Volume 234, Issue 4

Density functional theory (DFT) calculations have been performed on five models of periodic, polysynthetic twin interfaces in the ambient-temperature phase of KLiSO 4 , which has space group P 6 3 . The models represent the three merohedric twin laws ( m||z , 2⊥ z and 1̅) with boundary plane (1 0 1̅ 0), also with boundary plane (0 0 0 1) in case of m , and with boundary plane (1 2̅ 1 0) in case of 1̅. The models satisfy stoichiometry at the boundary plane and maintain the fourfold coordination of the Li and S atoms and the twofold coordination of the oxygen atoms. Relaxed lattice parameters and atomic positions were determined by DFT, using the DMol 3 code with functional PBEsol. The energy difference between polysynthetic twin and single crystal per primitive cell of the twin is 0.0009 eV for m (0 0 0 1), 0.09 eV for 1̅(1 0 1̅ 0), 0.58 eV for m (1 0 1̅ 0) and 0.55 eV for 2(1 0 1̅ 0). In KLiSO 4 crystals grown from aqueous solutions the first twin was frequently observed, similarly also the second twin in Cr-doped crystals, whereas the third twin appeared only rarely and the fourth was not observed. Not only for KLiSO 4 but also for quartz, the energy of twins and the frequency of their occurrence are closely connected for crystals grown from aqueous solutions, whereas for the formation of transformation twins the availability of twin nuclei plays a major role.

The aluminosilicate iodide sodalite |Na 8 I 2 |[AlSiO 4 ] 6 was examined by temperature-dependent neutron time-of-flight powder diffraction from 5 K to 290 K and X-ray diffraction from 298 K to 1200 K. The temperature-dependent properties of the mean structure in space group P 4̅3 n were obtained by Rietveld analysis. A negative slope for the thermal expansion coefficient below 50 K could be observed, and the displacement parameters of the iodide ions indicate anharmonic effects. Local structure models (8×8×8 super cells) were refined against pair-distribution functions calculated from total scattering data collected at 5 K, 165 K and 240 K. The results indicate isotropic displacements for all atoms except for I-atoms, showing the effects of an anharmonic potential around this anion at very low temperatures.

We report a systematic study of the antibacterial inhibitory potential of isoflavone natural products isolated from the seeds extracts of Millettia thonningii . In an effort to gain bond topological information which may have consequences for the observed bioactivities, the crystal structure of robustic acid was solved and refined using the independent atom as well as the invariom model, and the structures were compared. Robustic acid contains a fused tricyclic unit with a benzopyran moiety, with a phenylene ring substitution on the coumarin ring similar to the alpinumisoflavones isolated from this plant. At a minimum inhibitory concentration of ~1 mg/mL, alpinumisoflavone and robustic acid were found to be cytotoxic to Staphylococcus aureus ( ATCC 25923 ) showing a zone of inhibition (ZOI) of ~9 mm. On the other hand, at ~2 mg/mL, these compounds were found to be bacteriostatic to a hospital isolate of Salmonella typhi with about 7 mm ZOI. Taken together, these compounds offer potential new avenues for targeting both Gram positive and negative bacteria and could be useful as chemical probes for understanding these pathogens in an effort to overcome drug resistance.

The connection between austenite/cementite orientation relationships and crystal structure of both phases has been established. The nucleus formation mechanism at the mutual transformation of austenite and cementite structures has been proposed. Mechanism is based on the interpretation of the considered structures as crystallographic tiling onto triangulated polyhedra, and the said tiling can be transformed by diagonal flipping in a rhombus consisting of two adjacent triangular faces. The sequence of diagonal flipping in the fragment of the initial crystal determines the orientation of the fragment of the final crystal relative to the initial crystal. In case of the mutual austenite/cementite transformation the mutual orientation of the initial and final fragments is coinciding to the experimentally observed in steels Thomson-Howell orientation relationships: {1¯03}C||{111}A; <010>C ||<101¯>A; <301¯>C ||  <1¯21¯>A ${\left\{ {\bar 103} \right\}_{\rm{C}}}||{\left\{ {111} \right\}_{\rm{A}}};{\rm{}} < {\kern 1pt} 010{\kern 1pt} { > _{\rm{C}}}{\rm{||}} < {\kern 1pt} 10\bar 1{\kern 1pt} { > _{\rm{A}}};\; < {\kern 1pt} 30\bar 1{\kern 1pt} { > _{\rm{C}}}\;||\,\, < {\kern 1pt} \bar 12\bar 1{\kern 1pt} { > _{\rm{A}}}{\rm{}}$ The observed orientation relationship between FCC austenite and cementite is determined by crystallographic group-subgroup relationship between transformation participants, and non-crystallographic symmetry which is determining the transformation of triangulated clusters of transformation participants.

