Dynamic mechanical investigations of different substituted cellulose o-silyl ethers

In contrast to many cellulose derivatives, the cellulose O-silyl ethers with bulky side groups exhibit scarcely a change in glass transition temperature by a variation of the degree of substitution (DS) or degree of polymerization (DP) or by introducing phenyl carbamate groups for the remaining hydroxyls along the main chain. However, a substitution of these hydroxyls by flexible acetate groups lowers the glass transition temperature considerably. The secondary dispersion (relaxation) behavior is strongly influenced by the various substituents and can be correlated to specific motions of the molecules. The dynamic mechanical properties are also dependent on the kind of preconditioning of the samples.     

Geometry Optimization of Thermoelectric Modules: Deviation of Optimum Power Output and Conversion Efficiency

Besides the material research in the field of thermoelectrics, the way from a material to a functional thermoelectric (TE) module comes alongside additional challenges. Thus, comprehension and optimization of the properties and the design of a TE module are important tasks. In this work, different geometry optimization strategies to reach maximum power output or maximum conversion efficiency are applied and the resulting performances of various modules and respective materials are analyzed. A Bi₂Te₃-based module, a half-Heusler-based module, and an oxide-based module are characterized via FEM simulations. By this, a deviation of optimum power output and optimum conversion efficiency in dependence of the diversity of thermoelectric materials is found. Additionally, for all modules, the respective fluxes of entropy and charge as well as the corresponding fluxes of thermal and electrical energy within the thermolegs are shown. The full understanding and enhancement of the performance of a TE module may be further improved.     

Criticality of metal based functional materials – How multi-functional trans-technical metal based materials are mobilized and how they get lost by dissipation

The enormous diversity of chemical compounds now available is problematic for waste disposal and recovery of essential resources such as rare earth metals. Non-renewable resources are being depleted and need to be managed more effectively. To validate the potential of strategic metals, which often are multi-functional and thus find (competitive) applications in different technologies, a criticality concept is applied. This is based on qualitative and quantitative criteria characterizing the different transformations along supply chains: ranging from the resource deposit to the product and from there into the so-called re-phases or disposal and end-of-life. The trajectories of the resources in real space and time have to be transparent in order to optimize the resource efficiency and its long-ranging compatibility but also to minimize dissipation. This approach allows developing transparent narratives (“Stoffgeschichten”, “Stories of Stuff”) for a responsible and benign use of resources. Only then can re-integration of functional materials be achieved.     

Survey of chemical residues and biological evaluation of photochemically pre-vulcanized surgical gloves

Abstract  

Latex allergies arise from the presence of latex proteins as well as noxious rubber additives (mainly accelerators and activators used in conventional sulfur-accelerated vulcanization processes) in medical devices (e.g., medical gloves, catheters) made from natural rubber latex. As a new approach the ultraviolet (UV) light-initiated pre-vulcanization of natural rubber latex makes efficient cross-linking feasible without using any toxic, mutagenic, or irritating chemicals. The cross-linking in the latex particles is accomplished via the thiol-ene addition reaction in the presence of a polyfunctional thiol and a photoinitiator. The new process is carried out in a falling film photoreactor on a pilot scale which provides a continuous irradiation of the latex emulsion. The UV technique is suitable for an easy up-scaling and represents the entrance into large-volume industrial production. The surgical gloves are then made by a conventional coagulant dipping process comprising good physical properties and high ageing stabilities. The aim of this study was to evaluate the biological properties and skin compatibility of UV-pre-cured gloves in skin sensitization, skin irritation studies, and cytotoxic tests. In addition the biologically available chemical residues in the gloves were characterized by UV–visible spectroscopy, elementary analyses, and high-performance liquid chromatography coupled with mass spectroscopy. The results of the studies revealed that UV-cross-linked surgical gloves exhibit good skin compatibility together with low cytotoxicity and residual chemical levels in the range of 60 and 120 μg/g_glove.     

FeNH4(SO4)2·12H2O (alum)-catalyzed preparation of 1,4-dihydropyridines: improved conditions for the Hantzsch reaction

Abstract  

FeNH₄(SO₄)₂·12H₂O (alum) efficiently catalyzes the one-pot three-component reaction of dimedone, aldehydes, and 3-aminocrotonate to afford 1,4-dihydropyridines. The work-up is easy, and the products are obtained in good to excellent yields and high purity.     

