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SSRL Headlines Vol. 10, No. 10  April, 2010


Contents of this Issue:

  1. Science Highlight — The Structure of an Algal Hydrogenase Reveals the Assembly and Evolution of Complex Metalloenzymes
  2. Science Highlight — Scientists Find Unexpected Electron Behavior in the Pseudogap of High-temperature Superconductors
  3. Science Highlight — Reducing Fuel Cell Costs by Changing the Structure and Reactivity of Platinum
  4. Booster Klystron Repaired and User Operations Resumed in Just 5 Days
  5. Visit of Synchrotron SOLEIL Director General to SSRL
  6. Public Lecture May 25: Jeremy Dahl on Ultimate Atomic Bling
  7. Register for June 1-3 SSRL SRXRS School
  8. Update on July VUVX2010 Conference in Vancouver, Canada and Satellite Meeting at SLAC
  9. Upcoming June and July Deadlines for SSRL Proposals
  10. LCLS AMO, SXR, XPP and CXI Proposals due June 1

1.  Science Highlight — The Structure of an Algal Hydrogenase Reveals the Assembly and Evolution of Complex Metalloenzymes
       (contacts: D.W. Mulder,; J.W. Peters,

fe-s clusters
Pathway for Fe-S cluster insertion into [FeFe]-hydrogenase during complex Fe-S cluster assembly.
The potential for using biological enzymes to make hydrogen to use as a renewable energy source is a hot topic, but little is known about how these complex enzymes assemble and work. The [FeFe]-hydrogenase enzyme binds iron and sulfur ions to catalyze the reversible production of hydrogen ions from protons and electrons. The enzyme's active site, termed the H-cluster, uses a complex Fe-S cluster comprised of a [4Fe-4S] subcluster and a 2Fe subcluster to catalyze the reaction.

A group led by John Peters of Montana State University used SSRL Beam Lines 9-1 and 9-2 to solve the crystal structure of a green algae [FeFe]-hydrogenase enzyme. They used an intermediate form of the enzyme to acquire information about the mechanism of enzyme assembly and maturation. Their 1.97 Å structure revealed a positively charged channel linked to the [4Fe-4S] subcluster site, while the 2Fe subcluster was absent. The authors propose a stepwise mechanism in which the [4Fe-4S] subcluster is assembled first and then the 2Fe cluster is assembled and inserted through the channel, which collapses and disappears in the mature enzyme. This mechanism is similar to that seen in nitrogenase, which transforms nitrogen gas into ammonia, suggesting an evolutionary link.

The researchers suggest that knowledge obtained from this structure can inform efforts to engineer better hydrogenases, ultimately leading to more cost-effective renewable energy sources, such as hydrogen fuel cells. This work was published on April 25 on the Nature website.

To learn more about this research see the full scientific highlight

2.  Science Highlight — Scientists Find Unexpected Electron Behavior in the Pseudogap of High-temperature Superconductors
       (contacts: M. Hashimoto,; D. Lu,; Z.-X. Shen,

highlight figure
Particle-hole symmetry breaking in the antinodal dispersion of pseudogapped Pb-Bi2201.
Superconductivity is a hot topic in physics for good reason. With an electrical resistance of zero, superconductors transport electrical current with no loss of energy. Unfortunately, scientists have only found materials to be superconducting at very low temperatures, much too low for widespread use. In the 1980s, scientists discovered a class of "high-temperature" superconductors that can be used at the temperature of liquid nitrogen (~-200°C). This discovery has raised scientists' hopes that materials may exist that have superconductive properties at even higher temperatures. To find these, scientists are exploring the reasons why materials are superconducting, especially by researching the properties of special electron-pairs, called Cooper pairs, that form a coherent "dance" together. In high-temperature superconductors, a so-called pseudogap state occurs just above the superconducting temperature with no analogue in "low-temperature" superconductors. In this state, electron pairs were thought to form but not act in a coordinated manner. A full understanding of the pseudogap behavior is critical to understand why these materials are superconducting at such a high temperature and may lead to new materials with even higher superconducting transition temperatures, approaching the ultimate goal of finding room temperature superconductors.

A group of researchers led by Zhi-Xun Shen of Photon Science at SLAC and Applied Physics, Stanford University explored the behavior of electrons in a high-temperature superconducting material. They used SSRL Beam Line 5-4 for angle-resolved photoemission spectroscopy (ARPES) experiments at a variety of temperatures spanning the normal state, the pseudogap state, and the superconducting state. They were surprised to find that the electrons in the pseudogap state do not pair at all. Instead, they saw the tendency of electrons traveling in a density wave. The pseudogap state is not predominantly composed of electron pairs ready to take on Cooper pair properties but of an electronic state that probably competes with superconducting pairing by consuming electrons otherwise available for pairing.

