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MÖSSBAUER SPECTROSCOPY OF THE MODEL HEMOGLOBIN COMPOUND DICHELATED
PROTOHEME
E. Mielczarek, B. Balko, R. Berger, D. White, T. Traylor, T. Mincey
To cite this version:
E. Mielczarek, B. Balko, R. Berger, D. White, T. Traylor, et al.. MÖSSBAUER SPECTROSCOPY OF
THE MODEL HEMOGLOBIN COMPOUND DICHELATED PROTOHEME. Journal de Physique
Colloques, 1979, 40 (C2), pp.C2-495-C2-497. �10.1051/jphyscol:19792173�. �jpa-00218549�
JOURNAL DE PHYSIQUE Colloque C2, suppl6ment au no 3, Tome 40, mars 1979, page C2-495
MOSSBAUER SPECTROSCOPY OF THE MODEL HEMOGLOBIN COMPOUND D I C H E L A T E D PROTOHEME
E.V. Mielczarek, B. Balko*, R.L. Berger I
,
D.K. Whitexi, T.G. ~ r a ~ l o r * * and T. ~ i n c e ~ * *Physics Department, George Mason University, Fairfax, Va. 22030, U.S.A. and Laboratory of Technical Development, NationaZ Heart, Lung, and Blood I n s t i t u t e , National I n s t i t u t e s of Health, Bethesda, Md. 20014, U.S. A.
i Laboratory of Technical Development, National Heart, Lung, m d Blood I n s t i t u t e , National I n s t i t u t e s o f Health, Bethesda, Md. 20014, U.S.A.
wc Department of Chemistry, University of C a l i f o r n i a a t Sun Diego, La J o l l a , C a l i f . 92093, U.S.A.
R6sumb.- Des mesures Mijssbauer sur la protohsme chblatde (protohsme-di-3-(I-imidazole propylamide) ont Etd effectudes 1 des tempdratures allant de l'ambiante 1 5.4 K. A la temperature ambiante, le composd prdsente un doublet quadripolaire bien rdsolu avec dddoublement de raie de 1,954 t 0.004 w s - l et un dbplacement isodrique de +0,184
*
0,O 14 mm s-I par rapport au Fe normal. Ce dddoublement bien rbsolu persiste jusqu'l 17 K. A 17 K, les deux raies s'dlargissent dans un rapport de trois 1 un, la raie d'bnergie supbrieure diminuant d'intensitd par rapport 1 l'autre.Abstract.- Mijssbauer measurements of dichelated protoheme (protoheme-di-3-(1-imidazole propylamide) have been made from room temperature to 5.4 K. The compound shows a well-resolved quadrupole doublet at room temperature with a line splitting of 1.954 -+ 0.014 w s'.' and an isomer shift of +O. 184
+
0.014mm &with respect to natural Fe. This well-resolved splitting persists down to 17 K. At 17 K the onset of a hyperfine interaction is evident with both lines broadening by a factor of three with the higher velocity line decreasing in intensity with respect to the lower velocity line.
1. Introduction.- Iron porphyrins serve as model compounds for hemoglobins, myoglobins, and cytochro- mes. ~gssbauer spectroscopy has helped to characteri- ze the environment of the iron atom of many of these compounds 11-51. In addition to the review on por- phyrins by Hambright and Bearden 141, octaethylpor-
~ h y r i n complexes have been investigated by Dolphin et al. 161. In this paper the results of assbauer measurements on a protoporphyrin (protoheme-di-3-
(I-imidazole propylamide) (protoheme) as a function of temperature are reported on. The structure of the compound is given in figure 1.
liganded to an imidazole nitrogen. This protoporphy- rin is unique in that the imidazole is attached to a propylamide chain which is bound to the heme. Thus the orientation of the imidazole with respect to the heme plane is constrained. The impetus for the syn- thesis of such a compound is the development of a heme model that behaves kinetically like the active site of a biological heme (hemoprotein) 171. A des- cription of the synthesis of protoheme will be pu- blished in the Journal of the American Chemical So- ciety 181.
