A voltammetric investigation of TCNQ-containing bilayer lipid membranes

Vol. 119, No. 1, 1984

SIOCHEMICAL AND SIOPHYSICAL RESEARCH COMMUNICATIONS

February 29, 1984

Pages 372-375

A VOLTAMMETRIC INVESTIGATION OF TCNQ-CONTAINING BILAYER LIPID MEMBRANES H. Ti Tien Department Received

January

and Z.K.

Lojewska

of Physiology/Biophysics, Michigan East Lansing, Michigan 48824 25.

State

University

1984

SUMMARY: Cyclic voltammetry (CV) is a useful tool for investigating electrochemical redox reactions. A number of bilayer lipid membranes containing TCNQ (7,7,8,&tetracyanoquinodimethane) have been studied by the CV technique. The results indicate electron movement across the lipid bilayer and redox reactions at the membrane/solution interfaces. The mechanisms in,

on and/or

complexity

across

of living

investigating lipid

liposomes).

structures.

Numerous

better

or BLM for

under

separation

short

to be the principal evidence

somewhat

equivocal,

in

for

these

technique remedy

voltammetry (7).

lipid

(CV),

dye-sensitized

new type

Copyright All rights

stems

theoretical

basis

which

is

eminently

BLM (8).

in the course

In this

voltammetry

suited

paper

(CV)

$1.50 372

In the absence

has not

is

supportive

(4-6).

reactions

a suitable

in the

experimental

been

tried.

To

of cyclic

for

redox

investigating of our

studies

briefly

reactions

of photoeffects the

to the BLM system

TCNQ (7,7,8,8-tetracyanoquinodimethane)

0 1984 by Academic Press, Inc. of reproduction in any form reserved.

processes

of redox that

or

charge

BLMs and liposomes are

bilayer

BLMs and

to use the method

we describe

as applied

membranes

transduction.

demonstration fact

to the

(planar

electronic

data

place

been made in

on pigmented

in these

the

have

lipid

These

experimental

from

mainly

light-induced

energy

we have had occasion

of BLMs containing

0006-291X/84

certain

of CV was used

of cyclic

for

of a clean-cut

bilayers

situation,

(l-4).

processes

well-established

The method

aspects

reactions

for

takes

bilayers

especially

support

owing

however

bilayer

electronic although

attempts

to date,

reaction

understood

and spherical

mechanisms

the lack

with this

for

not well

lipid

provide redox

(redox)

artificial

obtained

and eventual

One reason

defined

illumination,

of light

dark

are

The results

liposomes

oxidation-reduction

biomembranes

simpler,

membranes

appear

by which

in

essential and report whose

a

BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS

Vol. 119, No. 1, 1984 electrical

properties

redox

reactions

from

one side

are

such as to leave

little

doubt

in the dark,

with

electrons

are occurring

of the BLM to the

that

transmembrane

being

transferred

other.

MATERIALS AND METHODS: All reagents and special organic compounds such as 7,7,8,8-tetracyanoquinodimethane (TCNQ) and crystal violet (gentian violet) were obtained commercially and were of the highest quality available. The bilayer lipid membranes (BLMs) were formed at room temperature according to the technique described elsewhere (1). The hole of 0.15 cm diameter in the Teflon cup was usually pretreated with the BLM-forming solution to be used later. The BLM-forming solution consisted of a mixture of phosphatidylethanolamine, PE (3.3%) and phosphatidylserine, PS (1.3%) in n-decane. To form TCNQ-containing BIM, aliquots of a saturated solution of TCNQ in CHCl were added to the lipid solution. The bathing solution usually contained 0.1 iI KC1 and O.lM sodium acetate buffer (pH 5.5). Unless otherwise noted, the outer solution also contained 0.5mM K3Fe(CN)6 and K4Fe(CN)6. The electrical properties of TCNQ-containing and other BLM were investigated by a voltammetric method known as cyclic voltammetry (CV). The basics of cyclic voltammetry consist of cycling the potential of a working electrode in an unstirred solution and measuring the resulting current. The potential of the working electrode is controlled relative to a reference electrode, which is provided by a triangular potential waveform generator. The current/voltage (I/V) response patterns obtained during the potential scan by measuring the current at the working electrode is known as a voltammogram. Interpreting such voltammograms based on electron transfer and subsequent redox reactions at the working electrode/solution interface has been well-established and widely employed (7,9). Typical working electrodes used in CV are either Pt, glassy carbon or carbon paste electrode. It is realized of course that an haves essentially as an excellent insulator (specific :~2::::~,"~0~~ n ) and does not function as a working electrode. It is necessary therefore to incorporate certain compounds into the BLM endowing it with the desired characteristics. For such purposes, we have tried a number OF compounds such as TPP (tetraphenylporphyrin) and organic conductor TCNQ. The other experimental details are given elsewhere (8). RESULTS AND DISCUSSION: certain

