An ultrasensitive iron(III)-complex based hydrogen peroxide electrochemical sensor based on a nonelectrocatalytic mechanism

In this communication, the first nonelectrocatalysis-type hydrogen peroxide electrochemical sensor is reported. The electroactive iron(III) diethylenetriaminepentaacetic acid (DTPA-Fe^III) complex is immobilized on the cysteamine (cys) modified nanoporous gold (NPG) films by covalent method. The immobilized DTPA-Fe^III complex quickly communicates an electron with the electrode. Upon addition of hydrogen peroxide, however, hydrogen peroxide inhibits the direct electron transfer of the DTPA-Fe^III complex due to the generation of nonelectroactive DTPA-Fe^III–H₂O₂ complex. Based on quenching mechanism, the first hydrogen peroxide electrochemical sensor based on a nonelectrocatalytic mechanism is developed. The novel hydrogen peroxide electrochemical sensor has the ultralow detection limit (1.0 × 10^–14 M) and wide linear range (1.0 × 10^–13 to 1.0 × 10^–8 M) with excellent reproducibility and stability.     

Simultaneous determination of tryptophan, uric acid and ascorbic acid at iron(III) doped zeolite modified carbon paste electrode

A new chemically modified electrode is constructed based on iron(III) doped zeolite modified carbon paste electrode (Fe(3+)Y/ZCME). The electrode was evaluated as a sensor for sub-micromolar determination of tryptophan (Trp), uric acid (UA) and ascorbic acid (AA) in aqueous solutions. The measurements were carried out by application of the differential pulse voltammetry (DPV) method in phosphate buffer solution with pH 3.5. Iron(III) loaded in zeolite can increase anodic peak currents by adsorption of Trp, UA and AA on electrode surface The analytical performance was evaluated with respect to the carbon paste composition, pH of solution, accumulation time and accumulation potential. The prepared electrode shows voltammetric responses with high sensitivity and selectivity for Trp, UA and AA in optimal conditions, which makes it very suitable for simultaneous determination of these compounds. The linear calibration range for AA in the presence of 50muM UA and 50muM Trp was 0.6muM to 100muM, with a correlation coefficient of 0.9992, and a detection limit of 0.21muM (S/N=3). A linear relationship was found for UA in the range of 0.3-700muM containing 10muM AA and 50muM Trp, with a correlation coefficient of 0.9990 and a detection limit of 0.08muM. The linear calibration range for Trp in the presence of 10muM AA and 50muM UA was 0.2-150muM, with a correlation coefficient of 0.9996, and a detection limit of 0.06muM. The proposed method was successfully applied for determination Trp, UA and AA in biological systems and pharmaceutical samples.     

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.     

Reverse flow injection spectrophotometric determination of iron(III) using norfloxacin

A reversed flow injection colorimetric procedure for determining iron(III) at the μg level was proposed. It is based on the reaction between iron(III) with norfloxacin (NRF) in 0.07 mol l⁻¹ ammonium sulfate solution, resulting in an intense yellow complex with a suitable absorption at 435 nm. Optimum conditions for determining iron(III) were investigated by univariate method. The method involved injection of a 150 μl of 0.04% w/v colorimetric reagent solution into a merged streams of sample and/or standard solution containing iron(III) and 0.07 mol l⁻¹ ammonium sulfate in sulfuric acid (pH 3.5) solution which was then passed through a single bead string reactor. Subsequently the absorbance as peak height was monitored at 435 nm. Beer's law obeyed over the range of 0.2–1.4 μg ml⁻¹ iron(III). The method has been applied to the determination of total iron in water samples digested with HNO₃–H₂O₂ (1:9 v/v). Detection limit (3σ) was 0.01 μg ml⁻¹ the sample through of 86 h⁻¹ and the coefficient of variation of 1.77% (n=12) for 1 μg ml⁻¹ Fe(III) were achieved with the recovery of the spiked Fe(III) of 92.6–99.8%.     

