.63 and <6.15%, respectively. Accuracy of CML and CEL determination (15 micromol/L) was 2.9 and 5.9% of the estimated theoretical value. The time from obtaining the urine sample to determination of the concentration from the chromatographic peak was 80 min or less. This method is sensitive, reproducible, accurate, relatively cheap and very simple. It can be useful for laboratories involved in the diagnosis and monitoring of age-related chronic diseases.     

Kinetic spectrophotometric determination of Fe(II) in the presence of Fe(III) by H-point standard addition method in mixed micellar medium

The H-point standard addition method was applied to kinetic data for simultaneous determination of Fe(II) and Fe(III) or selective determination of Fe(II) in the presence of Fe(III). The method is based on the difference in the rate of complex formation between iron in two different oxidation states and methylthymol blue (MTB) at pH 3.5 in mixed cetyltrimethylammonium bromide (CTAB) and Triton X-100 micellar medium. Fe(II) can be determined in the range 0.25-2.5 microg ml(-1) with satisfactory accuracy and precision in the presence of excess Fe(III) and other metal ions that rapidly form complexes with MTB under working condition. The proposed method was successfully applied to the simultaneous determination of Fe(II) and Fe(III) or selective determination of Fe(II) in the presence of Fe(III) in spiked real environmental and synthetic samples with complex composition.     

Influence of arsenate species on the formation of Fe(III) oxyhydroxides and Fe(II–III) hydroxychloride

Iron(III) oxyhydroxides were prepared by oxidation of aerated aqueous suspensions of Fe(II) hydroxide. The effects of arsenate species on their formation were studied by mixing FeCl₂·4H₂O, NaOH and Na₂HAsO₄ solutions. The intermediate and final products of the oxidation processes were characterised by X-ray diffraction, Infrared and Raman spectroscopy. Arsenate species were not reduced during the process but they influenced both oxidation stages, that is the formation of the intermediate Fe(II–III) compound and its subsequent oxidation into Fe(III) compounds. Arsenate species clearly inhibited the growth and hindered the crystallisation of GR(Cl^?), the Fe(II–III) hydroxychloride that would have formed in the experimental conditions considered here. For the largest arsenate concentrations, the intermediate product was nanocrystalline and more likely consisted of clusters showing an ordering of atoms similar to that of GR(Cl^?), isolated from each other by adsorbed arsenate species. The adsorption of As(V) prevented growth of these clusters into well-crystallised GR(Cl^?). The arsenate species influenced similarly the second reaction stage by inhibiting the formation of well-ordered and crystallised Fe(III) compounds. Lepidocrocite, the final product in the absence of arsenate, was replaced by “6-line” ferrihydrite with increasing As(V) concentration, then “6-line” ferrihydrite was replaced by another poorly ordered compound, feroxyhite. These crystallised compounds were obtained together with an increasing part of nanocrystalline Fe(III) ox(yhydrox)ide(s).     

Catalytic oxidation of Fe(II) aqua ions with atmospheric oxygen in the presence of Pd(II) tetraaqua complex and an aromatic compound

The effect of a series of aromatic compounds (toluene, benzyl alcohol, benzonitrile, phenylacetonitrile, and o-cyanotoluene) in a concentration of 0.01 M on the oxidation of Fe(II) aqua ions with oxygen in the presence of Pd(II) tetraaqua complex at 25–70°C was revealed. In the presence of an aromatic compound, palladium black is not formed, which results in an increased yield of Fe(III) in the Pd-catalyzed oxidation of Fe(II) with oxygen in a perchloric acid medium. A scheme involving the formation of a complex of palladium species in an intermediate oxidation state with arene and molecular oxygen was suggested.     

Hydrogen peroxide formation upon oxidation of oxalic acid in presence and absence of oxygen and of manganese(II)--III. Iron(III) and copper(II) as retarders

The formation of considerable amounts of hydrogen peroxide upon the slow addition of various oxidizing agents to oxalic acid in dilute sulphuric acid in the presence of oxygen and Mn(II) is greatly retarded in the presence of Fe(III) or Cu(II). With hydrogen peroxide as oxidizing agent and a trace of Fe(II) there is considerable decomposition of peroxide, under a nitrogen atmosphere, after a few hours at 25 degrees in light (from a tungsten lamp), and less decomposition in the dark. This decomposition is decreased by Mn(II) and also when the original mixture contains Fe(III). With oxygen as the oxidizing agent Fe(II) is about 100 times as effective an inhibitor of peroxide formation as Fe(III). With all oxidizing agents used, Cu(II) is some 6-10 times more effective as a retarder than Fe(III). The inhibition is accounted for by the reaction Fe(III) [or Cu(II)] + CO(-)(2) --> Fe(II) [or Cu(I)] + CO(2).     

