Vapor Phase Equilibration Research Articles

Growth of noncongruent LiTaO3 crystal by chemical vapor phase equilibration using niobium‐based two‐phase powder

AbstractNoncongruent nearly stoichiometric/lithium‐deficient LiTaO3 crystal was grown by lithium‐rich/lithium‐deficient chemical vapor‐phase‐equilibration (VPE) technique, and low‐cost two‐phase powder LiNbO3‐Li3NbO4 or LiNbO3‐LiNb3O8 instead of expensive LiTaO3‐Li3TaO4 or LiTaO3‐LiTa3O8 was used in the VPE experiments. The LiTaO3 crystalline phase in the lithium‐rich/lithium‐deficient crystal was confirmed by X‐ray analysis. The lithium‐rich/lithium‐deficient VPE‐induced lithium‐oxide (Li2O) molar content increase/reduction was measured as a function of VPE duration using gravimetric method, and empirical relations between them are presented for both cases. We show that both the lithium‐rich and lithium‐deficient VPE techniques based on the two‐phase powder LiNbO3‐Li3NbO4 or LiNbO3‐LiNb3O8 can be successfully used to adjust the lithium‐oxide content in a LiTaO3 crystal and produce a noncongruent nearly stoichiometric or lithium‐deficient crystal plate with desired lithium‐oxide content.

Depression of the Glass Transition Temperature of Sucrose Confined in a Phospholipid Mesophase

The glass transition of sucrose in 1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine (DOPE)/sucrose mixtures was studied by differential scanning calorimetry. Mole ratios of 1:2, 1:1, and 2:1 DOPE/sucrose mixtures were dehydrated at osmotic pressures ranging from 41 to 311 MPa through vapor-phase equilibration. Two glass transitions were observed in 1:2 DOPE/sucrose mixtures that were dehydrated at osmotic pressures >81 MPa. The first glass transition temperature (Tg) was lower than that of pure sucrose solutions that were dehydrated under identical conditions. The second Tg of the 1:2 DOPE/sucrose mixture was similar to the Tg of sucrose solutions that were dehydrated in the absence of DOPE. In the 2:1 and 1:1 DOPE/sucrose mixtures, only one Tg was observed at a temperature lower than that of pure sucrose. We propose that depression of the Tg of sucrose in the DOPE/sucrose mixtures is the result of a confinement effect that occurs in the sucrose solution that is sequestered in the aqueous cores of the h...

Raman study on vapor-phase equilibrated Er:LiNbO3 and Er:Ti:LiNbO3 crystals

Raman spectra of Er:LiNbO3 crystal and Ti-diffusedEr:LiNbO3 strip waveguide, in which the Li/Nb ratio was altered using a vapor-phase equilibration (VPE) technique, were measured at room temperature in the wave-number range 50–3500 cm-1. Both 488 and 514.5 nm radiations were used to excite Raman scattering, A1(TO) and E(TO) modes were recorded at backward scattering geometry. The results indicated that the lattice vibrational spectra of the as-grown Er:LiNbO3 are almost the same as those of pure LiNbO3 except for the little shift of the peak position and the change of relative intensity of some peaks. In comparison with the spectra of as-grown Er:LiNbO3 crystal the vapor-phase equilibrated Er:LiNbO3 and Er:Ti:LiNbO3 crystals in the lattice vibrational region exhibit the following features: firstly, Raman peaks become narrow, indicating that the VPE process has brought Er:LiNbO3 and Er:Ti:LiNbO3 crystals closer to a stoichiometric composition; secondly, relative intensity of some peaks varies with the VPE time; and finally, slight blue shifting in peak position was observed. Some of these features were correlated with the NbO6 octahedra and with the site distribution of the doped Er ions. In addition, green fluorescence peaks and/or bands associated with the electron transitions 2H11/2?4I15/2 and 4S3/2?4I15/2 of the doped Er3+ were also observed. For 488 nm excitation they appear in the wavenumber range of 1200–3000 cm-1 and are well separated from lattice vibrational region; for 514.5 nm excitation, however, these fluorescence peaks shift towards the low wavenumber region and overlap partially with the lattice vibrational spectra.

