Andreas Bernet

Formation of a supramolecular chromophore : a spectroscopic and theoretical study

Spectroscopic and theoretical investigations of the self-assembly of a particular 1,3,5-benzene trisamide-based low molecular weight hydrogelator are described. This trisamide is pH-sensitive, and surprisingly forms a photoluminescent supramolecular hydrogel. Controlled gel formation in combination with the luminescence properties allows studying the self-assembly process in detail. The experimental results are confirmed by Density Functional Theory (DFT) calculations, revealing that the photoluminescence originates from the formation of a supramolecular chromophore.

Synthesis and pharmacological activities of some sesquiterpene quinones and hydroquinones

Synthesis of protected siphonodictyal C was achieved via drim-7-en-11-al. Some sesquiterpene quinones and hydroquinones were tested for their pharmacological activities in assays in search of antiproliferative, cytotoxic, antiphlogistic, antirheumatic and anti-inflammatory drugs. Wiedendiol B is a ten times stronger cyclooxygenase-2 inhibitor than the reference compound indomethacine. Cyclooxygenase-2 inhibitors are drugs with antiphlogistic and antirheumatic activity.

Supramolecular nanotube-based fiber mats by self-assembly of a tailored amphiphilic low molecular weight hydrogelator

The amide-group containing amphiphile 4-N-octanoyl-aminobenzoic acid sodium salt is able to thermoreversibly form supramolecular hydrogels in aqueous solutions of alkanine sodium salts. The supramolecular assemblies can be transferred without destruction by a mold-casting/drying process into self-supporting macroscopic supramolecular nanofiber mats. These mats are thermally and mechanically stable, resistant to a large variety of organic solvents and therefore interesting for potential applications such as templating of inorganic materials and filtration. The nanotubular multi-walled morphology of the underlying supramolecular assemblies was revealed using field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray scattering (XRD) and Fourier-Transform infrared spectroscopy (FT-IR).

Supramolecular hydrogels based on antimycobacterial amphiphiles

Synthetic modification of antimycobacterial 4-alkoxy-anilines yields low molecular weight amphiphiles. The bioactivity is retained in these amphiphiles and shows alkyl chain length specificity. The self-assembly behaviour in aqueous media was investigated. It was found that several of these new compounds are capable of forming thermoreversible supramolecular hydrogels in alkaline aqueous media. The initial drug can be released from the hydrogel by thermal hydrolysis.

Sodium NMR Relaxation: A Versatile Non-invasive Tool for the Monitoring of Phase Transitions and the Estimation of Effective Pore Sizes of Supramolecular Hydrogels

Nuclear magnetic resonance (NMR) relaxometry of liquids is a widely used tool to characterize porous media. In particular, 23Na NMR is an especially suitable method when applied to gels and biological tissues. In this work we investigated the thermoreversible melting and gelation processes of supramolecular hydrogels formed by succinamic acid-based amphiphiles (SAn) in a saturated aqueous NaHCO3 solution (sat. aq. NaHCO3 sol.). We could show that it is not only possible to determine the melting points and to monitor the gelation process with 23Na relaxometry, but also to estimate the effective pore size based on the expanded Brownstein-Tarr model. Our findings are in good agreement with data from differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) experiments.

Hydrogelation Kinetics Measured in a Microfluidic Device with in Situ X-ray and Fluorescence Detection

Efficient hydrogelators will gel water fast and at low concentrations. Small molecule gelling agents that assemble into fibers and fiber networks are particularly effective hydrogelators. Whereas it is straightforward to determine their critical concentration for hydrogelation, the kinetics of hydrogelation is more difficult to study because it is often very fast, occurring on the subsecond time scale. We used a 3D focusing microfluidic device combined with fluorescence microscopy and in situ small-angle X-ray scattering (SAXS) to study the fast pH-induced gelation of a model small molecule gelling agent at the millisecond time scale. The gelator is a 1,3,5-benzene tricarboxamide which upon acidification assembles into nanofibrils and fibril networks that show a characteristic photoluminescence. By adjusting the flow rates, the regime of early nanofibril formation and gelation could be followed along the microfluidic reaction channel. The measured fluorescence intensity profiles were analyzed in terms of a diffusion-advection-reaction model to determine the association rate constant, which is in a typical range for the small molecule self-assembly. Using in situ SAXS, we could determine the dimensions of the fibers that were formed during the early self-assembly process. The detailed structure of the fibers was subsequently determined by cryotransmission electron microscopy. The study demonstrates that 3D focusing microfluidic devices are a powerful means to study the self-assembly on the millisecond time scale, which is applied to reveal early state of hydrogelation kinetics. In combination with in situ fluorescence and X-ray scattering, these experiments provide detailed insights into the first self-assembly steps and their reaction rates.

Supramolecular Chromaticity and Thermoresponsive Hydrogels: A Self-Assembly Study on Maleamic Acid-Based Amphiphiles

A new class of homologous low molecular weight amphiphiles based on maleamic acid was synthesized and investigated in terms of its self-assembly behavior in bulk and in solution. The unexpected yellow color as bulk material and in organic solvents was revealed by means of spectroscopic and theoretical investigations to originate from intermolecular π-π interactions yielding supramolecular chromophores. It was found that the length of the alkyl chain of the amphiphiles and the resulting hydrophilic/lipophilic balance dictates the aggregation mode in bulk. One special compound exhibiting an n-tetradecyl chain was found to form stable thermoreversible supramolecular hydrogels in aqueous sodium hydroxide solutions. The corresponding hydrogels feature a rare cellular bilayer-based morphology and can be transferred into viscoelastic solutions upon heating and vice versa.