Abstract:The kinetics of copper(II), nickel(II) and zinc(II) catalyzed oxidation of L-lysine by potassium permanganate in alkaline medium were studied spectrophotometrically. The reaction is first order with respect to [oxidant], [substrate] and [alkali] respectively. The results suggests the formation of a complex between the amino acid and lysine and the hydroxylated species of copper(II), nickel(II) and zinc(II). The reaction constants involved in the mechanism and the activation parameters have been calculated. The reactivity order of the catalyst is Cu(II) > Ni(II) > Zn(II).
Reduction of [PtCl 6 ] 2− by L-ascorbic acid (H 2 ASc) in 0.1 M aqueous acid medium has been investigated spectrophotometrically under pseudo-first order condition at [PtCl 6 The redox reaction follows the rate law:, where k is the second-order rate constant and [H 2 ASc] is the total concentration of ascorbic acid. Electron transfer from [H 2 ASc] to Pt(IV) center leading to the release of two halide ions and formation of the reaction products, square planner Pt(II) halide complex, and dehydrated ascorbic acid is suggested. This redox reaction follows an outersphere mechanism as Pt(IV) complex is substituted inert. Activation parameters were calculated corresponding to rate of electron transfer reaction k. Activation parameters favor the electron transfer reaction.
The kinetics and mechanism of the electron transfer ofdl-Aspartic acid (Asp) by Mn (VII) in alkaline medium has been studied spectrophotometrically over the range2.0≤103[Asp]≤5.0 mol dm−3;0.01≤[OH-]≤0.05 mol dm−3;298≤T≤318 K andI=0.05 mol dm−3(KNO3). The reaction exhibits first-order dependence in[MnO4-]Tbut shows fractional-order dependence in both[Asp]Tand[OH−]T. The reaction was studied in the presence of sodium dodecyl sulfate (SDS); an increase in the rate with the increase in the micellar concentration was observed. The products were characterized by spectral analysis. A mechanism involving free radicals is proposed. Asp bindsMnO4-to form a complex that subsequently decomposes to products. Activation parametersΔH° (kJ mol−1) andΔS° (JK−1 mol−1) for the reaction are5.62±0.35and−227.65±1.1, respectively. The negative value ofΔS° indicates that oxidation occurs via inner sphere mechanism.
The kinetics of electron transfer reaction of diclofenac sodium with 12-tungstocobaltate (III) complex has been studied spectrophotometrically over the range 2.0 × 10 -3 ≤ [diclofenac sodium] ≤ 6.0 × 10 -3 mol/L, 6.03 ≤ pH ≤ 8.0 and at 293 ≤ T ≤ 308 K in aqueous medium at constant ionic strength I (0.5 mol/L sodium perchlorate). The electron transfer reaction showed pseudo-first order dependence in [diclofenac sodium] and [12-tungstocobaltate(III)] and less than unit order in [OH -]T. The activation parameters calculated for the electron transfer reaction favoured the formation of a precursor complex between the reactants. The product is characterized by FTIR and NMR spectra and is found to be [2-(2,6-dichloro phenylamino)phenyl]methanol.
The kinetics of oxidation of antidiabetic drug metformin by vanadium(V) have been studied spectrophotometrically under pseudo-first order conditions in aqueous acidic and micellar medium. The observed rate of oxidation is first order with respect to both metformin and H +. The pseudo-first order rate constant is independent of ionic strength and varies inversely with dielectric constant of the medium. The effect of micelles (SDS and TX 100) on such reactions has been investigated. Sodiumdodecyl sulphate (SDS) and iso-octylphenoxy polyethoxyether (TX100) accelerate the rate of electron transfer reaction except for cationic CTAB due to the cloudiness of the reaction mixture. It is a one electron transfer process where vanadium(V)is reduced to vanadium(IV) supported by cyclic voltammetric study. The main oxidation product was identified as metformin N-oxide by FTIR and LCMS method. Activation parameters of such reaction have been calculated and reaction mechanism is suggested. Computational study based on Hartree-Fock method supports the reaction mechanism.
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