Theoretical probes of the host-guest complex: H-substituted cyclohexane encapsulated inside a self-assembled capsule

The weak interaction complexes of the cylindrical capsular host encapsulating H-substituted (methyl and hydroxyl) cyclohexane guest molecules within its cavity were investigated theoretically through two different DFT methods: B3LYP and PW91. This study addresses the question how the host and guest molecules match each other to form the stable weak interaction systems. Computational analyses revealed that PW91 functional provides better performance for the studied weak interaction systems than the popular B3LYP method. Although there are weak repulsive interaction energies between the host and guest molecules, the weak repulsions cannot disrupt the host-guest complex. An important factor is that numerous, stable hydrogen bonds (16 hydrogen bonds) at the center of the capsule largely decrease the total energy of the host-guest complex. Different from the methyl cyclohexane guest (at the middle of the molecular capsule), the hydroxyl cyclohexane guest may be nearer to the lower half of the molecular capsule in order to achieve hydrogen bonding with the cylindrical capsular host.