Separation of motional processes in a [2]catenane by combining synthetic, dual-frequency EPR and molecular modelling approaches.
Continuous-wave EPR of nitroxide spin labels at conventional (9.4 GHz) and high (94.2 GHz) frequencies is applied to characterize molecular dynamics in [2]catenanes composed of macrocycles with rigid phenyleneethynylene and flexible alkyl chain building blocks. By using a set of compounds with increasing complexity, which were all labelled at the centre of a rigid building block, it was possible to find regimes where spectral lineshapes were dominated by local motion of the spin label or those that contained information on tumbling of the building blocks. In chloroform, the macrocycles do not move as rigid objects, rather the rigid building block can reorient with some ease, with respect to the rest of the molecule. Furthermore, in that solvent the [2]catenane samples the co-conformational space on a timescale of microseconds or shorter. In a mechanical picture, chloroform can thus be considered as an effective lubricant that prevents the macrocycles from sticking together.
Godt
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Universität Bielefeld, Fakultät für Chemie, Universitätsstrasse 25, 33615 Bielefeld, Germany.
Jeschke
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