Experimental and theoretical charge distribution in (Z)-N-methyl-C-phenylnitrone

The total experimental charge density in (Z)-N-methyl-C-phenylnitrone (1) has been determined using high-resolution X-ray diffraction data in combination with neutron diffraction data measured at 100 K in terms of the rigid pseudoatom model. Multipole refinement converged at R = 0.03 for 7163 reflections with I > 2 sigma(I). Topological analysis of the total experimental charge density rho(r) and its Laplacian, -[symbol: see text]2 rho(r) and a comparison with high level theoretical gas-phase calculations reveals an unexpected electron distribution in the N-O group, both atoms having negative atomic charges, contrary to that commonly assumed in nitrone species. This observation is confirmed on examination of both the theoretical charges and the molecular electrostatic potential. Compound 1 contains a large number of hydrogen bonds and these are analysed using the atoms in molecules approach leading to quantitative values for bond strength, ranging from medium to very weak.     

Die Streuung kurzwelliger Strahlung durch Atome nach der Diracschen Strahlungstheorie

Zeitschrift für Physik A Hadrons and nuclei - Die Streuung kurzwelliger Strahlung durch Atome oder Atomsysteme wird nach den Methoden der Diracschen Dispersionstheorie behandelt. Es ergibt...     

Biodegradability of sol–gel silica microparticles for drug delivery

The biodegradability of porous sol–gel silica microparticles in physiological buffers has been investigated using a USP4 flow-through dissolution tester. In the open configuration, which most closely models in-vivo conditions, the particles dissolved rapidly at pH 7.4, with a rate dependent on the surface area and media flow rate. In the closed configuration, the fastest dissolving 4 mg silica sample was almost completely dissolved in 100 mL of buffer after 36 h. The initial dissolution rates appeared relatively linear but dropped off as dissolved SiO₂ concentrations approached 20–25 ppm. Addition of serum proteins acted to slow dissolution by 20–30%, suggesting a slower degradation in vivo. Silica microparticles administered for controlled release drug delivery would therefore be expected to be eliminated relatively rapidly from the body, depending on the sample size and local fluid flow conditions.     

Embeddings of covering projections of graphs

It is shown that any given k-fold covering projection of graphs p: G₁ → G₂ can be embedded in a k-fold covering projection of closed orientable surfaces π: S₁ → S₂ in the sense that there are embeddings of G₁ in S₁ and G₂ in S₂ such that p is the restriction of π. In the case of a regular covering projection p, which is the quotient map with respect to some group action on G₁, it is shown that there is a regular covering projection π of surfaces in which p can be embedded.     

Dimethylmetall-tropolonate des galliums,indiums und zinns

The reaction of GaMe₃ and InMe₃ (Me = CH₃) with equimolar amounts of α-tropolone forms dimethylgallium tropolonate and dimethylindium tropolonate, respectively, in high yields. Both compounds are monomeric in solution, almost planar 7-/5-ring bicyclic structures of C_2v symmetry can be discussed. According to the X-ray structure determination of Me₂GaTrop (Trop = C₇H₅O₂) this compound is dimeric in the solid state and crystallizes in the monoclinic space group P2₁/c with 4 formula units (2 dimers) per unit cell. Me₂SnTrop₂ is formed by the interaction of Me₂SnCl₂ with LiTrop in a $\text{1}\text{2}$ molar ratio. This ditropolonate is monomeric not only in solution but also in the solid state. The compound crystallizes in the triclinic space group P$\text{1}$ (Z = 4), and the molecules have a cis-structure of approximate C₂-symmetry. The vibrational and NMR spectra of all compounds were measured and are partly assigned.