Finding the 3D structure of a molecule in its IR spectrum

 The labile iron(II) and iron(III) species are complexed directly in the sample solution with 1,10 phenanthroline and ferron (8-hydroxy-7-iodoquinoline-5-sulfonic acid), respectively. The complexes thus formed are mutually adsorbed and separated by solid phase extraction. The direct determination of iron(III) and iron(II) species with flame atomic absorption spectrometry (FAAS) follows the elution of the iron(III)-ferron complex adsorbed by an anion-exchange and an iron(II)-phenanthroline complex adsorbed by a non-polar RP-18 phase. In the case of indirect determination, the iron(II)-phenanthroline complex that passes through the anion-exchange phase, is measured, and the content of iron(III) is calculated by the difference of the iron(II) and the total iron content. A direct determination with this method has been applied to the iron species analysis in wine samples and the results are compared with those obtained for the determination with adsorptive stripping voltammetry (ASV) as reference method. Received: 17 August 1995/Revised: 12 February 1996/Accepted: 14 February 1996     

Hexacyanoferrate(III) as a mediator in the determination of total iron in potable waters as iron(II)-1,10-phenanthroline at a single-use screen-printed carbon sensor device

Hexacyanoferrate(III) was used as a mediator in the determination of total iron, as iron(II)-1,10-phenanthroline, at a screen-printed carbon sensor device. Pre-reduction of iron(III) at −0.2 V versus Ag/AgCl (1 M KCl) in the presence of hexacyanoferrate(II) and 1,10-phenanthroline (pH 3.5-4.5), to iron(II)-1,10-phenanthroline, was complete at the unmodified carbon electrode surface. Total iron was then determined voltammetrically by oxidation of the iron(II)-1,10-phenanthroline at +0.82 V, with a detection limit of 10 μg l⁻¹.In potable waters, iron is present in hydrolysed form, and it was found necessary to change the pH to 2.5-2.7 in order to reduce the iron(III) within 30 s. A voltammetric response was not found at lower pH values owing to the non-formation of the iron(II)-1,10-phenanthroline complex below pH 2.5.Attempts to incorporate all the relevant reagents (1,10-phenanthroline, potassium hexacyanoferrate(III), potassium hydrogen sulphate, sodium acetate, and potassium chloride) into a modifying coated PVA film were partially successful. The coated electrode behaved very satisfactorily with freshly-prepared iron(II) and iron(III) solutions but with hydrolysed iron, the iron(III) signal was only 85% that of iron(II).     

Regioselectivity of aliphatic versus aromatic hydroxylation by a nonheme iron(II)-superoxo complex

Many enzymes in nature utilize molecular oxygen on an iron center for the catalysis of substrate hydroxylation. In recent years, great progress has been made in understanding the function and properties of iron(IV)-oxo complexes; however, little is known about the reactivity of iron(II)-superoxo intermediates in substrate activation. It has been proposed recently that iron(II)-superoxo intermediates take part as hydrogen abstraction species in the catalytic cycles of nonheme iron enzymes. To gain insight into oxygen atom transfer reactions by the nonheme iron(II)-superoxo species, we performed a density functional theory study on the aliphatic and aromatic hydroxylation reactions using a biomimetic model complex. The calculations show that nonheme iron(II)-superoxo complexes can be considered as effective oxidants in hydrogen atom abstraction reactions, for which we find a low barrier of 14.7 kcal mol(-1) on the sextet spin state surface. On the other hand, electrophilic reactions, such as aromatic hydroxylation, encounter much higher (>20 kcal mol(-1)) barrier heights and therefore are unlikely to proceed. A thermodynamic analysis puts our barrier heights into a larger context of previous studies using nonheme iron(IV)-oxo oxidants and predicts the activity of enzymatic iron(II)-superoxo intermediates.     

Successive determination of copper and iron by a flow injection-catalytic photometric method using a serial flow cell.

