Influence of organic modifiers on morphology and crystallization of poly(ϵ‐caprolactone)/synthetic clay intercalated nanocomposites

ε‐caprolactone was polymerized in the presence of neat montmorillonite or organomontmorillonites to obtain a variety of poly(ε‐caprolactone) (PCL)‐based systems loaded with 10 wt % of the silicates. The materials were thoroughly investigated by different X‐ray scattering techniques to determine factors affecting structure of the systems. For one of the nanocomposites it was found that varying the temperature in the range corresponding to crystallization of PCL causes reversible changes in the interlayer distance of the organoclay. Extensive experimental and literature studies on this phenomenon provided clues indicating that this effect might be a result of two‐dimensional ordering of PCL chains inside the galleries of the silicate. Small angle X‐ray scattering and wide angle X‐ray scattering investigation of filaments oriented above melting point of PCL revealed that polymer lamellae were oriented perpendicularly to particles of unmodified silicate, while in PCL/organoclay systems they were found parallel to clay tactoids. Calorimetric and microscopic studies shown that clay particles are effective nucleating agents. In the nanocomposites, PCL crystallized 20‐fold faster than in the neat polymer. The crystallization rate in nanocomposites was also significantly higher than in microcomposite. Further research provided an insight how the presence of the filler affects crystalline fraction and spherulitic structure of the polymer matrix in the investigated systems. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2350–2367, 2007     

Photoinduced Electron Transfer Reactions of alpha-Cyclopropyl- and alpha-Epoxy Ketones. Tandem Fragmentation-Cyclization to Bi-, Tri-, and Spirocyclic Ketones

Reductive photoinduced electron transfer (PET) reactions have been performed with various bicyclic alpha-cyclopropyl-substituted ketones and tertiary amines. The reaction resulted in a regioselective cleavage of one cyclopropyl bond under formation of an exocyclic radical with an endocyclic enolate unit. In the case of bicyclic ketones with an unsaturated side chain, various bicyclic, spirocyclic, and tricyclic products are accessible via radical cyclization, depending on the position of the alkenyl substituent. In addition to triethylamine, N-silylated amines have also been used as electron donors, leading to a variety of compounds, among them are silylated fragmentation products, indicating that a proton is transferred from not only the amine radical cation but also the cationic silyl group. The intramolecular Paternó-Büchi reaction has also been studied for cyclopropane derivatives of the jasmone type leading to tetracyclic oxetanes. Finally, alpha-epoxy-substituted ketones have been investigated under PET conditions, yielding ring-opened products.     

Graph products of groups and group spaces

An application of constructions from so-called Bass-Serre theory to group spaces in noncommutative geometry is discussed motivated by the question how to make visible the interplay of different structures coming together in the notion of a group space. A compact summary of basic notions and constructions from Bass-Serre theory up to the structure theorem is developed; it should serve as a brief guideline for further applications. Concluding prospects indicate a way for generalizing the methods from a categorical point of view.Dedicated to Professor Johannes André on the occasion of his 70th birthday     

Struktur von 7,11-Diphenyl-2,4-diazaspiro[5,5]undecan-1,3,5,9-tetraonen durch LIS-NMR

A semi-quantitative method for determining distances between a possible coordination centre and protons from LIS-NMR values is developed for the title compounds3, although these have four coordination points. This makes it possible to propose structures and conformations for the isomers of3.

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H.-H. Otto undH. Yamamura, Ann. Chem., im Druck.     

Aza-Claisen Rearrangement: Synthesis of 5′-branched 5′-aminothymidines

The syntheses of both diastereoisomers of 5′-ethyl-substituted thymidine dimers, the (5′R)- and (5′S)-configurated 33a and 33b respectively, in which the natural phosphodiester linkage is replaced by an amide group (C(3′)-CH₂CONH-CH(5′)(Et)), arc described. Their fully protected derivatives 35a and 35b , respectively, are suitable for incorporation into antisense oligonucleotides. Unexpectedly, an attempted Pd^II-catalysed aza-Claisen rearrangement of trichloroacetimidate 7 provided the diastereoisomerically pure cyclopropane derivative 17 , whose structure was confirmed by X-ray analysis.     

Copper—A “Modern” Bioelement

Copper is a bioessential element in biology with truly unique chemical characteristics in its two relevant oxidation states +I and +II. Significant progress has been made in recent years in the elucidation of the frequently surprising biochemistry of this trace element. Those advances were especially furthered through mutual stimulation involving results from biochemistry, molecular biology, and medicine on one hand and the synthesis as well as the structural and spectroscopic characterization of low molecular weight model complexes on the other. The most notable features of protein-bound active copper are its almost exclusive function in the metabolism of O₂ or N/O compounds (NO, N₂O) and its frequent association with oxidizing organic and inorganic radicals such as tyrosyl, semiquinones, superoxide, or nitrosyl. This unique biological role of copper can be rationalized given its chemical and assumed evolutionary background.     

Untersuchungen an Stickstoff—Jod-Verbindungen. VII. Das IR-Spektrum des Stickstofftrijodid-1-Ammoniaks im Bereich der N–J-Grundschwingungen und Kraftkonstanten der N–J-Bindungen

Studies on nitrogen iodine compounds. VII. The IR spectrum of nitrogen triiodide-1 ammonia in the range of N—I fundamental vibrations and the valence force constants of the N—I bonds New infrared spectra in the region 33—600 cm^?1 of ¹⁴NI₃ · ¹⁴NH₃, ¹⁵NI₃ · ¹⁵NH₃ and ¹⁴NI₃ · pyridine, respectively, have been obtained. In addition, the infrared spectrum of ¹⁴NI₃ · ¹⁴ND₃, which has been prepared for the first time, was obtained. All absorption frequencies can be coordinated on the ground of the molecule model for the NI₃ scaffold with 5 atoms Z₂XY₂ of the symmetry C_2v which has been proved by X ray examination. A set of force constants has been calculated by approximation. The various nitrogeniodine valence force constants are discussed.     

Modeling and numerical approximations for bubbles in liquid metal

In simulations of liquid metals, various model approximations, each of which justified by experimental results lead to a simplified two-phase flow problem. This paper discusses numerical justifications for these approaches and provides quantitative results for a single rising bubble as a benchmark. Representing a bubble as a rigid object is shown to be valid for low Eötvös numbers in contaminated systems. Qualitative differences can be observed for larger Eötvös numbers. Further simulations are undertaken with different ratios of inner and outer viscosity. The benchmark problem considered may also be interesting for more general applications.