• D S Mahadevappa

      Articles written in Journal of Chemical Sciences

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

      D S Mahadevappa Puttaswamy N M Made Gowda

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      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.

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

      T Asha Iyengar D S Mahadevappa Puttaswamy

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      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.

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

      T Asha Iyengar D S Mahadevappa

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      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$$k'_{H_2 O} /k'_{H_2 O} $$= 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.

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