Crystallography relevant to Mars and Galilean icy moons: crystal behavior of kieserite-type monohydrate sulfates at extraterrestrial conditions down to 15 K

Monohydrate sulfate kieserites (M ²⁺SO₄·H₂O) and their solid solutions are essential constituents on the surface of Mars and most likely also on Galilean icy moons in our solar system. Phase stabilities of end-member representatives (M ²⁺ = Mg, Fe, Co, Ni) have been examined crystallographically using single-crystal X-ray diffraction at 1 bar and temperatures down to 15 K, by means of applying open He cryojet techniques at in-house laboratory instrumentation. All four representative phases show a comparable, highly anisotropic thermal expansion behavior with a remarkable negative thermal expansion along the monoclinic b axis and a pronounced anisotropic expansion perpendicular to it. The lattice changes down to 15 K correspond to an 'inverse thermal pressure' of approximately 0.7 GPa, which is far below the critical pressures of transition under hydro-static compression (P_c ≥ 2.40 GPa). Consequently, no equivalent structural phase transition was observed for any compound, and neither dehydration nor rearrangements of the hydrogen bonding schemes have been observed. The M ²⁺SO₄·H₂O (M ²⁺ = Mg, Fe, Co, Ni) end-member phases preserve the kieserite-type C2/c symmetry; hydrogen bonds and other structural details were found to vary smoothly down to the lowest experimental temperature. These findings serve as an important basis for the assignment of sulfate-related signals in remote-sensing data obtained from orbiters at celestial bodies, as well as for thermodynamic considerations and modeling of properties of kieserite-type sulfate monohydrates relevant to extraterrestrial sulfate associations at very low temperatures.

CoSO4·H2O and its continuous transition compared to the compression properties of isostructural kieserite-type polymorphs

The kieserite-type compound cobalt(II) sulfate monohydrate, CoSO4·H2O, has been investigated under isothermal (T = 295 K) hydrostatic compression up to 10.1 GPa in a diamond anvil cell by means of single-crystal X-ray diffraction and Raman spectroscopy. The monoclinic α-phase (space group C2/c) undergoes a second-order ferroelastic phase transition at P c  = 2.40(3) GPa to a triclinic β-phase (space group P 1 ‾ $‾{1}$ ). Lattice elasticities derived from fitting third-order Birch-Murnaghan equations of state to the pressure dependent unit-cell volume data yield V 0 = 354.20(6) Å3, K 0 = 53.0(1.7) GPa, K′ = 5.7(1.8) for the α-phase and V 0 = 355.9(8) Å3, K 0 = 45.2(2.6) GPa, K′ = 6.6(6) for the β-phase. Crystal structure data of the high-pressure polymorph were determined at 2.98(6) and 4.88(6) GPa. The most obvious structural feature and thus a possible driving mechanism of the phase transition, is a partial rearrangement in the hydrogen bonding system. However, a comparative analysis of pressure-induced changes in the four kieserite-type compounds investigated to date suggests that the loss of the point symmetry 2 at the otherwise rather rigid SO4 tetrahedron, allowing symmetrically unrestricted tetrahedral rotations and edge tiltings in the β-phase, could be the actual driving mechanism of the phase transition.

N2–O2 icing in single-crystal in-house X-ray diffraction experiments using an open-flow helium cryostat

This note reports a study of the coating of a crystal with `ice' at temperatures below 45 K during single-crystal in-house diffraction experiments when using an open-flow helium cryostat. The `ice' consists mainly of crystalline oxygen and nitrogen. This suggests completely different techniques for avoiding this type of icing compared with water icing. With appropriate choices of crystal mount, crystal position with respect to the nozzle and gas flow conditions, it is possible to avoid detectable condensation. However, sometimes this cannot be achieved in practice (poor diffraction from a smaller crystal, necessity of positioning the crystal in certain orientations to achieve desired data completeness, need to reduce helium consumption etc.). The problem of icing seems to be less common for powder experiments where the laminar gas flow is parallel to the capillary containing the sample, and for synchrotron experiments where the sample is comparatively small and almost continuously rotated, which facilitates the ice covering being removed by the gas flow. This last technique can in principle also be applied to single-crystal X-ray diffraction using laboratory diffractometers – periodic rapid rotation of the crystal can help to minimize any icing, but this technique will not work when the condensation rate is comparable to or faster than one frame of data collection. The coating around a sample crystal reduces the quality of the diffraction data, and the temperature at the sample below the coating may differ significantly from that at the cryostat nozzle reported by the instrument.