Reversible conductivity control and quantitative identification of compensating defects in ZnSe bulk crystals

Donor compensation by associates of donor impurities and cation vacancies is investigated in vapor grown ZnSe : I and Al diffused melt grown bulk crystals. Both the (I SeV Zn) and the (Al ZnV Zn) A-centers could be identified by electron paramagnetic resonance (EPR) spectroscopy. The concentrations of the compensating defects can be reversibly changed by vapor-phase equilibration and a reproducible adjustment of room temperature (RT) carrier concentrations n e up to 1.4×10 18 cm −3 (ZnSe : I) and 2.7×10 18 cm −3 (ZnSe : Al) is possible. The results are explained in terms of a defect chemical model. The supposed high concentrations of one type of vacancy associated defects are confirmed using positron annihilation (PA). Lowered compensation leads to an increase of carrier mobility μ e with increasing n e. In low doped systems mobilities of 500 cm 2/Vs can be obtained. A similarly drastic shift of the absorption edge to lower photon energies is observed for both I- and Al-doped crystals.

Phase diagram of 1,2-dioleoylphosphatidylethanolamine (DOPE):water system at subzero temperatures and at low water contents

The phase behavior of partially hydrated 1,2-dioleoylphosphatidylethanolamine (DOPE) has been studied using differential scanning calorimetry and X-ray diffraction methods together with water sorption isotherms. DOPE liposomes were dehydrated in the H II phase at 29°C and in the L α phase at 0°C by vapor phase equilibration over saturated salt solutions. Other samples were prepared by hydration of dried DOPE by vapor phase equilibration at 29°C and 0°C. Five lipid phases (lamellar liquid crystalline, L α; lamellar gel, L β; inverted hexagonal, H II; inverted ribbon, P δ; and lamellar crystalline, L c) and the ice phase were observed depending on the water content and temperature. The ice phase did not form in DOPE suspensions containing <9 wt% water. The L c phase was observed in samples with a water content of 2–6 wt% that were annealed at 0°C for 2 or more days. The L c phase melted at 5–20°C producing the H II phase. The P δ phase was observed at water contents of <0.5 wt%. The phase diagram, which includes five lipid phases and two water phases (ice and liquid water), has been constructed. The freeze-induced dehydration of DOPE has been described with the aid of the phase diagram.

Crystallization and preliminary studies of lima bean trypsin inhibitor

Crystals of lima bean trypsin inhibitor (LBTI) were obtained by using the vapor phase equilibration technique with sodium/potassium tartrate as the precipitating agent. The space group was determined to be cubic, I213 with a= 110.2 Å. These crystals diffract to about 1.9 Å resolution. Preliminary analysis of self-rotation maps (calculated from native x-ray intensity data) suggests the presence of two monomers in the asymmetric unit. LBTI is very thermostable and retains activity even after boiling for 10 minutes. This property is exploited as part of its purification procedure. © 1997 Wiley-Liss, Inc.

Crystallization and preliminary studies of lima bean trypsin inhibitor

Crystals of lima been trypsin inhibitor (LBTI) were obtained by using the vapor phase equilibration technique with sodium/potassium tartrate as the precipitating agent. The space group was determined to be cubic, I2(1)3 with a = 110.2. A These crystals diffract to about 1.9 A resolution. Preliminary analysis of self-rotation maps (calculated from native x-ray intensity data) suggests the presence of two monomers in the asymmetric unit. LBTI is very thermostable and retains activity even after boiling for 10 minutes. This property is exploited as part of its purification procedure.

Crystallization and preliminary x‐ray crystallographic studies of recombinant bovine neurocalcin δ

Neurocalcins are novel brain-specific proteins that belong to a new subclass of the EF-hand super-family of calcium binding proteins, defined by the photoreceptor cell-specific protein recoverin (Terasawa et al., J. Biol. Chem. 267:19596-19599, 1992). Here we report the purification and crystallization of unmyristoylated recombinant bovine neurocalcin delta from Escherichia coli. Crystals of a bovine neurocalcin delta have been grown by macro-seeding at room temperature through vapor phase equilibration using the hanging drop technique with ammonium sulfate as the precipitating agent. The crystals diffract to at least 2.5 A resolution and belong to monoclinic space group P21 with unit cell dimensions a = 42.734 A, b = 94.343 A, c = 50.696 A, and beta = 98.37 degrees. The asymmetric unit contains two molecules, with corresponding crystal volume per protein mass (Vm) of 2.29 A3/Da and solvent fraction of 45% by volume, exhibiting an approximate 222 point symmetry.

