APPLIED PHYSICS – IRRADIATION EFFECTS
THE EXPERIMENTAL STUDY OF CORONA DISCHARGE ON YEAST
(SACCHAROMYCES CEREVISIAE)*
B. OPRESCU, D. GIOSANU, I. NEAGU
The Faculty of Science, University of Pitesti, Pitesti, Romania, Str. Târgul din Vale, Nr. 1,
e-mail: boprescu@yahoo.com
Received December 21, 2004
In this study was observed the influence of positive ions upon three types of
yeast strains. A different evolution for the different doses of irradiated cultures of yeast
is remarked. In the environment there are positive and negative ions, due to natural or
artificial factors (lightning, cable of high voltage, sources of ionising radiations,
electrical discharges with industrial applications, etc.). The living organisms are
differentley influenced by both types of ions. To conclude, the aim of this experimental
study is the possibility to obtain sterilized wines, before bottled, using corona discharge.
Key words: corona discharge, yeast.
1. INTRODUCTION
The living beings are open thermodynamical systems, which permanently
interact with the exterior medium. The continuous change of matter, energy and
information is an indispensable condition for the maintenance of this form of
matter organisation. The action of the environment on living systems could be
positive (by insurance of necessity of water, light and nutritive substances) or
negative (the transfer of energy surplus or toxic chemical substances into
organism).
Electromagnetic interactions dominate in function of biological systems
between the four fundamental forces which action in the Univers (strong, weak,
electromagnetic and gravitational). This kind of interaction is manifested by
statical fields (electric and magnetic), dynamic (electromagnetical radiations) or the
ions exchange between tissue and medium.
The environment is naturally ionisated by cosmic radiations, the radioactivity
of earth and atmospheric radioactivity. This ionisation depends on position
(generally increases with altitude and latitude) and season (with a maximum in
*
Paper presented at the 5th International Balkan Workshop on Applied Physics, 5–7 July
2004, Constanţa, Romania.
Rom. Journ. Phys., Vol. 51, Nos. 1–2, P. 131–140, Bucharest, 2006
132
B. Oprescu, D. Giosanu, I. Neagu
2
spring and directly depending on the solar activity). Another important factor of the
ionised medium is the electrical activity. It is known that before the storm, in the
atmosphere there are many positive ions, and after the storm the number of
negative ions increases.
The environment could be ionisated as well, by the artificial (human) factors,
like radioactive sources, electrical discharges used in industry, the generators of
electromagnetical waves, electrical network of high voltage.
The atmospheric ions carry an important amount of electrostatic energy with
significant biological effects. It was found that about 5 × 10-4 coulomb/sq cm of
such ions incident on Escherichia coli would kill them to 1/e. This amounts to
3 × 108 erg/gm and is about 8 times the amount of ultraviolet energy or 700 times
the amount of X-ray energy required to kill E. coli[1].
Talking about the important role of ions action on living bodies into account,
the aim of this paper is to present an experimental study about the positive and
negative ions on yeast culture.
2. EXPERIMENTAL PARTS
2.1 EXPERIMENTAL DEVICE
Like another electrical discharge in gases, the corona discharge is based on
the ionising of gases molecules and on the extract of electrons from cathode metal.
Due to the sharp form of the electrode, the electrical field is strongly located
around it (see Fig. 1).
600
400
E( r)
200
0
0
5
10
r
Fig.1 – The distribution of electrical field around the filiform electrode.
3
Corona discharge on yeast
133
Because the lines of electrical field are concentrated around the electrode
with short ray of warp, all the excitation and ionising processes for gases molecules
are done in a thin zone around the electrode. For this reason, one remarks that, at
the macroscopical level, the luminescence is only around the sharp electrode.
The carriers with opposite sign with electrical potential applied on filiform
electrode are attracted by this and the carriers with the same sign are rejected.
