Design magnetischer Materialien: Chemie der Magnete

The field of molecular based magnetism is an active area of research directed toward the design of new magnetic materials. The idea is to introduce molecular strategies in magneto-chemistry. This can open completely new synthetic routes to materials with previously unknown physical properties. Spin carriers used within this approach range from purely organic radicals to metal complexes and organometallic compounds. The design of new magnetic materials with tailor-made properties requires a detailed knowledge about the interactions between possible spin carriers and the strategies necessary to achieve interactions in all three dimensions. The latter is closely related to the field of crystal engineering. Starting from introductory remarks to magnetochemistry the underlaying concepts for the design of magnetic materials on the basis of molecular compounds as well as new developments and possible applications are described.     

Magnetic Interactions through Imidazolate‐Bridges: Synthesis,Spectroscopy, Crystal Structure and Magnetic Properties of μ‐Imidazolato‐Bridged Copper(II) Complexes

The synthesis, characterization and crystal structures of substituted imidazolate bridged binuclear copper(II) complexes, [Cu₂(dien)₂(L)](ClO₄)₃, where dien = diethylenetriamine, L = imidazolate (im^—) ( 1 ), 2‐methylimidazolate (mim^—) ( 2 ) and benzimidazolate (bim^—) ( 3 ), are reported. The copper(II) ions of 1 — 3 posses a square planar coordination environment with dien coordinating as a tridentate ligand and the fourth position being occupied by a nitrogen atom of the bridging μ‐imidazolato group. In all three compounds the tendency to form additional long apical bonds at the copper(II) ions to the oxygen atoms of the perchlorate anions is observed. Temperature depended susceptibility data of polycrystalline samples reveal an antiferromagnetic coupling of the copper(II) atoms in 1 — 3 with J = —63.8, —75.4 and —36.8 cm^—1, respectively. Significant changes for these coupling constants could not be observed for measurements on frozen aqueous solutions. ESR spectra for solids and frozen solutions are consistent with intramolecular antiferromagnetic exchange interaction between the metal ions. From the data reported it can be concluded that the predominate mechanism for transmitting exchange coupling through the imidazolate bridge is due to a σ exchange pathways.     

CsC2H: Synthese,Kristallstruktur und spektroskopische Eigenschaften

CsC₂H: Synthesis, Crystal Structure, and Spectroscopic Properties CsC₂H was synthesised by the reaction of caesium solved in liquid ammonia with acetylene. The crystal structure could be solved and refined from X‐ray and neutron powder diffraction data (space group: R3c, Z = 18). The structure is characterised by C₂H^– trimers which are surrounded by caesium ions. Spectroscopic investigations (IR and Raman) of the stable monoalkalimetal acetylides mainly confirm the data given in the literature and show that the alkalimetal cation has a marked influence on the vibrational properties of the C₂H^– anion.     

Abnormal resting-state cortical coupling in chronic tinnitus

Background  

Subjective tinnitus is characterized by an auditory phantom perception in the absence of any physical sound source. Consequently, in a quiet environment, tinnitus patients differ from control participants because they constantly perceive a sound whereas controls do not. We hypothesized that this difference is expressed by differential activation of distributed cortical networks.     

Heterometallic 3d–4f coordination polymers: Synthesis,characterization and magnetic properties of 1D zigzag chains containing samarium and terbium

Reaction of the copper precursor [Cu(MeOsaltn)(H₂O)] (H₂MeOsaltn = N,N′-bis(3-methoxysalicylidene)-1,3-diaminopropane) with Ln(NO₃)₃·6H₂O (Ln = Sm and Tb) and pyrazine-2,3-dicarboxylic acid (H₂pyrdic) results in the formation of 1D zigzag chains with the general formula of [Cu(MeOsaltn)Ln(NO₃)(pyrdic)]_n·nDMF. X-ray crystal structures reveal that the samarium and terbium compounds are isostructural and crystalize in the orthorhombic space group Pbcn. The chains are composed of heterodinuclear copper–lanthanide building blocks which are linked by the pyrazine-2,3-dicarboxylate bridging units. Temperature-dependent susceptibility measurements indicate antiferromagnetic exchange interactions for the samarium–copper chain whereas for the terbium–copper compound ferromagnetic interactions are observed.     