A flow injection-catalytic spectrophotometric method using a serial flow cell was proposed for the successive determination of trace amounts of copper and iron. This method is based on the oxidation coupling of p-anisidine with N,N-dimethylaniline in the presence of hydrogen peroxide to form a dye, which has an absorption maximum at 740 nm. In this indicator reaction, ligands such as 1,10-phenanthroline (phen) and diphosphate were achieved to improve the sensitivity and selectivity. Under the optimal experimental conditions, the determinable ranges were 0.05-5 ppb for copper and 0.5 - 100 ppb for iron, respectively. The RSDs (n = 10) were 0.78% for 0.5 ppb copper(II) and 0.5% for 200 ppb iron(III). The sample throughput was 30 h(-1). The present flow-injection method was applied to the determination of copper and iron in standard river water, tap water, and other natural water samples, and also to the analysis of labile and inert complexes in synthesized samples containing humic acid with copper(II) or iron(III).     

Reactivities of mononuclear non-heme iron intermediates including evidence that iron(III)-hydroperoxo species is a sluggish oxidant

There is an intriguing, current controversy on the involvement of iron(III)-hydroperoxo species as a "second electrophilic oxidant" in oxygenation reactions by heme and non-heme iron enzymes and their model compounds. In the present work, we have performed reactivity studies of the iron-hydroperoxo species in nucleophilic and electrophilic reactions, with in situ-generated mononuclear non-heme iron(III)-hydroperoxo complexes that have been well characterized with various spectroscopic techniques. The intermediates did not show any reactivities in the nucleophilic (e.g., aldehyde deformylation) and electrophilic (e.g., oxidation of sulfide and olefin) reactions. These results demonstrate that non-heme iron(III)-hydroperoxo species are sluggish oxidants and that the oxidizing power of the intermediates cannot compete with that of high-valent iron(IV)-oxo complexes. We have also reported reactivities of mononuclear non-heme iron(III)-peroxo and iron(IV)-oxo complexes in the aldehyde deformylation and the oxidation of sulfides, respectively.     

Determination of horseradish peroxidase and a peroxidase-like iron porphyrin at a Nafion-modified electrode.

A catalytic coupling reaction between 4-amino antipyrine and a N,N-disubstituted aniline derivative has been exploited in the indirect electrochemical detection of horseradish peroxidase (HRP) and of a biomimetic catalyst, the iron(III) sulfonated tetraphenyl porphyrin. In the presence of hydrogen peroxide and one of the two catalysts a cationic electroactive quinone-iminium dye P+ was formed and detected by linear scan voltammetry using a screen-printed electrode coated with a Nafion film. Detection limits of 10(-12) M for HRP and 4 x 10(-10) M for the iron porphyrin have been achieved. In conclusion the iron porphyrin is considered to be a promising alternative to the HRP label in enzyme immunoassays with electrochemical detection.     

Encapsulation of a guest sodium cation by iron(III) tris-(hydroxamate)s

An unprecedented encapsulation of an exogenous sodium ion by iron(III) tris(hydroxamate)s was observed upon crystallization of an iron(III) complex with isonicotinylhydroxamic acid. The sodium cation is bound by bridging coordination of the amide oxygen atoms from two mononuclear iron(III) fac-tris(hydroxamate)s.     

Arylation of a carbanion derived from a pyridazine; a route to a functionalized aren

1,4-Dichlorobenzene(cyclopentadienyl)iron(II) hexafluorophosphate reacts with the carbanion derived from 3-ethoxy-6-methylpyridazine N-oxide to give a Yanovsky-type adduct.     

Characterization of a Thiolato Iron(III) Peroxy Dianion Complex

Nucleophilic oxidant: The reaction between a thiolato iron(II) complex 1 and superoxide in aprotic solvent at -90?°C yields a novel thiolato iron(III) peroxide intermediate 2, which exhibits unusually high nucleophilic reactivity. Compound 2 is an isomer of the thiolato iron(II) superoxide intermediate that is invoked in the reaction between superoxide reductase and superoxide.     