2. Experimental Results.- Gssbauer transmission measurements were made on the sample as a function of temperature from 5.6 K to 300 K. Two different sources, 25 millicuries and 87 millicuries, "CO in palladium were used. The sample was 0.120 grams of powder compressed into a disk 9 rn in diameter and 3 mm thick. At all temperatures measured the sample exhibited a quadrupole split doublet. Figure 2 and 3 show the spectra taken at 5.6 K and 300 K. Table I gives the values of the quadrupole splitting measu- red and figure 4 is a plot of this data. The isomer shift at room temperature was measured to be +0.184
+
0.014 mm s-I with respect to natural iron. The va- Fig. 1 : The structure of protoheme-di-3-(I-imidazole lues of the isomer shift and quadrupole splitting propylamide) (protoheme).are indicative of low spin ( 2 ~ ) ferric porphyrin In this protoporphyrin the 5th and 6th coordination state 141. At 5.6 K the full width at half maximum positions (out of the heme plane) of the Fe are ot the high energy line is 1.17 -+ 0.03 mm s-' and
the low energy line is 1.06
*
0.03 m s-I.
33
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19792173
C2-496 JOURNAL DE PHYSIQUE
Fig. 2 : Mgssbauer spectrum of protoheme at 5.6 K. Fig. 3 : Gssbauer spectrum of protoheme at 300 K.
Table I
.*SO
I
-+.73 -3.80 -2.85 - L 90 4 S5 0.00 0 $5 L DO 2 w 2 a0 4 75
r E u c t n IWI)
.
Fig. 4 : Quadrupole splitting of Gssbauer doublet of protoheme as a function of temperature.
Temperature Quadrupole Splitting
(mm s-1)
This 9-10X difference in the line width persists up to about 120 K. Above 120 K both lines narrow until at 30C K the full width at half maximum is the same, 0.506 .t 0.1 mm s-'
,
for both lines, within the ex- perimental error. The value of 0.406 mm s-' is a reasonable line width for this sample thickness.This broadening of the quadrupole lines as the tem- perature is lowered and the even further broadening of the high energy line is indicative of the onset of a hyperfine interaction and can also be indicati- ve of a positive VZZ assuming that the magnetic and eIectric field gradient tensors are parallel. That is a hyperfine interaction would split the 2 312 state niore than the 2 112 state causing the higher energy line to be broader 191. At low temperatures where the electron spin relaxation time becomes lon- ger the nucleus is a'-le to sample the hyperfine field /2,9, 101. In some of the spectra the appea- rance of a third peak between the two major peaks is evident. Preliminary electron spin resonance
measurements show the sample to contain a mixture of both high and low spin ferric states at 5.4 K and
19.3 K. Thus it is assumed that the appearance of this third peak could be associated with the high spin state. However, no convincing unique fit to the spectra could be found which would include a fourth peak in order to complete the high spin ferric dou- blet. Although the overall decrease in quadrupole splitting with temperature, about I mm s-' is common for the low spin ferric state the curious temperatu- re behavior between 25 K and 65 K cannot be explai- ned.
References
/I/ May, L. An Introduction to ~gssbauer Spectroscopy, (Plenum Press, New York) 1971.
/2/ Lang, G., Quart. Rev. Biophys.
3
(1970) 1./ 3 / Goldanskii, V.I., and Herber, R.H., "Chemical
Applications of Gssbauer Spectroscopy" (Academic Press, New York) 1968.
/4/ Hambright, P., and Bearden
,
A.J. (Porphyrins and Metalloporphyrins, ed. Smith, K.M. Elsevier, Ams- terdam) 1975 and references therein.151 Oosterhuis, W.T., Struct. and Bond.
g
(1974) 59./6/ Dolphin, D., Sams, J.R., Tsin, T.B., and Wang, K.L., J. Am. Chem. Soc.
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in press.191 Moss, T.H., Bearden, A.J., and Caughey, W.S., J.
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(1969) 2624./lo/ ~osterhuis, W.T., and Lang, G., Phys. Rev.
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/Ill Kon, Ideo, private communication.
