The Electrochemistry of Tetraphenyl Porphyrin Iron(III) Within Immobilized Droplets Supported on Platinum Electrodes

For the first time, the voltammetry of an ensemble of immobilized benzonitrile microdroplets containing 5,10,15,20‐tetraphenyl‐21H,23H‐porphine iron (III) chloride, TPPFeCl immobilized at platinum electrodes immersed in various aqueous electrolytes has been explored. The reduction of TPPFeCl was observed with the voltammetric response seen to be highly dependent on the nature of ions in the surrounding aqueous phase. Unlike voltammetry in purely homogeneous solution the nature of the aqueous electrolyte can influence the voltammetry in the droplet phase. The electrochemical reduction of TPPFeCl contained within tetrabutylammonium chloride (TBACl) supported benzonitrile (PhCN) microdroplets immersed into an aqueous solution of TBACl was first studied. During TPPFeCl reduction the resulting [TPPFeCl]^? species is stabilized due to the excess of chloride anions inside the oil droplet. Voltammograms of homogeneous solutions of PhCN supported with TBACl show similar chemically reversible process which is also attributed to the stable [TPPFeCl]^? species. This anion stabilization was not observed when the oil droplets were supported with tetrabutylammonium perchlorate (TBAP) or when the PhCN solution bathing the microdroplet ensemble was supported with TBAP resulting in a chemically irreversible process. The voltammetry of unsupported droplets immobilized on a platinum electrode immersed in different aqueous electrolytes was also explored and the fate of the [TPPFeCl]^? species formed considered during the reduction sweep. Similarities and difference to voltammetry in purely homogeneous media are noted and the use of droplet voltammetry provides complimentary information.     

Preparation and Properties of Nickel and Iron Oxides obtained by Calcination of Layered Double Hydroxides

A constant pH precipitation method has been applied to obtain solids with Ni/Fe molar ratios of 2/1, 3/2, 1/1, 2/3, and 1/2. In all cases, a phase with the hydrotalcite‐like structure is obtained, containing Ni^II and Fe^III in the brucite‐like layers and carbonate in the interlayer, and, for samples with a Ni/Fe molar ratio lower than 2/1, amorphous hydrated iron oxides, undetected by X‐ray diffraction, are also formed. The solids have been characterized by element chemical analysis, powder X‐ray diffraction, differential thermal analysis, thermogravimetric and differential thermogravimetric analysis, FT‐IR spectroscopy, temperature‐programmed reduction and assessment of specific surface area by nitrogen adsorption at ?196 °C. In all cases reduction leads to zero‐valent state for the metals, reduced nickel particles probably favouring reduction of Fe^III species; the specific surface area increases with the iron content, probably due to the amorphous nature of the hydrated iron oxides formed. Calcination at 1200 °C in air leads to well crystallized solids, formed by NiFe₂O₄ spinel and, additionally, rocksalt‐type NiO for Ni/Fe ratios larger than 1/2. In this way, solids with tailored compositions of these two phases can be prepared.     

Kinetic-catalytic determination of traces of iron by the oxidative coupling reaction of 3-methyl-2-benzothiazolinone hydrazone with N,N-dimethylaniline

A new kinetic-catalytic method by the initial rate procedure for the determination of nanogram level of iron(III) is developed, which is based on its catalytic effect on the oxidative coupling of 3-methyl-2-benzothiazolinone hydrazone (MBTH) with N,N-dimethylaniline (DMA) to form an indamine dye (λ_max=590 nm) in the presence of hydrogen peroxide. Iron(II) is also determined, being oxidized to iron(III) by hydrogen peroxide. Calibration graphs obtained by the initial rate method are linear in the range 1–1000 ng ml⁻¹ Fe and as low as 10⁻⁸ M Fe(II, III) can easily be determined. The relative standard deviations are 6.6, 2.5 and 1.5% for ten determinations of 1, 20 and 60 ng ml⁻¹ of Fe(III), respectively. The method is applicable to the determination of iron in natural waters without preconcentration and separation.     

