High-temperature phase transitions and domain structures of KLiSO4: studied by polarisation-optics, X-ray topography and liquid–crystal surface decoration

The transitions between the room temperature phase III (space group P63) and the two high-temperature phases II (Pcmn) and I (P63/mmc) of KLiSO4 and the domain structures generated by them were investigated by high-temperature polarisation optics (birefringence) and room-temperature X-ray topography, optical activity and nematic–liquid–crystal (NLC) surface decoration. The transition from the polar hexagonal phase III into the centrosymmetric orthorhombic phase II at 708 K leads, due to the loss of the trigonal axis and the radial temperature gradient of the optical heating chamber used, to a roughly hexagonal arrangement of three sets of thin orthorhombic {110} lamelleae with angles of 60° (120°) between them. The associated twin law “reflection m{110}orth” corresponds to the frequent growth twin m{101̅0}hex of phase III. The domains are easily ferroelastically switched. Upon further heating above 949 K into phase I (P63/mmc) all domains vanish. Upon cooling back into phase II the three domain states related by 60°(120°) reflections m{110}orth re-appear, however (due to the higher thermal agitation at 949 K) with a completely different domain structure consisting of many small, irregularly arranged {110}orth domains. Particular attention is paid to the domain structure of the hexagonal room temperature phase III generated during the re-transition from the orthorhombic phase II. Curiously, from the expected three twin laws inversion 1̅, rotation 2⊥[001]hex and reflection m{101̅0}hex only the latter, which corresponds to the frequent growth twinning, has been found. Finally a short treatise of the structural relations of the KLiSO4 high-temperature polymorphs is given.

X-ray topographic study of the antiferroelectric phase transition and antiphase boundaries in copper formate tetrahydrate

Copper formate tetrahydrate, Cu(HCOO)2·4H2O, undergoes upon cooling below –38 °C a phase transition from a paraelectric (PE) into an antiferroelectric (AFE) phase, whereby its monoclinic point group 2/m is preserved and its lattice parameter c doubled. The boundary between the phases PE and AFE and the antiphase boundaries between the AFE domains have been imaged by X-ray diffraction topography (Lang technique), using a rotating-anode generator with Ag-Kα radiation. A simple cooling chamber allowed the adjustment of the transition isotherm (i.e. the phase boundary) across the plate-shaped crystal and its stepwise movement across the probe. This has been done for slices of orientation (010) and (001) with several directions of the temperature gradient. The phase boundary appears on the topographs by strong kinematical contrast, indicating considerable lattice strain in the transition region. For (001) plates the X-ray diffraction positions of the PE and AFE phase regions on both sides of the phase boundary are different so that the two regions had to be imaged in separate exposures with a small angular readjustment between them. As expected, the domain boundaries, imaged by section topography, show fringe contrast typical for antiphase boundaries. The various findings are described and discussed in detail.

The application of eigensymmetries of face forms to X-ray diffraction intensities of crystals twinned by 'reticular merohedry'

This paper is an extension of a previous treatment of `twins by merohedry' with full lattice coincidence [Σ = 1, Klapper & Hahn (2010). Acta Cryst. A66, 327-346] to `twins by reticular merohedry' with partial lattice coincidence (Σ > 1). Again, the sets of symmetrically equivalent reflections {hkl} are considered as sets of equivalent faces (face forms) {hkl}, and the behaviour of the oriented eigensymmetries of these forms under the action of a twin operation is used to determine the X-ray reflection sets, the intensities of which are affected or not affected by the twinning. The following cases are treated: rhombohedral obverse/reverse Σ3 twins, cubic Σ3 (spinel) twins, tetragonal Σ5 twins (twin elements m'(120), 2'[ ̅210]) and hexagonal Σ7 twins (m'(12 ̅30), 2'[2 ̅10]). For each case the twin laws for all relevant point groups are defined, and the twin diffraction cases A (intensity of twin-related reflection sets not affected), B1 (intensity affected), B2 (intensity affected only by anomalous scattering) and S (single, i.e. non-coincident reflection sets) are derived for all twin laws. A special treatment is provided for the cubic Σ3 twins, where the cubic face forms first have to be split into up to four rhombohedral subforms with a threefold axis along one of the four cube <111> directions, here [111]. These subforms exhibit different twin diffraction cases analogous to those derived for the rhombohedral obverse/reverse Σ3 twins. A complete list of the split forms and their diffraction cases for all cubic point groups and all Σ3 twin elements is given. The application to crystal structure determination of crystals twinned by reticular merohedry and to X-ray topographic mapping of twin domains is discussed.

