Cavity-Containing Supramolecular Gels as a Tool for Orthogonal Self-assembly Crystallization Processes
Final Report Abstract
In this project, two new low-molecular-weight supramolecular gels containing calixarenes have been synthesized to establish orthogonal self-assembly crystallization processes in which gelator and crystallization system form a weakly coupled arrangement. The gelators were based on two different concepts: One gelator was a one component approach, in which the functionalized calixaranes were hold together by h-bonding between N-H and C=O of the diformylhydrazine groups. The other gelation system contains of two different monomer units with two binding stations each which were forming the gel fibres by binding together as host guest complexes and can be easily switched back to solution by adding competitive binding cations. The gelation behavior of both has been characterized by a simple vial inversion test, rheology experiments and SEM pictures. Both systems provide a high surface area of exposed gel fibres where crystal growth can occur through a diffusion and nucleation controlled process. Due to the calixarane’s cavity which can complex small molecules with hydrophobic parts not only one special drug but a broad range of molecules can be tested to crystallize in the gel. A couple of small drug molecules like paracetamol or ibuprofen were already tested for their crystallization behaviour in these gels. For this, the drug molecule and the gelator were dissolved in different ratios. After the gel was formed, crystal growth could be obtained in some cases. The crystals have been analysed by X-ray and provide the proof of principle to use these gels as crystal growth media for drug molecules. In one case even crystal growth only occurs in presence of the gelator but not in the pure solvent. Further studies will be done to confirm the influence of the gelator. Also bigger calixarenes might be used to extend the range of drug molecules that can be attempted to crystallize.