Interaction between peroxide ion and phenol group which are coordinated to the same iron(III) ion

We have prepared several new iron(III) complexes with ligands which contain a phenol group; these are tetradentate [(X-phpy)H, X and H(phpy) represent the substituents on the phenol ring and N,N-bis(2-pyridylmethyl)-N-(2-hydroxybenzyl)amine, respectively] and pentadentate ligands [(R-enph-X)H; R=ethyl(Et) or methyl(Me) derivative and H(Me-enph) denotes N,N-bis(2-pyridylmethyl)-N″-methyl-N″-(2″-hydroxyl-benzylamine)ethylenediamine] and have determined the crystal structures of Fe(phpy)Cl₂, Fe(5-NO₂-phpy)Cl₂, and Fe(Me-enph)ClPF₆, which are of a mononuclear six-coordinate iron(III) complex with coordination of one or two chloride ion(s). These compounds are highly colored (dark violet) due to the coordination of phenol group to an iron(III) atom. When hydrogen peroxide was added to the solution of the iron(III) complex, a color change occurs with bleaching of the violet color, indicating that oxidative degradation of the phenol moiety occurred in the ligand system. The bleaching of the violet color was also observed by the addition of t-butylhydroperoxide. The rate of the disappearance of the violet color is highly dependent on the substituent on the phenol ring; introduction of an electron-withdrawing group in the phenol ring decreases the rate of bleaching, suggesting that disappearance of the violet band should be due to a chemical reaction between the phenol group and a peroxide adduct of the iron(III) species with an η¹-coordination mode and that in this reaction the peroxide adduct acts as an electrophile towards phenol ring. The intramolecular interaction between the phenol moiety and an iron(III)-peroxide adduct may induce activation of the peroxide ion, and this was supported by several facts that the solution containing an iron(III) complex and hydrogen peroxide exhibits high activities for degradation of nucleosides and albumin.     

Voltammetry of Dissolved Iron(III)–Nitrilotriacetate–Hydroxide System in Water Solution

The investigation of the dissolved iron(III)–nitrilotriacetate–hydroxide system in the water solution (I=0.1 mol L^?1 in NaClO₄; pH 8.0±0.1) using differential pulse cathodic voltammetry, cyclic voltammetry, and sampled direct current (DC) polarography, was carried out on a static mercury drop electrode (SMDE). The dissolved iron(III) ion concentrations varied from 2.68×10^?6 to 6×10^?4 mol L^?1 and nitrilotriacetate concentrations were 1×10^?4 and 5×10^?4 mol L^?1. By deconvoluting of the overlapped reduction voltammetric peaks using Fourier transformation, four relatively stable, dissolved iron(III) complex species were characterized, as follows: [Fe(NTA)₂]^3?, mixed ligand complexes [FeOHNTA]^? and [Fe(OH)₂NTA]^2?, showing a one‐electron quasireversible reduction, and binuclear diiron(III) complex [NTAFeOFeNTA]^2?, detected above 4×10^?4 mol L^?1 of the added iron(III) ions, showing a one‐electron irreversible reduction character. The calculations with the constants from the literature were done and compared with the potential shifts of the voltammetric peaks. Fitting was obtained by changing the following literature constants: log β₂([Fe(NTA)₂]^3?) from 24 to 27.2, log β₁([FeNTA]^?) from 8.9 to 9.2, log β₂([Fe(NTA)₂]^4?) from 11.89 to 15.7 and log β₂([Fe(OH)₂NTA]^3?) from 15.63 to 19. The determination of the electrochemical parameters of the mixed ligand complex [FeOHNTA]^?, such as: transfer coefficient (α), rate constant (k_s) and formal potential (E°') was done using a sampled DC polarography, and found to be 0.46±0.05, 1.0±0.3×10^?3 cm s^?1, and ?0.154±0.010 V, respectively. Although known previously in the literature, these four species have now for the first time been recorded simultaneously, i.e. proved to exist simultaneously under the given conditions.     

