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TRANSPORT OF IONS THROUGH BIOMEMBRANES Ph. D. THESIS By Nisar A. Bulla Department of Chemistry Aligarh Muslim University Aligarh (India) 1995

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Page 1: TRANSPORT OF IONS THROUGH BIOMEMBRANES · control, the cell utilizes a delicate membrane of about 70 A thick. At one time, the transport of materials across the mem branes was considered

TRANSPORT OF IONS THROUGH BIOMEMBRANES

Ph. D. THESIS By

Nisar A. Bulla Department of Chemistry

Aligarh Muslim University Aligarh (India)

1995

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T^(^3S

2 0 FEB 1995

/.) rivi A

r 3

T4639

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TO MY BELCVED MOTHER

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DEPARTMENT OF CHEMISTRY ALIGARH MUSLIM UNIVERSITY A L I G A R H—202 002

Dated. 0 4 . 0 5 . l y 9 5

C E R T I F I C A T E »••••*#•»•*«••**»•»*•

This is to certify that the thesis

deals with an original piece of research

work and is suitable for the submission

for the award of the Ph.D. degree.

CProf. Nurul Islam) Ph.D. (New York)

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A C K N O W L E D G M E N T

I would like to express my gratitude to my supervisor,

Prof. Nurul Islam and to Dr. Hasan Arif for helping me

during the progress of the work embodied here.

I am also thankful to my laboratory colleagues for

their cooperation.

Finally, I must express my deep sense of gratidute to

my mother and elder brothers without whose inspiration this

work would not have been possible.

[ NISAR A. BULLA ]

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ABSTRACT

The electrical conductance, capacitance, and impedance

of aqueous solutions of several electrolytes, viz., NaCl,

NaF, NaNO^, Na^SO^, KF, KNO^, K^SO^, KCi, CaCl^, MgCl^, FeCl^,

CrCl„, CuCl and CoCl_ were recorded across the peritoneal

membrane of buffalo (Bof. bubalis) aged between 18-24 months

in a thermostated bath of + 0.1 thermal stai-ility. Such

measurements were made for several concentrations of each of

these electrolytic solutions at several temperatures : 15, 20,

25, 30 and 35 C. The specific conductances have been found to

increase with increase in the concentration of each of the

above electrolytes. These values (i.e., specific conductance)

have also been found to increase with increase in temperature.

The absolute reaction rate theory has been applied to evaluate

the enthalpy-, the free-energy, the entropy-, and the energy-

of activations : /:SH^, /^¥^, AS"^ and Ea.

Similarly, the values of capacitance have been found to

increase with increases in electrolytic concentration and tem­

perature. The values, however, have been found to decrease

with an increase in the applied frequency over the range :

lO^Hz to lO^Hz.

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It is noteworthy that unlike the behaviour of specific

conductance and capacitance, the values of impedance have

been found to decrease with an increase in the concentration

of the electrolyte and just like capacitance, the impedance

values decrease with an increase in the applied frequency.

It has been found that the permeation of ions across the

peritoneal membrane takes place easily with an increase in the

electrolyte concentration. Such a behaviour may be ascribed

to the accumulation of ions within the membrane as well as to

the electrical double layer at the membrane/electrolyte in­

terface which seem to control the diffusion processes. It has

also been noted that the diffusion of ions across the biomem-

brane turns out to be selective in nature in allowing certain

ions with more ease than those of the others. The preferential

permeation of ions as well as diffusion of solvent and solvated

entities in a controlled manner seem to be responsible/essential

for the vitality of biological systems comprising essentially

of a large number of cells/cell membranes directly involved in

controlling the flow of much needed ionic or molecular entities

for the growth and maintenance of living beings. The prelimi­

nary investigations carried out here may throw some light on

these aspects eventhough a thorough study is required for con­

clusive theoretical formulation.

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CHAPTER - I

C O N T E N T S

General Introduction

PAGE NO.

1 - 1 4

CHAPTER - II Electrical Conductances of

Ions Across Peritoneal

Membrane.

AND

Application of Absolute

Reaction Rate Theory to

Conductances.

15 - 49

CHAPTER - III Resistance, Capacitance,

Impedance, and Electrical

Double Layer.

50 - 68

References 69 - 79

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C H A P T E R - I * • * * • * * • • * * * • • * » • ) » • • *

GENERAL INTRODUCTION

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The study of transport of ions through membranes have

acquired much importance during the last few decades. An

enormous increase in the study of biological membranes in

several related areas like physiology, biochemistry, biophysics,

anatomy, medicine, pathology and pharmacology has been noted.

Eventhough, the transport behaviour has been investigated in

several systems as such but the processes like oxidative meta­

bolism, protein synthesis and several other synthetic processes

seem to be apparently intimately connected with as well as

dependent on the membrane processes.

It is well known that membranes of varying degrees of per­

meability and semipermeability are found in plants as well as

in animals. These membranes turn out to be devices which help

in regulating the material flow across them essential for the

sustenance of life. A membrane, therefore, acts as a barrier

to prevent the mass movement of ionic or molecular species but

allows only the restricted and/or regulated passage of one or

several types of species through it.

Membranes may be broadly classified into two types :

natural and artificial. The natural membranes are found in

living organisms, such as those of the cells (cell membrane,

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: 2

organelle membrane and myelin membrane) or those covering

the viscera (viz., duramater, pericardium, peritoneum, etc.).

Concerning the physico-chemical nature of these membranes,

they may be treated as non-covalent having supra-molecular

structure with amorphous or solid state of aggregation at

the temperature at which they normally operate.

The artificial membranes are prepared in the labora­

tories from various substances such as lipids, ion exchange

resins, inorganic substances, etc. Similarly, several other

membranes like parchment supported and cellophane types have

also been prepared artificially. In addition to these, few

membranes are also prepared by extracting the constituents

of biomembranes, e.g., monolayer and bilayer lipid membranes

(BLM) which have been employed in such studies in recent

years (1 - 6). Similarly, some of the complex membranes have

also been reported earlier (7 - 13).

Structure of Biomembranes : Natural or the biomembranes

existing in the biological systems are considered to be built

of several/simple fundamental unit membrane structures consis­

ting of oiomolecular leaflets of lipids with their polar groups

oriented towards the two aqueous, the extracellular and the

intracellular, phases of the cell, while the protein part may

be found close to the polar heads of the leaflets U 4 ) .

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The activity of a biomembrane may be understood in terms

of its structural organisation (15). According to Davson and

Uanielli, the membrane consists of a continuous hydrocarbon

phase contributed by the lipids and later on Robertson (16)

made modifications by proposing that the membrane consists of

a bilayer of mixed polar lipids, with their hydrocarbon chains

oriented inwards to form a continuous hydrocarbon phase and

their hydrophillic heads oriented outwards. Each surface was

thought to be coated with a molecular layer of protein mole­

cules, with the polypeptide chains in the extended form.

Later on, Singer and Nicholson (17) proposed the 'Fluid

Mosaic Model' according to which the phospholipids are arran­

ged in a bilayer to form a fluid, liquid-crystalline matrix

or a core. The individual lipid molecules of bilayer move

laterally which, in turn, may account for some of their phy­

sical behaviour like fluidity, flexibility and a characteri­

stically high electrical resistance as well as relative

impermeability to highly polar molecules. The various membr­

anes being globular in nature may form a mosaic - like

structure in the otherwise fluid phospholipid bilayers. Such

a mosaic type arrangement is not a fixed or a static one but

rather seems to have some dynamic equilibria between several

possible structural entities. Such a fluid mosaic model

accounts for the electrical properties and the permeability

of membranes. In addition, it also accounts for the observa-

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tion that some of the protein components of the cell membranes

are found to move in a plane of the membrane at a rather higher

rate.

Composition : The biomembranes are composed of mainly

lipids, proteins and carbohydrates in variable proportions.

The sugar residues are attached to either lipids or protein

components or to both of them. Most of the biological membra­

nes contain around 40^ lipids and close to 60% proteins and

such a composition varies from membrane to membrane which

itself depends on the age of the animal. The membrane proteins

have been classified into extrinsic and intrinsic proteins (18)

Furthermore, the intrinsic proteins that protude all the way

through the membrane are known to provide structural channels

or pores through which water soluble substances, especially,

the ions can diffuse between the extracellular and intracellu­

lar fluid. However, these cause preferential diffusion of

some of the substances more than those of the others, while

some of them also act as a carrier protein for the transport

of the substances that are too large to diffuse through the

pores and there are still others which act as enzymes.

The peripheral proteins, on the other hand, that are

attached to the surface of the membrane and do not penetrate,

occur either entirely or almost entirely on the inside of the

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membrane. These peripheral proteins function almost entirely

on enzymes.

