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The Zhabotinsky Reaction as a Model of Pattern Formation

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Automatisierte Medienanalyse

Erkannte Entitäten
The Zhabotinski-reaction depends on simple chemical compounds triggering off a complex redox reaction.
Bromate ions serve as oxidants.
Bromide ions inhibit the oxidation reaction.
On adding bromide, the brown colour indicates release of bromine. Malonic acid is the third reactant.
The entire reaction is sustained by the decarboxylation of malonic acid. The solution decolourizes - as shown in slight time lapse - within
a matter of minutes, as bromine continues to react. Finally, ferroin is added as redox catalyst.
Its chemical name is phenanthrobe ferrous sulphate. This compound catalyses the oxidative decarboxylation of malonic acid.
The homogeneous mixture is poured out into a thin layer. The catalyst changes its stage of oxidation periodically. As phenanthroline ferrous sulphate it is orange coloured; as phenanthroline
ferric sulphate it is pale blue. It serves as a redox indicator. Throughout the homogeneous solution, points of origin arise and produce pale blue rings, which are succeeded by broader orange-coloured rings - shown here in slight time lapse. The propagation of the rings depends on the interplay of diffusion and reaction between the redox reactants. Like colours correspond to like states of oxidation. In the middle, two centres lie close together. The rings emanating from them approach one another, and rings of the same colour merge. The rings produced by different centres are of various breadths, depending on the various reaction and diffusion velocities. The bubbles result from the CO 2 produced during the reaction. The two centres in the upper part of the picture are producing narrower rings at shorter intervals. During the course of the experiment, the centres with the narrowest rings impart their reaction velocity to the other centres. They function as pacemakers. At the outset of the experiment, the entire fluid layer is in the same state of oxidation. Therefore the colour change affects the whole area at once. Due to autocatalytic reactions, differences in reaction velocity between neighbouring regions gradually occur, giving rise to the patterns. Let us now observe a single pacemaker centre, marked with a black ring. Lower time-lapse frequency clearly shows the periodic colour changes: the pacemaker oscillates. Oscillations can also be observed at every other part of the picture. Systems of the Zhabotinski type are characterized by the occurrence of pacemaker centres as well as by the wavelike propagation of chemical reactions. They are crosslinked, coupled and autocatalytically regulated. The oscillations persist only as long as chemical energy is available. In producing it, malonic acid is used up and CO 2 released. Once a chemical equilibrium has been achieved, the patterns disappear. On account of the necessary energy flux we refer to them as dissipative patterns. Biological systems also exhibit analogous processes, particularly during morphogenesis, as these film sequences produced in 1963 show. During the aggregation stage
of the slime mould Dictyostelium pacemaker centres are formed and
give rise to concentric waves.
This process is shown repeatedly in time lapse.
Amoeboid cells
migrating to a number of aggregation centres produce the wave
pattern by rhythmical changes in their cell form.
At higher magnification, the rhythmical extension and
contraction of the individual amoebae towards the pacemaker centre at bottom right is clearly recognizable. Extension is induced by cyclical AMP being produced periodically at the pacemaker centre. The wavelike
distribution of cyclic AMP, which is due to autocatalytic processes,
is the chemical basis of this amoeboid aggregation.
Chemische Reaktion
Propagation <Chemie>
Bukett <Wein>
Chemische Verbindungen
Homogenes System
Systemische Therapie <Pharmakologie>
Chemische Nomenklatur
Setzen <Verfahrenstechnik>
Chemischer Prozess
Chemische Energie
Hydroxybuttersäure <gamma->


Formale Metadaten

Titel The Zhabotinsky Reaction as a Model of Pattern Formation
Alternativer Titel Die Zhabotinsky-Reaktion als Modell einer Musterbildung
Autor Hock, Bertold
Bolze, Alfred
Mitwirkende Trude Hard (Redaktion)
Horst Wittmann (Kamera und Schnitt)
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DOI 10.3203/IWF/C-1473eng
IWF-Signatur C 1473
Herausgeber IWF (Göttingen)
Erscheinungsjahr 1983
Sprache Englisch
Produzent IWF (Göttingen)
Produktionsjahr 1980

Technische Metadaten

IWF-Filmdaten Film, 16 mm, LT, 99 m ; F, 9 min

Inhaltliche Metadaten

Fachgebiet Chemie
Abstract Dissipative patterns form in originally simple chemical compounds. Starting from pacesetting centers, chemicalwaves of a redox reaction are transmitted. This can be seen in the change in color of a redox catalyst. The decarboxylation of malonic acid drives the total reaction. Pattern formation in the aggregation of Dictyostelium proceeds analagously (film/photos in cooperation with G. Gerisch, 1963).
Schlagwörter synergetics / Zhabotinsky reaction
dissipative pattern / Zhabotinsky reaction
pattern formation / Zhabotinsky reaction
Zhabotinsky reaction
cell biology

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