Non-crystallographic Point Group Research Articles

Crystal Structure of Soluble Domain of Malaria Sporozoite Protein UIS3 in Complex with Lipid

Malaria parasite UIS3 (up-regulated in infective sporozoites gene 3) is essential for sporozoite development in infected hepatocytes. UIS3 encodes for a membrane protein that is localized to the parasite parasitophorous vacuolar membrane in infected hepatocytes. We describe here 2.5-Å resolution crystal structure of Plasmodium falciparum UIS3 soluble domain (PfUIS3130-229) in complex with the lipid phosphatidylethanolamine (PE). PfUIS3130-229 is a novel, compact, and all α-helical structure bound to one molecule of PE. The PfUIS3130-229-PE complex structure reveals a novel binding site with specific interactions between PfUIS3130-229 and the PE head group. One acyl chain of PE wraps around part of PfUIS3130-229 and docks onto a hydrophobic channel. We additionally provide new structural and biochemical evidence of PfUIS3130-229 interactions with lipids (phosphatidylethanolamine), with phospholipid liposomes, and with the human liver fatty acid-binding protein. The direct interaction of PfUIS3130-229 with liver fatty acid-binding protein most likely provides the parasite with a conduit for importing essential fatty acids/lipids. Therefore, our analyses have implications for lipid transport into the parasite during the rapid growth phases of sporozoites. Given that PfUIS3 is essential for establishment of liver stage infection by P. falciparum, our data provide a new target for abrogating parasite development within liver cells before typical symptoms of malaria can manifest.

GRcut: a modeling tool for nanoparticles including five-fold symmetries

A new modeling tool GRcut was developed to be used for atomistic simulation of isolated nanoparticles. It generates atomic coordinates in crystalline nanoparticles with equivalent crystallographic surfaces. In addition to 32 crystallographic point groups, nine non-crystallographic point groups with five-fold symmetries are implemented for modeling icosahedral and decahedral clusters in a systematic way. Curved surfaces with spherical, ellipsoidal and cylindrical shapes in arbitrary orientation are also available. This software is useful as a pre-processing tool for molecular simulation on metallic clusters, quantum dots, or fullerenes in high symmetries. The GRcut is distributed as a Java applet via the Internet to be used on web browsers.

Group-theoretical method for physical property tensors of quasicrystals

In addition to the phonon variable there is the phason variable in hydrodynamics for quasicrystals. These two kinds of hydrodynamic variables have different transformation properties. The phonon variable transforms under the vector representation, whereas the phason variable transforms under another related representation. Thus, a basis (or a set of basis functions) in the representation space should include such two kinds of variables. This makes it more difficult to determine the physical property tensors of quasicrystals. In this paper the group-theoretical method is given to determine the physical property tensors of quasicrystals. As an illustration of this method we calculate the third-order elasticity tensors of quasicrystals with five-fold symmetry by means of basis functions. It follows that the linear phonon elasticity is isotropic, but the nonlinear phonon elasticity is anisotropic for pentagonal quasicrystals. Meanwhile, the basis functions are constructed for all noncrystallographic point groups of quasicrystals.

Structure Determination of the TMA2HgCl4by X-Ray Diffraction and Maximum Entropie Method

The crystal structure of [N(CH 3 ) 4 ] 2 HgCl 4 has been studied by single crystal X-ray diffraction. the structure is orthorhombic Pnma with lattice parameters 12.419(7), b = 9.068(4), and c = 15.684(2) A at room temperature. Each TMA cation disorderly occupies two orientations (TMA is tetramethylammonium). Refinements using restrictions of the non-crystallographic tetrahedral point group for the TMA cations and refinements without restrictions are used to show that TMA has tetrahedral symmetry at all temperatures. The HgCl 4 anions are distorted, but the distortions are independent of the temperature.

Plesiotwinning: oriented crystal associations based on a large coincidence-site lattice

AbstractOriented crystal associations with a low degree of restoration of lattice nodes are discussed and it is shown that they are based on a large coincidence-site lattice (CSL). In this type of associations the oriented crystals are related by symmetry or pseudo-symmetry elements expressed by high indices in the crystal lattice. The relative orientations of the crystals correspond to rotations belonging to non-crystallographic point groups. In spite of the low number of common lattice nodes, these associations are not uncommon, especially in layer compounds. Since this kind of associations does not enter either in the definition of twinning or in that of cell-twinning, we propose to introduce the definition ofplesiotwinning. It is suggested that plesiotwins may form when two or more crystals coalesce or exsolve. A plesiotwin orientation may require a minor adjustment of the relative orientations, whereas a more stable configuration, such as a parallel growth or to a twin, may require a larger, kinetically more hindered rotation.