The lipids of biomembranes are largely polar, phospho-

glycerides predominates with much smaller amounts of sphingo-

lipids. In fact, nearly all the polar lipids of the cells

are localized in their membranes. Among the phospholipids,

the biomembranes usually contain high proportions of phospha­

tidylcholine, phosphatidylethanolamine, sphingomyelin, phos-

phatic acid and cardiolipin. All of them occupy interfacial

space in the membrane but do not contribute to the surface of

fixed ionic groups and give rise to an electrostatic field

extending into the surrounding electrolytes. The other groups

constituting the membranes are glycoproteins, glycolipids and

proteoglycans. The glycoproteins alongwith the glycolipids

constituting the class of glycoconjugates, result from the

covalent association of carbohydrate moities with proteins.

Transport Through Biomembranes : The living cells, being the

fundamental units of the entire biological activities, maintain

the continuity of their properties in the midst of drastically

and everchanging environment. An important mechanism by which

a cell achieves a constancy is the regulation of movement in

or out of it. Eventhough, the materials are not distributed

uniformally within the cell, yet a definite regulation of inter-

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6 :

change of materials is encountered. To achieve a satisfactory

control, the cell utilizes a delicate membrane of about 70 A

thick.

At one time, the transport of materials across the mem­

branes was considered to be determined by the concentration

gradient, but it has been also observed that in most of the

biological tissues or biomembranes the movement of materials

take place against the concentration gradient. For example,

K is usually accumulated in plant as well as in animal cells

to a concentration many times higher than that of the medium

surrounding the cell. Such a transport requires energy by

the cells and has been called an active transport or net meta-

bollically linked transport, while that which corresponds to

a concentration gradient is a passive transport. The energy

required for the active transport comes from the ATP or from

the higher energy source. However, in the case of cells,

there is no passive transport due to the fact that no direc­

tional movement across the cell membranes occurs without the

expenditure of energy by the molecules involved. The kinetic

energy accounts for the random movement of the molecules while

the chemical potential of higher concentration of a particular

substance outside the cell than that inside the cell is dissi­

pated as the molecule of that substance outside the cell moves

into the cell and reduces the concentration gradient of the

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7

substances between the outside and the inside of the cell

(19).

Some of the species like water and ions move directly

through the pores in the cell membranes. It has been repor­

ted (20) that other molecules are attached to the carrier

forming a complex which aids its passage through the membrane.

Since the carrier protein, which shuttles the molecules or

ions through the membrane, facilitates the diffusion, the move­

ment of such a type is called the facilitated diffusion which

differs from that of the simple diffusion by the kinetics of

entry relative to concentration. Although, the flux through

the membrane increases proportionally with an increase in

concentration of the diffusing substances while in facilitated

diffusion the flux approaches a maximum limiting value as the

concentration of the substance increases. It has been repor­

ted (21) that the carrier sites in the membrane get more and

more occupied such that no further additional sites can be

occupied. Although, the carrier complex requires the energy

of activation for its transport, less energy is required for

the facilitated diffusion than for the activated diffusion

because of the affinity of carrier protein for lipids in the

membrane. The flux for a given substance is, therefore ,

greater when a carrier is involved than in its absence. The

kinetics of facilitated diffusion resembles with that of the

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8

active transport but the actual mechanism of active transport

is stiil uncertain. However, it has been assumed that in both

the cases the carrier protein is involved in the transport of

molecules or ions and thus, the energy from ATP or from some

high energy phosphate bond is available for the active trans­

port.

Since, the studies on the transport of ions (.organic as

well as inorganicJ, sugars and amino acids have been in pro­

gress, it seems necessary to mention some of the significant

investigations carried out in this area.

The effect of space charge on the transport of ions

through biomembranes has been reported earlier (22-23). It

has been suggested that there may be local regions having

high dielectric constant values and thus, admitting ions from

the aqueous regions with relative ease. Such regions could

possibly be provided oy the giant protein molecules which are

thought to penetrate the membrane. Mitsuru Sugarwara et al.

(24), while investigating the changes in permeation rate of

organic anions through the rat intestinal brush-border mem­

brane, suggested that the penetration of anionic species

across the membrane is dependent on the surface potential

which originate from the surface negative charge.

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2 + The susceptibility of membraneous Ca - ATPase of sacro-

plasmic reticulum to enzymatic inactivation at hyperthermic

temperatures was investigated by Demita Paleez et al. (25) and

it was concluded that the presence of nucleotide fails to

2+ inactivate Ca - ATPase during the malignant hyperthermia

and that the native environment of the lipid bilayer provides

2+ stabilization of membrane - embedded and Ca - translocating

2+ domain of the Ca - ATPase.

A number of positively charged antitumor drugs, including

anthracyline, antibiotic, adriamycin and the ellipticine family

have been shown to have strong interaction with the negatively

charged phospholipid components of various cellular membranes.

Thesenembraneous interactions resulting in the changes in

polarizations are believed to play an important role either in

their antitumor effects or in certain cytotoxic action of

adriamycin (26-27^.

Shukla and co-workers (28-32J have carried out their

studies on the mammalian (goat) urinary bladders using the

aqueous solutions of the mixtures of constituents of urine as

the permeants under the normal and pathological conditions.

Some developments in establishing the probable structures

and determining the functions of biological membranes have been

reported by Sitaraman (33). In addition, a theoretical view

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10

on the fluctuations in the behaviour of the processes like

catalysis/transport and their relationship with the fluctua­

tions in lipid bilayers have been examined. The importance

of the osmotic inhibition in the activity of the membrane-

bound protein as a consequence of these fluctuations has

also been discussed (34-36).

Recently, Repieke and Rudolf Schon (37) reviewed the

proposed mechanisms and the energetics of transphorylations

in understanding the mechanism of Na /K transporting the

ATPase whereas Stephen (38) has proposed the mechanism of sub­

strate translocation by the mammalian passive glucose trans­

porter in human erythrocytes.

Bamo et al. (39) has derived an equation that describes

the overall rate of uptake and the metabolism of a substrate

that is translocated across the plasma membrane by the process

of facilitated diffusion. According to them the tacilitated

difussion is particularly suitable for the substrates that are

rapidly converted into the metabolities.

Taenet et al. (.40) examined the likely mechanisms for

understanding the transport of zinc ions across the brush-

border membrane of small intestine of pigs isolated in the

vascular form.

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11

Consequently, in view of the investigations carried out

in the transport of ions/molecular entities through some of

the biomembranes described above, the peritoneal membrane of

Buffalo (Bof. bubalis) was chosen to study some of the trans­

port properties. There were two-fold reasons for selecting

this membrane. First of all it was easily available and

secondly it found its application/utility in the peritoneal

dialysis in treating the patients of uremia.

Peritoneum : It is the largest moist serous membrane which

embodies the stomach and the intestine in the abdominal ca­

vities and allows these organs to slide freely over one ano­

ther in the cavity. The peritoneum possesses the perietal

and visceral portions and the space between the layers of

these portions is known as peritoneal sac. The free and smooth

surface of the membrane is covered with a layer of flattened

endothelium which is lubricated by a small quantity of serous

fluid, whereas the attached surface is rough being connected

to viscera. The peritoneum differs from other serous membranes

of the body due to the presence of much more complex arrange­

ments (41-44).

Transport Studies on Peritoneum : The dialysis rate studies

were carried out comparing the control rats with eviscerated

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12

ones to show the contribution of viscera to the system of

membrane used in peritoneal dialysis. It has been found that

the rats without viscera have the mass transfer coefficients

equal to or greater than those of the rats with viscera (45).

The ethacryline acid and furosemide have been found to

affect the Na -transfer across the human peritoneal membrane.

It has been observed that the mesothelial cells of the peri-

teal peritoneum react with the pharmacological agents with

altered transport properties (45-47). Nolph (48) has discussec

the cause and the control on regulating the sodium and pota­

ssium losses during the peritoneal dialysis.

In order to have the quantitative description of the

peritoneal transport of drug, a kinetic model based on the

pore theory of transcapillary exchange was proposed by

Nakashima et al. (49). The quinoline transport across the

peritoneal membrane was also studied which was found to be

diffusion limited.

Walleys et al. (50) discussed the possible mechanism

involved in the transfer of chromium dlalyzate to the blood

during the peritoneal dialysis. Wideroe (51) has studied the

water transport across the peritoneal membrane necessitated

in different clinical problems. The results were based on the

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13

mathematical modelling employed to stimulate the structural

alteration in the peritoneal dialysis.

The experimental studies employing the peritoneal mem­

brane of rabbits were made to investigate the alteration in

the transperitoneal flux of uric acid by furosemide. The

results were found to support the view that furosemide can

affect the peritoneal excertion of uric acid during dialysis

but at the same time, the mechanism regulating the transpe­

ritoneal uric acid passage may be a complex one (52). The

role of ascites and phospholipase A^ in understanding the

changes in peritoneal permeability in acute experimental

pancreatitis in rats was studied (53). A direct link between

the neutralization of anionic sites by protamine and rise in

protein passage to the peritoneal cavity during the iso-osmotic

peritoneal dialysis in rats was demonstrated by Galdi et al.

