On the Material Symmetry of Elastic Rods

This paper presents a treatment of material symmetry for hyperelastic rods. The rod theory of interest is based on a Cosserat (or directed) curve with two director fields, and was developed in a series of works by Green, Naghdi and several of their co-workers. The treatment is based on Murdoch and Cohen's work on material symmetry of Cosserat surfaces. Two material symmetry groups are discussed: one pertains to the strain-energy function, while the other pertains to the response functions. The paper closes by showing how the treatment relates to the form-invariant approach used in Green and Naghdi's papers and a treatment proposed recently by Cohen. This revised version was published online in July 2006 with corrections to the Cover Date.     

Characterization of rubber particles and rubber chain elongation in <Emphasis Type="Italic">Taraxacum koksaghyz</Emphasis>

Background  

Natural rubber is a biopolymer with exceptional qualities that cannot be completely replaced using synthetic alternatives. Although several key enzymes in the rubber biosynthetic pathway have been isolated, mainly from plants such as Hevea brasiliensis, Ficus spec. and the desert shrub Parthenium argentatum, there have been no in planta functional studies, e.g. by RNA interference, due to the absence of efficient and reproducible protocols for genetic engineering. In contrast, the Russian dandelion Taraxacum koksaghyz, which has long been considered as a potential alternative source of low-cost natural rubber, has a rapid life cycle and can be genetically transformed using a simple and reliable procedure. However, there is very little molecular data available for either the rubber polymer itself or its biosynthesis in T. koksaghyz.     

Advances in the preparation of porous polymer monoliths in capillaries and microfluidic chips with focus on morphological aspects

Porous polymer monoliths have emerged as unique materials for many applications, including liquid-chromatographic analyses at an unrivaled speed, solid-phase extraction, and enzyme immobilization in capillary and microfluidic chip format. This article reviews the state of the art in the preparation of monoliths in narrow-bore capillaries and microfluidic chips and their miniaturization under conditions of spatial confinement. New developments in their preparation mainly using free radical polymerization techniques with a focus on morphological aspects in view of homogeneous porous materials are described. The suitability of monoliths for analysis of both large and small molecules is also discussed.     

Discovery and Structure Determination of an Unusual Sulfide Telluride through an Effective Combination of TEM and Synchrotron Microdiffraction

The structure elucidation of the novel sulfide telluride Pb₈Sb₈S₁₅Te₅ demonstrates a new versatile procedure that exploits the synergism of electron microscopy and synchrotron diffraction methods for accurate structure analyses of side‐phases in heterogeneous microcrystalline samples. Suitable crystallites of unknown compounds can be identified by transmission electron microscopy and relocated and centered in a microfocused synchrotron beam by means of X‐ray fluorescence scans. The refined structure model is then confirmed by simulating HRTEM images of the same crystallite. Pb₈Sb₈S₁₅Te₅ consists of chains of heterocubane‐like units. Cation coordination polyhedra form unusually entwined chains of edge‐ and face‐sharing bicapped trigonal prisms. The structure data are precise enough for bond‐valence calculations, which confirm the disordered atom distribution. On this basis, optimization of physical properties becomes feasible.     

Pd-Catalyzed Difluoromethylations of Aryl Boronic Acids,Halides, and Pseudohalides with ICF2H Generated ex Situ

An expedient ex-situ generation of difluoroiodomethane (DFIM) and its immediate use in a Pd-catalyzed difluoromethylation of aryl boronic acids and ester derivatives in a two-chamber reactor is reported. Heating a solution of bromodifluoroacetic acid with sodium iodide in sulfolane proved to be effective for the generation of near stoichiometric amounts of DFIM for the ensuing catalytic coupling step. A two-step difluoromethylation of aryl (pseudo)halides with tetrahydroxydiboron as a low-cost reducing agent, both promoted by Pd catalysis, proved effective to install this fluorine-containing C₁ group onto several pharmaceutically relevant molecules. Finally, the method proved adaptable to deuterium incorporation by simply adding D₂O to the DFIM-generating chamber.