Kinetics and mechanism of osmium(VIII)-catalyzed oxidation of D-proline and L(–)-methionine by hexacyanoferrate(III)

The osmium(VIII)-catalyzed oxidation of D -proline and L (–)-methionine by alkaline hexacyanoferrate(III) has been studied spectrophotometrically. The reactions follow kinetics different from those of the oxidation of many amino acids investigated earlier, being first order in hexacyanoferrate(III) and osmium(VIII). The order in proline or methionine and OH^? decreases from unity to zero at higher concentrations of proline or methionine and OH^?, respectively. A mechanism consistent with the kinetic data is proposed and discussed.     

Osmium(VIII)-Catalyzed Oxidation of Some Cyclic Amines by Potassium Hexacyanoferrate(III) in Alkaline Media: a Kinetics and Mechanistic Study

Reactions of morpholine, piperidine, and piperazine with Os(VIII)-catalyzed hexacyanoferrate(III) in alkaline media to produce the corresponding lactam have been studied at constant temperature and ionic strength. The reactions followed first-order kinetics with respect to [amine] and [Os(VIII)] but were independent of [Fe(CN)₆ ^3-] and [OH^-]. The effects of introduced electrolytes, potassium hexacyanoferrate(II), relative permitivity, and temperature have also been studied. A mechanism accounting for these results has been proposed.     

Kinetics and mechanism of Os(VIII) catalysed oxidation of malate ion by alkaline hexacyanoferrate (III)

In the reaction between alkaline hexacyanoferrate(III) and malic acid catalysed by Os(VIII), the rate of hexacyanoferrate (III) disappearance was found to be proportional to the concentrations of malate ion, hydroxyl ion and Os(VIII), but independent of the concentration of hexacyanoferrate(III). The reaction was studied at different temperatures, various thermodynamic parameters ΔE, pZ, ΔS* etc were evaluated.     

Studies in nickel(IV) chemistry. Electron transfer kinetics of the reaction between tris(dimethylglyoximato)nickelate(IV) and hexacyanoferrate(II) in aqueous medium

The kinetics of electron transfer from hexacyanoferrate(II) to tris(dimethylglyoximato)-nickelate(IV), Ni(dmg)₃^2?, to produce Fe(CN)₆^3? and Ni(dmgH)₂, follows a pseudo-first-order disappearance in the Ni(IV). The pseudo-first-order rate constants k_obs are linearly dependent on [Fe(CN)₆^4?]₀ in a fiftyfold range of 2 × 10^?4?1 × 10^?2M, and the average values of k_obs/[Fe(CN)₆^4?]₀ range from 194M^?1·s^?1 at pH = 5.20 to 0.2M^?1·s^?1 at pH = 9.07 in aqueous medium at 35°C and μ = 0.57M. Results are interpreted in terms of a probable mechanism involving rate-determining outer sphere one-electron transfer steps from the reductant and one-protonated reductant species to the unprotonated and one-protonated Ni(IV) species present in solution. The more electrophilic one-protonated reductant species apparently reacts several orders of magnitude faster than the unprotonated one.     

Photometric determination of osmium with thiourea after extraction of the tetroxide

A general method for the determination of 5–1000 γ of osmium involves extraction of osmium tetroxide with chloroform or carbon tetrachloride, followed by shaking the organic solvent with a sulfuric acid solution, of thiourea to form red Os(NH₂CSNH₂)₆⁺³, whose color intensity is measured photometrically. A sharp separation of osmium from ruthenium can be obtained by reducing Os(VIII) and Ru(VIII) with ferrous sulfate and then oxidizing Os(IV) to Os(VIII) with nitric acid; ruthenium remains reduced and is not extracted by chloroform or carbon tetrachloride.     

A rapid method for the spectrophotometric determination of palladium(II) and osmium(VIII)

Propionyl promazine phosphate is proposed as a new reagent for the rapid spectrophotometric determination of microgram amounts of Pd(II) and Os(VII). PPP instantaneously forms an orange-red 1:1 complex with Pd(II) in sodium acetate-hydrochloric acid buffer of pH 0.8 to 4.0 at room temperature. The reagent also forms an orange-red radical cation with Os(VIII) in 0.5 to 2.0 M hydrochloric acid. The Pd-PPP complex exhibits an absorption maximum at 490–500 nm with molar absorptivity of 7.1 × 10³ liter mol^?1 cm^?1. The Os-PPP radical cation has an absorption maximum at 505–515 nm with molar absorptivity of 2.21 × 10⁴ liters mol^?1 cm^?1. The Sandell sensitivity is 0.022 μg/cm² (Pd) and 0.008 μg/ cm² (Os). Beer's law is valid over the concentration range 0.2 to 21 ppm (Pd) and 0.2 to 4.2 ppm (Os). The proposed method offers the advantages of simplicity, rapidity, and without the need for heating or extraction. The reagent is used for the determination of Pd in the synthetic mixtures corresponding to Pd alloys used in jewelery and Os in osmiridium alloy.     

