Changes In Cell Parameters Research Articles

Structural Studies and Computer Simulation of the Inclusion of Aromatic Hydrocarbons in a Zinc 2,6-Naphthalene Dicarboxylate Framework Compound

We have examined the structural response of a zinc 2,6-naphthalene dicarboxylate framework solid, isostructural with MOF-105, to the inclusion during crystallization of dimethylformamide, benzene, toluene, and p-xylene. These compounds, which are made up of a stacked arrangement of four-connected layers, crystallize in the space group P21/c with [Zn2(ndc)2(DMF)2]·1.6DMF (1), a = 8.075(1) Å, b = 16.891(2) Å, c = 12.673(2) Å, β = 92.90(1)°, [Zn2(ndc)2(DMF)2]·C6H6 (2) a = 8.340(2) Å, b = 15.660(4) Å, c = 13.008(4) Å, β = 91.340(5)°, [Zn2(ndc)2(DMF)2]·C7H8 (3), a = 8.183(2) Å, b = 16.245(3) Å, c = 12.920(3) Å, β = 91.976(4)°, and [Zn2(ndc)2(DMF)2]·C8H10 (4), a = 7.973(2) Å, b = 16.946(3) Å, c = 12.922(3) Å, β = 92.798(4)°. The structure is found to include p-xylene with high selectivity from mixtures of xylene isomers. In the presence of only o- or m-xylene as an additive, the structure does not crystallize. The mobility of fully deuterated benzene and toluene within compounds 2 and 3 over the temperature ranges 123−294 and 173−294 K, respectively, has been measured by 2H NMR using the quadrupole echo technique. Benzene is found to execute rapid hopping around its C6 axis over the entire temperature range studied with an activation energy of 6(1) kJ mol-1. The only motion of the toluene is rapid rotation of the −CD3 group. Computational modeling of the structures successfully reproduces the crystal structures and the changes in unit cell parameters and indicates that the binding energies of m-xylene within the structure are less favorable than those for p-xylene, predominantly as a result of the distortion of the framework required to accommodate the m-xylene. These lower binding energies explain the high selectivity for the uptake of p-xylene during crystallization.

Nearly constant magnetic entropy change involving twoclosely spaced transitions in the compound LaFe11.375Al1.625

A large change in the magnetic entropy, |ΔS|, was observed in the Fe-basedNaZn13-typecompound LaFe11.375Al1.625,which was nearly temperature independent over a wide temperature range (an about 70 K spanfrom ∼ 140to 210 K). This behaviour of the magnetic entropy change is associated with twoclosely spaced magnetic transitions. X-ray diffraction investigation at differenttemperatures indicates that the crystal structure remains cubic, of NaZn13type, when the magnetic state changes with temperature, but the cellparameter changes dramatically at the first-order transition point.

Stepwise dehydration of Sr-exchanged heulandite: A single-crystal X-ray study

A Sr-exchanged heulandite crystal of composition Sr4.35Ca0.13(Al8.96Si27.04O72)·26H2O was used for stepwise dehydration experiments. The crystal was heated for approximately 12 h from room temperature to 250 ∞C in steps of 50 ∞C using an airflow-heater device. For single-crystal X-ray data collection the crystal was quenched to ‐173 ∞C with liquid-N2 on the diffractometer. Due to pronounced Sr order deviating from the topological symmetry C2/m, the structure was refined in space group Cm for each dehydration state. The initial H2O content of 26 molecules per formula unit (pfu) at room temperature decreased to 17 molecules pfu after heating at 250 ∞C. Heating to 270 ∞C mechanically destroyed the crystal and a completely dehydrated state could not be studied. The loss of H2O and accompanying migration of Sr caused a change of cell parameters: a and c slightly decreased, b decreased, and β remained invariant, leading to a reduction of the cell volume. As Sr loses H2O upon dehydration, it moves toward the C rings and forms stronger bonds to the tetrahedral framework. With increasing dehydration the A and B ring become slightly compressed and elongated. Initially highly populated Sr sites split into less populated sites caused by the loss of surrounding H2O molecules.

