MOLECULAR RECOGNITION IN TERNARY COMPLEXES OF GAMMA-CYCLODEXTRIN WITHNAPHTHALENEDICARBOXYLATE IONS AND A SPACE-REGULATOR ION

Complexation of gamma-cyclodextrin (gamma-CD) with the 2,6-naphthalene dicarboxylate ion (2,6-NDC) in alkaline D2O was greatly enhanced by th e 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 g amma-CD, 2,6-NDC, and 2,6-PMN was confirmed by means of H-1 NMR spectr oscopy, together with the measurements of induced circular dichroism s pectra and UV absorption spectra. Changes in chemical shifts (delta) o f the gamma-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 (K-6) for complexation of NDC's w ith a gamma-CD-2,6-PMN binary complex. The K-6 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 gamma-CD with 2 ,6-PMN is able to recognize the molecular structures of NDC's. The ope n space between the gamma-CD cavity and 2,6-PMN will be favorable for the accommodation of a slender molecule such as 2,6-NDC, but unfavorab le for the accommodation of a bulky molecule such as 1,5-NDC.