Fig. 2.

Chemical complexity created by physical fluctuations. a Relative changes of temperature (in blue) and pH (in red) are shown for each synthetic step for the continuous synthesis of purine RNA building blocks from small organic and inorganic molecules. Several wet–dry cycles establish fluctuations of the depicted physical parameters that enable the physical enrichment of intermediates. Gray backgrounds denote compounds that are enriched by crystallization from an aqueous solution. b Formation of an organic salt consisting of amidine derivatives 2a-d and (hydroxyimino)malononitrile 3. The salt is selectively crystalized by concentrating a dilute mixture of organic and inorganic compounds by slow evaporation. The crystal structures of the four crystalized organic salts are depicted (Supplementary Tables 1–4)