A structural study of polymorphism in phenyl salicylate: determination of the crystal structure of a meta-stable phase from X-ray powder diffraction data using a direct space systematic search method

In this paper we report the crystal structure solution of a meta-stable phase of phenyl salicylate (salol). This modification, which is obtained from a super-cooled melt, has been observed before, but the structure has not been previously determined. Structure solution was achieved by a procedure combining a computer based systematic search method with a subsequent Rietveld refinement of experimental X-ray powder diffraction data. A clustering procedure to group similar trial structures based upon energy minimisations is discussed. The best trial structure identified by the combination of a systematic search and clustering was refined using the Rietveld method and a final structure with a weighted pattern index Rwp of 0.0513 (excluding background) was obtained. The meta-stable phase of salol crystallises with a monoclinic unit cell with cell parameters a = 17.4047(8) Å, b = 5.9800(5) Å, c = 10.6882(7) Å, and β = 108.988(5)º. The space group is P21/n with four molecules in the unit cell. A structural comparison of the stable and meta-stable modifications is given.

Potassium lithium carbonate, KLiCO3: single-crystal X-ray structure analysis and thermal expansion

Single crystals of KLiCO3, the intermediate compound in the eutectic system K2CO3-Li2CO3, were synthesized from the melt and the crystal structure was redetermined at room temperature by single-crystal X-ray diffraction: a = 7.232(1 ) Å, b = 7.085(2 )Å, c = 6.579(1) Å, ß = 113.40(1)°, space group P21/n (No 14), Z = 4. Earlier literature results obtained by neutron time-of-flight powder diffraction are corroborated. The structure is composed of distorted face and edge sharing LiO5 and KO9 coordination polyhedra which are arranged in a layered manner and are connected by distorted but planar carbonate anions. In addition to the structure analysis, the thermal expansion of the crystal was measured and analyzed up to melting at 504.5 ± °C. It exhibits a significant anisotropy with a maximum in direction c* about three times as large as the almost equal expansions in the a,b plane. This anisotropy is clearly understood from the distribution of bonds in the structure rather than from its layered nature.

Physical properties of stable monoclinic and metastable trigonal 4-methylbenzophenone

Pyroelectric, dielectric and piezoelectric coefficients of metastable 4-methylbenzophenone, point group 3, have been determined by standard methods. Furthermore, thermal expansion and elastic properties of this phase and of the stable monoclinic phase have been studied. The pyroelectric effect is comparable with that of tourmaline, the piezoelectric effects to those of a-quartz. The differences between the two polymorphs with respect to thermal expansion and to elastic and thermoelastic properties are small, but nevertheless significant.

Non-linear optical properties and absolute structure of metastable 4-methyl benzophenone

Metastable 4-methyl benzophenone (4-MBP, C14H12O) crystallizes in the polar (pyroelectric) and enantiomorphic space groups (SG) P31 and P32. The optical rotation tensor has been measured for 670 nm and the material was tested for evidence of phase-matchability. The absolute structure was determined via three-beam diffraction, showing that the structural right-hand screw 31 is combined with positive (right-handed, i.e. clockwise when looking towards the light source) optical rotation, for both tensor components ρ 11 = ρ 22 = 26(5)°/mm, ρ 33 = 8.3(5)°/mm (contrary to low-quartz which shows negative optical rotation for ρ 33 and positive rotation for ρ 11 in right-hand SG P312).

The non-linear optical tensors for optical rotation, d-coefficients, electro-optic effect and electrogyration have been calculated using a set of electronic polarizabilities as input parameters for a dipole-dipole interaction model that reproduces the experimental refractive indices and optical rotation. Unusually high polarizability volumes are needed for hydrogen atom bonding to aromatic carbons in order to model the optical tensors. The non-linear optical coefficients are of medium size.

