Cyclic hexapeptide of D,L-alpha-aminoxy acids as a selective receptor for chloride ion.
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-.
Yang
Dan
D
Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, China. yangdan@hku.hk
Qu
Jin
J
Li
Wei
W
Zhang
Yu-Hui
YH
Ren
Yi
Y
Wang
De-Ping
DP
Wu
Yun-Dong
YD
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
D000596:Amino Acids; D018118:Chloride Channels; D002712:Chlorides; D009842:Oligopeptides; D010456:Peptides, Cyclic