Electronic structure of octacyanides of molybdenum IV and V according to the SCCC MO method

The SCCC MO method has been used to calculate the electronic structure and spectrum of Mo(CN) ₈ ^4– and Mo(CN) ₈ ^3– ions of a D _4d symmetry. All metal-ligand and ligand-ligand interactions and all overlap integrals (over products of HF atomic orbitals) have been included within the SCCC MO scheme. Basing on these calculations a new assignment of some absorption bands is proposed. The overall agreement between the calculated and observed electronic spectrum is satisfactory.

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Zusammenfassung Elektronenstruktur und Spektrum der [Mo(CN)₈]^–4- und [Mo(CN)₈]^–3-Ionen in D _4d -Symmetrie wurden mit der SCCC-MO-Methode berechnet. Alle Metall-Ligand- und Ligand-Ligand-Wechsel-wirkungen und Überlappungsintegrale wurden berücksichtigt. Die Bandenzuordnung wurde neu vorgenommen. Die Übereinstimmung der berechneten und gemessenen Spektren ist befriedigend.

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Résumé Application à Mo(CN) ₈ ^4– et Mo(CN) ₈ ^3– de la méthode SCCC MO basée sur des orbitales atomiques HF approchées, en tenant compte du recouvrement et de toutes les interactions ligand-ligand. Dans la partie I on discute le cas de la symétrie D _4d . L'accord global avec l'expérience est satisfaisant en ce qui concerne les spectres. On montre aussi que toutes les attributions antérieures basées sur la théorie du champ cristallin semblent inadéquates.

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The authors are grateful to Prof. W. Jakób, Dr. Z. Stasicka and Dr. A. Samotus for many interesting discussions, to Prof. J. Chojnacki for providing us with new X-ray results before publication and to Dr. A. J. Sadlej for a help in dealing with the computer.     

High-performance liquid chromatographic analysis of bile acids in hamster bile

A high-performance liquid chromatographic procedure has been developed for the determination of pentamidine concentrations in serum samples. A microbore, reversed-phase column was used with a mobile phase consisting of methanol and water with sodium heptanesulfonate and triethylamine as modifiers. Pentamidine could be extracted from serum only by the addition of an ion-pairing agent, di(2-ethylhexyl) phosphoric acid, to the chloroform used for extraction. The method can be used to reliably detect levels as low as 5 ng/ml. The pentamidine concentration in the serum of eleven patients 24 h after their tenth daily dose of pentamidine averaged 60 +/- 34 ng/ml.     

Trace-Aktivitätskoeffizienten und Ionenassoziation von Natriummetawolframat im System Natriummetawolframat-Natriumperchlorat-Wasser

Zusammenfassung In der vorliegenden Arbeit wird das Sedimentations-gleichgewicht des Systems Na₆[H₂W₁₂O₄₀]-NaClO₄-H₂O bei 25 °C untersucht. Die scheinbare Ladungszahl des Natriummetawolframats wird als Funktion der NaClO₄-MolalitätmNaClO₄ ermittelt. Aus dieser Abhängigkeit kann für die summarische Dissoziation des NatriummetawolframatsNa₂[H₂W₁₂O_4o] 6Na⁺ + [H₂W₁₂O₄₀]^6– die DissoziationskonstanteK in Gegenwart von NaClO₄ als Fremdelektrolyt zuK=0,08 mol⁶·kg^–6 bestimmt werden.Der Kreuzdifferentialquotient ( _PXz , ist der Trace-Aktivitätskoeffizient des Natriummetawolframats) wird ebenfalls als Funktion der NaClO₄-Molalität ermittelt.Die Konzentrationsabhängigkeit des Trace-Aktivitätskoeffizienten zeigt einen Verlauf, wie er unseres Wissens nach noch nicht von anderen Autoren beobachtet wurde.

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Summary An ultracentrifugal study of the sedimentation equilibrium of the system Na₂[H₂W₁₂O₄₀]-NaClO₄-H₂Oat 25 °C is presented. The dependency of the apparent charge of the sodium metatungstate on NaClO₄-molality is investigated. From these data the dissociation constant for the dissociation of the sodium metatungstate in the presence of NaClO₄ according to the equationNa[H₂W₁₂O₄₀] 6Na⁺ + [H₂W₁₂O₄₀]^6– is calculated toK=0.08 mol⁶·kg^–6. The cross differential quotient ( _PXz is the trace activity coefficient of the sodium metatungstate) shows a behavior in its dependence on NaClO₄-molality which to our knowledge has not yet been reported by other authors.