Dynamic proton disorder and the II-I structural phase transition in (NH(4))(3)H(SO(4))(2)

X-ray powder diffraction, differential scanning calorimetry (DSC)/thermogravimetry (TG) and single-crystal neutron diffraction methods were used to investigate triammonium hydrogen disulfate (NH(4))(3)H(SO(4))(2) (TAHS) in the temperature range between 293 and 493 K. The temperature-dependent X-ray powder diffraction measurements show a clear hysteresis of the I <-->II phase transition of TAHS with transition temperatures of T(up) = 412.9 (1) K on heating and of T(down) = 402.6 (1) K on cooling. From the existence of hysteresis and from the jump-like changes of the lattice parameters, the I <--> II phase transition of TAHS is considered to be first order. With DSC/TG measurements we confirmed that there is only one phase transition between 293 and 493 K. Through careful investigation on single crystals of TAHS using neutron diffraction, the correct space group (C2/c) of room-temperature TAHS-II phase was confirmed. Crystal structure analysis by single-crystal neutron diffraction showed a strongly elongated displacement ellipsoid of the proton which lies in the middle of the (SO(4))H(SO(4)) dimer with \bar 1 local symmetry. The protons of the NH(4) groups also show strongly enlarged anisotropic mean-square displacements. These findings are interpreted in terms of a characteristic proton disorder in the TAHS-II phase.

Diversity of calcium oxalate crystals in Cactaceae

The occurrence of various types of calcium oxalate crystals was studied in 251 species and subspecies of Cactaceae to determine whether they are useful characters for Cactaceae systematics. Crystal hydration states were identified by X-ray powder diffraction and polarizing microscopy as monoclinic calcium oxalate monohydrate (COM) and tetragonal calcium oxalate dihydrate (COD). Ninety-eight percent of taxa studied contained either COM or COD crystals, or both. Different morphologies of crystals were further defined by light microscopy and scanning electron microscopy as druses, raphides, styloids (prisms), and crystal sand. In particular, the preponderance of one of the hydration states (COM or COD) was characteristic for certain Cactus subfamilies. Data showed that in Pereskioideae, Maihuenioideae, and Opuntioideae COM is predominant, while in Cactoideae COD prevails. In the remainder of Cactoideae, the crystals were quite variable. In tribe Hylocereeae, many species form both COM and COD as well. In the genera Hylocereus , Epiphyllum , Selenicereus , and Weberocereus , COM forms were almost exclusively represented by raphides together with different crystal forms in their epidermal cells. In the remainder of the Cactoideae, crystals did not follow any observable patterns. Development of crystallographic standards for identifying crystal forms microscopically is proposed for future crystal studies.

The crystal structure of barstowite, Pb4Cl6(CO3) · H2O, determined on crystals from Etruscan slags and from a Late-Hellenistic shipwreck

Crystals of the rare lead mineral barstowite, Pb4Cl6(CO3) · H2O, were found on a lead object from a Late-Hellenistic shipwreck and within Etruscan iron slags. Its crystal structure was determined and refined to R = 0.023. Barstowite crystallizes in the monoclinic space group P21/m with a = 4.2043(8) Å, b= 9.199(2) Å, c= 16.663(3) Å, β = 91.82(1)°. The lead atoms are nine-fold coordinated in form of tricapped trigonal prisms by chlorine and oxygen atoms. The polyhedra, through sharing of faces, edges and corners, define structural layers which are linked together in a three-dimensional framework. Oxygen atoms belonging to the water molecules form hydrogen bonds with oxygens of the carbonate groups. The relationship of barstowite with cotunnite and phosgenite is shortly discussed.

Connective tissue growth factor mediates transforming growth factor beta-induced collagen synthesis: down-regulation by cAMP