These rejected carriers go out rapidly from the zone where are done the ionizing
processes (the corona layer, as is called) and come in a zone with a week electrical
field (the external space). In this external space, with geometrical dimensions much
more then the dimensions for corona layer, are a single type of charges carriers. For
this reason we can say that the electric current in this zone is unipolar (different
from the electrical current in corona layer which is bipolar). Due to a week
electrical field the charge carriers from external space move under the
concentration gradient (or draught, eventually) far away from interelectrode range.
So, around corona discharge it be formatted an atmosphere with electrical charge.
In this zone could be different objects (plants, for example).
Depending on the polarity of electrical voltage applied on the electrode with
a big ray of curve, it could be two types of corona electrical discharge: a negative
corona discharge (when the sharp electrode is the cathode) and positive corona
discharge (when the sharp electrode is the anode). These two types of corona
discharge have common characteristics but they have specific peculiarities, too. In
a negative corona discharge the positive ions that are produced nearly the filiform
electrode pull up the electrons from metal. The kinetics energy of electrons formed
in this way is null. So, they have to move some distance in electrical field in order
to be able to produce excitations and then ionizations of gases molecules. For this
reason, the lightly corona isn’t sticked to the cathode surface and begin from some
distance for its. One observed that in these conditions electrical discharge is
discontinuous, like current pulses with the frequency proportional direct with
medium intensity of electrical current. The apparition of these pulses is due to
some electronegative gases around the electrode. The electronegative atoms or
molecules retain a part of electrons and form negative ions. These ions are
collected around the cathode (like a muff of negative electrical charge) due to
reduced mobility of negative ions. This muff of negative electrical charge is
equivalent with a virtual cathode with its rays bigger than the metallic cathode rays.
The increase of cathodically ray causes the decrease of electrical field from the
inner zone and the interruption of ionizing processes, so that the discharge shutting.
After this moment, the conditions are good for the beginning of another electrical
discharge, due to slowly movement of negative ions to cathode. A supplementary
cause of interrupting of electrical discharge by negative ions is the diminuation of
auto-electrical emissions (the extract of electrons from metal is due only to the
electrical field) on micro-peak from the cathode surface due to the deposit of
particles (for example, particles of dust).
134
B. Oprescu, D. Giosanu, I. Neagu
4
For positive corona discharge, the electrical field necessary to beginning the
discharge is much more. The reason for this fact is that the negative ions formed
near cathode are dissociated to anode only for intense electrical field. The free
electron produces an avalanche of excitations and ionisations of gas atoms. This
way, appears a pulse of electrical current, with a luminescent zone just on the
electrode surface. The intensity of electrical field around this filiform electrode
decrease due to accumulation of positive ions, like in the case of negative corona
discharge. So, the electrical discharge is stopped and it begins immediately after
the dispersion of positive charge. As compared to the negative corona discharge, in
positive corona discharge the light is all around the anode surface if the voltage
increases.
If both the anode and the cathode are made of wires with small rays of warp
there will be two corona discharges: one positive and the other one negative. The
exterior space of two electrical discharges will not be a range of unipolar
conduction, but a bipolar one (assured by two types of electrical carriers).
µA
kV
-
+
Fig. 2 – Experimental set-up.
Therefore the corona electrical discharge is well known and intensely studied
for their technological applications (electro-photograph, electro-precipitation, etc.)
the papers about corona effect on living matter are recent and a few. The set-up for
experimental study of corona discharge on yeast culture is like in Figure 2.
The negative electrode was made from a wolfram wire, with 10-2 mm
diameter, introduced in a quartz capillary. The part of wire, out of capilar is the
active electrode, of 1cm long. The positive electrode was made from cylindrical
plate of stainless steel, with 10 cm diameter. The cathode was mounted on the
vernier on a vertical support, so we modified the distance between the electrodes.
The alimentation source for corona discharge could produce continuous voltage to
15 kV. The voltage applied on electrodes was read on an electrostatic voltmeter
and the current intensity on a digital microampermeter.
5
135
Corona discharge on yeast
The biological material put to the test was made from three strains of yeast:
1b1 (prelevated from Fetească Neagră sort of wine), 2b1 (prelevated from Merlot
sort of wine) and 3b2 (prelevated from Merlot sort of wine).
