Ring Opening Reactions of β-Propiolactam in Superacidic Media

The reaction of β-propiolactam in the superacidic systems HF/MF₅ (M=Sb, As) led to the formation of monoprotonated 3-aminopropanoyl fluoride in the form of [C(O)F(CH₂)₂NH₃][SbF₆] and [C(O)F(CH₂)₂NH₃][AsF₆]. In the presence of traces of water, the diprotonated species β-alanine [C(OH)₂(CH₂)₂NH₃][AsF₆]₂ was synthesized for the first time. All salts were characterized by low-temperature infrared and Raman spectroscopy. Additionally, single-crystal X-ray analyses were conducted in the case of [C(O)F(CH₂)₂NH₃][SbF₆] and [C(OH)₂(CH₂)₂NH₃][AsF₆]₂. By using SO₂ instead of HF as the solvent, the salt [C(OH)₂(CH₂)₂NHSO][SbF₆]₂ was obtained, and single-crystal X-ray analysis of this salt containing a thionylimide moiety was conducted. For the formation of these open-chain compounds, an acyl cationic species as intermediate is assumed, which is formed from N-protonated β-propiolactam. Quantum chemical calculations at the B3LYP/aug-cc-pVTZ and MP2/aug-cc-pVTZ levels of theory were carried out to gain a better understanding of the formation and the structural properties of protonated β-propiolactam.     

Green Precursors and Soft Templating for Printing Porous Carbon-Based Micro-supercapacitors

A combination of soft lithographic printing and soft templating has been used to fabricate high-resolution interdigitated micro-supercapacitors (MSC). Surfactant-assisted self-assembly produces high surface area ordered mesoporous carbons (490 m² g⁻¹). For the first time, such precursors have been printed by nano-imprint lithography as microdevices with a line width of only 250 nm and a spacing of only 1 μm. The devices are crack-free with low specific resistance (1.2×10⁻⁵ Ωm) and show good device capacitance up to 0.21 F cm⁻³.     

Systematic Access of Ternary Organotetrel-Copper Chalcogenide Clusters by [PhTE3]3− Anions (T=Si,Sn; E=S,Se)

Fragmentation reactions of organotetrel chalcogenide heteroadamantane-type clusters [(PhT)₄E₆] (T/E=Si/S ( 1 ); Si/Se; Sn/S, and Sn/Se) by addition of the corresponding sodium chalcogenide gave salts of the general formula Na₃[PhTE₃], with T/E=Si/S ( 2 ); Si/Se ( 3 ); Sn/S ( A ); Sn/Se ( 4 ). Reaction of these salts with [Cu(PPh₃)₃Cl] gave a series of organotetrel–copper chalcogenide clusters [(CuPPh₃)₆(PhTE₃)₂] with T/E=Si/S; ( 5 ), Si/Se ( 6 ), Sn/S ( 7 ) and Sn/Se ( 8 ). Compounds 5 – 8 share a common structural motif with two intact {PhTE₃} units coordinating a Cu₆ moiety, which was previously reported with other ligands, and for the Sn and Ge congeners only. If the Sn/Se reaction system was allowed to crystallize more slowly, single crystals of compound [(CuPPh₃)₆(PhSnSe₃)₃Cu₃SnSe] ( 9 ) were obtained, which are based on a larger cluster structure. Hence, 9 might form from 8 through incorporation of additional cluster fragments. The experimentally and quantum chemically determined optical properties were compared to related clusters.     

Effect of lysozyme adsorption on the interfacial rheology of DPPC and cholesteryl myristate films

A model tear film lipid layer composed of a binary mixture of cholesteryl myristate (CM) and 1,2-dipalmitoyl- sn-glycero-3-phosphocholine (DPPC) was characterized using surface tension measurements, Brewster angle microscopy (BAM) and interfacial stress rheology (ISR). Isotherms showed that films containing >or=90 mol % CM have a 17-fold greater % area loss between the first and second compressions than the films with less CM. BAM images clearly showed that CM films did not expand after compression, and solid-like regions extending 1-2 mm were observed at low pressures (1 mN/m). Lipid films with or=50 mol % CM became elastic at higher surface pressures. Increasing CM content reduced the surface pressure at which the mixed film became elastic. Lysozyme adsorption into a CM film increased the compressibility and resulted in a more expanded film. Lysozyme increased the ductility of the CM/DPPC films with no film breakdown occurring up to the highest pressure measured (40 mN/m). In summary, CM increased the elasticity of the lipid films, but also caused them to become brittle and incapable of expansion following compression. Lysozyme adsorption increased the ductility and decreased the isotherm hysteresis for CM/DPPC films.     

