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Internal structure, hygroscopic and reactive properties of mixed sodium methanesulfonate-sodium chloride particles Print
Friday, 13 May 2011 00:00

Scientists recently combined experimental approaches and molecular dynamics modeling to gain new insights into the internal structure of sea salt particles and relate it to their fundamental chemical reactivity in the atmosphere. This research shows that surface enhancement or depletion of chemical components in marine particles can occur because of the difference in the chemical nature of the species. Because the atmospheric chemistry of the salt particles takes place at the gas-particle interface, understanding their complex surfaces provides new insights about their effect on the environment and climate change. Article Link.

Read more about this publication in the EMSL News article Inside Sea Salt: Chemical imaging of individual sea salt particles advances aerosol research.

 
Coupled Crystallographic Order–Disorder and Spin State in a Bistable Molecule: Multiple Transition Dynamics Print
Monday, 07 March 2011 00:00

Within spin-crossover solids, strong intermolecular interactions afford a means for the propagation of molecular-scale changes and coupling with crystallographic phase transitions, which leads to intricate cooperative phenomena. In their Full Paper on page 3120 ff., J. S. Costa, O. Roubeau, G. Arom et al. report on a novel spin-crossover FeII complex that features a dense network of intermolecular interactions. This results in a large unsymmetrical hysteresis of the spin state, which correlates with a crystallographic order–disorder transition. Article Link (PDF)

 
Observation of Insulating-Insulating Monoclinic Structural Transition in Macro-Sized VO2 Single Crystals Print
Friday, 04 March 2011 10:35

To clarify the origin of metal–insulator transition (MIT) in VO2, it is of crucial importance to understand the interplay among monoclinic M1, monoclinic M2, and rutile R phases. The Letter by Bongjin Simon Mun et al. (pp. 107–109), based on data taken on ALS Beamline 12.3.2, reports the unusual insulator–insulator structural phase transition (SPT) of VO2 single crystals, which involves monoclinic M1 and M2 phase. The VO2 crystals exhibit an extremely abrupt MIT at 67.8 °C and an insulator–insulator transition (IIT) at ∼49 °C. Using synchrotron-based X-ray microdiffraction, it is found that the IIT in this VO2 crystal is related to a SPT between the M2 and M1 phases while the MIT occurs with a SPT of M1 and R phase. Also, a stable M2 phase is found at room temperature without any presence of external stress, which has not been reported previously. The authors believe that further investigations on this intriguing system will not only enrich the fundamental understanding of the system, but also will be exploited in future technologies. Article Link (PDF)

 
Crystal Structure of the Dynein Motor Domain Print
Friday, 04 March 2011 00:00

Artistic rendering of dynein motor proteins moving along microtubules, based on a crystal structure reported by Carter et al. on p. 1159. This study reveals the architecture of the molecular machine that powers the beating of cilia and intracellular transport and provides insight into the mechanism by which energy from adenosine triphosphate hydrolysis is converted into motion. Image: Graham Johnson, The Scripps Research Institute and grahamj.com. Article Link .

 
Vacuum-Ultraviolet Photoionization and Mass Spectrometric Characterization of Lignin Monomers Coniferyl and Sinapyl Alcohols Print
Saturday, 19 February 2011 00:00

The fragmentation mechanisms of monolignols under various energetic processes are studied with jet-cooled thermal desorption molecular beam (TDMB) mass spectrometry (MS), 25 keV Bi3+ secondary ion MS (SIMS), synchrotron vacuum-ultraviolet secondary neutral MS (VUV-SNMS) and theoretical methods. Experimental and calculated appearance energies of fragments observed in TDMB MS indicate that the coniferyl alcohol photoionization mass spectra contain the molecular parent and several dissociative photoionization products. Similar results obtained for sinapyl alcohol are also discussed briefly. Ionization energies of 7.60 eV ( 0.05 eV for coniferyl alcohol and <7.4 eV for both sinapyl and dihydrosinapyl alcohols are determined. The positive ion SIMS spectrum of coniferyl alcohol shares few characteristic peaks (m/z = 137 and 151) with the TDMB mass spectra, shows extensive fragmentation, and does not exhibit clear molecular parent signals. VUV-SNMS spectra, on the other hand, are dominated by the parent ion and main fragments also present in the TDMB spectra. Molecular fragmentation in VUV-SNMS spectra can be reduced by increasing the extraction delay time. Some features resembling the SIMS spectra are also observed in the desorbed neutral products. The monolignol VUVSNMS peaks shared with the TDMB mass spectra suggest that dissociative photoionization of ion-sputtered neutral molecules predominate in the VUV-SNMS mass spectra, despite the extra internal energy imparted in the initial ion impact. The potential applications of these results to imaging MS of biomolecules are discussed. Article Link (PDF)

