Molecular binding behavior of pyridine-2,6-dicarboxamide-bridged bis(beta-cyclodextrin) with oligopeptides: switchable molecular binding mode.
Bridged bis(beta-cyclodextrin) 1 with a pyridine-2,6-dicarboxamide linker was synthesized, and its inclusion complexation behavior with some aliphatic oligopeptides was investigated in aqueous buffer solution of pH 2.0 and 7.2 at 25 degrees C by means of circular dichroism, fluorescence, and 2D NMR techniques. The results show that the resulting inclusion complexes of 1 with oligopeptides adopt a cooperative "cyclodextrin-guest-cyclodextrin" sandwich binding mode in a neutral media, but a "guest-linker-cyclodextrin" coinclusion binding mode in an acidic media. These switchable binding modes consequently rationalize the binding ability of bis(beta-cyclodextrin) 1 at different pH values; that is, 1 shows the stronger association with oligopeptides in a neutral media. Because of the simultaneous contributions of hydrophobic, hydrogen bond, and electrostatic interactions, bis(beta-cyclodextrin) 1 affords length-selectivity up to 4.7 for the Gly-Gly/Gly-Gly-Gly pair at pH 2.0 and sequence-selectivity up to 4.2 for the Gly-Leu/Leu-Gly pair at pH 7.2. These phenomena are discussed from the viewpoint of the size-fit concept and the multipoint recognitions between host and guest.
Liu
Yu
Y
Department of Chemistry, State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, PR China. yuliu@public.tpt.tj.cn
Chen
Guo-Song
GS
Chen
Yong
Y
Ding
Fei
F
Liu
Tao
T
Zhao
Yan-Li
YL
D001665:Binding Sites; D001952:Bridged-Ring Compounds / Q000737:chemistry / Q000378:metabolism; D002236:Carbohydrate Conformation; D002942:Circular Dichroism / Q000379:methods; D009682:Magnetic Resonance Spectroscopy; D009842:Oligopeptides / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding; D011522:Protons; D011725:Pyridines / Q000737:chemistry* / Q000378:metabolism*; D047392:beta-Cyclodextrins / Q000737:chemistry* / Q000378:metabolism*
D001952:Bridged-Ring Compounds; D009842:Oligopeptides; D011522:Protons; D011725:Pyridines; D047392:beta-Cyclodextrins; C431043:bis(cyclodextrin-6-yl)2,2'-bipyridine-4,4'-dicarboxylate