(54) whereas Zakaria et al. (55) investigated the osmotic

barrier characteristics of rat's peritoneal membrane.

Eventhough, the peritoneal membrane used in peritoneal

dialysis is preferred over those of the other methods for

treating the patient of uremia, very little is known about its

biophysical properties. Such a consideration has led to under-

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14

take the investigations of transport of ions through the

peritoneal membrane. This included the measurements of

electrical properties like conductance, capacitance and

impedance.

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C H A P T E R - I I • * * • • * * * * • * * * * * * * • • •

ELECTRICAL CONDUCTANCES OF IONS ACROSS

PERITONEAL MEMBRANE

AND

APPLICATION OF ABSOLUTE REACTION RATE

THEORY TO CONDUCTANCES

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INTRODUCTION

The permeation of ions across a membrane has been reported

earlier ^56-59) to depend on the pores lined by charges, liquid

soluble carrier molecules and homogeneous dielectric medium

having the rate limiting 'gate mechanism' at its surface. Even

though, the permeation of ions across a natural or an artificia

membrane seems to be governed by similar laws, the membrane

structure and the boundary conditions at the membrane/electro­

lyte interface are the consequence of ion permeation. However,

as for the interior of any membrane is concerned, only four

mechanisms, viz., collision-, jump-, carrier-, and solvent

drag- mechanisms may be responsible for the ion permeation acre

the membranes.

The hydrophillic group in the membrane has been found

(60-61) to facilitate the membrane permeability due to the

formation of hydrogen bonds with water and the mechanism by

which ions permeate through the membrane has been proposed on

the basis of the hole type- and the alignment type- diffusions

(62). These proposed modes of diffusion have been further

confirmed by the measurement of electrical resistance of dift-

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16

erent membranes (63). The permeation process has also been

described in terms of the binding energetics of ion-protein

versus ion-water interaction (64-66).

Francioline and Anna Petris (67-68) have described the

transport mechanism in chloride channels of hipocampal neu­

rons. According to these workers, a penetrating ion forms

an activated complex which is composed of channel sites, a

cation and an anion. It was proposed that the channel site

was anionic and first attracted and retained a cation. The

resulting dipole facilitates a short-lived anion association.

Once the complex has been formed it can decay either by

dissociation of anion or by dissociation of anion/cation

pairs.

A number of theoretical approaches, such as irrever-

siblex- chemical engineering-, activation barrier-, and that

of phenomenological equation of motion- approaches have been

employed to explain the transport processes through the mem­

branes (69). Here, the activation energy barrier approach

which is based on the absolute reaction rate theory has been

applied to explain the transport processes. According to this

theory, pores are considered as a sequence of carriers existing

one behind the other, across which materials pass in order to

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17

cross the membrane. Such a consideration has been applied

to explain the diffusion processes in membranes by several

investigators (70-/5).

In this chapter, the specific conductances of aqueous

solutions of various electrolytes (viz., NaCl, NaF, NaNO^,

Na2S0^, KF, Kul, KNO^, K^SO^, MgCl2, FeCl^, CrCl^ CuCl^,

CoCl2» MnCl„) recorded across the peritoneal membrane as

functions of concentration and temperature have been examined

The absolution reaction rate theory has been applied to eva­

luate the thermodynamic parameters, viz., entropy-, free-

irc

^H''' and Ea).

4= l

energy-, enthalpy-, and energy- of activations ( AS^, AF^,

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18

EXPERIMENTAL

The fresh peritoneal membranes were obtained from the

slaughtered buffalo (Bof. bubalis) aged between 18-24 months

from the local abattoir and were immediately immersed into

an ice cold Ringer's solutions (76-78) for the preservation

of the memorane tissues. The Ringer's solution had the follow­

ing composition in gms/litre :

NaCl , B.CX); KCl, 0.20; CaCl2, 0.20; MgCl^, 0.10;

NaHCO^, 1.00; NaH2P0^, 0.05 and Glucose, 1.00.

The peritoneal membrane in the form of small pieces of

desired size were washed several times with distilled water

to remove any traces of Ringer's solution. It was then

placed between the two halves of the cell compartment having

platinium electrodes to establish the electric contact. The

LCR bridge (Systronics, India) was employed to measure the

conductances of ions across the membrane. All the measure­

ments were made in a thermostated bath of water maintained at

the desired temperature , 15 to 35 C) with +0,1 thermal sta­

bility. The following electrolyte solutions were prepared

from the analytical grade reagents (.BDH) in double distilled

water :

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19

NaCl, NaF, NaN03, Na2S0^, KF, KCi, KNO^, K^SO^,

MgCl2, CaCl^* MnCl2, ^^^^3' CrCl^, CUCI2, CoCl^.

RESULTS Am DISCUSSION

The specific conductances of aqueous solutions of electro­

lytes (viz.NaF, NaCl, NaNO^, Na2S0^, KF, KCI, KNO^, '<2S04»

MgCl2» CaCi , FeCl , MnCl , CrCl„, CuCl , CoCl ) have been

measured in the two compartments of the cell at several tem­

peratures between 15 C and 35 C (+0.1 C). These results are

given in Tables 1.1 to 1.8. An examination of these tables

shows that the specific conductance increases with an increase

in the [electrolyte] and attains a maximum limiting value at

higher concentrations. This trend has been observed in all

the electrolyte solutions under investigation. This may be

attributed to a progressive accumulation of ionic species with­

in the membrane. As such the membrane becomes more and more

conductive to incoming ions. The tendency to attain a limiting

value seems to be due to the fact that an electrically neutral

pore which is specific for a particular ion is unlikely to

contain more than one type of ion. Consequently, at high ele­

ctrolyte concentration, the pore saturates and the conductance

approaches a limiting value. Also, since the biomembranes

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20

TABLE 1.1: Values of Specific Conductance, K (m JX" cm" ) ot

Aqueous Solutions of NaF and NaNO^ Across Peritoneal

Membrane as Functions of Concentration and

Temperature.

Electrolyte Concentration Temperature (+ 0,1 C) (mol I"-'-) 15 20 25 30 35

NaF

0 .001 0 .085 0.086 0 .088 0.089 0 . 0 9 0

0,002 0 .095 0.010 0 . 0 1 1 0.012 0 . 0 1 3

0 .005 0 .195 0 .225 0 .249 0 .285 0 . 3 4 5

0 . 0 1 0 .492 0.574 0 .622 0.772 0 .921

0 .02 0 .734 0.772 0 .933 1.24 2 .34

0 .05 1.87 2.99 3 .73 4 .48 4 .98 0 . 1 3 .60 4 .50 5 .40 6 .40 7 .23

0 .2 5 .10 6.82 7 .16 8.04 8.83

NaNO^

0 .001

0.002

0 .005

0 ,01

0 .02

0 . 0 5

0 . 1

0 .2

0.088

0.109

0.299

0.640

0.986

2.49

4 .40

6.03

U.090

0.115

0.325

0.723

1.04

3.73

5.49

6.93

0 .091

0.136

0.373

0.862

1.32

4 .48

6.56

8.24

0.094

0.184

0.448

0.996

2 .60

4 .86

7.52

8.43

0 .095

0.226

0.498

1.72

3.49

5.98

8.52

10.02

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21

TABLE 1.2: Values of Specif ic Conductance, IC (m Si' cm" ) of

Aqueous Solut ions of NaCl and Na^SO. Across Per i tonea l

Membrane as Functions of Concentration and Temperature.

o. Electrolyte Concentration Temperature (+ O.l^C)

-1 ^^°^ ^ ^ 15 20 25 30 35

Ikci 0.001 0.128 0.132 0.155 0.160 0.172 0.002 0.179 0.197 0.246 0.279 0.295 0.005 0.373 0.407 0.467 0.528 0.621 0.01 0.747 0.815 0.996 1.42 2.28 0.02 1.49 1.72 2.95 3.49 4.73 0.05 4.48 4.87 6.30 7.29 8.32 0 .1 6.89 7.72 9.53 10.20 10.70 0.2 9.21 9.84 10.8 11.20 12.20

0.001 0.179 0.204 0.224 0.249 0.269 0.002 0.249 0.299 0.345 0.408 0.498 0.005 0.597 0.659 0.723 0.786 0.896 0.01 1.04 1.51 2.54 3.79 4.94 0.02 2.79 3.54 4.49 5.39 6.48 0.05 4.98 6.27 6.96 7.75 8.80 0 .1 8.44 9.96 10.30 11.0 11.80 0.2 10.40 10.70 11.30 12.10 13.00

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22

TABLE 1 . 3 : V a l u e s of S p e c i f i c C o n d u c t a n c e , IC (m J l " cm" ) of

Aqueous S o l u t i o n s of KF and KNO- A c r o s s P e r i t o n e a l

Membrane a s F u n c t i o n s of C o n c e n t r a t i o n and T e m e p r a t u r e .

