Synthesis and processability into textile structures of radiopaque,biodegradable polyesters and poly(ester‐urethanes)

Radiopaque biodegradable polymers have been synthesized by ring‐opening polymerization of l /dl ‐lactide and caprolactone with the iodine‐containing starter molecule 2,2‐bis(hydroxymethyl)propane‐1,3‐diyl bis(2,3,5‐triiodobenzoate) followed by chain elongation with a diacid chloride or diisocyanates. The resulting polyesters and poly(ester‐urethanes) exhibited a radiopacity of 60?124% relative to an aluminium sample of the same thickness. The polymers were processed into monofilament fibres by melt‐spinning and into fibre meshes by electrospinning. All polymers were biodegradable in simulated body fluid medium under in vitro conditions and showed an excellent in vitro cytocompatibility even after several months of hydrolytic degradation. A current drawback is the relatively low tensile strength of the polymer monofilaments, which needs to be improved for applications as textile structures. Nevertheless, the new radiopaque and biodegradable polymers are promising candidates in fields of application where radiopacity of implants is an important parameter.     

Analysis of oxylipins by high-performance liquid chromatography with evaporative light-scattering detection and particle beam-mass spectrometry

The metabolism of 13 S-hydroperoxy-9Z,11E,15Z-octadecatrienoic acid was investigated in a crude enzyme extract from mung bean seedlings (Phaseolus radiatus L.). Hydroperoxide-metabolizing activity was mainly due to a hydroperoxide lyase and, to a lesser extent, to an allene oxide synthase and a peroxygenase. Oxylipins originating from hydrolysis and cyclization of the allene oxide synthase product 12,13-epoxy-9Z,11,15Z-octadecatrienoic acid and from peroxygenase catalysis were identified by high-performance liquid chromatography (HPLC) particle beam-mass spectrometry (PB-MS) and quantified by normal-phase HPLC with an evaporative light-scattering detector (ELSD). An advantage of this methodology was the possibility to avoid extensive derivatization procedures commonly used for the gas chromatographic analysis of oxylipins. Owing to a comparable sample inlet system, the ELSD served an important analytical pilot function for the PB-MS: Qualitatively identical chromatographic patterns were obtained with both detection systems. The HPLC system enabled the separation of methyl 12-oxo-phytodienoate, methyl 11-hydroxy-12-oxo-9Z,15Z-octadecadienoate, methyl 12-oxo-13-hydroxy-9Z,15Z-octadecadienoate, methyl 9-hydroxy-12-oxo-10E,15Z-octadecadienoate, methyl 13-hydroxy-9Z,11E,15Z-octadecatrienoate, methyl 15,16-epoxy-13-hydroxy-9Z,11E,15Z-octadecatrienoate, and methyl 13-hydroperoxy-9Z,11E,15Z-octadecatrienoate on a Lichrospher DIOL column within 33 min. Compared with a diode array detector, the ELSD proved to be more sensitive, in the case of methyl 12-oxo-13-hydroxy-9Z, 15Z-octadecadienoate by a factor of about 15. In addition, volatile metabolites were analyzed by capillary gas chromatography. The yield of the hydroperoxide lyase product 2E-hexenal was 49%, whereas the sum of oxylipins reached about 15%.     

Defect Chemistry of Donor-Doped and Undoped Strontium Titanate Ceramics between 1000° and 1400°C

The electrical conductivity, sigma, of donor-doped and undoped strontium titanate (SrTiO₃) ceramics and, in some cases, single crystals, Sr1-xLaxTiO₃ (0 ≤ to x ≤ 0.1), was investigated in the temperature range of 1000°-1400°C under oxygen partial pressures, PO₂, of 10_-20-1 bar. In conjunction with Hall data and thermopower data from related papers, a set of constants for a defect-chemical model was determined, precisely describing point-defect concentrations and transport properties of these materials. In contrast to former works, temperature-dependent transport parameters and their non-negligible influence on the determination of the constants was considered, as well as the equilibrium restoration phenomena of the cation sublattice, which can be studied only at such high temperatures. It was shown that defects in the cation sublattice completely govern the electrical behavior of donor-doped and undoped SrTiO₃. In the latter case, frozen-in strontium vacancies act as intrinsic acceptors, determining the sigma(PO₂) curves at lower temperatures. This intrinsic acceptor concentration also can be calculated with this model. The very good agreement between calculation and measurement is shown in many examples.     