Finding positive meaning and its association with natural killer cell cytotoxicity among participants in a bereavement-related disclosure intervention.

This study tested the hypothesis that cognitive processing about a past bereavement would produce increases in goals and priorities indicative of finding positive meaning from the loss. It was further hypothesized that increases in meaning-related goals would be associated with changes in immune function, specifically increased natural killer cell cytotoxicity (NKCC). Cognitive processing was manipulated using written emotional disclosure. Forty-three women who had lost a close relative to breast cancer wrote about the death (cognitive processing/disclosure group) or about nonemotional topics weekly for 4 weeks. Contrary to predictions, written disclosure did not induce changes in meaning-related goals or NK cell parameters. However, women in both experimental groups who reported positive changes in meaning-related goals over the study period also showed increases in NKCC. Results suggest that prioritizing goals emphasizing relationships, personal growth, and striving for meaning in life may have positive biological correlates but that solitary written disclosure may not be sufficient to induce changes in these goals in response to a past bereavement.

Order-disorder phase transition inZn1−xMnxGa2Se4: Long-range order parameter versusx

The opportunity of the ${\mathrm{Zn}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}{\mathrm{Ga}}_{2}{\mathrm{Se}}_{4}$ $(0<~x<~1)$ series for exploring the possibilities of ordering-disordering processes as a function of x is shown. A pumping of Mn ions from one particular site of the crystal lattice to another occurs in this system on addition of Zn. As a consequence, the tetragonal diluted magnetic semiconductor ${\mathrm{Zn}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}{\mathrm{Ga}}_{2}{\mathrm{Se}}_{4}$ series exhibits an order-disorder phase transition at ${x}_{c}=0.50\ifmmode\pm\else\textpm\fi{}.01$ with ${(c/a)}_{c}=1.964\ifmmode\pm\else\textpm\fi{}.005.$ The disordering process is accompanied by an abrupt change in the tetragonal unit cell parameters c and $2\ensuremath{-}(c/a),$ a modification of the crystal lattice from defective chalcopyrite to defective stannite and a crossover from space group $I\ensuremath{-}4$ to $I\ensuremath{-}42\mathrm{m}.$ The order-disorder phase transition has been quantified through the direct determination of a long-range order parameter \ensuremath{\eta} within its whole range of existence $(0<~\ensuremath{\eta}<~1).$

X-ray diffraction analysis of lanthanum and titanium substituted lead zirconate

The change in the orthorhombic structure of PbZrO3 was studied as a function of the La substitution for Pb and Ti substitution for Zr. Two types of changes can occur: (1) a change in the atom coordinates toward the positions for a perfect cubic perovskite lattice; and (2) a change of orthorhombic unit cell parameters so that ao, bo, and co exactly fit with the cubic cell parameter ac. Therefore, ao=ac√2, bo=ac.2√2, and co=ac.2, where ao, bo, and co are the orthorhombic cell parameters, and ac is the cubic cell parameter. Substitution of Pb by La in the orthorhombic PLZT leads to both a change in atom coordinates and a change in unit cell parameters toward the perfect cubic structure, especially for La≥4. Substitution of Zr by Ti in the orthorhombic PLZT leads to similar atom coordinate changes, but the unit cell parameters do not change. The composition 0/92.5/7.5 contains a major tetragonal phase and a minor orthorhombic phase. There are only small differences in the orthorhombic structure between the A and the B composition of PLZT. The A composition has a structure closer to the cubic structure than the B composition.

Electrical properties of stoichiometric and non-stoichiometric calcium zirconate

Stoichiometric calcium zirconate and calcium zirconate with calcia or zirconia excess sintered bodies were prepared. Electrical properties of these materials were investigated at 950 °C using the dc four-probe and ac impedance spectroscopy methods. XRD analysis was used to determine the changes of cell parameters. The Rietveld method was used to refine calcium zirconate structure. The emf measurements of galvanic cells were used to determine the ionic transference numbers in the selected samples. Stoichiometric calcium zirconate appeared to be a rather poor and mixed electron-oxygen ion conductor, whereas calcium zirconate samples with excess of calcia or zirconia exhibit purely oxygen ion conductivity. In both cases, introduction of a respective cation excess led to the significant enhancement in conductivity. The simple point defect model for calcium zirconate with calcia or zirconia excess was proposed.

