P 18 ISSRNS 2012: Abstracts / Synchrotron Radiation in Natural Science Vol. 11, No 1 – 2 (2012)
XANES EVALUATION OF IRON LOCAL STRUCTURES IN MONOMER AND DIMERSED FORMS OF PORPHYRINS
K. Dziedzic-Kocurek∗ and J. Stanek
M. Smoluchowski Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Krak´ow, Poland Keywords: synchrotron radiation, XANES, porphyrins
∗e-mail : k.dziedzic-kocurek@uj.edu.pl
There is a great deal of evidence that the biolog- ical function of the heme proteins is determined by the convoluted conformational and electronic prop- erties of the heme group. Various spectroscopic methods have supplied valuable information about the active site of the heme proteins, but they can- not by themselves yield a detailed and consistent description at the molecular level. In no other class of proteins so much effort has been devoted to find a relationship between structure, function and the properties of the active constituent [1]-[3]. Starting from the preparation stage, the variety of slightly differing porphyrin complexes, in respect of their energetic form, causes basic complications in their analysis. Each of the prepared / synthesized com- plexes is individual, and the properties depend on the details of the preparation. One of the most in- teresting features of porphyrins is how small varia- tions of the basic structural tetrapyrrolic macrocy- cle lead to a wide diversity of biochemical functions.
The aim of the project is to study iron local states in compounds that reveal slightly different structures. The crucial compound in performed analysis was protoporphyrin IX, its monomer and dimerised form substituted with iron. Iron substi- tuted PPIX (protoporphyrin IX) is a “real part” of the heme, while mostly heme-model investigations are based on TPP (tetraphenylporphyrin) that in fact differs from an actual heme-builing compound (differences in ligands). The EXAFS and XANES analysis of the PPIX-based compounds have been already reported [4].
However, due to the complex structure of a stud- ied dimerised form of Fe-PPIX (it is a synthesized compound, that contains partially monomer admix- ture) it was important to compare obtained results with a pure monomer and dimerised compounds.
As the standard compounds TPP derivatives has been selected. Nevertheless, provides information on Fe-PPIX-Cl and its dimerised derivatives, which are the most adequate model compound for the haemoglobin.
The dimerisation reduces the s-electron density at the Fe nuclei and shifts the absorption edge as
measured by the XANES spectra (Fig. 1). Also, a different rising edge respect to dimerised compound, suggesting a different and larger charge transfer of the samples containing Fe-O-Fe bridges, has been shown. Additionally, supporting M¨ossbauer spec- troscopy studies have been also performed.
Figure 1 : The first derivative of the edge region of the XANES spectra.
Acknowledgments: This work has been supported by HASYLAB-DESY under the contract RII3-CT-2004- 506008 and by EC (FP7/2007 – 2013) under grant agree- ment n◦312284 (DESY, Hamburg).
References
[1] J.E. Penner-Hahn, K.O. Hodgson, Iron Porphyrins, Part III (VCH Publishers, New York 1989).
[2] A. Bianconi et al., “XANES study of iron displace- ment in heam of myoglobin,” FEBS Lett. 178 (1884) 165 – 170.
[3] P. D’Angelo et al., “X-Ray absorbtion spectroscopy of hemes and hemeproteins in solution: Mul- tiple scatterin theory,” Inorg. Chem. 47 (2008) 9905 – 9918.
[4] K. Dziedzic-Kocurek, J. Stanek, K. Burda, “Dy- namics of iron in Fe-porphyrin aggregates studied by X-ray absorption and M¨ossbauer spectroscopy,”
Hyperfine Interact. 185 (2008) 87 – 93.
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