N2 Stream Research Articles

3′-Azidothymidine Potently Inhibits the Biosynthesis of Highly Branched N-Linked Oligosaccharides and Poly-N-acetyllactosamine Chains in Cells

3′-Azidothymidine Potently Inhibits the Biosynthesis of Highly Branched N-Linked Oligosaccharides and Poly-N-acetyllactosamine Chains in Cells

EFFECT OF AGING ON PARTICLE SIZE AND OXIDATION RATE IN THE FORMATION OF NEEDLE-LIKE GOETHITE PARTICLES BY AIR OXIDATION OF AQUEOUS FERROUS HYDROXIDE SUSPENSION

Needle-like goethite particles were synthesized by air oxidation of an alkaline suspension of ferrous hydroxide using a standard-type bubble column of 10cm in internal diameter and 64 cm in height at a constant temperature of 40°C. Specifically, the effect of aging step by N2 stream prior to the oxidation step was investigated on both the oxidation rate and the final particle size based on the major axis of needle-like goethite particle. The time dependence of the fractional oxidation of total ferrous species with incorporated aging step exceeded that in the absence of aging step. The velocity of N2 in the aging step had negligible influence on the time dependence of the fractional oxidation. For the aging period exceeding 30min, the mean particle size was almost independent of the aging period. The mean size could be correlated considerably well with the oxidation rate, that is, decreased with increasing oxidation rate with and without incorporated aging step.

Thermophoretic Mist Deposition onto a Tube Wall Cooled by Liquid Nitrogen

Variations of the concentration of water components (vapor + mist) at the outlet of an open-column cold trap with time are determined under different gaseous streams of N2, He, and H2. Ice mist generated in the trap is deposited from a laminar convection flow in a vertical circular tube onto a wall surface cooled by liquid nitrogen. The mist deposition rate from the He or H2 stream is greater than that from the N2 stream at the same volumetric flow rate and inlet water vapor pressure. This is because a thermophoretic force acts on mist particles more strongly in the He and H2 streams than in the N2 stream. The experimental mist deposition rate is compared with calculations using previous theoretical equations on thermophoresis. The open-column cold trap cooled by liquid nitrogen shows good performance to remove ice mist almost completely from gaseous streams with a comparatively small velocity.

Preparation of Long-chain Esters of Starch Using Fatty Acid Chlorides in the Absence of an Organic Solvent

An efficient method of synthesizing fatty acid esters of starch without organic solvents is described. The octanoate of starch was prepared by gelatinization of native starch with formic acid, followed by treatment with octanoyl chloride. Esterification was readily carried out under a stream of N2 at a stirring rate of 500 min -1 at 25—130°C for a reaction duration of 20—120 min. Formic acid enabled esterification of starch by long-chain acyl chlorides with minimum degradation. The major factors affecting the esterification reaction were optimized. The results indicated that the octanoyl degree of substitution (DS8) was increased with increase in fatty acid chloride concentration (from 3—12 eq. per anhydroglucose unit) and rise in temperature (25°C to 130°C). Higher octanoyl chloride concentrations and temperatures led to a reduction in yield due to acid hydrolysis of starch chains. A maximum DS8 of 1.7 was reached after 40 min of reaction, and high concentrations of formic acid decreased the octanoyl substitution. On the other hand, higher concentration of octanoyl chloride, higher temperatures and longer reaction times increased the substitution of the long acyl chain into starch.

Trivaric Acid, a New Tridepside in the Ramalina americana Chemotype Complex (Lichenized Ascomycota: Ramalinaceae)

Trivaric Acid, a New Tridepside in the Ramalina americana Chemotype Complex (Lichenized Ascomycota: Ramalinaceae)

Effect of raw materials on carbothermal reduction synthesis of γ-aluminum oxynitride spinel powder

The effect of starting Al2O3 materials on synthesis of γ-aluminum oxynitride spinel (γ-AlON) powder by carbothermal reduction has been investigated. Whether using Al(OH)3, boehmite, dried gel, or calcined alumina as an alumina source, the reaction rate is faster than that using α-Al2O3. That is because the oxygen distribution in γ-Al2O3 is cubic close packed as the non-metal arrangement in AlON spinel is whereas that in α-Al2O3 is hexagonal close packed. When hydrated aluminas used lose structural water and transform into γ-Al2O3 in heating cycle, γ-Al2O3 is easily reduced and nitrided into AlON spinel after a slight adjustment in the cation positions and proportions is made in the reduction process of alumina. The particle morphology of the product after carbothermal reduction was strongly influenced by the type of alumina source employed, which suggests the mechanism of Al2O3/C powder mixtures in a flowing N2 stream is the absorption of aluminum-containing gas, such as Al(g), Al2O(g), etc., on the surface of aluminum oxide in the initial stages, followed by reaction with N2 gas to form AlON and AlN phases with nucleation, and growth on Al2O3 particle surfaces.