Resonance Raman spectra of tris(acetylacetonato)iron(III) and ruthenium(III) complexes and their solvent effect

The resonance Raman spectra of tris(acetylacetonatoiron(III)) and ruthenium(III) complexes in various solvents and in water-acetonitrile (W-AN) mixtures were measured. The resonance Raman spectra of both complexes indicated peaks near 460 and around 1580 cm^–1. Thev(C-O) peak (around 1580 cm^–1) is shifted to low frequency with an increase in the dielectric constant _T of the solvents, whereas thev(M-O) (M=Fe and Ru, near 460 cm^–1) are constant, independent of _T. It implies that the C-O bond in the acac^– ligand is lengthened by the polarizability effect of the solvents, while both the Fe-O and Ru-O bonds, which are located in the inside of the complexes, are not influenced by the solvents indicating that the interaction does not depend on the properties of individual solvent molecules but on those of the aggregate.     

Speciation of iron (II) and (III) by using solvent extraction and flame atomic absorption spectrometry

A method for speciation, preconcentration and separation of Fe²⁺ and Fe³⁺ in different matrices was developed using solvent extraction and flame atomic absorption spectrometry. PAN as complexing reagent for Fe²⁺ and chloroform as organic solvent were used. The complex of Fe²⁺-PAN was extracted into chloroform phase in the pH range of 0.75-4.0 and Fe³⁺ remains in water phase in the pH range 0.75-1.25. The optimum conditions for maximum recovery of Fe²⁺ and minimum recovery of Fe³⁺ were determined as pH = 1, the stirring time of 20 min, the PAN amount of 0.5 mg and chloroform volume of 8 mL. The developed method was applied to the determination of Fe²⁺ and Fe³⁺ in tea infusion, fruit juice, cola and pekmez. It is seen that there is high bioavailable iron (Fe²⁺) in pekmez. The developed method is sensitive, simple and need the shorter time in comparison with other similar studies.     

The sorption mechanism of Au(III) on sulfur-containing chelating resin poly[4-vinylbenzyl (2-hydroxyethyl) sulfide]

The sorption mechanism of sulfur-containing chelating resin, poly[4-vinylbenzyl (2-hydroxyethyl) sulfide], towards Au(III) was investigated by Fourier transform infrared spectra (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy dispersive X-ray microanalysis (EDX), and X-ray diffraction (XRD). It was showed that the sulfide bond in the resin was oxidized into sulfoxide and sulfone bond, and Au(III) was deoxidized into Au(0).     

Synthesis and characterization of high-spin iron(III)-sulpha drug complexes and their biological activity

Summary The iron(III) complexes with sulphathiazole, sulphamethoxazole, sulphadiazine, sulphapyridine and sulphadimidine having the stoichiometric ratio 1:2 (metal:ligand) were prepared and characterized on the basis of elemental analysis, conductivity measurements and electronic absorption spectra. The infrared spectra of the complexes revealed that the terminal amino group of the sulpha molecules is not involved in coordination. Similarities in the position of iron-nitrogen and iron-oxygen stretching modes indicate identical configuration of the complexes prepared. Conductivity measurements showed that they are nonelectrolytes. X-ray powder diffraction patterns showed that two of them are crystalline and others are amorphous. Electron spin resonance and iron-57 Mössbauer measurements indicated that the complexes contain high-spin Fe³⁺ species. Thermogravimetric analyses showed that all complexes contain coordinated water which is lost at 141–160°C. All the complexes proved to possess higher bacteriostatic activity than the corresponding ligand.

