Exploring new aspects of radical molecular machinery: studies and perspectives in the field of paramagnetic architectures.

The challenge of achieving molecular devices able to reproduce the impressive features of biological nano-machines has been attracting the interest of many scientists during the last decades. At present, several examples of artificial molecular machines based on mechanically interlocked molecules (MIMs) have been reported, which are able to perform a wide set of highly complex motions. On the other hand, the increasing complexity of molecular machines designed by scientists requires also new analytical approaches capable to characterize the nanoscale processes affecting these kind of systems. To this aim, the covalent incorporation of stable paramagnetic moieties inside the structure of artificial MIMs enables to use Electronic Paramagnetic Resonance spectroscopy (EPR) for monitoring the dynamics of the target structures. In this scenario, this research focused on the design, synthesis and EPR study of novel supramolecular architectures containing persistent nitroxide groups and employable in the field of radical molecular machines. The Chapter 3 of this manuscript describes the design, synthesis and EPR reduction kinetic studies of two novel crown-ether macrocycles containing a persistent nitroxide group into their structure. In Chapter 4 the use of 2-phenyl-2-cyanopropanoic acid as single fuel for promoting the full back and forth cycle of motions of an acid-base switchable nitroxide-labelled rotaxane was investigated. In the investigation reported in Chapter 5, EPR studies combined with GC-MS analysis were performed for monitoring the aerobic catalytic cycle of oxidation of 4-methoxy benzyl alcohol in the presence of a nitroxide-based macrocycle and cerium ammonium nitrate as co-catalyst. Chapter 6 describes the synthesis of a novel synthetic crown-ether macrocycle containing a stable nitroxide moiety into the structure and the EPR investigation of its complexation properties toward organic and inorganic guests.