A study of corrosion on a rotating iron disk electrode

Corrosion of iron in slightly acidified sodium sulphate solutions (mainly pH 4.5) in the open air was studied with a rotating disk electrode method at room temperature.Microscopic observations of corroded iron disk surfaces in the pH 4.5 solution revealed that iron initially corrodes locally with the formation of round pits of 10–30 μm in diameter and of(0.6–1.3) × 10³ in number per apparent square centimetre followed by the U-shaped brown protective wall formation of precipitates (rust) outside the pits. Each protective wall is formed along the lines of flow of the solution adjacent to the iron surface and each pit is located near the upstream end of the wall. Steady state of corrosion sets in when the parts of surface area surrounded by the wall are completely covered with a microscopically non-porous rust film.The amount of iron in the rust film and the total amount of corrosion of iron including that in the film increase parabolically with the increase in the time of immersion. The amount of iron in the film increases in proportion to the total amount of corrosion independently of the speed of rotation of the disk electrode even in the steady state.The fraction of area of iron surface not covered with the film decreases with time and reaches a certain fixed value in the steady state: the value is smaller at higher rotational speed. The corrosion rate is proportional to the uncovered area, as the corrosion is near the steady state. The pH of the bulk solution increases as corrosion progresses.The corrosion rate of iron can be well interpreted by assuming that the rate is controlled by the diffusion of oxygen from the bulk solution to the surface of iron and that the rust film on iron impedes the diffusion of oxygen.     

Silylation of iron-bound carbon monoxide affords a terminal Fe carbyne

A series of monocarbonyl iron complexes in the formal oxidation states 0, +1, and +2 are accessible when supported by a tetradentate tris(phosphino)silyl ligand (SiP(iPr)(3) = [Si(o-C(6)H(4)PiPr(2))(3)](-)). X-ray diffraction (XRD) studies of these carbonyl complexes establish little geometrical change about the iron center as a function of oxidation state. It is possible to functionalize the terminal CO ligand of the most reduced carbonyl adduct by addition of SiMe(3)(+) to afford a well-defined iron carbyne species, (SiP(iPr)(3))Fe≡C-OSiMe(3). Single-crystal XRD data of this iron carbyne derivative reveal an unusually short Fe≡C-OSiMe(3) bond distance (1.671(2) ?) and a substantially elongated C-O distance (1.278(3) ?), consistent with Fe-C carbyne character. The overall trigonal bipyramidal geometry of (SiP(iPr)(3))Fe≡C-OSiMe(3) compares well with that of the corresponding carbonyls, (SiP(iPr)(3))Fe(CO)(-), (SiP(iPr)(3))Fe(CO), and (SiP(iPr)(3))Fe(CO)(+). Details regarding the electronic structure of the carbyne complex have been explored via the collection of comparative M?ssbauer data for all of the complexes featured and also via DFT calculations. In sum, these data point to a strongly π-accepting Fischer-type carbyne ligand that confers stability to a low-valent iron(0) rather than high-valent iron(IV) center.     

Sorption-spectrophotometric determination of iron(II, III) with the use of organic reagents immobilized in a polymethacrylate matrix

The interaction of iron(II) with 2,2′-dipyridyl and 1,10-phenanthroline immobilized in a polymethacrylate matrix was studied. The optimum conditions of the complexation of iron(II) with the immobilized reagents and the chemical analytical properties of the complexes in the polymethacrylate matrix were determined. A sorption-spectrophotometric procedure was developed for the determination of iron(II) and the total of iron(II, III) after the reduction of iron(III) by ascorbic acid. The procedure with 2,2′-dipyridyl was used for the analysis of samples of tap, well, and mineral water and a solution of glucose.     

