Interactions between dendrimers and ionic liquids revealed by pulsed field gradient and nuclear overhauser effect NMR studies

The host-guest interactions of cationic and anionic poly(amidoamine) (PAMAM) dendrimers with three ionic liquids including 1-butyl-3- methylimidazolium 2-(2-methoxyethoxy)ethyl sulfate ([BMIM][MDEGSO₄]), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][TFSI]), and trihexyltetradecylphosphonium bis((trifluoromethyl)sulfonyl)imide ([THTDP][TFSI]) were investigated by several NMR techniques such as ¹H and ¹⁹F NMR, pulsed field gradient (PFG) NMR, and 2D nuclear Overhauser enhancement spectroscopy (NOESY). Anionic PAMAM dendrimer interacts with the ionic liquids via ionic interactions. However, almost no interaction is observed between cationic PAMAM dendrimer and the ionic liquids without pH adjustment. Besides, no inclusion formation between the PAMAM dendrimers and the ionic liquids is observed on the basis of NOE NMR studies. The interactions between dendrimers and ionic liquids are very different from those between dendrimers and surfactants or amphiphilic drugs. The results obtained from PFG and NOE studies provide new insights into dendrimer-based host-guest systems.