Kinetics and mechanism of photolysis of the iron(III) complex with tartaric acid

The formation of MV^•+ radical cations was observed upon the laser flash photolysis of the iron(III) tartrate complex [Fe^IIITart]⁺ (1) in the presence of methyl viologen (MV²⁺). The rate constants of the reactions involving MV^•+ were measured. The intramolecular electron trans-fer to form Fe^II and escape of the organic radical to the solvent bulk upon the photolysis of 1 were proposed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 866–869, May, 2007.     

Kinetics of iron(III) chloride extraction with n-tributyl phosphate

The equilibrium and rate of solvent extraction of FeCl₃ complexes from HCl solutions into benzene solutions of tributyl phosphate (TBP) has been studied. The extracted species was found to be FeCl₃·3TBP. The results show that the extraction is first order in both Fe(III) and TBP. The rate constant of adduct formation equals ～1.24M min^?1. The reaction order is zero for the aqueous phase acidity. The rate-controlling steps are discussed in the light of the results.     

Kinetics of iron(III) bromide extraction with n-tributyl phosphate

The equilibrium and rate of solvent extraction of FeBr₂ complexes from HBr solutions into benzene solutions of tributyl phosphate (TBP) have been investigated. It is found that two reactions control the iron(III)-TBP extraction from hydrobromic acid solutions. From HBr activity of 1.2–1.55 (molarity based) the reaction is inverse third order with respect to the aqueous phase acidity. From HBr activity of 1.7–6 (molarity based) the reaction is first order in HBr concentration in the aqueous phase. Both of these reactions are first order for both Fe(III) and TBP. The rate constants for these reactions were calculated and the rate-controlling steps are discussed.     

Kinetics and mechanism of stripping of Np(IV) by acetohydroxamic acid using a Lewis cell

Kinetic studies of stripping of Np(IV) from 30% Tri-Butyl-Phosphate/Odourless Kerosene (TBP/OK) into a nitric acid solution containing acetohydroxamic acid (CH₃CONHOH) have been investigated using a Lewis cell. The different parameters affecting the back-extraction rate of Np(IV) such as Np, TBP, nitric acid, nitrate, acetohydroxamic acid(AHA) concentration in addition to temperature, stirring speed and special interfacial area were separately studied and a rate equation was deduced. Results have been compared among themselves and other published works on similar systems. Mechanisms of stripping processes have been proposed.     

Kinetics and mechanism of iron(III) dissociation from the dihydroxamate siderophores alcaligin and rhodotorulic acid

The kinetics and mechanism of siderophore ligand dissociation from their fully chelated Fe(III) complexes is described for the highly preorganized cyclic tetradentate alcaligin and random linear tetradentate rhodotorulic acid in aqueous solution at 25 degrees C (Fe2L3 + 6H+ reversible 2 Fe3+ aq + 3 H2L). At siderophore:Fe(III) ratios where Fe(III) is hexacoordinated, kinetic data for the H(+)-driven ligand dissociation from the Fe2L3 species is consistent with a singly ligand bridged structure for both the alcaligin and rhodotorulic acid complexes. Proton-driven ligand dissociation is found to proceed via parallel reaction paths for rhodotorulic acid, in contrast with the single path previously observed for the linear trihydroxamate siderophore ferrioxamine B. Parallel paths are also available for ligand dissociation from Fe2(alcaligin)3, although the efficiency of one path is greatly diminished and dissociation of the bis coordinated complex Fe(alcaligin)(OH2)2+ is extremely slow (k = 10(-5) M-1 s-1) due to the high degree of preorganization in the alcaligin siderophore. Mechanistic interpretations were further confirmed by investigating the kinetics of ligand dissociation from the ternary complexes Fe(alcaligin)(L) in aqueous acid where L = N-methylacetohydroxamic acid and glycine hydroxamic acid. The existence of multiple ligand dissociation paths is discussed in the context of siderophore mediated microbial iron transport.     

