Space Group F4 Research Articles

Crystal growth and characterization of the cubic semiconductor Cu2SnSe4

X-ray powder diffraction study of the p-type semiconductor Cu2SnSe4 shows that this material crystallizes in the cubic structure, space group F4¯3m, with unit cell parameter a=5.6846(3) Å. The temperature variation of the hole concentration between 120 and 300 K, obtained from the Hall effect and electrical resistivity measurements, is due to the thermal activation of an acceptor level with ionization energy of about 0.02 eV. The temperature variation of the hole mobility is explained by considering the scattering of charge carriers by ionized impurities and acoustic phonons. From this analysis, the density-of-states effective mass of the holes is estimated to be about 0.8 me, me being the free electron effective mass. From the optical absorption spectra, the fundamental absorption edge is found to be direct. The value of the lowest energy gap and the spin-orbit splitting were estimated to be about 0.35 and 0.20 eV, respectively. The temperature dependence of the magnetization measurements shows that Cu2SnSe4 is paramagnetic, indicating that most of the copper atoms have the divalent charge state.

A cuboctahedral supramolecular capsule by 4:4 self-assembly of Tris(Zn(II)-cyclen) and trianionic trithiocyanurate in aqueous solution at neutral pH (cyclen=1,4,7,10-tetraazacyclododecane).

A 1:1 mixture of a tris(Zn(II)-cyclen) (1: [Zn(3)L(1)], L(1)=1,3,5-tris(1,4,7,10-tetraazacyclododecan-1-ylmethyl)benzene) and trithiocyanuric acid (TCA) yielded a 4:4 self-assembly complex [(Zn(3)L(1))(4)-(TCA(3-))(4)] (6) through the formation of Zn(II)-S(-) coordination bonds and hydrogen bonds between 1,3,5-triazine N and cyclen NH (cyclen=1,4,7,10-tetraazacyclododecane); the supramolecular capsule structure was revealed by X-ray crystal structure analysis. The capsule exterior represents a twisted cuboctahedral framework containing a nanoscale truncated tetrahedral cavity. The crystal data: formula C(144)H(308)N(72)O(58)S(12)Zn(12) (6[NO(3)](12) x 22 H(2)O), M(r)=5145.75, cubic, space group F432 (No. 209), a=39.182(1) A, V=60153(3) A (3), Z=8, R=0.100, R(w)=0.259. Lipophilic organic molecules with the matching sizes, for example, ([D(4)]-2,2,3,3)-3-(trimethylsilyl)propionic acid (TSP), 1-adamantanecarboxylic acid, 2,4-dinitrophenol (2,4-DNP), adamantane (ADM), or the tetra-n-propylammonium (TPA) cation, are encapsulated in the inner cavity, as revealed by remarkable upfield shifts of the (1)H NMR signals of these guest molecules. The encapsulation of ADM was confirmed by X-ray crystal structure analysis. Crystal data of the ADM-encapsulating complex: formula C(154)H(334)N(72)O(63)S(12)Zn(12) (6-ADM[NO(3)](12) x 27 H(2)O), M(r)=5372.06, cubic, space group F432 (No. 209), a=39.061(1) A, V=59599(3) A(3), Z=8, R=0.103, R(w)=0.263. The 4:4 self-assembly was stabilized by incorporation of one of these guest molecules. The apparent 4:4 self-assembly constants for 6 in the presence of an excess amount of a guest TPA, log K(app) (K(app)=[6-TPA]/[1](4)[TCA](4)) (M(-7))), were determined to be 34.0+/-2.0 and 35.5+/-3.0 by potentiometric pH and UV spectrophotometric titrations, respectively. An apparent encapsulation constant for 2,4-DNP, log K(enc) (K(enc)=[6-2,4-DNP]/[6][2,4-DNP] (M(-1))), was 6.0+/-0.1 at pH 7.0 (50 mM HEPES with I=0.1 (NaNO(3))), as determined by UV titrations. The lipophilicity of the inner cavity was close to that of 2-propanol, as a quantum yield (phi) of 0.24+/-0.1 for the fluorescent emission of 7-diethylaminocoumarin-1-carboxylic acid (20 microM) in the capsule was close to the phi of 0.22 found for 2-propanol. Encapsulation properties of the present Zn(II)-containing cage have been compared with those of cyclodextrins and Fujita's Pd(II)-containing supramolecular cage. The exterior chirality of the 4:4 complex was controlled from within by an encapsulated chiral guest molecule, 2,10-camphorsultam, as indicated by Cotton effects in the circular dichroism spectra.

