Kinetics and mechanism of the oxidation of DL-methionine bybis(2,2′-bipyridyl)copper(II) permanganate

Summary The oxidation ofDL-methionine (MT) bybis(2,2-bipyridyl)copper(II) permanganate (BBCP) to the corresponding sulphoxide is first order in BBCP. Michaelis-Menten-type kinetics were observed with respect to MT. The formation constant of the intermediate complex and the rate constant for its decomposition were evaluated. The thermodynamic and activation parameters were also evaluated. The reaction is catalysed by H⁺ but 2,2-bipyridine does not affect the reaction rate. A mechanism is proposed.     

Fourth-derivative spectrophotometric determination of fungicide ferbam (iron(III) dimethyldithiocarbamate) in a commercial sample and wheat grains using 2,2′-bipyridyl

A procedure has been developed for the direct fourth-derivative spectrophotometric determination of iron(III) dimethyldithiocarbamate by converting it into an iron(II) 2,2'-bipyridyl complex, which is then dissolved in Triton X-100. Beer's law is obeyed over the concentration range 0.5-20 microg mL(-1 )in the final solution. Various parameters such as the effect of pH and interference of large number of ions on the determination of ferbam have been studied in detail. The method is sensitive, highly selective and can be used for the determination of ferbam in a commercial sample and in mixtures with various dithiocarbamates (ziram, zineb, maneb, etc.) and from wheat grains.     

Spectrophotometric studies on oxidation of some primary alcohols by 2,2′-bipyridinium chromate. A kinetic study

Some primary alcohols were oxidized by 2,2-bipyridinium chromate (BPC) in the presence of oxalic acid and TsOH giving aldehyde as major product. The reactions were carried out in 80% MeCN-DMF (v/v) medium under varied experimental conditions. The rate depends on the first power of the concentration of BPC and fractional power on the concentrations of alcohol, oxalic acid and TsOH.     

Electrochemiluminescence from tris(2,2′-bipyridyl) ruthenium (Ⅱ) in the presence of aminocarboxylic acid co-reactants

Due to the highly sensitive electrochemiluminescence (ECL), tris(2,2′-bipyridyl) ruthenium(II) (Ru(bpy)32+) is often used in the field of bioarrays with the help of co-reactants. However, the generally used co-reactant, tripropylamine (TPA), is toxic, corrosive and volatile. Therefore, the search for safe, sensitive and economical co-reactants is critical. Herein, three aminocarboxylic acids, ethylenediamine-tetraacetic acid (EDTA), nitrilotriacetic acid (NTA), and 2-hydroxyethylethylene diaminetriacetic ac...     

Kinetic study of the reaction between protonatedtrans-dioxotetracyanomolybdate(IV) and 2,2′-bipyridyl

Summary The kinetics of the reaction between the protonated forms of [MoO₂(CN)₄]^4– and 2,2-bipyridyl (bpy) have been studied in the 8.5–11.7 pH range. This study showed that the diprotonated form, [MoO(OH₂)(CN)₄]^2– is the only reactive species. The rate-limiting step is the substitution of the aqua ligand. This is followed by fast closure of the chelate ring, accompanied by the substitution of a cyanide ligand. With excess bpy the relatively slow formation of an adduct occurs. The nature of this adduct is discussed.     

Shift of reaction pathway by added chloride ions in the oxidation of aromatic ketones by dichloroisocyanuric acid—A kinetic study

Role of added chloride ions on the shift of reaction pathway of oxidation of aromatic ketones (acetophenone, desoxybenzoin) by dichloroisocyanuric acid (DCICA) was studied in aqueous acetic acid—perchloric acid medium. Participation of enolic and protonated forms of ketones in the rate determining steps is manifested from zero and first orders with respect to the oxidant in absence and presence of added chloride ions, respectively. Positive and negative effects of acid and dielectric constant on the reaction rate were observed. The observations deduce plausible mechanisms involving (i) rate-determining formation of enol from the conjugate acid of the ketone (SH⁺) in the absence of added chloride ions and (ii) rapid formation of molecular chlorine species from HOCl (hydrolytic species of DCICA) in the presence of added chloride ions, which then interacts with SH⁺ in a rate-determining step prior to the rapid steps of product formation. The order of Arrhenius parameters substantiate the proposed plausible mechanisms based on order of reactants both in presence and absence of added chloride ions.     

