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Spectrophotometric method was used to study the kinetics of charge-transfer (CT) complexes of pantoprazole with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and iodine. The reactions of DDQ and iodine with pantoprazole have been investigated in different solvents at three different temperatures. The products of the interactions have been isolated and characterized using UV-vis, GC-MS, FT-IR, and far-IR spectral techniques. The rate of formation of the product has been measured and discussed as a function of solvents and temperature. The iodine complex indicates the formation of the tri-iodide CT complex with a general formula [(PTZ)I] + I − 3 . The characteristic strong absorptions of I − 3 are observed around 360 and 290 nm in the electronic spectra, and the far-IR spectrum exhibits three characteristic vibrations of I − 3 unit at 156, 112, and 69 cm −1 assigned to ν as (I-I), ν s (I-I), and δ(I − 3 ), respectively. The activation parameters ( G # , S # , and H # ) were obtained from the temperature dependence of the rate constants. The influence of relative permittivity of the medium on the rate indicated that the intermediate is more polar than the reactants, and this observation was further well supported by spectral studies. Based on the spectrokinetic results, plausible mechanisms for the interaction of the drug with the chosen acceptors, which proceed via the formation of CT complexes and its transformation into final products, have been proposed.

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The oxidation of methionine by quinolinium chlorochromate (QCC) has been studied, in the presence of chloroacetic acid, and in water-acetic acid mixtures of varying mole fractions. The reaction is first order with respect to methionine, QCC and acid. The reaction rates were determined at three different temperatures (25, 35 and 45 ?C) and the activation parameters were computed. The reaction rate increased with increasing mole fraction of acetic acid in the mixture and specific solvent-solvent-solute interactions were found to predominate (81 %). A solvation model and a suitable mechanism for the reaction are postulated.