Chemical wave in the un-illuminated aminophenol-bromate beads system

Article abstract of DOI:10.1016/j.cplett.2009.06.093

We report observation of slow oscillations and slow waves in the aminophenol system. The system with slow oscillations in the stirred batch reactor does not always exhibit slow waves. The unperturbed system exhibits more than 2 days of wave activity, whil

Full text of DOI:10.1016/j.cplett.2009.06.093

Chemical Physics Letters 477 (2009) 126–129
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Chemical Physics Letters
journal homepage: www.elsevier.com/locate/cplett
Chemical wave in the un-illuminated aminophenol-bromate beads system
Mohammad Harati *
Department of Chemistry and Biochemistry, University of Windsor, Ontario, Canada N9B 3P4
a r t i c l e i n f o
a b s t r a c t
Article history:
We report observation of slow oscillations and slow waves in the aminophenol system. The system with
slow oscillations in the stirred batch reactor does not always exhibit slow waves. The unperturbed system
exhibits more than 2 days of wave activity, while the perturbed system shows about 5 days of wave activ-
ity. The longest lifetime of wave propagation stage and quiescent window were 30 and 11 h, respectively.
Ó 2009 Elsevier B.V. All rights reserved.
Received 23 April 2009
In final form 29 June 2009
Available online 2 July 2009
1
. Introduction
Slow oscillations (SOs) and waves are the subject of ongoing re-
ion-exchange resin (Dowex 50 W-X4) was purchased from the
Fisher Scientific Co. All chemicals were used as received grade
without further purification.
search in biological systems such as waves in the brain and the
nerve systems [1–3]. Chemical reactions may exhibit oscillations
in well stirred conditions. According to the Journal of Neurosci-
ence, slow oscillations are oscillations with frequency of less than
To initiate our 2-D experiment, we started the reaction in a stir-
red batch reactor where the total volume of reaction solution was
fixed at 30 ml in all experiments and it was illuminated with
2
150 mW/cm light until it evolved into oscillatory window. Then
1
Hz [4]. Slow wave may be observed if reaction occurs in non-stir-
we turned off light and transferred the whole sample to a Petri dish
(9 cm in diameter) and mixed with 3.0 (±0.1) g of cation-exchange
resin beads (100–200 mesh) loaded with 0.003 M ferroin. To load
the catalyst ferroin onto the resin, filtered resin was mixed with
ferroin solution and the mixture was stirred vigorously for over-
night. The ferroin solution became transparent at the end of the
process, presumably due to the complete absorption of ferroin by
the cation beads. The mixture was left unstirred for 30 min and
then we removed the solution on top of the beads. Ferroin loaded
beads were washed three more times through adding 60 ml of
doubly distilled water and stirred for 10 min each time. This wash-
ing procedure is useful in removing imperfect beads, i.e., reducing
the amount of beads floating on the top of reaction mixture in the
Petri dish. The Petri dish was maintained at room temperature of
24 ± 1 °C.
red conditions or reaction–diffusion medium. Recent studies found
that Dopamine (DA) plays an important role in the core molecular
mechanism of the circadian clock [4–12]. There was considerable
progress made in characterizing and understanding oscillation
and wave activities in chemical and biological systems in the past
several decades [13–19]. However, there is a significant gap be-
tween these two types of systems, namely that there has been
no clear experimental demonstration of SOs in a simple, controlla-
ble chemical system. Slow oscillations in the aminophenol system
are similar to those in Dopamine. While it remains mysterious how
exactly the information is encoded in DA neurons, evidence sug-
gests that SOs may play a role in the information processing [20].
Slow oscillations and waves in this simple aminophenol system
may shed new light on natural waves and patterns in these biolog-
ical systems.
Evolution of the spatially extended medium was monitored
with a CCD camera equipped with a zoom lens. The CCD camera
was connected to a personal computer running a frame GRABBER
program (Matrox Imaging Library). Images were stored on an
external hard disk for future analysis. The perturbation of light
was implemented with a halogen lamp equipped with dual bifur-
cated optic fibers and continuous variable light level (Fisher Scien-
2
. Experimental
3
Stock solutions NaBrO (Aldrich, 99%), 0.6 M, and sulfuric acid
(
Aldrich, 95–98%), 4.0 M, were prepared with double-distilled
water. 4-Aminophenol (Aldrich, 98+%) was directly dissolved in
the reaction mixture. The volume of the reaction mixture was fixed
at 30.0 ml in all experiments. Ferroin, 0.025 M, was prepared from
2
tific, Model DLS-100HD, 150 mW/cm ). The illumination was
implemented by placing one of the fibers on top of the Petri dish.
a calculated amount of FeSO
nanthroline (Aldrich, 99+%). The analytical grade 100–200 mesh
4
Á7H
2
O (Aldrich, 99+%) and 1,10-phe-
3. Results and discussion
Fig. 1 presents a series of snapshots of slow chemical waves in
the ferroin-aminophenol-acidic bromate system. Our earlier
kinetic studies in a batch reactor show that in the absence of light
*
Present address: Department of Chemistry, The University of Western Ontario,
London, Ontario, Canada N6A 5B7. Fax: +1 519 661 3022.
E-mail address: mharati@uwo.ca
0
009-2614/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.cplett.2009.06.093

