Periodic changes in the oxidation states of the center ion in the cobalt-histidine complex induced by the BrO - SO pH-oscillator.

The coupling of acid-base type pH-dependent equilibria to pH-oscillators expanded significantly the number and type of species which can participate in oscillatory chemical processes. Here, we report a new version of oscillatory phenomena that can appear in coupled oscillators. Oscillations in the oxidation states of the center ion bound in a chelate complex were generated in a combined system, when the participants of the oscillator as dynamical unit and the components of the complex formation interacted with each other through redox reaction.

pH-oscillations in the bromate-sulfite reaction in semibatch and in gel-fed batch reactors.

The simplest bromate oxidation based pH-oscillator, the two component BrO3(-)-SO3(2-) flow system was transformed to operate under semibatch and closed arrangements. The experimental preconditions of the pH-oscillations in semibatch configuration were predicted by model calculations. Using this information as guideline large amplitude (ΔpH∼3), long lasting (11-24 h) pH-oscillations accompanied with only a 20% increase of the volume in the reactor were measured when a mixture of Na2SO3 and H2SO4 was pumped into the solution of BrO3(-) with a very low rate.

Periodic changes in the distribution of species observed in the Ni(2+)-histidine equilibrium coupled to the BrO3(-)-SO3(2-) pH oscillator.

The dynamical behavior of the system comprising of the pH-dependent complex formation between histidine and Ni(II) ions coupled to the BrO3(-)-SO3(2-) pH oscillator was studied. The pH oscillator was demonstrated to be capable of forcing the pH-sensitive nickel ion-histidine equilibrium to alternate periodically between the unreacted and the fully complexed states. The periodic interconversions gave rise to an oscillatory distribution of the species that participate in the equilibrium and resulted in oscillations in the free [Ni(2+)], [NiHis(+)], and [Ni(His)2].

[Recent results in research on oscillatory chemical reactions].

The mechanisms of the complicated periodical phenomenas in the nature (e.g. hearth beat, sleep cycle, circadian rhythms, etc) could be understood with using the laws of nonlinear chemical systems.

Oscillations in the permanganate oxidation of glycine in a stirred flow reactor.

Oscillatory behavior is reported in the permanganate oxidation of glycine in the presence of Na2HPO4 in a stirred flow reactor. In near-neutral solutions, long-period sustained oscillations were recorded in the potential of a Pt electrode and in the light absorbance measured at λ = 418 and 545 nm, characteristic wavelengths for following the evolution of the intermediate [Mn(IV)] and reagent [MnO4(-) ] during the course of the reaction. No evidence of bistability was found.

Generation of pH-oscillations in closed chemical systems: method and applications.

All pH-oscillators reported to date function only under open (flow reactor) conditions. We describe an approach to generating pH-oscillations in a closed system by starting from an open system pH-oscillator, finding semibatch conditions under which it oscillates with an inflow of a single reactant to an otherwise closed reactor containing the remaining components, and replacing this inflow with a layer of silica gel impregnated with the key reactant. We present data showing the successful application of this technique to the BrO(3)(-)-Mn(2+)-SO(3)(2-), IO(3)(-)-Fe(CN)(6)(4-)-SO(3)(2-), and BrO(3)(-)-Fe(CN)(6)(4-)-SO(3)(2-) systems.