The reactions were carried out in sealed, evacuated glass ampoules in a temperature gradient 170 -+ 100°C. Te,o] and Te4[Bi2BrR] were both obtained as black, cubclike crystals with a violet lustre in reflecting light. Both compounds were found to be readily hydrolyzed by moist air. The preparations were accompanied by the formation of several by-products. All of these were found to have a higher tellurium content than the characterized compounds and were predominantly formed when a greater than stoichiometric amount of tellurium was used in the reaction When the amount of tellurium did not exceed the stoichiometry for Te4[Bi&!120] and Te4[Bi2Br8], these two compounds were formed as the principal products in yields of over 40%. Crystal Structure of Te4[Bi6ClZnJThe crystal structure is built up of discrete Tea' and polymeric [Bi6C120]2p ions. Table 1 contains the crystallographic data and the atomic coordinates, Figure I The chlorobismutate ion [Bi6C120]2-has a remarkable and complex structure. It consists of two distorted BiClh octahedra around Bi( 1) and Bi(3) and trigonal-pyramidal BiCl; units around Bi(2). The two BiCI6 octahedra are connected by a common corner with Cl(1) in the bridging position, while a BiCl, group is attached to Ri(1) by a common Cl(4) atom. These groups are connected by C1 atoms C1(2), Cl(3) and Cl(5) via common octahedral edges and corners to a two-dimensional sheet extending parallel to the crystallographic a-b plane. The Bi-CI bond lengths are depicted in Figure 3 in the form o f a histogram, which highlights the great variation in the coordination of the Bi atoms. The Bi(l)-Cl and Bi(3)-CI distances range from 248.9(3) to 306.6(4) pm. indicating strong distortion of the BiC16 octahedra. The coordination of Bi(2) also shows marked deviation. Three short Bi-CI bonds are seen, with an average length of 248.3 pm. while the next nearest coordinating CI atoms are more than 70 pin more distant. Thus, the local
In several filarial genera the first stage larvae (microfilariae) are enclosed by an eggshell-derived sheath that provides a major interface between the parasite and the host immune system. Analysis of the polypeptide constituents of the microfilarial sheath from the cotton rat filaria Litomosoides sigmodontis identified two abundant surface glycoproteins: Shp3a and Shp3. The corresponding genes and the orthologues of the human parasite Brugia malayi and the rodent filaria Brugia pahangi were cloned and sequenced. They encode secreted, mucin-like proteins with N-terminal Ser/Thrrich repeats and a C-terminal anchor domain rich in aromatic amino acids. About 75% of the protein molecular masses result from post-translational modifications. The Ser/Thr-rich motifs are supposed to serve as targets for dimethylaminoethanol-phosphate substitutions. These modifications were detected only on the sheaths of the late developmental stage of stretched microfilariae, corresponding with the expression of the proteins in the epithelium of the distal part of the uterus and the specific transcription of shp3 and shp3a in the anterior female worm segment. Genomic analysis of all three species demonstrated a conserved linkage of the two genes. Their transcripts undergo cis-and transsplicing. The transcription start sites of the primary transcripts were determined for the L. sigmodontis genes. The core promoter regions are remarkably conserved between the paralogue genes Ls-shp3a and Lsshp3 and their orthologues in Brugia, implicating conserved regulatory elements.The parasitic nematodes Brugia malayi, Brugia timori, and Wuchereria bancrofti are the causative agents of human lymphatic filariasis, a disease that afflicts an estimated 128 million people throughout the tropics (1) and in its final form results in severe obstructive alterations (elephantiasis). The adult lymphatic-dwelling parasites survive for years, and the viviparous females release large amounts of first stage larvae, microfilariae, into the blood stream. Completion of the filarial life cycle involves the uptake of the microfilariae by mosquitos, development to third stage larvae and transmission back to the vertebrate host. The microfilariae are completely surrounded by a bag-like, antibody-impermeable structure, the microfilarial sheath, which derives from the embryonic eggshell but is altered by maternal components secreted by the uterus epithelium (2). Parasitaemic hosts develop a parasite stage-specific immunological tolerance and fail to mount an antibody response to the microfilarial sheath surface proteins (3, 4). Therefore, it is of considerable interest to identify and characterize sheath surface components. The cotton rat filaria Litomosoides sigmodontis represents a suitable model organism for the lymphatics dwelling filarial parasites because of, in principle, a corresponding structure and genesis of the sheath (5). Previous studies with this parasite had identified two sheath proteins: Ls-Shp3a and Ls-Shp3 (40 and 120 kDa on SDS-PAGE) that appeared to ...
Tribometer measurements are used to simulate and investigate friction and wear mechanisms in sliding solid state systems. In metal forming and especially in deep drawing, tribometers are used to study the friction characteristics in the area of the stamp edge and draw edge rounding of a deep drawing tool. To replicate the reality of the deep drawing process a commercially available pin-on-disc tribometer is only useable to a certain extent because only a circular path can be traversed. At the Upper Austria University of Applied Sciences in Wels a spiral tribometer has been developed that can measure the friction coefficient along the desired friction distance. During the deep drawing process the temperature on the surface of a deep drawing tool rise due to the friction and wear conditions caused by the process. In order to investigate the influence of temperature the spiral tribometer is equipped with a heating system. To verify the results, comparison tests are performed with a commercially available pin-on-disc tribometer. Comparative tests confirm that the results obtained with the developed spiral tribometer match the values of the pin-on-disc tribometer.
Tellurium Polycations Stabilized by Halogenobismutates -Syntheses and CrystalStructures of Te4(Bi6Cl20) and Te4(Bi2Br8). -Black single crystals of the title compounds are prepared in ¿ 40% yield by reaction of Te, TeX4, and BiX3 (X: Cl, Br) in sealed evacuated glass ampoules in a temperature gradient 170 → 100 . degree.C. As revealed from the single-crystal XRD data, the compounds, which both adopt the triclinic space group P1 with Z = 2, are built-up from discrete Te2+4 cations and polymeric (BiCl20)2and (Bi2Br8)2-anions, respectively. The (Bi6Cl20)2-anion consists of a twodimensional sheet of distorted corner-and edge-sharing BiCl6 octahedra with attached BiCl3 groups. In the bromobismutate anions, the BiBr6 octahedra share cis-edges, forming infinite zigzag chains. -(BECK, J.; KASPER, M.; STANKOWSKI, A.; Chem.
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