Spectral and Mechanistic Investigation of the Osmium(VIII) Catalyzed Oxidation of Diclofenac Sodium by the Copper(III) Periodate Complex in Aqueous Alkaline Medium

The kinetics of the osmium(VIII) (Os(VIII)) catalyzed oxidation of diclofenac sodium (DFS) by diperiodatocuprate(III) (DPC) in aqueous alkaline medium has been studied spectrophotometrically at a constant ionic strength of 1.0 mol⋅dm⁻³. The reaction showed first order kinetics in [Os(VIII)] and [DPC] and less than unit order with respect to [DFS] and [alkali]. The rate decreased with increase in [periodate]. The reaction between DFS and DPC in alkaline medium exhibits 1:2 [DFS]:[DPC] stoichiometry. However, the order in [DFS] and [OH⁻] changes from first order to zero order as their concentration increases. Changes in the ionic strength and dielectric constant did not affect the rate of reaction. The oxidation products were identified by LC-ESI-MS, NMR, and IR spectroscopic studies. A possible mechanism is proposed. The reaction constants involved in the different steps of the mechanism were calculated. The catalytic constant (K _C) was also calculated for Os(VIII) catalysis at the studied temperatures. From plots of log ₁₀ K _C versus 1/T, values of activation parameters have been evaluated with respect to the catalytic reaction. The activation parameters with respect to the slow step of the mechanism were computed and discussed, and thermodynamic quantities were also determined. The active osmium(VIII) and copper(III) periodate species have been identified.     

Mechanistic study of osmium(VIII) promoted oxidation of crotonic acid by aqueous alkaline solution of potassium bromate

Kinetics and mechanism of the Os(VIII) catalysed oxidation of crotonic acid (CA) by KBrO₃ in alkaline medium have been investigated. Zero order dependence in [KBrO₃] was observed, while first order with respect to CA in its lower concentration range tends to zero order at its higher concentration range. The order in [Os(VIII)] was found to be unity and a positive effect of [OH⁻] was observed. Variation of the ionic strength (μ) and dielectric constant of the medium and addition of Hg(OAc)₂ (used as Br⁻ scavenger) had an insignificant effect on the rate of reaction. Thermodynamic parameters have also been calculated and reported. A suitable mechanism consistent with the observed kinetic results has been suggested and the related rate law deduced.     

Kinetics of the oxidation of aliphatic aldehydes by Os(VIII) in alkaline solution

Kinetics of oxidation of six aliphatic aldehydes by Os(VIII) in alkaline solutions have been studied. The reaction is of first order with respect to each of the aldehyde and Os(VIII). The pseudo-first order rate constants decreased with an increase in the concentration of hydroxyl ions. The oxidation of deuterioacetaldehyde (MeCDO) exhibited a substantial primary kinetic isotope effect. Separate rate constants for the oxidation of hydrate and free aldehyde forms have been evaluated. The aldehyde hydrate is postulated as the active reductant. Ionic strength has no noticable effect on the rate. The rate-determining step is, therefore, postulated to be a bimolecular reaction between the aldehyde hydrate and [OsO₄(OH)₂]^?2. The value of the limiting rate constant exhibited an excellent correlation with Taft σ* values; reaction constant being negative. A mechanism involving transfer of a hydride ion from the aldehyde hydrate to Os(VIII) has been proposed.     

Investigation into Charge Transport Dynamics of [Os(bpy)2(picolinate)]Cl Nafion Films

This work examines the charge transport properties of redox films of the immobilized enzyme mediator [Os(bpy)₂(picolinate)]Cl ([Os(bpy)₂Pic]⁺). Chronoamperometry was used to calculate D_CT values (typically of the order of 1.5×10^?8 cm² s^?1) and the effect of %loading of redox material was determined for three electrolytes over a range of concentrations. The data obtained implies that charge transfer within the film occurs via a redox site diffusion mechanism. The concentration of redox sites was determined using an approximate film thickness of 7 μm, as determined from profilometry studies. Experiments were also performed using immobilized carbon nanotubes within the redox film in order to examine the impact of the increased surface area and conductivity. The presence of the carbon nanotubes had the effect of doubling the surface coverage values and enhancing D_CT^1/2 C_M values from 1.9×10^?9 to 16.1×10^?9 mol cm^?1 s^?1.     

