The structure of defect Ru4Si3

The nature of the defect structure of Ru₄Si₃ has been studied with electron diffraction and electron microscopy methods. Lattice image pictures, interpreted with histogram analysis, reveal that planar defects of chemical twinning type are common in the crystals.     

1,1-(1-Propene-1,3-diyl)-ferrocene: modified synthesis, crystal structure, and polymerisation behaviour

The dehydro[3](1,1^′)ferrocenophanes, 1,1^′-(1-propene-1,3-diyl)-ferrocene (3a), and 1,1^′-(3-phenyl-1-propene-1,3-diyl)-ferrocene (3b) were synthesised under Shapiro conditions from the tosylhydrazones of the corresponding α-oxo-[3](1,1^′)ferrocenophanes. Electrochemistry shows 3a is oxidised at smilar potential to ferrocene; according 3a can be chemically oxidised using silver trifluoromethanesulfonate. The structure of 3a shows a ring tilt of 11.3°. Attempts to polymerise 3a using the ROMP initiator Mo(CHCMe₂Ph)[N(2,6-ⁱPr₂C₆H₃)][OCMe(CF₃)₂]₂ led to a mixture of insoluble material and a soluble mixture of apparently cyclic oligomers ([3a]_n).     

Modeling anhydrous and aqua copper(II) amino acid complexes: a new molecular mechanics force field parametrization based on quantum chemical studies and experimental crystal data

This paper presents the vacuum structures of aquacopper(II) bis(amino acid) complexes with glycine, sarcosine, N,N-dimethylglycine, and N-tert-butyl-N-methylglycine estimated using the B3LYP method. The differences between the B3LYP vacuum structures and experimental crystal structures suggested considerable influence of crystal lattice packing effects on the changes in the complexes' geometries. A previously developed molecular mechanics force field for modeling anhydrous copper(II) amino acidates was reoptimized to simulate these changes and predict the properties of both trans and cis anhydrous and aqua copper(II) amino acid complexes. The modeling included experimental molecular and crystal structures of 13 anhydrous and 10 aqua copper(II) amino acidates with the same atom types (Cu(II), C, H, N, and O) but various copper(II) coordination polyhedron geometries, crystal symmetries, and intermolecular interactions. The empirical parameters of the selected potential energy functions were optimized on the B3LYP vacuum copper(II) coordination geometries of three anhydrous copper(II) amino acidates and on experimental crystalline internal coordinates and unit cell dimensions of six anhydrous and six aqua copper(II) amino acid complexes. The respective equilibrium structures were calculated in vacuo and in simulated crystalline environment. The efficacy of the final force field, FFW, was examined. The total root-mean-square deviations between the experimental and theoretical crystal values were 0.018 A in the bond lengths, 2.2 degrees in the valence angles, 5.5 degrees in the torsion angles, and 0.395 A in the unit cell lengths. FFW reproduced the unit cell volumes in the range from -8.1 to 9.6%. The means of Cu to axial water oxygen distances were 2.4 +/- 0.1 A (experiment) and 2.6 +/- 0.1 A (FFW). This paper describes the ability of the molecular mechanics model and FFW force field to simulate the flexibility of the metal coordination polyhedron. The new force field proved effective in predicting the most stable molecular conformation of copper(II) amino acidato systems in vacuo.     

The Grob/Eschenmoser fragmentation of cycloalkanones bearing β-electron withdrawing groups: a general strategy to acyclic synthetic intermediates

Introduction of a β-electron withdrawing group to cycloalkanones allows facile C-C bond fragmentation. The reaction has been demonstrated with a large range of ring sizes, bearing various leaving and electron withdrawing groups, and using a variety of nitrogen and oxygen containing nucleophiles (>30 examples). The application of fragmentation products to the preparation of substituted γ-lactones has been demonstrated. Mechanistic studies are reported which are suggestive of a Grob/Eschenmoser type reaction.     

The thermodesorption mechanism of ammonia from Ru(0 0 0 1)

Thermodesorption rates for the desorption of ammonia from Ru(0 0 0 1) are calculated by Transition State Theory including small curvature tunneling corrections. The potential energy surface is derived on a model cluster employing hybrid density functional theory (B3LYP). Two desorption pathways can be identified, just distinguished by the orientation of the leaving ammonia entity. It is found that the rate dominating mechanism comprises an umbrella-like flipping movement of the hydrogen atoms during the desorption. Nevertheless tunneling does not play any significant role in the reaction as the hydrogen movements are shown to occur at the low energy regions of the barrier.     

