Controlling the mechanical behavior of novel supramolecular materials is of the utmost importance and requires a fundamental understanding of the underlying physical processes. We present a multimethods approach to the dynamics of entangled transient polyisoprene networks. Small-angle neutron scattering (SANS) on randomly functionalized chains shows homogeneous supramolecular melts with Gaussian chain conformations. The H-bond lifetimes (dielectric α*-process) and the rheological response in terms of the loss modulus G″ differ by 2 orders of magnitude in time. Within the concept of a compact random walk (RW), where the random walker (urazole group acting as a sticker) undergoes multiple returns to its starting point and following the concept of theoretical proposed renormalized sticky bond lifetimes, we quantitatively solve this longstanding and unexplained large discrepancy: While the bond opening gives rise to the dielectric response, for rheological relaxation the association with a new partner is relevant. This takes place only after multiple returns to the original binding partner.

Multifunctional POSS may be incorporated into dental adhesives to provide a bioactive potential without changing material properties adversely.

C-C coupling reactions between arylsilanes and alkylfluorides are efficiently catalyzed by disilyl cation 1. Primary as well as secondary alkylfluorides were quantitatively coupled with arylsilanes; however, in the case of tertiary fluorides, the hydrodefluorination reaction predominated. Primary alkylfluorides were found to give arenes with mostly rearranged alkyl substituents. In all cases subsequent Friedel-Crafts-type chemistry occurred.

Supramolecular groups in polymeric systems lead to responsive materials which are ideally suited for applications in dynamic environments. The key to their advanced properties such as shape-memory or self-healing is the reversibility of secondary interactions which can be triggered by external stimuli such as temperature, light, or pH-value. Controlling the (mechanical) behavior of such systems requires a precise understanding of intrinsic properties. We present a multimethod study of transient polyisoprene networks that were functionalized with different amounts of hydrogen bonding urazole groups. This work aims at understanding rich rheological features on the basis of their microscopic origin. First, the thermorheological simple behavior is validated experimentally. Subsequently, we characterize the underlying microscopic processes by broadband dielectric spectroscopy (a-process and a Ã-process), differential scanning calorimetry (glass transition behavior), and Fourier-transform infrared spectroscopy (thermodynamics of group association/dissociation). Based on these results, the influence of the supramolecular groups on the rheological response is analyzed. The observed features such as the onset of elastomeric properties in the flow regime, a drastic increase in the chain relaxation time with an increasing amount of functional groups, and the occurrence of a second rheological relaxation process, which is the most prominent effect, are discussed and related to their physical origin. V

Amyloid-β (Aβ) oligomers represent a promising biomarker for the early diagnosis of Alzheimer's disease (AD). However, state-of-the-art methods for immunodetection of Aβ oligomers in body fluids show a large variability and lack a reliable and stable standard that enables the reproducible quantitation of Aβ oligomers. At present, the only available standard applied in these assays is based on a random aggregation process of synthetic Aβ and has neither a defined size nor a known number of epitopes. In this report, we generated a highly stable standard in the size range of native Aβ oligomers that exposes a defined number of epitopes. The standard consists of a silica nanoparticle (SiNaP), which is functionalized with Aβ peptides on its surface (Aβ-SiNaP). The different steps of Aβ-SiNaP synthesis were followed by microscopic, spectroscopic and biochemical analyses. To investigate the performance of Aβ-SiNaPs as an appropriate standard in Aβ oligomer immunodetection, Aβ-SiNaPs were diluted in cerebrospinal fluid and quantified down to a concentration of 10 fM in the sFIDA (surface-based fluorescence intensity distribution analysis) assay. This detection limit corresponds to an Aβ concentration of 1.9 ng l-1 and lies in the sensitivity range of currently applied diagnostic tools based on Aβ oligomer quantitation. Thus, we developed a highly stable and well-characterized standard for the application in Aβ oligomer immunodetection assays that finally allows the reproducible quantitation of Aβ oligomers down to single molecule level and provides a fundamental improvement for the worldwide standardization process of diagnostic methods in AD research.