Electrochemistry and Ion Sensing Properties of Conducting Hydrogel Layers Based on Polypyrrole and Alkoxysulfonated Poly(3,4‐ethylenedioxythiophene) (PEDOT‐S)

Acidic aqueous solutions containing pyrrole and alkoxysulfonated PEDOT derivative (PEDOT‐S) were found to undergo polymerization in the absence of an external oxidizing agent. The product was a nearly black‐colored conducting hydrogel that after separation could be dispersed in water or acetone. The suspensions could be used to deposit cast films on a polycrystalline gold electrode. The polymer modified electrode showed a nearly Nernstian potentiometric response to Ag⁺ cations in the concentration range of 10^?5–10^?1 M with the slope of 54 mV/decade. The response was specific to Ag⁺ compared to a series of alkali and transition‐metal cations (pK_Ag/M>3.7).     

Oxidation of lysine by ferricyanide in presence of osmium(VIII)

Osmium(VIII) catalysed oxidation of lysine by ferricyanide in excess ferrocyanide shows a complex kinetics. The order in lysine falls, from 1 to 0 while that in ferricyanide increases from 0 to 2 with large increase in lysine concentration. The rates were directly proportional to [Os(VIII)] and {Const.+[Fe(CN) ₆ ⁴ ]}. A suitable mechanism is proposed and discussed.

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Oxidation von lysin mittels ferricyanid in der gegenwart von osmium(VIII)

Zusammenfassung Die von Os(VIII) katalysierte Oxidation von Lysin mit Ferricyanid in überschüssigem Ferrocyanid zeigt eine komplexe Kinetik. Bei starker Steigerung der Lysinkonzentration fällt die Ordnung bezüglich Lysin von 1 auf 0, während bezüglich Ferricyanid eine Erhöhung, von 0 auf 2 festzustellen ist. Die Geschwindigkeitskonstanten waren direkt proportional zu [Os(VII)] und {Const.+[Fe(CN) ₆ ⁴ ]}. Es wird ein möglicher Mechanismus vorgeschlagen und diskutiert.

     

Ultratrace Osmium,Ruthenium and Lead in Airborne Particulate Matter: Peak Area as Instrumental Datum to Improve Their Simultaneous Voltammetric Determination

Peak area as instrumental datum for determining the concentration of metals in solution instead of peak height is proposed for the simultaneous voltammetric determination in particulate matter of ultratrace Os(VIII), Ru(III) and Pb(II), species linked to vehicle emissions. In the case of species present at ultratrace concentration level or having low reversibility degree of the electrodic processes, the employment of peak area, instead of peak current, permits to achieve limits of detection lower even more of one order of magnitude. The method is based on the catalytic current of the Os(VIII)‐, Ru(III)‐ and Pb(II)‐bromate system by differential pulse voltammetry. 0.3 mol L^?1 acetate buffer pH 4.5+6.9×10^?2 mol L^?1 NaBrO₃+2.3×10^?4 mol L^?1 EDTA‐Na₂ was employed as the supporting electrolyte. For all the elements, the accuracy, expressed as relative error e%, and the precision, expressed as relative standard deviation s_r%, were satisfactory being lower than 6 %. To better validate the analytical procedure, a comparison with spectroscopic (electrothermal atomic absorption spectroscopy, ET‐AAS) is also reported.     

Kinetic Study of the Bromine-Catalyzed Isomerization of Maleic Acid in Aqueous Ce(IV)-Br−-H2SO4 Medium

