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Iron porphyrins reinvestigated by a new method: Mössbauer spectroscopy using synchrotron radiation
Journal of Inorganic Biochemistry
DO4
HEME IRON AND METALLOPORPHYRINS
81
IRON PORPHYRINS REINVESTIGATED BY A NEW METHOD: MOSSBAUER SPECTROSCOPY USING SYNCHROTRON RADIATION
A. X. Trautwein a, H. Winkler a, H. Griinsteudel a, W. Meyer-Klaucke a, O. Leupold b, D. Riiter b, E. Gerdau b, M.Haas c, E. Realo c, D. Mandon d, and R. Weiss d a Medizinische Universit~it zu L~ibeck, Ratzeburger Allee 160, 23538 Liibeck, Germany b II.Institut fiir Experimentalphysik, Universit~it Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany c Institute of Physics, Estonian Academy of Science, 2400 Tartu, Estonia d Institut le Bel, Universit~ Louis Pasteur, 4, rue Blaise Pascal, 67070 Strasbourg, France Nuclear resonant forward scattering (NFS) of synchrotron radiation represents M6ssbauer spectroscopy in the time domain. This new technique complements the conventional nuclear resonance absorption, e.g. M6ssbauer spectroscopy in the energy domain, by supplying highly brilliant, polarized, collimated and timed radiation [ 1]. In NFS the hyperfine interaction of coherently excited nuclei manifests itself as quantum beat spectrum, i.e. as modulation of the time behavior of the nuclear decay [2]. We have applied NFS to test first biophysical applications. FeO2(SC6HF4)(TPpivP), which was designed to mimic the 02 binding in heme proteins, was investigated in a frozen solution and as polycrystalline sample. The latter, providing higher effective thickness, was measured at various temperatures (4.2 K - 175 K), with and without reference scatterer K4Fe(CN)6, with and without applied field. The temperature dependence of the effective thickness of the sample (Debye-Wailer-factor), which can be determined much easier and with much higher accuracy by NFS than by conventional M6ssbauer spectroscopy, provides information about intramolecular dynamics. The ferrous high-spin complex Fe(CH3CO2)(TPpivP), which was synthesized to model the prosthetic group termed P460 of the multiheme enzyme hydroxylamine oxidoreductase, was measured as powder sample at different temperatures (3 K - 250 K) and applied fields (up to 6 T, [[ and 2_ to the synchrotron beam, [[ and ± to c polarization). The measured time dependencies of the NFS intensity were simulated with a calculationai procedure (SYNFOS, [3]) which was developed for this purpose and which is based on the spin-Hamiltonian formalism. Under strong applied fields (6 T) the magnetic pattern changes from the slow relaxation regime at low temperature (3 K) to the fast relaxation regime (> 50 K). The NFS spectra measured at 3 K exhibit fast quantum beats due to the dominating magnetic hyperfine interaction, while at 50 K and above slow quantum beats from the combined electric quadrupole and nuclear Zeeman interaction are observed. In the intermediate relaxation regime (- 17 K) the beats vanish at much shorter times in comparison to the slow and fast relaxation regime. This is caused by the stochastic relaxation of the spins which destroys the fixed phase relation of otherwise coherently reemitted 7-radiation. The spin-crossover system [Fe(tpa)(NCS)2] is described in more detail elsewhere in this volume [4]. This work was supported by the Deutsche Forschungsgemeinschaft and the Bundesministerium ftir Bildung, Wissenschaft, Forschung und Technologie. [1] E. Gerdau and U. van Btirck, in Resonant anomalous X-ray scattering. G. Materlik, C. J.. Sparks and K. Fischer (ed.s). Elsevier, N. Y., p. 589 (1994) [2] J. B. Hastings, D. P. Siddons, U. van Btirck, R. Hollatz and U. Bergmann, Phys. Rev. Lett. 66, 770 (1991) [3] M. Haas, E. Realo, H. Winkler, W. Meyer-Klaucke, A. X. Trautwein, O. Leupold and E. Gerdau, Phys. Rev. B. (submitted) [4] H. Griinsteudel, A. I. Chumakov, H. F. Grtinsteudel, A.Q.R. Baron, R.Rtiffer, A. X. Trautwein, H. WinNer and H. Toflund, this volume
