Binding behavior of aliphatic oligopeptides by bridged and metallobridged bis(β-cyclodextrin)s bearing an oxamido bis(2-benzoic) carboxyl linker

Abstract

β-Cyclodextrin dimers bearing an oxamido bis(2-benzoic) carboxyl linker (1) or its metal complexes (2)

and 3) were newly synthesized, and their inclusion complexation behavior with a series of

representative aliphatic oligopeptides, i.e., Leu-Gly, Gly-Leu, Gly-Pro, Glu-Glu, Gly-Gly, Gly-Gly-

Gly, and Glu(Cys-Gly), was elucidated by means of UV/vis, circular dichroism, fluorescence, and 2D

NMR spectroscopy in Tris-HCl buffer solution (pH 7.4) at 25 °C. The results obtained indicated that

metallobridged bis(β-cyclodextrin)s 2 or 3 could significantly enhance the original molecular binding

abilities of parent bis(β-cyclodextrin) 1 toward model substrates through the cooperative binding of

two cyclodextrin moieties and the additional chelation effect supplied by the coordinated metal centers.

It is interesting that hosts 2 and 3 displayed an entirely different fluorescence behavior upon

complexation with guest oligopeptides. Among the guest peptides examined, 3 showed the highest

complex formation constant of 68 200 M-1 for Glu-Glu, up to 510-fold as compared with 1 (135 M-1),

while 1 gave excellent molecular selectivity for Glu(Cys-Gly)/Glu-Glu pair, up to 51-fold. The molecular

binding ability and selectivity were discussed from the viewpoints of the induced-fit and multiple

recognition mechanism between host and guest.