Agnieszka Szumna from the Polish Academy of Sciences, Kasprzaka, Poland, has used NMR to compare water-free and water-mediated recognition processes within a synthetic resorcinarene-based self-assembled capsule. Water was shown to change the stoichiometry of binding as well as the selectivity, and can substantially restrict guest dynamics within the binding site. 

'The unique polar environment created inside the capsule can induce changes in the structure of encapsulated guests' says Szumna. Although it is not possible to directly observe water in hydrophilic cavities, due to the fast exchange with labile protons, Szumna used a co-encapsulated guest molecule as a probe to investigate the effect of water in the capsule. 

'One of the most intriguing problems that motivated our studies was the effect of water on recognition processes at the molecular level' explains Szumna. 'This general but very poorly known aspect can be studied with our model system. Our results showed that water, once it is co-encapsulated with other hydrophilic molecules, can have various types of effects including changes in stoichiometry of binding, selectivity and guest mobility within the binding site.' 

Szumna explains that this work will help towards the use of molecular containers as reaction vessels, and hopefully also for asymmetric reactions. The next stage is to check whether this water-filled chiral nanoenvironment can perform additional actions, for example influence equilibriums or induce rearrangements for the co-encapsulated guests. 

Rachel Cooper