PowerPoint Presentation - BZ History and Overview of Chemical

Report
BZ History and Overview of
Chemical Oscillators at Brandeis
Irv Epstein
BZ boot camp
1
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)
BZ boot camp
2
BZ boot camp
3
(as of 1991)
BZ boot camp
4
The Lotka (-Volterra) model
•
•
•
•
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)
BZ boot camp
5
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)
BZ boot camp
6
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
BZ boot camp
7
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
BZ boot camp
8
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)
BZ boot camp
9
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)
BZ boot camp
10
BZ boot camp
11
Coupled BZ Oscillators
M. F. Crowley and I. R. Epstein, "Experimental and Theoretical Studies of
BZ boot camp
a Coupled Chemical Oscillator: Phase
Death, Multistability and In- and
Out-of-Phase Entrainment," J. Phys. Chem. 93, 2496-2502 (1989)
12
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
BZ boot camp
13
time
BZ double emulsion
dimer
100 mm
tetrahedron
time 70 min
BZ boot camp
14
Beyond the BZ – the CSTR
BZ boot camp
15
Beyond the BZ –
Taxonomy of chemical oscillators
BZ boot camp
16
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
BZ boot camp
17
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
BZ boot camp
18

similar documents