Aldehydselektivität von alkylhafnium-komplexen in aldehyd-keton-konkurrenzversuchen; vergleich zu zirkonium- und titan-analogen komplexen sowie theoretische deutung

Cl₃Hf-Me, in contrast to MeLi is not able to attack an ester or a nitrile group and fails to discriminate in competition experiments between heptanal and diethylketone. To the contrary, Cl ₃Hf-Bu and (EtO)₃Hf-Me are highly aldehyde-selective. An explanation of these findings in comparison with alkylzirconium and alkyltitanium complexes is given.     

A linear-time algorithm for edge-disjoint paths in planar graphs

In this paper we discuss the problem of finding edge-disjoint paths in a planar, undirected graph such that each path connects two specified vertices on the boundary of the graph. We will focus on the “classical” case where an instance additionally fulfills the so-calledevenness-condition. The fastest algorithm for this problem known from the literature requiresO (n ^5/3(loglogn)^1/3) time, wheren denotes the number of vertices. In this paper now, we introduce a new approach to this problem, which results in anO(n) algorithm. The proof of correctness immediately yields an alternative proof of the Theorem of Okamura and Seymour, which states a necessary and sufficient condition for solvability.     

Molecular thermodynamics of fluid mixtures containing molecules differing in size and potential energy

Recent computer-simulation work by Shing and Gubbins (1983) for binary mixtures has shown that common semiempirical models (van der Waals n-fluid models) are in error when the molecules of the two components differ appreciably in size; the error is most severe in the dilute region. While perturbation theories are much better, they (like computer simulations) are not as yet useful for engineering work because of prohibitive computer requirements.This work proposes an algebraic expression for the Helmholtz energy of a mixture which gives results in very good agreement with those reported by Shing and Gubbins. This expression, using the local-composition concept, is based on a simplified but realistic picture of a fluid mixture: short-range order and long-range disorder. The proposed expression uses the Mansoori-Carnahan-Starling-Leland equation for the contribution of repulsive forces. For the contribution of attractive forces, it uses a new expression based on not one but several radii for the first-neighbor shell, one radius for each component.With reasonable simplifications, the resulting equation for the Helmholtz energy indicates that the van der Waals “constant” a is a strict quadratic function of mole fraction only at very low densities; at advanced densities, there are small deviations from the quadratic mixing rule. For practical calculations, the computer requirements are nearly the same as those for conventional engineering models.     

Confirmation of okadaic acid, dinophysistoxin-1 and dinophysistoxin-2 in shellfish as their anthrylmethyl derivatives using UV radiation

A rapid and simple method for confirmation of the diarrhetic shellfish poisons (DSP): okadaic acid (OA), dinophysistoxin-1 (DTX-1) and dinophysistoxin-2 (DTX-2) using fluorescence detection following derivatization with 9-chloromethylanthracene, has been established as an alternate to LC/MS. Exposure of the anthrylmethyl derivatives of OA, DTX-1 and DTX-2 to near UV light (300-400 nm) resulted in the loss of these compounds to below detection limits within 30 min, with a concurrent appearance of two additional compounds. Based on the mass spectral evidence, we propose that these newly formed compounds are the decarboxylation products of the derivatized diarrhetic shellfish poisons. UV radiation is, therefore, proposed as a rapid and simple confirmation technique for these DSP in mussel samples.