Bestimmung der Verteilungskoeffizienten von Praseodym und Neodym im System n-Tributylphosphat und Salpeters?ure

Zusammenfassung Es wurden die Verteilungskoeffizienten von Praseodym und Neodym im System n-Tributylphosphat und Salpetersäure bestimmt. Die Messung des in der wäßrigen Phase zurückgebliebenen Erdmetalles erfolgte photometrisch nach Abhebern der organischen Phase. Die Verteilungskoeffizienten sind stark von der Molarität der Salpetersäure abhängig und erreichen bei Extraktion aus dreimolarer bzw. hochkonzentrierter Salpetersäure Höchstwerte. Durch Ausbau der apparativen Anordnung sind Anreicherungs- bzw. Trennmöglichkeiten gegeben, worüber zur gegebenen Zeit berichtet werden soll.     

Measurement of isotope ratios on transient signals by MC-ICP–MS

Precise and accurate isotope ratio measurements are an important task in many applications such as isotope-dilution mass spectrometry, bioavailability studies, or the determination of isotope variations in geological or nuclear samples. The technique of MC-ICP–MS has attracted much attention because it permits the precise measurement of isotope compositions for a wide range of elements combined with excellent detection limits due to high ionisation efficiencies. However, the results are based mainly on measurements using continuous sample introduction. In the present study the determination of isotope ratios on various transient signals with a time duration of 30 to 60 s has been achieved by coupling high-performance liquid chromatography to a multicollector inductively coupled plasma mass spectrometer. In order to investigate the origin of ratio drifts across the transient signals for this hyphenated technique, measurements with the same standard solutions were also carried out using a flow-injection device for sample introduction. As a result of this application it could be concluded that the main source of the bias in the measured isotope ratios is within the ICP–MS instead of fractionation effects on the chromatographic column material. Preliminary studies on short transient signals of gaseous samples (dry plasma) showed a reverse fractionation effect compared with wet plasma conditions (flow injection and HPLC).Presented at the 2003 European Winter Conference on Plasma Spectrochemistry, Garmisch-Partenkirchen, Germany, January 2003     

Continuity of the eigenvalues of self-adjoint operators with respect to the strong operator topology

Let T_n, T, and S be self-adjoint operators such that T_n converges to T in the sense of strong resolvent convergence. If S is bounded from below, _e(S) (–,O) = Ø, and T_n S for all n, then the negative eigenvalues of T_n converge to the negative eigenvalues of T. The corresponding eigenfunctions converge in norm. This generalizes a result due to T. Kato, where T_n T is assumed, and a recent result of the author for the case T_n T_n+1.     

Observation of highly flexible residues in amyloid fibrils of the HET-s prion

We report the observation of undetected (until now) residues of the prion protein fragment HET-s(218-289) which give rise to well-resolved (13)C, (15)N, and (1)H NMR resonances under high-resolution magic-angle spinning (HRMAS) conditions. The observed signals belong to large polymeric units as shown by measuring the lateral diffusion constants. The amino acids identified in the spectra are compatible with their localization in the segments of the protein which could not be detected in earlier solid-state NMR experiments. The observed chemical shifts indicate that these residues are in a random-coil conformation. Complementary experiments which detect only dynamic or static residues, respectively, strongly suggest that they belong to different parts of the same molecule.     

Harness processes and harmonic crystals

In the Hammersley harness processes the R$\mathbb{R}$-valued height at each site i∈Z^d$i\in {\mathbb{Z}}^d$ is updated at rate 1 to an average of the neighboring heights plus a centered random variable (the noise). We construct the process “a la Harris” simultaneously for all times and boxes contained in Z^d${\mathbb{Z}}^d$. With this representation we compute covariances and show L²$L^2$ and almost sure time and space convergence of the process. In particular, the process started from the flat configuration and viewed from the height at the origin converges to an invariant measure. In dimension three and higher, the process itself converges to an invariant measure in L²$L^2$ at speed t^1−d/2$t^{1-d/2}$ (this extends the convergence established by Hsiao). When the noise is Gaussian the limiting measures are Gaussian fields (harmonic crystals) and are also reversible for the process.     

Aufbau der Ligandsysteme des C,D-Tetradehydrocorrins und Isobakteriochlorins durch Sulfidkontraktion. Kurzmitteilung

Synthesis of C, D-Tetradehydrocorrins and Isobacteriochlorins via Sulfide Contraction The reaction sequences shown in Schemes 4 and 5 illustrate the use of the sulfide contraction method for the synthesis of isobacteriochlorins and (metal free) C, D-tetradehydrocorrins. The tetradehydrocorrin synthesis fills a gap in a spectrum of corrinoid (A → D) ring closures that ranges from A.W. Johnson's oxidative (A → D)-cyclizations to octadehydrocorrinoids on the one side to the photochemical 1, 19-secocorrin → corrincycloisomerization on the other (Scheme 7). Such a multiplicity of reaction paths towards corrinoids is of interest in connection with the problem of the origin of the corrin structure.