Kinetics of oxidation of ethylenediamine tetraacetic acid by aromatic N-bromamines in buffer medium

Kinetics of oxidation of disodium ethylene-diamine-tetraacetic, acid (EDTA) by bromamine-B (BAB) and bromamine-T (BAT) was investigated at 30°C in acetate buffer of pH 5. The oxidation behaviour is similar, with a first-order dependence of rate on [oxidant] and fractional orders in [EDTA] and [H⁺]. The influence of the reaction products, halide ions, ionic strength and dielectric constant of medium on the rate has been studied. A possible mechanism is suggested.     

Kinetics of oxidation of glycylglycine by bromamine-T in acid medium

The kinetics of oxidation of a typical dipeptide glycylglycine (GG) by bromamine-T have been studied in HClO₄ medium at 40°C. The rate shows first-order dependence on [BAT]₀ and is fractional order in [GG]₀ which becomes independent of [substrate]₀ at higher [GG]₀. At [H⁺ ] > 0.02mol dm⁻³, the rate is inverse fractional in [H⁺ ] but is zero order at lower [H⁺ ] (≤0.02 mol dm⁻³). Variation in ionic strength or dielectric constant of the medium had no significant effect on the rate. The solvent-isotope effect was measured and = 1.45. Proton inventory studies have been made. The reaction has been studied at different temperatures (308-323 K) and activation parameters have been computed.     

Kinetics and mechanism of oxidation of chloramphenicol by 1-chlorobenzotriazole in acidic medium

Chloramphenicol (CAP) is an antibiotic drug having a wide spectrum of activity. The kinetics of oxidation of chloramphenicol by 1-chlorobenzotriazole (CBT) in HClO₄ medium over the temperature range 293–323 K has been investigated. The reaction exhibits first-order kinetics with respect to [CBT]_o and zero-order with respect to [CAP]_o. The fractional-order dependence of rate on [H⁺] suggests complex formation between CBT and H⁺. It fails to induce polymerization of acrylonitrile under the experimental conditions employed. Activation parameters are evaluated. The observed solvent isotope effect indicates the absence of hydride transfer during oxidation. Effects of dielectric constant and ionic strength of the medium on the reaction rate have been studied. Oxidation products are identified. A suitable reaction scheme is proposed and an appropriate rate law is deduced to account for the observed kinetic data.     

Mechanistic investigation of oxidation of a diketone by bromamine-B in acid medium

Oxidation of acetylacetone (AA) by bromamine-B (BAB) in HC1 medium (0.1 to 0.6 mol dm⁻³) at constant ionic strength has been investigated at 40°C. The rate is first order in [BAB]₀ and fractional order each in [AA]₀ and [H⁺]. The reaction is also catalysed by chloride ion. Michaelis-Menten type of kinetics is observed. Decrease in dielectric constant of medium increases the rate. A solvent isotope effect κ′H₂O/κ′D₂O = 0.96 has been noted. Activation parameters for the rate limiting step have been computed. The mechanism involves the enol form of the diketone.     

Oxidation of some catecholamines by sodium N-chloro-p-toluenesulfonamide in acid medium: A kinetic and mechanistic approach

The kinetics of the oxidation of five catecholamines viz., dopamine (A), L-dopa (B), methyldopa (C), epinephrine (D) and norepinephrine (E) by sodium N-chloro-p-toluenesulfonamide or chloramine-T (CAT) in presence of HClO₄ was studied at 30±0.1 °C. The five reactions followed identical kinetics with a first-order dependence on [CAT] _o , fractional-order in [substrate] _o , and inverse fractional-order in [H⁺]. Under comparable experimental conditions, the rate of oxidation of catecholamines increases in the order D>E>A>B>C. The variation of ionic strength of the medium and the addition of p-toluenesulfonamide or halide ions had no significant effect on the reaction rate. The rate increased with decreasing dielectric constant of the medium. The solvent isotope effect was studied using D₂O. A Michaelis-Menten type mechanism has been suggested to explain the results. Equilibrium and decomposition constants for CAT-catecholamine complexes have been evaluated. CH₃C₆H₄SO₂NHCl of the oxidant has been postulated as the reactive oxidizing species and oxidation products were identified. An isokinetic relationship is observed with β=361 K, indicating that enthalpy factors control the reaction rate. The mechanism proposed and the derived rate law are consistent with the observed kinetics.     