The synthesis of disilylfluoronium ions 4 with a naphthalene-1,8-diyl backbone via the corresponding arenium ions 3 is reported. The cations were isolated in the form of their [B(C6F5)4]− salts. The borates 3[B(C6F5)4] and 4[B(C6F5)4] are active in catalytic hydrodefluorination reactions using fluorodecane as substrate. Methylphenyl-substituted arenium ions 3c,d undergo an interconversion reaction via a formal 1,3-methyl group migration at room temperature. This rearrangement was shown by DFT methods to proceed by a multiple-step sequence involving a methonium-like transition state. The NMR parameters for disilylfluoronium ions 4 indicate, in agreement with DFT calculations, the presence of a symmetric Si–F–Si linkage in these cations. QTAIM, NBO, and VB analyses reveal that the high ionic contributions to the bonding in the SiFSi moiety are responsible for the symmetric structures of these cations.

In this work we present the synthesis of poly(1,2-butylene oxide) (PBO) functionalized with the complementary hydrogen bond forming groups 2,4-diaminotriazine (DAT) and thymine. PBO is a rubbery polymer. Due to its semi-polar nature PBO is expected to suppresses non-directed cluster formation of the supramolecular groups but not influence their directed interactions. For the synthesis of backbone functionalized polymers we developed a procedure which allowed randomly copolymerizing BO with 1,2-epoxy-7-octene using anionic ring opening polymerization with potassium tert-butanolate as initiator. The vinyl groups were converted to OH-groups by oxidation. In addition, PBO with one alcoholic end group was obtained by homopolymerization of BO. For the variant with OH-groups at both chain ends a procedure was developed which was based on the cleavage of the tert-butyl initiator group. In all the polymers the alcohol groups were basically quantitatively transformed into NH 2 -groups.DAT and thymine functionalities were attached to the NH 2 -groups again in almost quantitative conversion. All reaction steps were monitored by 1 H-NMR using pyridine-d 5 as solvent. This method allowed determining the conversions of the different synthesis steps with high precision. The materials were examined in linear rheology in order to study the effect of the hydrogen-bonds on the dynamics of the resulting supramolecular structures. The results corroborate the exclusive existence of directed interactions between the supramolecular groups.

carbenes · main-group elements · multiple bonds · organosilicon compoundsDespite the impressive progress made in the last decade in the chemistry of multiple-bonded main-group compounds, triple bonds between carbon and its heavier homologues still have the touch of unattainability.[1] Efforts to synthesize stable or even only persistent compounds that feature an E À C triple bond (E = Si, Ge, Sn, Pb) face several principal obstacles. On the one hand, there is the essential reluctance of the heavier elements to engage in multiple bonds. As a result only relatively weak p bonds with small HOMO/ LUMO energy differences are formed and consequently these compounds show extreme reactivity towards addition reactions and nucleophilic and electrophilic attack. This problem has been solved for compounds containing homonuclear EE bonds by using extremely bulky substituents. In addition, heteroleptic EE' bonds are always polarized owing to the different electronegativity of the constituent atoms. Because of the relative high electronegativity of carbon, the polarization of the triple bond is extreme for carbynes, RE CR'. This further increases the reactivity of these compounds and severely complicates their synthesis and isolation.All recent high-level calculations of the [CSiH 2 ] potential energy surface predict that the classical linear silyne 1, the analogue of acetylene, is not at an energy minimum, but that a second-order Jahn-Teller distortion forces it into a trans bent structure 2.[2] This parallels the situation found for disilynes, RSiSiR. The results of the calculations, however, reveal a second important aspect: Silyne 2 is thermodynamically and kinetically unstable, and undergoes unimolecular isomerization to silavinylidene 3. Specifically, trans bent silyne 2 is less stable than monocoordinated silylene 3 by 143 kJ mol À1 and the barrier for the 1,2-H shift which converts 2 into 3, is rather small, merely 21 kJ mol À1