M. Harati / Chemical Physics Letters 477 (2009) 126–129
127
Fig. 1. Slow wave activity in aminophenol-bromate system under condition: [bromate] = 0.06 M, [acid] = 1.0 M, [AP] = 0.017 M. Snapshots are taken at: (a) 20, (b) 300, (c)
34, (d) 426, (e) 560, (f) 682, (g) 715, (h) 873, (i) 974, (j) 1057, (k) 1146, (l) 1349, (m) 1383, (n) 1608, (o) 1642, (p) 1916, (q) 1952, (r) 2137, times are in minutes.
3
not only is the uncatalyzed system not capable of showing oscilla-
tory behaviour, but also there is not much progress in the overall
reaction [21,22]. Light is critical to the progress of the reaction
and upon application of an above threshold illumination, sponta-
neous oscillations are obtained [22]. More specifically, turning off
the light in the stirred system resulted in an immediate disappear-
ance of the spontaneous oscillation, unless a high concentration of
ferroin is added to the mixture. However, as we take a sample from
the same reaction mixture and transfer it to a Petri dish filled with
a beads system loaded with ferroin, the medium is capable of sup-
porting wave activity for a very long time even in the absence of
light. For example, under the specified conditions used in Fig. 1,
the system shows wave activity for about 50 h. Notably, after
wave(s) propagate out of the medium, there is a period of time
when there is no wave activity in the reaction–diffusion medium.
To describe wave activity periods and quiescent windows, we will
deem each wave activity period and each quiescent period as one
stage.
As mentioned earlier, in the uncatalyzed bromate-aminophenol
reaction in a stirred batch reactor, if we turn off the light, sponta-
neous oscillations stop immediately. The system exhibited the
same kind of behaviour even if low concentration of ferroin was
added to the stirred batch reactor at the same time as turning off
the light. Yet, if we transfer the system to the Petri dish waves
developed in the beads system loaded with ferroin even in the ab-
sence of light. To gain insight into the above surprising phenome-
non we carried out a series of studies in a stirred batch reactor via
adding ferroin to the reaction mixture after turning off the light.
These experiments showed that when the concentration of ferroin
reaches 0.002 M, the catalyzed system would exhibit low fre-
quency oscillations, SOs. Summary of this systematic study is pre-
sented in Fig. 2.
As it is shown in Fig. 1b once the waves disappeared, the med-
ium exhibited a distinctive, uniform red color indicating that ferr-
oin is in its reduced state. In general, disappearance of wave
activity was believed to be due to the consumption of reactants,
but after awhile, the unperturbed reaction medium showed an-
other wave activity and this scenario is repeated nine times under
the condition presented here. In the photo-controlled aminophe-
nol-bromate system, light creates an exclusive approach of certain
intermediates [22]. Therefore, after transferring the solution to a
Petri dish which is not illuminated, there is not a significant reac-
tivity in the system. Our earlier published results [21,22] also
showed that the nonlinear feedback raises from the autocatalytic
production of HBrO
icals by aminophenol, the same as classic BZ reaction. Conse-
quently, HBrO consumes bromide ions and produces HOBr acid.
2
through the reduction of bromine dioxide rad-
2
Notably, the longest and the shortest stages of pattern propagation
lasted for 240 min and 74 min, respectively; and shortest and lon-
gest quiescent windows (no wave activity) persisted for 72 min
and 225 min, respectively. The illuminated system just showed
one oscillatory stage in the stirred batch reactor and one stage of
wave activity if transferred to a Petri dish containing beads loaded
with ferroin under illumination. In the earlier stages the system
showed multiple wave activity. On the other hand, in the later
stages we only observed single wave propagation through the
medium (Supplementary Fig. S1).
Fig. 2. Time series of aminophenol-bromate system under condition: [bro-
mate] = 0.06 M, [acid] = 1.0 M, [AP] = 0.016 M, concentration of added ferroin is
À4
À3
(
a) 5 Â 10 M and (b) 3 Â 10 M. ferroin added to the system immediately after
turning off the light.

