Speaker
Ms
Desiree Heintz
(DESY-Hasylab)
Description
Oxidation state changes of metal organic complexes play an important role in many chemical and biological processes. X-ray absorption near edge spectroscopy (XANES) is a powerful tool to follow these changes since it can directly probe the oxidation state of a metal center[1]. However, X-rays themselves are known to cause photoreduction in photosensitive samples[2, 3,]. In order to reduce X-ray induced photoreduction, t is important to gain a deeper understanding of this process. XANES was used to investigate the influence of temperature, solvent content and chemical composition on three model systems.
Based on our results, we could propose a model for X-ray induced photoreduction of metal organic complexes: A low energy electron[4] generated upon X-ray irradiation attaches to the metal center, yielding a short-lived excited state. Photoreduction of the metal center becomes permanent by an oxidation in the ligand, accompanied by the release of a leaving group and an electron. A possible temperature dependence can be explained by the temperature dependence of the oxidation reaction.
[1] D.C. Koningsberger, R. Prins, X-ray Absorption: Principles, Applications, Techniques
of EXAFS, SEXAFS, and XANES, Chemical Analysis, John Wiley & Sons, New York, 1988.
[2] J. Yano et al., PNAS 102, 12047-12052, 2005.
[3] I. Schlichting, K. Chu, Curr. Op. Struct. Biol. 10, 744-750, 2000.
[4] B. Boudaiffa et al., Science 287, 1658-1660, 2000.
Primary author
Ms
Desiree Heintz
(DESY-Hasylab)
Co-authors
Alke Meents
(DESY-Hasylab)
Anja Burkhardt
(DESY-Hasylab)
Edgar Weckert
(DESY-Hasylab)
Maarten Nachtegaal
(Paul-Scherrer-Institut)
