The synthetic peptide (C18H37)(2)NCOCH2OCH2CON-(Gly)(3)-Pro-(Gly)(3)-OCH2Ph forms chloride-selective channels in liposomes and exhibits voltage-gating properties in planar phospholipid bilayers. The peptide fragment of the channel is based on a conserved motif in naturally occurring chloride transporters. Membrane-anchoring residues at the N- and C-terminal ends augment the peptide. NMR spectra (1D and 2D) of the channel in CDCl3 showed significant variation in the absence and presence of stoichiometric tetrabutylammonium chloride (Bu4NCl). One-dimensional solution-state NMR titration studies combined with computational molecular simulation studies indicate that the peptide interacts with the salt as an ion pair and H-bonds chloride. To our knowledge, this is the first structural analysis of any synthetic anion-channel salt complex.