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Cooperative Multipoint Recognition of Organic Dyes by Bis( β ‐cyclodextrin)s with 2,2′‐Bipyridine‐4,4′‐dicarboxy Tethers
Author(s) -
Liu Yu,
Chen Yong,
Li Bin,
Wada Takehiko,
Inoue Yoshihisa
Publication year - 2001
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20010618)7:12<2528::aid-chem25280>3.0.co;2-9
Subject(s) - chemistry , circular dichroism , cyclodextrin , fluorescence , rhodamine b , bipyridine , acridine , stereochemistry , aqueous solution , crystallography , organic chemistry , crystal structure , physics , quantum mechanics , photocatalysis , catalysis
A series of novel 6,6′‐bis( β ‐cyclodextrin)s linked by 2,2′‐bipyridine‐4,4′‐dicarboxy tethers; that is, 2,2′‐bipyridine‐4,4′‐dicarboxy‐bridged bis(6‐ O ‐ β ‐cyclodextrin) ( 2 ) and N , N ′‐bis(2‐aminoethyl)‐2,2′‐bipyridine‐4,4′‐dicarboxamide‐bridged ( 3 ), N , N ′‐bis(5‐amino‐3‐azapentyl)‐2,2′‐bipyridine‐4,4′‐dicarboxamide‐bridged ( 4 ) and N , N ′‐bis(8‐amino‐3,6‐diazaoctyl)‐2,2′‐bipyridine‐4,4′‐dicarboxamide‐bridged bis(6‐amino‐6‐deoxy‐ β ‐cyclodextrin) ( 5 ), has been synthesized as cooperative multipoint‐recognition receptor models. The inclusion complexation behavior of 2 – 5 with organic dyes; that is, ammonium 8‐anilino‐1‐naphthalenesulfonate, Brilliant Green, Methyl Orange, Acridine Red, and Rhodamine B, has been investigated in aqueous phosphate buffer solutions (pH 7.20) at 25 °C by means of ultraviolet, fluorescence, and circular dichroism spectrometry as well as by fluorescence lifetime measurements. The spectral titrations gave the complex stability constants ( K S ) and Gibbs' free energy changes (Δ G °) for the inclusion complexation of 2 – 5 with the organic dyes and other thermodynamic parameters (Δ H ° and Δ S °) for the inclusion complexation of 2 – 4 with the fluorescent dyes Acridine Red and Rhodamine B. Bis( β ‐cyclodextrin)s 2 – 5 displayed higher binding abilities toward most of the examined dye molecules than native β ‐cyclodextrin 1 ; this is discussed from the viewpoints of the size/shape‐fit concept, the induced‐fit interaction, and cooperative, multipoint recognition by the bridging chain and the dual hydrophobic cavities. Thermodynamically, the inclusion complexation of 2 – 4 with Acridine Red is totally enthalpy driven with a negative or minor positive entropic contribution, but the inclusion complexation with Rhodamine B is mainly entropy‐driven with a mostly positive, but occasionally negative, enthalpic contribution; in some cases this determines the complex stability.