Oxidationsreaktionen am 1-(3,3-Dimethyl-5-norbornen-2-yl)ethanon und ein neuer Zugang zuendo-konfigurierten Isocamphanderivaten

The synthesis of some new compounds with the isocamphane skeleton obtained by oxidation reactions on the bicyclic ketone3 and its derivatives is described. Some possible routes to theendo-configurated camphenilanic acid (2) have been explored which yet have to be improved to furnish better yields. Separation of mixtures of the acids1 and2 failed. Carboxylation of camphenilone yielded only theexo-configurated isocamphenilanic acid (1).2, however, an important starting material for the preparation ofendo-configurated isocamphane derivatives, can be obtained easily with high yields and sterically pure by oxidation of camphene with H₂O₂/HCOOH. Thus a cheap, one-step method for the preparation of pure2 even in larger quantities is introduced.

Auszugsweise vorgetragen auf der 3. Wissenschaftlichen Tagung der Österreichischen Pharmazeutischen Gesellschaft am 18. Oktober 1982 in Innsbruck.     

An unprecedented mode of ligation for a bridged amido-cyclopentadienide (constrained geometry) ligand; pi-olefinic interactions with gallium and indium

The surprising reaction of GaCl3 or InBr3 with the di-Grignard reagent [Me2Si(C5Me4)(N-t-Bu)](MgCl)2 x THF results in salts of the bimetallic anions of composition [X3M[C5Me4(N-t-Bu)]MX2]- (M = Ga, X = Cl; M = In; X = Br) in which the MX2 moiety undergoes an eta2-interaction with one of the double bonds of the localized cyclopentadienide ring.     

Models of the cores of dislocations in metals and disclinations in liquid crystals

The development of dislocation core models in metals with non-close-packed crystalline structure is reviewed. The paper starts with the Peierls-Nabarro model generalized to the case of non-planar cores to describe dislocation splitting in bcc metals. Atomistic studies of dislocations cores in bcc metals and intermetallic compounds with L1₂ and B2 structures are then discussed and the principal features of non-planar cores emphasized. Finally, an analogy between dislocations in solid and disclination in liquid crystals is presented and similarities and differences in the treatment of core structures of these defects in solid and liquid crystals discussed.Dedicated to Dr. Frantiek Kroupa in honour of his 70^th birthday.This work was supported by the U.S.-Czech S & T Program under contract No. 94048, by the National Science Foundation-International Programs, INT-93-07418 and by the Grant Agency of the Czech Republic under contract No 106/93/0513.     

An Atomistic Study of Interfacial Diffusion in Lamellar TiAl Alloys

In this paper we investigate self-diffusion of Ti and Al along interfaces present in the lamellar L1₀ TiAl by atomistic computer modeling. The interactions between the atoms are described by central-force many-body potentials. The approach adopted is similar to that used in earlier atomistic modeling of bulk diffusion in TiAl [1, 2]. Both the formation and migration of vacancies is examined. The interfaces studied are the three types of –interfaces: ordinary twin, pseudotwin and 120° rotational fault. For the latter two interfaces the diffusion was investigated not only for the stoichiometric case but also when the interfaces possess a surplus of titanium in the form of a layer with the composition and structure of Ti₃Al, as was found in an earlier Monte Carlo study of titanium segregation to these interfaces. The calculations suggest that the diffusivity along –interfaces is higher than in the bulk. However, the difference between bulk and interfacial diffusivity is not as drastic as it may be encountered in grain boundaries. At the same time the above mentioned surplus of Ti appears to affect the interfacial diffusion only marginally.     

Analytic environment-dependent tight-binding bond integrals: application to MoSi2

We present the first derivation of explicit analytic expressions for the environmental dependence of the sigma, pi, and delta bond integrals within the orthogonal two-center tight-binding approximation by using the recently developed bond-order potential theory to invert the nonorthogonality matrix. We illustrate the power of this new formalism by showing that it not only captures the transferability of the bond integrals between elemental bcc Mo and Si and binary C11(b) MoSi2 but also predicts the absence of any discontinuity between first and second nearest neighbors for the ddsigma bond integral even though large discontinuities exist for ppsigma, pppi, and ddpi.     

Determination of abamectin, doramectin, emamectin, eprinomectin, ivermectin, and moxidectin in milk by liquid chromatography electrospray tandem mass specrometry

The avermectin and milbemycin families of compounds are derived from naturally occurring yeasts. They have proven to be potent preventatives against a variety of pests such as insects and parasites. Only eprinomectin and moxidectin are currently approved for use on lactating cattle with tolerances in milk of 12 microg/kg for eprinomectin and 40 microg/kg for moxidectin. Detection of misuse or inadvertent contamination in milk requires a sensitive and definitive analytical method. A method has been developed for the determination of 5 avermectins and 1 milbemycin in milk using a simple liquid-liquid extraction and liquid chromatography/tandem mass spectrometry (LC/MS/MS) analysis. Ivermectin (IVR), doramectin (DOR), abamectin (ABA), eprinomectin (EPR), emamectin (EMA), and moxidectin (MOX) were extracted from whole milk by partitioning into acetonitrile with a subsequent solvent exchange into methanol-water. Simultaneous confirmation and quantification were achieved with LC separation, positive electrospray ionization (ESI+), and MS/MS. The limits of detection ranged from 16 pg/g (ppt) for EMA to 1.7 microg/g (ppb) for MOX.