No abstract available

[en] The crystal structure of buckminsterfullerene C₆₀ determined below 249 K shows a temperature-dependent twofold orientational disorder of the molecules with ΔH=1.06(5) kJ mol^-1 and ΔS=0.0(4) JK^-1 mol^-1. In agreement with the small energy difference, the intermolecular contacts are found to be very similar for both molecular orientations. The C-C bond lengths are 1.450(3) and 1.387(3) A. (orig.)

[en] Existence of a new exponent is reported in the problem of nonintersecting self-avoiding random walks. It is connected with the asymptotic behaviour of the growth of number of such walks of larger and larger length. The value of the exponent is found to be nearly 0.90 for all two-dimensional and nearly 0.96 for all three-dimensional lattices studied here. (author)

[en] The statistics of the atom-by-atom dissection of planes, in the atom-probe field-ion microscope, have been investigated. Tungsten specimens oriented in the [110] direction, with the probe hole over the center of the plane, were slowly pulse field-evaporated on a plane-by-plane basis, and statistical analyses were made on the number of tungsten atoms detected per plane; twenty-four separate slow dissection experiments were performed. Observed fluctuations in the number of atoms per plane are used to infer a range of allowable values for the detection efficiency

[en] The crystal structure of dumontite has been determined by X-ray diffraction. The accurate tridimensional structure is detailed. 10 refs, 2 tabs, 3 figs

No abstract available

[en] The symmetry of the similarity of the surface step structure in zinc blende (sphalerite) type structures is investigated by studying the crystal planes that are parallel to the [01 anti 1] axis. The symmetry transformations of the similar plane pairs are derived. Plane sets (111) and (311) are the planes of symmetry. The similarity of the surface step structure exists among three sets of planes. The surface geometric characteristics of similar planes are discussed. The result can be applied to explain dual epitaxy and optimize the interface quality by designing dual epitaxy in the heteroepitaxy. (orig.)

[en] PA4991 is a FAD-dependent oxidoreductase from the pathogen P. aeruginosa that is essential for virulence and survival in the infected host. The structure of this enzyme, determined to 2.4 Å resolution, reveals that PA4991 belongs to the GR_2 family of flavoenzymes. The locus PA4991 in Pseudomonas aeruginosa encodes an open reading frame that has been identified as essential for the virulence and/or survival of this pathogenic organism in the infected host. Here, it is shown that this gene encodes a monomeric FAD-binding protein of molecular mass 42.2 kDa. The structure of PA4991 was determined by a combination of molecular replacement using a search model generated with Rosetta and phase improvement by a low-occupancy heavy-metal derivative. PA4991 belongs to the GR_2 family of FAD-dependent oxidoreductases, comprising an FAD-binding domain typical of the glutathione reductase family and a second domain dominated by an eight-stranded mixed β-sheet. Most of the protein–FAD interactions are via the FAD-binding domain, but the isoalloxazine ring is located at the domain interface and interacts with residues from both domains. A comparison with the structurally related glycine oxidase and glycerol-3-phosphate dehydrogenase shows that in spite of very low amino-acid sequence identity (<18%) several active-site residues involved in substrate binding in these enzymes are conserved in PA4991. However, enzymatic assays show that PA4991 does not display amino-acid oxidase or glycerol-3-phosphate dehydrogenase activities, suggesting that it requires different substrates for activity

No abstract available

[en] In past years, most of the X-ray structure determinations of oligopeptides were for cyclic peptides or for short linear peptides. Longer peptides usually presented many difficulties in obtaining suitable crystals since the molecules are intrinsically very flexible. More recently, it has been appreciated that the aminoisobutyric acid residue (Aib), which occurs naturally in many peptides of microbial origin, initiates helix folding. Several score of 7- to 15-residue linear peptides containing Aib have been synthesized, crystallized and had their structures determined to high resolution. Many of the peptide structures have been determined in more than one crystalline form. These peptide structures have yielded a plethora of information on types of helices, modes of hydration, water penetration into helical backbones, helices bent by Pro residues, parallel and antiparallel association of helices, effects of Leu residues on association of peptides, an example of a zipper assembly by side chains, and an example of a possible ion channel with a gating mechanism. (orig.)