Radikalische Fragmentierung bei der Photolyse von Aryldiazoniumsalzen

Homolytic Fragmentation in the Photolysis of Aryldiazonium Salts The photolysis of 4-benzyloxy-( 4a ), 4-(p-methoxy-benzyloxy)-( 4b ) and 4-benzhydryloxy benzenediazonium ( 4c ) tetrafluoroborates in methanol under nitrogen and at λ > 300 nm were studied. Only the benzyloxy derivate gives rise to the products of the normal ionic and homolytic substitution. Besides this, the diazonium salts 4b and 4c are cleaved giving the arylmethyl radicals 9b and 9c and 1-carbena-cyclohexadien-4-on, which partly combine, and partly abstract hydrogen from the methanol solvent. Moreover, the aryl-methyl radicals are oxidized by the parent aryldiazonium compounds, giving arylmethyl carbonium ions which react with methanol to the products of an apparent ionic fragmentation. An ionic fragmentation occurs, if at all, to a very small extent.     

Chemical Zymogens: Specificity and Steroidal Control of Reactivation

Activating and masking enzymatic activity on demand is of the highest importance in nature. It is achieved by chemical interconversion of enzymes and the corresponding zymogens through, for example, proteolytic processing or reversible phosphorylation, and affords on-demand activation of enzymes, controlled in space and/or time. In stark contrast, examples of chemical zymogens are very few, and in most cases these are based on disulfide chemistry, which is largely indiscriminate as to the nature of the activating thiol. In this work, we address an outstanding challenge of specificity of reactivation of chemical zymogens. We achieve this through engineering affinity between the chemical zymogen and the activator. Additional, higher-level control over zymogen reactivation is installed in a nature-mimicking approach using steroidal hormones. Taken together, the results of this study take a step towards establishing the specificity of reactivation of synthetic, chemical zymogens. We anticipate that the results of this study will contribute significantly to the development of chemical zymogens as tools for diverse use in chemical biology and biotechnology.     

Nanoparticle-Based Strain Gauges: Anisotropic Response Characteristics,Multidirectional Strain Sensing,and Novel Approaches to Healthcare Applications

Directional strain sensing is essential for advanced sensor applications in the field of human-machine interfaces and healthcare. Here, the angle dependent anisotropic strain sensitivity caused by charge carriers percolating through cross-linked gold nanoparticle (GNP) networks is studied and these versatile materials are used for the fabrication of wearable triaxial pulse and gesture sensors. More specifically, the anisotropic response of 1,9-nonanedithiol cross-linked GNP films is separated into geometric and piezoresistive contributions by fitting the measured data with an analytic model. Hereby, piezoresistive coefficients of g₁₁ ∼ 32 and g₁₂ ∼ 21 are extracted, indicating a slightly anisotropic response behavior of the GNP-based material. To use the material for healthcare applications, arrangements of three GNP transducers are patterned lithographically and fully embedded into a highly flexible silicone polymer (Dragon Skin 30). The new encapsulation method ensures good and robust electrical contacts and enables facile handling and protection from external influences. A facile read-out with wireless data transmission using off-the-shelf electrical components underlines the great potential of these devices for applications as skin-wearable healthcare sensors.     

Dediazoniation of 2,5-di(n-butoxy)-4-morpholino-benzenediazonium tetrafluoroborate sensitized by zinc phthalocyanine tetrasulfomorpholide (ZnPcTSM) in di-n-butyl phthalate

The dediazoniation of 2,5-di-(n-butoxy)-4-morpholino-benzenediazonium tetrafluoroborate ( 1 ) sensitized by zinc phthalocyanine tetrasulfomorpholid (ZnPcTSM) is studied in di-n-butylphthalate. The life-time of singlet-excited ZnPcTSM (τ_s = 3.0 ns) is not decreased by 1 whereas the static fluorescence at 689 nm is quenched. Thus, a ground-state complex is formed, K_eq = 1730 M⁻¹ showing an absorption band at 714 nm. A similar complex is formed with mono-n-butylphthalate being present if di-n-butylphthalate was not distilled in a good vacuum (1 torr), K_eq = 1545 M⁻¹. The decay of the triplet state in the presence of 1 is adequately treated as a reaction from the triplet-excited ground-state complex. K_eq of the ZnPcTSM-diazonium salt complex is also obtained from quantum yields of the sensitized dediazoniation. A rather low intersystem crossing quantum yield of the complex amounting to 0.17 is deduced. ZnPcTSM is also bleached, but much weaker than expected for an oxidative electron transfer. The system works well – even under air – in dibutylphthalate micro droplets in gelatine coated on a PET-base.     

Wear Behavior of Roller-Burnished High Interstitial Austenitic Stainless Steel Parts in Glass-Reinforced Plastic Melt

Herein this investigation, profiled high interstitial austenitic stainless steel parts are burnished on a profile-rolling machine, and afterward, the wear behavior is analyzed in a melt of glass-reinforced polypropylene. Wear and corrosion resistance are significant properties of steel parts in the plastics and food industries. The high work-hardening ability of high interstitial austenitic stainless steel enables burnishing parts with a significant local hardness to increase up to maximum values of ≈600 HV 1. Wear tests on a recently developed test stand reveal that the burnished austenitic stainless steel surface performs similarly to a nitrided surface of the standard nitriding steel 31CrMoV9 + QT with a hardness of ≈830 HV 0.5. Regarding the given advantage of corrosion resistance, it is concluded that roller burnishing supports the applicability of high interstitial austenitic stainless steel in plastics and food industries.     

How Wetting Properties Influence the Wear of Radial Lip Sealing Systems

Increased wear on radial lip seal systems is observed when sealing modern lubricants, such as polyglycols and esters. This can impair the function of the sealing system and ultimately lead to leakage. This work, carried out within the AiF research project “Welleneinlauf” (wear of counter faces) [1], shows methods to identify and predict excessive wear of radial lip sealing systems based on their wetting properties and pumping rate. The knowledge gained will support users by providing faster and more cost-effective testing methods early in the design process, thus enables a significant increase in the service life of radial lip sealing systems.     

Photoinduzierte H-Abstraktionen an Benzylarylethern durch Benzophenon

Photoinduced H-Abstraction on Benzyl Aryl Ethers by Benzophenone The triplet state of benzophenone abstracts in benzene of benzyl aryl ether 6 hydrogen atom from the CH₂-group. The formed α-ether radicals 1 and diphenylhydroxymethyl radicals 8 react to form the three possible reaction products in statistical distribution. Benzaldehydes 2 and phenols 11 are formed in a side reaction. From quantum yield measurements of the benzophenone reduction in dependence upon the concentration of benzyl phenyl ether 6a follows a rate constant of the H-abstraction of 9.5 ·10⁵ M⁻¹s⁻¹ which is in good agreement with measurements in presence of naphthalene as a quencher. The quenching constant for benzophenone triplet by naphthalene is 2 · 10⁹ M⁻¹s⁻¹. For benzyl phenyl ethers substituted in the benzyl ring the reaction constant for the H-abstraction reaction was determined, ϱ = −0,68,     

Elastohydrodynamic Simulation of Pneumatic Sealing Friction Considering 3D Surface Topography

This contribution presents an elastohydrodynamic lubrication (EHL) model for pneumatic spool valves. For an accurate estimation of the transient friction of this tribological sealing system, the surface topography of the cylindrical sealing counterfaces of the valve housings are measured and analyzed with an optical surface measurement instrument. Based on the surface topography data, tribological properties and flow factors of the system are derived. It has been found that the consideration of the surface topography has a significant influence on the simulation results of the EHL model, lowering the calculated friction force by up to 20 %.