A new enantioselective approach to the core structure of hypoxia selective prodrugs related to the duocarmycins

The indoline scaffold of hypoxia selective prodrugs of DNA-alkylating agents related to the duocarmycin natural products was synthesized via an enantioselective Friedel-Crafts alkylation. Easily accessible starting materials and good stereoselectivity in the alkylation step provide an enantioselective synthesis of the DNA-alkylating subunit.     

Substituent increments for the 1H-NMR. Chemical shifts of the 18- and 19-methyl protons of steroids. Part II: 9alpha, 10beta(normal)-steroids

In Part II of this series we report 292 substituent increments for the ¹H-NMR. chemical shifts (solvent: CDCl₃) of the 18- and 19-methyl protons of 9α,10β(normal)-steroids relative to 5α,9α,10β,-androstane. The increments were calculated by a least-squares procedure from 988 spectra of 681 different steroids.     

Diffraction microtomography with sample rotation: influence of a missing apple core in the recorded frequency space

Diffraction microtomography in coherent light is foreseen as a promising technique to image transparent living samples in three dimensions without staining. Contrary to conventional microscopy with incoherent light, which gives morphological information only, diffraction microtomography makes it possible to obtain the complex optical refractive index of the observed sample by mapping a three-dimensional support in the spatial frequency domain. The technique can be implemented in two configurations, namely, by varying the sample illumination with a fixed sample or by rotating the sample using a fixed illumination. In the literature, only the former method was described in detail. In this report, we precisely derive the three-dimensional frequency support that can be mapped by the sample rotation configuration. We found that, within the first-order Born approximation, the volume of the frequency domain that can be mapped exhibits a missing part, the shape of which resembles that of an apple core. The projection of the diffracted waves in the frequency space onto the set of sphere caps covered by the sample rotation does not allow for a complete mapping of the frequency along the axis of rotation due to the finite radius of the sphere caps. We present simulations of the effects of this missing information on the reconstruction of ideal objects.      

Possibilities for the Physical Modification of Cellulose Shapes Using Ionic Liquids

Summary: Functional cellulose shapes offer valuable properties for innovative application potentials in textile and medical products. Thereby excellent textile physiological properties of cellulose are allowed to be connected with novel application characteristics like bioactivity, electrical conductivity, heat storage or ability to adsorb liquids or gases. A very advantageous way to modify the properties of fibres, films or textile structures is to introduce particular additives via the Lyocell process. Regard to technical applications, functional additives will be able to incorporate themselves in the shape matrix and, in the case of using N-methylmorpholine-N-oxide monohydrate (NMMO) as solvent, implicate massive technological difficulties and deterioration of properties of the spinning dope. Beside a couple of limiting moments, ionic liquids (ILs) offer as direct solvents an excellent chance for physical modification of cellulose shapes. In contrast to NMMO, they exhibit a significantly higher thermal stability as well as a higher chemical resistance. ILs exhibit most widely a better dissolving capability for a number of different polymers. First results of the development of adsorber materials as well as novel bioactive fibres will be discussed and fibre characteristics will be given.     

Efficient Finite Element Analysis of Inelastic Structures with Iterative Solvers

This article treats the efficient solution of linear systems of equations which arise during the iterative process within the finite element analysis of inelastic structures. For the finite element analysis high order time integration methods and diagonally implicit Runge–Kutta methods (DIRK), in combination with an inexact Multilevel–Newton algorithm (MLNA) are applied. Up to 80% of the total computation time is spent by the solver for the linear systems, which suggests investigating this process. Two simple strategies to speed up the solution of the linear systems are described. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

From the onset of damage to rupture: construction of responses with damage localization for a general class of gradient damage models

We propose a construction method of non-homogeneous solutions for the traction problem of an elastic damaging bar. This bar has a softening behavior that obeys a gradient damaged model. The method is applicable for a wide range of brittle materials. For sufficiently long bars, we show that localization arises on sets whose length is proportional to the material internal length and with a profile that is also a material characteristic. From its onset until the rupture, the damage profile is obtained either in a closed form or after a simple numerical integration depending on the model. Thus, the proposed method provides definitions for the critical stress and fracture energy that can be compared with experimental results. We finally discuss some features of the global behavior of the bar such as the possibility of a snapback at the onset of damage. We point out the sensitivity of the responses to the parameters of the damage law. All these theoretical considerations are illustrated by numerical examples.     

Studies on the Thermostability of Modified Lyocell Dopes

Modification of Lyocell dopes with special additives enables the creation of new innovative materials. Additives with functional groups and active surfaces may initiate complex chemical reactions in cellulose/N-methylmorpholine-N-oxide monohydrate (NMMO) solutions. The effect of carboxylic groups on the thermostability was investigated by incorporating of sugar acids, acidic ion exchange resins (IER) and superabsorbing polymers (SAP) into the solutions. Whereas the sugar acids show strict correlations between the carboxyl group content in solution and onset temperature, viscosity reduction, coloration and by-product formation, the additives show an induction time, which finally leads to accelerated degradation reactions. The cellulose/NMMO solutions were additionally characterized by means of UV/VIS spectroscopy.