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X-FEL Experiments on Organic and Biological Systems

X-FEL Experiments on Organic and Biological Systems. Karim Fahmy Division of Biophysics Institute of Radiochemistry Helmholtz-Zentrum Dresden-Rossendorf. High energies and densities do not necessarily help to reveal the secrets of life. X-FEL Experiments on Organic and Biological Systems.

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X-FEL Experiments on Organic and Biological Systems

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  1. X-FEL Experiments on Organic and Biological Systems Karim Fahmy Division of Biophysics Institute of Radiochemistry Helmholtz-Zentrum Dresden-Rossendorf

  2. High energies and densities do not necessarily help to reveal the secrets of life X-FEL Experiments on Organic and Biological Systems Talking about biological systems in the context of HED physics is challenging

  3. Problem-solving applications of X-FEL should address: photo-induced electron transfer metal organic systems photo-induced conformational transitions in proteins X-FEL Experiments on Organic and Biological Systems • Two fundamental processes govern organic and biological chemistry: • formation and breaking of chemical bonds • => involves electron transfer reactions • conformational freedom / restriction • => involves isomerization / protein folding, aggregation...

  4. photo-induced conformational transitions in proteins 3) Photoreaction of rhodopsin (basis of vision and molecular model for hormone reception) Three systems to be discussed for X-FEL experiments photo-induced electron transfer metal organic systems 1) Uranyl photochemistry: excited state electron transfer affects redox state - light-dependent solubility changes, relevance to environmental mobility - technological applications (separation / photon-induced partitioning) structural basis: ligand to metal charge transfer LMCT 2) Dye-sensitized photovoltaics - ligt-induced injection of electrons from an organic chromophore into the conductance band of a semiconductor structural basis: metal to ligand charge transfer MLCT

  5. Aqueous coordination chemistry and photochemistry of uranyl(VI) oxalate revisited: a density functional theory study Satoru Tsushima, Vinzenz Brendler and Karim Fahmy 2010, 39, 10953–10958 • Photo-induced electron transfer metal organic systems • Uranyl photochemistry • Observation: Complexes of UO22+ with organic acids decompose under light • reaction products CO2, CO, UVI -> UIV , depends on pH, stoichiometry... How does the coordination structure define the chemical reaction pathway? hydrogen abstraction / charge transfer Can it be predicted from first principles? solution complexes of Uranyl oxalate Zhang et al.Radiochimica Acta (2010). Uranyl photochemistry: decarboxylation of gluconic acid

  6. Photo-induced electron transfer metal organic systems • Uranyl photochemistry • Reaction coordinate predicted from DFT calculations based on spin • density in the excited triplet state of UO22+ Suggestion: optical pump / X-ray probe experiment in (poly)crystalline state requires a) strong pump beam (optical transition in Uranyl is forbidden) b) single shot probe X-ray: pumping is chemically destructive

  7. DSP is beyond prototype and on the market Photo-induced electron transfer metal organic systems 2) Dye-sensitized photovoltaics An organic dye transfers an electron into the conductance band of a semi onductor

  8. nano-crystalline TiO2 electrode Michael Grätzel, EPFL Photo-induced electron transfer metal organic systems 2) Dye-sensitized photovoltaics Principle of Dye-Sensitized Solar Cells

  9. Photo-induced electron transfer metal organic systems 2) Dye-sensitized photovoltaics Optical transition has the character of a Metal-to-Ligand-Charge Transfer (MLCT), large cross-section, e-injection into TiO2 within fs-ps. Suggestion: Structural and dynamic properties of dye to semiconductor electron transfer. Studies on selfassembled 2D arrays may profit from high intensity beams by enlarging the pumped surface More general field for X-FEL studies: photocatalysis at liquid / solid interfaces

  10. Photo-induced conformational transitions in proteins 3) Time-resolved protein conformational changes • The central goal in modern Structural Biology: • resolve the 3D structure of large proteins • identify the structural basis of biological function • rational design of drugs, which enhance or inhibit function by interfering with key structural elements of their protein targets

  11. low T trapping of intermediates in the crystal Photo-induced conformational transitions in proteins 3) Time-resolved protein conformational changes Limitations and challenges 1) The classical approach: crystallization and isomorphic replacement - Crystallization difficult for proteins residing in the cell membrane However: 50% of pharmaceuticals target membrane proteins • 2) Obtained structures are static • However: structural transitions are the basis of biological function • dynamics not resolved, crystal contacts lock flexible domains Bacteriorhodopsin currently Rhodopsin

  12. Photo-induced conformational transitions in proteins 3) Time-resolved protein conformational changes Suggestion: Follow structural changes in rhodopsin, a photosensitive membrane protein Primary photoreaction (200 fs) followed by slow thermally activated conformational changes

  13. Photo-induced conformational transitions in proteins 3) Time-resolved protein conformational changes Rhodopsin can be prepared in a variety of states: 3D and 2D crystals, micelles, liposomes, nanodiscs functionality in these states is well characterized a = 44 Å b = 131 Å Davies et al., 1996 JStrBiol

  14. Photo-induced conformational transitions in proteins 3) Time-resolved protein conformational changes • high energy pump and probe may allow sampling large spot sizes • in lateraly extended samples • visualize photoisomerization in real-time (fs-ps) at atomic resolution • alternatively: small angle X-ray scattering may resolve helical movements • visualize large domain movements over ~100 µs The longer time scales are more informative for pharmacology

  15. non-native fish native olive oil SUMMARY • There is large interest in studying biological photoreaction mechanisms • at atomic resolution and in real time: • metal organic systems in photosynthesis and photocatalysis are attractive • proteins should be studied for which crystal structures have been solved • fs to ps data are relevant to quantum yields (primary photoreaction) • longer time scales are required to elucidate protein function • rhodopsin has become a paradigm for membrane proteins • and will surely find its way into time-resolved X-ray studies • but where: at synchrotron or at X-FEL? • many aspects have not been addressed but may become crucial: • liquid sample handling, flow through systems, hydration control... • a.o. efforts to maintain nativeness THANK YOU FOR YOUR ATTENTION

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