The reaction of the superoxide ion with iron(III)protoporphyrin IX dimethyl ester perchlorate: Evidence for a stable dioxygen complex

Vol. 56, No. :3, 1974

BIOCHEMICAL

AND BIOPHYSICAL

RESEARCH COMMUNICATIONS

THE REACTION OF THE SDPEROXIDE ION WITH IRON(III)PROTOPORPHYRIN DIMSTHYL ESTER PERU&ORATE:

H. Allen Inorganic

IX

EVIDENCE FOR A STABLE DIOXYGEN COMPLEX.

0. Hill*, Chemistry

David R. Turner Laboratory, Oxford,

England.

and Georgio Istituto Received

Pellizer di Chimica,

December

Universita

di Trieste,

Italy,

7,1973

SUMMARY: The reaction of superoxide ion with one equivalent of iron(III)protoporphyrin IX dimethyl ester perchlorate in NNdimethylformsmide at -50% yields a complex with an absorption spectrum comparable to that of oxymyoglobin. The complex decomposes at -loo to iron(II)protoporphyrin IX dimethyl ester which does not react with oxygen.

The nature

of

continues the

the

to attract

role

of

the

been numerous chemistry

of

As part

metal

complexes.

proposal

we have

that

be formulated

study

the

the

reaction

biological interest

* Author

its by the

dioxygen

complexes

some aspects

in simpler

revival

of

(9)

superoxide IX dimethyl

with ester

should

@ 19 74 by Academic Press, Inc of reproduction in any form reserved.

There

have

of

the

complexes.

with

a number

heme proteins iron(III)

a simple perchlorate,

be addressed.

the

superof

of an earlier

coboglobins),

ion

to

of

(I)

to whom enquiries

iron

regard

chemistry

(7)

of the

derivatives

investigated

complexes.

reactions

739 Copyright AN rights

with

(61 in the

Intrigued

iron(III)protoporphyrin cloq-'

particularly the

systems

investigated

of

and hemoglobin

to reproduce

(3-5)

as superoxide

extensively

(1,2)

of myoglobin

in stabilising

of a continuing ion,

the

protein

these

complexes

attention

attempts

oxide

to

dioxygen

(8) could

(analgous we chose

to

heme derivative, ~e(III)(PPDEl]'

Vol. 56, No. 3, 1974

BIOCHEMICAL

AND BIOPHYSICAL

RESEARCH COMMUNICATIONS

1 II

‘

-T \ -5

. \

500

Fig.1.

(al

Absorption at -50%

(b)

RESULTS:

The spectrum

NN-dimethylformamide heme.

(11)

same solvent. in Figure of

the

compared lengths

of

various with

This

that

the visible

is

(2,12)

C104-

typical

(101 at

proteins,

the

product

-50%

with

in DMF

of this

740

I in dry spin

iron(III1

an electrochemically-

is

U.V.

2. Soret

shown

to those

vxyperoxidase

in Figure and the

in the

reaction similar

oxyhemoglobin,

a- and S-bands

-50%(----l

superoxide,(

has many features

of oxymyoglobin

of

of a high

tetrabutylammonium of

in DMF at

of a solution

rapidly

spectrum

oxy-heme

@e(III)(PPDEa+

of Fe(II)(PPDE)

I(a))

reacts

The spectrum

2(a).

of

spectrum

(DMF),

solution

of )

(Figure

Such a solution

prepared

spectrum (-

Absorption

11OO"m

700 703

and is

The wavebands

are

Vol.

56,

No.

3, 1974

BIOCHEMICAL

AND

BIOPHYSICAL

RESEARCH

COMMUNICATIONS

10

10

:’ 0 “; ,

c;,

I

-5

.

\ 400

300

Fig.2.

(a)

Absorption

500

spectrum

(b)

Absorption at

similar;

-50°C,

the

importantly a pronounced

20%.

700 700

of

the

900

product

1lOOnm

of

the

reaction

between

superoxide

in

( -)

spectrum

(2,121

of oxymyoglobin

in water

pH 7

c----l

u-band there

i

and tetrabutylammonium

Fe(III)PPDE]+C104DMF at

\

6ca

is more is

shoulder

absorption

intense

than

in the

at 825 nm, compared

741

the .nfra-red

p-band

and most

in the

form

of

to 950 nm in oxymyoglobin.

Vol. 56, No. 3, 1974

BIOCHEMICAL

The absolute

intensities

oxymyoglobin

though

of closer

bands

of oxymyoglobin

bands

may be comparable

complex.

absorption different

of

to oxyperoxidase

the

product

maxima

(particularly

the

trans

to the

environment

of

reaction

is

revealed

in Figure

at a 1:l

ratio

of

I to

again

reaction

being

II,

a dioxygen

complex

ke(III)(PPDE)]+C104On warming I and II, Figure S.C.E

a solution the

l(b), in DMF.

