Thermal Decomposition and Dehydration Kinetics of Tetra(piperidinium) Octamolybdate Tetrahydrate in Air

Thermal decomposition of tetra(piperidinium) octamolybdate tetrahydrate, [C₅H₁₀NH₂]₄[Mo₈O₂₆]·4H₂O, was investigated in air by means of TG‐DTG/DTA, DSC, TG‐IR and SEM. TG‐DTG/DTA curves showed that the decomposition proceeded through three well‐defined steps with DTA peaks closely corresponding to mass loss obtained. Kinetics analysis of its dehydration step was performed under non‐isothermal conditions. The dehydration activation energy was calculated through Friedman and Flynn‐Wall‐Ozawa (FWO) methods, and the best‐fit dehydration kinetic model function was estimated through the multiple linear regression method. The activation energy for the dehydration step of [C₅H₁₀NH₂]₄[Mo₈O₂₆]·4H₂O was 139.7 kJ/mol. The solid particles became smaller accompanied by the thermal decomposition of the title compound.     

A chip-based platform for the in vitro generation of tissues in three-dimensional organization

We describe a multi-purpose platform for the three-dimensional cultivation of tissues. The device is composed of polymer chips featuring a microstructured area of 1-2 cm(2). The chip is constructed either as a grid of micro-containers measuring 120-300 x 300 x 300 microm (h x l x w), or as an array of round recesses (300 microm diameter, 300 microm deep). The micro-containers may be separately equipped with addressable 3D-micro-electrodes, which allow for electrical stimulation of excitable cells and on-site measurements of electrochemically accessible parameters. The system is applicable for the cultivation of high cell densities of up to 8 x 10(6) cells and, because of the rectangular grid layout, allows the automated microscopical analysis of cultivated cells. More than 1000 micro-containers enable the parallel analysis of different parameters under superfusion/perfusion conditions. Using different polymer chips in combination with various types of bioreactors we demonstrated the principal suitability of the chip-based bioreactor for tissue culture applications. Primary and established cell lines have been successfully cultivated and analysed for functional properties. When cells were cultured in non-perfused chips, over time a considerable degree of apoptosis could be observed indicating the need for an active perfusion. The system presented here has also been applied for the differentiation analysis of pluripotent embryonic stem cells and may be suitable for the analysis of the stem cell niche.     

Synthesis and characterisation of PC(sp3)P phosphine and phosphinite platinum(II) complexes. Cyclometallation and simple coordination

New and improved preparative routes to the previously known PCP ligands cis-1,3-bis(di-isopropylphosphinito)cyclohexane and cis-1,3-bis[(di-tert-butylphosphino)methyl]cyclohexane are reported. They react with 1 equivalent of dichloro(1,5-cyclooctadiene)platinum(II) [(COD)PtCl2] to give the cis coordinated complex cis-[PtCl2{cis-1,3-bis(di-isopropylphosphinito)}cyclohexane] and the C(sp3)-H activated complex trans-[PtCl{cis-1,3-bis(di-tert-butylphosphino)}cyclohexane]. The new PCP ligand cis-1,3-bis(di-tert-butylphosphinito)cyclohexane was synthesised and reacts with [(COD)PtCl2] giving the di-nuclear trans-[PtCl2{cis-1,3-bis(di-tert-butylphosphinito)cyclohexane}]2, which is highly insoluble. All metal complexes were characterised with X-ray crystallography. DFT calculations indicate that the inability of the phosphinite ligands to cyclometallate is due to a kinetic barrier, possibly involving an axial-equatorial conformational change necessary for the C-H activation process.     

