An international collaboration that included researchers at SSRL has used x-ray scanning microprobe fluorescence techniques at BL6-2 to characterize the elemental chemistry of samples from comet 81P/Wild-2 brought back aboard the Stardust spacecraft last January. Twenty-three aerogel samples containing cometary particles were analyzed by the 175-member Preliminary Examination Team, and five of those samples were studied at SSRL. This collaboration provided the first look at the Stardust samples after the return, and results are presented in several publications in the December 15 issue of Science.
Approximately 1,700 scientists visit SSRL annually to conduct experiments in broad disciplines including life sciences, materials, environmental science, and accelerator physics. Science highlights featured here and in our monthly newsletter, Headlines, increase the visibility of user science as well as the important contribution of SSRL in facilitating basic and applied scientific research. Many of these scientific highlights have been included in reports to funding agencies and have been picked up by other media. Users are strongly encouraged to contact us when exciting results are about to be published. We can work with users and the SLAC Office of Communication to develop the story and to communicate user research findings to a much broader audience. Visit SSRL Publications for a list of the hundreds of SSRL-related scientific papers published annually. Contact us to add your most recent publications to this collection.
December 2006
X-ray Absorption Spectroscopy
BL6-2
December 2006
Researchers have obtained the highest-resolution image of a didomain structure in a modular polyketide synthase (PKS), revealing new structural features. PKS enzymes catalyze the synthesis of polyketides, which include a number of antibiotics, anticancer agents, antiparasitics, and immunosuppressants. The researchers solved the x-ray crystal structure of a didomain of 6-deoxyerythronolide B synthase (DEBS), a model PKS using data measured at SSRL Structural Molecular Biology Beam Line 11-1. They imaged a 194-kDA fragment of module 5 of the enzyme with multiwavelength anomalous dispersion (MAD).
Macromolecular Crystallography
BL11-1
November 2006
Researchers have for the first time obtained a high-resolution structure of a three-molecule receptor-ligand complex that could help shed light on neurodegenerative diseases such as Parkinson's. The complex includes two receptor molecules, called GFRα3, bound with its ligand, artemin, which fit together like a lock and key. These molecules play a key role in chemical signal transmission and in the development and health of neurons.
Macromolecular Crystallography
BL11-1
November 2006
Scientists have for the first time used an extremely short and intense coherent soft x-ray laser pulse to successfully obtain a high-resolution image of a nano-scale object before the sample was destroyed by the energy impact of the pulse. The experiment, conducted at Deutsches Elektronen-Synchrotron (DESY) in Hamburg by a collaboration that included researchers from the Photon Science Directorate at SLAC, also set a speed record of 25 femtoseconds for the duration of the x-ray pulse used to acquire the image. The results are published in the November 12 online edition and the December printed edition of Nature Physics.
X-ray diffraction
November 2006
Billions of years ago, primitive bacteria developed a way to harness sunlight to split water molecules into protons, electrons and oxygen-the cornerstone of photosynthesis. Now, a team of scientists has taken a major step toward understanding this process by deriving the precise structure of the catalytic metal-cluster center containing four manganese atoms and one calcium atom (Mn4Ca) that drives this water-splitting reaction. This catalytic center resides in a large protein complex, called photosystem II, found in plants, green algae, and cyanobacteria. The international team was led by scientists from LBNL, and includes scientists from Germany's Technical and Free Universities in Berlin, the Max Planck Institute in Mülheim, and from SSRL.
X-ray Absorption Spectroscopy
BL9-3
October 2006
Uranium (U) contamination of ground and surface water is a serious problem in many parts of the world. Agricultural practices, mining, and nuclear weapons production have resulted in elevated levels of this heavy metal at a variety of locations, which threatens human health by seeping into groundwater and dispersing over large areas.
BL11-2
October 2006
Uranium contamination is a major concern at Department of Energy sites and decommissioned mining and ore processing facilities around the U.S. Migration of uranium has contaminated ground water in several locations, and the threat remains for further contamination unless costly measures are taken to isolate the contaminates and stop their spread.
X-ray Absorption Spectroscopy
September 2006
Fiber optic communication relies on the strength of a signal of light to deliver information, but over long distances that signal becomes dim and can lose its integrity. Amplifying the signal along the way can decrease signal loss, and scientists have been searching for new materials to build photonic signal amplifiers that are inexpensive and easily mass produced. Now, researchers from UCLA, working in part at the Stanford Synchrotron Radiation Laboratory Beam Line 11-2, have demonstrated how to deposit a special thin film with photoluminescent erbium (Er) onto silicon wafers. This technique could lead to the development of miniaturized optical amplifiers integrated with microchips for their incorporation into communications hardware.
BL11-2
September 2006
The toxicity of arsenic is widely known, but perhaps less widely appreciated is that it's the level of toxicity critically depends on the chemical form. The fern Pteris vittata, is one of a small group of plants that actively accumulates to a startling degree - an arsenic hyperaccumuatlor. P. vittata absorbs arsenic from soil, typically present as the relatively benign arsenate, and changes its chemical form to arsenite, which is one of the more toxic kinds of arsenic. The plant thrives on this toxic regimen, and it most likely does this to defends itself from hungry herbivores. The ability of P. vittata to take up arsenic has generated much excitement because of potential applications for environmental cleanup of drinking water and of contaminated sites.
X-ray Absorption Spectroscopy
BL9-3
August 2006
Genes, which are made of nucleic acids (DNA or RNA) contain the instructions for how to make proteins, but still enzymes made of proteins are needed to replGenes, which are made of nucleic acids (DNA or RNA) contain the instructions for how to make proteins, but still enzymes made of proteins are needed to replicate the genes. This paradox was addressed ~20 years ago with the realization that some kinds of RNA can act as enzymes. These RNA enzymes, or ribozymes, are accordingly made of the genetic RNA material, but they act as chemical catalysts. This means that ribozymes would have enabled the first self-replicating molecules, also made of RNA, to copy themselves.
Macromolecular Crystallography
BL1-5
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