Determination of metal traces in tantalum by proton activation analysis

Procedures for determining traces of calcium, titanium, vanadium, chromium, iron, copper, niobium, molybdenum and tungsten in tantalum are described utilizing 11 MeV proton activation. The instrumental method of analysis with the use of a Ge(Li) detector and the radiochemical separation of the corresponding fractions are described. The formula for the calculation of the concentration of traces with the use of thick target yields is given. Experimental data on the thick target yields of radioisotopes⁴⁴Sc,⁵²Mn,⁵⁶Co,⁶⁵Zn,^93mMo,⁹⁶Tc are presented. Based on the experimental data, the detection limits are estimated at 1–10 ppb for the above mentioned metal traces in tantalum. The successful solution of the task of the simultaneous determination of nine elements in tantalum confirms the wide applicability of proton activation analysis.     

Statistical mechanical treatment of protein conformation. III. Prediction of protein conformation based on a three-state model.

The method proposed for the evaluation of statistical weights in paper I, and the three-state model [alpha-helical (alpha), extended (epsilon), and other (c) states] formulated in paper II, have been used to develop a procedure to predict the backbone conformations of proteins, based on the concept of the predominant role played by shortrange interactions in determining protein conformation. Conformational probability profiles, in which the probabilities of formation of three consecutive alpha-helical conformations (triad) and of four consecutive extended conformations (tetrad) have been defined relative to their average values over the whole molecule, are calculated for 19 proteins, of which 16 had been used in paper I to evaluate the set of statistical weights of the 20 naturally occurring amino acids. By comparing these conformational probability profiles to experimental x-ray observations, the following results have been obtained: 80% of the alpha-helical regions and 72% of the extended conformational regions have been predicted correctly for the 19 proteins. The percentage of residues predicted correctly is in the range of 53 to 90% for the alpha-helical conformation and in the range of 63 to 88% for the extended conformation for the 19 proteins in the two-state models [alpha-helical (alpha) and other (c) states, and extended (epsilon) and other (c) states]. In the three-state model, the percentage of residues predicted correctly is in the range of 47% to 77 for 19 proteins. These results suggest that the assumption of the dominance of short-range interactions, on which the predictive scheme is based, is a reasonable one. The present predictive method is compared with that of other authors.     

Lifetimes of Hg(3P0) complexes with methanol,ammonia, and water

Lifetimes of Hg(³P₀) complexes were determined by simultaneous observation of Hg(³P₀) optical absorption and complex emission, using a modulation technique and phase sensitive detection. The lifetimes of the mercury complexes with methanol, (1.4 ± 0.7) × 10^-8 s, and water, ? 8 × 10^-8 s, were found to be much shorter than reported in earlier work. For the ammonia complex, however a lifetime was measured which is in good agreement with previous determinations. Reasons for the large errors in earlier work where the methanol and water complex lifetimes were determined from complex emission data alone are discussed, and these data are reinterpreted. In the reaction rate of Hg(³P₀) with methanol no detectable contribution from the termolecular process Hg(³P₀) + 2CH₃OH → (Hg·CH₃OH)^* + CH₃OH could be observed.     

Pyridazines. LXV. Reactions of some I-phenacylazolopyridazinium halides with 2,3-diphenylcyclopropenone, -thione,or hydrazine

I-Phenacylazolopyridazinium bromides reacted with 2,3-diphenylcyclopropenone or -thione in the presence of triethylaminc to give 3,4,6-triphenyl-2-pyrone or -2-thiopyrone and the corresponding azolopyridazine. Quaternized azolopyridazines reacted with hydrazine to give either 3,6-diphenylpyridazine and the corresponding azoloazine or hy ring opening of the azine part to give 1-methyl-2-(pyrazolyl-5′)imidazole.     