Given their surprising findings, the researchers conclude that room temperature superconductivity, if it can exist, may rely on a different electronic behavior than what was previously assumed. They are currently working on understanding the nature of the density wave they observed and its effects on the underlying high-temperature superconductivity. This research was published online on April 4 by Nature Physics.

To learn more about this research see the full scientific highlight

3.  Science Highlight — Reducing Fuel Cell Costs by Changing the Structure and Reactivity of Platinum
       (contacts: H. Ogaswara,; M.F. Toney,; A.R. Nilsson,

staff scientists
(from left) H. Ogasawara, A. Nilsson, and M. Toney (Photo courtesy K. Tuttle)
Hydrogen fuel cells are a green alternative to fossil fuels for powering vehicles, since the byproduct of fuel cell energy production is simply water. A problem with using fuel cells is their high cost, largely due to the use of the expensive element platinum in their design. The platinum is used at the cathode of the fuel cell, where it catalyzes the reduction of oxygen molecules into oxygen atoms. It is a good choice for this role because it binds the reactant well, breaks the O-O bond efficiently, and does not bind too tightly to the products.

A collaboration between SIMES, SSRL, the University of Houston and the Argonne and Oak Ridge National Labs has provided a fundamental understanding of a method used to increase the reactivity of platinum so that 80% less needs to be used for the same power generation. Using so much less platinum would allow a dramatic reduction in fuel cell cost. To accomplish this, the University of Houston research group of Peter Strasser reacted platinum with copper, then partially removed the copper, in a process called dealloying, leaving the platinum in a different configuration. The SSRL research groups of Anders Nilsson, Hiro Ogasawara and Mike Toney analyzed the structure of the dealloying materials at SSRL Beam Lines 2-1, 4-2 and 13-2; this revealed that the increased reactivity was due to lattice strain between the platinum atoms. Because of decreased spacing of atoms at the surface, the platinum creates weaker connections to the oxygen atom products and thus has better reaction rate.

The researchers plan to test other processes that alter platinum structure, aiming to further optimize its reactivity and reduce the amount required for fuel cell use. This research brings us a step closer to making a green energy alternative affordable. This study was published on April 25, 2010 online and will appear in the June issue of Nature Chemistry.

P. Strasser, S. Koh, T. Anniyev, J. Greeley, K. More, C. Yu, Z. Liu, S. Kaya, D. Nordlund, H. Ogasawara, M.F. Toney and A. Nilsson, "Lattice-strain Control of the Activity in Dealloyed Core-shell Fuel Cell Catalysts", Nat. Chem. (2010) doi: 10.1038/nchem.623

SLAC Press Release:

4.   Booster Klystron Repaired and User Operations Resumed in Just 5 Days
       (contact: J. Schmerge,

On Thursday, April 8 the SPEAR3 booster klystron, which had been in operation since the injector was first commissioned in 1990, failed. Testing to diagnose the problem was completed later that evening, and the klystron was replaced in just 14 hours starting the following day. After removing the failed tube, it was determined that the problem was due to water leaking into the oil tank causing breakdown at high voltage. Fortunately, there was a spare klystron available, last used to power the SPEAR RF cavity in 2003 during the final days of SPEAR2 operation. Cathode thermal processing began immediately after installation. The tube required over two days of thermal processing before it was feasible to raise the cathode heater to full power. High voltage testing began Monday morning which caused the vacuum pressure to rise to an unacceptable level requiring further cathode processing. A second HVPS was implemented to raise the voltage to the allowable limit to speed up the processing as much as possible. By Tuesday morning the vacuum pressure had dropped to acceptable levels and full voltage was applied on the tube. Operations staff were able to establish booster beam and inject into SPEAR3 a few hours later. Replacing the klystron required prompt assistance in strong coordination from numerous staff across many SLAC departments who are gratefully acknowledged. Additional appreciation is extended to those who gave up most their accelerator physics time on April 19-20 for user operations to make up some of the lost beam time, and to the SSRL staff who accommodated this late change in schedule.

5.   Visit of Synchrotron SOLEIL Director General to SSRL

Dr. Michel van der Rest, Director General for the Synchrotron SOLEIL, the third-generation synchrotron facility in Saint-Aubin, France, visited SSRL on April 20. Having a life science background and career, Dr. van der Rest's visit focused in particular on the SSRL Structural Molecular Biology program, including beam lines, facilities and science. A beam line tour included the microfocus Beam Line 12-2 with the newly installed PILATUS 6M detector for macromolecular crystallography, the biological small-angle scattering beam line 4-2, the biological XAS Beam Line 9-3, and the microXAS imaging Beam Line 2-3.

