title: Cyclic hexapeptide of D,L-alpha-aminoxy acids as a selective receptor for chloride ion.
abstract: Cyclic hexapeptide 2, prepared from linear hexapeptide 1 of alternating d- and l-alpha-aminoxy acids, was found to adopt a C3 symmetric and bracelet-like conformation with consecutive eight-membered-ring hydrogen bonds (N-O turns) in nonpolar solvents, similar to that of valinomycin, a cyclodepsipeptide that binds cations selectively. However, 2 showed affinities for halide ions with selectivity following the order of Cl- > F- > Br-. The observed higher selectivity for Cl- (Ka = 11880 M-1) over F- (Ka = 30 M-1) in CD2Cl2 suggested that the selectivity of 2 for halide ions is mainly governed by the size complementarity rather than the hydrogen-bonding strength. Upon Cl- ion binding, the original bracelet-like conformation of 2 turned into a rather flat conformation with all six amide NHs pointing inward to form hydrogen bonds with Cl-.
authors.affiliation: Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, China. yangdan@hku.hk
authors.forename: Dan
authors.initials: D
authors.lastname: Yang
authors.forename: Jin
authors.initials: J
authors.lastname: Qu
authors.forename: Wei
authors.initials: W
authors.lastname: Li
authors.forename: Yu-Hui
authors.initials: YH
authors.lastname: Zhang
authors.forename: Yi
authors.initials: Y
authors.lastname: Ren
authors.forename: De-Ping
authors.initials: DP
authors.lastname: Wang
authors.forename: Yun-Dong
authors.initials: YD
authors.lastname: Wu
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D018118:Chloride Channels / Q000737:chemistry* / Q000378:metabolism; D002712:Chlorides / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D009842:Oligopeptides / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology; D010456:Peptides, Cyclic / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation
chemical_list: D000596:Amino Acids; D018118:Chloride Channels; D002712:Chlorides; D009842:Oligopeptides; D010456:Peptides, Cyclic