Untersuchungen zur Temperaturabhängigkeit charakteristischer IR-Absorptionen, 9. Mitt.: Zur Tautomerie des “o-Hydroxymandelsäurelactons”

Zusammenfassung Die Abhängigkeit der Struktur des o-Hydroxymandelsäurelactons von Lösungsmittel und Temperatur wird mit Hilfe IR- und NMR-spektroskopischer Methoden nachgewiesen.

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The temperature and solvent dependence of the structures of 2-hydroxymandelic acid lactone and dioxindole have been shown by IR and NMR spectroscopy.

     

Methods and Results of Optical Investigations on Semiconductor Interfaces

Measurement of the state of polarization of reflected light (ellipsometry) permits the determination of the thickness and refractive index of thin layers formed on a surface. The IR absorption spectra of such thin layers, which can be measured by means of internal reflection spectroscopy (IRS), provide information about their chemical composition. These methods have been used to study adsorption processes and the formation of reaction layers at semiconductor interfaces, and may also be used for measurements of free charge carriers in the space-charge region and in surface states. Results of such investigations are given in this article.     

Existence of a photodecolorization reaction of the colored form of spiropyrans under the influence of initiating UV irradiation

The kinetics of photochromic transformations of spiropyrans of the indole series with various substituents in the 1 and 5 positions were studied. The existence of a photodecolorization reaction under the influence of activating UV light was proved, and the effect of substituents on the quantum yields of the photocoloration and photodecolorization reactions was studied.     

Synthese und Konfiguration von Methylestern der diastereomeren (±)-3-Amino-2,3-diarylpropansäuren,der (±)-3-Amino-2,3-diarylpropanole und ihrer Derivate

Zusammenfassung Durch Umsetzung von Hydramiden mit am aromatischen Ring m,p-dialkoxysubstituierten Arylessigsäureestern in Gegenwart von wasserfr. AlCl₃ entstehen Gemische aus Estern der (±)-erythro- und (±)-threo-3-Amino-2,3-diarylpropansäuren. Bei der Umsetzung von Piperonalhydramid mit dem Methylester der Homoveratrumsäure konnte lediglich daserythro-Diastereomere isoliert werden.Die diastereomeren Ester wurden zu den jeweiligen (±)-erythro- und (±)-threo-3-Amino-2,3-diaryl-1-propanolen reduziert, die als N,O-Dibenzoylderivate charakterisiert wurden. Ihre relativen Konfigurationen und die der zugehörigen Ester wurden auf Grund der IR-Spektren der diastereomeren Aminopropanole bestimmt. Die NMR-Spektren eines Diastereomerenpaares von Aminopropanolen bestätigen die ihnen chemisch zugeordneten Konfigurationen und ermöglichen den Nachweis auch ihrer bevorzugten Konformationen.

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Synthesis and configuration of methyl esters of the diastereomeric (±)-3-amino-2,3-diarylpropanoic acids, the (±)-3-amino-2,3-diaryl-1-propanols and their derivatives

Reaction of hydramides with m,p-dialkoxysubstituted arylacetates in the presence of anhydrous AlCl₃ generally leads to mixtures of the esters of the (±)-erythro- and (±)-threo-3-amino-2,3-diarylpropanoic acids. However, in the reaction of piperonal hydramide with methyl homoveratrate, only the correspondingerythro-diastereomer was obtained.Reduction of the diastereomeric esters gives the corresponding (±)-erythro- and (±)-threo-3-amino-2,3-diaryl-1-propanols, which can be characterized as N,O-dibenzoyl derivatives. Relative configurations of both alcohols and esters were determined by means of their IR spectra. Configurations were confirmed for one pair of diastereomeric amino alcohols by means of NMR spectra and preferred conformations deduced.

