Spontaneous Formation of Cellular Chemical System that Sustains Itself far from Thermodynamic Equilibrium

Article abstract of DOI:10.1021/jp036417j

We report the observation of the spontaneous formation of a cellular structure in a simple inorganic system. The system is obtained by immersing a pellet of calcium and copper chlorides in an alkali solution containing sodium carbonate, sodium iodide, and hydrogen peroxide. The system produces a cell surrounded by a semipermeable membrane. Reactants diffuse and react inside the cell with copper ions serving as catalyst. The products diffuse out of the cell. The system sustains itself far from thermodynamic equilibrium.

Full text of DOI:10.1021/jp036417j

© Copyright 2004 by the American Chemical Society
VOLUME 108, NUMBER 16, APRIL 22, 2004
LETTERS
Spontaneous Formation of Cellular Chemical System that Sustains Itself far from
Thermodynamic Equilibrium
Jerzy Maselko*,† and Peter Strizhak*,‡
Department of Chemistry, UniVersity of Alaska, Anchorage, Alaska 99508, and L.V. PisarzheVskii Institute of
Physical Chemistry, National Academy of Sciences of Ukraine, pr.Nauki 31, KieV 03039 Ukraine
ReceiVed: August 13, 2003; In Final Form: December 4, 2003
We report the observation of the spontaneous formation of a cellular structure in a simple inorganic system.
The system is obtained by immersing a pellet of calcium and copper chlorides in an alkali solution containing
sodium carbonate, sodium iodide, and hydrogen peroxide. The system produces a cell surrounded by a
semipermeable membrane. Reactants diffuse and react inside the cell with copper ions serving as catalyst.
The products diffuse out of the cell. The system sustains itself far from thermodynamic equilibrium.
Patterns in nature are formed spontaneously in systems which
are exposed to energy and matter fluxes. These systems sustain
themselves far from thermodynamic equilibria. In these systems,
the temporal and spatial structures may appear spontaneously
and complexity increases. Experimental studies of these patterns
are conducted in chemical reactors where chemicals flow in,
react, and flow out. In biological systems, membranes forming
the cell separate the system from its surroundings. Chemicals
diffuse in and react, and products diffuse out. These constitute
examples of systems which are far from equilibrium. Here we
report the spontaneous formation of a similar system.
A pellet of calcium chloride (the weight of the pellet is 0.20
g with a diameter of 6.0 mm. The pellet has been prepared using
Perkin-Elmer press) immersed in a solution of 1.5 M of sodium
carbonate produces a cell surrounded by a semipermeable
membrane as shown in Figure 1. This membrane is transparent
and elastic.1,2 The omposition of the membrane may be
Figure 1. Formation of a membrane when a pellet of calcium chloride
is submerged in a solution of 1.5 M of sodium carbonate. The weight
described as Cax(CO3)y(OH)z(H2O)V and a detailed structure is
still unknown. Because of osmotic pressure, water diffuses into
of the pellet is 0.20 g with a diameter of 6.0 mm. The picture was
the cell, and the cell grows, to about 1.0 cm in diameter. The
taken 1 h after mixing all reagents. The pellet is dissolved and only a
membrane surrounding the cell is visible.
* To whom correspondence should be addressed. E-mail: afjm1@
uaa.alaska.edu (J.M.) or pstrizhak@hotmail.com (P.S.).
cell may produce daughter cells that separate from the mother
cell or may form a structure with many cells connected together.
† University of Alaska.
‡ National Academy of Sciences of Ukraine.
10.1021/jp036417j CCC: $27.50 © 2004 American Chemical Society
Published on Web 03/26/2004

