Self-Assembled Multi-Component Catenanes: Structural Insights into an Adaptable Class of Molecular Receptors and -Catenanes
journal contributionposted on 2012-07-18, 00:00 authored by Mee-Kyung Chung, Peter S. White, Stephen J. Lee, Marcey L. Waters, Michel R. Gagné
Under acidic conditions (50 equiv of TFA), combinations of hydrazide A-B monomers self-assemble into octameric -catenanes with high selectivity for 2, where 1 is a d-Pro-X (X = Aib, Ac4c, Ac6c, l-4-Cl-PhGly)-derived monomer and 2 is an l-Pro′-l-arylGly (Pro′ = Pro, trans-F-Pro, trans-HO-Pro, aryl = naphthyl, phenyl)-derived monomer. Five different combinations of monomers were studied by X-ray crystallography. In each case, the unique aryl glycine unit is located in the core of the structure where the aryl ring templates a CH−π–CH sandwich. Analysis of metrical parameters indicates that this core region is highly conserved, while the more peripheral zones are flexible. 1H NMR spectroscopy indicate that the solid-state structures are largely retained in solution, though several non-C2-symmetric compounds have a net C2-symmetry that indicates accessible dynamic processes. Catenane dynamic processes were additionally probed through H/D exchange, with the core being inflexible relative to the peripheral structure. Mass spectrometry was utilized to identify the constitutional isomerism in the minor asymmetric  catenanes.