Eine einfache und schnelle Trennung von Ni, Mn, Co, Cu und Zn mit Hilfe der Papierchromatographie

Ohne Zusammenfassung     

Die colorimetrische Bestimmung von Fetts?ureestern im Serum

Ohne Zusammenfassung     

Restricted open-shell Kohn-Sham theory: simulation of the pyrrole photodissociation

The authors study the photodissociation reactions of pyrrole and N-methylpyrrole using first-principles molecular dynamics. The first excited state is described with restricted open-shell Kohn-Sham theory. They find a small barrier in the excited state potential energy surface. The possibility of energy redistribution near the Franck-Condon region leads to two different reaction channels in on-the-fly simulations on a single diabatic potential energy surface. The results are discussed in comparison with previous ab initio calculations and with experiments.     

The role of metal ions in dopaminergic neuron degeneration in Parkinsonism and Parkinson’s disease

Abstract  

Parkinson’s disease is characterized by the selective degeneration of neuromelanin-containing dopaminergic neurons in the substantia nigra and locus coeruleus. Although the cause of this disease remains unknown, several transition metals, including manganese and copper, have been associated with the development of the atypical form of Parkinsonism, and iron accumulation has been associated with the development of Parkinson’s disease. Manganese³⁺ is a strong oxidizing agent, which oxidizes dopamine to aminochrome (dopaminochrome), the precursor of neuromelanin. Aminochrome formation in cell culture medium induces acute cell death in cells that uptake aminochrome, explaining the role of manganese in the development of atypical Parkinsonism. Copper accumulation in Wilson’s disease also induces Parkinsonism as one of the main symptoms, and an atypical Parkinsonism has also been observed in young copper miners. Interestingly, copper is able to complex with dopamine, which can be taken up by cells expressing the dopamine transporter, inducing caspase-independent cell death with formation of autophagic vacuoles. Iron is also able to form a complex with dopamine, the neurotoxic action of which also depends on the cellular expression of the dopamine transporter. The neurotoxicities of these transition metals to cells expressing the dopamine transporter all involve dopamine oxidation to quinones and require the inhibition of DT-diaphorase.     

Modified chemistry of siloxanes under tensile stress: interaction with environment

We present first principles molecular dynamics simulations of stretched siloxane oligomers in an environment representative of that present in single molecule atomic force microscopy experiments. We determine that the solvent used (hexamethyldisiloxane) does not influence the stretching of the siloxane in the high force regime or the rupture process, but trace amounts of water can induce rupture before the maximum siloxane extension has been attained. This would result in a significantly lower rupture force. The simulations show that the rupture of a covalent bond through a reaction with a molecule from the environment, which would not normally occur between the species when the polymer is not stressed, is possible, opening a route to mechanically induced chemical reactions. The attack of the normally hydrophobic siloxane by water when it is stretched has wider implications for the material failure under tensile stress, where trace amounts of water could induce tearing of the material.     

EFTEM and EELS Analysis of a Pt/NiO Interface

 Energy-filtering transmission electron microscopy (EFTEM) is more and more becoming an important nanoanalytical technique in both materials science and biology. The main advantage of the method lies in the possibility to obtain two-dimensional chemical information from large specimen areas as well as from features on a nanometer scale. Due to its excellent lateral resolution it is perfectly suited for the investigation of nanometer sized features (e.g. interfaces). In this paper we will show how EFTEM can be used to characterize the interface between a Pt layer and a NiO crystal as part of a coulometric titration cell. In addition to elemental distribution maps electron energy-loss spectra (EELS) across the interface (EELS linescans) have been acquired to obtain quantitative compositional profiles. By employing these methods the following interfacial layers could be identified, all of which containing Pt, Ni and O in different proportions: 13 nm Pt-rich, 32 nm Ni-rich and 29 nm Pt-rich. The origin of these is discussed in terms of displacement reactions.     

Chirality and Order in Binary Molecular Crystals of Inert Cobalt(III) Complexes

Starting from the enantiomerically pure and racemic chiral Lewis bases 1‐phenylethylamine and 1‐(1‐naphthyl)ethylamine inert cobalt(III) complexes of the general composition Co(Hdmg)₂(lig)X (Hdmg = dimethylglyoximate; lig = Lewis base; X = CN, NCO, NO₂) were synthesized and characterized by single crystal X‐ray diffraction. The enantiopure complexes were used as building blocks for the synthesis of binary crystals. Solid solutions resulted from cocrystallizing isomorphous compounds of equal chirality whereas complexes of opposite chirality formed well‐ordered heterochiral solids with efficient packing. Two binary crystals of the latter type could be studied by X‐ray diffraction: Cocrystallization of two isomorphous phenylethylamine derivatives gave a quasiracemic solid. Starting from two non‐isomorphous naphthylethylamine complexes of opposite chirality cocrystals with an unexpected composition were obtained: Their asymmetric unit comprises four independent complex molecules in a 3:1 ratio between the constituents.