XFEL Experiments on Organic and Biological Systems Karim

X-FEL Experiments on Organic and Biological Systems Karim Fahmy Division of Biophysics Institute of Radiochemistry Helmholtz-Zentrum Dresden-Rossendorf X-FEL Workshop, Dresden-Rossendorf, Sep. 5 th to 10 th 2011 Karim Fahmy, Div. Biophysics

X-FEL Experiments on Organic and Biological Systems Talking about biological systems in the context of HED physics is challenging High energies and densities do not necessarily help to reveal the secrets of life X-FEL Workshop, Dresden-Rossendorf, Sep. 5 th to 10 th 2011 Karim Fahmy, Div. Biophysics

X-FEL Experiments on Organic and Biological Systems Two fundamental processes govern organic and biological chemistry: 1) formation and breaking of chemical bonds => involves electron transfer reactions 2) conformational freedom / restriction => involves isomerization / protein folding, aggregation. . . Problem-solving applications of X-FEL should address: photo-induced electron transfer metal organic systems photo-induced conformational transitions in proteins X-FEL Workshop, Dresden-Rossendorf, Sep. 5 th to 10 th 2011 Karim Fahmy, Div. Biophysics

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 photo-induced conformational transitions in proteins 3) Photoreaction of rhodopsin (basis of vision and molecular model for hormone reception) X-FEL Workshop, Dresden-Rossendorf, Sep. 5 th to 10 th 2011 Karim Fahmy, Div. Biophysics

Photo-induced electron transfer metal organic systems 1) Uranyl photochemistry Observation: Complexes of UO 22+ with organic acids decompose under light reaction products CO 2, CO, UVI -> UIV , depends on p. H, 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 Aqueous coordination chemistry and photochemistry of uranyl(VI) oxalate revisited: a density functional theory study 2010, 39, 10953– 10958 Satoru Tsushima, Vinzenz Brendler and Karim Fahmy Zhang et al. Radiochimica Acta (2010). Uranyl photochemistry: decarboxylation of gluconic acid X-FEL Workshop, Dresden-Rossendorf, Sep. 5 th to 10 th 2011 Karim Fahmy, Div. Biophysics

Photo-induced electron transfer metal organic systems 1) Uranyl photochemistry Reaction coordinate predicted from DFT calculations based on spin density in the excited triplet state of UO 22+ 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 X-FEL Workshop, Dresden-Rossendorf, Sep. 5 th to 10 th 2011 Karim Fahmy, Div. Biophysics

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 DSP is beyond prototype and on the market X-FEL Workshop, Dresden-Rossendorf, Sep. 5 th to 10 th 2011 Karim Fahmy, Div. Biophysics

Photo-induced electron transfer metal organic systems 2) Dye-sensitized photovoltaics Principle of Dye-Sensitized Solar Cells nano-crystalline Ti. O 2 electrode Michael Grätzel, EPFL X-FEL Workshop, Dresden-Rossendorf, Sep. 5 th to 10 th 2011 Karim Fahmy, Div. Biophysics

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, einjection into Ti. O 2 within fs-ps. Suggestion: Structural and dynamic properties of dye to semiconductor electron transfer. Studies on selfassembled 2 D arrays may profit from high intensity beams by enlarging the pumped surface More general field for X-FEL studies: photocatalysis at liquid / solid interfaces X-FEL Workshop, Dresden-Rossendorf, Sep. 5 th to 10 th 2011 Karim Fahmy, Div. Biophysics

Photo-induced conformational transitions in proteins 3) Time-resolved protein conformational changes The central goal in modern Structural Biology: resolve the 3 D structure of large proteins Þ identify the structural basis of biological function Þ rational design of drugs, which enhance or inhibit function by interfering with key structural elements of their protein targets X-FEL Workshop, Dresden-Rossendorf, Sep. 5 th to 10 th 2011 Karim Fahmy, Div. Biophysics

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 low T trapping of intermediates in the crystal X-FEL Workshop, Dresden-Rossendorf, Sep. 5 th to 10 th 2011 Karim Fahmy, Div. Biophysics

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 X-FEL Workshop, Dresden-Rossendorf, Sep. 5 th to 10 th 2011 Karim Fahmy, Div. Biophysics

Photo-induced conformational transitions in proteins 3) Time-resolved protein conformational changes Rhodopsin can be prepared in a variety of states: 3 D and 2 D crystals, micelles, liposomes, nanodiscs a = 44 Å b = 131 Å Davies et al. , 1996 JStr. Biol functionality in these states is well characterized X-FEL Workshop, Dresden-Rossendorf, Sep. 5 th to 10 th 2011 Karim Fahmy, Div. Biophysics

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 Þvisualize large domain movements over ~100 µs The longer time scales are more informative for pharmacology X-FEL Workshop, Dresden-Rossendorf, Sep. 5 th to 10 th 2011 Karim Fahmy, Div. Biophysics

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 X-FEL Workshop, Dresden-Rossendorf, Sep. 5 th to 10 th 2011 non-native fish native olive oil Karim Fahmy, Div. Biophysics