Extending the Stability Field of Polymeric Carbon Dioxide Phase V beyond the Earth's Geotherm

We present a study on the phase stability of dense carbon dioxide (CO_{2}) at extreme pressure-temperature conditions, up to 6200 K within the pressure range 37±9 to 106±17  GPa. The investigations of high-pressure high-temperature in situ x-ray diffraction patterns recorded from laser-heated CO_{2}, as densified in diamond-anvil cells, consistently reproduced the exclusive formation of polymeric tetragonal CO_{2}-V at any condition achieved in repetitive laser-heating cycles. Using well-considered experimental arrangements, which prevent reactions with metal components of the pressure cells, annealing through laser heating was extended individually up to approximately 40 min per cycle in order to keep track of upcoming instabilities and changes with time. The results clearly exclude any decomposition of CO_{2}-V into the elements as previously suggested. Alterations of the Bragg peak distribution on Debye-Scherrer rings indicate grain coarsening at temperatures >4000  K, giving a glimpse of the possible extension of the stability of the polymeric solid phase.

P21/c Postorthopyroxene γ-LiScGe2O6, a New Dense High-Pressure Polymorph and Its Direct Transformation from the Pbca Structure

Orthorhombic β-LiScGe₂O₆ single crystals were compressed hydrostatically up to 10.35 GPa using a diamond anvil cell and investigated in situ by means of X-ray diffraction and Raman spectroscopy. Crystal-structure investigations at ambient conditions and at high pressure show a structural transition from an orthopyroxene-type Pbca structure (a ≈ 18.43 Å, b ≈ 8.85 Å, and c ≈ 5.34 Å at 8.6 ± 0.1 GPa) to a postorthopyroxene type P2₁/c structure of the new dense γ-LiScGe₂O₆ (a ≈ 18.62 Å, b ≈ 8.85 Å, c ≈ 5.20 Å, and β ≈ 93.1° at 9.5 ± 0.1 GPa). The structure refinements reveal displacive shifts of O atoms associated with a rotation of every other tetrahedral-chain unit from the O- to S-type position similar to the postorthopyroxene-type MgSiO₃. As a consequence of the oxygen displacement, the coordination number of Li atoms is changing from [5 + 1] to a proper 6-fold coordination. The transition around P_c = 9.0 ± 0.1 GPa is associated with a volume discontinuity of ΔV = −1.6%. This orthopyroxene (OEn-Pbca) to postorthopyroxene (pOEn-P2₁/c) transition is the second example of this type of transformation. Precise lattice parameters have been determined during isothermal compression. The fit of the unit-cell volumes of β-LiScGe₂O₆, using a third-order Birch–Murnaghan equation of state, yields V₀ = 943.63 ± 0.11 ų, K₀ = 89.8 ± 0.6 GPa, and dK/dP = 4.75 ± 0.18 as parameters. Evaluation of the data points beyond the critical transition pressure using a second-order Birch–Murnaghan equation suggests V₀ = 940.6 ± 4.4 ų and K₀ = 82.4 ± 4.8 GPa. A series of high-pressure Raman spectra confirm the symmetry-related structural transition, with band positions shifting in a noncontinuous manner, thus confirming the proposed first-order transition.

Synthetic lithium−scandium germanate crystals (space group Pbca at ambient conditions) were the subject of in situ high-pressure solid-state investigations (single-crystal X-ray diffraction, lattice parameter, and Raman spectra) in a diamond anvil cell up to 10 GPa. One phase transition, apparently of first order, is identified at 9.0 ± 0.1 GPa. The Birch−Murnaghan equations of state were fitted to the P−V data, and the obtained parameters are given. The transition is of the type orthoenstatite (Pbca) to postorthoenstatite (P2₁/c).

