MOLECULAR MECCANO .3. CONSTITUTIONAL AND TRANSLATIONAL ISOMERISM IN [2]CATENANES AND [N]PSEUDOROTAXANES

The mutual molecular recognition expressed between two classes of comp ounds has led to the self-assembly of a range of [2]catenanes, compose d of cyclic polyethers intercepted by pi-electron donors, and a range of [n]-pseudorotaxanes, composed of similar acyclic polyethers, and va rious tetracationic cyclophanes. These molecular self-assembly process es rely upon the recognition between (i) pi-electron rich and pi-elect ron deficient aromatic units and (ii) hydrogen bond donors and accepte rs, within the different components. The constitution of the pi-electr on rich and the pi-electron deficient structural components in these m olecular and supramolecular structures has a profound effect on the or ganization of the various assemblies and on their dynamic properties w ith respect to each other both in solution and in the solid state. The techniques of X-ray crystallography, fast-atom bombardment mass spect rometry, H-1, C-13, and dynamic nuclear magnetic resonance, ultraviole t/visible spectroscopies, and electrochemistry have been used in the s olid and solution states to assess the nature of the structures of the catenanes and the superstructures of the pseudorotaxanes. The success ful assembly of these catenanes and pseudorotaxanes, through the trans cription of programmed molecular information, in the form of noncovale nt bonding interactions, lends support to the contention that self-ass embly is a viable paradigm for the construction of nanometer-scale mol ecular and supramolecular structures incorporating a selection of simp le building blocks.