Neelu Kambo

Kinetics and mechanism of the ruthenium(III) catalysed oxidation of reducing sugars by chloramine-T in alkaline medium

The kinetics of the ruthenium(III) catalysed oxidation of reducing sugars, viz. arabinose, xylose, galactose, glucose, fructose, lactose and maltose by chloramine-T have been studied in alkaline medium. The reactions exhibit a first order rate dependence with respect to: [substrate], [chloramine-T] and [OH−]. The rate is proportional to {k′ + k″[RuIII]}, where k′ and k″ are rate constants for uncatalysed and catalysed path respectively. A suitable mechanism, consistent with the kinetic data, is proposed and discussed.

Inhibition of TX‐100 on the Rate of Hexacyanoferrate(III) Oxidation of Reducing Sugars: A Kinetic Study

An inhibition effect of nonionic micelles (polyoxyethylene (10) octyl phenol, commonly known as TX‐100) on the rate of oxidation of the reducing sugars, fructose, glucose, and maltose by alkaline hexacyanoferrate(III) has been observed. The kinetic data support a 1:1 association/binding between substrate and micelles. The binding constant and free energy transfer from water to micelle have been determined.

Inhibition Effect of {Cationic Surfactant-Ascorbic Acid} Premicellar Aggregation on the Rate of Hexacyanoferrate(III) Oxidation of Ascorbic Acid: A Kinetic Study

The kinetics of oxidation of ascorbic acid by acidic hexacyanoferrate(III) have been investigated in presence of cationic surfactant viz. cetyltrimethylammonium bromide (CTAB). An inhibition effect of CTAB (below its critical micelle concentration) on the rate of oxidation has been observed. The spectrophotometric and kinetic data support a 1:1 premicellar association between substrate and surfactant. A mechanism has been proposed and a rate law consistent with kinetic results has been derived.

Premicellar/Micellar Inhibition in Alkaline KMnO4 Oxidation of Reducing Sugars: A Kinetic Study

An inactive premicellar {Surfactant- } aggregate in case of sodium lauryl sulphate (NaLS, anionic surfactant), cetyltrimethyl ammonium bromide (CTAB, cationic surfactant) and an inactive micellar {Surfactant- } aggregate/complex in case of Triton X-100 (Tx-100, nonionic surfactant) has been observed during the alkaline KMnO4 oxidation of glucose and fructose in micellar medium. The reaction showed a first-order dependence of rate with respect to . The order of reaction in substrate and alkali was found to decrease from unity at higher [Substrate] and [OH–], respectively. An inhibition effect of each surfactant on the rate of oxidation has been observed. A mechanism involving an inactive {Surfactant- } aggregate/complex and consistent with kinetic data has been proposed. The observed rate constants were in the order of which has been explained in terms of electrostatic and hydrophobic forces.

Nonionic Micellar Catalyzed Oxidation of Vitamins by Chloramine-T in HClO4 Medium: A Kinetic Study

The kinetics of oxidation of vitamin B1 (thiamine hydrochloride) and vitamin B6 (pyridoxine hydrochloride) by chloramine-T (CAT) in perchloric acid medium and in presence of a non ionic surfactant (Triton x-100) have been investigated. A catalytic effect of the nonionic micelle on the rate of oxidation has been observed and rate is found to be proportional to 7lcub;k′ + k″ [Triton x-100]}, where k′ and k″ are the rate constants in absence and presence of surfactant, respectively. The rate shows a first-order, a fractional order and a zero order dependence on [Chloramine-T]o, [Vitamin]o and [H+]0, respectively in absence as well as in presence of surfactant. A mechanism involving association/binding between the oxidant and the surfactant micelle, which is supported by spectrophotometric evidence has been proposed. The binding parameters have also been evaluated using a pseudo-phase kinetic model.

Hydrotropic Enhancement of Rate of the Browning Reaction; A Kinetic Study

The rate of a nonenzymatic browning reaction, that is, the reaction between reducing sugar and amino acid(commonly known as Millard reaction) is strongly enhanced in the presence of a common hydrotrope viz. sodium benzoate or sodium salicylate even below its minimal hydrotropic concentration (MHC). The effect of hydrotrope on the rate has been studied in four systems taking combination of different reducing sugars (glucose and fructose) and amino acids (glycine and alanine) in alkaline conditions. The kinetic data support the formation of the mixed aggregation between the hydrotrope and the reactants. The kinetic rate law consistent with experimental results has been derived on the basis of the proposed mechanism.

Interaction of Nonionic Surfactants with Cerium(IV) in HClO4Medium: A Kinetic Study

The kinetics of interactions of cerium(IV) with nonionic surfactants viz. Titron x‐100 (polyoxyethylene (10) octyl phenol) and Brij‐35 (polyoxyethylene glycol dodecyl ether) have been studied spectrophotometrically in HClO4 medium in the temperature range of 35 to 55°C. The reaction rate showed a first order dependence with respect to cerium(IV). The observed rate constant was found to be proportional to [surfactant] at lower concentration while at higher [surfactant] the rate was independent to surfactant. A spectrophotometric evidence for association/complexation of cerium(IV) with surfactant monomer has been obtained. A mechanism for the interaction has also been proposed.