dyes,

voltage

(examples:

violet

when incorporated

violet

violet,

altered

consistent

with

the

electron bathing redox

solution, reaction

1 shows

the

membranes

(crystal

violet,

malachite

a minute Fe2+ - e *

amount

2+

373

This found

that

and Janus to one side

present.

of BLM

observation

of them are

green

was always

place

resistance

can move in the

most

crystal

to investigate

the

who have

that

open-circuit

ZB, -82mV;

that

Fe3+ was added

of Fe

Fe3+ takes

violet

(liposomes) because

only

large

increased.

(lo),

easily,

Although

was observed

unusually

clearly

bilayer

(8).

it

dyes we decided

is

of Sudo et al. lipid

such dyes

acceptors

Of these Fig.

findings

(8)

E, 86mV; Methyl

as the dye concentration

and penetrate study

study

BLM, exhibit

-1lOmV).

dyes in spherical-bilayer

In our

Black

in more detail.

is greatly

phase

into

Chlorozol

or gentian

gentian

In an earlier

certain lipid

amphipathic. green)

act

of the

Therefore,

at the membrane/solution

is

the interface

as

Vol. 119, No. 1, 1984

I I1

BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS QAJ

I (CURRENT

DENSITY,

W5A/cm2)

T3

-150_ _.-.A._

-100

0 +/

-7

C

/“o /

/

/+

0

/ 0

02

/o

Fig.

1. Effect of gentian violet (crystal violet) on PE/PC BLM voltammograma. BLMs were formed in O.lM KC1 and O.lM sodium acetate at pE 5.6. The bathing solution on both sides of the membrane also contqined gentian vigfet at three qjfferent concentrations: (a) 7.8 X 10 M (b) 1.25 X 10 M (c) 5 x 10 M. 2. Typical voltammograms for TCNQ-containing BLMs except (a). All BLMs were formed from the PE/PC lAgid solution in O.lM KCl. Other con-4 itions were: (a) 5 X 10 M K Pe(CN) + K Fe(CN) // BLM // 2.4 X 10-4M ascorbic acid. (b) O.lMKt?? // TCbQ-BLti // 0.P M KCl. (c) 5 X 10 M K3PeQN) + K Fe(CN) // TCNQ-BLM // 2.4 X 10s5M genrtan violet. (d) 5 X 10 M a,,Fe(eN)6 + a4Fe(CN)6 /I TCNQ-BLM /I 9.4 X 10 M ascorbic acid.

Fig.

mediated

by the dye-containing

violet)

is

corroborated

An unmodified not

function organic

results

are

have -lcm-1 gain

BLM behaves

obtained.

1.

It

is

large

of E'e(CN)i-/Fe(CN),

other

role

experimental

coincides

with

of a working conditions

the x-axis

as already

that

into

class

insulator

incorporation

BLM, very

exciting

of molecular

conductors,

radical

(11).

