Synthesis of the 2-aza-7-oxatricyclo[4.3.2.04,8]undecane nucleus of some gelsemium alkaloids

The preparation of a key tricyclic intermediate for the eventual total synthesis of the alkaloids gelsemicine and gelsedine is described.     

Critical phenomena in polymer mixtures: Monte Carlo simulation of a lattice model

A lattice model of a symmetrical binary (AB) polymer mixture is studied, modelling the polymer chains by self-avoiding walks withN _A =N _B =N steps on a simple cubic lattice. If a pair of nearest neighbour sites is taken by different monomersAB orBA, an energy _ab is won; if the pair of sites is taken by anAA or aBB pair, an energy is won, while the energy is reduced to zero if at least one of the sites of the pair is vacant. To allow enough chain mobility, 20% of the lattice sites are vacancies. In addition to local motions of the chain segments we use a novel grand-canonical simulation technique:A chains are transformed intoB chains and vice versa, keeping the chemical potential difference fixed. The phase diagram is obtained forN=4, 8,16 and 32; the critical behaviour is analysed by finite-size scaling methods. It is shown that the critical exponents are those of the Ising model (=0.32,=0.63) rather than those of the Flory-Huggins meanfield theory (==1/2). Implications of these results for real polymers are briefly discussed.Paper presented at the Frühjahrstagung 1986, Polymerphysik, der Deutschen Physikalischen Gesellschaft, Kaiserslautern, March 12–14, 1986.     

Determination of total arsenic by use of a zinc-column arsine generator

A method for the measurement of total arsenic in extracts of environmental materials is described. Arsenic is reduced to arsine with a zinc reductor column, the evolved arsine is decomposed in a heated carbon-tube furnace, and arsenic determined by measurement of its atomic-absorption at 193.7 nm. The detection limit is 0.002 mug/ml and the coefficient of variation is 1.4% at 0.01 mug/ml.     

Comparison of standards in the Karl Fischer method for water determination.

The use of 4-(5-nonyl)pyridine oxide and trioctylamine oxide for the extraction of niobium(V) from different mineral acid solutions is described. The influence of the concentration of the solvents, acids and salting-out agents is discussed. Separations of niobium(V) from tantalum(V) and zirconium(IV) have been achieved.     

Coulomb interaction in the one-dimensional free-electron model

In the limiting case of the free-electron theory where the electron motion is constricted to one dimension, the one-dimensional Coulomb potential gives rise to divergent interaction integrals. It is shown that a proposal by Olszewski to remove the divergenses by first evaluating the integrals in the three-dimensional case and then passing to the limit of one dimension only is incorrect, and that convergent integrals may only be obtained by suitably modifying the original one-dimensional Coulomb potential between particles.

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Zusammenfassung In dem Grenzfall des Modells der Freien Elektronen, in dem die Elektronenbewegung auf eine Dimension eingeschrÄnkt ist, ergibt das eindimensionale Coulombpotential divergente Wechselwirkungsintegrale. Es wird gezeigt, da\ ein Vorschlag von Olszewski zur Aufhebung der Divergenz durch übergang von dreidimensionalen zum eindimensionalen Integral falsch ist. Konvergente Integrale können nur durch geeignete VerÄnderung des ursprünglichen eindimensionalen Coulombpotentials erhalten werden.

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Résumé Dans le cas limite de la théorie de l'électron libre à une dimension, le potentiel coulombien donne lieu à des intégrales d'interaction divergentes. On montre que la proposition d'Oszewski pour éliminer les divergences, en évaluant d'abord les intégrales tridimensionnelles et en passant à la limite à une dimension, est incorrecte et que des intégrales convergentes ne peuvent Être obtenues qu'en modifiant le potentiel coulombien unidimensionnel entre particules.

     

Chemical analysis of ceramic materials, containing uranium and plutonium, arising from the development of nuclear fuels

A comprehensive and critical review of analytical methods used in nuclear fuel technology.     

Der Abbau des Insektizides GS 13005 in der Ratte. Strukturaufklärung der wichtigsten Metabolite [1]

The structures of the essential metabolites which are excreted by the rat after oral application of GS 13005 (O,O-dimethyl-S-[(2-methoxy-1,3,4-thiadiazole-5(4H)-one-4-yl)-methyl] dithiophosphate) have been elucidated. The product of final oxidation, CO₂, was found to be the main metabolite (up to 36% of the dose applied). Among the degradation products excreted in the urine (up to 45% of the dose applied) the two most important were isolated. They are 4-methylsulfinylmethyl and 4-methylsulfonylmethyl derivatives respectively of the intact 2-methoxy-1,3,4-thiadiazole-5-one heterocycle (metabolites III and II, in amounts of 20–25% and 5–7% of the dose applied, respectively). These metabolites originate by methylation and subsequent oxidation from the mercaptomethyl derivative liberated after hydrolysis of the P S bond of the dithiophosphoric acid ester.     

The phase change in potassium chloride

Equations for the interaction of ions in an ionic crystal, developed earlier¹, which allow for the variation of compressibility with pressure, have been applied to calculation of properties connected with the phase transition of potassium chloride under pressure. The data used were only for the high pressure form of the compound. It was found that the calculated transition pressure was much closer to the observed value, if these equations were used; but simpler equations which use a constant compressibility were somewhat better in their calculated values for the lattice energy, molar volume, and change of volume with pressure for the low pressure form of potassium chloride (NaCl structure). It is concluded that, while calculations on these equations form a sensitive test of these equations, the fitting of the equation to the structure needs to be more elaborate.     

Selective separations by reactive ion exchange : Part III. Preconcentration and separation of oxo anions

A new procedure for simultaneous preconcentration, separation, and determination of permanganate, chromate and vanadate was developed for aqueous solutions containing p.p.b. levels of these anions (and molybdate). The presence of other (non-complexing) ions in p.p.m. concentrations did not interfere. The procedure consisted of reactive adsorption of all three anions as their reduced cations, on iron(II)-treated resin, followed by elution of vanadium(IV) with 0.01 M HNO₃/H₂O₂, manganese(II) with 0.35 M HCl, and chromium(III) with 4M HCl. Concentration factors of 40 were obtained with 1-l “samples” 10 p.p.b. concentrations were determined with standard deviations of 4–5 % by a.a.s. and conventional spectrophotometry.