Self-Assembled Multi-Component Catenanes: Structural Insights into an Adaptable Class of Molecular Receptors and [2]-Catenanes

摘要

Under acidic conditions (50 equiv of TFA), combinations of hydrazide A-B monomers self-assemble into octameric [2]-catenanes with high selectivity for [1_32]_2, where 1 is a D-Pro-X (X = Aib, Ac_4c, Ac_6c, 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 glydne 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-C_2-symmetric compounds have a net C_2-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 [l_52_3] catenanes.