Further Saponins from Phytolacca dodecandra L′HERIT

Three new bidesmosidic saponins 1 – 3 have been isolated from the berries of Phytolacca dodecandra L′HERIT (Phytolaccaeae). The structures have been established by spectroscopic (¹H-NMR, ¹³C-NMR, FAB-MS, DCI-MS, and GC/MS) and chemical methods (acid, basic, and enzymatic hydrolysis). Saponins 1 and 3 are tetra- and pentaglycosides of oleanolic acid, whereas 2 is a tetraglycoside of bayogenin. The corresponding prosapogenins 1a - 3a , obtained by cleavage of a glucose unit esterified at C(28), exhibited strong molluscicidal activity against schistosomiasis-transmitting snails.     

The potts glass in uniform and random fields: a monte carlo investigation

As a simple model of an anisotropic orientational glass with short range forces, the 3-state Potts model on the simple cubic lattice with nearest neighbor interactions drawn from a Gaussian distribution is considered. With Monte Carlo methods we study the response of the system to a uniform “field” which favors one of the states. This is motivated by experiments which apply stress that favors one molecular orientation of the quadrupolar glass. The responsem to that fieldh=H/k _BT is analyzed in terms of an expansionm= χ₁ h+χ₁ h ²+χ₁ h ³+..., where χ₁ is the linear susceptibility, and χ₂,χ₁₃ are nonlinear susceptibilities. Unlike the case of spin glasses, where the spin inversion symmetry of the system in the absence of fields implies χ₂≡0,χ₂ is nonzero here and diverges to −∞ at the zero temperature transition of the model, while χ₃ diverges to +∞ as in spin glasses. At inifinite temperature, however, χ₁=1/3, χ₂=1/18 and χ₃=-1/54, i.e. the nonlinear susceptibilities have a different sign as at low temperature. In contrast, a random field does not induce a uniform order parameterm but only a glass order parameterq. The temperature dependence of this glass order parameterq(T) shows for intermediate field strength order parameterq(T) shows for intermediate field strength a maximum of the slopedq(T)/dT very similar to corresponding experiments.     

Photoionization of 1,1-difluoroethane: The structure of the C2H3F2+ ions

In order to explain the photoionization efficiency curve of the ions with m/e = 65 from CH₃CHF₂, we have carried out ab initio calculations predicting energy differences and structural parameters for different isomers and conformers of both the neutral system and the ion. Also, some heats of formation are estimated.     

Zur Affinoberfläche konvexer Körper

Ohne ZusammenfassungHerrn Martin Barner zum 65. Geburtstag gewidmet     

Logical Processing for Integer Programming

This paper reviews tools which have great potential for reducing the difficulty of solving IP (and also MIP) problems, if well implemented in solvers. Recent experiments with Branch and Bound solvers, in connection with “Short Start Features”, have shown that implementations need and can still be improved. Concepts which are likely to be specially important for (0,1) MIP are pointed out.