Synthesis and Electrochemical Investigation of Phosphine Substituted Diiron Phosphadithiolate Complexes

This work reports on ligand exchange reactions between a [FeFe] hydrogenase model containing the higher homologue ( PhosDT ) and phosphines selected to cover a variety of electronic properties and possible coordination modes. Additionally, the amount of the phosphines and the reaction temperature were varied to study the formation of complexes with multiple phosphines or altered binding modes. Due to steric effects caused by the position of the bridgehead, the phosphines bind preferentially at the more accessible iron centre on the phosphinate averted side. While all ligand exchanges resulted in a ligand-specific main product at room temperature, reflux conditions induced decomposition in case of PhosDT-(κ²-dppe) and PhosDT-(κ²-dppv) and a change in the binding mode for the dppm containing complex. Moreover, we highlight two novel iron complexes obtained as side products of the reactions with dppe and dppv, while in case of dppm an additional model with two bridging phosphine ligands was generated. Finally, the six novel phosphine substituted PhosDT models were electrochemically investigated, revealing a cathodic shift compared to the starting material due to the increased electron density at the iron atoms. Moreover, the models with monodentate ligands exhibit a different CV pattern for the Fe^IFe^I/Fe^IFe⁰ process than complexes with bidentate phosphines.     

Chaotic actions of topological semigroups

In this paper we propose and explore a general notion of chaos in the abstract context of continuous actions of topological semigroups and show that any chaotic action on a Hausdorff uniform space is sensitive to initial conditions.     

Electrochemical CO2 and Proton Reduction by a Co(dithiacyclam) Complex

While [Ni(cyclam)]²⁺ and [Ni(dithiacyclam)]²⁺ complexes were shown to be potent electrocatalysts for the CO₂ conversion, their respective Co complexes hitherto received only little attention. Herein, we report on the Co^II complexes of the cyclam and dithiacyclam platform, describe their synthesis and reveal their rich solvent dependent coordination chemistry. We show that sulfur implementation into the cyclam moiety leads to a switch from a low spin Co^II complex in [Co(cyclam)]²⁺ to a high spin form in [Co(dithiacyclam)]²⁺. Notably, while both complexes are capable to perform the reduction of CO₂ to CO, H₂ formation is generally preferred. Along this line, the complexes were shown to enable proton reduction from acetic acid. However, in comparison to [Co(cyclam)]²⁺, the altered electronics make [Co(dithiacyclam)]²⁺ complexes prone to deposit on the glassy carbon working electrode over time leading to an overall low faradaic efficiency for the reduction of protons or CO₂.     

Development of a simple sample preparation technique for gas chromatographic–mass spectrometric determination of nicotine in edible nightshades (Solanaceae)

The purpose of this study was to develop a rapid analytical method for the reliable determination of low concentrations of nicotine in foods for large numbers of samples. Food material was extracted using a simple liquid–liquid extraction method. For processed foods, further clean-up steps had to be employed to eliminate interfering compounds. The determination of nicotine was performed by gas chromatography–mass spectrometry. Quantitative analysis was accomplished using deuterium labeled nicotine as an internal standard. Recoveries of over 95% were obtained for a single step extraction, as well as for a multiple-stage extraction procedure, respectively. The method has been applied to the determination of nicotine in edible nightshades (i.e. tomatoes, potatoes and aubergines) and their processed products.     

Existence of Finite-Time Hyperbolic Trajectories for Planar Hamiltonian Flows

We present a shadowing theorem on the existence of hyperbolic trajectories on finite time intervals based on the EPH partition by George Haller and apply it to an example which is inspired by the problem of two-dimensional symmetric vortex merger.     

Moduli of simple holomorphic pairs and effective divisors

In this note we identify two complex structures (one is given by algebraic geometry, the other by gauge theory) on the set of isomorphism classes of holomorphic bundles with section on a given compact complex manifold. In the case ofline bundles, these complex spaces are shown to be isomorphic to a space of effective divisors on the manifold. The second author was partially supported by SNF, nr. 2000-055290.98/1.     

Normal Forms for Control Systems at Singular Points

A normal form for open loop control systems is provided, based on their interpretation as skew product flows and on normal forms for nonautonomous differential equations.     

Über die katalytische Spaltung von Orthoestern an Aluminiumoxyd

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