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Synthese und Charakterisierung von High-Spin Eisen(III)-Sulfapräparate-Komplexen und ihre biologische Aktivität

Zusammenfassung Es wurden die (Metall:Ligand) 1:2 Eisen(III)-Komplexe von Sulfathiazol, Sulfamethoxazol, Sulfapyridin und Sulfadimidin hergestellt und mittels Elementaranalyse, Leitfähigkeitsmessungen und Elektronenabsorptionsspektroskopie charakterisiert. Die IR-Spektren der Komplexe zeigten, daß die Amino-Gruppen der Sulfa-Moleküle nicht an der Koordination beteiligt sind. Ähnlichkeiten im Bereich der Eisen-Stickstoff- und Eisen-Sauerstoff-Streckschwingungen zeigten idente Konfiguration der Komplexe an. Leitfähigkeitsmessungen beweisen den Nichtelektrolytcharakter. Röntgen-Pulverdiagramme zeigten, daß zwei der Komplexe kristallin, die anderen hingegen amorph waren. High-Spin Eisen(III)-Spezies wurden mittels Elektrononspinresonanz und Eisen-57-Mössbauer-Messungen nachgewiesen. Die thermogravimetrische Analyse zeigte, daß alle Komplexe koordiniertes Wasser enthielten, das zwischen 141 und 160°C verloren wurde. Alle Komplexe zeigten eine höhere bakteriostatische Aktivität als die entsprechenden Liganden allein.

     

Conductance behavior of some tris(ethylenediamine)cobalt(III) complexes and their ion association in aqueous solutions

The conductance behavior of some tris(ethylenediamine)cobalt(III) complexes was studied in dilute aqueous solutions at 25°C to investigate the ion-pair formation. The thermodynamic formation constants of the ion pairs [Co(en)₃]³⁺·X^– are 28 (chloride), 28 (bromide), 19 (nitrate), and 15 (perchlorate). These values were compared with theoretical values calculated by using Bjerrum's theory of ion association. The formation constant of [Co(en)₃]³⁺·Cl^– was larger than that obtained from the spectrophotometric measurement in solutions containing perchlorate ion. This difference in the formation constants was explained by considering the contribution of ion association of the complex cation with perchlorate ion.     

A mild method for the deprotection of tetrahydropyranyl (THP) ethers catalyzed by iron(III) tosylate

A mild method for the deprotection of THP ethers catalyzed by iron(III) tosylate (2.0 mol %) in CH₃OH has been developed. Iron(III) tosylate, Fe(OTs)₃·6H₂O, is a commercially available solid that is inexpensive, noncorrosive, and easy to handle. The room temperature reaction conditions make this method attractive for deprotection of a range of THP ethers.     

8-羟基喹啉铁配合物对锐钛矿型TiO2(101)表面的敏化机理

用密度泛函理论和DMol3程序包对锐钛矿型TiO2(101)表面复合三(8-羟基喹啉-5-羧酸)铁的敏化机理进行了研究. 计算结果表明, 该染料敏化剂经式结构的HOMO(最高占据分子轨道)-LUMO(最低未占据分子轨道)能隙非常小, 很容易受到激发; TiO2纳米晶吸附染料后, HOMO、LUMO 和费米能级都升高, 导致吸附染料后开路电压VOC升高. 并进一步探讨了三(8-羟基喹啉-5-羧酸)铁在TiO2(101)表面复合过程及作用机理.     

An rhodamine-based fluorescence probe for iron(III) ion determination in aqueous solution

An “off-on” rhodamine-based fluorescence probe for the selective signaling of Fe(III) has been designed exploiting the guest-induced structure transform mechanism. This system shows a sharp Fe(III)-selective fluorescence enhancement response in 100% aqueous system under physiological pH value and possesses high selectivity against the background of environmentally and biologically relevant metal ions including Al(III), Cd(II), Fe(II), Co(II), Cu(II), Ni(II), Zn(II), Mg(II), Ba(II), Pb(II), Na(I), and K(I). Under optimum conditions, the fluorescence intensity enhancement of this system is linearly proportional to Fe(III) concentration from 6.0 × 10⁻⁸ to 7.2 × 10⁻⁶ mol L⁻¹ with a detection limit of 1.4 × 10⁻⁸ mol L⁻¹.     