Effects of the physicochemical properties of titanium dioxide nanoparticles, commonly used as sun protection agents, on microvascular endothelial cells

Until now, the potential effects of titanium dioxide (TiO₂) nanoparticles on endothelial cells are not well understood, despite their already wide usage. Therefore, the present work characterizes six TiO₂ nanoparticle samples in the size range of 19 × 17 to 87 × 13 nm, which are commonly present in sun protection agents with respect to their physicochemical properties (size, shape, ζ-potential, agglomeration, sedimentation, surface coating, and surface area), their interactions with serum proteins and biological impact on human microvascular endothelial cells (relative cellular dehydrogenase activity, adenosine triphosphate content, and monocyte chemoattractant protein-1 release). We observed no association of nanoparticle morphology with the agglomeration and sedimentation behavior and no variations of the ζ-potential (?14 to ?19 mV) in dependence on the surface coating. In general, the impact on endothelial cells was low and only detectable at concentrations of 100 μg/ml. Particles containing a rutile core and having rod-like shape had a stronger effect on cell metabolism than those with anatase core and elliptical shape (relative cellular dehydrogenase activity after 72 h: 60 vs. 90 %). Besides the morphology, the nanoparticle shell constitution was found to influence the metabolic activity of the cells. Upon cellular uptake, the nanoparticles were localized perinuclearly. Considering that in the in vivo situation endothelial cells would come in contact with considerably lower nanoparticle amounts than the lowest-observable adverse effects level (100 μg/ml), TiO₂ nanoparticles can be considered as rather harmless to humans under the investigated conditions.     

Completely spirocyclopropanated macrocyclic oligodiacetylenes and their permethylated analogues: preparation and properties

The acyclic dehydrotrimer (12) and -hexamer (28) of 1,1-diethynyl-2,2,3,3-tetramethylcyclopropane were prepared from 1-chloro-1-(trimethylsilylethynyl)-2,2,3,3-tetramethylcyclopropane (4) in six and nine steps, respectively, in 36 and 8 % overall yield, respectively, using Cadiot-Chodkiewicz or Hay coupling procedures as key steps. Mono-tert-butyldimethylsilyl (TBDMS) protection of the acyclic dehydrotrimer (20) and -hexamer (23) of 1,1-diethynylcyclopropane followed by Hay coupling and protiodesilylation furnished the acyclic dehydrohexamer (23) and -dodecamer (29) in 35 and 56 % overall yield, respectively. Subsequent cyclizing oxidative dimerization of 12 or cyclization of 28 using a modified Glaser protocol produced the first completely permethylspirocyclopropanated macrocyclic oligodiacetylene, compound 30 in 49 and 21 % yield, respectively. The cyclic dehydrohexa- (31) and dehydrododecamer (32) have been prepared from 23 and 29 in 49 and 7 % yield by applying the same protocol. The macrocycle 32 is particularly interesting in that it contains 60 carbon atoms in the inner ring, and indeed a decomposition mode consecutively cleaving off ethylene units from it as well as from 31 and tetramethylethylene from the permethylated exp-[6]rotane 30 has been proved by differential scanning calorimetry with evolved gas analysis. The thermal decomposition of these "exploding" [6]rotanes 31 and 30 set on at 100 and 135 degrees C, respectively, and release energies of 478 and 285 kcal. mol(-1), respectively, significantly more than the energy release of the explosive hexogen with 143 kcal mol(-1).     

An oligomeric ser-pro dipeptide mimetic assuming the polyproline II helix conformation

A hexapeptide assembled from dipeptide building blocks assumes the secondary structure of the polyproline II (PPII) helix. Side chain-to-backbone hydrogen bonds stabilize peptide torsions next to the fused ring systems. The solution structure of the polyhydroxylated peptide was studied by spectroscopic methods.     

Numerical characterization of high harmonic attosecond pulses

A numerical simulation of attosecond harmonic pulse generation in a three-dimensional field-ionizing gas is presented. Calculated harmonic efficiencies quantitatively reproduce experimental findings. This allows a quantitative characterization of attosecond pulse generation revealing information currently not accessible by experiment. The rapid phase variation and spatiotemporal distortions of harmonics are smaller than anticipated, allowing focusing of 30-nm, 750-as pulses to intensities in excess of 10(13) W/cm(2). Feasibility of such pulses brings novel applications such as extreme ultraviolet nonlinear optics and attosecond pump probe spectroscopy within reach.