Synthesis and structural characterization of the novel cluster compound.

Reaction of [Mo3Y(mu-S)3(dtp)4(H2O)] (Y = O, S; dtp = S2P(OC2H5)2(-)) with HgI2 gave the novel compound [[Mo3S7(dtp)3]4 x I][(HgI3)3] x 4H2O (1), which contains a [[Mo3S7(dtp)3]4 x I] tetramer and (HgI3)-. Compound 1 has been characterized by IR, Raman, UV/Vis, and NMR spectroscopy and single-crystal X-ray diffraction analysis. It is shown that this formation process can be referred to as a new cluster reaction. The structure and spectroscopic data of the tetramer is also compared with that of the related discrete cluster [Mo3S7(dtp)3 x I]. Crystal data: space group F23, a = 26.786(3) A, V = 19218.7(4) A3, Z = 4, R = 0.059.

ゼオライトＬＴＡ中の配列した金属カリウムクラスターの結晶構造解析と新物性

Potassium clusters stabilized in regular cages of aluminosilicate zeolite LTA are investigated in detail in term of structure as well as magnetic properties. A ferromagnetic properties have been observed when more than two potassium atoms are adsorbed into each α cage of LTA. When the average number of adsorbed K metal exceeds two atoms per α cage, new diffraction lines are observed at the forbidden indices of original framework structure of LTA. The crystal structure is well analyzed by the space group F23 with a larger unit cell. The origin of the forbidden diffraction lines is assigned to the superstructure of two different potassium clusters stabilized periodically in adjacent α cages. Most of adsorbed K atoms occupy the side positions of 4-membered rings in the α cage. The periodic difference of their occupancy is main origin of the superstructure reflection. At higher densities of K adsorption, an atom occupies one of the centers of clusters. A discussion is given for the relation between the structure and the magnetic properties.

The crystal chemistry of superconducting Sr3.66Bi0.28Ca6.02Cu16.45O28.63 and nonsuperconducting Sr5.97Ca3.13Y0.53Al0.25Bi0.12Cu16.66O28.64 compounds

The title compounds from the family of the [M2Cu2O3]5[CuO2]7-type cuprates were synthesized by the flux growth method in the system SrCO3-CaO-Bi2O3-CuO. The crystal structures of Sr3.66Bi0.28·Ca6.02Cu16.45O28.63 (SC) and Sr5.97Ca3.13Y0.53Al0.25Bi0.12·Cu16.66O28.64 (non-SC) were determined. SC: Space group F222, a=11.319(2) Å, b=12.763(2) Å, c=19.491(12) Å, Z=4, R=0.0811 based on 802 reflections with F>4 σ (F). Non-SC: Space group F222, a=11.346(3) Å, b=12.996(3) Å, c=19.585(9) Å, Z=4, R=0.0769 based on 736 reflections with F>4 σ(F). The first crystal (SC) is superconducting (Tc=80K). The structural differences for two compounds in questions have been established: the Cu-Cu distances from the Cu atoms of a ladder plane to the Cu atoms of the ribbons and the bond distances from Cu to the apical oxygen at the plane of the Cu-O ribbons are smaller in the SC compound as compared with those in the non-SC phase.

Powder diffraction data of semimagnetic semiconductors Hg0.80Mn0.20S, Hg0.89Fe0.11S and Hg0.98Co0.02S

Powder X-ray diffraction data are reported for semimagnetic semiconductor Hg0.89Fe0.11S and Hg0.98Co0.02S crystals grown by the Bridgman method and for Hg0.80Mn0.20S crystal synthesized by a solid-state reaction method. The crystals have the sphalerite structure of metacinnabar (sphalerite-type high-temperature polymorph of HgS, space group F4¯3m). Phase analysis does not show any trace of other phases. The lattice parameters of the studied samples are a=5.803 20(5) Å, 5.8063(1) Å and 5.839 80(6) Å, respectively. The calculated density is reported.

