Oxyhalogen-sulfur chemistry — Kinetics and mechanism of the oxidation of cysteamine by acidic iodate and iodine

Abstract

The oxidation of cysteamine by iodate and aqueous iodine has been studied in neutral to mildly acidic conditions. The reaction is relatively slow and is heavily dependent on acid concentration. The reaction dynamics are complex and display clock behavior, transient iodine production, and even oligooscillatory production of iodine, depending upon initial conditions. The oxidation product was the cysteamine dimer (cystamine), with no further oxidation observed past this product. The stoichiometry of the reaction was deduced to be IO3– + 6H2NCH2CH2SH → I– + 3H2NCH2CH2S-SCH2CH2NH2 + 3H2O in excess cysteamine conditions, whereas in excess iodate the stoichiometry of the reaction is 2IO3– + 10H2NCH2CH2SH → I2 + 5H2NCH2CH2S-SCH2CH2NH2 + 6H2O. The stoichiometry of the oxidation of cysteamine by aqueous iodine was deduced to be I2 + 2H2NCH2CH2SH → 2I– + H2NCH2CH2S-SCH2CH2NH2 + 2H+. The bimolecular rate constant for the oxidation of cysteamine by iodine was experimentally evaluated as 2.7 (mol L–1)–1 s–1. The whole reaction scheme was satisfactorily modeled by a network of 14 elementary reactions.Key words: cysteamine, cystamine, Dushman reaction, oligooscillations.

Kinetics and mechanism of the oxidation of a ferrous complex with an α,α′-diimine chelate ligand by ceric sulfate in aqueous acidic medium by UV-vis absorption spectroscopy

“…The characteristic wavelengths at Ȝ max for the complex compound in the ultraviolet and visible regions were in excellent agreement with the values reported in the literature [12,13] and those established for the complex cation through Job's method of continuous variation. However, for further confirmation and characterization, the complex cation [Fe(bipy) 3 complex species is formed between ferrous ion and bipyridine.…”

“…In order to study the effect of [H + ] on the reaction rate, kinetic runs were carried out using acetic acid-sodium acetate buffer at pH 4.82 as the solvent for the [Fe(bipy) 3 …”

“…For k obs , the excess of cerium(IV) is small when Ce(SO 4 )3 2-is the only species of cerium(IV) present at significant concentrations under the experimental conditions employed, i.e. at low concentrations of SO 4 2-[18].…”

“…Redox reactions have drawn the attention of chemists and numerous kinetic investigators [2][3][4]. Studies involving electron transfer between ferrous/ferric ions and their complexes have been widely reported in recent years [5,6].…”

Detailed mechanistic investigation into the S-nitrosation of cysteamine

“…Although a series of studies have been performed on the metabolism of this thiol and its metabolites with respect to oxidation by reactive oxygen species, 39–41 nothing has been done on the elucidation of its mechanism of nitrosation by NO and (or) NO-derived metabolites (N 2 O 3 and NO + ). Its nitrosation is well-known and has been reported in several manuscripts, 42,43 but the exact mechanistic details are still unknown.…”