Interactions in pseudorotoxanes based on crown ether-secondary ammonium motifs. A theoretical study.

A theoretical analysis of the nature of the interactions in dibenzo[24]crown-8 (DB24C8)-n-dibutylammonium (DBM)--pseudorotaxane complex at the MP2 and DFT levels shows that the main contribution to the binding energy is the electrostatic interaction with moderate (20-25%) correlation stabilization. The total binding energy in the DB24C8-DBM complex represents a sum of the binding energies of two NH-O and one CH-O hydrogen bonds and the latter constitutes about 25% of the total interaction energy, giving the total binding energy of -41.2 kcal mol(-1) at the BHandHLYP/6-311 + + G** level. Deprotonation of the DB24C8-DBM complex reduces the binding energy by some 50 kcal mol(-1), giving metastable complexes DB24C8-DBA-1 or DB24C8-DBA-2, which will dissociate to give free crown ether and n-dibutylamine because of the strong exchange repulsion that prevails in neutral complexes.