Modes of micromolar host-guest binding of beta-cyclodextrin complexes revealed by NMR spectroscopy in salt water

Abstract

Multitopic supramolecular guests with finely tuned affinities toward widely explored cucurbit[n]urils (CBs) and cyclodextrins (CDs) have been recently designed and tested as functional components of advanced supramolecular systems. We employed various spacers between the adamantane cage and a cationic moiety as a tool for tuning the binding strength toward CB7 to prepare a set of model guests with K-CB7 and K beta-CD values of (0.6-5.0) x 10(10) M-1 and (0.6-2.6) x 10(6) M-1, respectively. These accessible adamantylphenyl-based binding motifs open a way toward supramolecular components with an outstanding affinity toward beta-cyclodextrin. H-1 NMR experiments performed in 30% CaCl2 /D2O at 273 K along with molecular dynamics simulations allowed us to identify two arrangements of the guest@beta-CD complexes. The approach, joining experimental and theoretical methods, provided a better understanding of the structure of cyclodextrin complexes and related molecular recognition, which is highly important for the rational design of drug delivery systems, molecular sensors and switches.