1. Synchrotron techniques in bio-physics
Yulia Pushkar
Department of Physics, Purdue University 1

2. Analyze electronic structure of molecules and proteins with
high spatial and temporal resolution

3. Synchrotron

4. Synchrotrons of the World

5. Argonne National Laboratory

6. X-ray spectroscopy

11. Oxygenic photosynthesis
Where do plants oxidize water?
Mn4OxCa cluster
Umena, Y. et al. Nature 2011

12. Objective: reproduce the efficiency of natural
light-driven water splitting in a man made device.
4hn
2H2O O2 + 4H+ + 4e-
Mn4CaOxCl

13. Question: why have we not yet achieved this objective?
Possible answer: we still understand too little about
the mechanism of water oxidation.
Kok cycle was proposed in 1970
Liang et al. JACS 2000
Messinger et al. JACS, 2001
Pushkar et al. PNAS 2008

14. X-ray Absorption Spectroscopy of Mn4Ca cluster
1.8Å

15. Structural Changes in the Catalytic Cycle- S1, S2 and S3
Range-Extended Mn EXAFS S1
1) S1 to S2 no major changes in di-µ-oxo bridges
2) S2 to S3 - major structural changes in di-µ-oxo bridges

17. Photon-in-Photon-out spectroscopy
2p to 1s (K)
Oxidation State
3p to 1s (K)
Oxidation and
spin state
valence to 1s
Ligands
Information accessible: metal oxidation state, spin state, ligand environment
Messinger et al JACS; Pushkar et al Angew. Chem.; Davis et al. J. Phys. Chem. Lett

18. High resolution X-ray emission spectroscopy
Point by point detection
is not optimal for time resolved measurements
monochromator
Si(111), Si (221), Si(400)
sample
detector
tunable analyzer
~ 1 eV
X-ray beam
Messinger et al JACS; Pushkar et al Angew. Chem.

19. Dispersive miniXES spectrometer
Image on position sensitive detector:
Davis et al. J. Phys. Chem. Lett. 2012

20. Laser pump X-ray probe Time-resolved XES analysis
Will be used in analysis of PS II
as well as artificial sun-light to fuel assemblies.
MMCT in Mn-O-Ti chromophores will be studied. (Heinz Frei, Walter Weare)