Metalorganic Chemical Vapor Deposition Growth of GaN Using a Split-flow Reactor

We developed a split-flow reactor for growing epitaxial films in an atmospheric metalorganic chemical vapor deposition (MOCVD), where the reactant gas stream is separated from the wall by a buffer gas stream. This reduces the use of reactant gases, thereby minimizing operating costs. Wall deposits were also minimized. The reactor was fan-shaped with an inclined upper wall. To reduce the interdiffusion of the reactant and buffer streams, the substrate was placed upstream, near the gas inlet. The downward inclined upper wall maintains a constant cross sectional area and therefore constant velocity in the radial direction. The result is that the flow is stabilized. We demonstrated this reactor by growing undoped GaN epitaxial films on a two-inch substrate using a two-step growth process, where the epitaxial layer is grown on a buffer layer. The highest quality GaN films were grown using a buffer stream of H2, but the lowest consumption of the reactant gases was achieved using a buffer stream of N2.

Characterization and Low‐Temperature Sintering of Reactive Mn‐Zn Ferrite Powder

Highly sinterable Mn‐Zn ferrite powder consisting of sub‐micrometer‐size particles with structural distortion has been prepared by grinding a coprecipitated powder with a media agitation mill. Dense pure Mn‐Zn ferrites (>98% of theoretical) with an average grain size of 1.9 μm can be fabricated by heating at 900°C in a stream of N2. They show high permeability of 820 at 10 kHz through 1 MHz and an electric resistivity of 50 Ω cm at 1 kHz.

Phosphatidylinositol 4,5-Bisphosphate Binding to the Pleckstrin Homology Domain of Phospholipase C-δ1 Enhances Enzyme Activity

The pleckstrin homology (PH) domain is a newly recognized protein module believed to play an important role in signal transduction. While the tertiary structures of several PH domains have been determined, some co-complexed with ligands, the function of this domain remains elusive. In this report, the PH domain located in the N terminus of human phospholipase C-delta1 (PLCdelta1) was found to regulate enzyme activity. The hydrolysis of phosphatidylinositol (PI) was stimulated by phosphatidylinositol 4,5-bisphosphate (PIP2) in a dose-dependent manner with an EC50 = 1 microM (0.3 mol%), up to 9-fold higher when 5 microM (1.5 mol%) of PIP2 was incorporated into the PI/phosphatidylserine (PS)/phosphatidylcholine (PC) vesicles (30 microM of PI with a molar ratio of PI:PS:PC = 1:5:5). Stimulation was specific for PIP2, since other anionic phospholipids including phosphatidylinositol 4-phosphate had no stimulatory effect. PIP2-mediated stimulation was, however, inhibited by inositol 1,4, 5-triphosphate (IP3) in a dose-dependent manner, suggesting a modulatory role for this inositol. When a nested set of PH domain deletions up to 70 amino acids from the N terminus of PLCdelta1 were constructed, the deletion mutant enzymes all catalyzed the hydrolysis of the micelle forms of PI and PIP2 with specific activities comparable with those of the wild type enzyme. However, the stimulatory effect of PIP2 was greatly diminished when more than 20 amino acid residues were deleted from the N terminus. To identify the specific residues involved in PIP2-mediated enzyme activation, amino acids with functional side chains between residues 20 and 40 were individually changed to glycine. While all these mutations had little effect on the ability of the enzyme to catalyze the hydrolysis of PI or PIP2 micelles, the catalytic activity of mutants K24G, K30G, K32G, R38G, or W36G was markedly unresponsive to PIP2. Analysis of PIP2-stimulated PI hydrolysis by a dual substrate binding model of catalysis revealed that the micellar dissociation constant (Ks) of PLCdelta1 for the PI/PS/PC vesicles was reduced from 558 microM to 53 microM, and the interfacial Michaelis constant (Km) was reduced from 0.21 to 0.06 by PIP2. The maximum rate of PI hydrolysis (Vmax) was not affected by PIP2. These results demonstrate that a major function of the PH domain of PLCdelta1 is to modulate enzyme activity. Further, our results identify PIP2 as a functional ligand for a PH domain and suggest a general mechanism for the regulation of other proteins by PIP2.