The presence of ceric and bromide ions catalyzes the isomerization of maleic acid (MA) to fumaric acid (FA) in aqueous sulfuric acid. A kinetic study of this bromine-catalyzed reaction was carried out. The reaction between ceric ion and maleic acid is first order with respect to Ce(IV). For [Ce(IV)]₀=5.0×10^?4 M, [H₂SO₄]₀=1.2 M, μ=2.0 M (adjusted by NaClO₄), and [MA]₀=(0.5–1.0)M, the observed pseudo-first-order rate constant (k₀₃) at 25° is k₀₃=7.622×10^?5 [MA]₀/(1+0.205[MA]₀). The reaction between ceric and bromide ions is first order with respect to Ce(IV). For [Ce(IV)]₀=5.0×10^?4 M, [H₂SO₄]₀=1.2 M, μ=2.0 M, and [Br^?]₀=(0.025–0.150)M, the pseudo-first-order rate constant (k₀₂) at 25° is k₀₂= (4.313±0.095)x10^?2[Br^?]²+(2.060±0.119)x10^?3[Br^?]. The reaction of Ce(IV) with maleic acid and bromide ion is also first order with respect to Ce(IV). For [Ce(IV)]₀=5.0×10^?4 M, [MA]₀=0.75 M, [H₂SO₄]₀=1.2 M, μ=2.0 M, and [Br^?]₀= (0.025–0.150)M, the pseudo-first-order rate constant (k₀₃) at 25° is k₀₃= (5.286±0.045)x10^?2[Br^?]²+(3.568±0.056)x10^?3[Br^?]. For [Ce(IV)]₀=5.0 × 10^?4 M, [Br^?]₀=0.050 M, [H₂SO₄]₀=1.2 M, μ=2.0 M, and [MA]₀=(0.15–1.0)M at 25°, k₀₃=(2.108×10^?4+2.127×10^?4[MA]₀)/(1+0.205[MA]₀). A mechanism is proposed to rationalize the results. The effect of temperature on the reaction rate was also studied. The energy barrier of Ce(IV)—Br^? reaction is much less than that of Ce(IV)—MA reaction. Maleic and fumaric acids have very different mass spectra. The mass spectrum of fumaric acid exhibits a strong metastable peak at m/e 66.5.     

Chiral Sensing of Various Amino Acids Using Induced Circularly Polarized Luminescence from Europium(III) Complexes of Phenanthroline Dicarboxylic Acid Derivatives

Circularly polarized luminescence (CPL) was observed from [Eu(dppda)₂]^? (dppda=4,7‐diphenyl‐1,10‐phenanthroline‐2,9‐dicarboxylic acid) and [Eu(pzpda)₂]^? (pzpda=pyrazino[2,3‐f][1,10]phenanthroline‐7,10‐dicarboxylic acid) in aqueous solutions containing various amino acids. The selectivity of these complexes towards amino acids enabled them to be used as chiral sensors and their behavior was compared with that of [Eu(pda)₂]^? (pda=1,10‐phenanthroline‐2,9‐dicarboxylic acid). As these Eu^III complexes have achiral D_2d structures under ordinary conditions, there were no CPL signals in the emission assigned to f–f transitions. However, when the solutions contained particular amino acids they exhibited detectable CPL signals with g_lum values of about 0.1 (g_lum=CPL/2 TL; TL=total luminescence). On examining 13 amino acids with these three Eu^III complexes, it was found that whether an amino acid induced a detectable CPL depended on the Eu^III complex ligands. For example, when ornithine was used as a chiral agent, only [Eu(dppda)₂]^? exhibited intense CPL in aqueous solutions of 10^?2 mol dm^?3. Steep amino acid concentration dependence suggested that CPL in [Eu(dppda)₂]^? and [Eu(pzpda)₂]^? was induced by the association of four or more amino acid molecules, whereas CPL in [Eu(pda)₂]^? was induced by association of two arginine molecules.     

Complex Formation Reactions of Divinyltin(IV) Complexes with Amino Acids,Peptides, Dicarboxylic acids and Related Compounds

Complex formation equilibria of divinyltin(IV) with amino acids, peptides, and dicarboxylic acids have been investigated. Stoichiometry and stability constants for the complexes formed were determined at 25°C and ionic strength 0.1 M NaNO₃. The results showed the formation of ML, MLH, and ML₂ (organotin : ligand : hydrogen) complexes with amino acids. Peptides form ML complexes and the corresponding deprotonated amide species MLH_?1. In the latter species the binding with divinyltin(IV) occurs through the terminal amino group, carboxylate oxygen, and the amide nitrogen atoms (CO^? ₂, N^? _amide, NH₂). The results showed the formation of ML and ML₂ complexes with dicarboxylic acids. The concentration distribution of the complexes in solution was evaluated. The bonding sites of the divinyltin(IV) complex in solid state with oxalic acid was investigated by means of elemental analyses, FTIR, and mass spectra. Non-isothermal decomposition of the above complex has been studied and the result was statistically analyzed. The main steps were identified for the thermal decomposition reaction and each step proved to be a first order reaction. The kinetic parameters E _a and A were calculated for each step in the reaction. The thermodynamic functions H, G, and S* were calculated for each step of the reaction.     

