Researchers in Japan developed a simpler method to synthesize interlocked carbon nanohoops called catenanes, molecules whose rings lock together mechanically like chain links without chemical bonds. Associate Professor Tomohito Ide of the National Institute of Technology, Tokyo College and Assistant Professor Yoshitaka Tsuchido of Tokyo University of Science led the work published in Angewandte Chemie International Edition.
The team combined gold and copper to build nitrogen-doped cycloparaphenylenes (CPPs), which are ring-shaped molecules derived from carbon nanotubes. The strategy uses two types of reversible chemical bonds: gold(I)-carbon bonds and copper(I)-nitrogen coordination bonds. When the researchers added copper(I) salt to a nitrogen-containing gold(I) complex and heated it, both bond types worked together to assemble an interlocked gold-copper complex in a single step. Removing the metals left a metal-free catenane with two fully conjugated nitrogen-doped nanohoops.
The new synthesis requires eight steps from commercial starting materials and achieves 2.9% overall yield. Conventional approaches typically need more than 10 steps with yields ranging from 0.02% to 4.3%.
The researchers found that the catenane exhibits co-conformational chirality, adopting right-handed or left-handed forms depending on how its rings orient relative to each other. When they added a chiral aluminum complex reagent, circular dichroism spectroscopy showed the molecule biased toward one handedness. A non-interlocked nanohoop showed nearly no such effect, confirming the chirality comes from the interlocked structure.
Tsuchido stated the approach could enable synthesis of topologically complex materials and noted that controlling the catenane's handedness through guest complexation may lead to chiral materials with tunable optical and electronic properties.