Zur Kenntnis der Hydrolyse substituierter Imidazolidinthione-(4)

Imidazolidine-thiones-(4) are hydrolyzed in acid solutions or by ammonium hydroxide. Selective formation of α-aminothioneamides, α-aminocarbonamides, α-aminoesters or α-aminoacids takes place in good yields as a function of the reaction conditions. Hydrolysis of the imidazolidinones-(4) leads predominantly to α-aminoacids. α-Aminothioneamides can be converted into α-aminocarbonamides, α-aminoesters or α-aminoacids under relatively mild conditions.     

Summation methods of Coulomb interactions in computer simulations of a system with one—dimensional periodic boundary conditions

The Ewald-type method, its modified version and the Lekner-type method for summing Coulomb interactions in a system periodic along one direction are presented and compared. Advantages and disadvantages of these methods are discussed, and the methods are tested in molecular dynamics simulations of acetone molecules confined to cylindrical silica pores.     

Electrostatic interactions in molecular dynamics simulation of a three-dimensional system with periodicity in one direction

The Mellin transform and Poisson summation formula are used to derive an expression for the Coulomb interaction energy of a three-dimensional system with periodicity in one direction. Initially, calculations are performed for interactions characterized by any inverse power and, using the analytical continuation of the energy function, one obtains the final expression for the interaction energy of charges. We consider also a special case when two different charges are located on a line parallel to the periodicity direction. The energy and force expressions are identical to those obtained from the Lekner summation which is simply a sum over reciprocal lattice terms. The convergence behaviour of the Lekner summation is compared with that based on the Ewald type approach.     

Bacterial biosynthesis and maturation of the didemnin anti-cancer agents

The anti-neoplastic agent didemnin B from the Caribbean tunicate Trididemnum solidum was the first marine drug to be clinically tested in humans. Because of its limited supply and its complex cyclic depsipeptide structure, considerable challenges were encountered during didemnin B's development that continue to limit aplidine (dehydrodidemnin B), which is currently being evaluated in numerous clinical trials. Herein we show that the didemnins are bacterial products produced by the marine α-proteobacteria Tistrella mobilis and Tistrella bauzanensis via a unique post-assembly line maturation process. Complete genome sequence analysis of the 6,513,401 bp T. mobilis strain KA081020-065 with its five circular replicons revealed the putative didemnin biosynthetic gene cluster (did) on the 1,126,962 bp megaplasmid pTM3. The did locus encodes a 13-module hybrid non-ribosomal peptide synthetase-polyketide synthase enzyme complex organized in a collinear arrangement for the synthesis of the fatty acylglutamine ester derivatives didemnins X and Y rather than didemnin B as first anticipated. Imaging mass spectrometry of T. mobilis bacterial colonies captured the time-dependent extracellular conversion of the didemnin X and Y precursors to didemnin B, in support of an unusual post-synthetase activation mechanism. Significantly, the discovery of the didemnin biosynthetic gene cluster may provide a long-term solution to the supply problem that presently hinders this group of marine natural products and pave the way for the genetic engineering of new didemnin congeners.     

Determination of the Energy Flux of a Commercial Atmospheric‐Pressure Plasma Jet for Different Process Gases and Distances Between Nozzle Outlet and Substrate Surface

The energy flux of an atmospheric‐pressure plasma jet for surface treatment has been investigated by a calorimetric probe. Generally, the investigations exhibit that the main contributions of the total energy influx from the plasma to the substrate surface originate from the neutrals regarding high gas temperature coupled with a high gas flow. The use of nitrogen as process gas shows a higher energy flux compared to oxygen and air presumably caused by increased gas temperature as well as by higher molecule formation and recombination energy of N₂. Moreover, the lateral expansion of the plasma beam could be roughly determined by a spatially resolved analysis of the energy influx. A top part mounted on the nozzle, commonly used for the injection of additional precursor gases, showed a significant effect on the flow behavior and collision entailed relaxation of the excited plasma species leading to a restraining of the plasma jet. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A multiscale hp-FEM for 2D photonic crystal bands

A multiscale generalised hp-finite element method (MSFEM) for time harmonic wave propagation in bands of locally periodic media of large, but finite extent, e.g., photonic crystal (PhC) bands, is presented. The method distinguishes itself by its size robustness, i.e., to achieve a prescribed error its computational effort does not depend on the number of periods. The proposed method shows this property for general incident fields, including plane waves incident at a certain angle to the infinite crystal surface, and at frequencies in and outside of the bandgap of the PhC. The proposed MSFEM is based on a precomputed problem adapted multiscale basis. This basis incorporates a set of complex Bloch modes, the eigenfunctions of the infinite PhC, which are modulated by macroscopic piecewise polynomials on a macroscopic FE mesh. The multiscale basis is shown to be efficient for finite PhC bands of any size, provided that boundary effects are resolved with a simple macroscopic boundary layer mesh. The MSFEM, constructed by combing the multiscale basis inside the crystal with some exterior discretisation, is a special case of the generalised finite element method (g-FEM). For the rapid evaluation of the matrix entries we introduce a size robust algorithm for integrals of quasi-periodic micro functions and polynomial macro functions. Size robustness of the present MSFEM in both, the number of basis functions and the computation time, is verified in extensive numerical experiments.