DO4
HEME IRON AND METALLOPORPHYRINS
81
IRON PORPHYRINS REINVESTIGATED BY A NEW METHOD: MOSSBAUER SPECTROSCOPY USING SYNCHROTRON RADIATION
A. X. Trautwein a, H. Winkler a, H. Griinsteudel a, W. Meyer-Klaucke a, O. Leupold b, D. Riiter b, E. Gerdau b, M.Haas c, E. Realo c, D. Mandon d, and R. Weiss d a Medizinische Universit~it zu L~ibeck, Ratzeburger Allee 160, 23538 Liibeck, Germany b II.Institut fiir Experimentalphysik, Universit~it Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany c Institute of Physics, Estonian Academy of Science, 2400 Tartu, Estonia d Institut le Bel, Universit~ Louis Pasteur, 4, rue Blaise Pascal, 67070 Strasbourg, France Nuclear resonant forward scattering (NFS) of synchrotron radiation represents M6ssbauer spectroscopy in the time domain. This new technique complements the conventional nuclear resonance absorption, e.g. M6ssbauer spectroscopy in the energy domain, by supplying highly brilliant, polarized, collimated and timed radiation [ 1]. In NFS the hyperfine interaction of coherently excited nuclei manifests itself as quantum beat spectrum, i.e. as modulation of the time behavior of the nuclear decay [2]. We have applied NFS to test first biophysical applications. FeO2(SC6HF4)(TPpivP), which was designed to mimic the 02 binding in heme proteins, was investigated in a frozen solution and as polycrystalline sample. The latter, providing higher effective thickness, was measured at various temperatures (4.2 K - 175 K), with and without reference scatterer K4Fe(CN)6, with and without applied field. The temperature dependence of the effective thickness of the sample (Debye-Wailer-factor), which can be determined much easier and with much higher accuracy by NFS than by conventional M6ssbauer spectroscopy, provides information about intramolecular dynamics. The ferrous high-spin complex Fe(CH3CO2)(TPpivP), which was synthesized to model the prosthetic group termed P460 of the multiheme enzyme hydroxylamine oxidoreductase, was measured as powder sample at different temperatures (3 K - 250 K) and applied fields (up to 6 T, [[ and 2_ to the synchrotron beam, [[ and ± to c polarization). The measured time dependencies of the NFS intensity were simulated with a calculationai procedure (SYNFOS, [3]) which was developed for this purpose and which is based on the spin-Hamiltonian formalism. Under strong applied fields (6 T) the magnetic pattern changes from the slow relaxation regime at low temperature (3 K) to the fast relaxation regime (> 50 K). The NFS spectra measured at 3 K exhibit fast quantum beats due to the dominating magnetic hyperfine interaction, while at 50 K and above slow quantum beats from the combined electric quadrupole and nuclear Zeeman interaction are observed. In the intermediate relaxation regime (- 17 K) the beats vanish at much shorter times in comparison to the slow and fast relaxation regime. This is caused by the stochastic relaxation of the spins which destroys the fixed phase relation of otherwise coherently reemitted 7-radiation. The spin-crossover system [Fe(tpa)(NCS)2] is described in more detail elsewhere in this volume [4]. This work was supported by the Deutsche Forschungsgemeinschaft and the Bundesministerium ftir Bildung, Wissenschaft, Forschung und Technologie. [1] E. Gerdau and U. van Btirck, in Resonant anomalous X-ray scattering. G. Materlik, C. J.. Sparks and K. Fischer (ed.s). Elsevier, N. Y., p. 589 (1994) [2] J. B. Hastings, D. P. Siddons, U. van Btirck, R. Hollatz and U. Bergmann, Phys. Rev. Lett. 66, 770 (1991) [3] M. Haas, E. Realo, H. Winkler, W. Meyer-Klaucke, A. X. Trautwein, O. Leupold and E. Gerdau, Phys. Rev. B. (submitted) [4] H. Griinsteudel, A. I. Chumakov, H. F. Grtinsteudel, A.Q.R. Baron, R.Rtiffer, A. X. Trautwein, H. WinNer and H. Toflund, this volume