Cooperative molecular recognition of dyes by dyad and triad cyclodextrin-crown ether conjugates.
Three beta-cyclodextrin (beta-CyD) derivatives with crown ether units, that is N-(4'-benzo-15-crown-5)-6-imino-6-deoxy-beta-CyD (2), 6,6'-[N-(4,4'-dibenzo-18-crown-6)-imino]-bridged bis(beta-CyD)(3), and 2,2'-[O-(4',5'-benzo-15-crown-5)-ethyl]-bridged bis (beta-CyD)(5), were synthesized as cooperative recognition receptor models. Their molecular binding behavior with four representative fluorescent dyes, i.e., ammonium 8-anilino-1-naphthalenesulfonate (ANS), sodium-6-toluidino-2-naphthalene-sulfonate (TNS), Acridine Red (AR) and Rhodamine B (RhB), was investigated in buffer solutions (pH = 7.20) at 25 degreesC by means of circular dichroism, NMR and fluorescence spectroscopy. 2D-ROESY experiments showed that dyad host 2 and triad host 3 adopted a CyD-guest-crown ether binding mode, while triad host 5 adopted a CyD-guest-CyD binding mode, upon inclusion complexation with guest molecules. Therefore, hosts 2 and 3 showed high molecular recognition ability towards charged guests, giving an enhanced binding ability up to 115 times for ANS by 3 and fairly high molecular selectivity up to 1450 times for the ANS/AR pair by 2 as compared with native beta-CyD in an aqueous phosphate buffer solution. On the other hand, host 5 was found to be able to effectively recognize the shape of a guest molecule, showing significantly higher binding ability towards linear guests. The binding affinities and molecular recognition abilities of these CyD-crown ether conjugates towards guest molecules are discussed from the viewpoint of electrostatic and/or hydrophobic interactions, size/shape-fit concept, and multiple recognition mechanism 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
Yang
Ying-Wei
YW
Li
Lei
L
Chen
Yong
Y
D000817:Anilino Naphthalenesulfonates / Q000737:chemistry; D001665:Binding Sites; D002942:Circular Dichroism; D043844:Crown Ethers / Q000737:chemistry*; D003505:Cyclodextrins / Q000737:chemistry*; D005456:Fluorescent Dyes / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D008958:Models, Molecular; D015394:Molecular Structure; D009282:Naphthalenesulfonates / Q000737:chemistry; D012235:Rhodamines / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D055672:Static Electricity; D047392:beta-Cyclodextrins
D000817:Anilino Naphthalenesulfonates; D043844:Crown Ethers; D003505:Cyclodextrins; D005456:Fluorescent Dyes; D008024:Ligands; D009282:Naphthalenesulfonates; D012235:Rhodamines; D047392:beta-Cyclodextrins; C032527:acridine red; C027132:1-anilino-8-naphthalenesulfonate; C009497:2-(4-toluidino)-6-naphthalenesulfonic acid; C031215:betadex; C029773:rhodamine B