E l e c t r o l y t e T e m p e r a t u r e (+ O.l^^C) C o n c e n t r a t i o n 1 1—

(mol I"-'-) 15 20 25 30 35

KF

0 . 0 0 1 0 . 0 9 5 0 . 0 9 6 O.U97 0 . 0 9 8 0 . 1 0 3

0 . 0 0 2 0 . 1 3 2 0 . 1 4 0 0 . 1 4 9 0 . 1 6 5 0 . 1 8 9

0 . 0 0 5 0 . 3 2 0 0 . 3 4 5 0 . 3 7 3 0 . 4 4 8 0 . 4 7 2

0 . 0 1 0 . 5 9 7 0 . 6 8 9 0 . 7 7 2 0 . 8 6 9 0 . 9 9 6

0 . 0 2 0 . 9 3 3 1.07 1.32 1.79 2 . 6 2

0 , 0 5 1.95 3 . 2 0 3 . 7 3 4 . 4 8 5 . 3 8

0 . 1 4 . 9 8 5 . 6 0 6 . 4 0 7 . 4 7 8 . 5 3

0 , 2 6 . 1 9 6 . 7 2 7 . 5 0 8 .64 9 . 4 0

KNO3

0 . 0 0 1 0 . 1 0 2 0 . 1 0 4 0 . 1 0 9 0 . 1 1 5 0 . 1 2 1

0 . 0 0 2 0 . 1 4 0 0 . 1 5 4 0 . 1 6 6 0 . 1 7 9 0 . 2 0 5

0 . 0 0 5 0 . 3 7 3 0 . 4 4 8 0 . 4 8 2 0 . 5 2 7 0 . 5 6 0

0 . 0 1 0 . 7 4 7 0 . 8 4 5 0 . 9 3 3 1.07 1 .28

0 . 0 2 0 . 9 3 2 1.28 1.60 1 .95 2 . 9 9

0 . 0 5 2 . 9 9 4 . 4 8 4 . 7 7 5 . 4 3 5 . 6 0

0 . 1 7 . 4 7 8 . 2 8 8 . 9 0 9 . 2 8 1 0 . 0 0

0 . 2 9 . 1 2 9 . 7 9 1 0 . 1 0 1 0 . 5 0 1 1 . 1 0

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23

TABLE 1.4: Values of Specific Conductance, IC (m XL cm" ) of

Aqueous Solutions of KNO_ and K^SO Across Peritoneal

Membrane as Functions of Concentration and Temperature.

E l e c t r o l y t e Concen t r a t i on

(moi 1"-^;

KNO- O.CX)l

0 .002

0 .005

0 . 0 1

0 .02

0 .05

0 . 1

0 . 2

^ 2 ^ ^ 0 .001

0 .002

0 .005

0 . 0 1

0 .02

0 . 0 5

0 . 1

0 . 2

15

0 .128 0 .179

0 .498

0 .896 1.54

4 .98

8.30

10.10

0 .140

0 .264

0 .540

1.12 2 .19

5 .60

9.96 12.0

Tempera

20

0.143 0.195

0.527

0.996

1.66

5.33

9.26

11.10

0.149 0 .295

0 .600

1.28 2.74

6.14

11.10

12.60

i t u r e ( +

25

0 .145 0 .213

0 .560

1.09

2 . 4 5

5 .60

9.86

11.40

0 .154

0 .333

0 .660

1.79 3 .50

6 .60

11.60

13 .10

0 .1°C)

30

0.154

0 .234

0 .640

1.32

2 .99

6.40

10.50

11.70

0 .179

0 .373

0.726

2 .46

4 .48

7 .39

12.40

13.80

35

0 .166 0 . 2 6 4

0 .700

1.79

3 .80

7 .43

11.10

12.20

0 .213 0 .448

0 .814

3.83

5 .42

8.46

13.40

14.60

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24

TABLE l.b JValues of Specific Conductance, K (m if cm" ) of

Aqueous solutions of MgCl2 and FeCl^ Across Peritoneal

Membrane as Functions of Concentration and Temperature.

Electrolyte Concentration Temperature (+ 0.1 C)

, - 1 (mol 1 ) 15 20 25 30 35

MgCl2

0 .001 0 .132 0 .140 0 .149 0 .154 0 .166

0 .002 0 .204 0 .224 0 .264 0.272 0 .302

0 .005 0 .448 0.492 0 .515 0 .546 0 . 6 0 5

0 . 0 1 0 .896 0.974 1.09 1.38 1.57

0 .02 1.49 1.68 2 .04 2 .49 3.20

0 . 1 7 .32 7.96 8.46 9.20 10 .10

0 .2 8.43 9 .01 9 .43 10.00 11 .60

FeCl3

0 .001 0 .160 0.172 0 .179 0 .204 0 .224

0.002 0 .249 0.279 0 .315 0.358 0 .401

0 .005 0 .521 0 .560 0.622 0 .669 0 .747

0 . 0 1 0 .996 1.19 1.61 2 .19 3.00

0 .02 1.79 2 .23 2 .69 3.23 4 .67

0 .05 4 .98 5.37 5.77 6 .40 6.79

0 . 1 7 .93 8.30 9 .0 9.79 10.07

0 .2 9.04 9.42 10.01 10.80 11 .10

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25

TABLE 1.6 rvalues of Specific Conductance, K (m Jl cm" ) of

Aqueous Solutions of CrCl,, and CuCl Across Perito­

neal Membrane as Functions of Concentration and

Temperature,

Electrolyte Concentration

(mol l"- ) 15

Temperature C+ 0.1 C)

20 25 30 35

CrCl3

0.001

0.002

0.005

0.01

0.02

0.05 0.1

0.2

0.179

0.299

0.589

1.12 2.24

5.46

8.34

9.73

0.187

0.345

0.64O

1.38

2.99

5.89

8.90

10.20

0.213

0.400

0.679

1.60

3.82

6.69

9.49

10.70

0.224

0.438

0.728

2.39

4.88

7.40

10.30

11.60

0.242

0.553

0.802

3.20

5.37

8.21

10.90

12.00

CuCl,

0.001

0.002

0.005

0.01

0.O2

0.05

0.1

0.2

0.187 0 .320

0 .614

1.21

3 .20

6.22 9.00

10.20

0.204 0 .353

0.659

1.56

3.78 7.U0

9.90

11.00

0 .224

0 .372

0 .700

2 .19

4 .40

7 .89

10.60

11 .70

0 .230 0 .410

0.747

2 .84

5 .00

8.39

11.50

12.30

U.240 0 .440

0 .800

3.60

6 .04

9.47

12.UO

13.20

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26

TABLE 1.7 : Values of S p e c i f i c Conductance, )C Cm j T cm" ) of

Aqueous S o l u t i o n s of CoCl^ and MnCl_ Across

P e r i t o n e a l Memorane as F u n c t i o n s of C o n c e n t r a t i o n

and Temperature .

E l e c t r o l y t e Concen t r a t i on

(mol l"-^) 15

Temperature (+ 0 .1°C)

20 25 30 35

CoCl^

0 .001

0.002

0.005

0 . 0 1

0 .02

0 .05

0 . 1

0 .2

MnCl2

0 .001

0.002

0 .005

0 . 0 1

0 .02

0 .05 0 . 1

0 .2

0.249

0.373

0.727

2.04

4.67

7.23

9.82

10.90

0.280

0 .418

0 .853

3.94

5.42

8.30

10.30

11.20

0.253

0.412

0 .768

2.62

5.29

7.86

10.60

11.70

0.300

0 .451

0.854

4.49

6.10

8.76

10.80

11.70

0 .262

0 .458

0 .836

3.60

5.97

8.96

11.20

12.30

0 .313

0 .470

0 .904

5.02

6 .53

9 .60

11 .50

12.30

0 .283

0 .513

0.912

4 .32

6.64

9 .53

11.70

12.30

0 .324

0.522

0 .950

5.68

7.22

10.30

12.20

13.OO

0 .300

0 .549

1.54

5.02

7 .19

10.30

12 .50

13.40

0 .342 0 .564

1.02 6 . 4 9

8.10

11 .10

13 .00

14 .10

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27

TABLE 1,8: Values of Specific Conductance, IC (m ^ cm" ) of

Aqueous Solutions of CaCl^ Across Peritoneal Membrane

as Functions of Concentration and Temperature.