Structures and phase transitions of the A7PSe6 (A = Ag, Cu) argyrodite-type ionic conductors. II. Beta- and gamma-Cu7PSe6

The crystal structures of two of the three polymorphic forms of the Cu7PSe6 argyrodite compound are determined by means of single-crystal X-ray diffraction. In the high-temperature form, at 353 K, i.e. 33 K above the first phase transition, gamma-Cu7PSe6 crystallizes in cubic symmetry, space group F43m. The full-matrix least-squares refinement of the structure leads to the residual factors R = 0.0201 and wR = 0.0245 for 31 parameters and 300 observed independent reflections. In the intermediate form, at room temperature, beta-Cu7PSe6 crystallizes again in cubic symmetry, but with space group P2(1)3. Taking into account a merohedric twinning, the refinement of the beta-Cu7PSe6 structure leads to the residual factors R = 0.0297 and wR = 0.0317 for 70 parameters and 874 observed, independent reflections. The combination of a Gram-Charlier development of the Debye-Waller factor and a split model for copper cations reveals the possible diffusion paths of the d10 species in the gamma-Cu7PSe6 ionic conducting phase. The partial ordering of the Cu+ d10 element at the phase transition is found in concordance with the highest probability density sites of the high-temperature phase diffusion paths. A comparison between the two Cu7PSe6 and Ag7PSe6 analogues is carried out, stressing the different mobility of Cu+ and Ag+ and their relative stability in low-coordination chalcogenide environments.

Synthesis of stable crystals of a self-assembled centered icosahedral samarium cluster formed by bis(L-prolinato)nickel(II) ligands.

A centered icosahedral 12-coordinate samarium cluster formed by six bis(L-prolinato)nickel(II) ([Ni(pro)2]) ligands, [Sm(Ni(pro)2)6]3+, was prepared. The reaction of Sm with [Ni(pro)2] in a small excess (a 2-fold excess) and also in a large excess (even a 10-fold excess) of the latter produced the cluster. Therefore, this system is a self-assembly. In the cluster, each nickel atom is surrounded by six atoms: two amino nitrogens, two carboxylate oxygens which form chelate rings with the nitrogen atoms, and two carboxylate oxygen atoms which link the neighboring nickel atoms. The samarium atom is coordinated by six [Ni(pro)2] ligands, and the metal is in an icosahedral environment formed by 12 oxygen atoms. The icosahedral geometry is almost ideal. Crystals of [Sm(Ni(pro)2)6](ClO4)3.6MeOH, which were prepared from a methanol solution, immediately decompose after filtration because of loosely trapped MeOH molecules in the crystal lattice. Therefore, crystals without MeOH molecules, which must be stable, were prepared by recrystallization from acetonitrile with tetramethylammonium perchlorate (TMAP). According to the X-ray crystal analysis, the cluster is TMA[Sm(Ni(pro)2)6](ClO4)4, cubic of space group F23, with a = 21.273(9) A, V = 9626(1) A3, and Z = 4; R = 0.053 (Rw = 0.049) for 1296 reflections. In addition, several crystals of cluster salts that have different counteranions, i.e., tetrafluoroborate (BF4-), hexafluorophosphate (PF6-), iodide (I-), and nitrate (NO3-), were prepared. The order of increasing ease of crystallization of the cluster salts was I- > PF6- approximately ClO4- > BF4- >> NO3-. The cluster structure is retained in alcohol and acetonitrile solutions; the UV-vis spectra of the solutions are perfectly consistent with the powder diffuse reflection spectrum. Cyclic voltammograms of [Sm(Ni(pro)2)6]3+ in acetonitrile proved that the structure of [Sm(Ni(pro)2)6]3+ is retained in the redox process and that the nickel atoms electrochemically interact with one another. Thermal analysis of the cluster salts with different counteranions was investigated. The results imply that the cluster is very stable until bis(L-prolinato)nickel(II) ligands, which form the cage structure, disintegrate and that the thermal decomposition processes of the cluster salts depend on their counteranions.

Expression, purification and crystallization of enterococcus faecium streptogramin A acetyltransferase.

