180
V. Schünemann
Fig. 4.5 NIS sample holder for liquid samples (e.g. 57 Fe enriched protein solution). The liquid can
be filled via the holes seen on the upper part of the holder. A thin self adhesive Kapton ® film is
glued on the sample holder prior to filling and acts as window material for the NIS signal. Since in
case of 57 Fe 6.4 keV radiation contributes to ~90% of the NIS signal the film has to be as thin as
possible
allow fast sample change at cryogenic temperatures. In order to achieve reasonable
acquisition times iron containing chemical complexes should be prepared with 50–
100% enrichment in
57 Fe even when working with solid chemical compounds. In
rare cases when
57 Fe enrichment is not possible and the scientific case is very strong
one might also get beam time at a synchrotron to work with unenriched samples.
However, for synchrotron experiments with iron protein solutions enrichment with
57 Fe is still a must to date. Also the concentration of
57 Fe should be as high as possible
in order to minimize acquisition time. It is desirable to have
57 Fe concentration of
5–10 mM but even in that case a NIS experiment at one experimental condition may
take several hours with nowadays synchrotron sources.
4.2.2 Spectral Analysis: Thin Absorber Approximation
and Transmission Integral
Conventional Mössbauer spectra of biological systems and model complexes which
are not enriched in
57 Fe can be conveniently analyzed by means of the thin absorber
approximation using lorentzian line shape for the absorption lines observed. The
same holds at least to the experience of the author for
57 Fe enriched iron proteins
V. Schünemann
Fig. 4.5 NIS sample holder for liquid samples (e.g. 57 Fe enriched protein solution). The liquid can
be filled via the holes seen on the upper part of the holder. A thin self adhesive Kapton ® film is
glued on the sample holder prior to filling and acts as window material for the NIS signal. Since in
case of 57 Fe 6.4 keV radiation contributes to ~90% of the NIS signal the film has to be as thin as
possible
allow fast sample change at cryogenic temperatures. In order to achieve reasonable
acquisition times iron containing chemical complexes should be prepared with 50–
100% enrichment in
57 Fe even when working with solid chemical compounds. In
rare cases when
57 Fe enrichment is not possible and the scientific case is very strong
one might also get beam time at a synchrotron to work with unenriched samples.
However, for synchrotron experiments with iron protein solutions enrichment with
57 Fe is still a must to date. Also the concentration of
57 Fe should be as high as possible
in order to minimize acquisition time. It is desirable to have
57 Fe concentration of
5–10 mM but even in that case a NIS experiment at one experimental condition may
take several hours with nowadays synchrotron sources.
4.2.2 Spectral Analysis: Thin Absorber Approximation
and Transmission Integral
Conventional Mössbauer spectra of biological systems and model complexes which
are not enriched in
57 Fe can be conveniently analyzed by means of the thin absorber
approximation using lorentzian line shape for the absorption lines observed. The
same holds at least to the experience of the author for
57 Fe enriched iron proteins