EPR investigation of supramolecular architectures

The always increasing complexity of supramolecular systems requires not only new and efficient synthetic approaches but also the development of analytical methods capable of measuring the molecular scale phenomena exhibited by supramolecular assemblies. EPR spectroscopy, a magnetic resonance spectroscopic technique, has proven to be a useful tool for the investigation of supramolecular systems. My Ph.D. was devoted to the application EPR spectroscopy to the investigation of several supramolecular architectures. Among them, the investigation of an important non-covalent interaction, analogue of hydrogen bond (HB), called halogen bond (XB). The study of this interactions has been realized by the design and synthesis of a suitable spin probe. Exploiting these spin probes allowed us to measure the kinetic and thermodynamic parameters for this interaction in solution by performing complexation experiments with XB acceptors. A derivative of a dibenzo-24-crown-8 ether (DB24C8) containing the BTBN motif for the investigation of its host properties toward guests such as alkali metal cations and organic guests was then studied. The EPR analysis enabled the measurement of the degree of complexation and to discriminate the guest from the experimental EPR readout. The formation of a pseudorotaxane with a thread molecule containing both the dialkylammonium and bipyridinium recognition sites, and the switching of the ring between the two stations of the guest was detected directly in solution. The 4th chapter is devoted to the development and optimization of a mild and high yielding synthetic method for the synthesis of spin labelled [2]-rotaxanes by exploiting the active metal template copper catalysed azide alkyne cycloaddition (AT-CuAAC). The EPR investigation of these NN labelled rotaxanes provided many useful information on the conformational dynamics in solution. Their ability to form complexes with metal cations, and the effect it has on the EPR spectra of the spin labelled rotaxanes and threads was also investigated.