 
Writing Nanostructures: Scanning Probe Direct-Write of Germanium Nanostructures Print
Tuesday, 02 November 2010 00:00

The cover image depicts the direct writing of a germanium nanostructure with the tip of an atomic force microscope (AFM). Germanium writing occurs when the AFM tip traces the desired shape along a biased silicon sample while immersed in an organometallic precursor (diphenylgermane). The high-electric field and the electrons emitted from the tip cause the precursor to locally react and yield germanium nanostructures. This innovative AFM strategy creates sub-30 nm carbon-free germanium nanostructures with desired geometries and placement, as reported on p. 4639 by Marco Rolandi and co-workers. Article Link (PDF)

 
Synchrotron IR Spectromicroscopy: Chemistry of Living Cells Print
Monday, 01 November 2010 00:00

Advanced analytical capabilities of synchrotron IR spectromicroscopy meet the demands of modern biological research for studying molecular reactions in individual living cells. Article Link (PDF)

 
[MnIII4LnIII4] Calix[4]arene Clusters as Enhanced Magnetic Coolers and Molecular Magnets Print
Wednesday, 22 September 2010 00:00

The [Mn4Gd4] cluster pictured is a promising candidate for refrigeration in the ultra-low-temperature region, providing for example a valid alternative to the use of 3He, which is becoming rare and expensive. Article Link (PDF)

 
An Open-Faced Chaperonin: Crystal Structures of a Group II Chaperonin Reveal Open and Cosed States Print
Thursday, 16 September 2010 14:37

Chaperonins are complexes that promote the proper folding of newly synthesized or denatured proteins by encapsulating them in a protective shell. Chaperonins come in two classes, group I and group II, which differ in their localization and closing requirements; group I members require a ring-shaped cofactor to fully close the folding chamber whereas group II members contain a built-in “lid.” Interestingly, as of yet, the structures of group II chaperonins have only been solved in the closed conformation, but in this Paper of the Week, Jose Pereira and colleagues present crystal structures of the group II chaperonin from the archaeal Methanococcus maripaludis in both closed and open states. This comparative information revealed that the closing mechanism for group II chaperonins is quite distinct from group I; during closing, all three domains—equatorial, apical, and intermediate—rotate as a single rigid body, whereas in group I chaperonins the equatorial domains remain relatively stationary. As a result, there is a significant reduction in the size and shape of the folding chamber during closing. However, substrate binding sites and sites for allosteric regulation are conserved between the two groups, suggesting they arose from a common ancestor. Together, the structures shed new light on this important class of proteins. Article Link (PDF)

 
The Nature of Nitrate at the Ice Surface Studied by XPS and NEXAFS Print
Friday, 20 August 2010 15:41

Trace contaminants such as strong acids have been suggested to affect the thickness of the quasi-liquid layer at the ice/air interface, which is at the heart of heterogeneous chemical reactions between snowpacks or cirrus clouds and the surrounding air. We used X-ray photoelectron spectroscopy (XPS) and electron yield near edge X-ray absorption fine structure (NEXAFS) spectroscopy at the Advanced Light Source (ALS) to probe the ice surface in the presence of HNO3 formed from the heterogeneous hydrolysis of NO2 at 230 K. We studied the nature of the adsorbed species at the ice/vapor interfaces as well as the effect of HNO3 on the hydrogen bonding environment at the ice surface. The NEXAFS spectrum of ice with adsorbed HNO3 can be represented as linear combination of the clean ice and nitrate solution spectrum, thus indicating that in the presence of HNO3 the ice surface consists of a mixture of clean ice and nitrate ions that are coordinated as in a concentrated solution at the same temperature but higher HNO3 pressures. ... Article Link (PDF)

 
Imaging Cell Wall Architecture in Single Zinnia elegans Tracheary Elements Print
Wednesday, 30 June 2010 00:00

The chemical and structural organization of the plant cell wall was examined in Zinnia elegans tracheary elements (TEs), which specialize by developing prominent secondary wall thickenings underlying the primary wall during xylogenesis in vitro. Three imaging platforms were used in conjunction with chemical extraction of wall components to investigate the composition and structure of single Zinnia TEs. Using fluorescence microscopy with a green fluorescent protein-tagged Clostridium thermocellum family 3 carbohydrate-binding module specific for crystalline cellulose, researchers working at ALS Beamline 1.4 found that cellulose accessibility and binding in TEs increased significantly following an acidified chlorite treatment. ...