First Synthesis of a Binuclear [Mn(II)(bipy)-Fe(III)(porphyrin)] Complex: Spectroscopic Characterization and First Evidence of Reversible Formation of Manganese(III) as Manganese Peroxidase

A [(P)Fe(III)-Mn(II)] bimetallic complex, mimicking the active site of manganese peroxidase, has been synthesized. A modified highly fluorinated porphyrin, 5,10,15-tris(pentafluorophenyl)-20-(o-aminophenyl)porphyrin, has been used to introduce, through a short spacer linked to the amino function, a manganese auxiliary ligand, 6-aminomethyl-2,2'-bipyridine. Two successive metalations by FeCl(2) and MnCl(2) afforded the [(P)Fe(III)-Mn(II)] bimetallic complex that has been characterized by elemental analysis and FAB(+) mass spectrometry. X-band EPR spectroscopy and magnetic susceptibility measurements were in agreement with two high spin Fe(III) and Mn(II) centers without magnetic exchange interaction. Moreover, there is no higher intermolecular association through &mgr;-chloro bridging as observed by EPR with a simpler chloromanganese complex, Mn(bipy)(2)Cl(2), at high concentration. Addition of pentafluoroiodosobenzene in methanol at 0 degrees C led to the progressive and complete disappearance of the EPR Mn(II) signals, that were recovered after addition of a phenol. This result is consistent with Mn(III) formation. This production of Mn(III) requires the presence of the iron porphyrin and is proposed to occur through the intermediate formation of a Fe(IV) dimethoxide species which can be related to the oxidation of Mn(II) catalyzed by manganese peroxidase compound II.     

Superoxide anion radical generation in the NaOH/H(2)O(2)/Fe(III) system: a spin trapping ESR study

Formation of free radical intermediates in a NaOH/H(2)O(2)/Fe(III) system has been studied by ESR spectroscopy in the presence of the spin trap 5,5-dimethy-1-pyrroline N-oxide (DMPO). DMPO/O(2(*) ) (-) and DMPO/(*)OH signals were simultaneously detected in this system, but only the DMPO/(*)OH signal could be observed in the absence of Fe(III). Effects of pH values and Fe(III) concentrations on the ESR signal intensities were investigated in detail. Formation of DMPO/O(2(*) ) (-) adduct was inhibited by the addition of superoxide dismutase (SOD), catalase or nitro blue tetrazolium (NBT), and by chelating the Fe(III) with some chelators, including ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), and desferrioxamine (DFO). Deoxygenation from the NaOH/H(2)O(2)/Fe(III) mixture had a slight effect on the formation of DMPO/O(2(*) ) (-). DMPO/O(2(*) ) (-) signal was also detected from the NaOH/H(2)O(2)/Fe(II) mixture, but it can be totally suppressed under anaerobic conditions. Considering the hydrolysis of Fe(III) into polymerization iron species with oxide phases in the alkaline medium, Fe(2)O(3) was directly suspended into a mixture of NaOH/H(2)O(2) for comparison. Fortunately, the presence of Fe(2)O(3) suspension was found to be of benefit to the production of DMPO/O(2(*) ) (-). Influence of aging time of hydrolytic iron species on the superoxide anion radical generation was also studied. These results suggest that the generation of O(2(*) ) (-) from the NaOH/H(2)O(2)/Fe(III) system was probably caused by the heterogeneous surface catalysis initiated by hydrolytic iron species.     

Simultaneous determination of Fe(II) and Fe(III) by kinetic spectrophotometric H-point standard addition method

The H-point standard addition method (HPSAM) for simultaneous determination of Fe(II) and Fe(III) is described. The method is based on the difference in the rate of complex formation of iron in two different oxidation states with Gallic acid (GA) at pH 5. Fe(II) and Fe(III) can be determined in the range of 0.02–4.50 μg ml⁻¹ and 0.05–5.00 μg ml⁻¹, respectively, with satisfactory accuracy and precision in the presence of other metal ions, which rapidly form complexes with GA under working conditions. The proposed method was successfully applied for simultaneous determination of Fe(II) and Fe(III) in several environmental and synthetic samples with different concentration ratios of Fe(II) and Fe(III).     

