Self-assembled nanotubes from the supramolecular polymerization of discrete cyclic entities

Inspired by the extraordinary attributes displayed by nanotubes in Nature, the creation of self-assembled nano-sized hollow tubes is an area of significant and growing interest given its potential application in transmembrane ion channels, ion sensing or catalysis, among others. One of the most utilized strategies employed to build these supramolecular entities implies the stacking of discrete cyclic units. Given the intrinsic dynamicity of the forces that drive the self-assembly processes, this approach offers substantial advantages when compared to inorganic or covalent approaches, ranging from tunable pore designs to error correction, to name a few. Herein we focus on the different approaches explored to design discrete cyclic entities as building blocks for the construction of self-assembled nanotubes, as well as the analytical tools used to elucidate the resulting structures. Attending to the nature of the bond involved in the formation of the cycle, we have distinguised three main categories: covalent, non-novalent and dynamic-covalent cycles. This review thus constitutes a roadmap to build self-assembled nanotubes based on soft matter and paves the way to expand their current applications.