An investigation of the structure of the so-called phenarsazine : Mass spectroscopical evidence for the thermal formation of phenarsazine

The structure of Wieland and Rheinheimer's “phenarsazine” has been reinvestigated. The proposed aromatic structure 3 is not correct, spectral and chemical evidence showing that this compound is 10,10′-bis(5,10-dihydrophenarsazinyl) 16. An attempt to synthesize phenarsazine 3 by base-induced hydrogen chloride elimination was unsuccessful. However, mass spectroscopic evidence indicates that phenarsazine is formed by thermal elimination of either hydrogen chloride or methanol from 10-chloro-5,10-dihydrophenarsazine 7 or 10-methoxy-5,10-dihydrophenarsazine 10, respectively.     

Quadrupole moment of the first excited state of 32S

The static quadrupole moment and B(E2; 0⁺ → 2⁺) value for the first excited state of ³²S were measured using the reorientation effect in Coulomb excitation of ³²S projectiles. Silicon surface barrier detectors were used to detect ³²S ions scattered from ²⁰⁸Pb at mean laboratory angles of 90° and 174°, for bombarding energies in the range 122 to 160 MeV. The results for constructive (destructive) interference from the second 2⁺ state in ³²S are QP_2⁺ = ?16.0±2.2 (?13.3±2.2) e·fd² and B(E2; 0⁺ → 2⁺) = 292±17 (307±17) e²·fm⁴     

On the nature of the “free electron pair” on phosphorus in aromatic phosphorus compounds: The photoelectron spectrum of 2-phosphanaphthalene

The electronic structure of the 2-phosphanaphthalene system has been studied by photoelectron spectroscopy. The assignment of bands in the PE spectra of 2-phosphanaphthalene and 3-methyl-2-phosphanaphthalene has been performed with the aid of two useful generalisations, one pertaining to the energies of the the π ionizations, and the other to the phosphorus n ionization, as well as by calculations using the extended CNDO/S method. The n ionization of the 2-phosphanaphthalenes can be observed as a well separated single band. From the breadth of this n band the “lone pair” is seen to have considerable bonding character resulting from orbital mixing with other σ-orbitals of the molecule. This appears to be the first evidence of appreciable delocalization of ldlone pair” phosphorus electrons in aromatic molecules, which, judging from the breadth of the bands, is almost as large as with pyramidal phosphorus atoms.     

THE ACTION SPECTRA FOR UV-INDUCED SUPPRESSION OF MLR and MECLR SHOW THAT IMMUNOSUPPRESSION IS MEDIATED BY DNA DAMAGE

-Ultraviolet-B (UVB,280–320 nm) radiation can promote the induction of skin cancer by two mechanisms: damage of epidermal DNA and suppression of the immune system, allowing the developing tumor to escape immune surveillance. The mixed lymphocyte reaction (MLR) and the mixed epidermal cell lymphocyte reaction (MECLR) are commonly used methods to study the immunosuppressive effects of UVB radiation. To obtain a better understanding of the mechanism by which UVB radiation decreases the alloactivating capacity of in vitro-irradiated cells, action spectra for the MLR and MECLR were determined. Suspensions of peripheral blood mononuclear cells or epidermal cells were irradiated with monochromatic light of 254, 297, 302 or 312 nm and used as stimulator cells in the MLR or MECLR. Using dose-response curves for each wavelength, the action spectra were calculated. Both MLR and MECLR action spectra had a maximum at 254 nm and a relative sensitivity at 312 nm that was a thousand times lower than at 254 nm. Strikingly, the action spectra corresponded very closely to the action spectra that were found by Matsunaga et al. (Photochem. Photobiol. 54,403–410, 1991) for the induction of thymine dimers and (6-4)photoproducts in irradiated calf thymus DNA solutions, strongly suggesting that the UV-induced abrogation of the MLR and MECLR responses is mediated by UV-induced DNA damage. Furthermore, the action spectra for the MLR and MECLR were similar, suggesting that they share a common mechanism for UV-induced suppression.     

Organosilver(I) chemistry: On the reaction of RAg and R2AgMgCl compounds with conjugated enynenitriles

The addition of RAg and R₂AgMgCl to enynenitriles

is described. RAg reagents prefer to transfer their R group to the double bond of these nitriles, so that after protolysis 2,3-alkadienenitriles are obtained, while the homoargentates generally give 2,4-alkadienenitriles. The regio- and stereo-chemical course of the reactions are compared with those in additions of RCu and R₂CuMgCl to the enynenitriles.     

On the stereochemistry of an alkylcuprate induced conversion of a bromoallene into an alkylallene

By preparing $\text{levorotatory}$$\text{2}$ following a route of known stereochemistry, we were able to elucidate the stereochemistry of the conversion of the levorotatory bromoallene $\text{1}$ into levorotatory $\text{2}$ by $\text{t}$-Bu(CN)CuLi: the reaction occurs with retention of configuration in the allenyl moiety.     

On the stereochemistry of allene formation from mestranol methanesulfinate by t-butylsilver(I).

The reaction of [t-BuAgBr]MgCl·2LiBr with mestranol methanesulfinate ($\text{1}$) in a mixture of THF and HMPT leads to (S)-allene $\text{2}$ via a syn 1,3-substitution process. This stereochemistry is identical to that observed for the corresponding cuprate reaction.     

Die Bestimmung des Schwefels in organischen Substanzen. IV

Zusammenfassung Eine reduktive automatisierte Bestimmungsmethode von ppm Schwefel in organischen Substanzen wird vorgeschlagen. Die Substanz wird im Wasserstoffstrom in einem weiten Rohr über Quarzwolle bei einer Temperatur von 1050°C hydriert. Der Schwefelwasserstoff wird in 1-m KOH und 1,5-m Hydroxylamin absorbiert und sofort in dieser Lösung mit einer 2 · 10^–4-m Blei(II)maßlösung titriert. Die Titration wird mit einer ionenspezifischen Elektrode verfolgt und bei einem vorher gewählten Potentialwert beendet. Ein System, bei dem die Titrantzugabe proportional der Abweichung vom erwünschten Endpunktsignal ist, ermöglicht eine Bestimmungsdauer von 5–6 min, unabhängig von der vorgelegten Menge Schwefel. Die Standardabweichung der Bestimmung von mehr als 5 ppm S ist durchschnittlich besser als 3 % rel. Stickstoffhaltige Substanzen stören erst in größeren Mengen.

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The determination of sulphur in organic substances. IV

Summary A reductive automated method for the determination of a few p. p. m. S in organic compounds is proposed. The sample is hydrogenated in a wide tube in a stream of hydrogen at a temperature of about 1050° C over quartz wool. The resulting hydrogensulfide is absorbed in a solution of 1 M KOH and 1.5 M hydroxylamine and immediately titrated with a 2 · 10^–4 M lead (II)-titrant solution. The titration is automatically carried out until the preset signal of an ion selective electrode is reached. A system, in which the titrant flow is proportional to the difference between the actual signal and the preset value, enables a total time of analysis of about 5–6 min. This time depends not on the quantity of sulfur to be determined. The standard deviation of the determination of more than 5 p. p. m. is better than 3% rel. as a mean value. Nitrogen containing compounds interfere only in large amounts.