Synthesis and reactivity of Haloacetato derivatives of iron(II) including the crystal and the molecular structure of [Fe(CF3COOH)2(micro-CF3COO)2]n

The syntheses of haloacetates of iron(II) and their reactivity are described. The compound Fe(CF3COO)2, 1, crystallizes from CF3COOH/(CF3CO)2O solution as the polynuclear [Fe(CF3COO)2(CF3COOH)2]n, 2, which contains bridging trifluoroacetates and monodentate trifluoroacetic acid groups. Fe(CF3COO)2(DMF)x, as obtained from Fe(CO)5 and CF3COOH/(CF3CO)2O in DMF, reacts with dioxygen at room temperature to give two micro3-oxo compounds, namely, [Fe3(micro3-O)(CF3COO)6(DMF)3], 3, a Fe(II)-Fe(III)-Fe(III) derivative, and [Fe4(micro3-O)2(micro2-CF3COO)6(CF3COO)2(DMF)4], 4, containing Fe(III) atoms only, which have been characterized by X-ray diffraction methods. Iron(II) chloro- and bromoacetates can be isolated by exchange reactions of iron(II) acetate with chloro- and bromo-substituted acetic acids in moderate to good yields. The stability of iron(II) haloacetates decreases on increasing the atomic weight and the number of halogens on the alpha-carbon atom. The species Fe(CX3COO)2 (X = Cl, 7; Br, 8), in THF solution, slowly convert into [Fe3(micro3-O)(CCl3COO)6(THF)3], 11, or [Fe3(micro3-O)(CBr3COO)6(THF)3][FeBr4], 10, respectively. Likewise, when iron(II) acetate (or trifluoroacetate) is left for several hours in the presence of a variety of haloacetic acids in THF, selective formation of different species, depending on the nature of the starting compound and of the acid employed, is observed. The formation of these products is the result of C-X bond activation (X = Cl, Br) and haloacetato decomposition, which occurs with concomitant oxidation at the metal centers. Carboxylic acid degradation species (CH2XCOOH, CX4, CX3H, CX2H2, X = Cl, Br) have been observed by GC-MS.     

Synthesis and reaction of Schiff base 4-(pyridin-3-ylmethylimino)-pent-2-en-2-ol with FeCl3

A potentially tridentate Schiff base 4-(pyridin-3-ylmethylimino)-pent-2-en-2-ol was synthesized in the condensation reaction of 3-picolylamine and acetylacetone. The compound was characterized by ¹H,¹³C-NMR and IR spectra. The reaction of Schiff base with Fe(III) in the acetone solution and the presence of pyridine led to its hydrolysis and the formation of the octahedral complex [Fe(acac)Cl₂(py)₂]. The structure of the complex was determined by the single crystal X-ray diffraction analysis. The magnetic properties and the molar conductivity of the complex compound were also derived.     

Identification of radical species derived from allergenic 15-hydroperoxyabietic acid and insights into the behaviour of cyclic tertiary allylic hydroperoxides in Fe(II)/Fe(III) systems

To understand the skin sensitization mechanism of 15-hydroperoxyabietic acid, the major allergen in colophony, we first examined the formation of potential reactive radicals derived from its reaction with light, heat and TPP-Fe³⁺. Trapping with 1,1,3,3-tetramethylisoindolin-2-yloxyl nitroxide confirmed the formation of carbon-centred radicals derived from allyloxyl/allylperoxyl radicals as a consequence of the hydroperoxide scission. Particular interest was further given to the reactivity with Fe(II)/Fe(III) due to the biological importance of haem containing enzymes. Using a monocyclic 15-hydroperoxyabietic acid-like compound as a model of allergenic allylic hydroperoxides, we evidenced, by the ESR spin-trapping technique, the competition between carbon and oxygen-centred radicals formed in the presence of Fe(II)/Fe(III) in organic/aqueous media. We complemented the study by showing the possibility of formation, via a radical mechanism induced by ferric chloride, of an adduct between the allylic hydroperoxide and N-acetyl-cysteine ethyl ester. The results gave new knowledge on the possible generation of highly reactive radicals that could lead to the formation of antigenic structures.     