Connective tissue growth factor (CTGF) is a cysteine-rich peptide synthesized and secreted by fibroblastic cells after activation with transforming growth factor beta (TGF-beta) that acts as a downstream mediator of TGF-beta-induced fibroblast proliferation. We performed in vitro and in vivo studies to determine whether CTGF is also essential for TGF-beta-induced fibroblast collagen synthesis. In vitro studies with normal rat kidney (NRK) fibroblasts demonstrated CTGF potently induces collagen synthesis and transfection with an antisense CTGF gene blocked TGF-beta stimulated collagen synthesis. Moreover, TGF-beta-induced collagen synthesis in both NRK and human foreskin fibroblasts was effectively blocked with specific anti-CTGF antibodies and by suppressing TGF-beta-induced CTGF gene expression by elevating intracellular cAMP levels with either membrane-permeable 8-Br-cAMP or an adenylyl cyclase activator, cholera toxin (CTX). cAMP also inhibited collagen synthesis induced by CTGF itself, in contrast to its previously reported lack of effect on CTGF-induced DNA synthesis. In animal assays, CTX injected intradermally in transgenic mice suppressed TGF-beta activation of a human CTGF promoter/lacZ reporter transgene. Both 8-Br-cAMP and CTX blocked TGF-beta-induced collagen deposition in a wound chamber model of fibrosis in rats. CTX also reduced dermal granulation tissue fibroblast population increases induced by TGF-beta in neonatal mice, but not increases induced by CTGF or TGF-beta combined with CTGF. Our data indicate that CTGF mediates TGF-beta-induced fibroblast collagen synthesis and that in vivo blockade of CTGF synthesis or action reduces TGF-beta-induced granulation tissue formation by inhibiting both collagen synthesis and fibroblast accumulation.

Fluid-phase marker transport in rat liver: free-flow electrophoresis separates distinct endosome subpopulations

Free-flow electrophoresis (FFE) was used to investigate the intracellular compartments involved in fluid-phase marker, fluoresceine isothiocyanate (FITC)-dextran, transport in the isolated perfused rat liver. One to 2 min after uptake at 37 degrees C, FITC-dextran was found in endosomes with the same electrophoretic mobility as early sorting endosomes labeled either by the hepatocyte-specific marker asialoorosomucoid (ASOR) or by transferrin that enters all liver cells. Labeling at low temperature (16 degrees C) blocked transport of ASOR and dextran in early endosomes. With increasing internalization time (3-13 min) at 37 degrees C, FITC-dextran-labeled compartments co-localized with late, ASOR-containing endosomes. Since localization of FITC-dextran in late transcytotic compartments was not observed upon FFE separation, it is concluded that the majority of internalized markers is directed to lysosomes. The FITC-label did not account for the predominant lysosomal targeting of the dextran, since [3H]dextran-labeled endosomes exhibited an identical FFE pattern. Taken together, these data indicate that the fluid-phase marker dextran is transported through intracellular compartments with identical characteristics as endosome subcompartments of the receptor-mediated lysosomal route.

Free-flow electrophoretic analysis of endosome subpopulations of rat hepatocytes

The separation of functional early and late endosomes from other cellular compartments by free-flow electrophoresis (FFE) has been previously demonstrated in nonpolarized cells. Here, using 125I-labeled anti-secretory component antibodies ([125I]SC Ab) and FITC-labeled asialoorosomucoid (FITC-ASOR) as markers of the transcytotic and lysosomal pathway, respectively, we demonstrate the separation of three distinct endosome subpopulations from polarized rat hepatocytes. Internalization of both markers at 16 degrees C resulted in their accumulation in a common endosome compartment, indicating that both the transcytotic and the lysosomal pathways are arrested in the sorting early endosome at temperatures below 20 degrees C. After chase of the markers from early endosomes into the transcytotic or the degradative route at 37 degrees C, transcytotic endosomes carrying [125I]SC Ab migrated with an electrophoretic motility between early and late endosomes while late endosomes labeled with FITC-ASOR were deflected more towards the anode than early endosomes. These data indicate that in rat hepatocytes, the transcytotic and lysosomal pathways utilize a common (i.e. early endosomes) and two distinct endosome subpopulations (i.e. transcytotic endosomes, late endosomes) prior to delivering proteins for biliary secretion or lysosomal degradation, respectively.

