Unidentified Impurity Research Articles

Purification from a human lung cancer cell line of a water soluble molecule mediating leukocyte adherence inhibition for patients with lung cancer.

Soluble lung tumor activity as determined by LAI2 was enriched by physicochemical methods from chemically - defined spent medium of a lung cancer cell line (NCI-H69). To identify the polypeptide carrying the antigenic determinant, splenic lymphocytes of BALB/c mice were immunized with the enriched isolate and hybridized with mouse plasmacytoma cells. Eight hybrids were cloned successfully and produced MAbs that immunoprecipitated principally a single chain of Mr 40,000 (p40) as well as minor chains of Mr 25,000 (p25) and Mr 13,000 (p13) which were probably degradation products of p40. On 2D gels, p40 was composed of 7 spots with a p1 of 6.3 to 7.6, which was not altered by neuraminidase digestion. Affinity chromatography with MAb anti-p40 absorbed p40 and LAI activity. The bound and recovered fraction was enriched for p40 and LAI activity. Affinity-purified p40 also contained the previously identified p25 and p13 as well as a Mr 32,000 peptide (p32). MAb anti-p40 was directed to a common framework determinant on p40 since MAb anti-p40 bound to cancer cells from other organs. The comparatively lung cancer organ-specific determinant recognized by leukocytes from lung cancer patients was not recognized by the MAb. Affinity-purified p40 triggered LAI for leukocytes from patients with lung cancer but not for leukocytes from control subjects or patients with colon cancer or malignant melanoma in rigorous blind testing. Crossreactivity was observed with leukocytes from patients with breast cancer. LAI activity of affinity-purified p40 seems unlikely to result from an unidentified impurity. Thus a p40 molecule has been purified that is expressed on the membranes of lung cancer cells and triggers immunologically-mediated LAI.

The variation in europium(III) AND terbium(III) luminescence lifetimes with concentration in rare earth oxysulphide matrices

The transient properties of the Eu 3+ 5D 2, 5D 1, 5D 0 emitting levels in oxysulphide matrices at various doping concentrations were analysed under either charge transfer state or direct 5D J selective excitation using pulsed laser light. At low Eu 3+ concentrations the data can be described in terms of the step process 5D 2 → 5D 1 → 5D 0 (a more complete calculation will be published elsewhere). The decrease in the 5D 2 and 5D 1 lifetimes with concentration can be interpreted by cross-relaxation (Eu-Eu) processes, whereas the presence of an (unidentified) impurity in the phosphors is proposed to explain the concentration quenching of 5D 0. This conclusion is supported by the observation of similar behaviour for Tb 3+ 5D 4 emission in the same matrices which is attributed to Eu 3+ ions acting as traps.

Aminopyrine accumulation by mammalian gastric glands: an analysis of the technique

Isolated gastric glands from rabbits and parietal cells from dogs have recently become useful in studying the control and enzymatic mechanisms of gastric H+ secretion. The present studies were performed to determine the experimental variables that account for widely differing aminopyrine accumulation reported in various publications. We found that two principle factors were responsible for wide differences in aminopyrine accumulation. First, we found that commercially available aminopyrine contained an unidentified impurity that increased with storage. A procedure for purification is included. The contaminant is not accumulated in secreting gastric glands and thereby reduces the aminopyrine ratio that can be achieved. Mixing of glands appeared to be the second important variable. It was found that incubation in 1.5-ml capped conical polypropylene centrifuge tubes in the horizontal position with shaking in the long axis of the tubes gave aminopyrine ratios that were more than double the results obtained by other mixing techniques. In addition a gland density of 1--2 mg dry wt/ml glands and a mixing rate of 110 cycles/min gave the best results. Calculations indicate that, at high gland densities, even modest amounts of impurity in the aminopyrine will significantly reduce aminopyrine ratios. With optimal conditions our greatest aminopyrine ratio was 1,050, which suggests an H+ concentration of approximately 67 mM in the canaliculi and tubulovesicular membrane system of the parietal cell. Such a level of function approaches that of the intact in vivo organ.

ChemInform Abstract: NAFION‐TMS‐ AND TMS‐TRIFLUOROACETATE‐INDUCED REARRANGEMENTS OF CYCLOPROPYL KETONES ‐ A PROCEDURE FOR THE REGIOSELECTIVE CONVERSION OF SEMIBULLVALENES TO BARRELENES

AbstractA Procedure for the Regioselective Conversion of Semibullvalenes to Barrelenes.

