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.