A combined theoretical and experimental study of efficient and fast titanocene-catalyzed 3-exo cyclizations

The mechanism of titanocene mediated 3-exo cyclizations was investigated by a combined theoretical and experimental study. A gradient corrected density functional theory (DFT) method has been scaled against titanocene dichloride, the parent butenyl radical, and in bond dissociation energy (BDE) calculations. The BP86 method using density fitting, and a basis set of triple-zeta quality emerged as a highly reliable tool for studying titanocene mediated radical reactions. The computational results revealed important kinetic and thermodynamic features of cyclopropane formation. Surprisingly, the beta-titanoxy radicals, the first intermediates of our investigations, were demonstrated to possess essentially the same thermodynamic stabilization as the corresponding alkyl radicals by comparison of the calculated BDEs. In contrast to suggestions for samarium mediated reactions, the cyclization was shown to be thermodynamically favorable in agreement with earlier kinetic studies. It was established that stereoselectivity of the cyclization is governed by the stability of the intermediates and thus the trans disubstituted products are formed preferentially. The observed ratios of products are in good to excellent agreement with the DFT results. By a combination of computational and experimental results, it was also shown that for the completion of the overall cyclopropane formation the efficiency of the trapping of the cyclopropylcarbinyl radicals is decisive.     

The Ru(dipy)32+-Bromate-Malonic acid oscillating system

The Ru(dipy) ₃ ²⁺ -bromate-malonic acid oscillating system was in vestigated. It has been established that at early stages of the reaction the period of oscillation is about 20 sec and the potential change is about 170 mV; chloride at concentrations hiherg than 10^–3M is an inhibitor. The rates of both heat evolution and formation of bromomalonic acid are periodic. The activation energy of the oscillating (E) is 16.2 kcal mol^–1. Ru(dipy) ₃ ²⁺ -- . , 20 , 170 ; , - 10^–3 M, . . (E) 16,2 /.     

Multiparametric microsensor chips for screening applications

The identification of drug targets for pharmaceutical screening can be greatly accelerated by gene databases and expression studies. The identification of leading compounds from growing libraries is realized by high throughput screening platforms. Subsequently, for optimization and validation of identified leading compounds studies of their functionality have to be carried out, and just these functionality tests are a limiting factor. A rigorous preselection of identified compounds by in vitro cellular screening is necessary prior to using the drug candidates for the further time consuming and expensive stage, e.g. in animal models. Our efforts are focused to the parallel development, adaptation and integration of different microelectronic sensors into miniaturized biochips for a multiparametric, functional on-line analysis of living cells in physiologically environments. Parallel and on-line acquisition of data related to different cellular targets is required for advanced stages of drug screening and for economizing animal tests.     

[PtIn6][GaO4]2 – das erste Oxid mit [PtIn6]‐Oktaedern. Darstellung,Charakterisierung und Rietveldverfeinerung – mit einer Bemerkung zur Mischkristallreihe [PtIn6][GaO4]2–x[InO4]x (0 < x ≤ 1)

[PtIn₆][GaO₄]₂ – The First Oxide Containing [PtIn₆] Octahedra. Preparation, Characterisation, and Rietveld Refinement – With a Remark to the Solid Solution Series [PtIn₆][GaO₄]_2‐x[InO₄]_x (0 < x ≤ 1) The novel oxides [PtIn₆][GaO₄]_2–x[InO₄]_x (0 < x ≤ 1) are formed by heating intimate mixtures of Pt, In, In₂O₃, and Ga₂O₃ in the corresponding stoichiometric ratio in corundum crucibles under an atmosphere of argon (1220 K, 70 h). The compounds are black, stable in air at room temperature, reveal a semiconducting behaviour, and decompose only in oxidizing acids. X‐ray powder diffraction patterns can be indexed by assuming a face centered cubic unit cell with lattice parameters ranging from a = 1001.3(1) pm (x = 0) to a = 1009.3(1) pm (x = 1). According to a Rietveld refinement [PtIn₆][GaO₄]₂ crystallizes isotypic to the mineral Pentlandite (Fm3m, Z = 4, R(profile) = 6.11%, R(intensity) = 3.95%). The characteristic building units are isolated [PtIn₆]¹⁰⁺ octahedra which are linked via [GaO₄]^5– tetrahedra to a three dimensional framework. Starting from [PtIn₆][GaO₄]₂ the substitution of Ga³⁺ ions by larger In³⁺ ions leads to the formation of a solid solution series according to the general formula [PtIn₆][GaO₄]_2–x[InO₄]_x and becomes apparent in an increase of the lattice parameter.     

Composite hydrogels with temperature sensitive heterogeneities: influence of gel matrix on the volume phase transition of embedded poly-(N-isopropylacrylamide) microgels

The thermo-responsive behaviour of poly-(N-isopropylacrylamide) (PNiPAM) microgels embedded in covalently cross-linked non-temperature-sensitive polyacrylamide (PAam) hydrogel matrixes with different compositions was investigated by using small angle neutron scattering (SANS). The composition of the composite hydrogel was varied by (a) increasing the cross-linker and acrylamide concentration leading to strong hydrogel matrixes and (b) by increasing the microgel concentration to obtain composite gels with an internal structure. Additionally we synthesized composite hydrogels by using γ-irradiation as initiation for the polymerisation. This leads to the formation of chemical bonds between the PNiPAM microgels and the surrounding polyacrylamide matrix. Thus it is possible to synthesize hydrogels without an additional cross-linker, as well as pure particle networks. Some samples were prepared at two different temperatures, below and above the volume phase transition temperature of PNiPAM, resulting in highly swollen or totally collapsed microgels during the incorporation step. The volume phase transition of microgels is not influenced by a hydrogel matrix with high acrylamide concentration independent of the preparation temperature. However, an increased cross-linker concentration leads to a corset like constraint on microgel swelling. Microgels, which are embedded in the collapsed state (at 50 °C), are not able to swell upon cooling, whereas microgels embedded in the swollen state can collapse upon heating. For samples with an increased microgel concentration, the close microgel packing was disturbed by the formation of the polyacrylamide matrix. The hydrogel matrix squeezes the microgels together and leads to partial aggregation. The experiments demonstrate how composite hydrogels with stimuli-sensitive heterogeneities can be prepared such that the full responsiveness of the embedded microgels is retained while the macroscopic dimensions of the gel are not affected by the volume phase transition of the microgels.     

Limited stability of the pH reference material sodium tetraborate decahydrate (“borax”)

Thermogravimetric and X-ray powder diffraction analyses revealed that the pH reference material sodium tetraborate decahydrate (“borax”) is not a stable substance but, loosing some of its water of crystallization, transforms slowly into the pentahydrate. The connected pH changes of the solutions are opposite to and larger than, those expected according to the dilution value of the decahydrate as shown by differential potentiometric measurements. The transformation rate depends on the storing time in the closed original container, the time of and after the first exposure of the material to the atmosphere, the frequency of and the relative humidity during subsequent exposures, and the temperature. The transformation reaction is not understood in detail. However, the experiments showed that sodium tetraborate decahydrate is a reliable pH reference material, whose pH is constant within ΔpH=±0.005 within at least two years after preparation, even if occasionally exposed to the atmosphere. Further work will show whether this time limit can be somewhat extended.