Transcript PowerPoint Presentation - BZ History and Overview of Chemical

BZ History and Overview of
Chemical Oscillators at Brandeis
Irv Epstein
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What is the BZ?
• Named for discoverer (Boris Belousov)
and developer (Anatol Zhabotinsky)
• Bromination and oxidation of an organic
substrate (e.g., citric acid, malonic acid) by
bromate in acidic (usually sulfuric acid)
solution in the presence of a metal ion
catalyst (e.g., cerium, ferroin, Ru(bipy)3)
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(as of 1991)
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The Lotka (-Volterra) model
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A + X  2X
X + Y  2Y
YP
A = food, X = prey, Y = predator, P = dead
With A fixed, gives periodic, antiphase
oscillations of predator and prey for any set of
rate constants
Can be solved analytically
Attractor is not a limit cycle, but a continuous set
of orbits around a neutrally stable center (bad)
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Do chemical oscillators violate
thermodynamics?
• A serious question until the 1970’s
• A chemical oscillator is not a pendulum – it
doesn’t pass through equilibrium
• Prigogine – irreversible thermodynamics –
must be far from equilibrium
• In a closed system (beaker), oscillations
must necessarily be transient
• Can maintain oscillations indefinitely in an
open system (flow reactor, organism)
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BZ history
• Discovered by Belousov in the Soviet Union in
1951 accidentally while searching for a model of
the Krebs cycle
• Unable to publish in refereed journals, B
publishes 1-page abstract in 1958 conference
proceedings, circulates recipe and manuscript to
colleagues in Moscow
• In 1961, Zhabotinsky repeats experiments, goes
on to develop mechanism, find chemical waves
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BZ history (cont’d)
• Zhabotinsky publishes papers in 1960’s in
Russian journals, but largely ignored
• In 1968, Zhabotinsky demonstrates reaction
at Prague conference on biological and
biochemical oscillators, catching the
attention of Western scientists
• In 1971, Field, Koros and Noyes develop
the FKN mechanism and F&N simplify it to
the Oregonator model
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What’s so special about the BZ?
• Can run for many (hundreds) of cycles in a
closed system
• Reactants are cheap, easily obtainable (but not
biocompatible)
• Convenient time scale (minutes)
• Oscillations easily monitored visually,
spectrophotometrically, potentiometrically
• Can be controlled photochemically
• Rich variety of spatial and temporal phenomena
• Good mechanism/model (FKN/Oregonator)
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Chemical Oscillators at Brandeis
• 1970’s – experiments with undergrads on
perturbed and modified BZ reactions (Jacobs,
Kaner, Heilweil)
• 1980’s – first systematically designed chemical
oscillators (Kustin, De Kepper, Orban),
mechanistic studies
• 1990’s – increasing focus on spatiotemporal
behavior (Lengyel), interaction with
neuroscientists (Marder), Zhabotinsky arrives
• 2000’s – patterns in microemulsions (Vanag),
coupled oscillators via microfluidics (Fraden)
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Coupled BZ Oscillators
M. F. Crowley and I. R. Epstein, "Experimental and Theoretical Studies of
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a Coupled Chemical Oscillator: Phase
Death, Multistability and In- and
Out-of-Phase Entrainment," J. Phys. Chem. 93, 2496-2502 (1989)
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Hexagonal closed packing 2D arrays
I.
X
II.
0
160
Drop Intensity (a.u.)
time
in sec
140
80
165
240
80
85
75
6
7
5
7
6
5
7
6
5
7
6
5
7
6
120
100
80
60
40
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time
BZ double emulsion
dimer
100 mm
tetrahedron
time 70 min
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Beyond the BZ – the CSTR
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Beyond the BZ –
Taxonomy of chemical oscillators
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Another system – CIMA/CDIMA
• Chlorite-iodide-malonic acid (chlorine dioxideiodine-malonic acid)
• Batch oscillator, discovered at Brandeis (IRE, De
Kepper, Orban) in 1982
• Used in first successful experiments on Turing
patterns (Castets, De Kepper, 1990)
• Key is use of gel, starch indicator to get
separation of effective diffusion coefficients
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Structured media – the future
• Limitations of aqueous solution –
convection, no chemo-mechanics, all D’s
nearly equal, can’t make a flow reactor
• Instead use surfaces, membranes, beads,
microemulsions, droplet arrays, gels
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