Determination of Phenylbutazone Residues in Bovine Milk by Liquid Chromatography with UV Detection

A published liquid chromatographic (LC) method was modified for quantitation of phenylbutazone (PBZ) residues in the range of 25-300 ng/mL in bovine milk. Milk samples (1 mL) were diluted with absolute ethanol and 25% NH4OH. Diethyl ether and petroleum ether were added sequentially to the milk extract and the mixture was agitated on a Vortex mixer to partition out milk fat. The organic phase was removed and discarded. Tetrahydrofuran-hexane (1 + 4) was added to the aqueous phase and the extract was acidified with 3M HCl. The samples were mixed on a Vortex mixer for 30 min, and centrifuged. The organic layer, containing PBZ, was transferred to a clean test tube. The organic solvents were evaporated to dryness under a stream of N2 at room temperature. The resulting extract was dissolved in 1 mL mobile phase and filtered before injection. The chromatographic system was a C18 reversed-phase column connected to a UV detector set at 264 nm. Recoveries of PBZ from raw bovine milk fortified at 25-300 ng/mL ranged from 79 to 84%; relative standard deviations (RSDs) ranged from 6 to 7%. The RSDs for incurred PBZ quantitated from 34 to 229 ng/mL ranged from 1 to 4%.

Hollow‐fiber membrane‐based rapid pressure swing absorption

AbstractA novel gas purification technique called rapid pressure swing absorption (RAPSAB) was developed by integrating the best features of membrane contacting, gas‐liquid absorption, and pressure swing adsorption (PSA). In this cyclic separation process, a well‐packed microporous hydrophobic hollow‐fiber module was used to achieve nondispersive gas absorption from a high‐pressure feed gas into a stationary absorbent liquid on the module shell side during a certain part of the cycle followed by desorption of absorbed gases from the liquid in the rest of the cycle. The total cycle time varies between 20 s and upwards. Separation of mixtures of N2 and CO2 (around 10%) where CO2 is the impurity to be removed was studied using absorbent liquids such as pure water and a 19.5% aqueous solution of diethanolamine (DEA). Three RAPSAB cycles studied differ in the absorption part. Virtually pure N2 streams were obtained with DEA as absorbent demonstrating the capability of bulk separation to very high levels of purification. Numerical models developed predict the extent of purification for pure water and the DEA solution for one of the simpler cycles. Model simulations describe the observed behavior well.

Synthesis and Pyrolysis of Polyborosilazane with Low Oxygen Content

Polyborosilazane with a low oxygen content was synthesized by reacting perhydrosilazane with tris (dimethylamino) borane. The chemical structure of this polymer was investigated by infrared and nuclear magnetic resonance spectroscopies. The borazine ring structure was observed in the polymer. Amorphous silicon nitride was obtained by pyrolysis of this polymer in a stream of N2 at 1000°C with about 80mass% ceramic yield. The pyrolysis product remained amorphous after further heating to 1700°C under N2. The oxygen content in the pyrolysis product was 1.1mass%. Crystallization to β-Si3N4, β-SiC and α-Si3N4 took place on annealing in N2 at 1800°C for 1h. These results indicate that this polyborosilazane is a good precursor for amorphous silicon nitride-based materials with low oxygen content.

Determination of Nitrophenol Pesticides in Mineral Water and Tap Water by HPLC with Ultraviolet and Amperometric Detection

A simultaneous analytical method was developed for 9 nitrophenol pesticides and 2 aromatic nitro pesticides in drinking water by HPLC. The analytical HPLC was run on a Wakosil II 3C18AR column (4.6mm i. d. ×15cm) with a gradient formed from A: 0.1M monochloroacetic acid (pH 2.5)-MeCN-0.01M sodium butanesulfonic acid (10:30:60) and B: 0.1M monochloroacetic acid (pH 2.5)-MeCN (10:90), UV detection at 280nm and amperometric detection (AMD) with a glassy-carbon electrode (+1.2V). A drinking water sample was adjusted to pH 4 with 0.1M hydrochloric acid and purified on a Sep-pak Plus PS-2 cartridge. The cartridge was washed with water, and retained substances were eluted with MeCN. The eluate was concentrated under an N2 stream and was analyzed by HPLC. Recoveries for pesticides spiked into drinking water were 58.0-98.6% at the level of 20μg/L. The detection limits of these pesticides in water are 1μg/l.

