Spectrophotometric Study of Selective Binding Behaviors of Dye Molecules by Pyridine- and Bipyridine-Modified β-Cyclodextrin Derivatives with a Functional Tether in Aqueous Solution

Four β -cyclodextrin ( β -CD) derivatives bearing pyridine or bipyridine linkers, i.e., mono[6-(3-pyridinecarboxamide)ethyleneamino-6-deoxy]- β -CD ( 2 ), mono[6-(4-pyridinecarboxamide)ethyleneamino-6-deoxy]- β -CD ( 3 ), N,N ‘ -bis(2-aminoethyl)-2,2‘-bipyridine-4,4‘-dicarboxamide-bridged bis(6-amino-6-deoxy- β -CD) ( 4 ), N,N ‘ -bis(2-aminoethyl)-2,2‘-bipyridine-3,3‘-dicarboxamide-bridged bis(6-amino-6-deoxy- β -CD) ( 5 ), and their copper(II) complexes ( 6 and 7 ) were selected as molecular receptors to explore the conformation−function relationship of oligo( β -CD)s. The original conformations of hosts 4 − 7 and their inclusion complexation behaviors with some guest molecules, i.e., ammonium 8-anilino-1-naphthalenesulfonate (ANS), sodium 6-( p -toludino)-2-naphthalenesulfonate (TNS), and rhodamine B (RhB), were comprehensively investigated by means of UV−vis, 2D NMR, and fluorescence spectroscopy. The results indicated that these oligo( β -CD)s, especially bis( β -CD) 5 and its copper(II) complex 7, exhibited the significantly enhanced binding abilities toward guest molecules as compared with native β -CD. Typically, hosts 5 and 7 efficiently enhanced the original binding ability of native β -CD toward ANS by a factor of 38−42 times. These increased binding abilities of oligomeric hosts were discussed from the viewpoint of the size/shape-fit and multipoint recognition between host and guest.