Iron(III) chemistry with ferrocene-1,1'-dicarboxylic acid (fdcH2): an Fe7 cluster with an oxidized fdc(-) ligand

The synthesis and properties are reported of a new Fe(7) cluster obtained from the reaction of ferrocene-1,1'-dicarboxylic acid (fdcH(2)) with FeCl(2)·4H(2)O in MeOH under ambient light conditions. The compound is the mixed-anion salt [Fe(7)O(3)(OMe)(fdc)(6)(MeOH)(3)][FeCl(4)]Cl(2) (1; 8Fe(III)), containing six (fdc(n-)) groups as peripheral ligands. The cation of 1 has virtual C(3) symmetry and contains a central [Fe(4)(μ(3)-O)(3)(μ(3)-OMe)](5+) cubane unit whose three oxide ions each become μ(4) by attaching to a fourth Fe atom outside the cubane. The resulting [Fe(7)(μ(3)-O(3))(μ(3)-OMe)](14+) core is surrounded by six fdc(n-) (n = 1, 2) groups, which divide into two sets by virtual symmetry. The blue color of the complex suggested that some of these ligands are in their oxidized fdc(-) ferricenium (Fe(III)) state, and various data point to there being one fdc(-) ligand in the compound, the initial example of the group acting as a ligand in inorganic chemistry. Variable-temperature, solid-state DC and AC susceptibility measurements reveal the cation to be antiferromagnetically coupled, as expected for high-spin Fe(III), and to have an S = 2 ground state, consistent with an S = (5)/(2) Fe(7) inner core coupled antiferromagnetically to the one paramagnetic fdc(-) (S = (1)/(2)) ligand. Complex 1 displays multiple reductions and oxidations when investigated by electrochemistry in MeCN. (57)Fe Mo?ssbauer spectroscopy supports the presence of only five fdc(2-) ligands, but cannot resolve the signals from the various Fe(III) sites.     

Photoinduced transformation of camptothecin in the presence of iron(III) ions

To obtain the information on the photoactivated action of camptothecin (CPT) promoted by transition metals, CPT was UVA irradiated (λ = 365 nm) in dimethylsulfoxide (DMSO) solutions. Fe(III) ions present were efficiently reduced to Fe(II) under argon and also in the presence of oxygen. The photoinduced electron transfer under argon resulted into the generation of carbon-centered radicals identified by EPR spin trapping evidencing the cleavage of CPT skeleton. Whereas the absorption UV/vis experiments with equimolar ratio Fe(III):CPT excluded the formation of charge-transfer complexes, the fluorescence spectra of CPT in the presence of Fe(III) revealed a significant fluorescence quenching indicating the probability of physical association between Fe(III) and CPT species in DMSO solutions confirming Fe(III) involvement in the photoinduced transformation.     

Application of the H-point standard addition method to the speciation of Fe(II) and Fe(III) with chromogenic mixed reagents

Simultaneous determination of Fe(II) and Fe(III) or selective determination of each oxidation state of iron in the presence of the other one by H-point standard addition method (HPSAM) is described. Mixed reagents of 1,10-phenanthroline and salicylic acid was used as a selective chromogenic system for speciation of Fe(II) and Fe(III). It was shown that with appropriate selection of wavelength pairs, both Fe(II) and Fe(III) can be considered as analyte. The results showed that Fe(II) and Fe(III) can be determined simultaneously with the concentration ratios of Fe(II) to Fe(III) varying from 10:1 to 1:20 in the mixed sample. The accuracy and precision of the method are all satisfactory.     

Identification of the carboxymethyllysine residue in the advanced stage of glycated human serum albumin.

As an advanced stage of glycation, glycated human serum albumin (G-HSA; glucose content, 2 mol of 5-hydroxymethylfurfural equivalent/mol of HSA) was incubated at 37 degrees C up to 30 d in 0.2 M phosphate buffer, pH 7.4, with 100 microM Fe3+. G-HSA incubated for 30 d (G-HSA-30(Fe)) was subsequently hydrolyzed at 110 degrees C for 24 h in 6 N HCl. In the hydrolysate, N epsilon-carboxymethyllysine (CML) was identified by cochromatography with synthesized CML on an amino acid analyzer. pI of HSA (4.8) shifted to 4.5 in G-HSA. A more acidic fraction, pI 4.3, appeared in G-HSA-30(Fe). CML content (mol of CML/mol of HSA) of HSA and G-HSA was as follows; 0 in HSA, 0.2 in HSA-30(Fe), 0.4 in G-HSA and 1.5 in G-HSA-30(Fe) pI 4.3. The amino acid compositions also changed in lysine, arginine and tyrosine at the advanced stage of the reaction.     