Potentiometric and antimicrobial studies on the asymmetric Schiff bases and their binuclear Ni(II) and Fe(III) complexes; synthesis and characterization of the complexes

The protonation constants of two nitro-Schiff bases SB¹, SB² and three asymmetric tetradentate diimines H₂L¹, H₂L² and H₂L³ and the stability constants of their ML type binuclear Ni(II) and Fe(III) complexes have been determined potentiometrically. The asymmetric diimines are (2OH) RCHNC₆H₄CHNR′ (2OH) type compounds [where R = R′ = phenyl for H₂L¹; R = naphthyl, R′ = phenyl for H₂L² and R = R′ = naphthyl for H₂L³]. The effect of tautomeric forms on the acid-base properties of the diimines has been investigated and discussed. In addition, dimeric and binuclear Ni(II) and Fe(III) complexes of the diimines have been synthesized and characterized by physical and spectroscopic techniques. Also, in vitro antimicrobial activities of the diimines and the complexes have been evaluated against three bacteria: Micrococcus luteus (NRLL B-4375), Bacillus cereus (RSKK 863), Escherichia coli (ATCC 11230) and the fungus: Candida albicans (ATCC 10239).     

Preparation of trout liver microsomes for iron speciation in P-450 enzymes by AE–FPLC with ICP–(ORS)MS detection

Cytochromes P-450 are members of a superfamily of hemoproteins involved in the oxidative metabolism of various physiological and xenobiotic compounds in eukaryotes and prokaryotes. The multiplicity of this group of enzymes has been widely studied by chromatographic techniques, mainly high-performance liquid chromatography (HPLC). Because these enzymes are membrane-bound proteins, sample preparation for chromatographic separation of P-450 enzymes requires a solubilization step. The sample-preparation procedures are critical, because detergents affect not only the efficiency of protein solubilization but also their further chromatographic resolution. Trout liver microsomes have been taken here as a model sample to investigate iron speciation in cytochrome P-450. Trouts were treated intraperitoneally with -naphthoflavone, a potent inducer of some P-450 enzymes, and a microsomal suspension containing 7.4±0.1 nmol mL^–1 P-450 enzymes was obtained by ultracentrifugation. Lubrol PX was selected as detergent for solubilization, resulting in about 90% solubilization recovery. The solubilized cytochromes P-450 were further separated by AE–FPLC, with UV detection, or coupled to ICP–MS with an octapole reaction system, ICP–(ORS)MS (monitoring Fe signals at masses 54, 56, and 57). A sampling procedure and chromatographic conditions are developed and were successfully applied to iron speciation in trout liver P-450 enzymes. ICP–(ORS)MS detection of P-450 enzymes is Fe-specific and so will give accurate information on the prosthetic group of the protein, which can constitute an advantageous alternative to classical methods for detection of these hemoproteins.     

痕量铁的光化学伏安分析法及其应用研究

在稀硫酸介质中及活化剂草酸存在下，痕量铁（Ⅲ）对结晶紫光化学褪色反应有强烈催化作用，结晶紫的光化学反应产物于－０．７０产生一灵敏的２．５次微分级谱波。     

Heteronuclear Nickel‐Iron Complexes and the Crystal Structure of [Fe2(CO)6(μ3‐S)2{Ni(dppe)}]

A series of heteronuclear nickel‐iron complexes [Fe₂(CO)₆(μ‐SH)(μ₃‐S){NiCl(PPh₃)₂}] ( 1 ), [Fe₂(CO)₆(μ‐SH)(μ₃‐S){NiCl(dppe)}] ( 2 ), [Fe₂(CO)₆(μ₃‐S)₂{Ni(PPh₃)₂}] ( 3 ), [Fe₂(CO)₆(μ₃‐S)₂{Ni(dppe)}] ( 4 ) and [Fe₂(CO)₆(μ‐SPh)(μ₃‐S){NiCl(dppe)}] ( 5 ) have been prepared. The structure of 4 has been determined by X‐ray crystallography. The central metal‐sulfur core of 4 has a trigonal bipyramidal shape with a NiFe₂ base plane with two axial sulfur atoms. Each iron atom is 5‐coordinate forming a distorted square pyramid; the nickel is square planar coordinated by two sulfur atoms and two phosphorus atoms.     

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.