The high-temperatureP21/c-C2/cphase transition in Fe-free pyroxene (Ca0.15Mg1.85Si2O6): Structural and thermodynamic behavior

A high-temperature in situ single-crystal X-ray diffraction study was performed from room T to 1150 °C on two crystals of Fe-free P2 1 /c clinopyroxenes of composition Ca 0.15 Mg 1.85 Si 2 O 6 [cell parameters at room T: a = 9.651(2) Å, b = 8.846(2) Å, c = 5.202(1) Å, b = 108.38(2)°, V = 421.4 (2) Å 3 ] synthesized by isothermal annealing for 624 h at T = 1370 °C, P = 1 atm. A first order P2 1 /c-C2/c phase transition was found slightly below 1000 °C [T c = 926(39) °C]. The transition was revealed by discontinuous changes in intensities and cell parameters. Prolonged heating at high temperature induced a non-reversible increase in the transition temperature up to more than 1150 °C, without apparent changes in the order of the phase transition. Coupling with strain due to incipient exsolution in a formerly almost defect-free sample is suggested to be responsible for increase in T c . TEM observations of a sample from the same starting material after further annealing for 72 h at T = 1050 °C, P = 1 atm are consistent with the proposed incipient exsolution model. Annealing was found to induce the formation of a mottled texture oriented parallel to (101). Results from structure refinement of data collected below the transition at T = 25, 500, 650, 800, and 1000 °C showed only minor changes in the chain configurations, which are highly differentiated up to 1000 °C, confirming the strong first-order character of the transition.

Effects of commonly used fixatives on size parameters of freshwater planktonic protists

We tested the effect of four commonly used fixatives (Lugol's iodine, mercuric chloride, glutaraldehyde and formaldehyde) on cell length, width and volume of six species of freshwater planktonic protists. Most of the fixatives significantly influenced the cell dimensions of these species. Significant changes in the volume of protists, expressed as a percent of the average live cell volume, ranged from -64 to +59%. Changes in cell volume were highest for heterotrophic flagellates and scuticociliates, indicating that the biomass of these protists in freshwater systems has probably been underestimated in experiments in which volume estimates were based on fixed samples. The effects were, in the order of increasing change in cell parameters: formaldehyde < glutaraldehyde < Lugol's iodine < mercuric chloride. We observed differences between taxa in their response to the same treatment, particularly for the mercuric chloride fixation. In addition, opposite responses were noted for the scuticociliate species. In the light of our study and other works, we recommend the application of conversion factors of 1.4 and 1.7 for Lugol's and glutaraldehyde-fixed cells, respectively, to accurately estimate the biovolume of protists in fixed samples.

Polyethylene Unit Cell and Crystallinity Variations as a Consequence of Different Cross-Linking Processes

Changes of crystallinity and unit cell parameters for a low-density polyethylene as a consequence of cross-linking by dicumyl peroxide and by electron beam irradiations are compared. Polyethylene samples cross-linked by irradiation in the solid state present variations essentially only of the a unit cell parameter while those cross-linked in the melt state present similar variations of both a and b unit cell parameters. A strict analogy with unit cell variations observed for ethene random copolymers with propene and with bulkier comonomers, respectively, is shown. This suggests inclusion of cross-links for solid-state cross-linked samples, which would lead to a gradual transformation from an orthorhombic to a pseudohexagonal phase, and exclusion of cross-links for melt state cross-linked samples, which would generate tensions at the orthorhombic crystallite interphases.

