Experiments chemical oscillators

Schneider, F. W. (1985). Periodic perturbations of chemical oscillators experiments. Ann. Rev. Phys. Chem., 36, 347-78. 

P. Aroca, Jr., and R. Aroca, Chemical Oscillations A Microcomputer-Controlled Experiment, J. Chem. Ed. 1987,64, 1017 J. Amrehn, P. Resch, and F. W. Schneider, Oscillating Chemiluminescence with Luminol in the Continuous Flow Stirred Tank Reactor, J. Phys. Chem. 1988,92, 3318 D. Avnir, Chemically Induced Pulsations of Interfaces The Mercury Beating Heart, ... 

Further experiments to examine the ion exchange mechanism for the acceleration in the relaxation process of the chemical oscillation were also performed. We varied the kind of hydrophilic anions (Cl , Br and I ) in the oil phase and investigated the dependence of the desorption rate of DS ions on the standard free energy of transfer of those anions. Since the ion exchange should occur at the oil/water interface, we expected that the more the standard free energy of transfer of the anions from the interface to the water phase would decrease, the more efficiently the ion exchange would occur between the hydrophilic anions and DS ions, resulting in the acceleration of the desorption... 

As in the case of Olsen and Degn experiment (1977), a new mode of research as application of new mathematical findings to reevaluate chemical reactions clearly signaled a turning trend in research on chemical oscillations. 

The peroxidase reaction provides another prototype for periodic behaviour and chaos in an enzyme reaction. As noted by Steinmetz et al. (1993), in view of its mechanism based on free radical intermediates, this reaction represents an important bridge between chemical oscillations of the Belousov-Zhabotinsky type, and biological oscillators. In view of the above discussion, it is noteworthy that the model proposed by Olsen (1983), and further analysed by Steinmetz et al. (1993), also contains two parallel routes for the autocatalytic production of a key intermediate species in the reaction mechanism. As shown by experiments and accounted for by theoretical studies, the peroxidase reaction possesses a particularly rich repertoire of dynamic behaviour (Barter et al, 1993) ranging from bistability (Degn, 1968 Degn et al, 1979) to periodic oscillations (Yamazaki et al, 1965 Nakamura et al, 1969 ... 

Hynne, F. Sprensen, P. Quenching of chemical oscillations. J. Phys. Chem. 1987, 91, 6573-6575 Sprensen, R Hynne, R Amplitudes and phases of small-amplitude Belousov-Zhabotinskii oscillations derived from quenching experiments. J. Phys. Chem. 1989, 93, 5467-5474. 

This example shows that mixed-mode oscillations, while arising from a torus attractor that bifurcates to a fractal torus, give rise to chaos via the familiar period-doubling cascade in which the period becomes infinite and the chaotic orbit consists of an infinite number of unstable periodic orbits. Mixedmode oscillations have been found experimentally in the Belousov-Zhabotin-skii (BZ) reaction 2.84 and other chemical oscillators and in electrochemical systems, as well. Studies of a three-variable autocatalator model have also provided insights into the relationship between period-doubling and mixedmode sequences. Whereas experiments on the peroxidase-oxidase reaction have not been carried out to determine whether the route to chaos exemplified by the DOP model occurs experimentally, the DOP simulations exhibit a route to chaos that is probably widespread in the realm of nonlinear systems and is, therefore, quite possible in the peroxidase reaction, as well. 

In these experiments, the volume of the confined gel is constant its main role is to damp hydrodynamical motions that would otherwise perturb the chemical intrinsic patterns. More recently it has been shown experimentally that the coupling of a volume phase transition with a chemical oscillator can generate a self-oscillating gel (i, 4). More precisely, if one of the chemical species taking part in the chemical reaction modifies the threshold for the phase transition, then the time periodic variation of this concentration can generate autonomous swelling-deswelling cycles of the gel even in absence of any external stimuli (5, 6). This device thus provides a novel biomimetic material with potential biomedical and technical applications. 

As chemists have become more sophisticated in their ability to design and understand chemical oscillators, and as they have increasingly sought systems that are relevant to biological processes, oscillatoiy systems with feedback have become an area of growing interest. We describe here experiments (13) and computer simulations (14) on a photosensitive variant of the BZ reaction, in which the catalyst is a ruthenium bipyridyl complex, Ru(bpy)3 (15). 

Noyes and coworkers (Sharma and Noyes, 1975) revived the work of Bray and Liebhafsky in the 1970s and, through careful experiments and mathematical modeling, building on the theoretical groundwork that had been laid by studies of nonequilibrium thermodynamics, succeeded in convincing the chemical community that the Bray reaction represented a genuine chemical oscillator. 

Diode array spectrophotometers can be especially useful because a complete spectrum can be collected in a short interval of time, making it possible to follow several species in a single experiment by taking repeated spectra. Also, several diode array instruments come with an open sample compartment, which makes it relatively easy to construct a flow reactor that can be placed in the light path of the instrument. The metal ion catalysts used in the BZ system absorb in the visible spectrum, so that UV/vis studies of the cerium-catalyzed or ferroin-catalyzed reaction are easy to perform. Iodine is another strongly absorbing species that is found in a number of chemical oscillators. Frequently, iodide ion is present as well, and the system is monitored at the iodine-triiodide isosbestic point at 471 nm. 

Figure 4.8 Systematic design of a chemical oscillator, (a) The fundamental bistable system, with the steady-state concentration of. v shown as a function of the parameter X. Steady states SSI and SSII are two distinct, stable steady states. Dashed line shows third, unstable steady state, (b) The system in part a perturbed by a feedback species z. The actual value of X is A.Q. The arrows indicate effective increase in X caused by the perturbation, (c) Time course followed by x corresponding to the values of Xq and z illustrated in part b. (d) Phase diagram obtained when experiments like that shown in part b are performed at different levels of i. Panel (a) corresponds to r = 0.

It is worth asking whether perturbation methods might yield as much or more information about oscillating reactions, where it might be possible to probe not only constant or monotonically varying concentrations but also amplitude and phase relationships. Schneider (1985) reviewed a variety of model calculations and experiments on periodically perturbed chemical oscillators. The results, which show such features as entrainment, resonance, and chaos, are of considerable interest in the context of nonlinear dynamics, but shed little light on the question of mechanism. 

Vance, W. Ross, J. 1988. Experiments on Bifurcation of Periodic Structures into Tori for a Periodically Forced Chemical Oscillator, J. Chem. Phys. 88, 5536-5546. 

We start with experiments on a multi-variable system, the bromate oxidation of ferroin, [1], also called the minimum bromate oscillator. The bistability and chemical oscillations of this system were characterized in [2]. 

There is a substantial fractional change, a decrease, in the dissipation as chemical oscillations begin to appear. These results of calculations on this simple model have been substantiated by experiments, see Fig. 16.8. 

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