Electrolyte Temperature (+ 0.1°C) Concentration _—

(mol l"-*-) 15 20 25 30 35

CaCl^

0,001 0.373 0.382 0.402 0.413 0.434

0,002 0.516 0.549 0.602 0.630 0.683

0,005 0.922 1.04 1.32 1.84 2.21

0.01 4.96 5.90 6.48 7.02 8.01

0.02 7.00 7.80 8.21 8.90 9.81

0.05 9.86 10.60 11.10 11.90 12.80

0 ,1 11,80 12,40 12.80 13.50 14.40

0.2 12.60 13.20 13.50 14.20 15.30

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28

possess protein which acts as a carrier, picks up ion on one

side and then returns for more ions. In such a mode, the flow

of ions through the membrane reaches a saturation value as the

concentration of the electrolyte solution is increased as all

the carriers in the membrane get themselves bound to the ions.

The values of specific conductance (Table : 1.1 to 1.8)

measured for different electrolyte solutions across the peri­

toneal membrane at any given temperature follow the sequence 2— — — —

for anions : SO. > Cf > NO- > F whereas for the cations the

sequence is : K" > Na" ; Ca " > Mn " > Co " > c u " > Mg^^,

Cx - > Fe^-^.

In addition, the diffusion of the electrolyte through

the membrane depends upon the charge on the membrane and its

porosity. The membrane porosity in relation to the size of

the hydrated species flowing through the membrane seems to

determine the above sequence, AS the diffusional paths in

the membrane oecome more difficult in aqueous solutions, the

mobility of large hydrated ions get impeded by the membrane

framework and due to the interaction with the fixed charge

groups on the membrane matrix. Consequently, the conductance

of small ion which is much hydrated gets reduced by the membr­

ane pores. The increase in specific conouctance with rise in

temperature may be due to the fact that the state of hydration

Page 39: TRANSPORT OF IONS THROUGH BIOMEMBRANES · control, the cell utilizes a delicate membrane of about 70 A thick. At one time, the transport of materials across the mem branes was considered

29

of penetrating electrolyte may be considered to exist in a

dynamic condition so that at a higher temperature, conside­

rably higher fraction of total number of given species would

possess excess energy per mole in accordance with the Boltzman

distribution, f a e~ ' . Under these conditions, those

ionic species which have lost sutficient water of hydration

to be smaller than the size of the membrane pores would enter

through the pores. Thus, the specific conductance increases

with the rise in temperature provided that there has been no

irreversible changes in the membrane structure and such an

argument seems justified by the linear plot of log IC versus

1/T (Fig. l.lj, the slope of which gives the activation energy.

The activation energies for the various electrolyte solutions

studied here (Tables : 1.9 to 2.6) reveal that the activation

energy decreases with an increase in [electrolyte] in their

respective solutions. It is noteworthy that at a particular

concentration the energy of activation follows the following

sequence for the cations as well as for the anions :

Ea^+ > E^^+, Ea^^2+ > Ea 24- > £3^,2+ > Eac^2+ ^

Page 40: TRANSPORT OF IONS THROUGH BIOMEMBRANES · control, the cell utilizes a delicate membrane of about 70 A thick. At one time, the transport of materials across the mem branes was considered

30

E

c o \J

C

o

12

\\

1.0

0.9

0.8

~''^~-!^^~"^~«_

^ ^ ^ ^

. I I I

*~~-—~~_„,jn(

^ ^ ^ ^ ^ ^ S ^ ^ i T ^ ^ - ^ ^ ^ ~ ^ = ^ = = ^ ^

^ " ^ ^ ^ ^ ^ r r ^ X V

I 1

o. VI

o

3.20 3 2S 3 30 3.3S

V^xio'

3.10 3 l,S

Arrhenius Plots of logK vs l/TxlO" electrolytes :(i) NaF (ii) (Iv) Na^SO/. (v) KF (vi)

for different NaNO^ (iii:

L -jw, vv/ ixi v.^, KNO^ (vii) KCl K,SO, (ix) CaCK (x) MnC]^^ (xi) CrC]^ F6C1^ (xlli) Cod.2 (xiv) CitCU and (xvl across peritoneal membrane.

NaCl (vi i 1 ) (xii )

MgClo

Page 41: TRANSPORT OF IONS THROUGH BIOMEMBRANES · control, the cell utilizes a delicate membrane of about 70 A thick. At one time, the transport of materials across the mem branes was considered

3 i

TABLE 1.9: Computed Values of En t ropy - , E n t h a l p y - , Energy- ,

and Free-Energy of A c t i v a t i o n s ( AS''', AH' ' ' , Ea, A F ^ }

for Conductances of NaF and NaNO^ Across t h e

P e r i t o n e a l Membrane,

AS^

(Calmor-'-deg"-'-;

-29.39

-29.17

-28.35

-27.60

-26.92

-25.85

-25.53

-25.47

(k

Parameters

AH^

cal mol"

1.42

1.26

1.20

0.94

0.73

0.42

0.35

0.17

•h (k

Ea

cal mol" )

2.01

1.85

1.79

1.53

1.32

1.01

0.94

0.76

(k

AF^

cal mol )

10.18

9.96

9.65

9.17

8.76

8.13

7.96

7.76

-29.25

-28.91

-27.93

-27.32

-26.78

-25.79

-25.37

-25.33

1.57

1.47

1.25

0.96

0.80

0.50

0.42

0.25

2.16

2.06

1.84

1.55

1.39

1.09

1.01

0.84

10.29

10.09

9.58

9.10

8.78

8.19

7.98

7.8U

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32

TABLE 2.0: Computed Values of Entropy-, Enthalpy-, Energy-, and

Free-Energy of Activations ( AS''', ^W , Ea, AF"^) for

Conductances of NaCl and Na2SU^ Across the Peritoneal

Membrane.

Electro­lyte Concen­tration

(moi r^)

NaCl

0.001

0.002

0.005

0.01

0.02

0,05

0.1

0.2

Na2S0^

0.001

0.002

0,005

0.01

0,02

0.05

0,1

0,2

AS +

(Calmol" deg" )

-28.89

-28.41

-27.74

-27.12

-26.49

-25.49

-25.04

-24.32

-28.45

-27.96

-27.48

-26.39

-25.65

-25.49

-25.29

-25,16

Parametei

(kcal mol )

1.75

1.56

1.41

1.00

0.87

0.59

0.50

0.40

2.11

1.70

1.47

1.25

0.94

0.77

0.63

0.50

s

Ea

(kcal mol )

2.34

2.15

2.00

1.59

1.46

1,18

1.09

0.99

2.70

2.29

2.06

1.84

1.53

1.36

1.22

1.09

(kcal mol )

10.36

10.03

9.68

9.09

8.77

8,19

7.97

7.65

10.59

10.04

9.66

9.12

8.59

8,37

8,17

8.U0

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33

TABLE 2 . 1 : Computed Values of En t ropy- , E n t h a l p y - , Energy- , and

Free-Energy of A c t i v a t i o n s ( AS"^, AH''', Ea, AF^^) f o r

Conductances of KP and KNO» Across the P e r i t o n e a l

Membrane.

Ea AF ^ Electro- Parameters lyte Con- ^ ^^^ centration

(mol l" ) (Calmol deg ) (kcal mol ) (kcal mol ) (kcal mol )

KF

0.001

0.002

0.005

0.01

0.02

0.05

0.1

0.2

KNO3

0.001

0.002

0.U05

0.01

0.02

0.05

0.1

U.2

-29.27

-28.87

-27.94

-27.42

-26.83

-25.89

-25.49

-25.37

-29.25

-28.75

-27.88

-27.30

-26.57

-25.77

-25.43

-25.33

1.50

1.39

1.33

1.04

0.75

0.50

0.43

0.24

1.71

1.60

1.50

1.14

0.87

0.55

0.50

0.32

2.09

1.98

1.92

1.63

1.34

1.09

1.02

0.83

2.30

2.19

2.09

1.73

1.46

1.14

1.09

0.91

10.23

10.00

9.66

9.58

8.75

8.22

8.03

7.80

10.43

10.17

9.81

9.28

8.79

8.23

8.08

7.87

Page 44: TRANSPORT OF IONS THROUGH BIOMEMBRANES · control, the cell utilizes a delicate membrane of about 70 A thick. At one time, the transport of materials across the mem branes was considered

34

TABLE 2.2 : Computed Values of Entropy-, Enthalpy-, Energy-, and

Li. I

Free-Energy of Activations { AS^, AH"^, Ea, AF^;

for Conductances of KCl and J<2S0^ Across the Peritoneal

Membrane, Electro­lyte Con­centration

(moi i"-"-;

KCl

0.001

0.002

0.005

0.01

0.02

0.05

0.1

0.2

^2°4

0.001

0.002

0.005

0.01

0.02

0.05

0.1

0.2

(Calmol deg )

-28.95

-28.53

-27.70

-26.92

-26.19

-25.65

-25.31

-25.25

-28.81

-28.11

-27.54

-26.80

-25.91

-25.57

-25.16

-25.10

Parameter

(kcal mol ) (k

1.94

1.67

1.63

1.23

0.94

0.67

0.62

0.47

2.32

1.81

1.75

1.33

1.00

0.76

0.73

0.53

Ea

cal mol )

2.53

2.26

2.22

1.82

1.53

1.26

1.21

1.06

2.91

2.40

2.34

1.92

1.59

1.35

1.32

1.12

(kcal mol )

10.57

10.18

9.89

9.26

8.75

8.32

8.17

8.00

10.91

10.19

9.96

9.32

8.73

8.38

8.23

8.01

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35

TABLE 2.3 : Computed Values of Entropy-, Enthalpy-, Energy-, and

Free-Energy of Activations ( AS''', A}V, Ea, AF"^)

for Conductances of MgCl^ and FeCl^ Across the Peri­

toneal Membrane.