Carboxylmethylation of the catalytic subunit of protein phosphatase 2A in insulin-secreting cells: evidence for functional consequences on enzyme activity and insulin secretion.

We report the carboxylmethylation of a 36-kDa protein in intact normal rat islets and clonal beta (INS-1) cells. This protein was predominantly cytosolic. Its carboxylmethylation, as assessed by vapor phase equilibration assay, was resistant to inhibition by N-acetyl-S-trans, trans-farnesyl-L-cysteine, a competitive substrate for cysteine methyl transferases. These data suggest that the methylated C-terminal amino acid is not cysteine. The methylated protein was identified as the catalytic subunit of protein phosphatase 2A (PP2Ac) by immunoblotting. The carboxylmethylation of the PP2Ac increased its catalytic activity, suggesting a key role in the functional regulation of PP2A. Therefore, we studied okadaic acid, a selective inhibitor of PP2A that acts by an unknown mechanism. Okadaic acid (but not 1-nor-okadaone, its inactive analog) inhibited (Ki = 10 nM) the carboxylmethylation of PP2Ac and phosphatase activity in the cytosolic fraction (from normal rat islets and clonal beta-cells) as well as in intact rat islets. Furthermore, methylated PP2Ac underwent rapid demethylation (t 1/2 = 40 min) catalyzed by a methyl esterase localized in islet homogenates. Ebelactone, a purported inhibitor of methyl esterases, significantly delayed (> 200 min) the demethylation of PP2Ac. Furthermore, ebelactone reversibly inhibited glucose- and ketoisocaproate-induced insulin secretion from normal rat islets. These data identify, for the first time, a methylation-demethylation cycle for PP2Ac in the beta-cell and suggest a key functional relationship between PP2A activity and the carboxylmethylation of its catalytic subunit. These findings thus suggest a negative modulatory role for PP2A in nutrient-induced insulin exocytosis.

Spectroscopic site determinations in erbium-doped lithium niobate.

Rare-earth (e.g., ${\mathrm{Er}}^{3+}$, ${\mathrm{Nd}}^{3+}$) based, guided wave optical amplification in lithium niobate (${\mathrm{LiNbO}}_{3}$) integrated optic systems is a new and important addition to the field of integrated optics. The application of total site selective spectroscopy to rare-earth-doped ${\mathrm{LiNbO}}_{3}$ provides the most complete spectroscopic characterization of this class of materials to date. In a previous publication we identified six spectroscopic sites in Er:${\mathrm{LiNbO}}_{3}$ using total site selective spectroscopy, two of which are cluster sites which upconvert light using nonradiative energy transfer between Er ions within a given site. In this paper ${\mathrm{Er}}^{3+}$ site identifications are made based on a consideration of solid solution defect equations in conjunction with an experimental study of the site distribution as a function of dopant concentration (0.4--2.0 mol % Er:${\mathrm{LiNbO}}_{3}$) and the Li/Nb ratio in the crystal. The Li/Nb ratio was altered using a vapor phase equilibration technique. Our results indicate that increasing the ${\mathrm{Li}}_{2}$O content of Er:${\mathrm{LiNbO}}_{3}$ not only reduces the cluster site concentration by \ensuremath{\sim}30% but also increases the amount of light absorbed in the crystal by \ensuremath{\sim}15%. This observation is, to the best of our knowledge, the first report of post growth materials processing in rare-earth-doped ${\mathrm{LiNbO}}_{3}$ to effect a change in absorption or cluster site concentration. In addition, increasing the dopant concentration increases ${\mathrm{Li}}_{2}$O deficiency in Er:${\mathrm{LiNbO}}_{3}$ crystals. Simple solid solution defect model calculations agree with these experimental results. \textcopyright{} 1996 The American Physical Society.

Crystallization and preliminary X-ray investigation of barstar, the intracellular inhibitor of barnase.

