Host–guest complexation of HMeQ[7] with alkyldiammonium ions and alkyldiamines: a comparative study

Abstract

This work presents the host–guest complexation of HMeQ[7] with a series of alkyldiammonium ions and the corresponding uncharged alkyldiamines (H₂N(CH₂)_nNH₂, n = 2, 4, 6, 8, 10, 12) in aqueous solution. ¹H NMR data indicate that all alkyldiamines and alkyldiammonium ions have inclusion interactions with HMeQ[7] except for the ethanediamine. The driving force for the formation of HMeQ[7]–alkyldiammonium inclusion complexes appears to be the ion–dipole interaction, while the complexation of HMeQ[7] with alkyldiamines mostly depends on the hydrophobic effect. ITC study points out that the host–guest complexation of HMeQ[7] with alkyldiammonium ions is driven by enthalpy and entropy, while the host–guest complexation of HMeQ[7] with alkyldiamines is driven exclusively by enthalpy. The features of weak basicity and absence of charged groups of the alkyldiamines are responsible for the large negative entropy and large enthalpy change in the complexation process of HMeQ[7] with alkyldiamines.