Additions- und SubstitutionsReaktionen an Tetrafluor- und Tetrachlordiboran(4)

Addition and Substitution Reactions at Tetrafluoro- and Tetrachlorodiborane(4) From equimolar mixtures of B₂F₄ and Me_nN(SiMe₃)_3-n (n = 0–3) the mono-addition products 1–4 are formed at low temperatures. By elimination of Me₃SiF the adduct 2 gives the dimeric monosubstituted diborane 8 , which slowly decomposes at room temperature to the aminoborane 6 and (BF)_n. The course of the reactions was studied by means of ¹¹B and ¹⁹F NMR spectroscopy and by measuring the vapor pressures. According to the ¹¹B and ³¹P NMR spectra the reaction of B₂Cl₄ with PCl₅ or [Me₄N]Cl in liquid hydrogen chloride at 0°C does not yield [PCl₄]₂⁺[B₂Cl₆]^2? or [Me₄N]₂⁺[B₂Cl₆]^2? but gives [PCl₄]⁺[BCl₄]^?, PCl₃ and BCl₃ or [Me₄N]⁺[BCl₄]^? and BCl₃ besides (BCl)_n.     

Sonication‐Induced Coiled Fibrous Architectures of Boc‐L‐Phe‐L‐Lys(Z)‐OMe

An ultra‐short peptide Boc‐L ‐Phe‐L ‐Lys(Z)‐OMe (Z=carbobenzyloxy) was shown to act as a highly efficient and versatile low molecular weight gelator (LMWG) for a variety of aliphatic and aromatic solvents under sonication. Remarkably, this simple dipeptide is not only able to form coiled fibres but also demonstrates self‐healing and thermal chiroptical switching behaviour. The formation of coiled assemblies was found to be influenced by the nature of the solvent and the presence of an additive. By exploiting these properties it was possible to modulate the macroscopic and microscopic properties of the organogels of this ultra‐short peptide, allowing the formation of highly ordered single‐domain networks of helical fibres with dimeric or alternatively fibre‐bundle morphology. The organogels were characterized by using FTIR, SEM, NMR and circular dichroism (CD) spectroscopy. Interestingly, CD experiments showed that the organogels of Boc‐L ‐Phe‐L ‐Lys(Z)‐OMe in aromatic solvents exhibit thermal chiroptical switching. This behaviour was hypothesized to stem from changes in the morphology of the gel accompanied by conformational transformation of the gelling agent. The fact that such a small peptide can demonstrate hierarchical assemblies and the possibility of controlling the self‐association is rather intriguing. The self‐healing ability, chiroptical switching and more importantly the formation of helical assemblies by Boc‐L ‐Phe‐L ‐Lys(Z)‐OMe under sonication, make this dipeptide an interesting example of the self‐assembly ability of ultra‐short peptides.     

Small‐Peptide‐Based Organogel Kit: Towards the Development of Multicomponent Self‐Sorting Organogels

The results presented here highlight the extremely useful nature of ultra‐short peptides as building blocks in the development of smart multicomponent supramolecular devices. A facile bottom‐up strategy for the synthesis of a small library of stimuli‐responsive smart organogelators has been proposed based on the predictive self‐assembly of ultra‐short peptides. More importantly, the narcissistic self‐sorting of the gelators has been evaluated as a simple method for the efficient co‐assembly of a donor–acceptor dual‐component gel, allowing the investigation of possible future applications of similar systems in the development of a supramolecular photo‐conversion device. Interestingly, it was observed that the self‐organization of the components can lead to highly ordered systems in which discrimination between compatible and non‐compatible building blocks directs the effective organization of the chromophores and gives rise to the formation of an excited‐state complex with exciplex‐like emission. The current report may prove important in the development of organogel‐based multicomponent smart devices.     

Ferrocenoyl glycylcystamine: organization into a supramolecular helicate structure

Extensive intermolecular hydrogen bonding in ferrocenoyl glycylcystamine gives rise to a novel ordered double helical arrangement with a helical pitch height of 14 A.     

Chemical behavior of electrochemically generated nanostructured silver surfaces

A simple electrochemical method has been proposed for the preparation of silver nanoparticles that can be used for the detection of cyanide. Both the electrochemical behavior and morphology of the Ag nanoparticles have been characterized in the presence of KCN or diethyl cyanophosphonate (DECP) as well as in alkaline media. These were investigated by cyclic voltammetry and scanning electron microscopy (SEM). DECP is a simulant of the chemical warfare agent tabun.