Fig.3.

containing

spectrum prepared

changes

consistent

the

Titration superoxide

the

of

to one identical

product

reduction

of the

of@'e(III)PPDE)+ in DMF at

-5O'C.

742

of

the

of

the

effective stoichiometry is observed

product

of

dimethyl

+ Bu4N+ClO the

reaction

to that of

decomposition

C104-

the

may be due to

protoporphyrin

product

the

a dioxygen

an end-point

02Fe(PPDE)

in

simple

different

with

iron +

is

The overall

3 where

by electrochemical

Neither

the

heme,

+ Bu4N+0 2

strengths

bands)

and/or

of

since

and wavelengths

infra-red

the

However

reaction

width

oxygen

than

and in the

of the

in line

are lower

oscillator

in the heme proteins

that

RESEARCH COMMUNICATIONS

(1).

the

differences

of the

the

and p-bands

the

ligands

dielectric

the a-

are narrower,

Assuming

heme complex,

AND BIOPHYSICAL

with

4

the ester:

-

(1)

between

of Fe(IIl(PPDE) I at of

-0.4V the

Vs dioxygen

tetrabutylsmmonium

Vol. 56, No. 3, 1974

complex from

BIOCHEMICAL

nor Fe(II)(PPDEl

25'

to -50%

not

overall

paramagnetic

product

is

formulated

complex

of

iron(

former

latter

would

reaction

since,

be diamagnetic. the

complex

intensity

DISCUSSION:

The results

that

nucleophilic,

can displace porphyrin

iron

temperature. solvent

is

coordinate

dioxygen

might

and the superoxi.de

derivatives

since,

example,

for

precede

suggestive.

to lend

electron

formation Efforts

of the to

isolate

transfer complex. the

displace

with

a five-

decomposition in the

a five

coordinate

iron

dioxygen

complex

described

formulation

the

heme proteins

This

need

from

superoxide However

presumed

FCKNOWLEDGEMENT: We wish to thank the Science support and a Studentship to one of us (D.R.T.), R.J.P.Williams and Mr. P.Skyte for advice. 743

with

cannot

protein

to the of

of iron(II1).

added.

at low

react

the

I, and

complex

of the

of

with

being

resulting

product

the

support

analogouscomplexes

ion,

must

functions

of

has been

nucleophil it

immediate

of preparation

be thought

presumably

a poor

One of the

II

to decomposition

presumably

the

of

the

diminishes

superoxide

and the

being

in that

and presumably

superoxide

may be to make available

The method

herein

the

the

or a dioxygen

be expected

porphyrin

respect

though

ccmplex.

therefore

complex.

with

complex,

the

solvent

oxygen,

Fe(II)(PPDEj iron

proteins

the

stable

Molecular

from

the

suggest

of iron<1111

of a solution

of the

of

as a convenient of whether

coupled

spectrum

= 2.04;

serves

would

On titration

e.p.r.

(gl

irrespective

as a superoxide of

II

also

be antiferromagnetically

of

of

in DMF at -120°C)

when one-equivalent

might

reaction

spectrum

has vanished

of

at temperatures

(2)

resonance

a loss

would

intensity

the

oxygen

--) 02 + Fe(II)(PPDE)

= 2.009; g3 = 2.004, g2 method of following the

the

that

molecular

RESEARCH COMMUNICATIONS

reversible.

The electron

the

with

suggesting

02Fe(PPDE) is

react

AND BIOPHYSICAL

not

it

dioxygen

of this as

necessarily

be so

to iron(II1) is

at

least

complex

continue.

Research Council for and Drs. D.Dolphin,

heme

BIOCHEMICAL

Vol. 56, No. 3, 1974

AND BIOPHYSICAL

RESEARCH COMMUNICATIONS

REFERENCES 1.

Blumberg, W.E., Peisach, J.,Wittenberg, (1968) J.Biol.Chem., 243, 1854-1862.

2.

Antonini, E., and Brunori, M., Hemoglobin and Myoglobin in their reactions with ligands, Frontiers of Biology, Eds., Neuberger, A., and Tatum, E.L., (1971) 2l, North-Holland Publishing Co.,Amsterdam.

3.

Wang, J.H. (1962) Oxygenases, New York, p.469-516.

4.

Baldwin,

5.

Chang, 5811.

6.

Turner,

7.

Wittenberg, J.B., Wittenberg, B.A., Peisach, J., (1973) Proc.Nat.Acad.Sci. U.S.A. 67, 1846-1853.

8.

Weiss,

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Hoffman, B.M., 67, 637-643.

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Smith,

11.

Maricle,

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Bowen,

J.E., C.K.,

and Huff,

(1973)

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J.,

J.,

and Traylor,

D.R.,

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and Hodgson, (1949)

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J.B.,

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and Petering,

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