Enantiomer Separation of a Novel Ca-Sensitizing Drug by simulated moving bed (SMB) – chromatography

The continuous chromatographic seperation by maens of Simulated Moving Bed (SMB) – Chromatography was used to produce the enantiomers of 5-(1,2,3,4-tetrahydroquinoline-6-yl)-6-methyl-3,6-dihydro-1,3,4-thiadiazin-2-one (EMD 53986), a precursor of the novel Ca-sensitizing drug 5-(1-(3,4-dimethoxybenzoyl)-1,2,3,4-tetrahydroquinoline-6-yl)-6-methyl-3,6-dihydro-1,3,4-thiadiazin-2-one (EMD 57033). The (+)-enantiomer EMD 57033 is a potent Ca-sensitizing drug, whereas its (−)-antipode is a pure phosphodiesterase-(PDE)-inhibitor without any Ca-sensitizing activity. A chromatographic seperation of the enantiomers was developed on two different chiral stationary phases: a cellulose-tri-(p-methyl-benzoate) phase and a polymeric silica based stationary phases. A process simulation software was used to calculate the starting parameters for the SMB-system. For both stationary phases the SBM-parameters were optimized and pure enantiomers were produced using a system with 8 columns of 26 mm internal diameter. A comparison of the purities and throughput achieved with both stationary phases is given.     

Electrospinning of pure polymer-derived SiBCN nanofibers with high yield

In this paper, we have discussed the synthesis of nanoscale silicoboron carbonitride (SiBCN) nanofibers by electrospinning of novel polyborosilazane precursor solutions, which were synthesized from boron trichloride, tris(dichloromethylsilylethyl)borane and hexamethyldisilazane using a one-pot method, followed by pyrolysis at 1000 °C under nitrogen atmosphere. The influence of the processing procedure (solution concentration, feeding rate and spinning voltage) of the electrospum fibers was also investigated. TGA and FT-IR experiments were employed to study the polymer-to-ceramic conversion and SEM was used to characterize the final materials. Combining the precursor derived ceramics route and electrospinning process enables to product SiBCN nanofibers for industrial applications.     

Modeling of surface intermediates under forced periodic conditions applied to CO2 methanation

Forced oscillations of the carbon dioxide concentration in a hydrogen feed were applied to the carbon dioxide methanation reaction with simultaneous gas phase and surface analysis. The response of the gas phase and surface species to these repeated dynamic conditions show a time shift following the sequence CO₂ → formate → CO → methane, but can be modeled by a simple model involving one single adsorbed surface intermediate and a reservoir in equilibrium with this intermediate. The dynamic behavior of this intermediate is very close to the variation of the IR absorption band associated with formate and carbonate species.     

The Thermal Conductivity of Polymer‐Derived Amorphous Si–O–C Compounds and Nano‐Composites

Silicon oxycarbide glasses can be produced over a range of Si–O–C compositions by the controlled pyrolysis of polymer precursors. We present measurements of the thermal conductivity of a silicon oxycarbide glass after two different heat treatments and two Si–O–C nano‐composites, hot‐pressed at 1600°C, up to 1000°C and compare them to fused silica, amorphous carbon, and SiC. The temperature dependence of their thermal conductivities is similar to other amorphous materials. The presence of low volume fractions of nanoparticles of hafnia (4.5 v/o) or zirconia (7.4 v/o) dispersed within the amorphous matrix only modifies the conductivity slightly, consistent with a simple Maxwell model, and does not affect the temperature dependence of the thermal conductivity above room temperature.     

Microwave Absorption of SiC/HfCxN1−x/C Ceramic Nanocomposites with HfCxN1−x‐Carbon Core–Shell Particles

The dielectric properties of high‐temperature stable single‐source precursor‐derived SiC/HfC_xN_1?x/C ceramic nanocomposites are determined by microwave absorption in the X‐band (8.2–12.4 GHz) at room temperature. The samples synthesized at 1700°C, denoted as SiC/5HfC_xN_1?x/C‐1700°C and SiC/15HfC_xN_1?x/C‐1700°C ceramics, comprising ≈ 1.3 and ≈ 4.2 vol% HfC_xN_1?x, respectively, show enhanced microwave absorption capability superior to hafnium‐free SiC/C‐1700°C. The minimum reflection loss of SiC/5HfC_xN_1?x/C‐1700°C and SiC/15HfC_xN_1?x/C‐1700°C are ?47 and ?32 dB, and the effective absorption bandwidth amount to 3.1 and 3.6 GHz, respectively. Segregated carbon, including graphitic carbon homogeneously dispersed in the SiC matrix and less ordered carbon deposited as a thin film on HfC_xN_1?x nanoparticles, accounts for the unique dielectric behavior of the SiC/HfC_xN_1?x/C ceramics. Due to their large reflection loss and their high chemical and temperature stability, SiC/5HfC_xN_1?x/C‐1700°C and SiC/15HfC_xN_1?x/C‐1700°C ceramics are promising candidate materials for electromagnetic interference applications in harsh environment.