Electron transfer to trans-dihydroxotetraoxoosmate(VIII). II. Kinetics of the oxidation of dimethylsulfoxide in aqueous alkaline media

The kinetics of the oxidation of dimethylsulfoxide by oxohydroxoosmate(VIII) complex ions in alkaline media follow pseudo-first-order disappearance in Os(VIII). The values of the observed pseudo-first-order rate constant are linearly dependent on initial dimethylsulfoxide concentrations in a fortyfold range, and increase with increasing [OH^?], leveling off at higher relative [OH^?]. The results are interpreted in terms of outer sphere interactions involving dimethylsulfoxide and various species of the Os(VIII) complex. The more nucleophilic dihydroxotetraoxoosmate(VIII) ion reacts about 50 times faster than the trihydroxotrioxoosmate(VIII) species.     

Oxidation of d-Glucose by Silver(III) Periodate Complex in the Presence of Ru(III)/Os(VIII) as a Homogeneous Catalyst: A Comparative Mechanistic Study (Stopped Flow Technique)

The kinetics of the oxidation of ruthenium(III) (Ru(III)) and osmium(VIII) (Os(VIII)) catalyzed oxidation of d-glucose (d-Glu) by silver(III) periodate complex (DPA) in aqueous alkaline medium at 298 K and constant ionic strength 0.003 mol·dm^?3 was studied spectrophotometrically. The reaction between d-Glu and DPA in alkaline medium exhibits 1:2 stoichiometry in both catalyzed reactions (d-Glu:DPA). The main products were identified as D-arabinonic acid and formic acid by spot tests, GC–MS spectra and chromatographic techniques. The reaction orders with respect to various species concentrations were determined. Also, the active species of catalyst and oxidant have been identified. Probable mechanisms were proposed. The activation parameters with respect to the slow step of the mechanism were computed and discussed and thermodynamic quantities were also calculated. It has been observed that the catalytic efficiency for the present reaction is in the order Os(VIII) > Ru(III).     

Kinetics and mechanisms of oxidation by metal ions,part XII [1] oxidation of formaldehyde by alkaline osmium(VIII)

The stopped-flow measurements on the disappearance of alkaline osmium(VIII) at 402 nm indicated a first-order dependence each in [Os(VIII)] and [HCHO]. The pseudo first-order rate constant k_obs ([HCHO] ? [Os(VIII)]) decreased with increasing [OH^?]. The ionic strength, however, had no effect on k_obs. The rapid scan spectra of the reaction mixture indicated the formation of an inert complex which absorbs at 319 nm. Therefore the rate determining step is considered to involve the bimolecular collision between OsO₄(OH) and hydrated formaldehyde. The values of the rate limiting constant k and the equilibrium constant K_ha for the formation of the alkoxide ion from the reaction of hydrated formaldehyde with OH^? are evaluated. The equilibrium constant K_ha, within the experimental limits, is independent of temperature. The pK_a value, calculated from K_ha, is 13.62 ± 0.05 which is in good agreement with the pK_a value 13.27 for formaldehyde. The activation parameters, ΔH? = 40 ± 2 kJ mol^?1 and ΔS? = ?51 ± 6 JK^?1 mol^?1, for the rate limiting constant k are determined.     

Thermodynamic quantities for the different steps involved in the mechanism of osmium(VIII) catalysed oxidation of l-lysine by a new oxidant,diperiodatoargentate(III) (stopped flow technique)

The kinetics of Os(VIII) catalysed oxidation of l-lysine by diperiodatoargentate(III) (DPA) in alkaline medium at T = 298 K and a constant ionic strength of 0.50 mol · dm^?3 was studied spectrophotometrically. The oxidation products are aldehyde (5-aminopentanal) and Ag(I). The stoichiometry is i.e. [l-lysine]:[DPA] = 1:1. The reaction is of first order in [Os(VIII)] and [DPA] and is less than unit order in both [l-lys] and [alkali]. Addition of periodate has no effect on the reaction. Effect of added products, ionic strength, and dielectric constant of the reaction medium have been investigated. The oxidation reaction in alkaline medium has been shown to proceed via a Os(VIII)-l-lysine complex, which further reacts with one molecule of deprotonated DPA in a rate determining step followed by other fast steps to give the products. The main products were identified by spot test, IR, and GC-MS. The reaction constants involved in the different steps of the mechanism are calculated at different temperatures. The catalytic constant (K_C) was also calculated at different temperatures. From the plots of lg K_C versus 1/T, values of activation parameters with respect to the catalyst have been evaluated. The activation parameters with respect to slow step of the mechanism are computed and discussed and thermodynamic quantities are also determined. The active species of catalyst and oxidant have been identified.