CuSO4/[Cu(NH3)4]SO4-Composite Thermochemical Energy Storage Materials

The thermochemical energy-storage material couple CuSO₄/[Cu(NH₃)₄]SO₄ combines full reversibility, application in a medium temperature interval (<350 °C), and fast liberation of stored heat. During reaction with ammonia, a large change in the sulfate solid-state structure occurs, resulting in a 2.6-fold expansion of the bulk material due to NH₃ uptake. In order to limit this volume work, as well as enhance the thermal conductivity of the solid material, several composites of anhydrous CuSO₄ with inorganic inert support materials were prepared and characterized with regard to their energy storage density, reversibility of the storage reaction, thermal conductivity, and particle morphology. The best thermochemical energy storage properties were obtained for a 10:1 CuSO₄-sepiolite composite, combining an attractive energy storage density with slightly improved thermal conductivity and decreased bulk volume work compared to the pure salt.

High-Pressure Behavior of Nickel Sulfate Monohydrate: Isothermal Compressibility, Structural Polymorphism, and Transition Pathway

Single crystals of synthetic nickel sulfate monohydrate, α-NiSO₄·H₂O (space-group symmetry C2/c at ambient conditions), were subject to high-pressure behavior investigations in a diamond-anvil cell up to 10.8 GPa. By means of subtle spectral changes in Raman spectra recorded at 298 K on isothermal compression, two discontinuities were identified at 2.47(1) and 6.5(5) GPa. Both transitions turn out to be apparently second order in character, as deduced from the continuous evolution of unit-cell volumes determined from single-crystal X-ray diffraction. The first structural transition from α- to β-NiSO₄·H₂O is an obvious ferroelastic C2/c–P1̅ transition. It is purely displacive from a structural point of view, accompanied by symmetry changes in the hydrogen-bonding scheme. The second β- to γ-NiSO₄·H₂O transition, further splitting the O2 (hydrogen bridge acceptor) position and violating the P1̅ space-group symmetry, is also evident from the splitting of individual bands in the Raman spectra. It can be attributed to symmetry reduction through local violation of local centrosymmetry. Lattice elasticities were obtained by fitting second-order Birch–Murnaghan equations of state to the p-V data points yielding the following zero-pressure bulk moduli values: K₀ = 63.4 ± 1.0 GPa for α-NiSO₄·H₂O, K₀ = 61.3 ± 1.9 GPa for β-NiSO₄·H₂O, and K₀ = 68.8 ± 2.5 GPa for γ-NiSO₄·H₂O.

Synthetic nickel sulfate monohydrate crystals (space group C2/c at ambient conditions) were subject to in situ high-pressure solid-state investigations (structure from single crystal X-ray diffraction, lattice parameter, Raman spectra) in a diamond-anvil cell up to 10.8 GPa. Two discontinuities, apparently phase transitions of second order, were identified at 2.47 ± 0.01 (obvious ferroelastic C2/c−P1̅) and 6.5 ± 0.5 GPa (P1̅−P1̅). Birch−Murnaghan equations of state were fitted to the P−V data, and the obtained parameters are given.

Cycle Stability and Hydration Behavior of Magnesium Oxide and Its Dependence on the Precursor-Related Particle Morphology

Thermochemical energy storage is considered as an auspicious method for the recycling of medium-temperature waste heat. The reaction couple Mg(OH)₂⁻MgO is intensely investigated for this purpose, suffering so far from limited cycle stability. To overcome this issue, Mg(OH)₂, MgCO₃, and MgC₂O₄·2H₂O were compared as precursor materials for MgO production. Depending on the precursor, the particle morphology of the resulting MgO changes, resulting in different hydration behavior and cycle stability. Agglomeration of the material during cyclization was identified as main reason for the decreased reactivity. Immersion of the spent material in liquid H₂O decomposes the agglomerates restoring the initial reactivity of the material, thus serving as a regeneration step.

The hydrocarbon-bearing clathrasil chibaite and its host-guest structure at low temperature

The natural sII-type clathrasil chibaite [chemical formula SiO2·(M12,M16), where Mx denotes a guest mol-ecule] was investigated using single-crystal X-ray diffraction and Raman spectroscopy in the temperature range from 273 to 83 K. The O atoms of the structure at room temperature, which globally conforms to space group [V = 7348.9 (17) Å3, a = 19.4420 (15) Å], have anomalous anisotropic displacement parameters indicating a static or dynamic disorder. With decreasing temperature, the crystal structure shows a continuous symmetry-lowering transformation accompanied by twinning. The intensities of weak superstructure reflections increase as temperature decreases. A monoclinic twinned superstructure was derived at 100 K [A2/n, V = 7251.0 (17) Å3, a' = 23.7054 (2), b' = 13.6861 (11), c' = 23.7051 (2) Å, β' = 109.47°]. The transformation matrix from the cubic to the monoclinic system is ai ' = (½ 1 ½ / ½ 0 -½ / ½ -1 ½). The A2/n host framework has Si-O bond lengths and Si-O-Si angles that are much closer to known values for stable silicate-framework structures compared with the averaged model. As suggested from band splitting observed in the Raman spectra, the [512]-type cages (one crystallographically unique in , four different in A2/n) entrap the hydro-carbon species (CH4, C2H6, C3H8, i-C4H10). The [51264]-type cage was found to be unique in both structure types. It contains the larger hydro-carbon mol-ecules C2H6, C3H8 and i-C4H10.