Siliceous spicules in marine demosponges (example Suberites domuncula)

All metazoan animals comprise a body plan of different complexity. Since--especially based on molecular and cell biological data--it is well established that all metazoan phyla, including the Porifera (sponges), evolved from a common ancestor the search for common, basic principles of pattern formation (body plan) in all phyla began. Common to all metazoan body plans is the formation of at least one axis that runs from the apical to the basal region; examples for this type of organization are the Porifera and the Cnidaria (diploblastic animals). It seems conceivable that the basis for the formation of the Bauplan in sponges is the construction of their skeleton by spicules. In Demospongiae (we use the model species Suberites domuncula) and Hexactinellida, the spicules consist of silica. The formation of the spicules as the building blocks of the skeleton, starts with the expression of an enzyme which was termed silicatein. Spicule growth begins intracellularly around an axial filament composed of silicatein. When the first layer of silica is made, the spicules are extruded from the cells and completed extracellularly to reach their the final form and size. While the first steps of spicule formation within the cells are becoming increasingly clear, it remains to be studied how the extracellularly present silicatein strings are formed. The understanding of especially this morphogenetic process will allow an insight into the construction of the amazingly diverse skeleton of the siliceous sponges; animals which evolved between two periods of glaciations, the Sturtian glaciation (710-680 MYA) and the Varanger-Marinoan ice ages (605-585 MYA). Sponges are--as living fossils--witnesses of evolutionary trends which remained unique in the metazoan kingdom.     

Nonsymmetrized Hyperspherical Harmonics with Realistic Potentials

The Schrödinger equation is solved for an A-nucleon system using an expansion of the wave function in nonsymmetrized hyperspherical harmonics. The present approach is based on a formalism developed by Gattobigio et al. (Phys. Rev. A 79:032513, 2009; Few-Body Syst. 45:127–131, 2009; Phys. Rev. C 83:024001, 2011). Spin and isospin degrees of freedom are included; this makes possible calculations with realistic NN potential models. The fermionic ground state is determined by introducing an additional potential term involving the Casimir operator such that the antisymmetric ground state becomes the lowest eigenstate of the A-body system. Results are discussed for ⁴He with the realistic AV18 NN potential and for ⁶Li with the semirealistic MTI/III NN potential.     

Creating and Modulating Microdomains in Pore‐Spanning Membranes

The architecture of the plasma membrane is not only determined by the lipid and protein composition, but is also influenced by its attachment to the underlying cytoskeleton. Herein, we show that microscopic phase separation of “raft‐like” lipid mixtures in pore‐spanning bilayers is strongly determined by the underlying highly ordered porous substrate. In detail, lipid membranes composed of DOPC/sphingomyelin/cholesterol/Gb₃ were prepared on ordered pore arrays in silicon with pore diameters of 0.8, 1.2 and 2 μm, respectively, by spreading and fusion of giant unilamellar vesicles. The upper part of the silicon substrate was first coated with gold and then functionalized with a thiol‐bearing cholesterol derivative rendering the surface hydrophobic, which is prerequisite for membrane formation. Confocal laser scanning fluorescence microscopy was used to investigate the phase behavior of the obtained pore‐spanning membranes. Coexisting liquid‐ordered‐ (l_o) and liquid‐disordered (l_d) domains were visualized for DOPC/sphingomyelin/cholesterol/Gb₃ (40:35:20:5) membranes. The size of the l_o‐phase domains was strongly affected by the underlying pore size of the silicon substrate and could be controlled by temperature, and the cholesterol content in the membrane, which was modulated by the addition of methyl‐β‐cyclodextrin. Binding of Shiga toxin B‐pentamers to the Gb₃‐doped membranes increased the l_o‐phase considerably and even induced l_o‐phase domains in non‐phase separated bilayers composed of DOPC/sphingomyelin/cholesterol/Gb₃ (65:10:20:5).