Oscillations of pH in the urea–urease system in a membrane reactor

Muzika, František; RůŽička, Matěj; Schreiberová, Lenka; Schreiber, Igor

doi:10.1039/c9cp00630c

Cited by 5 publications

(7 citation statements)

References 26 publications

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“…[11][12][13] Experimentally, urea-urease pH oscillations were observed so far in macroscopic reaction volumes. 9,14 Also, most analyses of pH oscillators to date have relied on deterministic reaction rate equations (RRE). Furthermore, there is a growing interest in chemical oscillators for applications.…”

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confidence: 99%

“…Experimentally, urea–urease pH oscillations were observed thus far in macroscopic reaction volumes. , Also, most analyses of pH oscillators to date have relied on deterministic reaction rate equations (RREs). Furthermore, there is a growing interest in chemical oscillators for applications. − This motivates the question whether stable limit cycles persist and how they change upon downscaling from the macroscopic to, e.g., intracellular reaction volumes.…”

mentioning

confidence: 99%

“…In this work, we consider the urea–urease reaction and study how the stable rhythmic variation of the pH level , is affected by intrinsic noise when decreasing reaction volumes to biologically relevant scales. Within one cycle, molecular copy numbers can vary from a few molecules to several thousands almost instantaneously, which is captured by the stochastic simulations.…”

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confidence: 99%

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Stochastic pH Oscillations in a Model of the Urea–Urease Reaction Confined to Lipid Vesicles

Straube

Winkelmann

Schütte

et al. 2021

J. Phys. Chem. Lett.

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The urea-urease clock reaction is a pH switch from acid to basic that can turn into a pH oscillator if it occurs inside a suitable open reactor. We study the confinement of the reaction to lipid vesicles, which permit the exchange with an external reservoir by differential transport, enabling the recovery of the pH level and yielding a constant supply of urea molecules. For microscopically small vesicles, the discreteness of the number of molecules requires a stochastic treatment of the reaction dynamics. Our analysis shows that intrinsic noise induces a significant statistical variation of the oscillation period, which increases as the vesicles become smaller. The mean period, however, is found to be remarkably robust for vesicle sizes down to approximately 200 nm. The observed oscillations are explained as a canard-like limit cycle that differs from the wide class of conventional feedback oscillators.

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confidence: 99%

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confidence: 99%

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confidence: 99%

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Stochastic pH Oscillations in a Model of the Urea–Urease Reaction Confined to Lipid Vesicles

Straube

Winkelmann

Schütte

et al. 2021

J. Phys. Chem. Lett.

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“…Instead, we observe that there exist well-separated time scales: 25,26 the fast species PH + adjusts quickly, on the scale of , to the slowly evolving concentrations of P and H + , which vary on the scale of several minutes. This justifies to perform a QSSA for PH + by rearranging eq 7d into (8) and neglecting the first term on the r.h.s., which yields the relation (9) with k′ = 1.8 × 10 9 M −1 for the rates given in Table 1. The high accuracy of this approximation is corroborated by Figure 2c, which shows that the temporal behavior of both sides of eq 9 coincides at all times, although none of the involved concentrations remains constant.…”

Section: Model Reductionmentioning

confidence: 75%

Accurate Reduced Models for the pH Oscillations in the Urea–Urease Reaction Confined to Giant Lipid Vesicles

2023

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This theoretical study concerns a pH oscillator based on the urea–urease reaction confined to giant lipid vesicles. Under suitable conditions, differential transport of urea and hydrogen ion across the unilamellar vesicle membrane periodically resets the pH clock that switches the system from acid to basic, resulting in self-sustained oscillations. We analyze the structure of the phase flow and of the limit cycle, which controls the dynamics for giant vesicles and dominates the pronouncedly stochastic oscillations in small vesicles of submicrometer size. To this end, we derive reduced models, which are amenable to analytic treatments that are complemented by numerical solutions, and obtain the period and amplitude of the oscillations as well as the parameter domain, where oscillatory behavior persists. We show that the accuracy of these predictions is highly sensitive to the employed reduction scheme. In particular, we suggest an accurate two-variable model and show its equivalence to a three-variable model that admits an interpretation in terms of a chemical reaction network. The faithful modeling of a single pH oscillator appears crucial for rationalizing experiments and understanding communication of vesicles and synchronization of rhythms.

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“…In aqueous-phase experiments the reaction displays pH-dependent feedback and a rapid switch, referred to as a pH clock, after an induction period where the pH increases slowly . The reaction is widely used in materials and sensing applications, − and urease has been encapsulated in vesicles and polymerosomes; − however, the influence (if any) of compartmentalization and chemical communication on the process is not well understood.…”

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confidence: 99%

Collective Behavior of Urease pH Clocks in Nano- and Microvesicles Controlled by Fast Ammonia Transport

Miele

Jones

Rossi

et al. 2022

J. Phys. Chem. Lett.

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The transmission of chemical signals via an extracellular solution plays a vital role in collective behavior in cellular biological systems and may be exploited in applications of lipid vesicles such as drug delivery. Here, we investigated chemical communication in synthetic micro- and nanovesicles containing urease in a solution of urea and acid. We combined experiments with simulations to demonstrate that the fast transport of ammonia to the external solution governs the pH–time profile and synchronizes the timing of the pH clock reaction in a heterogeneous population of vesicles. This study shows how the rate of production and emission of a small basic product controls pH changes in active vesicles with a distribution of sizes and enzyme amounts, which may be useful in bioreactor or healthcare applications.

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Oscillations of pH in the urea–urease system in a membrane reactor

Abstract: Urea–urease reaction in an open reservoir–membrane–reactor system displays regular spontaneous oscillations of pH.

Cited by 5 publications

References 26 publications

Stochastic pH Oscillations in a Model of the Urea–Urease Reaction Confined to Lipid Vesicles

Stochastic pH Oscillations in a Model of the Urea–Urease Reaction Confined to Lipid Vesicles

Accurate Reduced Models for the pH Oscillations in the Urea–Urease Reaction Confined to Giant Lipid Vesicles

Collective Behavior of Urease pH Clocks in Nano- and Microvesicles Controlled by Fast Ammonia Transport

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