Crystalline polymeric carbon dioxide stable at megabar pressures

Carbon dioxide is a widespread simple molecule in the Universe. In spite of its simplicity it has a very complex phase diagram, forming both amorphous and crystalline extended phases above 40 GPa. The stability range and nature of these phases are still debated, especially in view of their possible role within the deep carbon cycle. Here, we report static synchrotron X-ray diffraction and Raman high-pressure experiments in the megabar range providing evidence for the stability of the polymeric phase V at pressure-temperature conditions relevant to the Earth's lowermost mantle. The equation of state has been extended to 120 GPa and, contrary to earlier experimental findings, neither dissociation into diamond and ε-oxygen nor ionization was observed. Severe deviatoric stress and lattice deformation along with preferred orientation are removed on progressive annealing, thus suggesting CO₂-V as the stable structure also above one megabar.

Evolution of the α-BaMg(CO3)2 low-temperature superstructure and the tricritical nature of its α-β phase transition

The crystal structure of the synthetic double carbonate norsethite [BaMg(CO₃)₂] has been reinvestigated using X-ray diffraction data within the temperature range 100-500 K using a high-sensitivity PILATUS pixel detector. The previously assumed positional shift of the crystallographically unique oxygen atom is confirmed. The shift is associated with a coupled rotation of symmetry-equivalent carbonate groups. It was possible to follow the shift using high-accuracy experiments under varying temperature conditions between 100 K and the critical transition temperature occurring at T_c = 363 ± 3 K. The transition of the α-form (space group R{\bar 3}c; below T_c), which represents a superstructure of the β-form (space group R{\bar 3}m, with c' = c/2; above T_c) was studied in detail. The tricritical order character of this displacive phase transition was verified by tracking the intensities of the recorded superstructure reflections (l = 2n + 1) from single-crystal diffraction and using high-precision lattice parameters obtained from powder diffraction in transmission geometry. Thermodynamic properties suggest both rotation of the CO₃ group and a coordination change of the BaO₁₂ coordination polyhedra as the order parameters driving the temperature-dependent α-β phase transition. Nevertheless, a detailed structural analysis reveals the coordination change of the barium atoms to be the main driving force for the observed transformation.

Extending the single-crystal quartz pressure gauge up to hydrostatic pressure of 19 GPa

In situhigh-pressure diffraction experiments on single-crystal α-quartz under quasi-hydrostatic conditions up to 19 GPa were performed with diamond-anvil cells. Isotropic pressures were calibrated through the ruby-luminescence technique. A 4:1 methanol–ethanol mixture and the densified noble gases helium and neon were used as pressure media. The compression data revealed no significant influence of the pressure medium at room temperature on the high-pressure behavior of α-quartz. In order to describe its compressibility for use as a pressure standard, a fourth-order Birch–Murnaghan equation of state (EoS) with parametersKT0 = 37.0 (3) GPa,KT0′ = 6.7 (2) andKT0′′ = −0.73 (8) GPa−1was applied to fit the data set of 99 individual data points. The fit of the axial compressibilities yieldsMT0 = 104.5 (8) GPa,MT0′ = 13.7 (4),MT0′′ = −1.04 (11) GPa−1(aaxis) andMT0 = 141 (3) GPa,MT0′ = 21 (2),MT0′′ = 8.4 (6) GPa−1(caxis), confirming the previously reported anisotropy. Assuming an estimated standard deviation of 0.0001% in the quartz volume, an uncertainty of 0.013 GPa can be expected using the new set of EoS parameters to determine the pressure.

