Investigations on synthesis and polymerization of difunctional 7-membered cyclic ketenacetals

Summary. The synthesis of difunctional seven-membered cyclic ketenacetals was investigated and the new monomers were characterized by IR-, NMR-spectroscopy, and elemental analysis. It was shown that the bifunctional ketenacetal 5 undergoes a radical homopolymerization forming crosslinked polymers with a high degree of ring-opened units. The copolymerization of the difunctional ketenacetal 5 with the monofunctional ketenacetal 1 leads only to low molecular polymers. Received: 9 May 1997/Revised: 4 July 1997/Accepted: 10 July 1997     

Synthesis of bioactive 2,2-dichloropropionic acid esters of carboxymethyl cellulose and investigations on their release behavior

Polymer bound bioactive agents are prepared by linking 2,2-dichloropropionic acid to the hydroxyl groups of carboxymethyl cellulose (CMC) and enzymatically cleavable CMC networks, and to the carboxyl groups of CMC via enzymatically cleavable spacer units using a simple as well as effective CMC activation procedure. The hydrolytic release of the bioactive agent is mainly dependent on the hydrophilicity of the CMC esters. In the case of polymers containing enzymatically cleavable structural units the release can be accelerated by addition of esterases.     

Electrical basis of peristalsis in the mammalian upper urinary tract

1. Peristalsis in the mammalian upper urinary tract (UUT) is mostly myogenic in origin, originating predominately in the proximal pelvicalyceal regions of the renal pelvis, an area that is enriched with specialized smooth muscle cells termed 'atypical' smooth muscle cells. Propagating peristaltic contractions are little affected by blockers of either autonomic nerve function or nerve impulse propagation; however, blockers of sensory nerve function or prostaglandin synthesis reduce both the frequency and the strength of the spontaneous contractions underlying peristalsis. 2. The electrical drive for these peristaltic contractions has long been considered to involve mechanisms analogous to the heart, such that 'atypical' smooth muscle cells generate spontaneous 'pacemaker' action potentials. These pacemaker potentials trigger the firing of action potentials and contraction in the muscular regions of the renal pelvis, which propagate distally to the ureter, propelling urine towards the bladder. 3. Recent intracellular microelectrode and single cell/channel patch-clamp studies have revealed that the ionic conductances underlying the action potentials recorded in the UUT are likely to involve the opening and slow closure of voltage-activated 'L-type' Ca2+ channels, offset by the time-dependent opening and closure of both voltage- and Ca(2+)-activated K+ channels. 4. In the present review we summarize the current knowledge of the ionic mechanisms underlying action potential discharge in the UUT, as well as present our view on how this electrical activity supports the initiation and conduction of UUT peristalsis.     

Microstructure development in Cr-Al-Si-N nanocomposites deposited by cathodic arc evaporation

Phase and texture analysis using X-ray diffraction, analysis of the diffraction line broadening, analysis of the lattice parameters and high-resolution transmission electron microscopy were employed to characterize the microstructure development in the Cr-Al-Si-N thin film nanocomposites with a variable [Cr] / ([Al] + [Si]) ratio deposited by cathodic arc evaporation. At the highest chromium contents, a single face centered cubic phase formed in the coatings. Below [Cr] / ([Cr] + [Al] + [Si]) ≈ 0.52, a second crystalline phase developed that was identified as hexagonal AlN. The size of the fcc crystallites decreased with increasing aluminum and silicon contents until it reached 5 nm in the sample with the overall chemical composition Cr_0.40Al_0.52Si_0.08N. The small crystallite size and the presence of two crystalline phases were found to be responsible for a high hardness of the Cr-Al-Si-N nanocomposites. Analysis of the lattice parameters revealed strong crystal anisotropy of the elastic constants in the cubic phase that decreased with increasing aluminum and silicon contents.     

Effect of Potassium on the Physiochemical and Catalytic Characteristics of V<Subscript>2</Subscript>O<Subscript>5</Subscript>/TiO<Subscript>2</Subscript> Catalysts in <Emphasis Type="Italic">o</Emphasis>-Xylene Partial Oxidation to Phthalic Anhydride

Abstract

Vanadia species formed on the surface depend on the K/V atomic ratio. At small K/V ratios, Raman spectra show the formation of the K-doped and K-perturbed monomeric species. At K/V?=?1, kristalline KVO₃ is mainly present on the surface. In situ high temperature XRD-results exhibit a promoting effect on the anatase to rutile phase transformation in the presence of 0.03 and 0.21 wt% potassium. Large amount of K (3 wt%) provides thermal stability of V/Ti/O catalyst and no transformation is found up to 600?°C. Reduction of vanadia K-doped vanadia catalysts is moved to higher temperatures than for the catalyst without potassium. The catalyst having 0.21 wt% K possesses the highest activity in o-xylene oxidation. Furthermore, the K-doped monomeric vanadia species in this catalyst leads to a promoted adsorption or a prevented desorption of phthalide, resulting in a decreased selectivity towards phthalide and CO_x and a increased PA selecticity.

Graphical Abstract

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(R)-(+)-palasonin,a cantharidin-related plant toxin,also occurs in insect hemolymph and tissues

Gas chromatographic and mass spectroscopic analyses of extracts of cantharidin-containing meloid, clerid, and staphylinid beetles revealed the presence of minor to significant amounts of palasonin, previously only known from seeds and fruits of the Indian shrub Butea frondosa (Leguminaceae). Unlike (S)-(–)-palasonin (>99% ee) from B. frondosa, the insects produce palasonin of low ee with the (R)-(+)-enantiomer (0–50% ee) prevailing. The ee of palasonin from individual specimens of predatory insects (Trichodes apiarius), which acquire their chemical protection from cantharidin-producing insects, may vary considerably. The absolute configuration of (S)-(–)-palasonin, previously deduced from indirect chemical and spectroscopic methods, was confirmed by X-ray crystal structure analysis of a cyclic imide derived from (S)-(–)-palasonin and (S)-(–)-1-(4-nitrophenyl)-ethylamine.     

Coagulated concentrated anatase slurry leads to improved strength of ceramic TiO2 bone scaffolds

Slurry behaviour has an important influence on the properties of ceramic scaffolds produced by the polymer sponge method. By adding chloride salts to the TiO₂ slurry, the viscosity was increased depending on the chloride concentration at low pH and high particle concentration. Slurries with higher viscosity led to closed and dense scaffold struts combined with high porosity, resulting in a compressive strength over 1.6 MPa. Furthermore, scaffold prepared with 0.1 M CaCl₂ and SrCl₂ showed the formation of Ca- and Sr-rich phases at the grain boundaries. These ions were also shown to reduce the activation energy for grain growth in the TiO₂ scaffold as indicated by the significantly larger grain size. Ca²⁺-doped scaffolds had the highest compressive strength, while the strength of Sr²⁺-doped scaffolds was reduced by the formation of a solid solution phase below the sintering temperature.