Electro­lyte Con­centration

(moi i"-*-;

MgCl2

0.001

0.002

0.005

0.01

0.02

0.05

0.1

0.2

FeCl3

0.001

0.002

0.005

0.01

0.02

0.05

0.1

0.2

(Calmol deg )

-28,95

-28.43

-27.84

-26.92

-26.37

-25.79

-25.37

-25.27

-28.67

-28.14

-27.60

-26.49

-26.15

-25.69

-25.35

-25.23

P.

(kcal mol"

1.25

0.92

0.80

0.72

0.64

0.57

0.36

0.25

1.33

0.95

0.83

0.75

0.67

0.60

0.46

0.30

aramet ers

Ea

cal mol )

1.84

1.51

1.39

1.31

1.23

1.16

0.95

0.84

1.92

1.54

1.42

1.34

1.26

1.19

1.05

0.89

(kcal mol )

9.88

9.40

9.10

8.75

8.50

8.26

7.92

7.78

9.88

9.34

9.06

8.65

8.47

8.26

8.02

7.b2

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36

TABLE 2 .4 : Computed Values of En t ropy- , E n t h a l p y - , Energy- , and

Free-Energy of A c t i v a t i o n s ( AS^ , AH"*", Ea, AF*) for

Conductances of CrCl^ and CuCl Across the P e r i t o n e a l

Electrolyte Concentra­tion

(mol 1~^;

CrCl3

O.UOl

O.CX)2

0.005

0.01

0.U2

0.05

0.1

0.2

CUCI2

0.001

0.002

0.005

0.01

0.02

0.05

0.1

0.2

Membrane.

CCalmol deg )

-28.59

-27.84

-27.58

-26.63

-25.67

-25.35

-25.23

-25.18

-28.59

-28.10

-27.56

-26.11

-25.79

-25.41

-25.20

-25.12

Parameters

(kcal mol )

1.42

1.00

0.85

0.80

0.73

0.67

0.50

0.36

1.60

1.33

0.92

0.87

0.80

0.72

0.53

0.42

Ea

(kcal mol )

2.01

1.59

1.44

1.39

1.32

1.26

1.09

0.95

2.19

1.92

1.51

1.46

1.39

1.31

1.12

1.01

(kcal mol )

9.94

9.30

9.07

8.74

8.38

8.23

8.02

7.87

10.12

9.71

9.14

8.65

8.49

8.30

8.04

7.91

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37

TABLE 2.5 : Computed Values of Entropy-, Enthalpy, Energy-, and

Free-Energy of Activations (. AS^, AH^, Ea, AF'''}

for Conductances of CoCl^ and MnCl^ Across the Peritonea

Membrane.

Electrolyte Concentra­tion

(mol l"""*;

C0CI2

O.CX)l

0.002

0.00b

0.01

0.U2

0.05

0.1

0,2

MnCl^

0.001

0.002

0,005

0.01

0.02

0.05

0,1

0.2

(Calmol deg )

-28.45

-27.84

-27.36

-25.89

-25.67

-25.33

-25.20

-25.11

-28.34

-27.88

-27.40

-25.75

-25.53

-25.31

-25.18

-25.08

Parameters

(kcal mol )

1.78

1.41

0.95

0.89

0.87

0.75

0.55

0.44

2.00

1.42

1.25

1.00

0.95

0.82

0.60

0.57

Ea

(kcal mol" )

2.37

2.00

1.54

1.48

1.46

1.34

1.14

1.03

2.59

2.01

1.84

1.59

1.54

1.41

1.19

1.16

(kcal mol

10.26

9.57

9.11

8.61

8.52

8.30

8.06

7.93

10.45

9.73

9.42

8.68

8.56

8.37

8.11

8.05

-')

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38

TABLE 2 .6 : Computed Values of En t ropy- , E n t h a l p y - , Energy- , and

Free-Energy of A c t i v a t i o n s ( AS^, /iH^, Ea, /yF^)

f o r Conductances of CaCl^ Across the P e r i t o n e a l

Membrane.

E l e c t r o l y t e Concen t ra ­t i o n

(mol 1"

CaCl2

0 .001

0.002

0 .005

0 .01

0 .02

0 .05

0 . 1

0 . 2

• ' )

^ S ^

(Calmol'-'-d

-28 .13

-27 .69

-26 .78

-25 .55

- 2 5 . 4 1

-25 .20

-25 .10

-25 .00

eg"^ ;

Parameters

^K^

(kca l

2 .12

1.80

1.26

1.22

1.00

0 .95

0 .65 0 .60

mol' •h

Ea

( k c a l

2 . 7 1

2 .39

1.85

1.81

1.59

1.54

1.24

1.19

^ .F*

mol ) ( k c a l mol )

10 .51

10.06

9 .24

8.84

8.58

8.46

8.13

8.05

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39

which implies that the activation energy for the ionic

transport across the membrane follov/s the sequence of cry-

stallographic radii of ions accordingly.

According to Eyring the pores in the membranes may be

considered as a sequence of energy barriers over which the

ion has to jump in order to cross such barriers in the

process of diffusion/transport of ions.

The Eyring's equation,

based on the theory of absolute reaction rates has been

used to explain the said process. In equation {1) K is the

specific conductance; h, the Planck's constant; R, the gas

constant; N , the Avogadro Number; T, the absolute tempera­

ture, ^\V f the enthalpy of activation and Z S*, the entropy

of activation.

The applicability of the above equation has been exa­

mined by plotting log IC Nh/RT against 1/T (Fig. 1.2 to 1.9;

which gives straight line, the slope and intercept of which

have been used to calculate the values of AHvR and AS'^/R.

The derived values of AH"^ and AS"'" were then used to calcu­

late the tree-energy of activation, AF"^ and the energy of

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40

3.20 3.25 3.30 3 35 3 AO 3 ^ 5

V T X I O VT

l / y X l O

Figo 1.2: Eyring Plots of logKNh/RT vs 1/TxlO different concentrations of : (A) NaF and (B) NaNO„ across peritoneal membrane.

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41

cr

z ij.

o

- 1 2 . 2 0

- 1 2 . 5 0

-12 .80

-13.10

-13./io

-13.70

-K.OO

-U.30

-U.60F

3 20 3.25 3.30 3 35 3 AG 3C[

'/T )( 10 3

g. 1.3:

2

-13.10h

-13.40h

o< -13.70 o

-uooh

-U.30t

-K.60

Eyrlng Plots of logKNh/RT vs l/TxlO"^ for different concentrations of : (A) NaCl and (B) Na^SO, across peritoneal membrane.

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: 42

-12.70

-K.eoh

Fig. 1.4: Eyring Plots o£ logKNh/RT vs l/TxlQ- for different concentrations of : (A) KNO^ and (B) KF across peritoneal membrane.

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43

^ 0 3.25 3.30

- 1 2 . 5 0

- 12 .80^

3 35 3 to 3 t5

V| » 1 0 '

14-60

3 20 3.25 3 30 3 35 3 40 3 4 5

V, « 1 0 '

• i g . 1 . 4 ; Eyring Plots of logKNh/RT vs l/TxlO^ ?Rrrcn^ concentrtions of : (A) KCl ^a) ^250^ across peritoneal membrane.

for and

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44

Eyring Plots logKNh/RT vs l/TxlQ- for different concentrations of : (A) MgCl^ and (B) FeCl across peritoneal membrane.

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45

•12 s o b

Fig. 1.7: Eyring Plots of logKNh/RT vs 1/TxlO^ for different concentrations of : (A) CrCl^ and (B) CuCl„ across peritoneal membrane.

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46

320 3.25 3.30 3.35 3.^0

V T X 10 3

3 45

320 3.25 3.30 3.35

'/T '^ '0 3

3^0 3A5

Fig. 1.8; Erying Plots of logKNh/RT vs 1/lOxlO^ for different concentrations of : (A) CoCl^ and (B) MnCl„ across peritoneal membrane.