Nafion‐TMS‐ and TMS‐Trifluoroacetate‐Induced Rearrangements of Cyclopropyl Ketones ‐ A procedure for the regioselective conversion of semibullvalenes to barrelenes

AbstractTrimethylsilyl trifluoroacetate (TMSTFA) and the polymer‐supported sulfonate Nafion‐TMS exhibit selective reaction modes in the opening of cyclopropyl ketones. The yields are generally high. Nafion‐TMS rearranges the tricyclooctanones 1a and 1b to the bicyclooctenones 4a and 4b (while TMSTFA gives ring‐opened adducts 6a,b) with high regioselectivity. Aro‐semibullvalenes (8a, 14, 17a,b) are efficiently rearranged to arobarrelenes (7a, 13, 20a,b) by both reagents. The latter rearrangements have also been achieved in mixtures of trifluoroacetic acid and tetramethylsilane (TMS), where the acid combines with an unidentified impurity of commercial TMS to form a strong electrophilic agent. The electrophile‐assisted rearrangement of the naphtho‐semibullvalenes 14a+b resulted in conversion to the naphthobarrelenes 13a+b with the opposite regioselectivity to that observed for the thermal equilibration at 220°.

MOCVD growth and characterisation of GaAlAs/GaAs double heterostructures for opto-electronic devices

MOCVD has been used to grow GaAlAs/GaAs double heterostructures of excellent morphology and uniformity for a wide range of opto-electronic devices, including solar cells, lasers, multiple LED arrays and high power LEDs. Laser with J t <700 A cm -2 and high radiance LEDs with high internal quantum efficiencies >50% are reported. The ability to grow layers of high planarity over large areas has been used to advantage to prepare high yields of multiple LED arrays with every device working and showing identical characteristics. Device characteristics and performance were improved by oxygen gettering and careful control of the growth conditions during transitions in doping or alloy composition. High densities of a novel stacking fault/distribution complex found in heavily Zn doped GaAlAs layers are associated with an unidentified impurity.

Structure of theHandHAcenters in RbCaF3

Electron spin resonance (ESR) has been used to characterize the $H$ and ${H}_{A}$ centers in the tetragonal phase of RbCa${\mathrm{F}}_{3}$. The $H$ centers are produced by electron irradiation at 77 K. They consist of a radiation-induced interstitial fluorine atom bonded to a regular lattice fluorine ion, with the resultant $\mathrm{F}_{2}^{\ensuremath{-}}$ molecule centered on a single fluorine lattice site. The ESR spectrum of the $H$ centers is dominated by equivalent hyperfine interactions (${A}_{\ensuremath{\parallel}}=920.6 \mathrm{G}$) with the two fluorine nuclei in the primary $\mathrm{F}_{2}^{\ensuremath{-}}$ molecule; no additional hyperfine interactions with adjacent fluorines are resolved. Preferential alignment of the $H$-center molecules occurs along the [001] tetragonal axis of each domain. Near 125 K, the $H$ centers thermally anneal and a new spectrum, assigned to ${H}_{A}$ centers, appears. An ${H}_{A}$ center is formed when a migrating $H$ center becomes stabilized adjacent to an unidentified impurity substituting for a ${\mathrm{Rb}}^{+}$ ion. Thermal annealing of the ${H}_{A}$ centers occurs near 170 K. The hyperfine interactions with the two fluorine nuclei in the ${H}_{A}$ center are unequal (${A}_{1z}=1020.9 \mathrm{G}$ and ${A}_{2z}=782.2 \mathrm{G}$) and the ${H}_{A}$ center's molecular axis deviates approximately 11.9\ifmmode^\circ\else\textdegree\fi{} from the [001] tetragonal direction while remaining in the (100) or (010) planes.

Photoconductivity and luminescence of electron irradiated CaO

We report an experimental investigation of the electronic structure of $F$ and ${F}^{+}$ centers in electron-irradiated CaO using the spectral response and temperature dependence of photoconductivity, with associated luminescence and fluorescence lifetime measurements made on the same samples. Photoconductivity and optical-absorption measurements were made over the spectral range from 2 eV (620 nm) to 4.5 eV (275 nm). Photoconductivity and fluorescence measurements were made over the temperature range from 65 to 350 K. The photoresponse of ${F}^{+}$ centers increased sharply with increasing temperature between 210 and 300 K, where the zeroth moment, ${M}_{0}$, of the ${F}^{+}$ luminescence was decreasing with increasing temperature. Below 200 K, photoconductivity from the ${F}^{+}$ center was masked by photoconductivity from an unidentified impurity. The thermal activation energy for ${F}^{+}$-center photoconductivity was 0.24 eV. The photoresponse of $F$ centers showed no significant temperature dependence between 65 and 300 K. The $F$-center photoresponse could be optically bleached at all temperatures between 77 and 300 K and, then, fully restored by $\ensuremath{\gamma}$ irradiation at room temperature.

