Theoretical study of spin-labelled aliphatic chains in bilayers

BIOCHEMICAL

Vol. 58, No. 2, 1974

AND BIOPHYSICAL

RESEARCH COMMUNICATIONS

THEORETICAL STUDY OF SPIN-LABELLED ALIPHATIC Jacques

CHAINS IN BILAYERS

BELLE and Pierre

Centre

de Recherche Domaine

February

Pascal

Universitaire

- TALENCE - France

33405

Received

BOTHOREL

Paul

25,1974

SUMMARY Some authors have studied the spin-labelled order parameter in phospholipidic bilayers. It is now possible to calculate this parameter through rotation isomer theory and molecular interactions (WIRI model). Its variation along the chain is described. A good agreement is shown with experiments. Therefore an important theoretical parameter is the distance d between closed chains. Theoretical d values for agreement are a little too large. We recently properties

of aliphatic

implies

rotational

(dispersion

melting

a very

parameter

biological

membranes

or phospholipid

around

along this

s3 = ;

(3 < cos2

is e3 of the

the

angle

nitrogen

for

is

defined

some structural WIRI model

(l-4).

and chain

interactions

in an hexagonal More

chains

spin

box,

recently

: the

label

chain radical

order

large atoms).

in bilayers

is

to

bound change

the

parameter

of

have

fluidity

consecutively

First

calculation

techniques

fluidity

by putting

study

(n = 14 to 22 carbon

Microscopic

A theoretical It

to

chains,

large

A nitroxide

atom.

chain.

technique.

(4)

S For many years 3’ to study aliphatic (5).

bonds

to hexan

was calculated

carbon

the

carbon

are enclosed

applied

atom can be followed

atoms with

tool

model

in mono and bilayers

a new application

powerful

carbon

were

entropy

We now present label

chains

Two chains

calculations

chain

a theoretical

isomerism

forces),

of all,

spin

proposed

a fatty of the radical

proved and acid

labelled on carbon

S3 can be measured

as : (6)

e3> -1). between

the

atom of the

axis radical.

normal

to the

layer

and the

pH orbital

Vol. 58, No. 2, 1974

BIOCHEMICAL

/ &J---z \ L------l / \

d&/4

G2 \

0

- The two aliphatic

Fig,

2 - Order parameter as a function of number n* of the (semilog plot) : (0) theoretical data for various (X) experimental data for decanol-sodium decanoate stearic acid as spin label(see figure 8).

parameter is

now possible

earlier

that

interacting

only

for

Figure carbon

polar between

the

the

and large

box

(WIRI

are

enclosed

a semilog between

plot

model).

carbon d values mixture

of the

paramagnetic

atom

; and

in the

Calculations

order

been previously

a specific

d value were

an energy difference -1 mole . Lennard-Jones

(when

variations

is little

(see

2 shows a general

near

d values

described

polar dispersion

not

observed freedom

table

forces

when distance near

the

polar

434

(see

along

to

S3 versus

head.

For

n*

and

carried

out

at room

between

gauche

and

we have

used

3).

the

chain

a linear

cancel). small.

for

1).

distance

is

d is

figure

ring

potentials

S3 variation

are going

box

the

I in reference

S3 decrease

The log

head).

must be remembered

parameter

(T = 25OC) and with AU: = 600 cal.

It

methods

N-oxylaxazolidine

two

box.

(4).

with

in an hexagonal

to

chains

S3 parameter

chains

corresponds

isomers

have

(3)

chains

number

Figure

atoms

hexagonal

Each curve

temperature

is obtained

in the

to calculate

short

2 gives

atoms

head.

chains

calculation

described

have

/

1

It

trans

\

/

RESEARCH COMMUNICATIONS

Fig.

Order

the

\

AND BIOPHYSICAL

On the In both

very

small

(maximum one for contrary, cases,

value large linear

carbon

distances,

Vol. 58, No. 2, 1974

the

BIOCHEMICAL

parameter

S3

increases

rigid

chain

as in the

small

at the

chain

along

the

values).

chain

for

almost

crystalline

Disorder the

trans

ii)

a fluid

between

is

chain,

almost at the

"crystalline" "liquid

easy.