氨基酸的光辅助氧化化学发光及其分析应用

氨基酸与溴酸钾混合液经紫外光照射后与鲁米诺反应产生较强的发光信号,且在一定条件下氨基酸浓度与发光强度成线性关系,据此建立了一种氨基酸测定方法。在优化的条件下,该方法对五种氨基酸的检出限在0.004μg/mL~0.06μg/mL范围内;分别对0.5μg/mL的五种氨基酸平行测定7次,其相对标准偏差在2·3%~4.2%范围内。初步考察了该方法与液相色谱联用测定氨基酸的可行性。     

Kinetics of oxidation of alkanes and their derivatives byn-decanepersulfonic acid

The kinetics of interaction ofn-decanepersulfonic acid with linear, branched, and substituted hydrocarbons was studied. The oxidation ofcyclo-C₆H₁₂/C₆D₁₂ occurs with a moderate kinetic isotope effect,k ^H/k ^D=2.2±0.3. A satisfactory correlation between the partial rate constants and the structure of hydrocarbons in terms of the Okamoto-Brown equation was found. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 5, pp. 822–825, May, 2000.     

Chemical modification of usnic acid 2. Reactions of (+)-usnic acid with amino acids

The condensation of amino acids with (+)-usnic acid involves the 2-positioned acetyl group of the latter and gives derivatives containing an enamine fragment. Dedicated to the memory of Academician N. N. Vorozhtsov on the 100th anniversary of his birth. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1203–1205, June, 2007.     

Kinetics and mechanism of oxidation of some basic amino acids with bromamine-T

Kinetics of oxidative decarboxylation of arginine, glutamine, histidine and lysine by bromamine-T (BAT) was investigated in acid and alkaline media at 30° and 20° fespectively. The form of the rate law at low concentrations of HClO₄ has been worked out. Proton inventory studies in H₂O-D₂O mixtures with Arg as a probe have been made. The rate increases in the order: His > Lys > Arg > Glu - NH₂. In alkaline media, the rate shows a first order dependence on [BAT]₀ and is fractional in [S] and [OH].p-Toluene sulphonamide retards the rate. Mechanisms proposed are consistent with the experimental rate laws.     

Kinetics of ruthenium(III)-catalyzed oxidation of arylthioacetic acids by Ce(IV)

The kinetics of ruthenium(III)-catalyzed oxidation of several arylthioacetic acids by Ce(IV) have been studied. The proposed mechanism involves the formation of a 1∶1 complex between Ru(III) and arylthioacetic acid, which then reacts with Ce(IV).     

Ruthenium(III)-catalyzed oxidation of amides by sodium N-bromobenzenesulphonamide in hydrochloric acid: a kinetic and mechanistic study

The kinetics of the RuIII-catalyzed oxidation of urea and substituted ureas namely: methylurea, ethylurea and propylurea, to the corresponding hydrazines by sodium N- bromobenzenesulphonamide or bromamine-B (BAB) in HCl medium has been studied at 303K. The reaction rate shows a first order dependence each upon [BAB], [amide] and [RuIII] and is dependent on [H+]. Addition of halide ions and benzenesulphonamide do not significantly affect the rate. Proton inventory studies were made in H2O-D2O mixtures for urea and methylurea. A Taft linear free energy relationship is observed for the reaction with *=–2.95 and =–0.25, showing that electron-donating groups enhance the rate. An isokinetic relation is observed with =370K, indicating that enthalpy factors control the rate; this result is also confirmed by Exner Criterion which showed a linear plot for the logarithms of rate constants at the highest and lowest temperatures employed. The protonation constant of monobromamine-B has been evaluated and equals 7.5. A mechanism consistent with the observed kinetic data has been proposed.     

