SYNTHESIS AND ASSEMBLY OF NEW MOLECULAR HOSTS - SOLVATION AND THE ENERGETICS OF ENCAPSULATION

Experimental details are given for the preparation of ''softballs'', l arge self-complementary molecules capable of assembly into pseudo-sphe rical capsules. Evidence is presented for their existence as hydrogen bonded dimers:in organic solvents, and binding affinities for the reve rsible encapsulation of smaller molecules of suitable size and shape a re given. Studies at various temperatures result in calculated enthalp ies and entropies of encapsulation that are positive; accordingly, the process is entropy driven. It is proposed that the hosts in their res ting states contain two molecules of solvent such as benzene, and the encapsulation of a single large guest-the hostage-liberates the two so lvents. The resulting increase in the number of free molecules gives r ise to the increase in entropy observed for the exchange process. Expe riments involving solvent mixtures are consistent with this rationale. Calculation of the capsule's interior volume and molecular dynamics s imulations support the experimental observations, and hint at unexpect ed phenomena dealing with the occupancy factors of these systems.