Molecular recognition in ternary complexes of γ-cyclodextrin with naphthalenedicarboxylate ions and a space-regulator ion

Article abstract of DOI:10.1246/bcsj.71.2323

Complexation of γ-cyclodextrin (γ-CD) with the 2,6- naphthalenedicarboxylate ion (2,6-NDC) in alkaline D₂O was greatly enhanced by the addition of 2,6-bis(1-pyridiniomethyl)naphthalene dibromide (2,6-PMN) as a space-regulator. Formation of a ternary 1:1:1 complex between γ-CD, 2,6-NDC, and 2,6-PMN was confirmed by means of ¹H NMR spectroscopy, together with the measurements of induced circular dichroism spectra and UV absorption spectra. Changes in chemical shifts (δ) of the γ-CD protons in the presence of an excess amount of 2,6-PMN with the addition of NDC regioisomers were analyzed by a curve-fitting procedure to give binding constants (K₆) for complexation of NDC's with a γ-CD-2,6-PMN binary complex. The K₆ values increased in the order of 1,5-NDC < 1,4-NDC < 1,8-NDC < 1,3-NDC < 1,6-NDC < 2,3-NDC < 2,7-NDC < 2,6-NDC, indicating that a binary complex of γ-CD with 2,6-PMN is able to recognize the molecular structures of NDC's. The open space between the γ-CD cavity and 2,6-PMN will be favorable for the accommodation of a slender molecule such as 2,6-NDC, but unfavorable for the accommodation of a bulky molecule such as 1,5-NDC.