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47

-12.50h

-12.80

^ -n.ioh z

O -13.AO

-13.70

K.OOh

3.20 3.25 3.30 3.35 3.A0 3.A5

1/jxlO

Fig. 1.9; Eyring Plots of logOh/RT vs l/TxlO- for different concentrations peritoneal membrane.

of CaCl across

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: 48 :

activation, Ea using the following equations :

AF^^ = AH^^- T A S . . . (2)

and Ea = AH^ + RT . . . (3)

The values of the various thermodynamic parameters,thus,

obtained for the diffusion of various electrolytes through

the (peritoneal;) membrane are summarized in Tables l.v to 2.6.

These results indicate that the permeation of electrolytes

through the membrane gives rise to negative values of AS'

which means that there may be either formation of covalent

linkage between the penetrating species and the membrane

material or that the permeation through the membrane may not

be the rate determining step. But according to the 'zone

hypothesis'of Barrer (78), on the one hand, a high AS'' value

correlated with the high energy of activation for diffusion

means that there may exist either a large zone of activation

or loosening of more chain segments of the membrane. On the

other hand, low value of AS"^ implies either a small zone of

activation or no loosening of the membrane structure upon per­

meation. Based on these considerations, Schuler et al.(79).

who found negative values of AS"^ for the diffusion of sugar

through the colloidal membrane have proposed that in the case

of ions the small values of AS* may be interpreted as due to

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: 49 :

the interstitial permeation of the ionic species with the

partial immobilization in the membrane i.e., the small zone

of disorder; while Tien and Ting (70^, who found negative

values for the permeation of water through a very thin bilayer

membrane, suggested that the solution-membrane interface and

not the membrane itself may be the rate determining inter-

meadiary for permeation. The negative values of AS' may be

then considered as due to the partial immobilization of ions

and their interaction with the membrane fixed charged groups.

Thus, the results of all these investigations suggest

that the diffusion of electrolytes through the (peritoneal/'

membrane may be facilitated as soon the specific conductance

tends to approach some maximum limiting value with an increase

in the [electrolyte] in the solutions under investigation.

Furthermore, the membrane is positively charged and ionic

species retain their hydration shell at least partially while

crossing through the pores of the membrane. Moreover, the

negative values of AS^ suggest that the partial immobiliza­

tion of the ions takes place most probably due to the inter­

stitial permeation as well as the ionic interaction with the

fixed charge groups on the membrane.

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C H A P T E R - I I I

RESISTANCE, CAPACITANCE, IMPEDANCE

AND

ELECTRICAL DOUBLE LAYER

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INTRODUCTION

The electrical double layer formed at the membrane/

electrolyte interface is expected to influence and control

the transport of ions as also found by various investi­

gators (80-83j. It has been also found to be one of the

main factors for the relaxation time in electro-osmosis

(84-86). Similarly, measurements of impedance of ionic

systems across the membranes provide valuable data of rele­

vance (86-94). Lakshminarayanaiah, N. (95) has discussed

the importance of the impedance measurements, characteris­

tics of polysterene sulphonic acid and interpreted the data

in terms of resistance and capacitance characteristics of

simple membranes. The capacitance and conductance measure­

ments were employed to many active and passive membranes.

Such studies have revealed that the effect of electrolyte

concentration and frequency on the membrane capacitance may

be due to some structural changes in the membrane rather than

the electrode polarization (96-98). The effect of interactions

in the head groups on the monolayer structure and permeability

at the Hg/water interface with the diurete furosemide has

revealed that the surface layer of the monolayer structure

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51

expands and thus, decreases the thickness of the hydrocarbon

layer and increases the electrical capacitances. At higher

concentrations the excessive expansion of hydrocarbon layer

increases the tendency to form micelles which result in the

alteration in the monolayer with increase in ionic permea­

bility (99). Koji and Shero (100) investigated the membrane

admittance of cultured myoblasts muscle cells which indicates

that the capacitance and conductance of myotube membrane is

frequency dependent.

This chapter, therefore, deals with the measurements

of resistance, Rx, and capacitance, Cx, in aqueous solutions

of sodium chloride as functions of concentration, temperature

(ranging from 15 to 35 C), and frequency (ranging from

2 4 10 Hz to 10 Hz). The impedance, z has been analyzed in order

to understand the mechanism of ionic transport which has been

interpreted as due to the changes produced in the electrical

double layer at the membrane/electrolyte interface.

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52

RESULTS AND DISCUSSION

The values of resistance, Rx, and capacitance, Cx, have

been measured in aqueous solutions of sodium chloride across

the peritoneal membrane using the LCR bridg as functions of

2 4 temperature and frequency ranging from 10 Hz to 10 Hz. The

results (Tables : 2.7 to 3,u) reveal that the resistance, Rx,

across the peritoneal membrane decreases with an increase in

the concentration of sodium chloride in its aqueous solution

and applied frequency. An increase in temperature also causes

decrease in the value of Rx across the membrane. Since, the

increase in concentration of the electrolyte solution causes

a progressive accumulation of the ionic species within the

membrane, the membrane becomes more and more conducting to

ions and as such the resistance decreases with an increase

in the electrolyte concentration, whereas an increase in the

value of applied frequency results in a fast exchange of

polarity between the ions and the membrane material which, in

turn, causes the leakage of the memorane and thus, decreases

the resistance. Since the biomembranes, which can exist in

different structural phases, appear to be liquid crystalline

structure at higher temperatures with loose packing, high

fluidity and high rate of in-plane diftusion of proteins as

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53

TABLE 2.7 : Observed values of resistance, RxCKH ) in aqueous

solutions of sodium chloride across peritoneal

membrane as functions of concentration and temperatu:

Elec t ro ly te Concen Cmol l '

0.001

0.002

0.00b

0.01

0.02

0.05

0 . 1

0 . 2

tration -h 15

5 . 3 0

4 . 7 0

2 . 3 0

0 . 9 1

0 . 6 2

0 . 2 4

0 .U93

0 . 0 0 5

Terr

20

5 . 1 0

4 . 5 0

2 . 0 0

0 . 7 8

0 . 5 8

0 . 1 5

0 . 0 8 6

0 . 0 6 1

i p e r a t u r e

25

4 , 7 0

4 . 2 0

1 .80

0 . 7 2

0 . 4 8

0 . 1 2

0 . 0 8

0 . 0 5 5

(±0.1°C)

30

4.50

3.80

1.60

0.58

0.36

0.10

0.07

0.046

35

4.20

3.60

1.30

0.46

0.33

0.09

0.062

0.038

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54

TABLE 2.8 : Observed values of capacitance, Cx^nF) in aqueous

solutions of sodium chloride across peritoneal

membrane as functions of concentration and temperature

Electro Concent

^mol l'

O.CX)l

0.002

0.005

0.01

0.02

0.05

0.1

0.2

lyte ration

b 15

0.014

0.029

0.048

0.078

0.091

0.38

0.62

0.85

Temperat

20

0.016

0.031

0.050

0.08

0.094

0.41

0.65

0.87

ure (,jh 0.

25

0.019

0.034

0.053

0.083

0.097

0.45

0.67

0.89

i°c;

30

0.022

0.U35

0.055

0.087

0.10

0.48

0.69

0.92

35

0.025

0.038

0.059

0.091

0.15

0.52

0.72

0.95

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55

TABLE 2,9 : Observed values of r e s i s t a n c e , Rx(Kn ) in aqueous

so lu t ions of sodium chlor ide across pe r i t onea l

membrane as functions of concentra t ion and frequency,

E lec t ro ly t e Concentration (mol l"-'-)

0.001

0.002

0.005

0.01

0.02

0.05

0 . 1

0 . 2

102

4.70

4.20

1.80

0.72

0.48

0.12

0.08

0.055

Frequency (Hz)

io3

4.50

4.00

1.60

0.69

0.46

0.10

0.075

0.053

10^

4.30

3.90

1.40

0.67

0.44

0.08

0.07

0.050

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56

TABLE 3,0 : Observed values of capacitance, CxC|iFj in aqueous

solutions of sodium chloride across peritoneal

membrane as functions of concentration and frequency,

Electro Concent

Cmol l"

0.001

0.002

0.005

0.01

0.02

0.05

0.1

0.2

lyte ration

102

0.019

0.033

0.053

0.083

0.097

0.45

0.67

0.89

FreauencY (Hz)

10^

0.017

0.031

0.051

0.080

0.094

0.43

0.63

0.85

10^

0.015

0.027

0.048

0.077

0.091

0.39

0.59

0.81

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57

well as of phospholipids. But at low temperatures, the mem­

brane appears to be in gel phase, being more restrictive to

the permeants. Consquently, an increase in temperature

results in a corresponaing decrease in resistance.