Stimulation of fibroblast cell growth, matrix production, and granulation tissue formation by connective tissue growth factor

Connective tissue growth factor (CTGF) is a 36-to 38-kDa peptide that is selectively induced by transforming growth factor-beta (TGF-beta) in fibroblastic cell types. We compared the biologic activities of CTGF with TGF-beta on fibroblasts in culture and in animal models of fibroplasia. CTGF was active as a mitogen in monolayer cultures of normal rat kidney fibroblasts. CTGF did not stimulate anchorage-independent growth of NRK fibroblasts, however, or inhibit the growth of mink lung epithelial cells, distinguishing CTGF's growth-regulatory activities from those of TGF-beta. In NRK fibroblasts, both TGF-beta and CTGF significantly increased the transcripts encoding alpha 1 type I collagen, alpha 5 integrin, and fibronectin. Stimulation of type I collagen and fibronectin protein synthesis by TGF-beta and CTGF was confirmed by pulse labeling of cells with [35S]methionine. Subcutaneous injection of TGF-beta and CTGF into neonatal NIH Swiss mice resulted in a large stimulation of granulation tissue and fibrosis at the site of injection. In situ hybridization studies revealed that TGF-beta injection induced high levels of CTGF mRNA in the dermal fibroblasts at the injection site, demonstrating that TGF-beta can induce the expression of CTGF in connective tissue cells in vivo. No CTGF transcripts were detected in the epidermal cells in either control or TGF-beta-injected skin or in fibroblasts in control (saline-injected) skin. These results demonstrate that, like TGF-beta, CTGF can induce connective tissue cell proliferation and extracellular matrix synthesis.

Rat liver endocytic coated vesicles do not exhibit ATP-dependent acidification in vitro

Coated vesicle fractions from a variety of tissues have been found to contain a vacuolar proton ATPase. Since these fractions contain both plasma membrane- and Golgi-derived coated vesicles, we sought to determine specifically whether endocytic coated vesicles from rat liver contain an active vacuolar proton ATPase. Endocytic vesicles (coated vesicles and endosomes) were selectively labeled with pH-sensitive endocytic tracers (fluorescein isothiocyanate-dextran or -asialoorsomucoid). Coated vesicles were then separated from endosomes by sucrose density gradient centrifugation. Although the endosomal fractions were found to exhibit significant ATP-dependent acidification activity, highly purified coated vesicles containing pH-sensitive endocytic tracers were unable to generate a pH gradient in response to ATP addition. The coated vesicles could be passively acidified, however, by creating potassium diffusion potentials, indicating that they were in fact capable of maintaining proton gradients. Moreover, significant ATP-dependent acidification activity was observed when the coated vesicle fractions were assayed using the nonselective externally added pH probe acridine orange. Thus, it appears that rat liver endocytic coated vesicles do not contain a functional proton pump. The active vacuolar proton ATPase found in these fractions instead reflected the presence of Golgi-derived coated vesicles or contaminating membranes.

X-ray diffraction study of KTP (KTiOPO4) crystals under a static electric field

X-ray diffraction studies are made on ion-conducting potassium titanyl phosphate (KTP) crystals with in situ DC electric field along different crystallographic directions. The X-ray rocking curves recorded with an electric field along the polar b axis (which is the direction of ion conduction) show a strong enhancement of the 040 reflection intensity (reflecting planes normal to the b axis) whereas the h0l reflections (reflecting planes parallel to the polar axis) do not show any intensity change. For an electric field normal to the polar axis no intensity change, either in 040 or in h0l reflections, occurs. This observation is supplemented by X-ray topography. The 040 X-ray topographs recorded with in situ electric field along b exhibit strong extinction contrast in the form of striations parallel to the polar (ion-conduction) axis. The 040 intensity increase and the striation contrast are attributed to lattice deformation by the space-charge polarization due to the movement of the K+ ions under the influence of the electric field.

X-ray diffraction study of lithium hydrazinium sulfate and lithium ammonium sulfate crystals under a static electric field

X-ray diffraction studies are made on proton conducting polar lithium hydrazinium sulfate and ferroelectric lithium ammonium sulfate. The X-ray rocking curves recorded with in situ electric field along the polar b axis of lithium hydrazinium sulfate (direction of proton conductivity) show a strong enhancement of the 0k0 diffraction intensity. The corresponding 0k0 X-ray topographs reveal extinction contrast consisting of striations parallel to the polar axis. They disappear when the electric field is switched off. The effect is very strong in 0k0 but invisible in h0l reflections. It is present only if the electric field is parallel to the polar axis b. This unusual X-ray topographic contrast is correlated with the proton conduction. It is supposed that, under electric field, an inhomogeneous charge distribution develops, distorting the crystal lattice. Similar experiments on lithium ammonium sulfate also show contrast variations, but of quite different behaviour than before. In this case they result from changes of the ferroelectric domain configuration under electric field.