Kinetics and mechanism of the oxidation of tris(2,2′-bipyridine)iron(II) and tris(1,10-phenanthroline)iron(II) complexes by nitropentacyanocobaltate(III) in acidic aqueous medium

The kinetics of the oxidation of tris(2,2′-bipyridyl)iron(II) and tris(1,10-phenanthroline)iron(II) complexes ([Fe(LL)₃]²⁺, LL = bipy, phen) by nitropentacyanocobaltate(III) complex [Co(CN)₅NO₂]^3? was investigated in acidic aqueous solutions at ionic strength of I = 0.1 mol dm^?3 (HCl/NaCl). The reactions were carried out at fixed acid concentration ([H⁺] = 0.01 mol dm^?3) and the temperature maintained at 35.0 ± 0.1 °C. Spectroscopic evidence is presented for the protonated oxidant. Protonation constants of 360.43 and 563.82 dm³ mol^?1 were obtained for the monoprotonated and diprotonated Co(III) complexes respectively. Electron transfer rates were generally faster for [Fe(bipy)₃]²⁺ than [Fe(phen)₃]²⁺. The redox complexes formed ion-pairs with the oxidant with increasing concentration of the oxidant over that of the reductant. Ion-pair constants for these reaction were 160.31 and 131.9 dm³ mol^?1 for [Fe(bipy)₃]²⁺ and [Fe(phen)₃]^2+, respectively. The activation parameters measured for these systems have values as follows: ?H ^≠ (kJ K^?1 mol^?1) = +113.4 ± 0.4 and +119 ± 0.3; ?S ^≠ (J K^?1) = +107.6 ± 1.3 and 125.0 ± 1.6; ?G ^≠ (kJ K^?1) = +81 ± 0.4 and +82.4 ± 0.4; and E _a (kJ mol^?1) = 115.9 ± 0.5 and 122.3 ± 0.6 for LL = bipy and phen, respectively. Effect of added anions (Cl^?, $ {\text{SO}}_{4}^{2 - } $ and $ {\text{ClO}}_{4}^{ - } $ ) on the systems showed decrease in the electron transfer rate constant. An outer-sphere mechanism is proposed for the reaction.     

Kinetics and mechanism of the reduction of diaquatetrakis (2,2′-bipyridine)-μ-oxo diruthenium(III) by ascorbic acid

Summary The kinetics of the oxidation of ascorbic acid by diaquatetrakis (2,2-bipyridine)--oxo diruthenium(III) in aqueous HClO₄ were investigated. The dependence of the second order rate constantk ₂ on [H⁺] is given by k ₂=a+b[H⁺]^–, indicating that both the undissociated form and the monoanion of ascorbic acid are reactive. Marcus theory was used to estimate the redox potential for the Ru^III-O-Ru^III/Ru^III-O-Ru^II couple and a feasible mechanism has been proposed to explain the results.     

Free radical intervention,deamination and decarboxylation in the ruthenium(III)-catalysed oxidation of L-arginine by alkaline permanganate – a kinetic study

The kinetics of the Ru^III catalysed oxidation of L-arginine by alkaline permanganate was studied spectrophotometrically using a rapid kinetic accessory. The reaction follows a two stage process. In both the stages the reaction is first order with respect to [oxidant] and [catalyst] with an apparent less than unit order in [substrate] and [alkali]. The data suggest that oxidation proceeds via formation of a complex between the active Ru^III species and L-arginine, which then reacts with one mole of permanganate in a slow step to yield a L-arginine free radical, followed by a fast step to form the products. The reaction constants involved in the mechanism were evaluated. There is a good agreement between observed and calculated rate constants under different experimental conditions for both stages of reaction. The activation parameters for the slow step were calculated and are discussed.     

Kinetics and mechanism of the reduction of diaquotetrakis (2,2′-bipyridine)-µ-oxodiruthenium(III) ion by hypophosphorous acid in acidic medium

The kinetics and mechanism of the reduction of diaquotetrakis(2,2′-bipyridine)-µ-oxodiruthenium(III), [(H₂O)₂(bipy)₄Ru₂O]⁴⁺, by H₃PO₂ has been studied in aqueous acid at ionic strength = 0.5 mol dm^?3 (NaClO₄), [H⁺] = 5.0 × 10^?2 mol dm^?3 and temperature = 31 ± 1 °C. Measurement of the stoichiometry showed that 1 mole of [(H₂O)₂(bipy)₄Ru₂O]⁴⁺ was reduced by 1 mole of H₃PO₂. The reaction was found to be first order with respect to both [(H₂O)₂(bipy)₄Ru₂O⁴⁺] and [H₃PO₂], hence second order overall. Variations in the ionic strength and dielectric constant of the reaction medium had no effect on the rate. Also, addition of various ions to the reaction medium did not significantly alter the rate. Free radicals were identified during the course of the reaction by a polymerisation test. Spectroscopic information and Michaelis–Menten plots suggested the absence of an intermediate complex prior to electron transfer. [(H₂O)₂(bipy)₂Ru]²⁺, the reduction product of [(H₂O)₂(bipy)₄Ru₂O]⁴⁺, plus H₃PO₃, the oxidation product of H₃PO₂, were identified in the product solutions. It is suggested that the reaction proceeds through the outer sphere pathway. A mechanism for the reaction is proposed.     