Transformation pathways of structural transitions between BaMg(CO3)2polymorphs

In-situ investigations on BaMg(CO3)2 (= α-phase, space group R-3c) by means of single-crystal diffraction and Raman spectroscopy yield the existence of novel structural polymorphs at high-pressure (γ-phase, C2/c) and high-temperature (β-phase, R-3m) conditions. Isothermal hydrostatic compression at room temperature yield a high-pressure phase transition at Pc ≍ 2.3210.04 GPa, which is weakly first order in character and reveals significant elastic softening of the high-pressure form (α: K0 = 66.212.3 GPa, dK/dP = 2.011.8; γ: K0 = 41.910.4 GPa, dK/dP = 6.110.3). X-ray structure determination confirms a distorted but topologically similar crystal structure of the γ-phase, with Ba in twelve-fold and Mg in octahedral coordination together with characteristic CO3 units. Based on the experimental series of in-situ HPHT data points, the phase boundary of the α-to-γ-transition was determined with a Clausius-Clapeyron slope of 9.8(7) × 10-3 GPa K-1. In-situ measurements of the X-ray intensities carried out to identify the nature of the structural variation correspond to the previously reported transformation from α- to β-BaMg(CO3)2 at 343 K and 1 bar. The investigations revealed, in contrast to all X-ray diffraction data recorded at 298 K, the disappearance of the superstructure reflections and the observed reflection conditions confirm the anticipated R-3m space-group symmetry. The pathway of structural transformation follows a typically displacive fashion, involving exclusively positional shifts of the oxygen atoms for the α-β-transformation. In contrast, in the atomic displacement of the Ba atoms in addition to the three crystallographically independent oxygen sites is responsible for a comparably higher flexibility of the C2/c structure, which explains the origin of the remarkable elastic softening.

Multipurpose high-pressure high-temperature diamond-anvil cell with a novel high-precision guiding system and a dual-mode pressurization device

A novel diamond-anvil cell (DAC) design has been constructed and tested for in situ applications at high-pressure (HP) operations and has proved to be suitable even for HP sample environments at non-ambient temperature conditions. The innovative high-precision guiding mechanism, comparable to a dog clutch, consists of perpendicular planar sliding-plane elements and is integrated directly into the base body of the cylindrically shaped DAC. The combination of two force-generating devices, i.e., mechanical screws and an inflatable gas membrane, allows the user to choose independently between, and to apply individually, two different forcing mechanisms for pressure generation. Both mechanisms are basically independent of each other, but can also be operated simultaneously. The modularity of the DAC design allows for an easy exchange of functional core-element groups optimized not only for various analytical in situ methods but also for HP operation with or without high-temperature (HT) application. For HP-HT experiments a liquid cooling circuit inside the specific inner modular groups has been implemented to obtain a controlled and limited heat distribution within the outer DAC body.

Comparison between beryllium and diamond-backing plates in diamond-anvil cells: application to single-crystal x-ray diffraction high-pressure data

A direct comparison between two complete intensity datasets, collected on the same sample loaded in two identical diamond-anvil pressure cells equipped, respectively, with beryllium and diamond-backing plates was performed. The results clearly demonstrate that the use of diamond-backing plates significantly improves the quality of crystal structure data. There is a decrease in the internal R factor for averaging, structure refinement agreement factors, and in the errors and uncertainties of the atomic coordinates, atomic displacement parameters, and individual bond lengths.

The crystal structure of synthetic Rb2Sb8S12(S2) · 2 H2O, a new member of the hutchinsonite family of merotypes

The crystal structure of synthetic Rb2Sb8S12(S2) · 2 H2O was determined from single crystal X-ray diffraction data: space group P21/n, Z = 2, a = 7.0750(17) Å, b = 25.403(8) Å, c = 8.0527(19) Å, β = 97.842(10)° (R 1 = 4.88% for 1050 reflections with Fo > 4σ[Fo]). The structure is composed of slabs with formal composition [Sb8S12] that are based on (110)PbS cut-outs of the PbS archetype, are interspaced by channels with Rb+ and H2O, and separated by S2 2-disulfide groups which also interconnect the slabs. Rb2Sb8S12(S2) · 2 H2O is a N 1,2 = 1,2 member of the hutchinsonite family of merotypes.

