Diffusion and viscosity of a calamitic liquid crystal model studied by computer simulation

We report a molecular dynamics simulation study on an ensemble of rod-like particles, each composed of nine soft spheres held rigidly along a line. We have calculated translational mean square displacements and velocity autocorrelation functions in the fluid phases exhibited by the model, i.e., smectic A, nematic and isotropic. These quantities have then been used to compute diffusion coefficients. In addition, we have calculated viscosities in the nematic and isotropic phases. Despite its crude nature, the model is capable of providing a faithful reproduction of many features of the transport behavior observed in real liquid-crystalline materials. The simulation results have been compared with the predictions of the modified affine transformation theory, finding only a fair agreement.     

Regularity at the boundary for v onQ-pseudoconvex domainsonQ-pseudoconvex domains

Solvability for with regularity at the boundary of a domain Ω ⊂⊂ ℂ ⁿ for forms of any degreek≥1 was characterized by pseudoconvexity of ϖΩ in [16]. It is proved here thatq-pseudoconvexity suffices to guarantee solvability of forms of degreek≥q+1. The method relies on theL ² estimates in [13], and on their Sobolev version in [15] and [16].     

Self-healing generation of spatial solitons in liquid crystals

We demonstrate that, in suitably designed cells with undoped nematic liquid crystals, extraordinary-wave spatial solitons can be excited at every applied voltage without adjustments in the input polarization. Their walk-off, hence direction of propagation, is externally controlled over angles as large as 7 degrees. The results pave the way not only to polarization-forgiving generation but also to voltage readdressing of these extraordinary-wave nematicons.     

Highly diastereoselective allylic azide formation and isomerization. Synthesis of 3(2'-amino)-beta-lactams

The stereoselective anti SN2' attack of NaN3 to 3-alkenyl-3-bromo-azetidin-2-ones gave a mixture of diastereomeric azides in fast equilibrium. The [3,3]-sigmatropic rearrangement of allylic azides occurred with complete stereocontrol, allowing the equilibrium to be directed preferentially toward the (E)- or (Z)-isomer, useful precursors of 3(2'-amino)-beta-lactams. [reaction: see text]     

Base-promoted cyclization of 1-nitrohydrazones bearing a thioether function

Functionalized 1-nitrohydrazones 5 react with sodium hydride in boiling benzene to afford different types of ring-closed products. The formation of the latter can be ascribed to competitive modes of evolution of first-formed nitrile imines.     

The stability of the solutions of a class of integrodifferential systems with infinite delays

Various stability types, analogous to those in the theory of ordinary differential equations, are defined for some classes of integrodifferential systems of equations with infinite delays. Then, on the basis of a variation of constants formula and some results in functional analysis and Laplace transform theory, some necessary conditions and necessary and sufficient conditions are established in order that the trivial solution of a class of systems may be classified as one of the stability types considered in the definitions.     

Disidein,a pentacyclic sesterterpene condensed with an hydroxyhydroquinone moiety,from the sponge Disidea pallescens

A novel pentacyclic saturated sesterpene condensed with hydroxyhydroquinone moiety, which we named disidein (1), has been isolated from the marine sponge Disidea pallescens as disulfate sodium calcium salt. A minor accompaining compound, which seems a likely precursor of disidein, has been identified as 2-pentaprenylbenzoquinone (7).     

Mercury(II) derivatives of azoles

The reaction between mercury(II) chloride and azoles(pyrazole, 3,5-dimethylpyrazole, benzotriazole, 1,2,4-triazole) afforded mainly N-chloro mercury derivatives, although other reactions, such as the well known ring mercuration or the formation of a complex, were observed simultaneously. Therefore, no simple generalization explains the observed reactivity of azoles towards mercury(II) chloride, each reaction investigated being a different case.