The streptogramin A acetyltransferase from Enterococcus faecium (SWISS-PROT P50870) has been overexpressed in Escherichia coli, purified and crystallized. Crystallization conditions were screened using the hanging-drop vapor-diffusion method and resulted in two distinct crystal forms. Form I crystals diffract to 2.5 A and belong to space group P2(1)2(1)2(1), with unit-cell parameters a = 68.6, b = 102.6, c = 107.5 A. Form II crystals diffract to 2.7 A and belong to space group F222, with unit-cell parameters a = 185.8, b = 185.8, c = 186.5 A. Rotation-function and packing analyses for both crystal forms indicate that the asymmetric unit may contain one and two copies of the trimeric enzyme for crystal forms I and II, respectively.

Arrangement of K Clusters in the K-Doped Zeolite K-LTA

K clusters incorporated into zeolite K-LTA causes ferromagnetism below 8 K. Distribution of K+ ions in its α-cages was studied by X-ray powder diffraction. On the basis of space group F23, electron-density distribution was determined by Rietveld analysis followed by iteration of analysis by a maximum-entropy method and whole-pattern fitting. K+ ions were located in α-cages in such a way that K clusters between adjacent α-cages are not equivalent to each other, which will lead to the ferromagnetism with antiferromagnetic components.

Neutron powder diffraction study of potassium clusters in zeolite K-LTA

The crystal structures of K-doped K-LTA below and above the Curie temperature of 8 K were analyzed by neutron powder diffraction on the basis of space group F23. We found alternate ordering of Si and Al in a distorted framework and different K clusters in two kinds of α-cages. Additional K + ions are distributed mainly in four- and eight-membered rings of the framework and partially occupy the center of an α-cage. K + ions near the center of a six-membered ring form two kinds of tetrahedral assemblies occupied statistically. Our structural data suggest that the K clusters in the adjacent α-cages have different magnetic moments. This is consistent with a spontaneous magnetic moment, which is observable even if the K clusters interact antiferromagnetically.

Solution of the structure of tetrameric human glucose 6-phosphate dehydrogenase by molecular replacement.

Recombinant human glucose 6-phosphate dehydrogenase (G6PD) has been crystallized and its structure solved by molecular replacement. Crystals of the natural mutant R459L grow under similar conditions in space groups P212121 and C2221 with eight or four 515-residue molecules in the asymmetric unit, respectively. A non-crystallographic 222 tetramer was found in the C2221 crystal form using a 4 A resolution data set and a dimer of the large beta + alpha domains of the Leuconostoc mesenteroides enzyme as a search model. This tetramer was the only successful search model for the P212121 crystal form using data to 3 A. Crystals of the deletion mutant DeltaG6PD grow in space group F222 with a monomer in the asymmetric unit; 2.5 A resolution data have been collected. Comparison of the packing of tetramers in the three space groups suggests that the N-terminal tail of the enzyme prevents crystallization with exact 222 molecular symmetry.

Crystallization and preliminary X-ray diffraction studies of 6-phosphogluconate dehydrogenase from Lactococcus lactis.

6-Phosphogluconate dehydrogenase is one of the seven enzymes involved in the pentose phosphate pathway. Crystals of a mammalian and a protozoan enzyme have been obtained previously and structures determined. It is reported here that a bacterial 6-phosphogluconate dehydrogenase, from Lactococcus lactis, has been purified and used in crystallization trials. Large prisms suitable for a detailed structural analysis have been obtained and characterized as orthorhombic, space group F222, with a = 70.4, b = 105.7, c = 474.6 A. Diffraction has been observed to 2.2 A resolution using synchrotron radiation. Structural analysis, in combination with ongoing biochemical characterization, will assist the elucidation of the structure-activity relationships of this enzyme.

Structures and Phase Transitions of the A 7PSe6 (A = Ag, Cu) Argyrodite-Type Ionic Conductors. I. Ag7PSe6

The crystal structures of the two polymorphic forms of the argyrodite Ag7PSe6 compound are analysed by means of single-crystal X-ray diffraction. Above the phase transition at 453 K leading to the ionic conducting phase, γ-Ag7PSe6 crystallizes in cubic symmetry, space group F4¯3m, with a = 10.838 (3) Å, V = 1273.1 (12) Å3 and Z = 4 at 473 K. The refinement of the 473 K structure leads to a reliability factor of R = 0.0326 for 192 independent reflections and 33 variables. Diffusion paths for silver d 10 ions are evidenced by means of a combination of a Gram–Charlier development of the atomic displacement factors and a split model. Below the phase transition β-Ag7PSe6 crystallizes again in cubic symmetry, but with the space group P213 and a = 10.772 (2) Å, V = 1250.1 (6) Å3 and Z = 4 at room temperature. The refinement of the 293 K structure leads to a reliability factor of R = 0.0267 for 1125 independent reflections and 68 variables. In the β-Ag7PSe6 ordered phase the silver cations are found in various sites corresponding to the most pronounced probability density locations of the high-temperature diffusion paths. Those positions correspond to low coordination (2, 3 and 4) sites, in agreement with the silver preference for such environments. In addition, the Ag atoms are found slightly displaced from the true linear, triangular or tetrahedral coordination, as expected from second-order Jahn–Teller effects.

