Biquinolino-modified beta-cyclodextrin dimers and their metal complexes as efficient fluorescent sensors for the molecular recognition of steroids.
A series of bridged beta-cyclodextrin (beta-CyD) dimers possessing functional tethers of various lengths was synthesized in moderate yield by the treatment of 2,2'-biquinoline- 4,4'-dicarboxylic dichloride with beta-CyD or mono[6-oligo(ethylenediamino)-6-deoxy]-beta-CyDs. The products were 2,2'-biquinoline-4,4'-dicarboxy-bridged bis(6-O-beta-CyD) (8), N,N'-bis(2-aminoethyl)-2,2'-biquinoline-4,4'-dicarboxamide-bridged bis(6-amino-6-deoxy-beta-CyD) (9), and N,N'-bis(5-amino-3-azapentyl)-2,2'-biquinoline-4,4'-dicarboxamide-bridged bis(6-amino-6-deoxy-beta-CyD) (10). The reaction of 8-10 with copper perchlorate give their copper(II) complexes 11-13 in satisfactory yields of over 77 %. All the bis(beta-CyD)s 8-13 act as efficient fluorescent sensors and display remarkable fluorescence enhancement upon addition of optically inert steroids. The inclusion complexation behaviors of 8-13 when treated with the representative steroids cholate (14), deoxycholate (15), and glycocholate (16) in aqueous solution at 25 degrees C were investigated by means of UV/Vis spectroscopy, conductivity and fluorescence measurements, circular dichroism spectroscopy, and 2D NMR spectroscopy. The tether length of bis(beta-CyD) 9 allows it to adopt a cooperative host-tether-guest binding mode in which the spacer and guest are co-included in the two CyD cavities. As a result of this cooperation, 9 has a stability constant (K(s)) about 2x10(2) times higher than that of monomodified beta-CyD 4 for inclusion complexation with cholate. Metallooligo(beta-CyD)s with four beta-CyD units have enhanced binding abilities compared with monomodified beta-CyDs. These metallo compounds have binding affinities for guest steroids that are up to 50-4.1x10(3) times higher than those of CyDs 2-4. The guest-induced fluorescence enhancement of bis(CyD)s opens a new channel for the design of sensor materials. The complex stability constants of these compounds are discussed from the viewpoint of induced-fit interaction and cooperative multiple binding between host and guest.
Liu
Yu
Y
Department of Chemistry, State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, P.R. China. yuliu@public.tpt.tj.cn
Song
Yun
Y
Chen
Yong
Y
Li
Xue-Qing
XQ
Ding
Fei
F
Zhong
Rui-Qin
RQ
D002942:Circular Dichroism; D003300:Copper / Q000737:chemistry; D003505:Cyclodextrins / Q000138:chemical synthesis* / Q000737:chemistry; D005456:Fluorescent Dyes / Q000138:chemical synthesis* / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry; D011804:Quinolines / Q000737:chemistry*; D013050:Spectrometry, Fluorescence / Q000379:methods; D013237:Stereoisomerism; D013256:Steroids / Q000737:chemistry*; D013329:Structure-Activity Relationship; D013816:Thermodynamics
D003505:Cyclodextrins; D005456:Fluorescent Dyes; D009942:Organometallic Compounds; D011804:Quinolines; D013256:Steroids; D003300:Copper