Crystals of barstar, the intracellular inhibitor of the extracellular ribonuclease produced by Bacillus amyloliquefaciens (barnase), were obtained through vapor phase equilibration using the hanging drop technique. Three crystal forms have been characterized. Forms I and II, crystallized either in potassium phosphate or sodium citrate, are tetragonal; they exhibit a superstructure along the c-axis. Form III crystals, suitable for a high resolution structure determination, were grown from 55-65% ammonium sulfate. This crystal form is hexagonal and diffracts to at least 2 A resolution at a synchrotron radiation source. It belongs to the hexagonal space group P6, with unit cell dimensions a = b = 143.6 A, c = 35.6 A. There are four molecules of barstar in the asymmetric unit. X-ray data have been collected to 2.2 A Bragg spacing. The structure determination is underway in order to analyze conformational changes of barstar upon complexation with barnase.

Biochemical characterization and crystallization of porin from Rhodopseudomonas blastica

Oligomeric porin of the phototrophic bacterium Rhodopseudomonas blastica DSM 2131 was obtained from cell envelopes by differential temperature extraction in the presence of detergent and salt. The isolated porin exhibited strong porin activity after reconstitution into lipid bilayer membranes. The effective channel diameter for the trimer was estimated as 1.5 nm from single channel conductance measurements in the presence of 1 M KCl. Moderate cation-selectivity was observed. Oligomeric porin migrated as a single band (apparent molecular weight 81 kDa) on sodium dodecyl sulfate polyacrylamide gelelectrophoresis when solubilized below 70 °C. The oligomers were converted into monomers on heating to 70 °C or above forming two bands with apparent molecular weight of 36 kDa and 35 kDa. The oligomer was not sensitive to EDTA. Its molecular weight was determined to be 119.3 kDa by analytical ultracentrifugation. The isoelectric point was 5.7. Circular dichroism data indicated a high content of β-sheet structure. Gasphase sequencing of the N-terminal residues revealed the sequence: NH2-Glu-Ile-Ser-Leu-Asn-Gly-Tyr-Gly-Arg-Phe. Crystals with a maximal side length of 300 μm and diffracting to 0.32 nm resolution were obtained with the porin oligomer in the presence of C8E4 and 1,2,3-heptanetriol by using the vapor phase equilibration technique.

Crystallization and preliminary X‐ray diffraction studies of dogfish C‐reactive protein

Crystals of dogfish (Mustelus canis) C-reactive protein were obtained through vapor phase equilibration using the sitting drop rod technique with ammonium sulfate as the precipitating agent. The space group was determined to be P1 (triclinic lattice) with unit cell dimensions of a = 82.91, b = 92.25 and c = 103.40 A; alpha = 83.36 degrees, beta = 89.76 degrees, and gamma = 81.30 degrees. These crystals diffract to about 2.6 A resolution and contain two hexamers in the asymmetric unit.

A versatile reactor for temperature controlled crystallization of biological macromolecules

Accurate control of crystallization conditions, and accordingly reproducibility of experiments, is often hampered by the lack of adequate instrumentation in the laboratory. A versatile and inexpensive crystallization reactor allowing crystal growth by vapor phase equilibration (sitting, hanging or sandwiched drops) or by the batch technique is described here. In this reactor, temperature is controlled accurately by a Peltier device and the crystallization process monitored by a time-lapse video recorder. An application for evaluating the growth kinetics of tetragonal lysozyme crystals as a function of temperature is given. It was observed that the apparent growth rate decreased when temperature was lowered, although under such conditions supersaturation was increased and crystals appeared sooner.

Experiences with HANGMAN: a macromolecular hanging drop vapor diffusion technique

A variant of the hanging drop vapor diffusion microtechnique is presented which uses an adhesive tape surface to simultaneously support protein droplets and seal reservoir solutions. The tape is supported on a teflon and plexiglas framework during setup of the experiment. The framework containing the protein solution droplets can be inverted over a standard tissue culture plate conyaining reservoirs of solutions for vapor phase equilibration. The time and cost of set up are reduced using the adhesive tape crystallization technique (HANGMAN). Up to 24 protein droplets can be inverted simultaneously using the tape with framework as opposed to individual inversion with coverslips. No pretreatment of tape or plates is required prior to experimental setup. There have been no effects observed on crystallization of proteins due to the adhesive. The adhesive surface shows resistance to a wide variety of chemicals commonly used for macromolecular crystallization. Protein crystals do not adhere to the hydrophobic adhesive surface and are easily removed for use in diffraction experiments.

