2026-04-17T05:34:19Zhttps://recercat.cat/oai/request

oai:recercat.cat:2445/1585422025-12-04T20:58:55Zcom_2072_1057col_2072_478796col_2072_478917

00925njm 22002777a 4500 dc Pérez de Benito, Joaquín F. author Ferrando Benítez, Jordi author 2020-05-04T10:30:55Z 2020-05-04T10:30:55Z 2014-12-26 2020-05-04T10:30:55Z The reduction of permanganate ion to MnO2 Mn2O3 soluble colloidal mixed oxide by L-phenylalanine in aqueous phosphate-buffered neutral solutions has been followed by a spectrophotometric method, monitoring the decay of permanganate ion at 525 nm and the formation of the colloidal oxide at 420 nm. The reaction is autocatalyzed by the manganese product and three rate constants have been required to fit the experimental absorbance-time kinetic data. The reaction shows base catalysis and the values of the activation parameters at different pHs have been determined. A mechanism including both the non-autocatalytic and the autocatalytic reaction pathways, and in agreement with the available experimental data, has been proposed. Some key features of this mechanism are the following: (i) of the two predominant forms of the amino acid, the anionic form exhibits a stronger reducing power than the zwitterionic form; (ii) the non-autocatalytic reaction pathway starts with the transfer of the hydrogen atom in the  position of the amino acid to permanganate ion; and (iii) the autocatalytic reaction pathway involves the reduction of Mn(IV) to Mn(II) by the amino acid and the posterior re-oxidation of Mn(II) to Mn(IV) by permanganate ion. Cinètica química Oxidació Aminoàcids Chemical kinetics Oxidation Amino acids Three rate-constant kinetic model for permanganate reactions autocatalyzed by colloidal manganese dioxide: the oxidation of L-phenylalanine