Use of acetohydroxamic acid in the direct spectrophotometric determination of iron(III) and iron(II) by flow injection analysis

The direct spectrophotometric determination of iron(III) and iron(II) by flow injection analysis with acetohydroxamic acid and 1,10-phenanthroline as reagents is reported. The working ranges are 0.5–10 and 10–60 mg l^?1, respectively. Results obtained for synthetic mixtures of Fe(III) and Fe(II) and for acid extracts of haematite samples were accurate. Interference studies indicate that the method is highly selective.     

Kinetics and mechanism of oxidation of the chromium(III)-DL-aspartic acid complex/periodate reaction. Evidence for iron(II) catalysis

The kinetics of oxidation of the chromium(III)-DL- aspartic acid complex, [CrIIIHL]+ by periodate have been investigated in aqueous medium. In the presence of Fe^II as a catalyst, the following rate law is obeyed:

Kinetics and mechanism of pentacyanohydroxoferrate(III) formation from mono(aminocarboxylato)iron(III) complexes

Summary The kinetics and mechanism of the system: [FeL(OH)]^2–n + 5 CN^– [Fe(CN)₅(OH)]^3– + L^n–, where L=DTPA or HEDTA, have been investigated at pH= 10.5±0.2, I=0.25 M and t=25±0.1 C.As in the reaction of [FeEDTA(OH)]^2–, the formation of [Fe(CN)₅(OH)]^3– through the formation of mixed ligand complex intermediates of the type [FeL(OH)(CN)_x]^2–n–x, is proposed. The reactions were found to consist of three observable stages. The first involves the formation of [Fe(CN)₅(OH)]^3–, the second is the conversion of [Fe(CN)₅(OH)]^3– into [Fe(CN)₆]^3– and the third is the reduction of [Fe(CN)₆]^3– to [Fe(CN)₆]^4– by oxidation of L^n– The first reaction exhibits a variable order dependence on the concentration of cyanide, ranging from one at high cyanide concentration to three at low concentration. The transition between [FeL(OH)]^2–n and [Fe(CN)₅(OH)]^3– is kinetically controlled by the presence of four cyanide ions around the central iron atom in the rate determining step. The second reaction shows first order dependence on the concentration of [Fe(CN)₅(OH)]^3– as well as on cyanide, while the third reaction follows overall second order kinetics; first order each in [Fe(CN)₆]^3– and L^n–, released in the reaction. The reaction rate is highly dependent on hydroxide ion concentration.The reverse reaction between [Fe(CN)₅(OH)]^3– and L^n– showed an inverse first order dependence on cyanide concentration along with first order dependence each on [Fe(CN)_5– (OH)]^3– and L^n–. A five step mechanism is proposed for the first stage of the above two systems.     

Kinetics and mechanism of the oxidation of chromium(III)–dipicolinic acid complex by N-bromosuccinimide

The kinetics of oxidation of the chromium(III)–dipicolinic acid complex [Cr^III(DPA)₂(H₂O)₂]^– by N-bromosuccinimide (NBS) in aqueous solution to Cr^VI have been studied spectrophotometrically over the 20–40 °C range. The reaction is first order with respect to both [NBS] and [Cr^III], and increases with pH over the 5.92–6.93 range. Thermodynamic activation parameters were calculated. It is proposed that electron transfer proceeds through an inner-sphere mechanism via coordination of [NBS] to chromium(III).     

Some reactions of iron (III) and chromium (III) fluorides with oxides

Reactions of FeF₃ with several oxides at elevated temperatures are described. Reaction products were usually Fe₂O₃ and the fluoride of the other element. With higher valency elements complete fluorine exchange did not always occur and oxyfluorides were formed. Intermediates in the reactions include oxyfluorides and mixed oxides, again only found with higher valency elements. Some shorter studies on the reaction of CrF₃ with oxides are included for comparisons, the reactions observed being generally similar.     