Synthesis, morphological-structural characterization and magnetic properties of amorphous iron (III)-oxyhydroxy-phosphate nanoparticles

The synthesis, the chemical, morphological, structural characterization and the magnetic properties of amorphous iron oxyhydroxy phosphate nanoparticles are reported. Aggregated spherical particles (diameter: 5-12 nm) are obtained showing a ferrihydrite-like behavior similar to that of the bacterial ferritin iron oxyhydroxy-phosphate core. A superparamagnetic behavior is observed with blocking temperatures ranging from ∼20 to ∼50 K depending on the iron and phosphate content.     

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.     

Reversed phase HPLC determination of titanium(IV) and iron(III) with sodium 1,2-dihydroxybenzene-3,5-disulfonic acid

A highly sensitive method has been developed for the determination of titanium(IV) and iron(III) by ion-pair reversed phase liquid chromatography using sodium 1,2-dihydroxybenzene-3,5-disulfonic acid (Tiron) as a precolumn chelating reagent. The metal - Tiron chelates were separated on a C₁₈ (ODS) column; the mobile phase was a 2:8 (v/v) mixture of acetonitrile and acetate buffer (0.04 mol/L, pH 6.2) containing 2.0 × 10^?3 mol/L Tiron, 0.04 mol/L tetrabutylammonium bromide, and 0.1 mol/L potassium nitrate. The detection limits for titanium(IV) and iron(III) are 0.5 and 2.0 μg/L, respectively. The method has been applied to the simultaneous determination of titanium(IV) and iron(III) in river water samples and has furnished highly precise results.     

A highly sensitive amperometric sensor for oxygen based on iron(II) tetrasulfonated phthalocyanine and iron(III) tetra-(N-methyl-pyridyl)-porphyrin multilayers

The development of a highly sensitive sensor for oxygen is proposed using a glassy carbon (GC) electrode modified with alternated layers of iron(II) tetrasulfonated phthalocyanine (FeTsPc) and iron(III) tetra-(N-methyl-pyridyl)-porphyrin (FeT4MPyP). The modified electrode showed excellent catalytic activity for the oxygen reduction. The reduction potential of the oxygen was shifted about 330 mV toward less negative values with this modified electrode, presenting a peak current much higher than those observed on a bare GC electrode. Cyclic voltammetry and rotating disk electrode (RDE) experiments indicated that the oxygen reduction reaction involves 4 electrons with a heterogenous rate constant (k_obs) of 3 × 10⁵ mol⁻¹ L s⁻¹. A linear response range from 0.2 up to 6.4 mg L⁻¹, with a sensitivity of 4.12 μA L mg⁻¹ (or 20.65 μA cm⁻² L mg⁻¹) and a detection limit of 0.06 mg L⁻¹ were obtained with this sensor. The repeatability of the proposed sensor, evaluated in terms of relative standard deviation (R.S.D.) was 2.0% for 10 measurements of a solution of 6.4 mg L⁻¹ oxygen. The sensor was applied to determine oxygen in pond and tap water samples showing to be a promising tool for this purpose.     

磁性介孔碳负载纳米零价铁的制备及其去除高盐废水中Cr(III)有机配合物

采用液相还原法制备了磁性介孔碳(Fe₃O₄@C)负载纳米零价铁(nano zero-valent iron,nZVI)复合材料(Fe₃O₄@C-nZVI),并将其用于高盐水中 Cr(III)-EDTA(EDTA：乙二胺四乙酸)的去除。扫描电镜、透射电镜、X射线衍射等表征表明 nZVI成功负载且分散良好,可磁性分离,在碳层保护下 nZVI稳定性强,有利于材料的重复利用。nZVI的加入大大提高了 Fe₃O₄@C-nZVI对 Cr(III)-EDTA 的吸附能力,在 pH=4.0、反应温度为 25 ℃时,Fe₃O₄@C-nZVI 对 Cr(III)-EDTA 的最大吸附量为 10.24 mg·g^-1,显著高于Fe₃O₄@C(4.31 mg·g^-1)。吸附Cr(III)-EDTA的过程更符合Langmuir模型和准二级动力学模型。Fe₃O₄@C-nZVI对Cr(III)-EDTA的吸附能力随着溶液pH值的增加先增加后减小;低浓度络合剂(EDTA、柠檬酸)会促进Cr(III)-EDTA的吸附,而络合剂浓度增加时则表现为抑制;高浓度阳离子(Na⁺、K⁺、Ca²⁺)会促进Cr(III)-EDTA的吸附。Fe₃O₄@C-nZVI在盐和络合剂环境中对Cr(III)-EDTA仍表现出显著的吸附效果。经过3次再生循环后,Fe₃O₄@C-nZVI对Cr(III)-EDTA的吸附量达6.90 mg·g^-1。X射线光电子能谱分析表明,Fe₃O₄@C-nZVI通过表面Fe(III)与Cr(III)-EDTA之间的配位作用形成Fe(III)-EDTA-Cr(III)配合物从而将Cr(III)-EDTA去除,随后通过离子置换作用将Cr(III)置换出来,置换出的Cr(III)会与表面氧化铁共沉淀为Cr_xFe_1-x(OH)₃,进而沉积在nZVI表面被去除。     

