Front dynamics of pH oscillators with initially separated reactants

The spatiotemporal dynamics of the Landolt-type pH oscillators are studied both numerically and experimentally with initially separated reagents in space. This configuration results in an A + B → oscillator front type system with localized patterns. The generic Rábai model of the pH-oscillators predicts the formation of an asymmetric acidic domain at the interface of the two zones loaded by different sets of chemicals. This asymmetry is rather caused by the initial conditions than the difference in the diffusivities of the components. As the influence of the negative feedback process increases, this acidic zone becomes to be localized around the interface. At some point the acidic zone bifurcates, a less acidic zone separates and starts to move forward the oxidant rich zone. In a limited domain of parameters, spatiotemporal oscillations are found due to the instability of the main acidic zone. The appropriate conditions for the development of this periodic behaviour is characterized by simulations. The numerically predicted phenomena are supported by experiments performed with the bromate-sulfite-ferrocyanide and with the hydrogen peroxide-sulfite-ferrocyanide systems, except the oscillatory phenomena

Design of localized spatiotemporal pH patterns by means of antagonistic chemical gradients

Spatially localized moving and stationary pH patterns are generated in two-side-fed reaction-diffusion systems. The patterns are sandwiched between two quiescent zones and positioned by the antagonistic gradients of the reactants of the self-activatory process. Spatial bistability, spatiotemporal oscillations, and formation of stationary Turing patterns have been predicted by numerical simulations and observed in experiments performed by using different hydrogen ion autocatalytic chemical systems. The formation of stationary patterns due to long-range inhibition is promoted by a large molecular weight hydrogen ion binding polymer

From Master-Slave to Peer-to-Peer Coupling in Chemical Reaction Networks

Design strategy through linking a driving pH oscillator (master system) to a pH sensitive complexation, precipitation or protonation equilibrium (slave slave) has been widely used to create and control concentration oscillations of chemical entities (e.g., monovalent cations, DNA, nanoparticles) not participating in the pH oscillatory system. No systematic investigation has been carried out on how the components of these equilibria affect the characteristics of the driving pH oscillators, and this feedback effect has been often neglected in previous studies. Here we show that pH sensitive species (hydrogen carbonate, EDTA) through a pH dependent equilibrium could significantly affect the characteristics (time period and amplitude) of the driving pH oscillators. By varying the concentration of those species we are able to control the strength of the chemical feedback from slave system to master system thus introducing a transition from master-slave coupling to peer-to-peer coupling in linked chemical systems. To illustrate this transition and coupling strategies we investigate two coupled chemical systems, namely the bromate-sulfite pH oscillator and carbonate - carbon dioxide equilibrium and the hydrogen-peroxide-thiosulfate-copper(II) and EDTA complexation equilibrium. As a sign of the peer-to-peer coupling the characteristics of the driving oscillatory systems can be tuned by controlling the feedback strength and the oscillations can be canceled above a critical value of this parameter