Synthesis of peptide alkaloids-III. Amino acids and peptides-XXXII. Synthesis of dihydro-zizyphine A and B

Recently we described² a new cyclisation method for the synthesis of ansa peptides by hydrogenolysis of Z-pentafluorophenyl ester and ring closure on the surface of the palladium catalyst. We applied this reaction to the synthesis of the 14-membered ansa peptide dihydro-zizyphine G¹. Here we wish to report the synthesis of the 13-membered ansa peptides dihydro-zizyphine A ($\text{8a}$) and B ($\text{9a}$)³.     

Peralkynylated Tetraazaacene Derivatives

The synthesis of a decaethynylated tetraazapentacene is described. It was obtained by a combination of condensation reactions giving the two pyrazine rings and subsequent consecutive Stille-type couplings. This is the first example of any higher (hetero)acene that is peralkynylated. The presence of the four nitrogen atoms removes the peri interaction of the substituted alkyne groups, giving this rock-stable and highly twisted heteroacene.     

Bromination Improves the Electron Mobility of Tetraazapentacene

A cyclocondensation of TIPS‐ethynyl‐substituted diaminoarenes with in situ obtained 4,5‐dibromocyclohexa‐3,5‐diene‐1,2‐dione has led to the synthesis of tetrabromotetraazapentacene (BrTAP). BrTAP is easily reduced to its air‐stable radical anion and electron mobilities >0.56 cm² V^?1 s^?1 can be achieved in thin‐film transistors.     

Numerical Studies of Vanka-Type Smoothers in Computational Solid Mechanics

In this paper multigrid smoothers of Vanka-type are studied in the context of Computational Solid Mechanics (CSM). These smoothers were originally developed to solve saddle-point systems arising in the field of Computational Fluid Dynamics (CFD), particularly for incompressible flow problems. When treating (nearly) incompressible solids, similar equation systems arise so that it is reasonable to adopt the 'Vanka idea' for CSM. While there exist numerous studies about Vanka smoothers in the CFD literature, only few publications describe applications to solid mechanical problems. With this paper we want to contribute to closing this gap. We depict and compare four different Vanka-like smoothers, two of them are oriented towards the stabilised equal-order $Q_1/Q_1$ finite element pair. By means of different test configurations we assess how far the smoothers are able to handle the numerical difficulties that arise for nearly incompressible material and anisotropic meshes. On the one hand, we show that the efficiency of all Vanka-smoothers heavily depends on the proper parameter choice. On the other hand, we demonstrate that only some of them are able to robustly deal with more critical situations. Furthermore, we illustrate how the enclosure of the multigrid scheme by an outer Krylov space method influences the overall solver performance, and we extend all our examinations to the nonlinear finite deformation case.     

Efficient coherent population transfer among three states in NO molecules by Stark-Chirped rapid adiabatic passage

We present the experimental demonstration of a novel, efficient, and selective technique to prepare population inversion. The technique is an extension of Stark-chirped rapid adiabatic passage (SCRAP), i.e., SCRAP among three states. In this process a Lambda-type quantum system is driven by two laser pulses, the pump and Stokes pulses, which are appropriately detuned from transition frequencies. A third laser pulse induces a dynamic Stark shift in the upper energy level, and the timing of all three pulses is controlled in order to prepare population inversion between the two lower states in the Lambda-type level scheme. Our data on population transfer in nitric oxide (NO) molecules clearly show that SCRAP among three states provides an advantageous alternative to such techniques as stimulated Raman adiabatic passage.     

Localized in vivo H spectroscopy of human skeletal muscle: Normal and pathologic findings

To obtain high signal to noise ratio in small volume elements (8 cm³), in vivo ¹H NMR spectroscopy of normal and diseased human skeletal muscle was performed using a double spin-echo localization method on a 1.5-T whole body system. High resolved spectra of normal calf muscle show the well known resonances of lipids (methyl, methylene, olefinic, and other fatty acid resonances), creatine/phosphocreatine, choline/carnitine, taurine, and histidine with good intraindividual reproducibility. Pronounced intraindividual differences in the lipid range were found between different upper thigh muscle groups. On pathologic conditions like myopathia, myositis or irradiation damage the spectral lipid content was increased. Three months after local irradiation of the medial vastus muscle (50 Gy), the localized ¹H NMR spectrum showed a complete loss of the choline and creatine signals. In a case of M. Behçet with muscular involvement the relative reduction of the choline signal may provide an insight in the pathobiochemistry. The results of our investigations in nine healthy volunteers and three patients are presented in detail including relaxation times of the metabolites.