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Mit 5 Abbildungen und 1 Tabelle     

ESCA-Analysis of tin compounds on the surface of hydroxyapatite

The formation of tin compounds on the surface of hydroxyapatite, the main crystalline component of teeth, is discussed controversially. SnF₂ is used as an anticaries agent in toothpaste preparations. Pure hydroxyapatite (HAP) is treated with extracts of commercially available toothpastes containing tin fluoride and analyzed by electron spectroscopy (ESCA). Survey spectra and depth profiles are recorded. The chemical shifts measured for the HAP samples are compared with those of standard tin compounds. It is concluded that on the surface of hydroxyapatite a mixture of two-valent fluoro-phosphato compounds is formed. SnO is not found in the mixture.     

Intersequence cyclization in copolymers of N-vinyl carbamates

Monomer reactivity ratios determined for the copolymerization of tert-butyl N-vinylcarbamate (r_A = 0.55 ± 0.05) with phenyl N-vinylcarbamate (r_B = 2.08 ± 0.15) indicate that the monomer units are distributed randomly along the polymer chains. The following sequence of reactions was used to cause intersequence cyclization between tert-butyl N-vinylcarbamate and phenyl N-vinylcarbamate units in the copolymers. The extent of cyclization obtained was in accord with that expected for random copolymers.      

Measurement of the Compton profiles of CH4 and C2H4 by high energy electron impact spectroscopy

We present a new experimental determination of the Compton profiles of CH₄ and C₂H₄ molecules using high energy electron impact. The observable q range has been extended up to 10 au (6 au for C₂H₄). Good agreement is found with an earlier X-ray scattering experiment and with new theoretical calculations.     

Reaktionen mit Blei(IV)-acetat,XVI. Eine neuartige Umwandlung von 2-Acetoxy-3-oxo-4,5-epoxy-steroiden

Treatment of 3-oxo-4, 5-oxido steroids with lead tetraacetate results in acetoxylation in the 2α-position as could be shown by independent synthesis of the acetoxylated compounds. The products of this reaction rearrange even under very mild conditions (chromatography on silicagel or alumina) to the corresponding 2,3-dioxo-Δ⁴ compounds. The influence of structure and conformation of the various intermediates on their NMR.-spectra is discussed. A mechanism for this new transformation is proposed.     

Spektralphotometrische Bestimmung des Thioharnstoffs im Mikrogrammbereich

Zusammenfassung Eine spektralphotometrische Methode zur Bestimmung von Mikrogrammengen Thioharnstoff in Gegenwart von Biuret, Cyanat, Cyanursäure, Dicyandiamid, Harnstoff, Melamin und Rhodanid wird beschrieben. Sie beruht auf der Umsetzung des Thioharnstoffs mit salpetriger Säure zu Rhodanwasserstoffsäure, die mit Brom in Bromcyan übergeführt wird. Letzteres wird mit Pyridin und Barbitursäure zu einem intensiv gefärbten, stabilen Polymethinfarbstoff umgesetzt. Störungen durch andere Cyanamidderivate und -folgeprodukte werden untersucht.

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Summary A spectrophotometric method is described for the determination of micro amounts of thiourea in presence of biuret, cyanates, cyanuric acid, dicyanodiamide, urea, melamine and thiocyanates. The method bases on the reaction of thiourea with nitrous acid to thiocyanic acid, which is converted with bromine to cyanogen bromide. The latter forms with pyridine and barbituric acid an intensively coloured, stable polymethine dye. The interferences by other cyanamide derivatives and resultant products have been investigated.

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3. Mitteilune über die Analyse der Cyanamidderivate. 2. Mitteilung siehe ¹⁴.

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Frau S. Mohs möchten wir an dieser Stelle für ihre gewissenhafte Mitarbeit unseren Dank aussprechen.     

Determination of hexamethylene-based isocyanates in spray-painting operations. Part 1. Evaluation of a polyurethane foam sponge sampler

A polyurethane foam (PUF) sponge was mounted in a cassette sampler and evaluated as a sorbent for the collection of hexamethylene diisocyanate (HDI) monomer and HDI-based oligomers. Recovery studies indicated 112 +/- 34% average recovery of HDI monomer and 92 +/- 9% and 97 +/- 25% average recovery of HDI-based oligomers when using impregnated PUF sponges. The PUF sponge was also evaluated during actual spray-painting operations. In a series of side-by-side sampling events, an impinger filled with 1-(2-methoxyphenyl)piperazine (MOP) in toluene was compared directly with a cassette sampler containing a PUF sponge impregnated with MOP or 1-(9-anthracenylmethyl)piperazine (MAP) in dimethyl sulfoxide (DMSO). For the analysis of HDI-based oligomer, there is no significant difference (p < 0.05, n = 7) in the air concentration when sampling with either the PUF sponge cassette or the impinger. The results are significant because they indicate that a PUF sponge, which is more convenient than an impinger, may be used for the collection of HDI-based oligomer generated during spray-painting operations.