It is sometimes possible to remove strong template interactions by post-assembly modification, for example by deprotonation of an ammonium unit 22, 23, but this is often not straightforward and can require forcing conditions 23.Īctive template synthesis 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, in which a macrocycle accelerates a strand-forming reaction through the ring cavity, does not require strong pre-association of the starting materials. Strong binding modes generally ‘live on’ in the interlocked product, an outcome useful for the design of artificial molecular machinery 2, 3, 14, 15, 16, whether intended to operate in solution 17 or when organized on surfaces 18, 19 or within metal-organic frameworks 20, 21, but one that tends to override alternative weaker binding modes that could occur between the components. In practice such outcomes are rarely observed 4, 5, 6, 7, 8 because most rotaxane syntheses rely upon strong attractive interactions between the building blocks 2, 3, 9, 10, 11, 12, 13 to promote the rotaxane assembly process. In principle the enforced high local concentration of convergent functional groups brought about by such mechanical bonding can stabilize weak non-covalent interactions 4. The bulky axle end-groups of rotaxanes mechanically lock rings onto threads, preventing the dissociation of the components even if the interactions between them are not strong and attractive 1, 2, 3.
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