4 From Small Molecules to Complex Systems: A Survey of Chemical …
215
continue. Especially very complex iron centers like in the N 2 fixing protein nitrogenases have been investigated already, but how biological nitrogen fixation really
works has not been clarified yet and NIS is certainly one of the spectroscopic
methods which can shine light on the N 2 binding to the active site FeMo-cofactor of
nitrogenase.
But there are also novel experimental technique like time dependent optical pump
NRS probe techniques. With such experiments it will be possible to monitor the
response of optical excitable iron containing systems after photostimulation like in
molecular switches and magneto optical nanomaterials [97] or possibly even in iron
proteins. With X-ray free electron lasers delivering fs pulses of 14.4 keV radiation
on the horizon optical pump NIS probe experiments would enable to trace ultrafast
changes of the vibrational properties of iron ligand modes in chemical complexes
and proteins even in the fs time range.
4.7 Summary
The proceeding chapter tries to give a flavor to the reader of what can be achieved
with conventional and synchrotron-based Mössbauer spectroscopic techniques, both
in biology and chemistry. Since this contribution is meant as an introduction to the
broad field of chemical and biological applications of the Mössbauer effect, it is clear
that not all aspects of the field could be covered. Instead the reader is guided after
some practical aspects both in sample requirements and in evaluation techniques
through examples of scientific cases, which have been worked on in the group of
the author during the last two decades. These concern Mössbauer spectroscopic
studies of synthetic chemical complexes like SCO compounds and studies on NO
transporter heme proteins, the nitrophorins. Since Mössbauer spectroscopy is the
method of choice for the characterization of Fe–S centers in proteins, especially
when they occur in their EPR silent diamagnetic or integer-spin states, some examples
are presented starting from simple mononuclear Fe–S centers over dinuclear Fe 2 S 2
centers to Fe 4 S 4 centers. More complex cases like Fe–S centers in nitrogenases are
only briefly mentioned since the discussion of such complex structures like the FeMoCofactor are behind the scope of the text. Nevertheless, also some views on the future
of Mössbauer spectroscopy in chemistry and biology are presented. The author hopes
that the reader at the end is getting an impression about the intriguing possibilities of
the method. Considering the fact that the first biological and chemical applications of
the Mössbauer effect have been performed in the 1960s, a lot has been learned since
that time. On this footing there is a bright perspective of the technique especially
when it comes to the study of complex systems like iron containing reaction mixtures,
heterogeneous catalysts and biological cells.
215
continue. Especially very complex iron centers like in the N 2 fixing protein nitrogenases have been investigated already, but how biological nitrogen fixation really
works has not been clarified yet and NIS is certainly one of the spectroscopic
methods which can shine light on the N 2 binding to the active site FeMo-cofactor of
nitrogenase.
But there are also novel experimental technique like time dependent optical pump
NRS probe techniques. With such experiments it will be possible to monitor the
response of optical excitable iron containing systems after photostimulation like in
molecular switches and magneto optical nanomaterials [97] or possibly even in iron
proteins. With X-ray free electron lasers delivering fs pulses of 14.4 keV radiation
on the horizon optical pump NIS probe experiments would enable to trace ultrafast
changes of the vibrational properties of iron ligand modes in chemical complexes
and proteins even in the fs time range.
4.7 Summary
The proceeding chapter tries to give a flavor to the reader of what can be achieved
with conventional and synchrotron-based Mössbauer spectroscopic techniques, both
in biology and chemistry. Since this contribution is meant as an introduction to the
broad field of chemical and biological applications of the Mössbauer effect, it is clear
that not all aspects of the field could be covered. Instead the reader is guided after
some practical aspects both in sample requirements and in evaluation techniques
through examples of scientific cases, which have been worked on in the group of
the author during the last two decades. These concern Mössbauer spectroscopic
studies of synthetic chemical complexes like SCO compounds and studies on NO
transporter heme proteins, the nitrophorins. Since Mössbauer spectroscopy is the
method of choice for the characterization of Fe–S centers in proteins, especially
when they occur in their EPR silent diamagnetic or integer-spin states, some examples
are presented starting from simple mononuclear Fe–S centers over dinuclear Fe 2 S 2
centers to Fe 4 S 4 centers. More complex cases like Fe–S centers in nitrogenases are
only briefly mentioned since the discussion of such complex structures like the FeMoCofactor are behind the scope of the text. Nevertheless, also some views on the future
of Mössbauer spectroscopy in chemistry and biology are presented. The author hopes
that the reader at the end is getting an impression about the intriguing possibilities of
the method. Considering the fact that the first biological and chemical applications of
the Mössbauer effect have been performed in the 1960s, a lot has been learned since
that time. On this footing there is a bright perspective of the technique especially
when it comes to the study of complex systems like iron containing reaction mixtures,
heterogeneous catalysts and biological cells.