University of Stuttgart

About: University of Stuttgart is a education organization based out in Stuttgart, Germany. It is known for research contribution in the topics: Laser & Finite element method. The organization has 27715 authors who have published 56370 publications receiving 1363382 citations. The organization is also known as: Universität Stuttgart.

Cloning and characterization of a new laccase from Bacillus licheniformis catalyzing dimerization of phenolic acids.

Abstract: A new laccase gene (cotA) was cloned from Bacillus licheniformis and expressed in Escherichia coli. The recombinant protein CotA was purified and showed spectroscopic properties, typical for blue multi-copper oxidases. The enzyme has a molecular weight of ~65 kDa and demonstrates activity towards canonical laccase substrates 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), syringaldazine (SGZ) and 2,6-dimethoxyphenol (2,6-DMP). Kinetic constants K M and k cat for ABTS were of 6.5 ± 0.2 μM and 83 s−1, for SGZ of 4.3 ± 0.2 μM and 100 s−1, and for 2,6-DMP of 56.7 ± 1.0 μM and 28 s−1. Highest oxidizing activity towards ABTS was obtained at 85°C. However, after 1 h incubation of CotA at 70°C and 80°C, a residual activity of 43% and 8%, respectively, was measured. Furthermore, oxidation of several phenolic acids and one non-phenolic acid by CotA was investigated. CotA failed to oxidize coumaric acid, cinnamic acid, and vanillic acid, while syringic acid was oxidized to 2,6-dimethoxy-1,4-benzoquinone. Additionally, dimerization of sinapic acid, caffeic acid, and ferulic acid by CotA was observed, and highest activity of CotA was found towards sinapic acid.

A linear cobalt(II) complex with maximal orbital angular momentum from a non-Aufbau ground state

Abstract: INTRODUCTION The magnetic properties of a single metal center are determined by a combination of its total spin S and orbital angular momentum L . Orbital angular momentum gives rise to magnetic anisotropy, an essential property for applications such as information storage and high-coercivity magnets. Unquenched L arises from an odd number of electrons in degenerate orbitals and is typically observed only for free ions, as well as for complexes of the f elements. For the majority of transition metal ions, however, orbital angular momentum is quenched by the ligand field, which removes the requisite orbital degeneracies. Maximal L for a transition metal ( L = 3) would require an odd number of electrons in two sets of degenerate orbitals. Such a species would entail a non-Aufbau configuration, wherein the electrons do not fill the d orbitals in the usual order of lowest to highest in energy, and likely exhibit a large magnetic anisotropy. RATIONALE Previous efforts have identified the utility of linear coordination environments for isolating iron complexes with unquenched orbital angular momentum and large magnetic anisotropies. Crucially, transition metals in this environment are unaffected by Jahn-Teller distortions that would otherwise remove orbital degeneracies in the case of partially filled d orbitals. Separately, cobalt atoms deposited on a MgO surface—for which one-coordination of the metal is achieved, provided a vacuum is maintained—were shown to have L = 3, giving rise to near-maximal magnetic anisotropy. Calculations on the hypothetical linear molecule Co(C(SiMe 3 ) 3 ) 2 (where Me is methyl) also predicted that this system would possess a ground state with L = 3. Empirically, maximal L in a transition metal complex thus requires both a linear coordination environment and a sufficiently weak ligand field strength to allow for non-Aufbau electron filling. RESULTS The strongly reducing nature of the carbanion ligand hinders isolation of dialkyl cobalt(II) complexes. However, reducing the basicity of the central carbanion through the use of electron-withdrawing aryloxide groups allowed for the synthesis of the dialkyl cobalt(II) complex Co(C(SiMe 2 ONaph) 3 ) 2 , where Naph is a naphthyl group. Ab initio calculations on this complex predict a ground state with S = 3 / 2 , L = 3, and J = 9 / 2 arising from the non-Aufbau electron configuration (d x 2 –y 2 , d xy ) 3 (d xz , d yz ) 3 (d z 2 ) 1 . Much as for lanthanide complexes, the ligand field is sufficiently weak that interelectron repulsion and spin-orbit coupling play the key roles in determining the electronic ground state. dc magnetic susceptibility measurements reveal a well-isolated M J = ± 9 / 2 ground state, and simulations of the magnetic data from the calculations are in good agreement with the experimental data. Variable-field far-infrared (FIR) spectroscopy shows a magnetically active excited state at 450 cm −1 that, in combination with calculations and variable-temperature ac magnetic susceptibility experiments, is assigned to the M J = ± 7 / 2 state. Modeling of experimental charge density maps also suggests a d-orbital filling with equally occupied (d x 2 –y 2 , d xy ), and (d xz , d yz ) orbital sets. As a consequence of its large orbital angular momentum, the molecule exhibits slow magnetic relaxation and, in a magnetically dilute sample, a coercive field of 600 Oe at 1.8 K. CONCLUSION Isolation of Co(C(SiMe 2 ONaph) 3 ) 2 illustrates how an extreme coordination environment can confer an f-element–like electronic structure on a transition metal complex. The non-Aufbau ground state enables realization of maximal orbital angular momentum and magnetic anisotropy near the physical limit for a 3d metal. In this respect, the linear L–Co–L motif may prove useful in the design of new materials with high magnetic coercivity.