1
28
M. Harati / Chemical Physics Letters 477 (2009) 126–129
Propagation speed of the waves under different concentrations
of reagents is presented in Fig. 3. The propagation speed was
measured in each stage and there was a minuscule decrease in
the speed as the reaction evolved in time (Fig. S2). The propagation
rate increases as the concentration of bromate or acid increases,
but decreases with the increase of aminophenol concentration. In
all cases, wave propagation speeds slowed down in each subse-
quent stage. The lifetime of each stage of wave activity decreases
with the longest lifetime of 30 h for the first stage (presented in
Supplementary Fig. S3). Our investigations, i.e., conditions with
moderately higher bromate or acid concentration shown in
Fig. 3a or b, demonstrated that SO does not always induce slow
(
low frequency) wave in the reaction–diffusion medium. It might
show high frequency waves instead.
The lifetime of a quiescent window, the stage at which the med-
ium does not have wave activity, has a reverse relationship in com-
parison with the lifetime of wave activity. The last quiescent
window was the longest one in each experiment and can last for
up to 11 h, depending on the reaction conditions (please see S4).
Illuminating the system for a short time, 1 min, during wave activ-
ity causes lots of wave activity in just one stage (detailed results
presented in Fig. 4).
Light perturbation studies have been carried out using two dif-
ferent strategies: first we examined the influence of illumination
on existing wave activity. As shown in Fig. 4, we illuminated the
system with one fiber for 60 s with a light density of 100 mW/
2
cm . At the beginning, it seemed that light quenched wave activity
(
see Fig. 4c). However, after a short time, the system exhibited
wave activity at the illuminated place which ended up forming a
pair of spirals. This newly formed spiral eventually dominated
the whole medium in which the high frequency waves lasted for
about 35 h. Notably, the un-illuminated system shows several
stages of wave activity. However, when illuminated by light and
after the death of the formed spiral wave, the system did not exhi-
bit further wave activity. The system exhibited the same behaviour
when the illumination was as short as 10 s, indicating that the ami-
nophenol oscillatory system is highly photosensitive.
Fig. 3. Plot of the propagation speed versus (a) bromate, (b) acid, and (c)
aminophenol concentration, M, under condition: (a) [acid] = 1.0 M and
[
AP] = 0.016 M, (b) [bromate] = 0.06 M and [AP] = 0.016 M, and (c) [bro-
mate] = 0.06 M and [acid] = 1.0 M, in which (e) First, (j) second, (
D
) third, (Â)
fourth, (+) fifth, (ꢀ) sixth, (j) seventh, (N) eighth, (Ã) ninth, (d) tenth, and (–)
eleventh stage.
The second protocol was to illuminate the system when the
medium did not exhibit wave activity. Note that the light intensity
and illumination time were the same as those employed in the first
protocol. After illuminating the system locally for 60 s, one propa-
gating wave initially appeared (S5d). When this single propagating
wave moved out of the Petri dish and the system moved to a
Fig. 4. Light perturbation experiment under the condition: [bromate] = 0.06 M, [acid] = 1.0 M, and [AP] = 0.016 M, light intensity = 100 mW/cm2 and just one fiber used for
illumination. Images are taken after (a) 158 min, (b) 159 min, (c) 160 min, (d) 161 min, (e) 179 min, and (f) 218 min of injecting reaction solution in the Petri dish.

M. Harati / Chemical Physics Letters 477 (2009) 126–129
129
quiescent window as seen in S5f, the system showed another prop-
Acknowledgements
agating front after a brief period of delay and continued to exhibit
slow wave activity similar to the scene in Fig. 1. To test the behav-
iour of the light-induced wave activity, we illuminated the system
for the second time in the same manner as the first protocol. The
system formed a spiral with just one stage of wave activity, similar
to the behaviour shown in Fig. 4. The way that the system responds
to light illumination did not change in the 110 h following the
spreading of the reaction mixture into the beads-filled Petri dish.
Note that when the system was illuminated during the quiescent
period, high frequency waves did not form and each time just
one propagating front formed. Furthermore, light-induced waves
can be obtained, even 3 days after the disappearance of the last
stage, i.e., there are 5 days of wave activity in total.
I would like to thank financial support from National Science
and Engineering Research Council (NSERC), Canada, and Canada
Foundation for Innovation (CFI).
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.cplett.2009.06.093.
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