Tuning of Inter- versus Intrachain Magnetic Interactions in Cyano-Bridged NiII/MIII (M = Cr, Fe, Co) Chain Complexes

The reaction of [M(CN)6]3- (M = Cr3+, Fe3+, Co3+) with the nickel(II) complex of 2,4-diamino-1,3,5-triazin-6-yl-{3-(1,3,5,8,12-pentaazacyclotetradecane)} ([NiL]2+) in excess of ANO3 or ACl (A = Li+, Na+, K+, Rb+, Cs+, NH4+) leads to the cyano-bridged dinuclear assemblies A{[NiL][M(CN)6]}.xH2O (x = 2-5). X-ray structures of Li{[NiL][Cr(CN)6]}.5H2O, NH4{[NiL][Cr(CN)6]}.3.5H2O, K{[NiL][Cr(CN)6]}.4H2O, K{[NiL][Fe(CN)6]}.4H2O, Rb{[NiL][Fe(CN)6]}.3.5H2O, and Cs{[NiL][Fe(CN)6]}.3.5H2O, as well as the powder diffractometry of the entire Fe(III) series, are reported. The magnetic properties of the assemblies are dependent on the monocation A and discussed in detail. New efficient pathways for ferromagnetic exchange between Ni(II) and Fe(III) or Cr(III) are demonstrated. Field dependencies of the magnetization for the Fe(III) samples at low temperature and low magnetic field indicate a weak interchain antiferromagnetic coupling, which is switched to ferromagnetic coupling at increasing magnetic field (metamagnetic behavior). The interchain magnetic coupling can be tuned by the size of the A cations.

Encapsulation of Cyanometalates by a Tris-macrocyclic Ligand Tricopper(II) Complex: Syntheses, Structural Variation, and Magnetic Exchange Coupling Pathways

The reaction of [M(CN)(6)](3-) (M = Cr(3+), Mn(3+), Fe(3+), Co(3+)) and [M(CN)(8)](4-/3-) (M = Mo(4+/5+), W(4+/5+)) with the trinuclear copper(II) complex of 1,3,5-triazine-2,4,6-triyltris[3-(1,3,5,8,12-pentaazacyclotetradecane)] ([Cu(3)(L)](6+)) leads to partially encapsulated cyanometalates. With hexacyanometalate(III) complexes, [Cu(3)(L)](6+) forms the isostructural host-guest complexes [[[Cu(3)(L)(OH(2))(2)][M(CN)(6)](2)][M(CN)(6)]][M(CN)(6)]30 H(2)O with one bridging, two partially encapsulated, and one isolated [M(CN)(6)](3-) unit. The octacyanometalates of Mo(4+/5+) and W(4+/5+) are encapsulated by two tris-macrocyclic host units. Due to the stability of the +IV oxidation state of Mo and W, only assemblies with [M(CN)(8)](4-) were obtained. The Mo(4+) and W(4+) complexes were crystallized in two different structural forms: [[Cu(3)(L)(OH(2))](2)[Mo(CN)(8)]](NO(3))(8)15 H(2)O with a structural motif that involves isolated spherical [[Cu(3)(L)(OH(2))](2)[M(CN)(8)]](8+) ions and a "string-of-pearls" type of structure [[[Cu(3)(L)](2)[M(CN)(8)]][M(CN)(8)]](NO(3))(4) 20 H(2)O, with [M(CN)(8)](4-) ions that bridge the encapsulated octacyanometalates in a two-dimensional network. The magnetic exchange coupling between the various paramagnetic centers is characterized by temperature-dependent magnetic susceptibility and field-dependent magnetization data. Exchange between the CuCu pairs in the [Cu(3)(L)](6+) "ligand" is weakly antiferromagnetic. Ferromagnetic interactions are observed in the cyanometalate assemblies with Cr(3+), exchange coupling of Mn(3+) and Fe(3+) is very small, and the octacoordinate Mo(4+) and W(4+) systems have a closed-shell ground state.

How to couple Landau theory to an equation of state

We show how to construct a Landau-type free energy based on a primary order parameter coupled to finite strain with an elastic energy derived from an arbitrary equation of state V = V(P). The resulting class of models provides an excellent and efficient framework for the systematic study of phase transformations for a wide range of materials up to ultrahigh pressures.

Earth Materials at the Molecular Level

The extension of crystallographic methods to minerals at non-ambient conditions and materials of technical interest is of importance for understanding the mutual relationship between crystal structure and physico-chemical properties. We apply this approach to understand the physics of the interior of the Earth as well as to contribute to the search for efficient non-linear optical materials.

