November 2012
T. J. Reber, University of Colorado, D. S. Dessau, University of Colorado
In solids, Fermi surfaces are the boundaries between occupied and unoccupied electron levels, as defined in momentum space. Their properties dictate that each Fermi surface should form a single unbroken loop. To the surprise of physicists, disconnected segments of the Fermi surface – Fermi arcs – were discovered in cuprate superconductors in 1998.
In a study recently published in Nature Physics, researchers from the University of Colorado have used angle-resolved photoemission spectroscopy (ARPES) at SSRL Beam Line 5-4 to determine the origin of these Fermi arcs in the cuprates.
Angle-resolved photoelectron spectroscopy
BL5-4
November 2012
Alessandra Leri, Marymount Manhattan College (aleri@mmm.edu), Satish Myneni, Princeton University (smyneni@princeton.edu)
Recent work at SSRL has helped reveal a previously unrecognized wealth of bromine chemistry in the environment, where bromine in seawater has long been thought to exist as inorganic bromide, while bromides in soil were considered so unreactive that they've routinely been used as a hydrological tracer.
The reality bromine chemistry in the environment is much more complex. X-ray absorption spectroscopic (XAS) studies conducted by Leri, et al. at SSRL Beam Lines 2-3 and 4-3, as well as at the ALS and NSLS, reveal a complicated association between bromine and organic carbon in both sea water and soil.
X-ray Absorption Spectroscopy
BL2-3, BL4-3
October 2012
Rongsheng Jin, The Sanford-Burnham Research Institute
Botulinum neurotoxins (BoNTs) invade motor neurons at their junctions with muscular tissue, where the toxins disable the release of the neurotransmitter acetylcholine and subsequently paralyze the affected muscles. Accidental BoNT poisoning primarily occurs through ingestion of food products contaminated by Clostridium botulinum, the bacterium that produces BoNTs. However, BoNTs by themselves are fragile and sensitive to low pH environments and digestive proteases. So how do they survive the harsh environment of the host’s gastrointestinal tract?
Macromolecular Crystallography
BL9-2
October 2012
Corwin Booth, Lawrence Berkeley National Laboratory, Tsu-Chien Weng, SSRL
The structural, electronic, and magnetic properties of U and Pu elements and intermetallics remain poorly understood despite decades of effort, and currently represent an important scientific frontier toward understanding matter. The last decade has seen great progress both due to the discovery of superconductivity in PuCoGa5 and advances in theory that finally can explain fundamental ground state properties in elemental plutonium, such as the phonon dispersion curve, the non-magnetic ground state, and the volume difference between different phases of the pure element.
BL6-2
October 2012
Jeff Gelb, Xradia
Researchers at SSRL, General Motors, Imperial College London, National Taiwan University, and elsewhere have recently begun experimenting with 3-D transmission X-ray microscopy (TXM), in order to gain new insight into the microstructure of battery electrodes.
BL6-2
September 2012
Irimpan Mathews, SSRL, Amnon Kohen, University of Iowa
Flavin-dependant thymidylate synthases (FDTSs) are a class of recently identified family of thymidylate synthases that employ novel mechanism for the thymidylate synthase reaction. Thymidylate synthases use N5,N10-methylene-5,6,7,8-tetrahydrofolate (CH2H4folate) to reductively methylate 2’-deoxyuridine-5’-monophosphate (dUMP) producing 2’-deoxythymine-5’-monophosphate (dTMP). dTMP is one of the four DNA building blocks and is crucial for survival of all organisms. Unlike other deoxynucleotides, dTMP cannot be directly synthesized by a ribonucleotide reductase, and its de novo biosynthesis requires the enzyme thymidylate synthase. Therefore, inhibition of thymidylate synthesis stops DNA production, arresting cell cycle and eventually leading to “thymineless” cell death. The human enzyme has long been recognized as a target for anticancer drugs.
Since FDTS enzymes are mainly found in very pathogenic microbes including the pathogens causing leprosy, botulism, diarrhea, anthrax, pneumonia, syphilis, etc., the FDTS enzyme is an attractive target for antibiotic drugs.
Macromolecular Crystallography
BL9-2, BL12-2
September 2012
Claudia Y. Janda, Howard Hughes Medical Institute, Stanford University, Christopher Garcia, Howard Hughes Medical Institute, Stanford University
Wnt proteins engage an array of receptors and inhibitors to precisely regulate crucial processes during embryonic development and tissue homeostasis and repair in the adult, and deregulated Wnt signaling is observed in many types of cancers and degenerative diseases.
Macromolecular Crystallography
BL11-1
September 2012
Helen Nichol, University of Saskatchewan, Sam Webb, SSRL
Brain injuries from stroke are both common and costly. The NIH has estimated that the total annual cost of stroke in the United States is $43 billion including direct medical care and the costs related to lost productivity. It has been recognized that rapid diagnosis and treatment is essential to limit neuronal cell death from either a bleed into the brain (hemorrhagic stroke) or a blockage that deprives part of the brain of oxygen (ischemic stroke). The Synchrotron Medical Imaging Team, a group of Canadian, US, and European scientists from diverse backgrounds are collaborating to better understand the underlying chemistry of stroke and how to best image and treat stroke patients.
BL2-3, BL4-3, BL10-2
August 2012
Sarel Fleishman, Weizmann Institute of Science, David Baker, University of Washington, Ian Wilson, The Scripps Research Institute
Understanding the physical underpinnings of how proteins interact specifically with one another and not with the myriad other molecules that coexist in every cellular compartment is a major goal of molecular biology. The broad outlines of an answer were suggested by Linus Pauling in the 1940’s: the aggregate effect of numerous weak and nonspecific van der Waals, hydrogen-bonding, and electrostatic interactions underlie high specificity and affinity. Since Pauling’s days thousands of co-crystal structures have provided concrete examples for how molecular recognition is achieved in different biological contexts. Yet, the ultimate proof for understanding a natural phenomenon lies in recapitulating it; in the words of Thomas Edison, ‘until man duplicates a single blade of grass, Nature laughs at his so-called scientific knowledge’.
Macromolecular Crystallography
BL9-2
August 2012
Frank G. Bridges, University of California, Santa Cruz
A new magnetic state called a quantum spin liquid has been observed by a large international team of investigators from ten institutions1, including a group using SSRL. When magnetic ions are located within a crystal lattice there are usually strong local magnetic and electric forces between them. At low temperatures such forces lead to a preferred alignment of the atomic moments – in ferromagnets such as iron for example, the atomic magnets are aligned parallel to each other while in anti-ferromagnets they are antiparallel. In other cases the atomic magnetics are aligned along crystallographic axis within the crystal. So quite generally when cooled sufficiently, the atomic moments develop a definite alignment.
BL10-2
