57Co MÖSSBAUER EMMISSION SPECTROSCOPY IN COBALT-OCTAETHYLPORPHYRIN

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57Co MÖSSBAUER EMMISSION SPECTROSCOPY IN COBALT-OCTAETHYLPORPHYRIN

H. Sakai, Y. Maeda, H. Ogoshi, H. Sugimoto, Z. Yoshida

To cite this version:

H. Sakai, Y. Maeda, H. Ogoshi, H. Sugimoto, Z. Yoshida. 57Co MÖSSBAUER EMMISSION SPEC-

TROSCOPY IN COBALT-OCTAETHYLPORPHYRIN. Journal de Physique Colloques, 1979, 40

(C2), pp.C2-511-C2-513. �10.1051/jphyscol:19792179�. �jpa-00218555�

JOURNAL DE PHYSIQUE Colloque C2, supplkment au n ^O 3, Tome 40, mars 1979, page C2-5 1 1

H. Sakai, Y. Maeda, H. ogoshix, H. ~u~imoto" and 2. ~oshida*

Research Reactor Institute, Kyoto University, Kwnatori-cho, Sennan-gun, Osaka, 590-04, Japan

f Department of Synthetic Chemistry, Faculty of Engineering, Kyoto University, Yoshida, Kyoto, 606, Japan

RQsum6.- Les spectres Mgssbauer d'lmission du 5 7 ~ e dans les complexes 5 7 ~ o ( ~ ~ ) ~ ~ ~ et 5 7 ~ o ( ~ ~ ~ ) ~ ~ ~ . BsPy (OEP a octaEthylporphyrine) ont St& enregistres B diffsrentes tempEratures avec KbFe (CN)6

3H20 cormne absorbant. Le spectre du complexe divalent plan carre Co(1I)OEP est un ensemble de deux doublets quadrupolaires en-dessousde77 K. Le doublet principal peut Stre attribug au complexe de fer correspondant, Fe(II)OEP, avec un Qtat de spin intenn6diaire (S=l). Le spectre du complexe trivalent hexacoordinE Co(III)OEP.Br.Py est aussi rEsolu en deux doublets quadrupolaires dans le domaine de templrature 4.2 % 295 K; l'un des doublets est attribuQ 3 1'Qtat ferrique bas spin

(S=1/2) et l'autre 5 l16tat ferrique haut spin (S=5/2).

Abstract.- " ~ e Mgssbauer emission spectra of 5 7 ~ o ( ~ ~ ) ~ ~ ~ and 5 7 ~ o ( ~ ~ ~ ) ~ ~ ~ . ~ r . ~ y complexes (OEP=

octaethylporphyrin) have been measured at various temperatures versus KbFe(CN)6.3H20 as absorber.

The spectra of the divalent square planar complex, Co(II)OEP, consist of two sets of the quadrupo- le doublet below 77 K. The predominant doublet is identified as the corresponding iron complex, Fe(II)OEP, with the intermediate spin state (S-I). The spectra of the trivalent hexacoordinate Co(III)OEP.Br.Py complex are also resolved into two quadrupole doublets in the temperature range of 4.2 % 295 K, one being ascribed to the ferric low spin state ( S = 1 / 2 ) and the other to the ferric high spin state (S=5/2).

1. Introduction.- Iron porphyrins are of particular interest in exploring the nature of the heme moiety as the model compounds for hemoproteins. Because the iron(I1) porphyrins are, however, unstable for oxidation, there is no Mijssbauer spectroscopic stu- dy for the iron(I1) porphyrins with the molecular oxygen ligand except for the "picket fence porphy- rin" synthesized by Collmann et al. /I/. Chang and Traylor / 2 / have synthesized a heme-imidazole com- pound, ferropyrroporphyrin-N(3-(I-imidazoly1)pro- pyl) amide, which is capable of binding reversibly molecular oxygen. Unfortunately they did not mea- sure the Mgssbauer spectrum of this compound. On

the other hand, cobalt(I1) porphyrins also bind reversibly with molecular oxygen in the presence of amine in the solution 131. Furthermore, they are more stable to oxidation than iron(I1) porphy- rins. In this case the Gssbauer emission spectro- :copy of 5 7 ~ o ( ~ ~ ) porphyrins is favorable for the investigation of the electronic structure of mole- cular oxygen coordinated iron(I1) porphyrins

.

Recently Marchant et aZ. /4/ and we /5/ in- vestigated the Gssbauer emission spectroscopy of the oxygenated cobalt(I1) porphyrin, OX~-~'CO(II)PP (PP=protoporphyrin) and O~~-~~CO(II)OEP, in the frozen solution. These results of the oxygenated complexes were in good agreement with those of oxyhemoglobin. In this paper we wish to report the

Mgssbauer emission spectroscopic studies of the trivalent cobalt porphyrin as a model compound for ferric myoglobin and ferric hemoglobin in addition to the divalent cobalt porphyrin.

2. Experimental

.-

The complex 7 ~ o ( ~ ~ ~ ) ~ ~ ~ . Br.Py was prepared the following method: A glacial acetic

acid solution of cobalt acetate, containing 5 mCi of carrier free 5 7 ~ o ~ 1 2 , was added to ockaethylpor- phyrin (H20EP) dissolved in dichloromethane. The solution was boiled at 70°C for 2 hours and cooled to room temperature. A small amount of CO(III)OEP.C~

was reduced with sodium borohydride in methanol.

