Molecular shape sorting using molecular organic cages

• Published in: Nature chemistry 2013-04, Vol.5 (4), p.276-281
• Main Authors: Mitra, Tamoghna, Jelfs, Kim E., Schmidtmann, Marc, Ahmed, Adham, Chong, Samantha Y., Adams, Dave J., Cooper, Andrew I.
• Format: Article
• Language: English
• Subjects: 639/638/403; 639/638/549; Analytical Chemistry; Biochemistry; Chemistry; Chemistry/Food Science; Chromatography; Energy efficiency; Inorganic Chemistry; Organic Chemistry; Physical Chemistry; Raw materials; Simulation; Sustainability; Zeolites
• ISSN: 1755-4330; 1755-4349
• DOI: 10.1038/nchem.1550

The energy-efficient separation of chemical feedstocks is a major sustainability challenge. Porous extended frameworks such as zeolites or metal–organic frameworks are one potential solution to this problem. Here, we show that organic molecules, rather than frameworks, can separate other organic molecules by size and shape. A molecular organic cage is shown to separate a common aromatic feedstock (mesitylene) from its structural isomer (4-ethyltoluene) with an unprecedented perfect specificity for the latter. This specificity stems from the structure of the intrinsically porous cage molecule, which is itself synthesized from a derivative of mesitylene. In other words, crystalline organic molecules are used to separate other organic molecules. The specificity is defined by the cage structure alone, so this solid-state ‘shape sorting’ is, uniquely, mirrored for cage molecules in solution. The behaviour can be understood from a combination of atomistic simulations for individual cage molecules and solid-state molecular dynamics simulations. A crystalline porous organic cage molecule is shown to have exceptional specificity for separating different structural isomers of C9 aromatics. Uniquely, this solid-state specificity is preconfigured in the discrete molecular building block, which shows an analogous specificity in solution. Both solution and solid-state behaviours can be understood by molecular dynamics simulations.