Spin

in the

S3 values In the with

label and the

d value).

acid On the

phospholipid last

and bilayer

molec;les

of the

contrary

the

shape

small

and al.

bilayers

tried (8).

to

the

Unfortunately, bilayer

agreement

stearic the

to that

Each carbon gauche

of

atom

conformations. we can see along from

chains

form

results

often

on the

3

a

shows

curve

of the

a linear

not

curve

is

spin

label(6). versus large

with

a

bilayer.

analog

to the

our

label

(n = 16 and

10

carbon

The data

from

observed crystalline

experiment,

of sodium

acid

calculations

mclecule atoms

these

decanoate

has only

with

the

In the

theoretical

and decanol.

one chain

is longer

than

results

authors

the

of

studied As the

and is

bilayer

saturated.

chains

of the

respectively).

Seelig

with

and al. are included in figure 2. A good 0 d = 14A. But this theoretical value is very

state,

the

distance

435

between

the

chains

very The

with

linear

same lecithin-cholesterol

not

(5-7).

variation

variation is

is

different

nature

theoretical

experimental

compare

label

In the

S

experimental

spin

is

close

end).

(indeed

are very depend

In a particular

made of a mixture

molecules,

is

n*

is

transformation

ones

(as for

in the

of the

small

d values.

We have Seeling

label

(for

Therefore

alkanes.

log

label the

atom states

radical

and experimental

curve

bilayer

as spin

case,

one for

high.

theoretical

as a spin

chain

the

state).

between

shape

state

for

can be very

state

and numerous

"liquidV

value

nitroxide

a melting-like

to

second

lecithin-cholesterol a fatty

the

same as in liquid

sequences

Comparison

(at

level,

a rigid

This

conformation

molecular

carbon crystal"

state

the

two carbon

and the

conformation.

trans

the

: i)

head

is

S3 values

we can discern

polar

RESEARCH COMMUNICATIONS

1 which

contrary

d values

the

in the

chains

is delocalized

Therefore

between

towards

On the

intermediate

The chain

extended,

and tends

crystal.

end.

AND BIOPHYSICAL

is only

n

R

Vol. 58, No. 2, 1974

1.

4.8

In the

BIOCHEMICAL

liquid

crystal

AND BIOPHYSICAL

state,

this

distance

RESEARCH COMMUNICATIONS

must be higher

than

in

n

the

crystal

but

no

experiment

gives

parameter.

The local

atom than of the

stearic

in the

higher

the

actual

of this

made with

two packed

end can escape

agreement

loss

than with

due to

chains from

the

with

former

is

is

hexagonal

but

: i)

chain

with

of

that

this

decanol-decanoate the

the

spin

steric

length

label

carbon

hindrance

larger

than

neighbour

us an apparent

clear.

14 i is probably

Until

in an hexagonal this

theoretical

obtained

d

box

(the

box.

lower

For

(see

d value

th

fluidity

figure

Preliminary

they

higher

than

us to

increases out

1).

an experimental

allows

- 'a'

too

correct

The

were The actual

have

a little

S3 value, the

actual the

fluidity

as d).

in our laboratory, results

high.

calculations

Therefore

a d th value

are now carried chains.

now our

box

model.

with

difference,

10 interacting ones,

near

can give

value

in our two chains

New calculations box but

label

perturbation

enhancement

theory

the

higher

two reasons spin

important and not

3

theoretical

a a. The positive

value

the

also

one.

the

explanation

more fluidity

ii)

is

probably

for

experimental

However,

chain

is

It

S values

label

bilayer

group,

This

than

acid

fluidity

bulk

nitroxide

molecules.

as much as 14 A.

without

are in agreement

the with

d values.

REFERENCES 1. Bothorel, P., Lussan, C., Lemaire B. and Belle J. (1972) Compt. Rend. Acad. Sci. Paris -274 1541. 2. Belle, J. and Bothorel, P. (1972) Compt. Rend. Acaa. Sci. Paris a 355. 3. Bothorel, P., Belle, J. and Lemaire, B. (1974) Chem. Phys. Lipids (in press). B. (1974) FEBS Letters (in press). 4. Belle, J., Bothorel, P. and Lemaire, 5. Schreier-Muccillo, S. and Smith, Ian C.P. in Progress in Surface and Membrane Science (ea. Danielli, J.F., Rosenberg, M.D. and Cadenhead, D.A.) vol. 9 (1973) Academic Press, New York. 6. Hubbell,L. and MC Connel1,H.M. (1971) J. Amer. Chem. 93 314. 7. Seelig, J. (1970) J. Amer. Chem. Sot. 92 3881. 8. Seelig, J., Limacher, H. and Bader, P-71972) J. Amer. Chem. Sot. -94 6364.

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