In Situ Single-Crystal Diffraction Studies of the Structural Transition of Metal-Organic Framework Copper 5-Sulfoisophthalate, Cu-SIP-3

The flexibility of the metal-organic framework Cu-2(OH)(C8H3O7S)(H2O)center dot 2H(2)O (Cu-SIP-3) toward reversible single-crystal to single-crystal transformations is demonstrated using in situ diffraction methods at variable temperature. At temperatures below a dehydration-induced phase transition (T < 370 K) the structure is confirmed as being hydrated. In the temperature range where the transition takes place (370 K < T < 405 K) no discrete, sharp Bragg peaks can be seen in the single-crystal X-ray diffraction pattern, indicating significant loss of long-range order. At temperatures higher than 405 K, the Bragg peaks return and the structure can be refined as dehydrated Cu-SIP-3. The loss of guest water molecules can be followed at temperatures below the phase transition giving insight into the mechanism of the dehydration. Addition of nitric oxide gas to the material above the gating opening pressure of 275 mbar also leads to loss of Bragg scattering in the diffraction pattern.

Orientation effects in copper phthalocyanine films studied by electron paramagnetic resonance spectroscopy

The metallo-phthalocyanines (MPcs) are an interesting group of organic semiconductor materials for applications such as large area solar cells due to their optoelectronic properties coupled with the possibility of easily and cheaply fabricating thin films of MPcs [1, 2]. As for organic semiconductors in general, many of the interesting properties of the MPcs such as magnetism, light absorption and charge transport, are highly anisotropic [2, 3]. To maximise the efficiency of a device based on these materials it is therefore important to study their molecular orientation in films and to assess the influence of different growth conditions and substrate treatments.
X-ray diffraction is a well established and powerful technique for studying texture (and hence molecular orientation) in crystalline materials, but it cannot provide any information about amorphous or nanocrystalline films. In electron paramagnetic resonance (EPR) spectroscopy the signal comes from the spin of unpaired electrons in the material. This technique therefore does not require the sample to be crystalline. It works for any sample with paramagnetic centres such as the MPcs where the unpaired electrons are contributed by the metal. In this paper we present a continuous-wave X-band EPR study using the anisotropy of the EPR spectrum of CuPc [4] to determine the orientation effects in different types of CuPc films. From these measurements we gain insight into the molecular arrangement of films with different spin concentrations, and apply our technique to the study of molecular orientation in photovoltaic cells.

A Neutron Diffraction and Molecular Dynamics Investigation of Acetate-based Ionic Liquids as Solvents for Glucose

The liquid state structure of the ionic liquid, 1-ethyl-3-methylimidazolium acetate, and the solute/solvent structure of glucose dissolved in the ionic liquid at a 1: 6 molar ratio have been investigated at 323 K by molecular dynamics simulations and neutron diffraction experiments using H/D isotopically substituted materials. Interactions between hydrogen-bond donating cation sites and polar, directional hydrogen-bond accepting acetate anions are examined. Ion-ion radial distribution functions for the neat ionic liquid, calculated from both MD and derived from the empirical potential structure refinement model to the experimental data, show the alternating shell-structure of anions around the cation, as anticipated. Spatial probability distributions reveal the main anion-to-cation features as in-plane interactions of anions with imidazolium ring hydrogens and cation-cation planar stacking. Interestingly, the presence of the polarised hydrogen-bond acceptor anion leads to increased anion-anion tail-tail structuring within each anion shell, indicating the onset of hydrophobic regions within the anion regions of the liquid.

Structure of molten 1,3-dimethylimidazolium chloride using neutron diffraction

The model room temperature ionic liquid, 1,3-dimethylimidazolium chloride, has been studied by neutron diffraction for the first time. The diffraction data are used to derive a structural model of this liquid using Empirical Potential Structure Refinement. The model obtained indicates that significant charge ordering is present in the liquid salt and that the local order in this liquid closely resembles that found in the solid state. As in the crystal structure, hydrogen-bonding interactions between the ring hydrogens and the chloride dominate the structure. The model is compared with the data reported previously for both simple alkyl substituted imidazolium halides and binary mixtures with AlCl3. (C) 2003 American Institute of Physics.