Crystallization and preliminary X-ray diffraction studies of recombinant rabbit interferon-gamma

Two different crystal forms of recombinant rabbit IFN-γ were obtained under different crystallization conditions. The first, a tetragonal form with space group P4 32 12 or P4 12 12, was obtained through vapor phase equilibration using the sitting drop rods technique with ammonium citrate as the major precipitating agent. The unit cell dimensions of this crystal form are a = b = 82.1 A ̊ and c = 116.3 A ̊ . These crystals diffract to 2.8 Å resolution and contain a dimer in the asymmetric unit. A second crystal form was obtained by the batch method at pH 8.0 using sodium chloride as the precipitating agent. The crystals are hexagonal, space group P6 122 or P6 522, and with unit cell dimensions of a = b = 58.0 A ̊ and c = 169 A ̊ . This form contains monomer in the asymmetric unit and diffracts to greater than 2.7 Å resolution. Both forms appear to be eminently suitable for further analyses and crystal structure solution.

Crystallization and preliminary X-ray analysis of porin from Rhodobacter capsulatus

Porin monomers of the phototrophic bacterium Rhodobacter capsulatus were purified. Crystals were obtained from a solution of porin solubilized with the detergent octyltetraoxyethylene within 5 days using the vapor phase equilibration technique. The crystals were rhombohedral with an edge length of 0.4 mm. The space group was trigonal R3 with unit cell constants of a= b=95 Å, c=147 Å. Reflexions were observed to 3.2 Å.

Titanium diffusion into LiNbO3 as a function of stoichiometry

The diffusivity of Ti into LiNbO3 has been measured as a function of crystal orientation and Li/Nb ratio in the temperature range 980–1112 °C. The Li/Nb ratios of single crystal samples were adjusted by vapor phase equilibration with fixed Li2O activities. No anisotropy of diffusivity with crystal orientation could be detected. The diffusion constants for Ti in LiNbO3 decrease with increasing Li2O content. At 1050 °C, the values decrease from 2.60×10−12 cm2/s at the Li2O-deficient phase boundary (48.1 mol % Li2O) to 1.06×10−12 cm2/s at the congruently melting composition at (48.6 mol % Li2O) to 0.4×10−12 cm2/s at the Li2O-rich phase boundary (50.0 mol % Li2O). It is suggested that enhanced lateral diffusion observed for stripe geometry Ti sources results from increased diffusivity in a surface layer formed by Li2O outdiffusion.

Novel uses of the thermo-microbalance in the determination of nonstoichiometry in complex oxide systems

New uses of the thermo-microbalance are possible when studying complex oxide systems such as PbO-La2O3-ZrO2-TiO2 that incongruently and preferentially vaporize a single component. Several vapor phase equilibration procedures are possible when the microbalance is equipped with constant activity multiphase (CAMP) crucibles designed to provide an equilibrium source of, or sink for, PbO vapor. The compositional range of a compound's single-phase stability can be directly determined at temperature. The ionic substitutional lattice site, ionic valence, and resultant charge compensation mechanism that is associated with the solution of an impurity oxide into A-B-O compounds can be inferred from gravimetric data. The methods are applicable to the controlled sintering of these materials. An expanded version of the Knudsen effusion experiment is discussed whereby extensive information of the thermodynamics, phase equilibria, and nonstoichiometry of the oxide system can be generated by a single gravimetric experiment. The binary PbO-TiO2 system is offered as an illustration.

Intrinsic nonstoichiometry in the lead zirconate-lead titanate system determined by Knudsen effusion

The range of the intrinsic nonstoichiometry in lead zirconate-titanate at 1100 °C has been established independently by two gravimetric techniques. A modified Knudsen effusion experiment allowed for an extended interpretation of the vapor pressure data. A single experiment was used to determine the width of any Pb1−x □x (TiyZr1−y)O3−xφx single-phase region, the equilibrium PbO vapor pressure, activity data as a function of both temperature and composition, and the exact location of the stoichiometric composition within the single-phase region. The ``vapor phase equilibration'' (VPE) method was used as a supplemental measurement of the width of most PZT single-phase regions. Results obtained by the two methods for the extent of nonstoichiometry were in close agreement (xmax = 0.10 at y = 1.0; xmin = 0.016 at y = 0.40; T = 1100°C). The Knudsen effusion experiment established that for all the compositions studied, the stoichiometric composition, Pb(TiyZr1−y)O3, was coincident with the (liquid + PZT) phase boundary.