Synthesis and structural characterisation of rare-earth bis(dimethylsilyl)amides and their surface organometallic chemistry on mesoporous MCM-41†

Abstract: Rare-earth silylamides of type [Ln{N(SiHMe2)2}3(thf)x] (Ln = Sc, Y, La, Nd, Er or Lu) have been prepared in high yield by reaction of 2.9 equivalents of Li[N(SiHMe2)2] with [LnCl3(thf)x] in n-hexane or thf, depending on the solubility of the rare-earth halide precursor. The complexes [Ln{N(SiHMe2)2}3(thf)2] (Ln = Y, La to Lu) are isostructural in the solid state, adopting the preferred (3 + 2, distorted) trigonal bipyramidal geometry, whilst [Sc{N(SiHMe2)2}3(thf)] has a distorted tetrahedral co-ordination geometry and short Sc· · ·Si contacts in the solid state. The reaction of [Y{N(SiHMe2)2}3(thf)2] with varying amounts of AlMe3 resulted in desolvation and alkylation with formation of AlMe3(thf), {AlMe2[µ-N(SiHMe2]2}2 and heterobimetallic (Y/Al) species. The generation of surface-bonded ‘(SiO)xY[N(SiHMe2)2]y’ and ‘SiOSiHMe2’ moieties via the grafting of [Y{N(SiHMe2)2}3(thf)2] onto the mesoporous silicate MCM-41 is described in detail. Consideration is given to the factors governing the siloxide formation and silylation reactions, and the thermal stability of the surface species.

The validity of modulation equations for extended systems with cubic nonlinearities

Abstract: Modulation equations play an essential role in the understanding of complicated systems near the threshold of instability. Here we show that the modulation equation dominates the dynamics of the full problem locally, at least over a long time-scale. For systems with no quadratic interaction term, we develop a method which is much simpler than previous ones. It involves a careful bookkeeping of errors and an estimate of Gronwall type.As an example for the dissipative case, we find that the Ginzburg–Landau equation is the modulation equation for the Swift–Hohenberg problem. Moreover, the method also enables us to handle hyperbolic problems: the nonlinear Schrodinger equation is shown to describe the modulation of wave packets in the Sine–Gordon equation.

OpenTOSCA --- A Runtime for TOSCA-Based Cloud Applications

Abstract: TOSCA is a new standard facilitating platform independent description of Cloud applications. OpenTOSCA is a runtime for TOSCA-based Cloud applications. The runtime enables fully automated plan-based deployment and management of applications defined in the OASIS TOSCA packaging format CSAR. This paper outlines the core concepts of TOSCA and provides a system overview on OpenTOSCA by describing its modular and extensible architecture, as well as presenting our prototypical implementation. We demonstrate the use of OpenTOSCA by deploying and instantiating the school management and learning application Moodle.