Growth of perfect quasicrystals, from curiosity to reality

Ideal quasicrystalline form of matter is defined by an atomic structure that has a perfect orientational long range order, a non-periodic long range translational order, and a non-crystallographic point group symmetry. In view of these exotic structural properties, perhaps not so surprisingly were also called impossible crystals. These exotic structures do exist in nature and were first discovered in 1984 in an AI-Mn alloy. This particular alloy had a grain size of several microns, and was thermodynamically metastable. In eight short years, and after the discovery of many other quasicrystalline compounds, the quasicrystalline single grain size we could grow increased from microns to a few centimeters. Today, we can grow nearly defect-free and stable two- and three-dimensional quasicrystals with macroscopic dimensions. All quasicrystals discovered to date exhibit a universal non-congruent melting property which we exploit in our crystal growth techniques. This paper briefly reviews the remarkable progress made in growing single grain quasicrystals.

Theory of G-approximant crystals with G, a non-crystallographic point group. I

Theory of G-approximant crystals with G, a non-crystallographic point group. I

Crystallography of Quasicrystals; Application to Icosahedral Symmetry

Crystallographic concepts are extended to quasicrystalline structures. The fact is used that any d-dimensional non-crystallographic point group has D-dimensional representations (D > d) which are compatible with periodicity, i.e. can be viewed as point groups of D-dimensional periodic structures. These periodic structures can be classified by conventional crystallographic methods: Bravais lattices, point groups and space groups can be calculated. This program is carried out for icosahedral symmetry, for which the minimal dimension D is 6. There are surprisingly few types of 6-dimensional crystals with icosahedral symmetry: 3 Bravais lattice types, 2 point groups and totally 11 space groups can occur. The non-symmorphic space groups lead to systematic extinctions of Bragg peaks, similar to the case of ordinary crystals. These extinctions, if present, can help to distinguish between quasiperiodic and competing glass models for icosahedral quasicrystals.

Symmetry and phase transitions in decagonal quasicrystals

The possible non-crystallographic point group of the decagonal quasicrystal phase of Al-Mn alloys has been shown by Bendersky (1986) to be either D10h or C10h. For the physically irreducible representations of these groups, the authors derive the Clebsch-Gordan products extended integrity bases, stability spaces and tensorial covariants. The point groups which can arise in phase transitions are determined along with corresponding tensorial parameters which could drive the transition. It is shown that equilibrium tensorial properties whose components transform as the components of the electrogyration or elasto-optic tensors can distinguish between the D10h and C10h point group symmetry of the decagonal phase.

Diffraction approach to the structure of decagonal quasi-crystals

Neutron and X-ray diffraction data measured on Al 4Mn decagonal quasi-crystals, with a non-crystallographic point group 10/m, are reported. Contrast variations were produced by Fe/Mn isomorphous substitution on the transition metal sites. The independent measurements on the peak intensities allow suggestions about atomic correlations and lead to fruitful comparisons with icosahedral m 3 5 material and/or the crystalline modifications of related composition.

Quasicrystal with One-Dimensional Translational Symmetry and a Tenfold Rotation Axis

Studies of phase formation in rapidly solidified Al-Mn alloys (composition range 18-22 at.% Mn) show that an icosahedral phase is replaced by another noncrystallographic phase, a decagonal phase. The decagonal phase is another example of quasicrystal: It has a noncrystallographic point group ($\frac{10}{m}$ or $\frac{10}{\mathrm{mmm}}$) together with long-range orientational order and one-dimensional translational symmetry. The decagonal phase is an intermediate phase between an icosahedral phase and a crystal both from the symmetry and from the solidification condition points of view.

Quasicrystals with 1-D Translational Periodicity and A Ten-Fold Rotation Axis

ABSTRACTStudies of phase formation in rapidly solidified Al-Mn alloys (composition range 18-22 at% Mn) show that an icosahedral phase is replaced by another noncrystallographic phase, a decagonal phase. The decagonal phase is another example of quasicrystal: It has a noncrystallographic point group (10/m or lO/mmm) together with long-range orientational order and onedimensional translational symmetry. The decagonal phase is an intermediate phase between an icosahedral phase and a crystal both from the symmetry and from the solidification condition points of view.

A unified theory of the point groups. II. The general projective representations and their application to space groups

The general expressions of all inequivalent irreducible projective representations of crystallographic and noncrystallographic point groups (except for the icosahedral group) are given in terms of the vector representations of the proper double point groups. Its application to the representations of the space group of wave vector is discussed. Construction of the basis sets is discussed.