Nanocapsules

The creation of dynamic compartmentalization has potential ramifications throughout chemistry.  This program of research focuses on concave host molecules that assemble around guest molecules to form dynamic, nano-capsules.  Driven by the hydrophobic effect, the formation of these containers engenders a dry, inner-space quite distinct from the external aqueous environment.   Synthesis plays a key part in this work.  The hosts – deep-cavity cavitands – must be designed carefully so that they are able to dissolve in water at the required pH, bind the requisite guests, and spontaneously assemble into the desired supramolecular structure.  Characterization of the cavitands and their assemblies requires an array of NMR techniques, including: 1H/13C, NOESY, COSY, EXSY, and PGSE/DOSY experiments.

 

The engendering of compartmentalization can lead to many unusual and unique phenomena.  For example, the compartments can be used as yoctoliter (10-24 L) reaction vessels to carry out reactions that cannot normally be carried out in water.  Being of exceedingly small volume, the contents of these vessels are at high concentration (M range).  Additionally, the guest or guests are in intimate contact with the container.  Consequently, the packing of the guest and the manner by which it interacts with the walls of the container profoundly influence the reaction outcome.

 

Compartmentalization can also lead to separation technologies.  Two examples include the separation of hydrocarbon gases using aqueous solutions, and the kinetic resolution of mixtures via molecular protection.  In the former, passing a mixture of gases over a solution of a host leads to an equilibrium between free gas in the gas and aqueous phases, and bound gas within its corresponding complex.   Whichever guest leads to the most stable complex is therefore selectively removed from the gas phase.  Kinetic resolutions can be affected by using an aqueous medium for the host that is reactive to a (latent) guest mixture.  Because the stronger the assembly complex a guest forms, the longer its residency time in the dry nano-space, the presence of the host adds a bias to the intrinsic difference in the rates of reaction of the guests.  In other words, the kinetic resolution of compounds of similar or identical reactivity can be brought about when one forms tighter host-guest interactions than the other.