High pressure and very low temperature effects on the crystal structures of some iron(II) complexes

Abstract The crystal structures at 30 K of two iron(II) complexes, and their comparison with higher temperature crystal structures indicate that, outside of the spin transition range, the only intramolecular modification comes from dynamical aspects. The contraction of the packing is strong from 110 to 30 K and similar in both complexes. The high pressure (0.16 GPa, 0.40 GPa) crystal structures of another iron(II) complex of the same family show that strong changes are induced under pressure within the packing but that, to a first approximation, the effects of temperature (11 K) or pressure (0.40 GPa) on the intermolecular contacts are very similar even though one S···C intermolecular contact is significantly different. Moreover, slight differences in the cell parameter changes are noted. We also show that the deformation of the iron(II) coordination sphere does not depend on the applied constraint but on the spin state only.

An unusual phase transition in the crystal structure and physical properties of (TTF)9[Mo(CN)8]2·4H2O, where TTF = tetrathiafulvalene

At 270 K, the charge transfer salt (TTF)9[Mo(CN)8]2·4H2O, I, crystallizes in the triclinic space group P with a = 9.9094(2), b = 10.6781(2), c = 23.6086(7) A, α = 75.7910(8), β = 88.6010(9), γ = 78.5250(8)°, V = 2372.5(1) A3 and Z = 2. At 120 K, the space group is unchanged with a = 9.7990(7), b = 10.6630(5), c = 22.9940(2) A, α = 79.981(4), β = 89.798(4), γ = 79.013(4)°, V = 2321.5 A3 and Z = 2. On comparing the two sets of data, we see significant changes in the cell parameters, most notably in the angle α. Variable temperature crystallographic studies indicate a first order phase transition accompanied by hysteresis, which corresponds to a change in the transport properties. I is a semiconductor and the high temperature activation energy of 0.06 eV changes sharply to 0.15 eV below 236 K. Bulk magnetic susceptibility and ESR measurements indicate that the TTF molecules are antiferromagnetically coupled. The temperature dependence of the EPR spectrum changes from 300–200 K, in approximate agreement with the transport and structural results. The optical spectrum of (TTF)9[Mo(CN)8]2·4H2O consists of several broad bands assigned to TTF charged molecules, to [Mo(CN)8]4− and to charge transfer from the donors to the acceptor in the near infra-red range. Preliminary magnetic susceptibility measurements under light irradiation with a multi-line (752.5–799.3 nm) laser were also performed, but no photomagnetic effect was noted.

The semicrystalline morphology of aliphatic–aromatic polyamide blends

The morphology of a series of melt-miscible blends based on the combination of (crystalline) polyamide (PA) 4,6 and (amorphous) PA 6I has been investigated as a function of blend composition and thermal history. Wide-angle X-ray scattering (WAXS) was used to determine the unit cell structure and crystallinity index in PA 4,6 and the blends: the introduction of PA 6I resulted in no change in unit cell parameters and a monotonic decrease in bulk crystallinity. Dynamic mechanical studies revealed the coexistence of two amorphous phases in the crystallized blends: a mixed phase held between the crystal lamellae (interlamellar) and a PA 6I-rich phase excluded to interfibrillar and interspherulitic regions. There was no evidence of a separate crystal–amorphous interphase layer comprised of pure PA 4,6. Transamidation reactions over longer melt times led to the apparent homogenization of the two amorphous populations owing to the formation of increasingly random copolymers.