6.   Public Lecture May 25: Jeremy Dahl on Ultimate Atomic Bling

poster image
Diamonds exist in all sizes, from the Hope Diamond to minuscule crystals only a few atoms across. The smallest of these diamonds are created naturally by the same processes that make petroleum. Recently, researchers discovered that these "diamondoids" are formed in many different structural shapes, and that these shapes can be used like LEGO blocks for nanotechnology.

In the Panofsky Auditorium, Tuesday evening, May 25 at 7:30 p.m., diamondoids researcher Jeremy Dahl of the Stanford Institute for Materials and Energy Science (SIMES) will present a public lecture, "Ultimate Atomic Bling." Dahl will discuss the discovery of these nano-size diamonds and highlight current SLAC/Stanford research into their applications in electronics and medicine. The talk is free and open to all.

7.   Register for June 1-3 SSRL SRXRS School
       (organizers: M. Toney,; A. Mehta,; J. Bargar,

Register for the SSRL SRXRS School to be hosted by SSRL at SLAC June 1-3, 2010. This school will provide a practical users' guide to planning and conducting scattering measurements at SSRL beam lines. The school will cover important techniques, including surface and thin-film scattering, powder diffraction, in-situ x-ray scattering, and amorphous materials. It will cover topics that are not commonly addressed in text books or class lectures, but are typically obtained only through on-the-experiment training. Modern synchrotron-based x-ray scattering techniques offer the ability to probe nano- and atomic-scale structures and order/disorder relationships that critically govern the properties of advanced technological and environmental materials. Good planning and a working knowledge of beam lines, in addition to techniques, are keys to conducting successful SR-XRS measurements. The goal of the school is to provide this knowledge.

Register at:

8.   Update on July VUVX2010 Conference in Vancouver, Canada and Satellite Meeting at SLAC       

Over 500 abstracts have been submitted and more than 450 delegates from ~30 countries are expected to participate in the upcoming VUVX2010 conference July 11-16. If you wish to attend, please note that the early registration deadline is May 14. There will be an increased registration fee after that date. For those who have submitted abstracts, notification of the type and date of presentation will be sent by May 7 at the latest.

John Bozek (SLAC/LCLS) is organizing the Ultrafast Vacuum Ultraviolet & X-ray Physics Workshop, July 19-21 at SLAC, which is a satellite meeting of VUVX2010. Invited speakers will present the current state-of-the-art of FELs and laser-based ultrafast VUV/soft x-ray sources along with key new scientific discoveries. Participants will be given the opportunity to present their results in a poster session, with a few contributions selected to give brief oral presentations at the meeting. The location of the meeting will allow participants the opportunity to tour the electron and photon beam paths of the LCLS on July 21. For more information please see the conference web site at:

9.   Upcoming June and July Deadlines for SSRL Proposals
       (contacts: C. Knotts,; L. Dunn,

New X-ray/VUV proposals are due June 1 for beam time starting in fall 2010. Please note that our current experimental run ends July 26, 2010. We plan to resume user operations in late November or the beginning of December 2010.

Macromolecular Crystallography proposals are due July 1 for beam time starting in fall 2010.

10.   LCLS AMO, SXR, XPP and CXI Proposals due June 1
       (contact: C. Knotts,

In this next call for proposals, the world's research community is invited to submit scientific proposals for experiments to be carried out ~March-June 2011. During this period, the AMO, SXR, XPP and CXI instruments will be operational. We have demonstrated FEL operations over the energy range 540 eV to 10 keV, and we expect to be able to offer an energy down to 520 eV with the LCLS fundamental for the Spring 2011 run. Typically, the LCLS delivers about 2 mJ per pulse in the fundamental. Further, LCLS will deliver photons up to 20 keV from a second harmonic afterburner but reduced by roughly an order of magnitude in photon number. The pulse length can be tuned from 70-300 fs. Additionally, shorter pulses (10-40 fs) with reduced pulse energy are also available. The maximum repetition rate of the x-ray flashes is expected to be 120 Hz. For more information, see


SSRL Headlines is published electronically monthly to inform SSRL users, sponsors and other interested people about happenings at SSRL. SSRL is a national synchrotron user facility operated by Stanford University for the U.S. Department of Energy Office of Basic Energy Sciences. Additional support for the structural biology program is provided by the DOE Office of Biological and Environmental Research, the NIH National Center for Research Resources and the NIH Institute for General Medical Sciences. Additional information about SSRL and its operation and schedules is available from the SSRL WWW site.


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Last Updated: 30 April 2010
Content Owner: L. Dunn
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