Impurity-associated fluorine interstitial in KMgF3

The electron-spin-resonance (ESR) spectrum of an ${H}_{ A}$ center has been investigated in the cubic perovskite KMg${\mathrm{F}}_{3}$. The ${H}_{ A}$ centers were produced by electron irradiation near 77 K and are the result of an interstitial fluorine atom combining with two neighboring lattice fluorine ions to form a molecular ion stabilized adjacent to an unidentified impurity. The three fluorine nuclei are magnetically inequivalent and give rise to large anisotropic hyperfine splittings in the ESR spectrum. At 10 K, the axial parameters of the three hyperfine tensors are ${A}_{ 1,z}=1113.8$ G, ${A}_{ 2,z}=599.6$ G, and ${A}_{ 3,z}=50.7$ G. A partially averaged ESR spectrum is observed at 77 K and is explained in terms of a restricted motion of the interstitial about the neighboring impurity ion. The ${H}_{ A}$ center thermally decays at 195 K.

The influence of oxidation-sirtl etch condition on the stacking fault generation in (111) silicon wafers

The successive oxidation-Sirtl etch technique has been investigated to evaluate the perfection of silicon crystals by detecting extrinsic stacking faults produced during oxidation. Experiments were performed in (111) epitaxial wafers. Measured densities of stacking faults were found to epend on the conditions of thermal oxidation, and stacking fault densities were a maximum at an oxidation temperature of around 1100°C. The stacking fault densities were reduced appreciably when epitaxial wafers were chemically etched to remove several tens of microns prior to the test. The generation of stacking faults is thought to occur by heterogeneous nucleation due to a very small amount of unidentified impurity found in epitaxial crystals.

Sharp-line and broad-band emission in AgGaS2 crystals

The low-temperature photoluminescence spectra of AgGaS2 are investigated in this work. At 4.2°K, the luminescence spectra are dominated by many sharp lines as well as broad emission bands. A series of emission lines was found to be superimposed on the broad band peaking at ∼ 5000 Å. The series of emission lines are attributed to phonon-assisted transitions involving an unidentified impurity or defect. Two basic phonons with energies of 5.4 and 7.2 meV are identified from the phonon structure. The 7.2-meV mode is also seen in the Raman spectrum. They are tentatively identified as the lattice modes.

Structures revealed in zone refined aluminum by tritium decoration

A method is described for decorating structures in solid aluminum by precipitation of hydrogen onto them. Radioactive hydrogen is employed so that the deposition sites can be revealed by the use of autoradiographic techniques. The study was conducted with zone refined aluminum, and the primary structure that was revealed was that remaining after directional solidification during the last zone pass. The tritium was added to the specimen at 600°C and its precipitation was brought about by quenching the sample. As little as 0.05 ppm of tritium was sufficient to reveal complex structures in the cast metal that are attributed to association of unidentified residual impurity atoms with low angle subgrain boundaries that are thought to have resulted from polygonization occurring immediately behind the advancing solid-liquid interface. Wide-angle grain boundaries were also decorated. New structures were introduced by various levels of strain that accompanied different upsetting operations. Grain and subgrain boundaries that developed during strain anneals were “antisites” for hydrogen deposition. This opposite behavior is attributed to the absence of impurity atoms in these “new” boundaries. An explanation for the behavior of hydrogen in aluminum is given in terms of the condensation of vacancies vs their loss to vacancy sinks. These phenomena are shown to be involved in the enlargement of hydrogen-filled pores in aluminum.

An electron microscope study of precipitation in MgO single crystals

Abstract An electron microscope study was made of precipitation in vanadium and titanium-doped MgO single crystals. In both crystals cubic spinel precipitates form in parallel orientation with the cubic matrix lattice in the temperature range 1100°C-1500°c. Precipitation of the vanadium spinel, Mg2VO4 is accompanied by the nucleation and growth of dislocation loops composed of edge dislocation dipoles with their axes parallel to the principal axes of the cubic MgO matrix lattice. It is concluded that dislocation loop nucleation occurs by the condensation of vacancies previously existing in the form of clusters with solute ions in the as-grown crystals. Similar loops grow from existing edge dislocations constituting sub-grain boundaries and those formed by prismatic punching from unidentified impurity particles. The equilibrium structure at 1200°c is that of 0·5 μ diameter spinel particles decorating irregular dislocation networks. No similar dislocation configurations are developed on precipitation of the titanium spinel. It is tentatively suggested that in the latter case, which involves an increase in oxygen ion lattice spacing on precipitation, precipitate nuclei form from solute ion-vacancy clusters which are too small for dislocation loop nucleation.