The four experimental variants include a witness lot (unirradiated by corona
discharge). The geometry system was constant; the distance between electrodes
was of 30 mm. The exposition times and the intensity for discharge current are in
Table 1.
Table 1
The experimental parameters
Experimental variant
Exposition time
(minutes)
Current intensity (µA)
V1
5
V2
10
V3
15
15
15
15
One remarks that in such experiments is more important the irradiation dose
(product I x t) than each terms (I or t).
The irradiation doses were established by preliminary experiments, when we
observed the threshold after the effects are significant.
2.2 EXPERIMENTAL RESULTS
The results obtained after corona discharge on three strains of yeast are in the
following table.
Initially, the yeast cultures were in exponential evolution phase.
Table 2
The effect of corona discharge upon the yeast cultures
Stems
1b1
No. cells
x104 /ml
%
No. cells
x104 /ml
2b1
%
3b2
No. cells
x104 /ml
%
100
71,81
63,08
39,59
Time
(min)
0
1284
100
324
100
894
5
1038
80,84
216
66,66
642
10
990
77,10
174
53,70
564
15
954
74,29
126
38,88
354
The numbering of cells was made by using a Thoma camera. The table values
represent a media value obtained from 10 identically probes.
Is it more suggestive if the results are represented graphically (see Figure 3).
136
B. Oprescu, D. Giosanu, I. Neagu
6
120
100
%
80
0 min
5 min
60
10 min
15 min
40
20
0
1b1
2b1
3b2
EXPERIMENTAL VARIANTS
Fig.3 – The dependence of yeast cells by corona irradiation time.
It remarks that the corona irradiation time increases, the number of yeast cells
decreases.
3. INTERPRETATION
The biological cells have lower dimensions as compared with the contact
medium. From this reason, the medium could be considerated a thermodynamic
container for cells.
This means that the state parameters of cells could be modified under the
medium influence. But the medium parameters can’t be modified by the cell
changes. If we consider one-dimensional the interaction medium-cell is easier. This
means that the cell has a single permeable plain wall.
As known, between inside and outside of cell is a difference of potential. We
can admit, by convention, that the medium potential is null and the potential of
inside of cell is –V0.
If in the media around the cell is injected in a certain moment of time
negative ions, they tend to diffuse into the cell. In an infinitesimal layer in
membrane (see Figure 4), the variation speed of ions concentration will be:
X&dz = Φ X ( z ) − Φ X ( z + dz ) ,
because in the volume element the ions are not generated or recombined.
Enlarging the flux in power series and keeping just the terms of first grade,
we obtain:
∂Φ X
X& = −
∂z
(1)
7
137
Corona discharge on yeast
r
E
Media
Inner
cell
Z
ΦX-(z)
0
ΦX-(z+dz)
δ
Fig. 4 – The ions transport through infinitezimal element of membrane cell.
In the electrical field in the membrane the ions transport are made due to the
influence of free diffusion and the drift. So, the ions flux is described by the law:
Φ X ( z) = − DX
∂X
∂V
+ µX X
∂z
∂z
(2)
From (1) and (2) result:
∂2 X
∂X ∂V
∂ 2V
µ
µ
X& = D X
−
−
X
X
X
∂z ∂z
∂z 2
∂z 2
(3)
From Poisson equation, results:
∂ 2V e
= X
∂z 2 ε
In this relation we assume that the ions electrovalence is one. Using the
relation (3) we obtain:
∂2 X
∂X ∂V eµ X X
X& = D X
− µX
+
X
2
∂z ∂z
ε
∂z
(4)
138
B. Oprescu, D. Giosanu, I. Neagu
8
Because we are interested in the evolution of physical parameters inside the
cell, we will rewrite the above equations for the situation when z=δ. In this plain,
the derivate with z of the electrical potential is practically constant.