On the other hand, the capacitance, Cx, increases with

increases in electrolyte concentration and temperature. This

may be attributed to the fact that the changes are produced

in the dielectric properties (€ ) and the effective thickness

Cd) of the membrane/electrolyte in accordance with the follow­

ing equation for the parallel plate capacitor :

Cx = €/36xl0' d ... U ;

which means that the capacitance increases with an increase

in the dielectric constant { €. ) and the effective thickness

(d) of the membrane. Since the increase in the electrolyte

concentration results in an accumulation of ions within the

membrane and accordingly the effective thickness of the mem­

brane decreases due to squeezing of water molecules from the

membrane by incoming ions. The capacitance, therefore, in­

creases with the increase in electrolyte concentration.

In order to know the mechanism of flow of ions through

the membrane, the impedance, z, alongwith the membrane

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: 58 :

r e s i s t a n c e , Rm, and memiorane capaci tance, Cm, have been eva­

luated on the bas is of the following equation proposed by

Lakshminarayanaiah and Shanes (101) for an equivalent c i r c u i t

model :

Rm = Rx[l+(|^)2] ... (2}

^^ = (i^usi ••• ^'^

where u = 2nf, 'f the applied frequency (Hz) used to

measure Rx and Cx; Xx, the reactance the values of which have

been depicted in Table 3.1 - 3.3.

The impedance, Z is given by relation,

Z = V"Rx + Xx^ ... (.5)

and the derived values of Z are summarized in Table 3.4.

Which shows that the impedance decreases with the increases

in electrolyte concentration and applied frequency suggesting

that the flow of ions takes place with ease across the membrane

Electrical double layer theory (102) may also be used to

interpret the changes produced in the magnitude ot the

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59

TABLE 3.1 : Computed values of resistance, Rm(Kn^ in aqueous

solutions of sodium chloride across peritoneal

membrane as functions of concentration and

frequency.

Electro Concent (moi r

0.001

0.002

0,005

0.01

0.02

0.05

0 . 1

0 . 2

ilyte r a t i on

i o 2

19.71

9.69

6.80

5.73

5.81

1.16

0.79

0.82

Freauencv (Hz>

10^

4.69

4.07

1.66

0.75

0.52

0.11

0.084

0.047

10^

4.302

3.901

1.401

0.671

0.441

0.0802

0.0701

0.03501

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60

TABLE 3.2 Computed values of capacitance, CmxlO C^F) in

aqueous solutions of sodium chloride across

peritoneal membrane as functions of concentration

and frequency.

Electrolyte Concentration

(mol l"-) 10'

Frequency (Hz)

10^ 10

0.001

0.002

0.005

0.01

0.02

0.05

0.1

0.2

0.144

0.188

0.463

0.733

1.04

4.05

5.99

8.59

0.00706

0.00502

0.0188

0.0612

0.112

0.535

0.639

1.67

0.0000912

0.0U00616

0.000269

0.000733

0.00139

0.00876

0.0101

0.0255

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61

TABLE 3.3 : Computed values of reac tance , Xx x 10 ( K n ) in

aqueous so lu t ions of sodium chlor ide across

per i tonea l membrane as funct ions of concent ra t ion

and frequency.

E lec t ro ly t e Concentration

10 '

Frequency (Hz)

10^ 10

0.001

0.002

0.005

0.01

0.02

0.05

0.1

0.2

8 . 4

4 . 8

3 . 0

1.9

1.6

0.354

0.238

0.177

0.936

0.513

0.313

0.199

0.169

0.037

0.0253

0.0187

0.106

0.0589

0.0332

0.0207

0.0169

0.00408

0.0027

0.00197

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62

TABLE 3.4 : Computed values of impedence, Z{KSl ) in aqueous

so lu t ions of sodium chlor ide across pe r i t onea l

membrane as functions of concentra t ion and frequency

Electro Concent

(mol l"

0.001

0.002

0.005

0.01

0.02

0.05

0.1

0.2

lyte ration

10^

9.63

6.38

3.50

2.03

1.67

0.37

0.25

0.18

Frequency (Hz)

10^

4.60

4.03

1.63

0.72

0.49

0.11

0.079

0.042

10^

4.301

3.9004

1.4004

0.6703

0.4403

0.0801

0.0701

0.0351

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63

membrane capacitance with the changes in electrolyte con­

centration and this has been applied by several investigators

(80-83^ to account for various membrane behaviour. The

electrical double layer capacitance can be calculated in

the light of the following consideration :

To interpret the impedance characteristics of the double

layer effect, Armostrong (103) modified the equivalent circuit

model which represents a solid smooth surface in contact with

the penetrating electrolyte. The impedance expression of the

proposed equivalent circuit for the membrane/electrolyte is

1+juCdRt 1+juCgRb 1+juCmRm

where, Cg is the specific geometric capacitance which is

assumed to depend upon the structural details of the membrane

framework, Cd the interfacial double layer capacitance, Rb the

bulk resistance of the membrane and Rt is the charge transfer

resistance between the membrane electrolyte interface assuming

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64

the transfer to be a single step process.

The real and imaginary parts of equation ^6) are given

by

Rm Rb Rt . . . ( 7 ) 9 9 9 ~ 9 9 9 9 9 9

l+u'^Cm Rm^ i+u'^Cg^Rb'^ l+u^Cd'^Rt'^

CmRm^ _ CgRb^ 2CdRt^ . . . ( s ) 9 9 9 ~ 9 9 9 9 9 9

1+u^Cm^Rm^ 1+u^Cg^Rb^ l+u^Cd'^Rt^

At higher frequency, equation (9) can be approximated to

+ 7^— (9) Cm Cg Cd

This equation indicates that the membrane/electrolyte system

may be considered to be composed of three capacitors in series,

the geometric capacitor being placed between the two inter-

facial double layers as suggested by Armstrong (103).

When 1/Cg >> 2/Cd at high electrolyte concentration or

significant surface charge, Cm nearly approaches Cg, i.e.,

Cm ^ Cg. Taking the value of Cm as Cg at IM NaCl solution,

the different values of Cd at other electrolyte concentrations

have been calculated by using equation (9) and these calculated

values have been summarized in Table 3.5. It appears from these

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65

TABLE 3.5 : Values of electrical double layer capacitance,

Cd(|iF) calculated from equations C 9 ) and (14)

Cd(pF) from eqn. ( 9)

0.U14

0.038

0.074

0.124

0.230

1.21

1.49

5.31

Electro Concent (moi r

0.001

0.002

0.005

0.01

0.02

0.05

0 . 1

0 . 2

>lyte ;rat ion

Cd(^F) from eqn. (14)

7.199

10.18

16.10

22.77

32.20

48.71

71.99

101.18

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66

results that the increase in concentration of sodium chloride

solutions results in a decrease in the value ol Cd which means

that Cm depends on Cd.

When 1/Cg 2^ 2/Cd,

Cm differs from Cg and this happens due to the absence

of charge in low electrolyte concentration.

However, the exact form of double layer capacitance

depends upon the fixed charge (as) and the membrane potential

(Vm).

If as = 0, then

nA ^€u Sin ha , . C^ = (l/k)d ••• UO)

14 ^ where, o = 8.85x10 F/cm, €u is the dielectric

constant of water, a is a constant depending upon the struc­

tural details of the membrane and (l/k) is the Debye-Huckel

length given by

1 4.31x10"^ I T ' " , ,1/2 ••• ll''

where, \i is the ionic strength of the electrolyte solu­

tion, a is determined from the following relation,

L [— Sin ha + 2j = (^. K ... (12) (l/k)Cg 2{Rl/l-)

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67

or a l t e r n a t i v e l y ,

CmVm = op = 4Fc( l /k) Sin ha . . . (13)

where op i s the po la r i za t ion charge on the

capac i to r .

If Vm << RT/F, Sin ha = a, so tha t equation (11)

reduces to

nri ^ O ^ U . , ,

^ = ( l A ; ••• (1^)

The values of Cd, thus obtained at different concentra­

tions of sodium chloride solution are given in Table 3.5, it

appears that the values of Cd obtained using equations (9)

and (14) differ from each other which may be due to the pre­

sence of polarizing charge and other structural details of the

membrane matrix.

Since the membrane under investigation possesses the

positive charge and the counter ions form the double layer

at the membrane surface, the increase in concentration of

electrolyte in solution causes the counter ions, in the form

of double layer, to be pushed inside the membrane and thus

results in a decrease in the effective thickness of the mem­

brane and an increase in the ionic charge within the membrane.

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68

Consequently, the membrane becomes more conductive to the in­

coming ions which in turn supports the trend in the behaviour

of the membrane resistance under discussion.

Thus, the diffusion of ions through the membrane increases

with an increase in the concentration of electrolyte in solu­

tions due to the formation of a double layer by the counter

ions which get pushed inside the membrane, by the incoming

ions. Such a conclusion finds support in the light of the

trend in the behaviour of impedance data recorded in the systems

under discussion.

Page 80: TRANSPORT OF IONS THROUGH BIOMEMBRANES · control, the cell utilizes a delicate membrane of about 70 A thick. At one time, the transport of materials across the mem branes was considered

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