Exact Concentration Dependence of the Landolt Time in the Thiourea Dioxide–Bromate Substrate-Depletive Clock Reaction

Csekõ, György; Gao, Qingyu; Takács, Attila; Horváth, Attila

doi:10.1021/acs.jpca.9b02025

Cited by 11 publications

(14 citation statements)

References 45 publications

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“…The ratio of these rate coefficients provides the p K a1 of phosphoric acid to be 1.8 . This value worked consistently well in a number of previous systems investigated. − …”

Section: Discussionsupporting

confidence: 75%

Autoinhibition by Iodide Ion in the Methionine–Iodine Reaction

Csekõ

Horváth

2020

J. Phys. Chem. A

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The methionine–iodine reaction was reinvestigated spectrophotometrically in detail monitoring the absorbance belonging to the isosbestic point of iodine at 468 nm, at T = 25.0 ± 0.1 °C, and at 0.5 M ionic strength in buffered acidic medium. The stoichiometric ratio of the reactants was determined to be 1:1 producing methionine sulfoxide as the lone sulfur-containing product. The direct reaction between methionine and iodine was found to be relatively rapid in the absence of initially added iodide ion, and it can conveniently be followed by the stopped-flow technique. Reduction of iodine eventually leads to the formation of iodide ion that inhibits the reaction making the whole system autoinhibitory with respect to the halide ion. We have also shown that this inhibitory effect appears quite prominently, and addition of iodide ion in the millimole concentration range may result in a rate law where the formal kinetic order of this species becomes −2. In contrast to this, hydrogen ion has just a mildly inhibitory effect giving rise to the fact that iodine is the kinetically active species in the system but not hypoiodous acid. The surprisingly complex kinetics of this simple reaction may readily be interpreted via the initiating rapidly established iodonium-transfer process between the reactants followed by the subsequent hydrolytic decomposition of the short-lived iodinated methionine. A seven-step kinetic model to be able to describe the most important characteristics of the measured kinetic curves is established and discussed in detail.

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“…The ratio of these rate coefficients provides the p K a1 of phosphoric acid to be 1.8 . This value worked consistently well in a number of previous systems investigated. − …”

Section: Discussionsupporting

confidence: 75%

Autoinhibition by Iodide Ion in the Methionine–Iodine Reaction

Csekõ

Horváth

2020

J. Phys. Chem. A

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“…The TDO–iodate system was shown to display a clock feature first by Mambo and Simoyi, though the authors failed to report that the age of the stock TDO solution significantly affects the Landolt time . In contrast to this, in the case of the TDO–bromate reaction, no aging effect was observed as reported by Csekö et al The lack of aging effect was explained by the fact that the key TDO–bromine reaction is so rapid in the presence of fresh TDO that it hits almost the diffusion control limit, thus leaving no further place for an additional increase in the reaction rate.…”

Section: Introductionmentioning

confidence: 94%

On the Kinetics and Mechanism of the Thiourea Dioxide–Periodate Autocatalysis-Driven Iodine-Clock Reaction

et al. 2019

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The thiourea dioxide−periodate reaction has been investigated under acidic conditions using phosphate buffer within the pH range of 1.1−2.0 at 1.0 M ionic strength adjusted by sodium perchlorate. Absorbance−time series are monitored as a function of time at 468 nm, the isosbestic point of the I 2 −I 3 − system. The profile of these kinetic runs follows either sigmoidal-shaped or rise-and-fall traces depending on the initial concentration ratio of the reactants. The clock species iodine appears after a well-defined but reproducible time lag even in substrate excess, meaning that the system may be classified as an autocatalysis-driven clock reaction. It is also demonstrated that the age of the thiourea dioxide solution markedly shortens the Landolt time, suggesting that the original form of thiourea dioxide (TDO) rearranges into a more reactive form and reacts faster than the original one. The behavior found is consistent with that recently observed in other oxidation reactions of TDO. To characterize the system quantitatively, a 22-step kinetic model is constructed from adapting the kinetic model of the TDO−iodate reaction published recently by supplementing it with six different reactions of periodate. By the help of seven fitted rate coefficients a sound agreement between the measured and calculated absorbance− time traces is obtained.

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“…3) because the rate law of the rate determining step in this sequence is proportional to the concentration of product C. It should also be noted that the kinetics of several real chemical systems may easily be described by this core mechanism. [26][27][28][29][30] Among them the most well-known is the bisulfite-iodate (Landolt) reaction discovered more than a century ago [31] and, as a result, this sequence of reactions is called Landolt-type systems. [32] Figure 1 displays the concentration-time profiles of the autocatalyst at different k 2 /k 1 ratios meanwhile keeping the product of k and k constant at an arbitrarily chosen 10…”

Section: The Simplest Law Of Mass Action Type Autocatalytic Mechanismmentioning

confidence: 99%

Law of Mass Action Type Chemical Mechanisms for Modeling Autocatalysis and Hypercycles: Their Role in the Evolutionary Race

Horváth

2020

ChemPhysChem

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One of our most appealing challenge is to unravel the role of a presumably autocatalytic system in controlling the origin and spreading of Life on our entire planet. Here we show that in the simplest autocatalytic loop involving reactions capable of self‐replication and obeying law of mass action kinetics, concentration growth of the autocatalyst may be characterized by parametrization of direct and autocatalytic pathways rather than by kinetic orders of the autocatalyst. Extending this model by feasible elementary steps allows us to outline super‐exponential growth where kinetic order of the autocatalyst is higher than unity. Furthermore, it is shown in case of the simplest hypercycle that such a situation might appear where the otherwise more sluggish autocatalytic route receives a decisive support from the crosscatalytic pathway to become an apparently stronger autocatalytic loop even if the other route contains a more efficient autocatalysis. If the hypercycle is performed under flow conditions selection of autocatalyst depends on kinetic and flow parameters influenced by external factors mimicking that the most adaptive loop of hypercycle eventually finds its wining way in the evolutionary race.

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Exact Concentration Dependence of the Landolt Time in the Thiourea Dioxide–Bromate Substrate-Depletive Clock Reaction

Cited by 11 publications

References 45 publications

Autoinhibition by Iodide Ion in the Methionine–Iodine Reaction

Autoinhibition by Iodide Ion in the Methionine–Iodine Reaction

On the Kinetics and Mechanism of the Thiourea Dioxide–Periodate Autocatalysis-Driven Iodine-Clock Reaction

Law of Mass Action Type Chemical Mechanisms for Modeling Autocatalysis and Hypercycles: Their Role in the Evolutionary Race

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