Obviously, the second derivate with position for the ions concentration has to
be positive, in plain z=δ. We can assume that this derivate is depending linearily on
the difference between the ions concentration in inside and outside of cell. Using
this presumption, we can write:
•
X = a (b − X ) − cX 2
(5)
In this relation a and c are specific parameters for the cell and b represented
the ions concentration in outside of cell.
A last problem is connecting by the variation speed for cellular potential.
Let’s see the factors which determine the variation of this parameter. The speed of
potential variation is directly proportional to the variation speed of ions
concentration, because the cellular potential is proportional to the charge brought
by ions (-Y).
As the cellular potential from physiological equilibrium value involves
supplementary fluxes of essential ions in the determination of membrane potential
(Na+, K+ and Cl- ions). The aim of the migration of these ions (passive or active) is
to remake the equilibrium potential. Like another authors [2], we presume that the
variation speed of membrane potential determined by this factor is proportional
with the difference between the actual potential and the equilibrium potential.
Based on these considerations, we can write the following law of evolution for
cellular potential.
•
•
V = − d (V + V0 ) + e X
(6)
where d and e are two cellular parameters.
Using the equations (5) and (6), we can determine the influence of ions
concentration in the media around the cell upon its potential. The evolutions of ions
concentration inside the cell and of cellular potential are represented in Figures 5, 6
and 7 for three values of ions concentration in media. As we observed, the ions
concentration inside the cell arrives after a time to a stationary value. This fact is
due to the inverse diffusion process (from inside to outside of cell).
For a certain value of inner ions concentration, their flux from inside to
outside of cell compensates the ions flux from outside to inside.
The cellular potential evolves to a stationary value corresponding to
physiological equilibrium (V0=-1on the graphics). Interesting is the fact that for
rapid variations of ions concentration inside the cell the compensation processes of
the modification of physiological equilibrium potential couldn’t maintain a fix
value of it. Due to this impossibility, the cellular potential has a minimum.
9
139
Corona discharge on yeast
1
0.5
X
X, V [a.u.]
0
-0.5
V
-1
-1.5
0
0.5
1
1.5
t [a.u.]
2
2.5
3
Fig. 5 – The X and V dependence by time, for b=1.
6
4
2
X
V
X,V [a.u.]
0
-2
-4
-6
-8
0
0.5
1
1.5
t [a.u.]
2
Fig. 6 – The X and V dependence by time, for b=10.
2.5
3
140
B. Oprescu, D. Giosanu, I. Neagu
10
20
10
V
X
X,V [a.u.]
0
-10
-20
-30
-40
0
0.5
1
1.5
t [a.u.]
2
2.5
3
Fig. 7 – The X and V dependence by time, for b=100.
At the initial moment, the cellular potential is not equal with the potential for
physiological equilibrium (see Figure 5). This fact is due to an instantaneous
apparition of negative ions, at the initial moment, near the cell. From dependence
of minimum of cellular potential by the ions concentration nearly the cell, we can
observe a rapid increase of this parameter with the increase of ions concentration.
This fact could be an explication for the death of cell. If the number of injected
ions are too high in the culture media, at a certain moment, the difference between
the inside and outside cellular potential could be so high so the pressure of ions
from outside or inside the cell could be so high so the membrane will be broken.
This phenomenon, like the electroporosis, could determine the death of cell.
4. CONCLUSIONS
In this paper we observed that the injection of negative ions inside the culture
medium of yeast could lead to the death of cell. The number of death cells is
proportional to the corona irradiation dose. Also, one remarks that the corona
discharge effects on yeast culture depend on type of yeast.
For explication of this fact we modelated the transport through cellular
membrane using a linear differential equations system. Based on this model, the
cells destruction is explained by the broken membrane.
REFERENCES
1. K H Kingdon,Phys. Med. Biol. 5 (July 1960) 1–10.
2. Y. Loewenstein, H. Sompolinsky, Phy. Review, 65, 2002, 051926.
3. B. Oprescu and C. Topală, Revista de chimie (Bucureşti), 55(5), 341 (2004).