Spectrophotometric determination of iron(II) with 1,10-phenanthroline in the presence of large amounts of iron(III)

A study was made to establish proper conditions for the selective determination of Fe(II) by the 1,10-phenanthroline method in the presence of large amounts of Fe(III). It was shown that fe(III) is effectively masked by fluoride. The pH of the solution to be masked should be below 2.5 in order to prevent acceleration by the fluoride of aerial oxidation of Fe(II).     

Reactions of meso-hydroxyhemes with carbon monoxide and reducing agents in search of the elusive species responsible for the g = 2.006 resonance of carbon monoxide-treated heme oxygenase. Isolation of diamagnetic iron(II) complexes of octaethyl-meso-hydroxyporphyrin

To examine possible models for the g = 2.006 resonance seen when the hydroxylated heme-heme oxygenase complex in the Fe(III) state is treated with CO, the reactivities of CO and reducing agents with (py)(2)Fe(III)(OEPO) and [Fe(III)(OEPO)](2) (OEPO is the trianion of octaethyl-meso-hydroxyporphyrin) have been examined. A pyridine solution of (py)(2)Fe(III)(OEPO) reacts in a matter of minutes with zinc amalgam (or with hydrazine) under an atmosphere of dioxygen-free dinitrogen to produce bright-red (py)(2)Fe(II)(OEPOH).2py.0.33H(2)O, which has been isolated in crystalline form. The (1)H NMR spectrum of (py)(2)Fe(II)(OEPOH) in a pyridine-d(5) solution is indicative of the presence of a diamagnetic compound, and no EPR resonance was observed for this compound. Treatment of a solution of (py)(2)Fe(II)(OEPOH) in pyridine-d(5) with carbon monoxide produces spectral changes after a 30 s exposure that are indicative of the formation of diamagnetic (OC)(py)Fe(II)(OEPOH). Treatment of a green pyridine solution of (py)(2)Fe(III)(OEPO) with carbon monoxide reveals a slow color change to deep red over a 16 h period. Although a resonance at g = 2.006 was observed in the EPR spectrum of the sample during the reaction, the isolated product is EPR silent. The spectroscopic features of the final solution are identical to those of a solution formed by treating (py)(2)Fe(II)(OEPOH) with carbon monoxide. Addition of hydrazine to solutions of (OC)(py)Fe(II)(OEPOH) produces red, diamagnetic (OC)(N(2)H(4))Fe(II)(OEPOH).py in crystalline form. The X-ray crystal structures of (py)(2)Fe(II)(OEPOH).2py.0.33H(2)O and (OC)(N(2)H(4))Fe(II)(OEPOH).py have been determined. Solutions of diamagnetic (OC)(N(2)H(4))Fe(II)(OEPOH).py and (OC)(py)Fe(II)(OEPOH) are extremely air sensitive and are immediately converted in a pyridine solution into paramagnetic (py)(2)Fe(III)(OEPO) in the presence of dioxygen.     

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.     

Structures of beta-FeOOH particles formed in the presence of Ti(IV), Cr(III), and Cu(II) ions

beta-FeOOH particles were prepared by aging aqueous FeCl3 solutions containing Ti(IV), Cr(III), and Cu(II) at room temperature for 360 days. The structures of the formed particles were investigated by various techniques including TEM, XRD, XAFS, and adsorption of N2 and H2O. Ti(IV) markedly impeded the crystallization and particle growth of beta-FeOOH by coprecipitation with Fe(III) and disturbing the short-range structure of beta-FeOOH particles. In the presence of a large amount of Ti(IV), it was pronounced that the hydrolysis of Ti(IV) impeded beta-FeOOH formation by reducing the solution pH, whereas Cr(III) and Cu(II), which were hardly involved in the products, gave rise to no noticeable effects on the formation of beta-FeOOH particles. The knowledge obtained in this study can be available for interpretation of the anti-corroding function of Ti alloyed with steels in a Cl- -containing environment.