4938 J. Phys. Chem. B, Vol. 108, No. 16, 2004
Letters
Figure 2. Formation of a membrane when a pellet of calcium chloride
with copper chloride is submerged in a solution of 1.5 M of sodium
carbonate containing hydrogen peroxide, sodium iodide, and starch.
The weight of the pellet is 0.20 g with diameter of 6.0 mm. The pellet
contains 7% copper(II) chloride. The initial concentrations of the
reagents in the solution are the following: 0.08 M sodium iodide and
0.08 M hydrogen peroxide. 10 mL of 2% soluble starch solution was
added to the solution. The total volume of the system is 250 mL. The
violet “clouds” made by the complex of iodine with starch are visible.
Copper causes the green color inside the cell. The picture was taken
10 min after mixing all reagents.
Figure 3. Kinetic curves showing the iodine formation. Recording
started after addition of a solution. The initial concentrations of the
reagents in the solution were as follows: (a) 0.17 M sodium iodide,
0.17 hydrogen peroxide, (b) 0.17 M sodium iodide. 1 mL of 2% soluble
starch solution was added into the solution (volume 24 mL). Absorbance
was measured by a CECIL CE2041 Spectrometer at the wavelength of
504 nm. Thin noisy curves represent experimental data. Thick smooth
curves give their exponential approximation.
In the simplest way, the chemical transformations inside the
cell are the following set of reactions:12-17
The detailed mechanism of cell growth is unknown. Only
recently the initial studies on structures mechanism have been
conducted.3,4 Pictures taken by the Zeiss LSM 510 confocal
microscope suggest that when the surface of the cell is broken
under internal pressure, the solutions from inside and outside
mix producing a new segment of membrane. It has been
discovered that water and various small molecules may diffuse
easily through the membrane, whereas large molecules, such
as ferroin (the complex of iron(II) with 1,10-phenantroline) do
not diffuse. The spontaneous formation of cells surrounded by
a semipermeable membrane is a crucial step in the origin of
life and until now it has only been studied in organic sytems.5,6
Contrary to these studies, in the system reported here, a cell is
formed by common inorganic components. The origin of life
starting from inorganic compounds7-9 as opposed to organic
compounds10,11 should receive increased attention.
If the calcium chloride is doped with copper(II) chloride and
the solution also contains sodium iodide and hydrogen peroxide,
then the semipermeable membrane is also formed as shown in
Figure 2. In this case, we found iodine outside the cell. Starch
was added to the initial solution to visualize the formation of
iodine, a product of the reaction. If the pellet consists only of
calcium chloride, then no iodine formation is observed. The
mechanism of iodine formation appears to follow the following
steps. The reactants, iodide ions and hydrogen peroxide, diffuse
into the cell. They react inside the cell producing iodine and
hydroxyl ions. The process is catalyzed by copper(II) ions inside
the cell. The products diffuse out of the cell. We cannot also
exclude that transport of the reagents and products occurs also
due to convection. It is worth noting that the chemical reaction
occurs only inside the cell. Elemental iodine is not produced if
we form a precipitate by mixing solutions of copper(II) chloride
and sodium carbonate and add into it proper amounts of
solutions containing sodium iodide and hydrogen peroxide.
Moreover, we have not observed the I2 formation in those
experiments when there was no cell formation. These observa-
tions support our assumption that iodine is formed inside the
cell.
Cu2+ + I- f Cu+ + 1/2I2
Cu+ + H2O2 f Cu2+ + OH• + OH-
OH• + I- f OH- + 1/2I2
(1)
(2)
(3)
The net reaction is
H2O2 + 2I- f I2 + 2OH-
(4)
According to this mechanism, iodide ions and hydrogen peroxide
diffuse into the cell. There, iodide ions interact with copper(II)
ions producing elemental iodine and copper(I). Copper(I) reacts
with hydrogen peroxide, recovering copper(II) and producing
a hydroxyl radical and a hydroxyl anion. The hydroxyl radical
reacts with iodide producing more iodine. Finally, iodine diffuses
out of the cell. The actual process undoubtedly consists of a
larger number of reactions and events leading to iodine
production and cell growth. Among them, there are reactions
releasing oxygen from hydrogen peroxide and reactions with
oxygen catalyzed by copper(II),15 iodine hydrolysis producing
hypoiodous acid and it reactions,18 and the iodide-catalyzed
decomposition of hydrogen peroxide.19 Details of the whole
mechanism may be found elsewhere.12-19 Particularly, it directly
relates to the iodine clock reaction. However, there are two main
reactions that are responsible for the whole process: the copper-
(II) interaction with iodide and the copper(I) interaction with
hydrogen peroxide.
Curve (a) in Figure 3 gives the kinetics for the iodine
accumulation measured by the absorption at 504 nm due to the
iodine complex with starch. The reaction is characterized by
induction time before the appearance of a jump in absorption.
The induction time corresponds to the growth and development
of the cell. A part of the kinetic curve may be described by
first-order kinetics.

Letters
J. Phys. Chem. B, Vol. 108, No. 16, 2004 4939
formation of a cellular system that sustains far from thermo-
dynamical equilibrium. We produced this system by submersing
a pellet containing calcium and copper(II) chlorides into a
sodium carbonate solution that also contains sodium iodide and
hydrogen peroxide. Our chemical system is constructed from
two subsystems: (1) a pellet containing calcium and copper
chlorides submersed into a sodium carbonate solution producing
a cell with a semipermeable membrane and (2) oxidation of
iodide ions by hydrogen peroxide catalyzed by copper(II) ions.
The evolution of the first subsystem produces a separate
compartment in a chemically reactive medium in such a way
that it creates a flux of reagents into the cell. The catalytic
process occurs into the cell, and products diffuse outside.
Therefore, the system maintains by itself the flux of energy and
chemicals and is sustained far from thermodynamic equilibrium.
This system may produce multicellular chemical structures, and
separation of daughter cells form the mother cell has been
observed. It is probable that a variety of inorganic systems could
be constructed showing the same kind of behavior that we
reported here. The spontaneous formation of cellular chemical
systems that are sustained far from equilibrium may be an
important step in understanding the possibility of the formation
of different forms of life on other planets under other condi-
tions.20
Acknowledgment is made to the donors of the Petroleum
Research Fund, administered by the ACS, for partial support
of this research and to the National Research Council, Twinning
Program Grant.
Figure 4. Dependence of the rate constant on a copper concentration
in pellet. Experimental details are the same as indicated in Figure 3.
C(t) A(t) ) A∞(1 - exp(-kefft)) where C(t) gives the iodine
concentration, A is the absorption at time t, and keff is an effective
rate constant. The smooth curve (a) in Figure 3 gives an
exponential approximation of the experimental data. Despite the
noisy characteristics of the experimental points, the exponential
curve gives a relatively good quantitative description. Therefore,
the value of keff characterizes the rate of the chemical process.
As a comparison, curve b in Figure 3 gives the kinetic curve
for the system without hydrogen peroxide. The rate of the
process is much slower, and the final iodine concentration is
an order of magnitude less, compared to the system with
hydrogen peroxide. Therefore, atmospheric oxygen affects the
system, leading to the production of iodine. However, the
amount of iodine and the rate of its accumulation are negligible
compared to the system containing H2O2.
References and Notes
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According to the chemical reactions described, the value of
keff would be expected to be proportional to the catalyst
concentration. Therefore, the value of keff should increases with
an increase of the copper content in the pellet. This agrees with
the experimental results shown in Figure 4. These data indicate
of the existence of a threshold for the copper(II) contamination
in the pellet below which the rate of the iodine production is
comparable to the system without hydrogen peroxide. Possibly,
the appearance of such a threshold is a consequence of complex
kinetics for the chemical process as well as for the cell growth.
Our studies show, for the first time, an example of the
heterogeneous chemical composition that exhibits spontaneous
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