Novel Capsular Aggregates from Flexible Tripodal Triureas with C_s Symmetry

Abstract

Tris(2- and 3-ureidobenzyl)amines with C_s symmetry self-assemble in solution forming mixtures of regioisomeric capsular aggregates, one of which is chiral and the other centrosymmetric. Under certain conditions, a predominance of the centrosymmetric regioisomer is found before equilibrium, that is, a mixture close to the statistical ratio of the two species is reached. In the solid state, there is a preference for the centrosymmetric capsules. Molecular models of both regioisomeric aggregates have been built and analyzed for comparison. Guests inside capsules formed by self-assembly of desymmetrized tris(3-ureidobenzyl)amines feel different magnetic environments, depending on whether they are inside a chiral or an achiral regioisomeric container. Of special significance are the experiments with a more flexible triurea endowed with an ureidopropylic arm, which self-assembles with the same efficiency as the more rigid tris(ureidobenzyl)amines.