BZ boot camp 1

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) modelA + X 2XX + 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 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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0 80 165 240

80 85 75

II.

I.

60 70 80 90 100 110 12020

40

60

80

100

120

140

160

Dro

p In

tens

ity (a

.u.)

time (min)

drop number

2 3 4

5 5 5 56 6 6 6 67 7 7 7 7

time

X

time in sec

Hexagonal closed packing 2D arrays

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BZ double emulsion

100 mm time 70 min

dimer

tetrahedron

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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 dioxide-

iodine-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