Iron(Ⅱ) hydrides bearing a tetradentate PSNP ligand

Iron(II) hydrides bearing PSNP tetradentate ligand were synthesized and well characterized. The hydrido iron complex [2H(NCMe)](BF₄) is an extremely efficient catalyst for the hydroboration of aldehydes at room temperature.     

Coprecipitation with lanthanum phosphate as a technique for separation and preconcentration of iron(III) and lead

The usefulness of coprecipitation with lanthanum phosphate for separation and preconcentration of some heavy metals has been investigated. Although lanthanum phosphate coprecipitates iron(III) and lead quantitatively at pH 2.3, iron(II) can barely be collected at this pH. This coprecipitation technique was applicable to the separation and preconcentration of iron(III) before inductively coupled plasma atomic-emission spectrometric (ICP-AES) determination; the recoveries of iron(III) and iron(II) from spiked water samples were 103-105% and 0.2-0.7%, respectively. The coprecipitation was also useful for separation of 20 microg lead from 100 mL of an aqueous solution that also contained 1-100 mg iron. Coprecipitation of iron was substantially suppressed by addition of ascorbic acid, which enabled recovery of 97-103% of lead added to the solution, bringing the recovery to within 1.6-5.0% of the relative standard deviations. Lanthanum phosphate can also coprecipitate cadmium and indium quantitatively, although chromium(III), cobalt, and nickel and large amounts of sodium, potassium, magnesium, and calcium are barely coprecipitated at pH approximately/= 3.     

Stable isotope labels as a tool to determine the iron absorption by Peruvian school children from a breakfast meal

Fractional iron absorption from a breakfast meal was determined in Peruvian children employing stable iron isotopes as labels. Iron isotopic analysis was performed by the recently developed negative thermal ionization technique for high-precision iron isotope ratio measurements using FeF₄ ^– ions. By increasing the ascorbic acid content of the standard breakfast meal as served within the Peruvian school-breakfast program from 27 mg to 70 mg, it was possible to increase the geometric mean fractional iron absorption significantly from 5.1% (range 1.6–13.5%) to 8.2% (range 3.1–25.8%). Fractional iron absorption was calculated according to isotope dilution principles and by considering the non-monoisotopic character of the used spikes.     

Proton control of oxidation and spin state in a series of iron tripodal imidazole complexes

Reaction of iron salts with three tripodal imidazole ligands, H(3)(1), H(3)(2), H(3)(3), formed from the condensation of tris(2-aminoethyl)amine (tren) with 3 equiv of an imidazole carboxaldehyde yielded eight new cationic iron(III) and iron(II), [FeH(3)L](3+or2+), and neutral iron(III), FeL, complexes. All complexes were characterized by EA(CHN), IR, UV, M?ssbauer, mass spectral techniques and cyclic voltammetry. Structures of three of the complexes, Fe(2).3H(2)O (C(18)H(27)FeN(10)O(3), a = b = c = 20.2707(5), cubic, I3d, Z = 16), Fe(3).4.5H(2)O (C(18)H(30)FeN(10)O(4.5), a = 20.9986(10), b = 11.7098(5), c = 19.9405(9), beta = 109.141(1), monoclinic, P2(1)/c), Z = 8), and [FeH(3)(3)](ClO(4))(2).H(2)O (C(18)H(26)Cl(2)FeN(10)O(9), a = 9.4848(4), b = 23.2354(9), c = 12.2048(5), beta = 111.147(1) degrees, monoclinic, P2(1)/n, Z = 4) were determined at 100 K. The structures are similar to one another and feature an octahedral iron with facial coordination of imidazoles and imine nitrogen atoms. The iron(III) complexes of the deprotonated ligands, Fe(1), Fe(2), and Fe(3), are low-spin while the protonated iron(III) cationic complexes, [FeH(3)(1)](ClO(4))(3) and [FeH(3)(2)](ClO(4))(3), are high-spin and spin-crossover, respectively. The iron(II) cationic complexes, [FeH(3)(1)]S(4)O(6), [FeH(3)(2)](ClO(4))(2), [FeH(3)(3)](ClO(4))(2), and [FeH(3)(3)][B(C(6)H(5))(4)](2) exhibit spin-crossover behavior. Cyclic voltammetric measurements on the series of complexes show that complete deprotonation of the ligands produces a negative shift in the Fe(III)/Fe(II) reduction potential of 981 mV on average. Deprotonation in air of either cationic iron(II) or iron(III) complexes, [FeH(3)L](3+or2+), yields the neutral iron(III) complex, FeL. The process is reversible for Fe(3), where protonation of Fe(3) yields [FeH(3)(3)](2+).     