Significance of hyperintense vessels on FLAIR MRI in acute stroke

OBJECTIVE

To describe hyperintense vessels sign (HVS) in patients with acute stroke on fluid-attenuated inversion recovery (FLAIR) MRI and determine its clinical significance and utility.

BACKGROUND

Enhancement of vessels on postcontrast MRI in patients with acute stroke is considered an indicator of early brain ischemia. Recently, the FLAIR technique has shown promise in earlier and better detection of ischemic brain parenchymal lesions.

METHODS

Two observers retrospectively reviewed 304 MRI of patients with stroke and identified 30 patients with acute middle cerebral artery stroke and HVS on FLAIR obtained within 24 hours of symptom onset. These patients were evaluated with contrast-enhanced MRI (n = 9), MR angiography of carotid and intracranial circulation (n = 30), cerebral angiography (n = 8), transcranial Doppler (n = 17), and SPECT (n = 16). The extent of HVS was compared with final infarct size and NIH Stroke Scale score.

RESULTS

HVS on FLAIR was seen in 10% of the patients with acute stroke. HVS was associated with large vessel occlusion or severe stenosis (>90%). Intravascular enhancement on contrast MRI was observed in vessels that were hyperintense on FLAIR. Both cortical and subcortical infarcts demonstrated HVS. MR angiographic and cerebral angiographic findings of large vessel occlusion or severe stenosis (>90%), slow flow, low velocities by transcranial Doppler, and hypoperfusion on SPECT correlated with HVS. HVS was the earliest ischemic change in three patients scanned within 3 hours of ictus. Final infarct size was smaller than the area showing HVS in all patients.

CONCLUSION

HVS on FLAIR MRI is an indicator of slow flow and early ischemia as a result of large vessel occlusion or stenosis and inadequacy of collateral circulation. HVS does not mean that infarction has occurred but indicates brain tissue at risk of infarction. It should prompt consideration of revascularization and flow augmentation strategies.

The Use of Quartz as an Internal Pressure Standard in High-Pressure Crystallography

The unit-cell parameters of quartz, SiO2, have been determined by single-crystal diffraction at 22 pressures to a maximum pressure of 8.9 GPa (at room temperature) with an average precision of 1 part in 9000. Pressure was determined by the measurement of the unit-cell volume of CaF2 fluorite included in the diamond-anvil pressure cell. The variation of quartz unit-cell parameters with pressure is described by: a −4.91300 (11) = −0.0468 (2) P + 0.00256 (7) P 2 − 0.000094 (6) P 3, c − 5.40482 (17) = − 0.03851 (2) P + 0.00305 (7) P 2 − 0.000121 (6) P 3, where P is in GPa and the cell parameters are in ångstroms. The volume–pressure data of quartz are described by a Birch–Murnaghan third-order equation of state with parameters V 0 = 112.981 (2) å3, K T0 = 37.12 (9) GPa and K′ = 5.99 (4). Refinement of K′′ in a fourth-order equation of state yielded a value not significantly different from the value implied by the third-order equation. The use of oriented quartz single crystals is proposed as an improved internal pressure standard for high-pressure single-crystal diffraction experiments in diamond-anvil cells. A measurement precision of 1 part in 10 000 in the volume of quartz leads to a precision in pressure measurement of 0.009 GPa at 9 GPa.

Where the brain appreciates the moral of a story

To identify the distributed brain regions used for appreciating the grammatical, semantic and thematic aspects of a story, regional cerebral blood flow was measured with positron emission tomography in nine normal volunteers during the reading of Aesop's fables. In four conditions, subjects had to monitor the fables for font changes, grammatical errors, a semantic feature associated with a fable character, and the moral of the fable. Both right and left prefrontal cortices were consistently, but selectively, activated across the grammatical, semantic, and moral conditions. In particular, appreciating the moral of a story required activating a distributed set of brain regions in the right hemisphere which included the temporal and prefrontal cortices. These findings emphasize that story processing engages a widely distributed network of brain regions, a subset of which become preferentially active during the processing of a specific aspect of the text.