Read more...
 
Therapeutic Antibody Targeting of Individual Notch Receptors Print
Thursday, 15 April 2010 00:00

Notch receptors are widely expressed transmembrane proteins through which mammalian cells communicate to regulate cell fate and growth, and defects in Notch signalling are linked to many cancers. Using phage display technology, a multi-department team at Genentech has produced synthetic antibodies that act as potent and specific antagonists of Notch1 and Notch2. The cover, by Gregóire Vion of Salamander Design Studios (www.grgwr.com), depicts communication between a ligand-expressing cell (right) stimulating Notch signalling in an adjacent cell. The receptor-cell membrane expresses Notches 1 and 2 (red and blue); action of a specific antagonist means that only the blue signal is transduced to the nucleus. Article Link (PDF)

 
Doping Graphene into Superconductivity (Extended van Hove Singularity and Superconducting Instability in Doped Graphene) Print
Friday, 02 April 2010 00:00

Graphene’s singular transport characteristics derive from its band structure, whose features include saddle points at the edges of the Brillouin zone that affect the topology of the Fermi surface.

In their article in Physical Review Letters, Jessica McChesney and her collaborators from the US, Germany, and Spain check for superconductivity in graphene because of a similarity—also caused by a saddle point in the band structure (a van Hove singularity)—with the density of states of high-temperature superconductors.

They chemically dope graphene to significantly higher levels than previously achieved and then probe its band structure with angle-resolved photoemission spectroscopy. The saddle point becomes more extended than localized as the Fermi surface moves across it. The authors calculate that, under these conditions of doping and Fermi surface topology, graphene can achieve superconductivity, in principle due to electron-electron interactions alone. – Sami Mitra, (Physics Synopsis)

 
The Effect of π-Stacking, H-Bonding, and Eectrostatic Interactions on the Ionization Energies of Nucleic Acid Bases Print
Sunday, 14 March 2010 00:00

A combined theoretical and experimental study of the ionized dimers of thymine and adenine, TT, AA, and AT, is presented. Experimentally observed and computed adiabatic and vertical ionization energies (IEs) for monomers and dimers as well as thresholds for the appearance of the protonated species are reported and analyzed. Non-covalent interactions strongly affect the observed IEs. The magnitude and the nature of the effect is different for different isomers of the dimers. The computations reveal that for TT, the largest changes in vertical IEs (0.4 eV) relative to the monomer occur in asymmetric H-bonded and symmetric -stacked isomers, whereas in the lowest-energy symmetric H-bonded dimer the shift in IEs is much smaller (0.2 eV). The origin of the shift and the character of the ionized states is different in asymmetric H-bonded and symmetric stacked isomers. ... Article Link (PDF)

 
Probing the Hydrogen-Bond Network of Water via Time-Resolved Soft X-Ray Spectroscopy Print
Thursday, 28 May 2009 00:00

We report time-resolved studies of hydrogen bonding in liquid H2O, in response to direct excitation of the O–H stretch mode at 3 m, probed via soft X-ray absorption spectroscopy at the oxygen K-edge. This approach employs a newly developed nanofluidic cell for transient soft X-ray spectroscopy in the liquid phase. Distinct changes in the near-edge spectral region (XANES) are observed, and are indicative of a transient temperature rise of 10 K following transient laser excitation and rapid thermalization of vibrational energy. The rapid heating occurs at constant volume and the associated increase in internal pressure, estimated to be 8 MPa, is manifested by distinct spectral changes that differ from those induced by temperature alone. We conclude that the near-edge spectral shape of the oxygen K-edge is a sensitive probe of internal pressure, opening new possibilities for testing the validity of water models and providing new insight into the nature of hydrogen bonding in water. Article Link (PDF)

 
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