Response of the Iron Chalcogenide Glass Membrane Ion‐Selective Electrode in a Seawater Ligand Mimetic Calibration Buffer

As a continuation of recent mechanistic studies into the influence of seawater ligands on the surface chemistry of the iron chalcogenide glass membrane ion‐selective electrode (ISE), the present study has investigated the response of the iron(III) ISE in a seawater ligand mimetic system to examine its suitability as a calibration medium for the electroanalysis of raw or natural seawater. Significantly, dip method calibrations of the ISE in a mixture of salicylate, ethylene diamine tetraacetic acid (EDTA), ethylene diamine and minor amounts of dissolved iron(III) and copper(II) yielded the expected Nernstian response of 30 mV/decade according to the known ion‐exchange/electron transfer response mechanism of this ISE. Furthermore, ideal Nernstian response of the electrode is also obtained in a continuous flow analysis (CFA) mode, noting that this provides scope for using a hydrodynamic flow regime to minimize the electrode release of iron and the concomitant detection limit of the ISE. Ultimately, repetitive CFA analyses of free iron(III) in raw or natural seawater yielded a free iron(III) level commensurate with the expected inorganic and organic speciation of iron(III) in seawater.     

Dissolved iron analysis in estuarine and coastal waters by using a modified adsorptive stripping chronopotentiometric (SCP) method

An electrochemical method based on adsorptive stripping chronopotentiometry (SCP) with a rotating mercury film electrode has been developed for the determination of dissolved iron (III) at subnanomolar concentrations in estuarine and coastal waters. The detection limit was 0.11 nM after adsorption time of 60 s. Compared to the other chronopotentiometric methods available for dissolved iron measurement in natural and estuarine waters, the procedure described here exhibits a 15-fold better sensitivity. Therefore, it allows one to accurately quantify concentrations commonly found in estuarine and coastal waters. Moreover, by using the speciation scheme proposed by Aldrich and van den Berg (Electroanalysis 10 (1998) 369), several forms could be measured, i.e. reactive iron (Fe R) and reactive iron (III) (Fe^III R), or estimated, i.e. complexed iron (Fe C) and reactive iron (II) (Fe^II R). The method described here is reliable, fast, inexpensive and compact. It was applied successfully to the study of the chemical speciation of dissolved iron along the salinity gradient of the Aulne estuary (Brittany-France).     

Iron Extraction with Di(2-Ethylhexyl)dithiophosphoric Acid and a Binary Extractant Based on It

Iron(III) extraction with trioctylmethylammonium di(2-ethylhexyl)dithiophosphate and di(2- ethylhexyl)dithiophosphoric acid was studied. It was shown that di(2-ethylhexyl)dithiophosphoric acid extracts iron in the form of the complex FeA₂, regardless of the oxidation state of iron in the initial aqueous solution. It was also shown that the iron(III) extraction with trioctylmethylammonium di(2-ethylhexyl)dithiophosphate over a wide acidity range occurs primarily to produce extractable substance (R₄N)FeCl₄; and at pH > 1, iron(II) dialkyldithiophosphate is also extracted into the organic phase. It was established that, in a system with a binary extractant, iron can be efficiently stripped from the organic phase with water or diluted solutions of mineral acids.