A series of uranyl acrylate complexes with s-, p-, and d- monovalent cations (Li, Na, Tl, and Ag) was synthesized and characterized by single crystal X-ray diffraction and IR spectroscopy. We demonstrated that the nature of the monovalent cation strongly affects the composition and crystal structure of an uranyl acrylate. Li[UO 2 (acr) 3 ]·H 2 O ( 1 , acr=CH 2 CHCOO − ) crystallizes in the tetragonal crystal system and is built of chains which are connected through hydrogen bonding. The presence of an acrylic acid dimer in the reaction results in the monoclinic compound Na 3 [UO 2 (acr) 3 ][UO 2 (acr) 2.5 (CH 2 CHCOOCH 2 CH 2 COO) 0.5 ] 2 ·5H 2 O ( 2 ), in which the acrylic dimer shares a position with both the acrylate anion and a water molecule. Tl[UO 2 (acr) 3 ] ( 3 ) exists as two polymorphs and crystallizes in either P 1̅ ( 3a ) or P 2 1 3 ( 3b ) space groups. The polymorphs differ in the dimensionality, 2D for 3a and 3D for 3b , and density. Ag 2 [UO 2 (NO 3 ) 2 (acr) 2 ]·2Hacr ( 4 ) is the first example of the Ag atom coordination to the acrylate anion through the vinyl group. In 4 , the Ag–C bonds enhances the connectivity of the trinuclear [Ag 2 UO 2 (acr) 2 (Hacr) 2 (NO 3 ) 2 ] clusters into a layered coordination polymer. A detailed structural study of the obtained compounds was performed using Voronoi-Dirichlet tessellation.

Structure solution of molecular crystals from powder diffraction data by real-space methods becomes challenging when the total number of degrees of freedom (DoF) for molecular position, orientation and intramolecular torsions exceeds a value of 20. Here we describe the structure determination from powder diffraction data of three pharmaceutical salts or cocrystals, each with four molecules per asymmetric unit on general position: Lamivudine camphorsulfonate ( 1 , P  2 1 , Z =4, Z ′=2; 31 DoF), Theophylline benzamide ( 2 , P  4 1 , Z =8, Z ′=2; 23 DoF) and Aminoglutethimide camphorsulfonate hemihydrate [ 3 , P  2 1 , Z =4, Z ′=2; 31 DoF (if the H 2 O molecule is ignored)]. In the salts 1 and 3 the cations and anions have two intramolecular DoF each. The molecules in the cocrystal 2 are rigid. The structures of 1 and 2 could be solved without major problems by DASH using simulated annealing. For compound 3 , indexing, space group determination and Pawley fit proceeded without problems, but the structure could not be solved by the real-space method, despite extensive trials. By chance, a single crystal of 3 was obtained and the structure was determined by single-crystal X-ray diffraction. A post-analysis revealed that the failure of the real-space method could neither be explained by common sources of error such as incorrect indexing, wrong space group, phase impurities, preferred orientation, spottiness or wrong assumptions on the molecular geometry or other user errors, nor by the real-space method itself. Finally, is turned out that the structure solution failed because of problems in the extraction of the integrated reflection intensities in the Pawley fit. With suitable extracted reflection intensities the structure of 3 could be determined in a routine way.

A composite material based dual-emission probe for Fe 3+ was prepared by the hybridization of a three-dimensional framework with CdSe/ZnS quantum dots (QDs)-doped silica nanoparticles. The obtained probe showed characteristic fluorescence emissions of CdSe/ZnS QDs (red) and Cd-metal-organic framework (MOF, blue) under a single exciation wavelength. Upon the detection of Fe 3+ , only the fluorescence of Cd-MOF was quenched, whereas the red fluorescence of CdSe/ZnS QDs particles was mostly reserved. Consequently, the variation of the two fluorescence intensity ratios displays a continuous color change from blue to red upon exposure to different amounts of Fe 3+ ions, which can be easily observed under a UV lamp.

Single crystals of solid chlorine (Cl 2 ) were synthesized at room temperature and high pressure (HP, P =1.45 GPa) in a diamond anvil cell (DAC). At these conditions Cl 2 adapts the same structure as its corresponding low-temperature (LT) ambient pressure modification ( T <172 K), as concluded from HP single crystal diffraction experiments. Namely, it crystallizes in an orthorhombic symmetry ( Cmce spacegroup) with Cl 2 molecules forming monolayers parallel to the bc plane and this structure is preserved up to at least 64 GPa. The pressure of 1.45 GPa is to be considered as a solidification point of liquid Cl 2 at room temperature.