IRON PORPHYRINS REINVESTIGATED BY A NEW METHOD - MOSSBAUER-SPECTROSCOPY USING SYNCHROTRON-RADIATION

Nuclear resonant forward scattering (NFS) of synchrotron radiation rep resents Mossbauer spectroscopy in the time domain. This new technique complements the conventional nuclear resonance absorption, e.g, Mossba uer spectroscopy in the energy domain, by supplying highly brilliant, polarized, collimated and timed radiation. In NFS the hyperfine intera ction of coherently excited nuclei manifests itself as quantum bents, i.e. as modulation of the time-dependent intensity of the transmitted radiation, which is delayed with respect to the incoming synchrotron p ulse. We have investigated Fe-57-enriched iron porphyrins to test NFS for first biophysical applications. NFS spectra of the diamagnetic por phyrin FeO2(SC6HF4)(TPpivP) and of the paramagnetic porphyrin [Fe(CH3C OO)(TPpivP)](-) were recorded at various temperatures, with and withou t reference scatterer, with and without applied field. Dynamic molecul ar properties, e.g. dynamic structural disorder or spin-lattice relaxa tion document as variation of the time-delayed count rate. Measured NF S spectra were analysed theoretically by programs which are basically the analogue in the time domain compared to the usual calculations in the energy domain.