Co-Conformational Distribution of Nanosized [2]Catenanes Determined by Pulse EPR Measurements

• Published in: Chemphyschem Vol. 4; no. 12; pp. 1328 - 1334
• Main Authors: Jeschke, Gunnar, Godt, Adelheid
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 15.12.2003; WILEY‐VCH Verlag; Wiley
• Subjects: Atomic and molecular physics; catenanes; Electron resonance and relaxation; EPR spectroscopy; Exact sciences and technology; General molecular conformation and symmetry; stereochemistry; molecular devices; Molecular properties and interactions with photons; nanostructures; Physics; Properties of molecules and molecular ions; supramolecular chemistry; Pair correlation function; Catenane; molecular devices; catenanes; EPR spectra; nanostructures; supramolecular chemistry; EPR spectroscopy; Organic compounds; Conformation; Macrocycle
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.200300890

The co‐conformational ensembles of three differently sized [2]catenanes were studied by measuring pair correlation functions corresponding to the separation of nitroxide spin labels—one attached to each of the two macrocycles—with the double electron–electron resonance (DEER) experiment. A geometric model for the [2]catenanes was derived that approximates the macrocycles by circles and takes into account the topological constraint. Comparison of the experimental to the theoretically predicted pair correlation functions gives insight into the co‐conformational distribution and the size of the macrocycles. It was found that the macrocycles of the medium‐ and large‐sized catenanes in chloroform are close to fully expanded, while they are partially collapsed in glassy o‐terphenyl. For the small‐sized catenane, moderate interaction between the unsaturated sections of the macrocycles in chloroform is indicated by a slight overrepresentation of short label‐to‐label separations in the pair correlation function. Freely moving? The distance distribution of spin labels attached to the two macrocycles of [2]catenanes (see picture) can be characterized by EPR spectroscopy. Comparison to a theoretical model consisting of two perfect, infinitely thin circular rings reveals whether these molecules can be considered as an ensemble of simple geometric objects and whether all of the theoretically feasible co‐conformations are accessible. It turns out that the answers depend strongly on the solvent.