Formation thermodynamics of cucurbit[6]uril macrocycle molecules: a theory study

Macrocyclical molecules are very important molecular cavitands for the supramolecular chemistry in view of host-guest complexation which is a basis for design of molecular devices. One striking example of macrocycles is the family of cucurbit[ n]uril molecules (CB[n]). For effective application of the cavitands of this family it is needed to elucidate the stabilization mechanism of different homologues CB[n]. In this study we have carried out a thermodynamical analysis of macromolecule cyclization from a monomer to a pentamer and CB6. It was found that water molecules, which are formed as one of the products of the reaction of glicoluril with formaldehyde, construct dimer and oligomer CB(m) so that an angle between adjacent building units corresponds to the stable homologue CB[6]. In the framework of the density functional theory (DFT), the structures of hydrated oligomers were optimized. Calculated thermodynamical functions were used for a description of cyclization mechanism of oligomers up to formation of CB[6]. It is assumed that the proposed model can be extended to the formation of higher homologues in diluted water-acid solutions.