Maximum strontium content of piemontite formed by hydrothermal synthesis

In order to determine the maximum solubility of strontium in piemontite, hydrothermal syntheses of piemontite in the join Ca2Al2Mn3+Si3O12(OH)-Sr2Al2Mn3+Si3O12(OH) were attempted at pressures of 200-300 MPa, temperatures of 500-600°C, and fO2 defined by Mn2O3-MnO2 and CuO-Cu2O buffers. Ca-piemontite crystallized as almost a single phase from a starting material of Ca2Al2Mn3+Si3O12.5-oxide mixture with excess H2O. Sr-bearing piemontites crystallized from starting materials containing both Ca2Al2Mn3+Si3O12(OH)- and Sr2Al2Mn3+Si3O12(OH)-components. They were accompanied by slawsonite (SrAl2Si2O8), bixbyite (Mn2O3) and other minor phases. Piemontite did not crystallize from Sr2Al2Mn3+Si3O12.5-oxide mixture with excess H2O at 300 MPa and 550°C; slawsonite+SrSiO3+SrSi2O5·H2O+Al2O3+bixbyite assemblage was formed instead. Synthesized piemontites had variable Sr contents between grains even in the same run product. But average Sr content of the synthesized piemontite increases with increasing Sr content in the starting material from Ca : Sr=2 : 0 to Ca : Sr=1 : 1. The Sr content of piemontite crystallized from starting material with Ca : Sr=1 : 1 reaches 19.65 wt% SrO, which corresponds to about one Sr2+ atom per formula unit (O12(OH)), but piemontite containing more than one Sr atom per formula unit did not crystallize from starting material with Ca : Sr=0.8 : 1.2. The a- and c-dimensions and cell volume increase with increasing Sr content of the starting material from Ca : Sr=2 : 0 to 1 : 1, and reach the upper limit at Ca : Sr=1 : 1. These changes in cell parameters and chemical compositions of the synthesized Sr-bearing piemontite indicate that Sr substitutes for Ca up to one atom per formula unit. The results show that the maximum content of Sr in piemontite is limited to one atom per formula unit, and are in agreement with the published view that Sr2+-ions occupy only the ten-coordinated A(2) site in natural Sr-bearing piemontites.

Additives for the crystallization of proteins and nucleic acids

Numerous molecules have been described in literature as additives that were indispensable either for nucleation or growth of macromolecular crystals. In some cases, such additives were shown to improve the quality of the X-ray diffraction and to extend diffraction limits. We have investigated the effects of more than fifty compounds, belonging to several chemical families, on the crystallization of four model proteins (hen and turkey egg-white lysozymes, thaumatin, and aspartyl-tRNA synthetase from Thermus thermophilus). In addition, we have studied the crystallization of a ribonucleic acid from yeast, the transfer RNA specific for phenylalanine in the presence of synthetic polyamines. Crystals grown in the presence of the additives were optically evaluated and X-ray diffraction analyses were performed on selective crystals to compare their space group, cell parameters, and diffraction limit with those of controls. Whereas no changes in space group nor cell parameters were observed for the model proteins, significant improvements in diffraction limit were found when the transfer RNA was crystallized with certain synthetic polyamines.

Endothelial viability of organ-cultured corneas following penetrating keratoplasty.

To assess endothelial integrity following corneal transplantation using human corneas stored in organ culture in the Manchester Eye Bank. A prospective study was undertaken on 24 patients who had received full-thickness corneal grafts using corneas stored in organ culture. The donor corneal endothelium was photographed prior to transplantation using light microscopy. Specular microscopy and ultrasonic pachometry were performed at 30 days (+/- 3 days), 12 weeks (+/- 1 week), 26 weeks (+/- 2 weeks) and 52 weeks (+/- 4 weeks) following corneal transplantation. The following cell parameters were measured: density, area, coefficient of variation (CV) for area, perimeter, diameter, form factor and corneal thickness. One year after corneal transplantation there was a statistically significant decrease in endothelial cell density (-39.4%), and a statistically significant increase in endothelial cell area (+94.4%), perimeter (+36.1%), diameter (+57.1%) and form factor (+5.8%). However, no significant changes were seen in CV or corneal thickness with respect to time after transplantation. (There were no significant changes in endothelial cell parameters and corneal thickness for 12 control subjects.) Endothelial cell loss occurs at an accelerated rate from corneal transplants. This highlights the need for improving corneal endothelial viability during and after storage in order to improve the chances of longer-term survival of the transplanted cornea.