Time-of-flight neutron diffraction study on lithium dinitride iodide, Li 7N 2I

The structure of Li 7N 2I has been redetermined from neutron diffraction data using the high resolution powder diffractometer (HRPD) at the spallation source ISIS, UK. The title compound crystallizes in the space group F4¯3m (No.216), a=1038.797(1) pm with eight formula units per unit cell. The Li 7N 2I-structure comprises a cationic Li 13N 4 staggered+ framework which is built of monocapped octahedra. While all Li atoms at the vertices are shared between two neighbouring units, the capping metal atom is shared by four octahedra. The Li 13N 4 staggered+ network is closely related to the B 2X 6 octahedral framework observed in the pyrochlore structure. Large voids in the structure are occupied by iodide and a Li +T ion pair. There is evidence that the nonsphericity of the Li +I − dipole induces a complicated Lidisorder in the Li-N framework.

Lipase Activation by Nonionic Detergents: THE CRYSTAL STRUCTURE OF THE PORCINE LIPASE-COLIPASE-TETRAETHYLENE GLYCOL MONOOCTYL ETHER COMPLEX

The crystal structure of the ternary porcine lipase-colipase-tetra ethylene glycol monooctyl ether (TGME) complex has been determined at 2.8 A resolution. The crystals belong to the cubic space group F23 with a = 289.1 A and display a strong pseudo-symmetry corresponding to a P23 lattice. Unexpectedly, the crystalline two-domain lipase is found in its open configuration. This indicates that in the presence of colipase, pure micelles of the nonionic detergent TGME are able to activate the enzyme; a process that includes the movement of an N-terminal domain loop (the flap). The effects of TGME and colipase have been confirmed by chemical modification of the active site serine residue using diisopropyl p-nitrophenylphosphate (E600). In addition, the presence of a TGME molecule tightly bound to the active site pocket shows that TGME acts as a substrate analog, thus possibly explaining the inhibitory effect of this nonionic detergent on emulsified substrate hydrolysis at submicellar concentrations. A comparison of the lipase-colipase interactions between our porcine complex and the human-porcine complex (van Tilbeurgh, H., Egloff, M.-P., Martinez, C., Rugani, N., Verger, R., and Cambillau, C.(1993) Nature 362, 814-820) indicates that except for one salt bridge interaction, they are conserved. Analysis of the superimposed complexes shows a 5.4 degrees rotation on the relative position of the N-terminal domains excepting the flap that moves in a concerted fashion with the C-terminal domain. This flexibility may be important for the binding of the complex to the water-lipid interface.

Crystallization and analysis of the subunit assembly and quaternary structure of imidazoleglycerol phosphate dehydratase from Saccharomyces cerevisiae.

Imidazoleglycerol phosphate dehydratase (IGPD) from Saccharomyces cerevisiae has been crystallized in the presence of a range of divalent cations using the hanging-drop method of vapour diffusion with ammonium sulfate or polyethylene glycol (PEG) 4000 as the precipitants. X-ray precession photographs have established that the crystals formed with ammonium sulfate (form A) belong to the space group F432, with cell parameter a = 177.5 A and a single subunit in the asymmetric unit. A preliminary data set collected to 6 A resolution on a two-detector San Diego Multiwire area detector has established that the crystals formed with PEG 4000 (form B) belong to either of the special pair of space groups I23 or I2(1)3, with cell parameter a = 131.0 A. A self-rotation function has been calculated using these data and indicates that the cell axes show pseudo fourfold symmetry consistent with a dimer in the asymmetric unit in this crystal form. Light-scattering studies indicate that in the presence of Mn(2+) and a number of other divalent cations IGPD undergoes assembly to a particle of molecular weight approximately 500 kDa. Given the subunit molecular weight of 23 kDa together with the symmetry of the crystals it would indicate that the most likely quaternary structure for this enzyme is based on a 24-mer in 432 symmetry.