     

l-Leucanthemit als Inhaltsstoff von Gymnospermae

Zusammenfassung Die Bildung und das Vorkommen von Cycliten inThuja occidentalis wurden mit Hilfe der Methode der Photoassimilation in einer Atmosphäre von¹⁴CO₂ untersucht. Nebenmyo-Inosit, Sequoyit,d-chiro-Inosit undd-Pinit wurde auchl-Leucanthemit (l-1,2,4/3-Cyclohexentetrol), ein Cyclit, der bisher nur als Inhaltsstoff mehrerer Angiospermae bekannt ist, nachgewiesen. Das Vorkommen vonl-Leucanthemit konnte auch inPinus austriaca sichergestellt werden. Methoden zur Isolierung vonl-Leucanthemit ausThuja occidentalis wurden ausgearbeitet.

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The formation and the occurrence of cyclitols inThuja occidentalis has been studied, using the method of photoassimilation in an atmosphere of¹⁴CO₂. Besidesmyo-inositol, sequoyitol,d-chiro-inositol, andd-pinitol, alsol-leucanthemitol (l-1,2,4/3-cyclohexentetrol), a cyclitol which so far has only been found in Angiospermae, was identified. The occurrence ofl-leucanthemitol could also be established inPinus austriaca. Methods have been elaborated which permit the isolation ofl-leucanthemitol fromThuja occidentalis.

     

Photometric titrations. VIII

Summary Cadmium and zinc can be determined in one solution in the following manner. The sample is adjusted to p_H 9.4 with an ammonia-ammonium chloride buffer so that the total ammonia concentration is 0.01–0.03M. Zincon is added to attain a concentration of 0.06–0.18 mg/ml. The titration is performed photometrically at about 620 nm with EGTA as the titrant. The titration curve obtained shows two breaks which are related to the consecutive titration of cadmium and zinc. The influence of calcium impurities in the reagents used has been studied and a pre-titration method is proposed to deal with small calcium blanks. Calcium may also be added to the sample in order to obtain a titration curve which shows three breaks, which are related to the consecutive titration of cadmium, calcium, and zinc.

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Zusammenfassung Cadmium und Zink lassen sich nebeneinander in einer Lösung bestimmen. Man bringt die Probe durch Zusatz von Ammoniak-Ammoniumchlorid-Puffer auf p_H 9,4, so daß die totale Ammoniakkonzentration 0,01- bis 0,03-m ist. Pro ml werden 0,06 bis 0,18 mg Zincon zugesetzt, dann wird mit EGTA [Äthylenglykol-bis-(-aminoäthyläther)-N,N,N,N-tetraessigsäure] bei etwa 620 nm photometrisch titriert. Die Titrationskurve zeigt zwei Knickpunkte, die der aufeinanderfolgenden Titration von Cadmium und Zink entsprechen. Der Einfluß von Calcium-Verunreinigungen in den verwendeten Reagenzien wurde untersucht und eine Vortitration zur Bestimmung kleiner Calcium-Blindwerte vorgesehlagen. Man kann auch der Probe Calcium zusetzen und erhält dann eine Kurve mit drei Knickpunkten, entsprechend den aufeinanderfolgenden Titrationen von Cadmium, Calcium und Zink.

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Résumé On peut doser le cadmium et le zinc sur une seule solution de la manière suivante. On ajuste le p_H de l'échantillon à 9,4 par un tampon ammoniaque-chlorure d'ammonium de façon que la concentration totale en ammoniaque soit de 0,01–0,03M. On ajoute de la zincone jusqu'à l'obtention d'une concentration de 0,06–0,18 mg/ml. On effectue un dosage speetrophotométrique à 620 nm en utilisant l'EGTA comme agent titrant. La courbe de titrage montre deux points anguleux correspondant à la teneur en cadmium et en zinc. Après avoir étudié l'influence du calcium à l'état d'impuretés dans les réactifs utilisés, on propose une méthode de prétitrage pour faire les essais à blanc avec de petites quantités de calcium. On peut également ajouter du calcium à l'échantillon afin d'obtenir une courbe de titrage avec trois points anguleux relatifs aux titrages consécutifs du cadmium, du calcium et du zinc.

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See reference 1 for paper VII of the series.

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Dedicated to Prof.A. A. Benedetti- Pichler on the occasion of his 70th birthday.