Nonlinear scattering by anisotropic dielectric periodic structures

The combinatorial frequency generation by the periodic stacks of binary layers of anisotropic nonlinear dielectrics is examined. The products of nonlinear scattering are characterised in terms of the three-wave mixing processes. It is shown that the intensity of the scattered waves of combinatorial frequencies is strongly influenced by the constitutive and geometrical parameters of the anisotropic layers, and the frequency ratio and angles of incidence of pump waves. The enhanced efficiency of the frequency conversion at Wolf-Bragg resonances has been demonstrated for the lossless and lossy-layered structures. © 2012 O. V. Shramkova and A. G. Schuchinsky.

Criticality, factorization, and long-range correlations in the anisotropic XY model

We study the long-range quantum correlations in the anisotropic XY model. By first examining the thermodynamic limit, we show that employing the quantum discord as a figure of merit allows one to capture the main features of the model at zero temperature. Furthermore, by considering suitably large site separations we find that these correlations obey a simple scaling behavior for finite temperatures, allowing for efficient estimation of the critical point. We also address ground-state factorization of this model by explicitly considering finite-size systems, showing its relation to the energy spectrum and explaining the persistence of the phenomenon at finite temperatures. Finally, we compute the fidelity between finite and infinite systems in order to show that remarkably small system sizes can closely approximate the thermodynamic limit.

Characterization, crystallization and preliminary X—ray diffraction analysis of acutohaemolysin, a haemolytic toxin from Agkistrodon acutus venom

Acutohaemolysin, a phospholipase A2 (PLA2) from the venom of the snake Agkistrodon acutus, has been isolated and purified to homogeneity by anion-exchange chromatography on a DEAE-Sepharose column followed by cation-exchange chromatography on a CM-Sepharose column. It is an alkaline protein with an isoelectric point of 10.5 and is comprised of a single polypeptide chain of 13 938 Da. Its N-terminal amino-acid sequence shows very high similarity to Lys49-type PLA2 proteins from other snake venoms. Although its PLA2 enzymatic activity is very low, acutohaemolysin has a strong indirect haemolytic activity and anticoagulant activity. Acutohaemolysin crystals with a diffraction limit of 1.60 Å were obtained by the hanging-drop vapour-diffusion method. The crystals belong to the space group C2, with unit-cell parameters a = 45.30, b = 59.55, c = 46.13 Å, [beta] = 117.69°. The asymmetric unit contains one molecule

Microstructure evolution of 6061 O Al alloy during ultrasonic consolidation:An insight from electron backscatter diffraction

6061 O Al alloy foils were welded to form monolithic and SiC fibre-embedded samples using the ultrasonic consolidation (UC) process. Contact pressures of 135, 155 and 175 MPa were investigated at 20 kHz frequency, 50% of the oscillation amplitude, 34.5 mm s sonotrode velocity and 20 °C. Deformed microstructures were analysed using electron backscatter diffraction (EBSD). At all contact pressures deformation occurs by non-steady state dislocation glide. Dynamic recovery is active in the upper and lower foils. Friction at the welding interface, instantaneous internal temperatures (0.5-0.8 of the melting temperature, T), contact pressure and fast strain rates result in transient microstructures and grain size reduction by continuous dynamic recrystallization (CDRX) within the bonding zone. Bonding occurs by local grain boundary migration, which allows diffusion and atom interlocking across the contact between two clean surfaces. Textures weaken with increasing contact pressure due to increased strain hardening and different grain rotation rates. High contact pressures enhance dynamic recovery and CDRX. Deformation around the fibre is intense within 50 μm and extends to 450 μm from it. © 2009 Acta Materialia Inc.