Incorporation of OH species in fluorozirconate glasses: nature and influence on physical properties

Abstract The main purpose of the present study is to correlate the presence of controlled amounts of residual OH groups with the values of several physical properties, namely, the characteristic temperatures, linear thermal expansion coefficient, density, refractive index, microhardness, ultrasonic velocities, elastic constants and infrared transmission of ZrF4-based fluoride glasses. A series of glass samples were prepared in the ZrF4BaF2LaF3AlF3NaF system, with increasing NaF contents. Batches for the reference (dry) glass samples were first dried in a vacuum oven and were then melted in Pt crucibles in a dry box filled with high purity N2. Weakly hydrated glasses were prepared according to a similar procedure, but the batches were kept in water vapor saturated atmosphere for at least 24 h before fusion. Strongly hydrated glasses were melted in a fume hood, under a water vapor saturated stream of N2. For levels of OH incorporation up to 8 × 10−4 mol l−1 for ZBLA, 1.0 × 10−3 mol l−1 for ZBLAN6.6 and 1.5 × 10−3 mol l−1 for ZBLAN17.8, the density, refractive index and glass transition temperature, Tg, decrease with increasing OH content (by 0.8%, 0.25% and 3.0%, respectively) is similar to what has been observed for v-SiO2. At OH levels greater than 8 × 10−4 mol l−1 for ZBLA, 1.0 × 10−3 mol l−1 for ZBLAN6.6 and 1.5 × 10−3 mol l−1 for ZBLAN17.8, an increase in physical properties, such as the density, refractive index and Tg with increasing OH content, was noticed (of 0.8%, 0.4% and 2.8%, respectively), similar to what has been observed in silicate glasses. This behavior strongly suggests the presence of hydrogen bonded ZrOH species. A structural model is proposed for a typical fluorozirconate ZBLAN glass, based on structural data and physico-chemical properties. The model allows a correlation between the effect of residual OH groups and the values of some of the most representative properties of these glasses.

Determination of Gaseous and Dissolved Oxygen in a Closed Fat Cell Culture System

A novel method facilitates the determination of O2 content in the gas phase and in the culture medium of closed cell culture systems: Total O2 was swept out for 3 min by a stream of N2 under atmospheric pressure and carried to the measuring unit of a PBI Dansensor TIA-111-LV oxygen sensor, creating a peak-shaped signal, which was integrated over time. From the peak area, gas flow (determined by a Rotameter flow meter), and actual gas pressure and temperature, O2 content was calculated. The precision of the method was 1.1% (CV), recovery was 97.7%. O2 uptake was measured in white adipocytes, isolated by the collagenase method and cultured in a 3D matrix of agarose gel. As a basis of reference, DNA content of the cultures (9.5 pg/cell) was determined by a fluorimetric method. The viability of the cells was not affected by O2 determination, as shown by the maintenance of cellular adenine nucleotide content during the analytic procedure. The decline of O2 content in the cultures was constant over 72 h. The mean rate of cellular O2 consumption was 34.1 μmol/μg DNA·h.

Ferric Leghemoglobin in Plant-Attached Leguminous Nodules.

Leghemoglobin (Lb) is essential for nitrogen fixation by intact leguminous nodules. To determine whether ferric Lb (Lb3+) was detectable in nodules under normal or stressed conditions, we monitored the status of Lb in intact nodules attached to sweet clover (Melilotus officinalis) and soybean (Glycine max [L.] Merr.) roots exposed to various conditions. The effects of N2 and O2 streams and elevated nicotinate levels on root-attached nodules were tested to determine whether the spectrophotometric technique was showing the predicted responses of Lb. The soybean and sweet clover nodules' Lb spectra indicated predominantly ferrous Lb and LbO2 in young (34 d) plants. As the nodule aged beyond 45 d, it was possible to induce Lb3+ with a 100% O2 stream (15 min). At 65 d without inducement, the nodule Lb status indicated the presence of some Lb3+ along with ferrous Lb and oxyferrous Lb. Nicotinate and fluoride were used as ligands to identify Lb3+. Computer-calculated difference spectra were used to demonstrate the changes in Lb spectra under different conditions. Some conditions that increased absorbance in the 626 nm region (indicating Lb3+ accumulation) were root-fed ascorbate and dehydroascorbate, plant exposure to darkness, and nodule water immersion.