Poly(ethylene imine)-controlled calcium phosphate mineralization

The current paper shows that poly(ethylene imine) (PEI) is an efficient template for the fabrication of spherical calcium phosphate (CaP)/polymer hybrid particles at pH values above 8. The polymer forms spherical entities, which contain one or a few CaP particles with diameters of ca. 6 nm. The samples contain up to 20 wt % polymer, which appears to be wrapped around the small CaP particles. The particles form via a mineralization-trapping pathway, where at the beginning of the precipitation small CaP particles form. Further particle growth is then prevented by precipitation of the PEI onto these particles at pH values of ca. 8. Stabilization of the particles is provided by the re-protonation of the PEI, which is adsorbed on the CaP particles, during the remainder of the mineralization process. At low pH, much larger particles form. They most likely grow via heterogeneous nucleation and growth on existing, polymer-modified CaP surfaces.     

High Rate Silicification of Peptide‐Polymer Assemblies Toward Composite Nanotapes

Well‐defined silica composite nanofibers are generated in a silicification process of self‐assembled poly(ethylene oxide)‐peptide nanotapes. Inspired by biological silica morphogenesis processes the nanotapes exhibit strong binding capabilities for silicic acid. Thus, pre‐hydrolyzed tetramethoxysilane could be used as silica precursor. Very low concentrations (270 µM) and short contact times (10 s) are sufficient to form effectively integrated nano‐composite tapes.

     

Synthese und Kristallstruktur des ersten Cp*‐geschützten Cobalttelluridclusters: Darstellung von [(Cp*Co)4(μ3‐Te)4] durch milde Oxidation von [Cp*CoCl]2 mittels Li4Sn2Te6 · 8 en

Synthesis and Crystal Structure of the First Known Cp* Ligated Cobalt Telluride Cluster: Mild Oxidation of [Cp*CoCl]₂ by Li₄Sn₂Te₆ · 8 en to give [(Cp*Co)₄(μ₃‐Te)₄] Oxidation of cobalt(II) complex [Cp*CoCl]₂ (Cp* = pentamethylcyclopentadiene) with binary Zintl polyanion hexatellurodistannate(IV) [Sn₂Te₆]^4– in Li₄Sn₂Te₆ · 8 en (en = 1,2‐diaminoethane) leads to the formation of the first Cp* ligated cobalt telluride cluster [(Cp*Co)₄(μ₃‐Te)₄]. The compound crystallizes as black cuboids that are suitable for X‐ray structural analysis. Space group P 1, lattice dimensions at 203 K: a = 1127.9(2), b = 1156.2(3), c = 1882.3(4) pm, α = 83.27(2), β = 83.24(2), γ = 66.11(1)°, V = 2222.3(9) · 10⁶ pm³, R₁ = 0.0681. The molecular structure of the compound features a Co₄Te₄ heterocubane and thus distributes to the completion of the series of known transition metal chalcogenide heterocubanes.     

The use of an hourglass stabilized solid-shell finite element in forming simulations — theoretical aspects and first industrial applications

The method of reduced integration with hourglass stabilization is one of the most powerful techniques in the field of finite element technology. Caused by the use of a reduced number of integration points it leads to very efficient finite element formulations. To avoid the appearance of non-physical zero-energy modes an hourglass stabilization is necessary. This paper presents an adaptive hourglass stabilization strategy motivated by the hyperelastic formulation of finite inelasticity. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Finite deformation pseudo-elasticity of shape memory alloys – Constitutive modelling and finite element implementation

In this paper we suggest a new phenomenological material model for shape memory alloys. In contrast to many earlier concepts of this kind the present approach includes arbitrarily large deformations. The work is motivated by the requirement, also expressed by regulatory agencies, to carry out finite element simulations of NiTi stents. Depending on the quality of the numerical results it is possible to circumvent, at least partially, expensive experimental investigations. Stent structures are usually designed to significantly reduce their diameter during the insertion into a catheter. Thereby large rotations combined with moderate and large strains occur. In this process an agreement of numerical and experimental results is often hard to achieve. One of the reasons for this discrepancy is the use of unrealistic material models which mostly rely on the assumption of small strains. In the present paper we derive a new constitutive model which is no longer limited in this way. Further its efficient implementation into a finite element formulation is shown. One of the key issues in this regard is to fulfil “inelastic” incompressibility in each time increment. Here we suggest a new kind of exponential map where the exponential function is suitably computed by means of the spectral decomposition. A series expansion is completely avoided. Finite element simulations of stent structures show that the new concept is well appropriate to demanding finite element analyses as they occur in practically relevant problems.