Complexation of U(VI), Ce(III) and Nd(III) with acetohydroxamic acid in perchlorate aqueous solution

Complexes of UO₂ ²⁺, Ce³⁺ and Nd³⁺ (M) with acetohydroxamic acid (AHA or L) in an aqueous solution have been investigated by the pH-spectral titration method at 25 °C in an aqueous medium of 1.0 M NaClO₄ ionic strength. Cerium(III) and neodymium(III) form [ML]²⁺, [ML₂]⁺, [ML₃] complexes with acetohydroxamic acid, while in case of UO₂ ²⁺ form [UO₂L]⁺, [UO₂L₂] complexes with acetohydroxamic acid. Data processing with SQUAD program calculates the best values for the stability constants from pH-spectrophotometric titration data. The protonation constant obtained was pK₁ = 9.15 ± 0.04 at 25 °C. The stability constants for acetohydroxamic acid with UO₂ ²⁺, Ce³⁺ and Nd³⁺ were β₁ = 7.22 ± 0.011, β₂ = 14.89 ± 0.018 for UO₂ ²⁺ and β₁ = 5.05 ± 0.062, β₂ = 10.60 ± 0.076, β₃ = 16.23 ± 0.088 for Ce³⁺ and β₁ = 5.90 ± 0.028, β₂ = 12.22 ± 0.038, β₃ = 18.58 ± 0.042 for Nd³⁺, respectively.     

Kinetics and mechanism of the reactions of Au(III) complexes with some biologically relevant molecules

The kinetics of the substitution reactions between the mono-functional Au(III) complexes, [Au(dien)Cl](2+) and [Au(terpy)Cl](2+) (dien = 3-azapentane-1,5-diamine, terpy = 2,2';6',2'-terpyridine) and bi-functional Au(III) complexes, [Au(bipy)Cl(2)](+) and [Au(dach)Cl(2)](+) (bipy = 2.2'-bipyridine, dach = (1R,2R)-1,2-diaminocyclohexane) and biologically relevant ligands such as l-histidine (l-His), inosine (Ino), inosine-5'-monophosphate (5'-IMP) and guanosine-5'-monophosphate (5'-GMP), were studied in detail. All kinetic studies were performed in 25 mM Hepes buffer (pH = 7.2) in the presence of NaCl to prevent the spontaneous hydrolysis of the chloride complexes. The reactions were followed under pseudo-first order conditions as a function of ligand concentration and temperature using stopped-flow UV-vis spectrophotometry. The results showed that the mono-functional complexes react faster than the bi-functional complexes in all studied reactions. The [Au(terpy)Cl](2+) complex is more reactive than the [Au(dien)Cl](2+) complex, which was confirmed by quantum chemical (DFT) calculations. A more than 50% lower activation energy for the terpy than for the dien based complex was found. The bi-functional [Au(bipy)Cl(2)](+) complex is more reactive than the [Au(dach)Cl(2)](+) complex. The reactivity of the studied nucleophiles follows the same order for all studied systems, viz. l-His > 5'-GMP > 5'-IMP > Ino. According to the measured activation parameters, all studied reactions follow an associative substitution mechanism. Quantum chemical calculations (B3LYP/LANL2DZp) suggest that ligand substitution in [Au(terpy)Cl](2+) and [Au(dien)Cl](2+) by imidazole follows an interchange mechanism with a significant degree of associative character. The results demonstrate the strong connection between the reactivity of the complexes toward biologically relevant ligands and their structural and electronic characteristics. Therefore, the binding of gold(III) complexes to 5'-GMP, constituent of DNA, is of particular interest since this interaction is thought to be responsible for their anti-tumour activity.     

Kinetics and mechanism of oxidation of chromium(III)-l-arginine complex by periodate

Oxidation of the chromium(III)-l-arginine complex [CrIII(L)2(H2O)2]+ by periodate has been investigated. In aqueous solutions, [CrIII(L)2(H2O)2]+ is oxidized by IO−4 according to the rate law: d[CrVI]/dt=k2K5[CrIII]T [IVII]T/1 +([H+]/K1)+K5[IVII]T where k2 is the rate constant for the electron transfer process, K1 the equilibrium constant for the dissociation of [CrIII(L)2- (H2O)2]+ to [CrIII(L)2(H2O)(OH)]+H+, and K5 the pre-equilibrium formation constant. Values of k2= 4.02×10−3s−1, K1=5.60×10−4m and K5=171m−1 were obtained at 30°C and I=0.2m. Thermodynamic activation parameters were calculated. It is proposed that electron transfer proceeds through an inner-sphere mechanism via coordination of IO−4 to chromium(III). This revised version was published online in June 2006 with corrections to the Cover Date.     

