Remarkable selectivity of per-O-methylated tricationic 6A,6C,6E-tripyridinio-6A,6C,6E-trideoxy-α-cyclodextrin for basic anions over non-basic anions

摘要

The per-O-methylated tricationic 6A,6C,6E-tripyridinio-6A,6C,6E-trideoxy-α-cyclodextrin shows a high affinity fornbasic anions, especially highly charged phosphate and pyrophosphate anions, at near-neutral pH with associationnconstants of 7 000 and 9 000 Mu00011, respectively, but it did not bind non-basic anions, such as Iu0001, ClO4nu0001, SCNu0001 or evenndoubly charged SO4n2u0001, in contrast to the non-methylated counterpart. 1H NMR spectral studies verify a plausiblenstructure, in which the bound anion is located more closely to the pyridinio meta and para positions rather than tonthe ortho positions, due probably to the greater MeO- vs. HO-group hydrophobicity, which rejects deep intrusionnof the anion into the positive cavity. Molecular mechanics calculations supported the above conclusions.