The colloidal precipitate Co(1I)OEP was filtered off and washed with methanol. After the measurements of the Gssbauer spectra, this precipitate was dis- solved in pyridine and treated with aqueous HBr.

The solution was dried under vacuum and the Co(III)OEP.Br.Py complex was extracted with CH2C12 and dried. The complex was recrystallized from CH2 C12

.

3. Results and discussion.- The Gssbauer emission spectra of the Co(III)OEP.Br.Py powdered sample versus the KI,F~(CN)~.~H~O absorber at various tem- peratures are shown in figure 1. The experimental data were fitted with Lorentzian curves of two sets of the quadrupole doublet by the least square method. The dotted and dashed lines refer to the each component of the spectra.

34

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19792179

JOURNAL DE PHYSIQUE

Table I : The ~Sssbauer parameters of the

''

o(III)OEP.Br.Py complex as a function of temperature I),~?.

I

295 (A)

:

^0.12

(B)

: _,

^0.21

196 (A): 0.17 (B)

: _,

^0.27

77(A): 0.20 (B): 0.33

I

4.2 (A)

:

^0.27

(B): 0.39

I

Fe(II1)OEP .ClOk .Py 295

:

^0.21

1

77 0.27

I

4.2 0.27

ref. /a/

ref. /b/

ref. /a/

ref. /b/

ref. /a/

he

6, 2 ~ , and S are the isomer shift relative to a-Fe, the quadru- pole splitting, the half linewidth and relative area, respectively.

2)~ccuracies of the parameters are 6:?0.02 mm/s, 2~:+0.02 m / s , l':+0.02 m / s and S:?l%, respectively.

/a/ Harami. T.. Maeda. Y. and Morita. Y.. this ~roceedinn.

. - . , , . .

-

/b/ Lang. G., Asakura, T. and Yonetani, T., Biochim. Biophys. Acta

214

(1970) 381.

Fig. I : 5 7 ~ e MEssbauer emission spectra of the 5 7 ~ o (1II)OEP.Br.Py complex at various temperatures ver- sus the K,,Fe(CN) 6. 3H20 absorber.

The ~Sssbauer parameters obtained are summarized in table I together with the results for the ferric myoglobins.

The predominant quadrupole doublet (A) is attri- buted to the trivalent low spin iron (S=1/2) analog

of the cobalt parent from the values of the Mossbauer parameters. Unfortunately because of failing synthe- sis of the isomorphous iron compound, Fe(III)OEP.Br.

Py, it is not clear whether this doublet (A) arises from the corresponding iron complex. However, the values of the Gssbauer parameters of this doublet are in good agreement with those of a similar hexa- coordinate complex, F~(III)OEP.C~O,, .Py with the low spin state

(ueff

= 2.05 BM at 77 K), as shown in table I. On the other hand, the extra quadrupole doublet (B) may be ascribed'to the ferric high spin state (5-512) as well as met-myoglobin. When the source temperature is lowered at 4.2 K, the intensi- ty of this doublet drastically increases accompanying the decrease of the quadrupole doublet (A). This fact may suggest that the lifetime of the unstable high spin species becomes longer at low temperature.

It is often recognized that the high spin species appears in the Gssbauer emission spectra of the 5 7 ~ o complexes. As pointed out by Ensling et aZ./6/

t h e l i g a n d f i e l d s t r p n g t h a t t h e 5 7 ~ e d a u g h t e r atom seems t o b e reduced by f o l l o w i n g t h e EC decay pro- c e s s compared w i t h t h a t a t t h e c o r r e s p o n d i n g i r o n complex. T h i s r e d u c t i o n l e a d s t o t h e a p p e a r a n c e of t h e h i g h s p i n s p e c i e s , a l t h o u g h i t i s a l s o p o s s i b l e t o c o n s i d e r t h e o t h e r c o n s e q u e n c e s . T h i s r e s u l t i s c o n s i s t e n t w i t h t h e phenomena t h a t t h e f e r r i c myo- g l o b i n s w i t h t h e weak l i g a n d such a s F- and Hz0 a r e h i g h s p i n i n t h e ground s t a t e .

R e f e r e n c e s

/ I / Collman, J . P . , Gagne, R.R., Reed, C.A., H a l b e r t , T.R., Lang, G. and Robinson, W.T., J . Am. Chem.

SOC.

97

(1975) 1427.

/ 2 / Chang,C.K. and T r a y l o r , T.G., P r o c . Nat. Acad.

S c i . USA

70

( 1 9 7 3 ) 2 6 4 7 .

/ 3 / Hoffman, B.M. and P e t e r i n g , D.H., P r o c . Nat. Acad.

S c i . USA

67

(1970) 6 3 7 .

/ 4 / Marchant, L., S h a r r o c k , M., Hoffman, B.M. and Mznck, E . , P r o c . Nat. Acad. S c i . U S A 2 (1972) 2 3 9 6 . / 5 / S a k a i , H . , Maeda, Y . , Ogoshi, H . , Sugimoto, H. and

Yoshida, Z . , Chem. L e t t . ( 1 9 7 8 ) 353.

1 6 1 E n s l i n g , J . , F l e i s c h , J . , G i t l i c h , P. and Fitzsimmons, B.W., Chem. Phys. L e t t .

2

( 1 9 7 7 ) 22.