Massenspektrometrische Untersuchung Organischer Stickstoffverbindungen. XIV—Mechanismus der Piperidin-Eliminierung aus N.N′-(o-Xylylen)-Dipieridin

The electron-impact-induced elimination of piperidine from the title compound could be established by investigation of the unsymmetrically ²H-labelled compound. The mechanism of a 1,1-elimination can be excluded be unequivocally.     

Synthesis, structures, and strain energies of dispirophosphiranes. Comparisons with dispirocyclopropanes

Six novel dispirophosphirane complexes have been synthesized from the reaction of bicycloalkylidenes with the electrophilic phosphinidene complex PhPW(CO)(5). They contain a central phosphirane ring, which is spirofused on one side to a cyclopropane or cyclobutane ring and on the other side with a three-, four-, five-, or six-membered ring. Their crystal structures and MP2/6-31G-computed geometries for simplified parent systems suggest that spirofusion with small rings results in a tightening of the central three-membered phosphaheterocycle, while spirofusion with larger rings results in a relaxation of the phosphirane geometry. Similar theoretical predictions are made for the corresponding annulated hydrocarbons. Strain energies for both the hydrocarbon and phosphorus series of structures have been calculated at G3(MP2). Whereas the [3]triangulane hydrocarbon and phospha[3]triangulane have a significant excess strain of 8.1 and 5.2 kcal/mol per spiroatom, respectively, the excess strain for systems spirofused with larger rings are negligible for the hydrocarbons and even negative for the phosphorus-containing species because of hyperconjugative stabilization.     

Massenspektrometrische Untersuchung von Amiden: III—Intramolekulare Nucleophile Substitution bei der Methyl-Abspaltung aus Crotonsaurepiperidid und Vinylogen Derivaten

The methyl cleavage from piperidides of type CH₃(CH?CH)_nCONC₅H₁₀ with n = 1 to 3 does not proceed via ring contraction as shown earlier with n = 0. The fragmentation can be formulated with the concept of neighbouring group participation of the amide function which leads to a cyclic transition state. Investigations with a ²H-labelled compound in the case of n = 1 as well as energy measurements (AP, IP, E_k) agree with this assumption.     

Elucidation of the Reaction Products of Acetonitrile with Phosphorus Pentachloride

Abstract

The reaction of acetonitrile with PCl, results in the ionic compounds (1) to (4) containing the trichloro[2-chloro-2-[(trichlorophosphoranyli-dene)amino]ethenyl]phosphorus cations and not in the compounds [CH2?C?NPCl₃]PCl₆1 or trichloro[2-chloro-1 -[(trichlorophosphoranyli-dene)amino] ethenyl]phosphorus hexachlorophosphate (5) as assumed from ³¹P-NMR spectra [2, 3]. The crystal structures of the compounds (1) to (4) were determined with X-rays at 95K. As observed for the CI-C(NPCl₃); cation all the cations show cis-trans conformations with respect to their CI-C-X-P torsion angles. The wcl3 groups of the cations have two different orientations with one C?N?P?CI torsion angle of about 0° (cis) as in (1) or about 180° (trans) as in (3) and (4). In the salt (2) there are two formula units in the asymmetric unit with one cation showing the cis and the other showing the tram conformation.     

Solubilisation of camptothecin by nonionic surfactants and alkyldimethylamine oxides

The solubilisation of poorly soluble antineoplastic drug camptothecin by nonionic surfactants (polysorbates and octylphenol ethoxylates) and alkyldimethylamine oxide surfactants with the alkyl chain length 8 to 16 carbon atoms was investigated. The hydrophobicity of the solubilising agent turned out to be the primary structural parameter controlling the solubility efficiency of camptothecin in an aqueous solution. The quantitative parameter of solubilisation (drug loading coefficient) provided values in the range of 0.1–1.2% and 0.1–1.0% for alkyldimethylamine oxides and nonionic surfactants, respectively. The decreasing number of oxyethylene units and the extension of the hydrophobic part of nonionic surfactant molecule resulted in the increase of camptothecin solubility. From the dynamic light scattering measurements, the hydrodynamic diameter values of camptothecin-loaded alkyldimethylamine oxide and nonionic micelles were found in the range of 4–42 nm and 5–120 nm, respectively. The experimental values confirmed the increase in micellar size with the increasing alkyl chain length. The values of the packing parameter of camptothecin-loaded dodecyldimethylamine oxide micelles indicate their spherical shape at all the investigated surfactant concentrations. A simple computer model of camptothecin-loaded dodecyldimethylamine oxide micelle provided the diameter of the structure cross section which is consistent with the experimental values.      

Fast concentration of dissolved forms of cesium radioisotopes from large seawater samples

The method developed for cesium concentration from large freshwater samples was tested and adapted for analysis of cesium radionuclides in seawater. Concentration of dissolved forms of cesium in large seawater samples (about 100 L) was performed using composite absorbers AMP-PAN and KNiFC-PAN with ammonium molybdophosphate and potassium–nickel hexacyanoferrate(II) as active components, respectively, and polyacrylonitrile as a binding polymer. A specially designed chromatography column with bed volume (BV) 25 mL allowed fast flow rates of seawater (up to 1,200 BV h^?1). The recovery yields were determined by ICP-MS analysis of stable cesium added to seawater sample. Both absorbers proved usability for cesium concentration from large seawater samples. KNiFC-PAN material was slightly more effective in cesium concentration from acidified seawater (recovery yield around 93 % for 700 BV h^?1). This material showed similar efficiency in cesium concentration also from natural seawater. The activity concentrations of ¹³⁷Cs determined in seawater from the central Pacific Ocean were 1.5 ± 0.1 and 1.4 ± 0.1 Bq m^?3 for an offshore (January 2012) and a coastal (February 2012) locality, respectively, ¹³⁴Cs activities were below detection limit (<0.2 Bq m^?3).