铜取代Dawson结构杂多钨磷酸电荷转移配合物的合成与性质研究

Two new charge-transfer complexes, (DMAH)₁₀［CuP₂W₁₇O₆₂］·DMF·2H₂O and (DMAH)₁₄［Cu₂P₂W₁₆O₆₂］ have been prepared in aqueous solution from N,N′-dimethylaniline(DMA) and copper substituted polyoxotungstates with Dawson Structure, and characterized by elemental analysis, ICP, TG, IR, diffusion reflectance electronic spectra, polarography, and CV. The results indicate that the structure of anion has little change after the charge-transfer complexes are formed, but the characteristic vibrational bands have some red shift or blue shift. The charge transfer takes place under sunlight. There is a new absorption band at 625 nm in the solid reflectance electronic spectra of the complexes, it is ascribed to the IVCT (W(V)→W(Ⅵ) band of the reduced anion ［CuP₂W₁₇O₆₂］^10-. The conductivities at room temperature of title complexes are 3.6×10^-9 S·cm^-1 and 5.4×10^-9 S·cm^-1, respectively. Both of them are weak semiconductors.     

Isotope shifts and hyperfine structure in calcium 4snp and 4snf F Rydberg states

Isotope shifts and hyperfine structure have been measured in 4snp ¹ P₁ and Rydberg states for all stable calcium isotopes and the radioisotope ⁴¹Ca using high-resolution laser spectroscopy. Triple-resonance excitation via Rydberg state was followed by photoionization with a CO₂ laser and mass selective ion detection. Isotope shifts for the even-mass isotopes have been analyzed to derive specific mass shift and field shift factors. The apparent isotope shifts for ⁴¹Ca and ⁴³Ca exhibit anomalous values that are n-dependent. This is interpreted in terms of hyperfine-induced fine-structure mixing, which becomes very pronounced when singlet-triplet fine-structure splitting is comparable to the hyperfine interaction energy. Measurements of fine-structure splittings for the predominant isotope ⁴⁰Ca have been used as input parameters for theoretical calculation of the perturbed hyperfine structure. Results obtained by diagonalizing the second-order hyperfine interaction matrices agree very well with experimentally observed spectra. These measurements allow the evaluation of highly selective and sensitive methods for the detection of the rare ⁴¹Ca isotope. Received 17 December 1999 and Received in final form 29 March 2000     

Total Synthesis of (−)-Bafilomycin A1: Application of Diastereoselective Crotylboration and Methyl Ketone Aldol Reactions

A careful orchestration of protecting groups is an essential requirement for the total synthesis of the macrolide antibiotic bafilomycin A₁ ( 1 ). Key steps were the Suzuki cross-coupling reaction of two advanced, suitably protected intermediates prior to closure of the macrocycle, as well as a highly stereoselective methyl ketone aldol reaction.     

First results from the CRIS experiment

The ability to study rare isotopes with techniques such as mass spectrometry and laser spectroscopy is often prevented by low production rates and large isobaric contamination. This has necessitated the development of novel beam cleaning techniques that can efficiently isolate the isotope of interest. The Collinear Resonance Ionization Spectroscopy (CRIS) experiment at ISOLDE, achieves this by resonantly ionizing a bunched atom beam in a region of ultra high vacuum. This method is motivated by the need to measure the hyperfine structure and isotope shift at the extremes of isospin where typical production rates drop to 1 atom/s. The technique also offers the ability to purify an ion beam and even select long-lived isomeric states (> 1 ms) from the ground state, which can be subsequently studied by decay spectroscopy or mass spectrometry experiments. This paper will report on the successful commissioning of the CRIS beam line and the recent laser spectroscopy results and laser assisted nuclear decay spectroscopy on the neutron deficient francium isotopes.     

Enantioselective Zinc‐Catalyzed Hydrosilylation of Ketones using Pybox or Pybim Ligands

The combination of ZnEt₂ and chiral pyridinebisoxazoline (pybox) or pyridinebisimidazoline (pybim) ligands catalyzed the asymmetric hydrosilylation of aryl, alkyl, cyclic, heterocyclic, and aliphatic ketones. Under mild conditions, high yields and good enantioselectivities were achieved. ESI measurements allowed for the characterization of the active catalyst.