Positron emission tomographic imaging of cardiac sympathetic innervation and function

Sites of uptake, storage, and metabolism of [18F]fluorodopamine and excretion of [18F]fluorodopamine and its metabolites were visualized using positron emission tomographic (PET) scanning after intravenous injection of the tracer into anesthetized dogs. Radioactivity was concentrated in the renal pelvis, heart, liver, spleen, salivary glands, and gall bladder. Uptake of 18F by the heart resulted in striking delineation of the left ventricular myocardium. Pretreatment with desipramine markedly decreased cardiac positron emission, consistent with dependence of the heart on neuronal uptake (uptake-1) for removal of circulating catecholamines. In reserpinized animals, cardiac positron emission was absent within 30 minutes after injection of [18F]-6-fluorodopamine, demonstrating that the emission in untreated animals was from radioactive labeling of the sympathetic storage vesicles. Decreased positron emission from denervated salivary glands confirmed that the tracer was concentrated in sympathetic neurons. Radioactivity in the gall bladder and urinary system depicted the hepatic and renal excretion of the tracer and its metabolites. Administration of tyramine or nitroprusside increased and ganglionic blockade with trimethaphan decreased the rate of loss of myocardial radioactivity. The results show that PET scanning after administration of [18F]fluorodopamine can be used to visualize sites of sympathetic innervation, follow the metabolism and renal and hepatic excretion of catecholamines, and examine cardiac sympathetic function.

Neuronal uptake and metabolism of 2- and 6-fluorodopamine: false neurotransmitters for positron emission tomographic imaging of sympathetically innervated tissues

The neuronal uptake and metabolism of 2-fluorodopamine (2F-dopamine), 6-fluorodopamine (6F-dopamine) and tritium-labeled dopamine were compared in heart, submaxillary gland and spleen of rats to assess the utility of 18F-labeled 2F- or 6F-dopamine for positron emission tomographic imaging of sympathetically innervated tissues. Tritiated dopamine with and without 2F- or 6F-dopamine, or tritiated 2F-dopamine alone, were injected i.v. into rats that were or were not pretreated with desipramine to block catecholamine neuronal uptake or with reserpine to block vesicular translocation of catecholamines. Tissue and plasma samples were obtained at intervals up to 1 hr after injections. At 1 hr after injection of tritiated dopamine, tritium-labeled norepinephrine, dopamine, dihydroxyphenylacetic acid and dihydroxyphenylglucol accounted for less than 2% of the tritium in plasma but up to 92% of that in tissues; tritiated norepinephrine accounted for 70% or more of the tritium in tissues. In contrast, at 1 hr after injection of tritiated 2F-dopamine, tritiated 2F-norepinephrine accounted for 30 to 46% of the tritium in tissues. Desipramine and reserpine pretreatment blocked the tissue accumulation of tritiated and fluorinated dopamine as well as their dihydroxy-metabolites, indicating that accumulation of exogenous norepinephrine and dopamine analogs was within sympathetic storage vesicles. Relative to the doses of dopamine precursors, less 2F- and 6F-norepinephrine accumulated in tissues than tritiated norepinephrine, due largely to inefficient beta-hydroxylation of fluorinated dopamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Elimination of REM sleep rebound in rats by alpha-adrenoreceptor blockers, phentolamine and phenoxybenzamine

Two alpha-adrenoreceptor blocking agents, phentolamine (5 mg/kg, IP) and phenoxybenzamine (10 mg/kg IP) were administered to rats deprived of rapid eye movement (REM) sleep for 24 hours to test the hypothesis that reduced noradrenergic transmission may abolish REM sleep rebound. The hypothesis was based on results from our previous studies which showed that administration to rats of diethyldithiocarbamate (DDC), a dopamine beta hydroxylase inhibitor, decreased the concentration of brain norepinephrine and reduced REM sleep permanently without the subsequent appearance of REM sleep rebound. Present results show that administration of both alpha-adrenoreceptor blockers abolished REM sleep rebound. At the time of maximum reduction of REM sleep, the concentration of 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MOPEGSO4), a final product of norepinephrine metabolism in the brain, was found increased in the whole brains of rats suggesting that the selected doses of the drugs were sufficient to produce effective central alpha-adrenergic receptor blockade. These data indicate that the action of both alpha-adrenoreceptor blocking agents in noradrenergic system was paralleled by the permanent loss of REM sleep and support the hypothesis implicating reduced noradrenergic transmission in elimination of REM sleep rebound.