1H-NMR and electrochemical studies on ligated iron(III)perchlorates in acetonitrile-d 3

Summary Half-wave potentials,E _1/2, of Fe(ligand) ₆ ^3+/2+ , as ClO ₄ ^– salt, [ligand=N,N-dimethylformamide (dmf), acetamide (aa), N,N-dimethylacetamide (dma), trimethylphosphate (tmp), dimethylsulfoxide (dmso), and acetonitrile (MeCN) are given. A linear correlation betweenE _1/2 and Gutmann's donor numbers of the ligands, a parameter which expresses quantitatively the Lewis donor properties towards hard acceptors, was found. Ligand replacement on Fe(ligand) ₆ ³⁺ in acetonitrile-d ₃ was studied by means of¹H-NMR spectroscopy at 20°C. An average number of ligands coordinated to Fe³⁺,n _coord, is given.n _coord increases with the ligand's donor strength; i.e.tmp<dmf<dmso.Dedicated to Prof. Dr. mult. Viktor Gutmann on the occasion of his 70th birthday     

Water and time dependent interaction of iron(III) with indole-3-acetic acid

The influence of water on the interaction between iron(III) and indole-3-acetic acid (IAA) was studied in different organic solutions using rapid-scan stopped-flow spectrophotometry and rapid-freeze/quench Mössbauer spectroscopy. Measurements were also performed in ethanol–water and acetone–water mixtures. The results showed that the interaction between Fe^III and IAA resulted in dimeric Fe^III–IAA complex within 1 s, followed by a slow second step to give Fe²⁺ and IAA(oxidized). No such products were formed in the absence of water. The visible and Mössbauer spectra reflect the nature of the organic solvent and that of the anion of iron(III) salts.     

Steric stabilization of iron (III) hydroxide sols by various amino acids

The dispersion and coagulation phenomena of iron(III) hydroxide sols were investigated as a function of pH in the absence and presence of amino acids. The amino acids used were glycine,L--alanine,DL--amino-n-butyric acid,L-valine,L-leucine,L- isoleucine,L-glutamic acid andL-arginine. The turbidity measurements of the iron-(III) hydroxide sols, which were prepared by pouring an aqueous iron(III) chloride solution into boiling distilled water, were carried out using a spectrophotometer with an addermixer device and an automatic recording system. The zeta potentials of sol particles were obtained by ultra-microelectrophoresis. The change in turbidity of the sol, as a measure in stability of the sol, increased with increasing pH in the region of pH 2–8, and reached a maximum at the isoelectric point of the particles. The coagulation at the isoelectric point was prevented by adding amino acids, and the stabilization had an optimum point at concentrations which depended upon the kinds of amino acids. The remarkable dispersing effect of amino acids which occurred near the isoelectric point of the particles at the suitable concentration of the ammo acids may be due to the steric protection by amino acid adsorbed. The protective action was explained according to a modified DLVO theory, the modification for London-van der Waals force being applied in order to take the effect of the adsorption layer into account.