Time-resolved simultaneous SAXS/WAXS studies of peek during isothermal crystallization, melting, and subsequent cooling

Time-resolved simultaneous small- and wide-angle x-ray scattering (SAXS and WAXS, respectively) of poly(aryl ether ether ketone) (PEEK) during isothermal crystallization, melting, and subsequent cooling were conducted using synchrotron radiation. Unit cell parameters were determined using WAXS measurements, and the dimensions of lamellar-level moieties were extracted from SAXS profiles. It was found that the changes in unit cell parameters were reversible on heating and cooling, and there were remarkable differences in the thermal expansion coefficients in different lattice directions. The long period L, the lamellar thickness lc , and the thickness of amorphous layers la were calculated from the correlation function, and the changes of these dimensions during the processes mentioned above were traced. Sharp decreases in L and lc in the initial stage of isothermal crystallization and cooling from melt were observed, and a corresponding continuous distributed model is proposed. When cooling from the melt, the invariant Q exhibited a maximum. The maximum is attributed to a change in the difference of the densities of crystalline and amorphous phases (ρc - ρa) with decreasing temperature.

Stoichiometric deviations along an ingot of CuGaSe2

The dependence of the structural parameters on compositional deviations of CuGaSe2 has been studied. These deviations have been induced along an ingot by a single fusion of the components at 1150 °C and subsequent slow cooling in a stationary ampoule in a vertical furnace. All along the sample a single chalcopyrite phase is present and a compositional gradient along the ingot was found by energy-dispersive analysis of X-rays (EDAX) measurements, the upper part being rich in Ga (series B) and the lower part in Cu (series A), with Cu/Ga ratios of 0·95 and 1·1 respectively. A hypothesis of the existence of two phases in the melt is proposed to explain these facts. The unit cell parameters, anion displacement and Cu and Ga occupation numbers in their sublattices were analysed by X-ray powder diffraction and Rietveld refinement methods. In series A the occupation numbers are near stoichiometry, while in series B a Cu defect appears. In both series, changes in unit cell parameter are related to changes in Cu content, suggesting the presence of a fraction of Cu ions either as interstitials or at Ga sites when Cu is in excess, or of Cu vacancies in its sublattice when there is a Cu deficiency. © 1998 John Wiley & Sons, Ltd.

A novel nonmetric multivariate approach to the evaluation of biomarkers in terrestrial field studies

This study evaluated the usefulness of using groups of biomarkers as measures of exposure and which statistical approach wouldbe most robust for analysing such data. We used both analysis of variance (ANOVA) and nonmetric cluster and associationanalysis (NCAA) to look for patterns in biomarker responses of populations of gray-tailed voles (Microtus canicaudus)in field enclosures exposed to azinphos-methyl (Guthion2S) at 0.0, 1.55 and 4.67 kg active ingredient(AI)ha-1 (four enclosures per treatment level). Biomarkers measured were hematocrit,total leukocyte counts, leukocyte differentiation, plasma lactate dehydrogenase (LDH), isocitratedehydrogenase, creatine phosphokinase (CPK) activities, and plasma creatinine and blood urea nitrogenconcentrations. Brain cholinesterase (AChE) activity was measured in a subset of animals. The ANOVAwas able to distinguish differences between treatment groups only for brain AChE. The NCAA confirmedthe ANOVA analysis that brain AChE activity differed significantly among the treatment groups. However,NCAA also identified LDH and CPK activity, and neutrophil and lymphocyte numbers as importantdiscriminants of pesticide treatment. Additionally, changes in blood cell parameters due to spatialgradients were layered over the effects due to the pesticide.

Gap Junction Change in Supporting Cells of the Organ of Corti with Ryanodine and Caffeine

It has been demonstrated that the gap junctions of the supporting cells of the organ of Corti are controlled by H+ and Ca2+. Inside these cells there is a tubular structure. It is supposed that this network is endoplasmic reticulum. Calcium release from inside the cells, and the effect of calcium on the gap junctions of these cells, were investigated under whole cell clamping application of ryanodine and caffeine. Membrane capacitance and membrane resistance were calculated with corrections for changes in whole cell parameters. Ryanodine-treated cells (1