Synthesis and Pyrolysis of Thermosetting Copolymer of Polysilastyrene and Perhydropolysilazane

Copolymer of polysilastyrene and perhydropolysilazane was obtained by the reaction of polysilastyrene with zirconium n-butoxide and perhydropolysilazane. Zirconium n-butoxide and perhydropolysilazane were essential to render the thermosetting property. The thermosetting copolymers were converted into silicon carbide-based ceramics by pyrolysis at 1000°C in a stream of N2 with about 80 mass% ceramic yield. The main phase of the pyrolysis product at 1500°C in N2 was small crystallite β-SiC. Free carbon, based on rule-of-mixtures composition in the final ceramics could be reduced by varying the ratio of polysilastyrene/perhydropolysilazane. The copolymer was dry spun and pyrolyzed to produce a ceramic fiber. Pyrolysis in N2 at 1500°C yielded a silicon carbide-based fiber. Tensile strength of 1.0 GPa and elastic modulus of 190 GPa were obtained for the fiber from 10 to 12μ in diameter. Crystallization to α-Si3N4, β-Si3N4, β-SiC, and ZrN proceeded on annealing in N2 at 1700°C for 1 h.

Determination of Triazolam and Its Metabolites in Human Urine by EMIT, Gas Chromatography-Mass Spectrometry and Thermospray Liquid Chromatography-Mass Spectrometry.

EMIT, gas chromatography-mass spectrometric (GC-MS) and thermospray high performance liquid chromatography-mass spectrometric (LC-MS) methods for the determination of triazolam (TRZ) and its metabolites (1-hydroxymethyltriazolam (α-HT) and 4-hydroxytriazolam (4-HT)) in the human urine were investigated. TRZ was analyzed by EMIT st Urine Benzodiazepine Assay. EMIT cutoff was 50 ng/ml of TRZ. TRZ and its metabolites were extracted from the human urine using Sep-Pak C18 cartridge with dichloromethane-methanol (90 : 10 v/v) as the eluent. The eluate was evaporated to dryness under stream of N2. The residue was dissolved in 1 ml of methanol, 50 μl was injected into the LC-MS. LC analyses were performed on a TSKgel Octyl-80Ts in the solvent system of 100 mM ammonium acetate-methanol (50 : 50 v/v) at a flow rate of 1.0 ml/min. For GC-MS, the extract was derivatized at 90°C for 30 min with 50 μl BTZ. GC analyses were performed on a fused silica column DB-1. The column temperature was 290°C. The detection limits of these compounds by scan mode were 800 ng/ml for α-HT and 4-HT with GC-MS, 50 ng/ml for TRZ and α-HT, 100 ng/ml for 4-HT with LC-MS and those by selected ion monitoring mode were 50 ng/ml for α-HT, 100 ng/ml for 4-HT with GC-MS, 5 ng/ml for TRZ and α-HT, 10 ng/ml for 4-HT with LC-MS.

Effect of chemical additives on microfibre formation from SiO vapour condensed in flowing gas streams

SiO vapour has been allowed to condense from flowing gas streams in the presence of a wide range of inorganic and organic vapour species to determine the effect of these species on the known habit of SiO of condensing to form microfibres of potential use as reinforcing fillers. Major changes in fibre morphology have been observed on condensation of SiO in an N2 stream containing gaseous AlCl3, GeCl4 or C2H2, or by condensation of SiO with other molecular species formed when Ga2O3–SiO2–Si, In2O3–SiO2–Si or GeO2–SiO2–Si mixtures were heated in N2 or B–SiO2 was heated in H2. The fibre morphology changed surprisingly little when SiO was condensed with vapours of transition-metal halides. The products were studied by transmission electron microscopy (TEM), IR, X-ray photoelectron spectroscopy (XPS) and powder XRD. The work establishes that condensing SiO is an exceptionally versatile microfibre-forming system.

A method of calibration of the formic acid monomer concentration in the gas phase

Pyrolysis of t-butyl formate, (CH3)3C-O-CHO, has been carried out in a carrier gas stream of Ar or N2 in a temperature range of 200–400°C. Between 200 and 300°C, the pyrolysis yielded an equimolar mixture of HCOOH and (CH3)2C=CH2. The results have been used as a calibration method for determining the concentration of the gas-phase HCOOH monomer without interference from the formation of the formic acid dimer. Using this technique, the gas-phase infrared absorption cross-section of HCOOH at 1105 cm−1 (peak to valley) for the resolution of 0.5 cm−1 has been determined to be 6.76×10−19 cm2 molecule−1.