A crystallographic study of haem binding to ferritin.

Ferritin, the iron-storage protein, binds porphyrins, metalloporphyrins and the fluorescent dyes ANS (8-anilino-1-naphthalenesulfonic acid) and TNS (2-p-toluidinyl-6-naphthalenesulfonic acid), similarly to apo-myoglobin. Octahedral crystals of horse-spleen apo-ferritin (HSF; 174 amino acids) complexes prepared by the addition of haem, hematoporphyrin or Sn-protoporphyrin IX to a solution of apo-ferritin crystallize in space group F432 with cell parameter a = 184.0 A. X-ray crystallographic analysis of single crystals prepared from a mixture containing haem or Sn-protoporphyrin IX shows that the haem-binding sites in these crystals are occupied by protoporphyrin IX, which is free of metal, rather than by the original metalloporphyrin. The present paper describes the structure of horse-spleen apo-ferritin cocrystallized with Sn-protoporphyrin IX. The 6797 reflections up to 2.6 A resolution used in the refinement were obtained from a data set recorded on a Nicolet/Xentronics area detector with Cu Kalpha radiation from a Rigaku RU 200 rotating anode. The final structure comprises 1613 non-H atoms, two Cd atoms and 170 solvent molecules. Four residues are described as disordered. The root-mean-square deviations from ideal bond lengths and angles are 0.013 A and 2.88 degrees, respectively. Protoporphyrins are observed in special positions on the twofold axes of the ferritin molecule with a stoichiometry of 0.4 per subunit.

Crystallization and structural analysis of bullfrog red cell L‐subunit ferritins

Ferritin is a 24 subunit protein that controls biomineralization of iron in animals, bacteria, and plants. Rates of mineralization vary among members of the ferritin family, particularly between L and H type subunits of animal ferritins which are differentially expressed in various cell types. To examine ferritin from a highly differentiated cell type and to clarify the relationship between ferritin structure and function, bullfrog red cell L ferritin has been cloned, overexpressed in E. coli, and crystallized under two conditions. Crystals were obtained at high ionic strength in the presence of MnCl2 at a concentration comparable to that of the protein and in the presence of MgCl2 at a concentration much higher than that of the protein. Under both crystallization conditions, the crystals are tetragonal bipyramids in the space group F432 with unit cell dimensions a = b = c = 182 +/- 0.5 A. Crystals obtained in the presence of manganese and ammonium sulfate diffract to 1.9 A, while those obtained in the presence of magnesium and sodium tartrate diffract to 1.6 A. Isomorphous crystals have been obtained under similar conditions for a site-directed mutant with a reduced mineralization rate in which Glu-57, -58, -59, and -61 are all replaced by Ala. The structure of wild type L-subunit with magnesium has been solved by molecular replacement using the calcium salt of human liver H subunit (Lawson et al., Nature (London) 349:541-544, 1991) as the model. The crystallographic R factor for the 6-2.2 A shell is 0.21. The overall fold of human H and bullfrog L ferritins is similar with an rms difference in backbone atomic positions of 0.97 A. The largest structural differences occur in the D helix and the loop connecting the D and E helices of the four helix bundle. Because red cell L ferritin and liver H ferritin show differences in both rates of mineralization and three-dimensional structure, more detailed comparisons of these structures are likely to shed new light on the relationship between conformation and function.

A Regular 1:1 Complex of Two Allosteric States in the Single Crystal of l-Lactate Dehydrogenase from Bifidobacterium longum

Single crystals of the regular 1:1 complex of T and R-state tetramers of l -lactate dehydrogenase from Bifidobacterium longum have been grown from polyethylene glycol 6000 solution in the presence of NADH, fructose 1,6-bisphosphate and oxamate. The crystals belong to space group F222 with unit cell dimensions of a = 148·4 Å, b = 295·9 Å and c = 71·0 Å. The crystals are suitable for X-ray analysis and diffract to beyond 2·5 Å spacing. A crystallographic study showed that the asymmetric unit contains two subunits and that one of them belongs to the T-state tetramer and the other to the R-state tetramer.