Anion recognition using a simple cyclic peptide

The head-to-tail cyclic hexapeptide, [cyclo(Val-Thr)₃], was found to bind to a range of anions in DMSO-d₆ with higher affinity for tetrahedral oxo-anions than halides. ¹H NMR spectroscopy indicated that anion binding results in an overall change in peptide conformation with the binding of both sulphate and selenate leading to similar peptide conformations. In the more competitive solvent mixture of 2:8 v/v H₂O/DMSO-d₆ this cyclic peptide displayed five-fold stronger binding to sulphate than to selenate.