Electron Cryo-Microscopy of TPPS4•2HCl Tubes Reveals a Helical Organisation Explaining the Origin of their Chirality

A widely studied achiral porphyrin, which is highly soluble in aqueous solutions (TPPS4), is shown to self-assemble into helical nanotubes. These were imaged by electron cryo-microscopy and a state-of-the-art image analysis allows building a map at ∼5 Å resolution, one of the highest obtained so far for molecular materials. The authors were able to trace the apparent symmetry breaking to existing nuclei in the as received samples, while carefully purified samples show that both handnesses occur in equal amounts. © 2013 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.