Synthesis and single-molecule force spectroscopy of supramolecular capsules

Schröder T. Synthesis and single-molecule force spectroscopy of supramolecular capsules. Bielefeld (Germany): Bielefeld University; 2010.In this work, the synthesis and self-assembly dynamics of supramolecular capsules based on cavitands and calix[4]arenes is investigated. In the first part, large supramolecular coordination cages have been prepared by metal-directed self-assembly of functionalized cavitands. The synthesis of the hexameric coordination cage demonstrates, that functionalized cavitands can be used to obtain large metallosupramolecular capsules. By rigid attachment of terpyridyl units to the bowl-shaped cavitand moiety tetratopic ligands with an optimum geometry to self-assembly into cage structures have been obtained. Bis-terpyridine complexes of transition metal ions are especially well suited as stable connecting units, as indicated by successful detection of the intact coordination cage in ESI-MS. The encapsulation of guest molecules in the supramolecular assembly will be in the focus of future studies. In the second part of this work, the interactions in a hydrogen-bonded assembly have been studied using single-molecule force spectroscopy to evaluate the dynamics of the self-assembly process. The immobilization of the building blocks of the hydrogen-bonded supramolecular capsule introduced by Kobayashi et al. in 2003 was the basis for successful SMFS experiments. In the force spectroscopy experiments using diluted SAMs, specific single-molecule dissociation events which could be assigned to the dissociation of single supramolecular capsules were observed. In dynamic single-molecule force spectroscopy experiments, the mechanical stability of the supramolecular capsules at different loading rates was investigated. Quantitative evaluation of the obtained data according to the Bell-Evans model allowed the determination of the kinetic dissociation rate and an estimation of the equilibrium constant of association. These results demonstrate, that single-molecule force spectroscopy can provide important insights regarding the dynamic strength of supramolecular binding motifs. The consequent application of this technique will influence supramolecular design principles and the use of non-covalent interactions as construction elements