Ring-o-rings: joining the ends of poly[n]-catenanes to capture supramolecular torsion*

Recent  advancements  in  chemical  synthesis and self-assembly  as well as  modelling  and  simulations have offered a framework to design systems of interlocked rings with controllable properties. These systems can be produced at scales varying from a few nanometers to several micrometers, and  have  been  proposed  for  applications  ranging  from smart  materials,  to  catalyzers  and  nano-machines.   Of  particular  interest  are  poly[n]-catenanes,   sequences  of n mechanically  interlocked  circular molecules, which can be synthesised through self assembly.  Here we show that,  by joining the two ends of a linear poly[n]-catenane to form a supramolecular ring, it is possible to capture different amount of twist,  which alter significantly the average extension of the structure and the relative orientation of the elementary rings along the backbone.

Furthermore, by extending the notion of twist and writhe of ribbons to circular poly[n]-catenanes we show that their sum is, on average, conserved and follows a scaling relation with the length n of the catenane.  Our results indicate that versatile supramolecular structures can be designed in such a way to store a controlled amount of torsional stress, opening several potential applications for novel smart materials.