Absolutbestimmung der spezifischen Aktivität 35S-haltiger Substanzen

Als wesentlichste Vorausselzungen für eine präzise Absolutbestimmung der spezifischen Aktivität ³³S-haltiger Substanzen werden die Sorption von SO₂ an den Zählrohren und der Füllapparatur, die Beeinflussung des Gasentladungsmechanismus im beschränkten Proportionalbereich durch negativ geladene SO₂-Ionen und die kinetischen Isotopieeffekte bei nicht hundertprozentiger Überführung der Ausgangssubstanzen zu Meβgas untersucht. Speziell beschrieben werden die Umsetzung von Natriumsulfat bzw. Schwefelsäure in wäβriger Lösung und Thioharstoff zu Bariumsulfat und dessen Verbrennung zu Schwefeldioxid. Der Gesamtfehlre, mit dem die Angabe der spezifischen Aktivität für die genannten Ausgangssubstanzen behaftel ist, wird angegeben.     

Teil III. Edelgasdetektoren,Indirekter Elektron-Mobility-Detektor und Schlußfolgerungen

Die Multiplikation von Ladungsträgern durch feldbeschleunigte Elektronen erfolgt im Bereich der unselbständigen Entladung. Sie wurde von Lovelock [1] erstmals für β-Argondetektoren zur Steigerung der Empfindlichkeit E_N angewandt. Detektoren im Bereich der selbständigen Entladung [2] haben sich nicht bewährt.     

Solutions of the Equation of a Spinorial Yamabe-type Problem on Manifolds of Bounded Geometry

We consider a spinorial Yamabe-type problem on open manifolds of bounded geometry. The aim is to study the existence of solutions to the associated Euler–Lagrange-equation. We show that under suitable assumptions such a solution exists. As an application, we prove that existence of a solution implies the conformal Hijazi inequality for the underlying spin manifold.     

Dicobalt II-II, II-III, and III-III complexes as spectroscopic models for dicobalt enzyme active sites

A matched set of dinuclear cobalt complexes with II-II, II-III, and III-III oxidation states have been prepared and structurally characterized. In [(bpbp)Co2(O2P(OPh)2)2]n+ ( n = 1, 2, or 3; bpbp(-) = 2,6-bis(( N,N'-bis-(2-picolyl)amino)-methyl)-4-tertbutylphenolato), the nonbonded Co...Co separations are within the range 3.5906(17) to 3.7081(11) angstroms, and the metal ions are triply bridged by the phenolate oxygen atom of the heptadentate dinucleating ligand and by two diphenylphosphate groups. The overall structures and geometries of the complexes are very similar, with minor variations in metal-ligand bond distances consistent with oxidation state assignments. The CoIICoIII compound is a valence-trapped Robin-Day class II complex. Solid state 31P NMR spectra of the diamagnetic CoIIICoIII (3) and paramagnetic CoIICoIII (2) and CoIICoII (1) complexes show that 31P isotropic shifts broaden and move downfield by about 3000 ppm for each increment in oxidation state. Cyclic voltammetry corroborates the existence of the CoIICoII, CoIICoIII, and CoIIICoIII species in solution. The redox changes are not reversible in the applied scanning timescales, indicating that chemical changes are associated with oxidation and reduction of the cobalt centers. An investigation of the spectroscopic properties of this series has been carried out for its potential usefulness in analyses of the related spectroscopic properties of the dicobalt metallohydrolases. Principally, magnetic circular dichroism (MCD) has been used to determine the strength of the magnetic exchange coupling in the CoIICoII complex by analysis of the variable-temperature variable-field (VTVH) intensity behavior of the MCD signal. The series is ideal for the spectroscopic determination of magnetic coupling since it can occur only in the CoIICoII complex. The CoIICoIII complex contains a nearly isostructural CoII ion, but since CoIII is diamagnetic, the magnetic coupling is switched off, while the spectral features of the CoII ion remain. Analysis of the MCD data from the CoIICoIII complex has been undertaken in the theoretical context of a 4T1g ground-state of the CoII ion, initially in an octahedral ligand field that is split by both geometric distortion and zero-field splitting to form an isolated doublet ground state. The MCD data for the CoIICoII pair in the [(bpbp)Co2(O2P(OPh)2)2]+ complex were fitted to a model based on weak antiferromagnetic coupling with J = -1.6 cm (-1). The interpretation is confirmed by solid state magnetic susceptibility measurements.