Oxidation of ascorbic acid by air oxygen catalyzed by copper(II) ions in batch and continuous flow stirred tank reactors: bistability, oscillations and stochastic resonance

Abstract

We report various nonlinear phenomena observed in the oxidation of ascorbic acid by molecular (H 2 Asc) oxygen in the presence of copper(II) ions in a continuous Ñow stirred tank reactor (CSTR) as well as in a batch reactor (closed system). Transient irregular oscillations were observed in a batch reactor by varying the initial concentrations of and copper(II) ions. The behavior of the system in a CSTR was studied by varying the H 2 Asc Ñow rate and the inÑow concentrations of and copper(II) ions. At low inÑow concentrations of (k f ) H 2 Asc copper(II) ions the system exhibits bistability and small amplitude regular oscillations. In a two-dimensional parametric plot with coordinates and the regions of bistability and oscillations form a cross-shapedFor increasing values of oscillations emerge H 2 Asc k f via a Hopf bifurcation and disappear due to a homoclinic orbit. Simultaneously applied small amplitude periodic and stochastic perturbations imposed onto the Ñow rate close to the bistable region revealed the phenomenon of stochastic resonance, which is conÐrmed by an analysis of probability distribution functions, power spectra, and singular value decomposition.

The rich electrochemistry and redox reactions of the copper sites in the cellular prion protein

“…The resultant Cu(I) can be subsequently oxidized by O 2 , generating H 2 O 2 as a product. Using AA as a representative biological reductant, this cycle can be described as [61–64]: $$2\text{P}-\text{Cu}(\text{II})\text{or}\text{free}\text{Cu}(\text{II})+\text{AA}+{\text{H}}_2\text{O}\to 2\text{P}-\text{Cu}(\text{I})\text{or}\text{free}\text{Cu}(\text{I})+\text{DA}+2{\text{H}}^{+}$$ $$2\text{P}-\text{Cu}(\text{I})\text{or}\text{free}\text{Cu}(\text{I})+{\text{O}}_2+2{\text{H}}^{+}\to 2\text{P}-\text{Cu}(\text{II})\text{or}\text{free}\text{Cu}(\text{II})+{\text{H}}_2{\text{O}}_2$$…”

Minimizing the effects of galvanic corrosion during chemical mechanical planarization of aluminum in moderately acidic slurry solutions

“…In addition, if the C 6 H 6 O 6 generated from the bulk reaction adsorbs onto the metal surface, electrode interactions with the adsorbed oxygen would be further restricted by this DHA. However, in the absence of any catalysts, the efficiency of the aforementioned bulk reaction of O 2 with AA should be largely constrained [62,63]. Therefore, a sizable fraction of the [AA] used in the present experiments is expected to remain un-oxidized, although the solution might contain dissolved O 2 .…”

The influence of reducing substances on the oxygen consumption in model solutions.

“…Takové systémy se vyznačují netypickým kinetickým chováním, např. oscilačními reakcemi (Strizhak a Basylchuk 2000). V pomalých reakcích se postupně redukují oxidované formy.…”

“…Such systems are characterized by atypical kinetic behavior, such as oscillating reactions (Strizhak and Basylchuk 2000). The slow reactions will gradually reduce the oxidized forms.…”