Electrogenerated chemiluminescence of poly[(2,2′-bipyridyl)(4-(2-pyrrol-1-ylethyl)-4′-methyl-2,2′-bipyridyl)2]ruthenium (II) film

Elelctrogenerated chemiluminescence (ECL) of electropolymerized films based on [(2,2′-bipyridyl)(4-(2-pyrrol-1-ylethyl)-4′-methyl-2,2′-bipyridyl)₂]ruthenium (II) was firstly investigated in both organic and aqueous solution. The ECL behaviors have been explained by two typical mechanisms, namely, redox-cycling type and oxidative-reduction type. For the former, no co-reactant was required and for the latter, tripropylamine (TPA) and (NH₄)₂C₂O₄ were selected as co-reactants in the organic and aqueous system, respectively.     

Bis-(4-methyl-4′-pentyl-2,2′-bipyridyl)(dicyano)iron(II): a versatile solvatochromic solvation probe

We report the preparation, characterisation, and solvatochromic behaviour of bis-(4-methyl-4-pentyl-2,2-bipyridyl)(dicyano)iron(II). This is the first compound whose solubility characteristics permit its use as a solvatochromic indicator over the complete range of solvents from water to paraffins.     

Chemiluminescent determination of EDTA and related compounds using tris(2,2′-bipyridyl)ruthenium(III) photogenerated on-line

A rapid and sensitive chemiluminescence method using flow-injection has been developed for the determination of EDTA. The method is based on the chemiluminescent reaction of EDTA with tris(2,2'-bipyridyl)ruthenium(III), which is generated on-line through the photooxidation of tris(2,2'-bipyridyl)ruthenium(II) with peroxydisulfate. After optimizing the different experimental parameters, a calibration graph was obtained over the concentration range of 7 x 10(-8) M to 3 x 10(-6) M, with a minimum detectability of 7.2 x 10(-9) M (S/N = 3) observed. The correlation coefficient was 0.9992 (n = 8). The repeatability was 0.88 % (for a level of 4 x 10(-7) M) expressed as the relative standard deviation (n = 10), and the reproducibility (studied on five consecutive days) was 1.5%. The method was successfully applied to the determination of EDTA in ophthalmic collyrium and sauce samples. The method is also useful for determining other aminopolycarboxylic acids, such as NTA, EGTA, DTPA, DCTA and EDDS.     

Label free electrochemiluminescence protocol for sensitive DNA detection with a tris(2,2′-bipyridyl)ruthenium(II) modified electrode based on nucleic acid oxidation

Label free electrochemiluminescence (ECL) DNA detection based on catalytic guanine and adenine bases oxidation using tris(2,2′-bipyridyl)ruthenium(II) [$\mathrm{Ru}(\mathrm{bpy}{)}_3^{2+}$] modified glassy carbon (GC) electrode was demonstrated in this work. The modified GC electrode was prepared by casting carbon nanotubes (CNT)/Nafion/$\mathrm{Ru}(\mathrm{bpy}{)}_3^{2+}$ composite film on the electrode surface. ECL signals of double-stranded DNA and their thermally denatured counterparts can be distinctly discriminated using cyclic voltammetry (CV) with a low concentration (3.04 × 10⁻⁸ mol/L for Salmon Testes-DNA). Most importantly, sensitive single-base mismatch detection of p53 gene sequence segment was realized with 3.93 × 10⁻¹⁰ mol/L employing CV stimulation (ECL signal of C/A mismatched DNA oligonucleotides was 1.5-fold higher than that of fully base-paired DNA oligonucleotides). Label free, high sensitivity and simplicity for single-base mismatch discrimination were the main advantages of the present ECL technique for DNA detection over the traditional DNA sensors.     