MOVPE growth of strain-compensated 1300 nm In1−xGaxAsyP1−y quantum well structures

Different concepts for achieving strain-compensated quantum well structures emitting at 1300 nm have been investigated. Structures employing up to eight compressively strained wells with the same x in well and barrier exhibits excellent structural and optical properties, including very high photoluminescence efficiency. Increased number of quantum wells beyond 8 resulted in deteriorated materials quality, most likely due to accumulated strain-induced roughness of the growing surface. Good laser characteristics, including T₀ values of 64 K, were demonstrated for strain-compensated structures with tensile wells.     

Structure and dynamics of a partially folded protein are decoupled from its mechanism of aggregation

A common strategy to study the mechanism of amyloid formation is the characterization of the structure and dynamics of the precursor state, which is in most cases a partially folded protein. Here we investigated the highly dynamic conformational state formed by the protein domain HypF-N at low pH, before aggregation, using fluorescence, circular dichroism, and NMR spectroscopies. The NMR analysis allowed us, in particular, to identify the regions of the sequence that form hydrophobic interactions and adopt an alpha-helical secondary structure in the pH-denatured ensemble. To understand the role that this residual structure plays in the aggregation of this protein, we probed the mechanism of aggregation using protein engineering experiments and thus identified the regions of the sequence of HypF-N that play a critical role in the conversion of this dynamic state into thioflavin T-binding and beta-sheet containing protofibrils. The combination of these two complementary approaches revealed that the aggregation of pH-denatured HypF-N is not structure-dependent, meaning that it is not driven by the regions of the protein that are either less or more protected in the initial partially folded state. It is, by contrast, promoted by discrete protein regions that have the highest intrinsic propensity to aggregate because of their physicochemical properties.     

Evaluation of individual particle capillary electrophoresis experiments via quantile analysis

The number of particles in a sample heavily influences the shape of a distribution corresponding to the individual particle measurements. Selecting an adequate number of particles that prevents biases due to sample size is particularly difficult for complex biological systems in which statistical distributions are not normal. Quantile analysis is a powerful statistical technique that can rapidly compare differences between multiple distributions of individual particles. This report utilizes quantile analysis to show that the number of events detected affects the mobility distributions for rat liver and mouse liver mitochondria, sample individual particles, when analyzed via capillary electrophoresis with laser-induced fluorescence. When the mitochondrial sample is small (e.g. <78), there are not enough events to obtain statistically relevant mobility data. Adsorption to the capillary surface also significantly affects the mobility distribution at a small number of events in uncoated and dynamically coated capillaries. These adsorption effects can be overcome when the mitochondrial load on the capillary is sufficiently large (i.e. >609 and >1426 events for mouse liver on uncoated capillaries and rat liver on dynamically coated capillaries, respectively). It is anticipated that quantile analysis can be used to study other distributions of individual particles, such as nanoparticles, organelles, and biomolecules, and that distributions of these particles will also be dependent on sample size.     

Flawed Nuclear Physics and Atomic Intelligence in the Campaign to deny Norwegian Heavy Water to Germany, 1942–1944

The military campaign to deny Norwegian heavy water to Germany in World War II did not diminish as the threat posed by heavy water in German hands dwindled, mainly because of excessive security among the Allies. Signs that Albert Speer (1905–1981) had decided in 1942 to stop the German atomic-bomb project were kept secret and ignored. Prominent Allied advisers like Leif Tronstad (1903–1945) and even Niels Bohr (1885–1962) were not told about the plutonium path to a German atomic bomb. Physicists did not brief advisers, decision makers, and Allied officers on how many years Werner Heisenberg (1901–1976) would need to accumulate enough heavy water (deuterium oxide, D₂O) for an Uranmachine and then to extract and process plutonium for an atomic bomb. Had the flow of information been better, the military raids on the Norwegian heavy-water plant at Vemork could have been timed better, and the more costly of them could have been averted altogether.     

A Self-Organised Bilocal Magnetic Field in the Electron Plasma of Metals

Within the simplest model of metals, namely a gas of electrons with Coulomb interactions, in the presence of a uniform background of positive charge to enforce electric neutrality of the system, we have derived a mechanism by which the Coulomb interaction between the electrons generates a new kind of magnetism. The ground state of the metal is represented by a magnetically ordered state described by a non-local magnetic field. This non-local magnetic field does not produce spin polarisation of electrons, but induces a special long range correlation between electrons of opposite spin. This mechanism results in a theoretical value for the binding energy per electron, which is lower than the corresponding value for the unmagnetised state of the metal. The new magnetic order, proposed and analysed theoretically here, can in principle be experimentally tested.