[en] Modeling of crystallization process by the phase field crystal method (PFC) represents one of the important directions of modern computational materials science. This method makes it possible to research the formation of stable or metastable crystal structures. In this paper, we study the effect of computational domain size on the crystal pattern formation obtained as a result of computer simulation by the PFC method. In the current report, we show that if the size of a computational domain is changed, the result of modeling may be a structure in metastable phase instead of pure stable state. The authors present a possible theoretical justification for the observed effect and provide explanations on the possible modification of the PFC method to account for this phenomenon. (paper)

[en] Quasicrystals presumably grow obeying simple local growth rules such as avoiding parallel stacking of like Penrose rhombohedra. Most vertices thus generated are forbidden in a perfect quasilattice and hence constitute structural defects. It is suggested to quantify the defectiveness of a vertex by calculating the partial overlaps in its dual image. A simplified version that takes account only of interactions between vertices sharing a face is presented. Improvements of the method are outlined. (author). 19 refs

[en] The expression, purification and crystallization of the SARS coronavirus nsp16 RNA-cap AdoMet-dependent (nucleoside-2′O)-methyltransferase in complex with its activating factor nsp10 are reported. To date, the SARS coronavirus is the only known highly pathogenic human coronavirus. In 2003, it was responsible for a large outbreak associated with a 10% fatality rate. This positive RNA virus encodes a large replicase polyprotein made up of 16 gene products (nsp1–16), amongst which two methyltransferases, nsp14 and nsp16, are involved in viral mRNA cap formation. The crystal structure of nsp16 is unknown. Nsp16 is an RNA-cap AdoMet-dependent (nucleoside-2′-O-)-methyltransferase that is only active in the presence of nsp10. In this paper, the expression, purification and crystallization of nsp10 in complex with nsp16 are reported. The crystals diffracted to a resolution of 1.9 Å resolution and crystal structure determination is in progress

No abstract available

[en] Study of phase transitions in liquid crystalline materials are of very much importance due to their wide and various applications. Different experiments had been successfully done to show the existence of different liquid crystalline phases. Although the mean field theory of nematic liquid crystals by Maier and Saupe in 1960, can correctly predict the existence of a first order phase transition between the nematic and isotropic liquid states, no pressure dependence can be investigated using this formula. In 1980, Luckhurst and Romano had taken an anisotropic part of the potential along with the isotropic part and used this potential to computer simulation to find the phase diagram for some liquid crystals. But they had not done any pressure variation. Also a rigorous microscopic treatment of a nematic fluid system based on a pairwise interaction potential is immensely complex. For studying pressure dependence of such systems mean field theories are often the standard method of choice. In this paper we have chosen a simple effective potential U= u₄/v⁴ -u₂/v² -Au₂/v² 2> P₂ (cosθ) to study an isothermal-isobaric (NPT) ensemble describing a liquid crystalline system. Using this we have studied in particular the pressure dependence of liquid crystalline phase transitions. where, u₂, u₄ and A are constants, v is the mean molecular volume, θ is the angle between the director and the molecular long axis, is the nematic order parameter. (author)

[en] Tailor-made auxiliaries for the control of nucleation and growth of molecular crystals may be classified into two broad categories: inhibitors and promoters. Tailor-made inhibitors of crystal growth can be used for a variety of purposes, which include morphological engineering and etching, reduction of crystal symmetry, assignment of absolute structure of chiral molecules and polar crystals, elucidation of the effect of solvent on crystal growth, and crystallization of a desired polymorph. As for crystal growth promoters, monolayers of amphiphilic molecules on water have been used to induce the growth of a variety of three-dimensional crystals at the monolayer-solution interface by means of structural match, molecular complementarity or electrostatic interaction. A particular focus is made on the induced nucleation of ice by monolayers of water-insoluble aliphatic alcohols. The two-dimensional crystalline structures of such monolayers have been studied by grazing incidence X-ray diffraction. It has become possible to monitor, by this method, the growth, dissolution and structure of self-aggregated crystalline monolayers, and indeed multilayers, affected by the interaction of solvent molecules in the aqueous subphase with the amphiphilic headgroups, and by the use of tailor-made amphiphilic additives. (orig.)

No abstract available

[en] Two types of putative threonyl-tRNA synthetases with complementary functions from the crenarchaea A. pernix K1 and S. tokodaii strain 7 have been overexpressed, purified and crystallized. The crystal structure of one of the four proteins, the catalytic type ThrRS from A. pernix, has successfully been solved by the Se-MAD method. Threonyl-tRNA synthetase (ThrRS) plays an essential role in protein synthesis by catalyzing the aminoacylation of tRNA^Thr and editing misacylation. ThrRS generally contains an N-terminal editing domain, a catalytic domain and an anticodon-binding domain. The sequences of the editing domain in ThrRSs from archaea differ from those in bacteria and eukaryotes. Furthermore, several creanarchaea including Aeropyrum pernix K1 and Sulfolobus tokodaii strain 7 contain two genes encoding either the catalytic or the editing domain of ThrRS. To reveal the structural basis for this evolutionary divergence, the two types of ThrRS from the crenarchaea A. pernix and S. tokodaii have been overexpressed in Eschericha coli, purified and crystallized by the hanging-drop vapour-diffusion method. Diffraction data were collected and the structure of a selenomethionine-labelled A. pernix type-1 ThrRS crystal has been solved using the MAD method

[en] Many crystalline materials of interest to the Canadian Nuclear Program have the potential to undergo phase transitions in their range of application. During such phase transitions, a representation of the space group of the higher symmetry polymorph softens to induce the transition. This report is the first in a series of reports concerned with the group-theoretic properties of phase transitions in crystalline materials. The object of the research is to identify all spectroscopically-active soft modes for the 230 three-dimensional space groups. Identification of these soft modes will enable a detailed examination of phase transitions in materials of interest to the Canadian Nuclear Program and aid in the optimization of material properties. In this report, the group-theoretic properties of crystal structures and phase transitions are reviewed. It is demonstrated that the problem of extending a group reduces to that of determining its automorphisms. The automorphism groups of the crystallographic and icosahedral point groups are derived using a consistent presentation

No abstract available