Synthesis of Structurally Varied 1,3‐Disiloxanediols and Their Activity as Anion‐Binding Catalysts

A series of new 1,3‐disiloxanediols has been synthesized, including naphthyl‐substituted and unsymmetrical siloxanes, and demonstrated as a new class of anion‐binding catalysts. In the absence of anions, diffusion‐ordered spectroscopy (DOSY) displays self‐association of 1,3‐disiloxanediols through hydrogen‐bonding interactions. Binding constants determined for 1,3‐disiloxanediol catalysts indicate strong hydrogen‐bonding and anion‐binding abilities with unsymmetrical siloxanes displaying different hydrogen‐bonding abilities for each silanol group.     

Imaging of the formerly bonded area of individual fibre to fibre joints with SEM and AFM

Besides the determination of the force and the energy needed to break individual fibre to fibre joints, the investigation of the formerly bonded area (FBA) is of essential importance to learn more about the failure mechanisms of fibre–fibre bonds in general. In this study the surfaces of paper fibres and the FBA of fibre–fibre joints after the determination of the breaking force as well as the bonding energy were analysed by means of low voltage scanning electron microscopy and atomic force microscopy. A comparison between the contact zone of fibres broken at different loading rates as well as under cyclic loading showed that there seems to be no significant difference in the appearance of the FBA in these cases. Only minor delamination of the cell wall could be found in the bonding zone, which indicates no mechanical interlocking of fibrils in the bonding zone. Furthermore, it is shown that some glues used for specimen preparation of fibre–fibre bond strength measurement are forming a glue film on the fiber surface and migrate into the bonding region.     

Collective Total Synthesis of 4-Azafluorenone Alkaloids

4-Azafluorenones are typically obtained by acid-mediated cyclization of 2-arylnicotinates. However, this approach fails to give 5-oxygenated 4-azafluorenones due to lactonization of 2-(2-alkoxy)phenylnicotinate intermediates. Herein, we report two modifications of established approaches to 4-azafluorenone synthesis that, either in combination or by themselves, enable the flexible preparation of 4-azafluorenones with diverse oxygenation patterns in the benzenoid ring. Undesired lactonization was circumvented via tert-butyl hydroperoxide (TBHP)-mediated radical cyclization of 2-aryl-3-(hydroxymethyl)pyridines. In the absence of suitable protecting groups for phenolic intermediates, bromide substituents were regioselectively introduced as latent hydroxy groups and later converted under palladium catalysis. We present the first total syntheses of five 4-azafluorenone alkaloids muniranine, darienine, 5,8-dimethoxy-7-hydroxyonychine, 5,6,7,8-tetramethoxyonychine, and 6,8-dihydroxy-7-methoxyonychine in addition to new total syntheses of six 4-azafluorenone alkaloids and one related pyridocoumarin alkaloid.     

A prochelator peptide designed to use heterometallic cooperativity to enhance metal ion affinity

A peptide has been designed so that its chelating affinity for one type of metal ion regulates its affinity for a second, different type of metal ion. The prochelator peptide (PCP), which is a fusion of motifs evocative of calcium loops and zinc fingers, forms a 1 : 2 Zn : peptide complex at pH 7.4 that increases its affinity for Zn²⁺ ∼3-fold in the presence of Tb³⁺ (log β₂ from 13.8 to 14.3), while the 1 : 1 luminescent complex with Tb³⁺ is brighter, longer lived, and 20-fold tighter in the presence of Zn²⁺ (log K from 6.2 to 7.5). This unique example of cooperative, heterometallic allostery in a biologically compatible construct suggests the possibility of designing conditionally active metal-binding agents that could respond to dynamic changes in cellular metal status.     

Numerical study of adhesive and cohesive failure of structured interfaces

In this contribution, a numerical study is presented, which addresses the failure behaviour of structured interfaces within a computational homogenisation scheme. Different local phenomena, e.g. the surface roughness and different local failure types like cohesive failure of the polymer and adhesive failure of the local interface and their effects on the overall interface characteristics are investigated. (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)