Stereospecific Addition of Hydrogen to Fumaric Acid in irradiated Single Crystals of Succinic Acid

Pooley and Whiffon1 reported an interesting proton–deuteron exchange reaction of the primary radical HOOCCHβHβ′CHαCOOH (or DOOCCHβHβ′CHαCOOD)2 in an irradiated crystal of succinic acid. By means of an electron spin resonance technique, they detected DOOCCDβ Hβ′CHCOOD in addition to the primary species, but they did not detect DOOCCHβ Dβ′CHCOOD, nor DOOCCH2CDCOOD (hyperfine splitting constant for Hβ is larger than that for Hβ′2). It was shown later3,4, however, that formation of this DOOCCDβHβ′CHCOOD species is associated with an unidentified impurity in the crystal; the impurity is too low in concentration to be detected with ordinary experimental techniques. During the present investigation it was found that fumaric acid behaved quite similarly to the impurity: in a crystal of succinic acid which contained 0.001 mole fraction of fumaric acid, the ratio was found to be 0.2, that is, the same as the ratio found in the impure crystal3.

Nitridation of magnesium in the temperature range 400–650°

The reaction between sheet magnesium and gaseous nitrogen has been studied gravimetrically in the range 400–650° on a thermal balance and a vacuum microbalance of the Gulbransen type. The behaviour is complicated since weight is lost by evaporation as well as gained by nitridation. Evaporation is promoted by traces of water vapour but inhibited by oxygen, or by an unidentified impurity in nominally pure nitrogen, or by mechanical damage caused by abrasion or sawing. Evaporation is found with electropolished magnesium in very pure nitrogen at 500 and 525°(and probably above 525°) on the microbalance, but not on the thermal balance, where the characteristic effect is “breakaway”—a sudden increase in the rate of weight gain. The results can be explained in terms of the formation and growth of cavities at the nitride–metal interface, together with the rupture of the film covering the cavity. If at rupture the film is thin the magnesium vapour will escape, but if thick the vapour will react with nitrogen within the cracks to form the nitride.

Thermally Induced Acceptors in Germanium

When germanium is rapidly quenched from high temperature, acceptor centers are formed uniformly throughout the crystal. These centers have an energy of formation of about 2 ev. Each center is thought to contribute two acceptors, one near the valence band and one near the center of the gap. Experiments are described which indicate that these centers are either vacant lattice sites or a heretofore unidentified chemical impurity with radius smaller than that of germanium. Annealing has been studied in the temperature range 250\ifmmode^\circ\else\textdegree\fi{}C-450\ifmmode^\circ\else\textdegree\fi{}C. The annealing process is shown to depend markedly on both the density of dislocations and the concentration of copper. It has not been possible to ascribe a consistent physical model to conform with the observed characteristics of the annealing process.

Photoelectric Work Functions of (100) and (111) Faces of Silver Single Crystals and Their Contact Potential Difference

The work functions of the (100) and (111) faces of silver single crystals have been determined photoelectrically by the Fowler method of analysis, and were compared with the contact potential difference measured by the Kelvin null method. The equilibrium value of the work function for the (100) face is 4.81\ifmmode\pm\else\textpm\fi{}0.01 ev, and that for the (111) face is 4.75\ifmmode\pm\else\textpm\fi{}0.01 ev. These values were obtained after heating for more than 2000 hours at various temperatures up to visible red heat. The gas pressure in the tube during the final stages of outgassing was between 1 and 3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$ mm Hg with the crystals hot. Values of the measured contact potential difference obtained at frequent intervals during the outgassing agreed with the differences of the photoelectric work functions to within \ifmmode\pm\else\textpm\fi{}0.01 volt. After these equilibrium values were obtained the crystals became contaminated by an unidentified impurity from heated tantalum with the result that the photoelectric data no longer agreed with the Fowler theoretical curve or with the measured contact potential difference. The apparatus permitted deposition of silver from the vapor state onto the crystal faces, after two previous distillations of the silver had been made to eliminate gas effects. Presence of the contamination referred to above complicated the results following deposition, but evidence is presented to show that the deposited silver gave a more gas-free surface than heating alone. The rate of return of gas to the surface following the deposit was determined by a comparison of the experimental results with a theory presented by Emslie. The results are explained by postulating that long heating of the crystals produced a stable gas configuration of a monomolecular layer on their faces, and that deposition of a gas-free layer of silver produced a surface free of most, if not all, of this layer of gas. The work function of the gas-free surface is 0.09\ifmmode\pm\else\textpm\fi{}0.03 volt less than that of the underlying structure previous to deposit.