Oxyhalogen–sulfur chemistry — Kinetics and mechanism of the bromate oxidation of cysteamine

2008 ◽  
Vol 86 (5) ◽  
pp. 416-425 ◽  
Author(s):  
Moshood K Morakinyo ◽  
Edward Chikwana ◽  
Reuben H Simoyi
Keyword(s):  
Oxidation Product ◽  
Reducing Agent ◽  
Kinetics And Mechanism ◽  
Molecular Bromine ◽  
Sulfur Chemistry ◽  
Diffusion Controlled ◽  
Hypobromous Acid ◽  
Acidic Conditions ◽  
Acid Toxicity ◽  
Derivatives Of

The kinetics and mechanism of the oxidation of the biologically important molecule, cysteamine, by acidic bromate and molecular bromine have been studied. In excess acidic bromate conditions, cysteamine is oxidized to N-brominated derivatives, and in excess cysteamine the oxidation product is taurine according to the following stoichiometry: BrO3– + H2NCH2CH2SH → H2NCH2CH2SO3H + Br–. There is quantitative formation of taurine before N-bromination commences. Excess aqueous bromine oxidizes cysteamine to give dibromotaurine: 5Br2 + H2NCH2CH2SH + 3H2O → Br2NCH2CH2SO3H + 8Br– + 8H+, while excess cysteamine conditions gave monobromotaurine. The oxidation of cysteamine by aqueous bromine is effectively diffusion-controlled all the way to the formation of monobromotaurine. Further formation of dibromotaurine is dependent on acid concentrations, with highly acidic conditions inhibiting further reaction towards formation of dibromotaurine. The formation of the N-brominated derivatives of taurine is reversible, with taurine regenerated in the presence of a reducing agent such as iodide. This feature makes it possible for taurine to moderate hypobromous acid toxicity in the physiological environment.Key words: cysteamine, hypobromous acid, toxicities, antioxidant.

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

2006 ◽  
Vol 84 (1) ◽  
pp. 49-57 ◽  
Author(s):  
Alice Chanakira ◽  
Edward Chikwana ◽  
David H Peyton ◽  
Reuben H Simoyi
Keyword(s):  
Acid Concentration ◽  
Rate Constant ◽  
Oxidation Product ◽  
Initial Conditions ◽  
Reaction Dynamics ◽  
Reaction Scheme ◽  
Kinetics And Mechanism ◽  
Sulfur Chemistry ◽  
Bimolecular Rate Constant ◽  
Acidic Conditions

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.

Spectral properties of ionic derivatives of pyrene and their aggregates with anionic surfactant and polyelectrolyte

1995 ◽  
Vol 73 (11) ◽  
pp. 1948-1954 ◽  
Author(s):  
Pavol Hrdlovič ◽  
Lubica Horinová ◽  
Štefan Chmela
Keyword(s):  
Butyric Acid ◽  
Sodium Salt ◽  
Polyacrylic Acid ◽  
Sodium Dodecylsulfate ◽  
Green Emission ◽  
Water Soluble ◽  
Diffusion Controlled ◽  
Packed Structure ◽  
Bimolecular Quenching ◽  
Derivatives Of

A multifunctional probe based on pyrene, the chloride of the 2,2,6,6-tetramethyl-4-hydroxy-piperidinium ester of 4-(1-pyrene)butyric acid, at a concentration of 5 × 10−5 mol dm−3 exhibits excimer-like green emission with the maximum at 480 nm in the presence of sodium dodecylsulfate below its critical micelle concentration. A similar effect has been observed for this probe in the presence of the sodium salt of polyacrylic acid in the same concentration range. 1-Pyrenemethylammonium chloride exhibits a broad green excimer-like emission for sodium dodecylsulfate but not for the sodium salt of polyacrylic acid. The quenching constants of the monomeric and excimer-like emissions were determined for acrylamide, 1-oxo-2,2,6,6-tetramethyl-4-hydroxypiperidine, potassium iodide, and copper(II) sulfate, representing neutral, ionic, and free-radical types of quenchers. The rate constants of quenching for N-oxyl radicals indicate that the monomeric emission from both water-soluble probes is diffusion controlled. For other types of quenchers the rate constant of bimolecular quenching is lower. The quenching of the excimer-like emission of an aggregate of the chloride of the 2,2,6,6-tetramethyl-4-hydroxypiperidinium ester of 4-(1-pyrene)butyric acid is less efficient than in the case of 1-pyrenemethylammonium chloride, which indicates a more packed structure of the former aggregate. Keywords: pyrene, ionic derivative, emission, micelle, aggregation, quenching.

scholarly journals An Appraisal of Developments in Allium Sulfur Chemistry: Expanding the Pharmacopeia of Garlic

Molecules ◽  
2019 ◽  
Vol 24 (21) ◽  
pp. 4006 ◽  
Author(s):  
Peter Rose ◽  
Philip Keith Moore ◽  
Matthew Whiteman ◽  
Yi-Zhun Zhu
Keyword(s):  
Biological Effects ◽  
Sulfur Compounds ◽  
Biological Assessment ◽  
Nutrient Metabolism ◽  
Sulfur Chemistry ◽  
Anticancer Properties ◽  
Metabolic Systems ◽  
Models Of Disease ◽  
Synthetic Derivatives ◽  
Derivatives Of

Alliums and allied plant species are rich sources of sulfur compounds that have effects on vascular homeostasis and the control of metabolic systems linked to nutrient metabolism in mammals. In view of the multiple biological effects ascribed to these sulfur molecules, researchers are now using these compounds as inspiration for the synthesis and development of novel sulfur-based therapeutics. This research has led to the chemical synthesis and biological assessment of a diverse array of sulfur compounds representative of derivatives of S-alkenyl-l-cysteine sulfoxides, thiosulfinates, ajoene molecules, sulfides, and S-allylcysteine. Many of these synthetic derivatives have potent antimicrobial and anticancer properties when tested in preclinical models of disease. Therefore, the current review provides an overview of advances in the development and biological assessment of synthetic analogs of allium-derived sulfur compounds.

scholarly journals Phenacylation of 6-Methyl-Beta-Nitropyridin-2-Ones and Further Heterocyclization of Products

Molecules ◽  
2020 ◽  
Vol 25 (7) ◽  
pp. 1682
Author(s):  
Eugene V. Babaev ◽  
Victor B. Rybakov
Keyword(s):  
Pyridinium Salt ◽  
Phenacyl Bromides ◽  
Acidic Conditions ◽  
Phenacyl Derivatives ◽  
Derivatives Of

Reaction between the derivatives of 6-methyl-beta-nitropyridin-2-one and phenacyl bromides was studied, and the yields observed were extremely low. The pyridones were converted via chloropyridines to methoxyderivatives, which were N-phenacylated. N-Phenacyl derivatives of 4,6-dimethyl-5-nitropyridin-2-one under the action of base gave 5-hydroxy-8-nitroindolizine and under acidic conditions gave 5-methyl-6-nitrooxazole[3,2-a]pyridinium salt, which underwent recycization with MeONa to 5-methoxy-8-nitroindolizine.

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