FRA —  FEL Applications   (28-Aug-15   08:30—10:30)
Paper Title Page
FRA01
Radiation Damage Free Structure of Photosystem II at 1.95A Resolution  
 
  • M. Suga, F. Akita, Y. Nakajima, J.R. Shen, T. Shimizu
    Okayama University, Okayama, Japan
  • H. Ago, K. Hirata, H. Murakami, G. Ueno, M. Yamamoto, K. Yamashita
    JASRI/RIKEN, Hyogo, Japan
 
  The initial reaction of photosynthesis takes place in Photosystem II (PSII), a 700kD membrane protein complex which catalyses photo-oxidation of water into dioxygen through an S-state cycle of the oxygen evolving complex (OEC). The structure of PSII has been solved by XRD at 1.9Å resolution, which revealed the OEC is a Mn4CaO5-cluster*. However, EXAFS studies showed that the manganese atoms in the OEC are easily reduced by X-ray irradiation, and slight differences were found in the Mn-Mn distances between the results of XRD, EXAFS and theoretical studies. We present a radiation-damage-free structure of PSII from Thermosynechococcus vulcanus in the S1 state at 1.95Å resolution using femtosecond X-ray pulses of SACLA. Compared with the structure from XRD, the OEC in the XFEL structure has Mn-Mn distances that are shorter by 0.1-0.2Å. The valences of each manganese atom were assigned as Mn1D(III), Mn2C(IV), Mn3B(IV) and Mn4A(III). One of the oxo-bridged oxygens, O5, has significantly longer Mn-O distances in contrast to the other oxo-oxygen atoms, suggesting that it is a hydroxide ion instead of a normal oxygen dianion and therefore may serve as one of the substrate oxygen atoms**.
* Y. Umena et al., Nature, 473(7545): 55-60 (2011).
** M. Suga et al., Nature, 517(7532): 99-103 (2015).
 
slides icon Slides FRA01 [135.184 MB]  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
FRA02
Direct Observation of Bond Formation in Solution with Femtosecond X-Ray Scattering  
 
  • K.H. Kim
    IBS, Daejeon, Republic of Korea
  • H. Ihee, J.G. Kim
    KAIST, Daejeon, Republic of Korea
 
  Funding: This work was supported by IBS-R004-G2.
Bond breaking and bond making are essential processes in chemical reactions. While ultrafast dynamics of bond breaking have been studied intensively using time time-resolved techniques, it is challenging to keep track of structural dynamics of bond making due to its bimolecular nature. Time-resolved X-ray liquidography (TRXL) has been developed by using the X-ray pulse, instead of optical pulse, as a probe and gives the time-resolved scattering response sensitive to global molecular structure.(*, **) The time resolution of 3rd generation source is 100 ps and due to this limited time resolution, ultrafast structural dynamics involved in ultrafast excited-state dynamics and direct observation of bond-breaking and -making processes cannot yet be accomplished with TRXL. This limit is improved with X-ray free electron lasers (XFELs), which deliver 100 fs long X-ray pulses with ~1013 photons per pulse. With the advent of X-ray free electron laser (XFEL) generating ultrashort X-ray pulses, the exploration of chemical processes occurring on femtosecond time scale with pump-probe X-ray solution scattering is possible. With the aid of 4th generation X-ray sources (SACLA, Japan), ultrafast tight Au-Au bond formation process of [Au(CN)2-]3 oligomer upon 267 nm laser excitation was directly observed using TRXL.
* K.H. Kim et al., Nature, 2015, 518, 385-389.
** H. Ihee et al., Science, 2005, 309, 1223-1227.
 
slides icon Slides FRA02 [29.203 MB]  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
FRA03
Where are the Electrons? New Opportunities for Mapping Local Chemical Interaction Dynamics with Time-resolved Soft X-ray Spectroscopy at FELs  
 
  • Ph. Wernet
    HZB, Berlin, Germany
 
  Photochemically activated molecules catalyze chemical reactions, but a molecular-level understanding of how these short-lived and reactive intermediates catalyze reactions has remained elusive. I will discuss how time-resolved soft x-ray spectroscopy at free-electron lasers enables a fundamental understanding of local atomic and intermolecular interactions and their dynamics b on atomic length and time scales of Ångströms and femtoseconds[1]. In a recent application[2], we used femtosecond resonant inelastic x-ray scattering (RIXS) at the LINAC Coherent Light Source (LCLS, Stanford, USA)[3] to probe the reaction dynamics of the benchmark transition-metal complex Fe(CO)5 in solution. This highlights the ability of femtosecond soft x-ray spectroscopy at free-electron lasers to probe frontier-orbital interactions with atom specificity. I will end by discussing how the currently available methodology can be extended towards probing complex biomolecules in physiological conditions[4]. I will show how in particular high-repetition rate x-ray free-electron laser sources such as the planned LCLS-II will enable probing the local chemistry and it dynamical evolution in metalloproteins.
[1] Ph. Wernet. Phys. Chem. Chem. Phys. 13, 16941 (2011).
[2] Ph. Wernet et al., Nature, 520, 78-81 (2015).
[3] K. Kunnus et al., Rev. Sci. Instrum. 83, 123109 (2012).
[4] R. Mitzner et al., J. Phys. Chem. Lett. 4, 3641 (2013).
 
slides icon Slides FRA03 [61.138 MB]  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)  
 
FRA04
Measurements and Future Prospects for Coherent Control with FEL Radiation  
 
  • K.C. Prince
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
 
  FELs produce ultrafast, intense, polarised and coherent pulses of light, similar to optical lasers, and these properties have been exploited in FEL experiments, with one exception, namely longitudinal coherence. There have been few if any FEL applications of this property. The FERMI FEL is longitudinally coherent, and can be configured to produce simultaneous, different wavelengths which are mutually coherent, with a well-defined phase relationship. We have exploited this in recent experiments to produce overlapping pulses of first and second harmonic light with a tunable phase delay, and perform an experiment on neon atoms. The first harmonic was set to about 63 nm and high intensity, and the second harmonic to lower intensity and half of this wavelength. The first harmonic gave rise to two-photon photoemission, while the second harmonic caused single photon emission. At appropriate relative intensities of the two beams, the emitted photoelectrons interfered to give asymmetric angular distributions (Brumer-Shapiro type experiment.) The asymmetry depended on the value of the phase difference between the two wavelengths, thus demonstrating their correlation in phase. The relative phase was controlled with a precision of 3 attoseconds. This result opens the way to coherent control experiments in the short wavelength region, and some planned applications will be illustrated.  
slides icon Slides FRA04 [4.216 MB]  
Export • reference for this paper to ※ LaTeX, ※ Text, ※ IS/RefMan, ※ EndNote (xml)