Kinetics and mechanism of oxidation of chromium(III)-tetraoxalylurea complex by periodate

A novel chromium(III) complex of tetraoxalylurea was prepared. In aqueous solutions, [Cr^III(H₂L)(H₂O)]⁺ (H₂L = diprotonated tetraoxalylurea) is oxidized by IO ₄ ^– according to the rate law

Photochemistry of the iron(III) complex with pyruvic acid in aqueous solutions

Photochemistry of the 1: 1 Fe^pIII complex with pyruvic acid (PyrH) in aqueous solutions was studied by stationary photolysis and nanosecond laser flash photolysis with the excitation by the 3rd harmonics of an Nd:YAG laser. The quantum yield of [FeIIIPyr]2+ under the excitation at 355 nm is 1.0±0.1 and 0.46±0.05 in the absence and in the presence of dissolved oxygen, respectively. In experiments on laser flash photolysis, a weak intermediate absorption in the region 580–720 nm was found. The absorption was ascribed to the [FeII…MeC(O)COO•]^p2+ radical complex. Laser flash photolysis of [FePyr]^p2+ in the presence of methyl viologen dications (MV^p2+) resulted in the formation of the MV•+ radical cations. The proposed reaction mechanism includes the inner-sphere electron transfer in the light-excited complex accompanied by the formation of the [Fe^pII…MeC(O)COO•]^p2+ radical complex followed by its transformation into the reaction products.     

Kinetics and mechanism of the reactions of hexaaqua rhodium (III) with sulphur (IV) in aqueous medium

An O-bonded sulphito complex, Rh(OH₂)₅(OSO₂H)²⁺, is reversibly formed in the stoppedflow time scale when Rh(OH₂) ₆ ³⁺ and SO₂/HSO ₃ ⁻ buffer (1 <pH< 3) are allowed to react. For Rh(OH₂)₅OH₂₊+ SO₂ □ Rh(OH₂)₅(OSO₂H)²⁺ (k₁/k_-1), k₁ = (2.2 ±0.2) × 10³ dm³ mol⁻¹ s⁻¹, k₋1 = 0.58 ±0.16 s⁻¹ (25°C,I = 0.5 mol dm⁻³). The protonated O-sulphito complex is a moderate acid (K _d = 3 × 10⁻⁴ mol dm⁻³, 25°C, I= 0.5 mol dm⁻³). This complex undergoes (O, O) chelation by the bound bisulphite withk= 1.4 × 10⁻³ s⁻¹ (31°C) to Rh(OH₂)₄(O₂SO)⁺ and the chelated sulphito complex takes up another HSO ₃ ⁻ in a fast equilibrium step to yield Rh(OH₂)₃(O₂SO)(OSO₂H) which further undergoes intramolecular ligand isomerisation to the S-bonded sulphito complex: Rh(OH₂)₃(O₂SO)(OSO₂)^- → Rh(OH₂)₃(O₂SO)(SO₃)⁻ (k _iso = 3 × 10⁻⁴ s⁻¹, 31°C). A dinuclear (μ-O, O) sulphite-bridged complex, Na₄[Rh₂(μ-OH)₂(OH)₂(μ-OS(O)O)(O₂SO)(SO₃) (OH₂)]5H₂O with (O, O) chelated and S-bonded sulphites has been isolated and characterized. This complex is sparingly soluble in water and most organic solvents and very stable to acid-catalysed decomposition     

Kinetics and mechanism of oxidation of the chromium(III)-dl-valine complex/periodate reaction. Evidence for iron(II) catalysis

Oxidation of the chromium(III)-dl-valine complex [CrIII(L)2(H2O)2]+ by periodate has been investigated in aqueous medium. The kinetics of the reaction in aqueous medium in the presence of iron(II) as catalyst obeyed the rate law:Catalysis by iron(II) is believed to be due to the oxidation of iron(II) to iron(III), which acts as the oxidizing agent. The thermodynamic activation parameters were calculated and we propose that electron transfer proceeds through an inner-sphere mechanism via coordination of IO4– to chromium(III).