The free nucleobases and mononucleotides of RNA do not form Watson–Crick base pairs in water, a fact that presents several challenges for the prebiotic synthesis of RNA. 2,6-Diaminopurine and adenosine-5'-monophosphate (AMP) are shown to form supramolecular assemblies with cyanuric acid in water. These assemblies and their propensity to form liquid crystals suggest a possible means by which non-covalent structures might have originally selected the shape of the Watson–Crick base pairs. For more information see Li, Cafferty, Karunakaran, Schuster and Hud, Formation of supramolecular assemblies and liquid crystals by purine nucleobases and cyanuric acid in water: implications for the possible origins of RNA, Phys.Chem.Chem.Phys., 2016, 18, 20091