Mechanism of oxidation of diazepam by 1-chlorobenzotriazole in acidic medium. A kinetic approach

The kinetics of oxidation of diazepam (DZ) by 1-chlorobenzotriazole (CBT) has been studied in HClO₄ medium in the temperature range of 293–323 K. The reactions followed a first order dependence on [CBT], fractional order each in [H⁺] and [DZ]. Activation parameters were evaluated. A negative entropy of activation indicated the involvement of a rigid complex in the activated state. Variation of reaction rate with dielectric constant and the ionic strength are consistent with a mechanism involving the decomposition of a dipole in the rate-determining step. Rate equation is derived to account for the observed kinetic data and the proposed reaction mechanism.     

A compilation of amino acid analyses of proteins

The amino acid analyses of 186 proteins are given as residues per 1000 residues. Additional information as carbohydrate composition, content of uncomon amino acids, and sources of all proteins are also presented.     

Use of isothermal microcalorimetry for prediction of oxidative stability of several amino acids

Isothermal microcalorimetry has been applied as a method for predicting (in)stability of ascorbic acid and several amino acids that undergo oxidative degradation in aqueous media. The fast and simple method involved the addition of different amounts of hydrogen peroxide. The appearance of the heat flow curves gave a clear general indication of how stability was influenced. The accuracy of the microcalorimetric result was investigated by comparing it with an HPLC assay and a good agreement between the results of both methods was demonstrated. It was also established that susceptibility to oxidative degradation decreases in the following order: cysteine, methionine, ascorbic acid, tyrosine and tryptophan.     

Kinetics of oxidation of pantothenic acid by chloramine‐T in perchloric acid and in alkaline medium catalyzed by OsO4: A mechanistic approach

Kinetics of oxidation of pantothenic acid (PA) by sodium N‐chloro‐p‐toluenesulfonamide or chloramine‐T (CAT) in the presence of HClO₄ and NaOH (catalyzed by OsO₄) has been investigated at 313 K. The stoichiometry and oxidation products are same in both media; however, their kinetic patterns were found to be different. In acid medium, the rate shows first‐order dependence on [CAT]_o, fractional‐order dependence on [PA]_o, and inverse fractional‐order on [H⁺]. In alkaline medium, the rate shows first‐order dependence each on [CAT]_o and [PA]_o and fractional‐order dependence on each of [OH^?] and [OsO₄]. Effects of added p‐toluenesulfonamide and halide ions, varying ionic strength, and dielectric constant of medium as well as solvent isotope on the rate of reaction have been investigated. Activation parameters were evaluated, and the reaction constants involved in the mechanisms have been computed. The proposed mechanisms and the derived rate laws are consistent with the observed kinetics. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 201–210, 2005     

A compilation of amino acid analyses of proteins

The amino acid analyses of 183 proteins, as residues per 1000 residues, are given. In addition the carbohydrate content and the content of any noncommon amino acids are also given. The sources of all proteins are presented.     

Cu(II) catalyzed oxidation of mercaptoacetic acid by methylene blue in acidic medium: Influence of solvent and morphology

Kinetic studies on the Cu(II) catalyzed oxidation of mercaptoacetic acid (thioglycolic acid, TGA) by the model electron receptor methylene blue in acidic medium show that the reaction follows a second order kinetics in TGA. The order in methylene blue is unity but at higher [TGA], the order is 3/4. The rate shows an inverse relationship with [H⁺] and a second order dependence on [Cu(II)]. The reaction conforms to Arrhenius behavior in aqueous medium but resorts to anti-Arrhenius behavior in aqueous methanol and in aqueous acetone media. The reaction involves the in situ participation of nanoparticles which has been confirmed by SEM, XRD, and FTIR techniques. In aqueous medium, cauliflower shaped nanoparticles (44.21–74.33 nm) are obtained but in the presence of acetone and methanol, nanogranules (38.96–70.73 nm) and nanodisks (47.30–72.16 nm), respectively, are produced at 35°C as revealed by SEM images and XRD data. The reaction is characterized by the participation of two transition states in aqueous acetone medium and the kinetics of the reaction, especially the temperature dependence, is governed by the adsorption of methylene blue on copper nanoparticles as influenced by morphology inter alia dielectric constant of the reaction medium.