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Organic Solar Cells: Absolute Measurement of Domain Composition and Nanoscale Size Distribution Explains Performance in Solar Cells Print
Tuesday, 22 January 2013 00:00

This front cover represents the morphology and resulting device dynamics in organic solar cell blend films of PTB7 and PC71BM, as revealed by combined resonant x-ray scattering and microscopy done at the Advanced Light Source. Harald Ade and co-workers find that the fullerene molecules (red) are miscible in the polymer (blue) up to 30 wt.%, above which they begin to agglomerate (bottom). This agglomeration is important for the optoelectronic processes within the device, but the agglomerates must be kept to small sizes by the solvent processing additive diiodooctane (DIO). Correlation of this morphology with the spectrally resolved quantum efficiency shows that the yellow excitons created upon photoabsorption must arrive at the agglomerate interface for charge separation to occur. The blue electrons and green holes can then percolate through appropriate molecules in the mixed matrix to the electrodes for harvesting of electrical energy. Article Link (PDF)

Sequestering Uranium from Seawater: Binding Strength and Modes of Uranyl Complexes with Glutarimidedioxime Print
Sunday, 14 October 2012 00:00

The ocean is an important source of uranium if it can be extracted economically. Extraction of uranium from seawater is very challenging, not only because it is in an extremely low concentration, but also because it exists in seawater as very stable carbonate complexes in the presence of many other metal ions (Na, K, Ca, Mg, Al and transition metals), some of which are in overwhelmingly higher concentrations. Since the 1960s, various techniques have been studied and developed for the extraction of uranium from seawater. Among these, the Japanese process using amidoxime-based sorbents prepared by radiation grafting showed the most promise. A better understanding of the coordination modes and binding strength of the amidoxime group with uranium is the key to improving the extraction efficiency and selectivity. Article Link .

Molecular conformations, interactions, and properties associated with drug efficiency and clinical performance among VEGFR TK inhibitors Print
Monday, 17 September 2012 00:00

Pictured are crystals that contain VEGFR2 tyrosine kinase in complex with an inhibitor from a class of potent anticancer drugs. Michele McTigue et al. produced these and similar crystals to determine the structural basis for the significant variation in potency and clinical performance of members of this anticancer drug class. The authors found that conformations of an often-neglected kinase domain affect the efficiency with which inhibitors bind. Understanding the relationship between kinase conformation and inhibitor efficiency could help optimize drug design for in vivo performance. Article Link (PDF)

Image courtesy of Robert S. Kania.

Plant UVR8 Photoreceptor Senses UV-B by Tryptophan-Mediated Disruption of Cross-Dimer Salt Bridges Print
Friday, 23 March 2012 09:55

science-photoreceptor In plants, the UVR8 protein senses ultraviolet-B (UV-B) wavelengths in sunlight, triggering changes in growth and development, including the production of a protective chemical sunscreen. Pyramids of tryptophan rings intrinsic to UVR8 create a built-in light switch; no separate chromophore is required. Article link.

Metal Ion-Assisted Transformations of 2-Pyridinealdoxime and Hexafluorophosphate Print
Monday, 05 March 2012 15:26

Metal-ion mediated reactions of 2-pyridinealdoxime and hexafluorophosphate lead to ZnII complexes containing picolinic acid, picolinamide and monofluorophosphate (−2) as ligands. Article Link (PDF)

Read more about this publication in the ALS Science Brief Metal-Ion-Mediated Reactions.

Mollusk Shell Nacre Ultrastructure Correlates with Environmental Temperature and Pressure Print
Tuesday, 07 February 2012 00:00

Nacre, or mother-of-pearl, is the tough, iridescent biomineral lining the inner side of some mollusk shells. The micro-structure of nacre is correlated with the temperature at which nacre was deposited. It is therefore possible that mollusk shell nacre could be used as a thermometer for modern and past climates. Once validated nacre could become a physical, non-chemical temperature proxy. The shells shown here are representative of the three nacre-forming mollusk classes: gastropods, bivalves, and cephalopods, respectively (Haliotis rufescens, Pinctada margaritifera, Nautilus pompilius). Article Link (PDF)

Autophagy Ubiquitin-Like Protein Transfer In Trans Print
Friday, 04 November 2011 00:00

The cover depicts how the autophagy ubiquitin-like protein Atg8 is transferred from its E1, Atg7, to its E2, Atg3 (Taherbhoy et al., pp. 451–461). The two halves of the yin-yang represent the homodimeric Atg7. The circles within the yin-yang represent the Atg7 catalytic cysteines to which the ubiquitin-like protein Atg8 is transiently covalently linked. Each Atg7 monomer is capable of recruiting Atg3. Structural, biophysical, and biochemical data indicate that Atg3 binds to one Atg7 protomer and reaches across to accept Atg8 from the opposite protomer of Atg7 within the dimer. Article Link (PDF)

Read more about this publication in the ALS Science Brief Understanding the Autophagy Pathway.

XRCC4 Protein Interactions with XRCC4-like Factor (XLF) Create an Extended Grooved Scaffold for DNA Ligation and Double Strand Break Repair Print
Wednesday, 20 July 2011 00:00

The cover shows a protein plasticity and filament formation of XRCC4 (gold) in complex with ligase IV tandem BRCT domains (red) and with XLF (XRCC4-like factor, green). The article by Hammel et al., pages 32638–32650, describes the combination of crystallography, small angle x-ray scattering, and hydrogen-deuterium exchange mass spectrometry in the characterization of the XRCC4-XLF-DNA complex that permits multiple protein interactions leading to double strand break repair. Article Link (PDF)

Building of a Novel Mn12 Single Molecule Magnet by Assembly of Anisotropic Triangles Print
Wednesday, 06 July 2011 12:58

Assembly of triangular {MnIII3(O)(salox)3}+ fragments mediated by azido ligands, results in the dodecanuclear [Mn12O4(salox)12(N3)4(MeOH)4(H2O)2] complex with S = 8 ground state and SMM response. After the discovery of the Single-Molecule-Magnet (SMM) behaviour of [Mn6(O)2(salox)6(R-COO)2] (salox = salicylaldoxime, R = Me, Ph) complexes in 2004,1 the chemistry of this family of [Mn6] clusters has been studied in depth: the systematic change of the carboxylato ligands, the study of substitutedR-saloxH2 related ligands,2 the effect of variation of the oxidation state,3 the response under pressure4 or the one-dimensional assembly of [Mn6] units into chains of clusters5 with Single-Chain-Magnet behaviour in some cases,5c,d turn this system into one of the best known in the SMM field. One of the main goals of this work, developed by Brechin et al. has been to modulate the value of the ground spin level, reaching the maximum possible spin S = 12 by means of the adequate choice of methyl or ethyl substituted salicylaldoximes and the understanding of the structural features that control the coupling inside the triangles. Article Link (PDF)

Computing in Thermal Equilibrium With Dipole-Coupled Nanomagnets Print
Monday, 23 May 2011 00:00

In the 1970s, work at IBM by Charles Bennett suggested the possibility of a computer operating near thermal equilibrium and dissipating energy near the thermodynamic limits. Here, we demonstrate experimentally that a computing architecture based on dipole-coupled nanomagnets can operate near thermal equilibrium without the assistance of externally applied magnetic fields. The dynamics of digital signal propagation is demonstrated with micromagnetic simulation and then verified experimentally using time-lapse photoemission electron microscopy. A logic gate that computes using energy from the thermal bath without external fields is also demonstrated. Nanomagnetic logic circuits operating under these conditions are expected to dissipate energy near the fundamental thermodynamic limits of computation. Article Link (PDF)

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 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)

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