Fig.

that

2 shows

BLMs (curves b-d). With equal 4- on one side of the TCNQ-BLM, In the absence

electrode. the same,

on the

scale

the I/V used 374

is

(Curve

- lo3

("' lo2

molecule

"electron-poor"

noted.

and does

upon

at room temperature

symmetric,

concentration the

to the

conductivity

of TCNQ-containing

can play

found

such as TCNQ (11)

voltammograms

potential

as an excellent

We have

to become an anion

of the dye (crystal

membrane

essentially

TCNQ belongs

a planar,

an electron

dark

electrode.

semiconductors

shown remarkably

Such a behavior

by a negative

as a working

certain

BLM.

of

which R

can easily

the molar the membrane

of TCNQ in BLM with

linear;

it

A, Fig.

2).

practically In the absence

BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS

Vol. 119, No. 1, 1984 of redox curve

couples

remains

when redox

linear

Curve

the TCNQ-BLM,

the other

of crystal

Here

just

electrons

acid

moving

is

type

believed

of BLM containing

little electrons

doubt

that

being

applied

transmembrane

ACKNOWLEDGEMENTS:

Major

obtained

the cyclic

from funding

electrical

redox

of this

couple. is

via

of crystal 2.

with

technique are

occurring

was provided

D, Fig. acid

to a new

such as to leave in the

of the BLM to the other work

the

TCNQ-BLM.

voltammetric

are

by the

from

instead

of

The

caused

movement

properties

reactions

one side

on one side

to dehydroascorbic 4- side

seen

the bathing

as shown in Curve

to be oxidized

TCNQ, whose

transferred

electron

are

violet

which

is present

the Fe(CN)i3/Fe(CN)6

we have

dye,

acid

are

into

Fe(CN)z-/Fe(CN)z-

of the

BLM, the I/V

in voltammograms

of crystal

transmembrane

results

towards

In conclusion,

the

When ascorbic

TCNQ in the

introduced

the effect

on the side via

changes are

contained

violet

the opposite

ascorbic

Dramatic

2 shows

side

side.

but with

compounds

negative

Fe(CN)z-/Fe(CN)iviolet,

B).

C of Fig.

of Em is

reduction

(Curve

solution,

or membrane-active

solutions.

polarity

in the bathing

dark,

with

side.

by NIH GrantGM-14971.

REFERENCES: 1. Tien, H.T. (Ed.), Berns, D.S., Hong, F.T. and Strauss, G. (1976) Photochem. Photobiol., 3, 95-189. 2. Mauzerall, D. (1979) + Light-Induced Charge Separation in Biology and Chemistry (Ed. H. Gerischer and J.J. Katz) Verlag Chemie, Berlin. 241-254. 3. Ford, W.E. and Tollin, G. (1982) Photochem. Photobiol., 25, 809-819. 4. Tien, H.T. (1982) in Transport in Biomembranes: Model Systems and Reconstitution (EdTR. Antolini, A. Gliozzi and A. Gorio) Raven Press,N.Y., pp. 57-74. 5. Feldberg, S.W., Arme, G.H., Bell, J.A. and Cheng, C.K. (1981) Biophys. J., 2, 149-163. 6. Tien, H.T., Karvaly, B. and Shieh, P.K. (1977) J. Coll. Int. Sci., 62, 185-188. 7. Adams, R.N. (1969) Electrochemistry at Solid Electrodes, Dekker, Inc., New York, Chap. 5. 8. Tien, H.T. and Kutnik, J. (1984) Photobiochem. Photobiophys. in press 9. Bard, A.J. and Faulkner, L.R. (1980) Electrochemical Methods, Wiley, New York. 10. Sudo, Y., Knwashima, T. and Toda, F. (1980) Chemistry Letters, 355-359. 11. LeBlanc, O.H. (1967) In: Physics and Chemistry of the Organic Solid State, Interscience-Wiley, p. 182.

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