(728i) Assembly-State Switching: Alkane Guest Length Drives Assembly Transitions Between Multimeric Deep-Cavity Cavitand Complexes

Octa-Acid (OA)—a bowl-shaped molecule known as a deep-cavity cavitand—forms dimeric assemblies when in the presence of suitable hydrophobic guests. These dimeric assemblies have been used as reaction vessels and hydrocarbon gas separators. Tetra-Endomethyl Octa-Acid (TEMOA)—identical to OA, except that it has methyls in the endo position on the rim instead of hydrogens—not only forms dimeric assemblies, but also tetrameric and hexameric ones.

In this study we simulated a series of n-alkane guests inside of TEMOA dimers, tetramers, and hexamers. Using free energy calculations we demonstrate that the transitions between different assembly states are driven primarily by packing and not by the free energy of bringing together the hosts and guests into the assembly. Additionally we are able to accurately calculate the interior volume of each assembly state, showing that these structures are larger than systems formed by hydrogen bonding. This is significant because, unlike hydrogen-bonded structures, TEMOA multimers are biocompatible.