Tris (2,2′-bipyridyl)ruthenium(II) electrogenerated chemiluminescence in analytical science

Ru(bpy) ₃ ²⁺ electrogenerated chemiluminescence (CL) has rapidly gained importance as a sensitive and selective detection method in analytical science. The Ru(bpy) ₃ ²⁺ ECL is observed when Ru(bpy) ₃ ³⁺ reacts with Ru(bpy) ₃ ⁺ and yields an excited state Ru(bpy) ₃ ^2+* . ECL emission can also be obtained when a variety of oxidants and reductants react with the reduced or oxidized forms of Ru(bpy) ₃ ²⁺ . Either the reductant or the oxidant can be treated as an analyte. The Ru(bpy) ₃ ²⁺ ECL is used as a detection method for the determination of oxalate and a variety of amine-containing analytes without derivatization in flowing streams such as flow injection and HPLC. When the ECL format is used as a detector for HPLC, unstable post-column reagent addition can often be eliminated and, the problems of both sample dilution and band broadening can be avoided because the Ru(bpy) ₃ ³⁺ species are generatedin situ in the reaction/observation flow cell. Since NADH is sensitively detected with the Ru(bpy) ₃ ²⁺ ECL, many clinically important analytes can be detected by coupling them to dehydrogenase enzymes that utilize -nicotinamide adenine cofactors to convert NAD⁺ to NADH. Ru(bpy) ₃ ²⁺ -derivatives are used as CL labels for immunoassay and PCR assay with Ru(bpy) ₃ ²⁺ /tripropylamine ECL system. The Ru(bpy) ₃ ²⁺ ECL label can be sensitively determined at subpicomolar concentrations, along with an extremely wide dynamic range of greater than six orders of magnitude. Furthermore, it can eliminate disposal and lifetime problems inherent in radio immunoassays. In this paper, basic principles of the Ru(bpy) ₃ ²⁺ ECL are discussed. In addition, analytical applications of the Ru(bpy) ₃ ²⁺ ECL are illustrated with examples.     

Oxidation of glutathione by diaquatetrakis(2,2′-bipyridine)-μ-oxo diruthenium(III) ion in aqueous acidic solutions

Summary The kinetics of the oxidation of glutathione by diaquatetrakis(2,2-bipyridine)--oxo diruthenium(III) ion in aqueous HClO₄ have been investigated. The reaction obeys the empirical rate law:-2d[oxidant]/dt = k[oxidant][reductant]/[H⁺] where k = 7.42 ± 0.40 × 10^-3 s^-1 at 25.5 °C, [H⁺] = 0.005–0.05 M and I = 1.0 M (LiClO₄). Free radicals are important in the reaction and a mechanism consistent with the experimental results has been postulated.     

Tris(2,2′-bipyridyl)ruthenium(II) electrochemiluminescent determination of ethyl formate

Analytical and Bioanalytical Chemistry - Ethyl formate is extensively used as food flavor, fungicide, and larvicide. It naturally exists in coffee, fruits, honey, brandy, and rum as well as dust...     

Kinetics of oxidation of phenylhydrazine by a μ-oxo diiron(III,III) complex in acidic aqueous media

Phenylhydrazine (R) quantitatively reduces [Fe₂(μ-O)(phen)₄(H₂O)₂]⁴⁺ (1) (phen?=?1,10-phenanthroline) and its conjugate base [Fe₂(μ-O)(phen)₄(H₂O)(OH)]³⁺ (2) to [Fe(phen)₃]²⁺ in presence of excess 1,10-phenanthroline in the pH range 4.12–5.55. Oxidation products of phenylhydrazine are dinitrogen and phenol. The reaction proceeds through two parallel paths: 1?+?R?→?products (k ₁), 2?+?R?→?products (k ₂); neither RH⁺ nor the doubly deprotonated conjugate base of the oxidant, [Fe₂(μ-O)(phen)₄(OH)₂]²⁺ (3) is kinetically reactive though both are present in the reaction media. At 25.0°C, I?=?1.0?M (NaNO₃), the rate constants are k ₁?=?425?±?10?M^?1?s^?1 and k ₂?=?103?±?5?M^?1?s^?1. An inner-sphere, one-electron, rate-limiting step is proposed.     

Synthesis,crystal structures and characterization of iron(III) and cobalt(III) complexes bearing 2,2′-bipyridylcarboxylate ligands

Transition Metal Chemistry - The Fe(III) complex [FeIII(bpdc)(Hbpdc)] (1) (bpdc?=?2,2′-bipyridyl-6,6′-dicarboxylate and...