Molecular Recognition of Naphthalenedicarboxylic Acid Regioisomers by Cyclodextrins

Abstract

Abstract Complexation of cyclodextrins (CD’s) with some regioisomers of naphthalenedicarboxylic acid (NDC) was examined in 0.1 mol dm−3 NaHCO3 at 25 °C by means of 1H NMR spectroscopy, together with the measurement of induced circular dichroism spectra of NDC’s with the addition of CD’s. The 1H NMR spectra of 2,6- and 2,7-NDC’s showed characteristic AB-type patterns, which changed continuously with increasing CD concentration in accord with the Pople theory. The binding constants (Ka) for β-CD complexes with NDC’s increased in the order of: 1,4-NDC ≈ 1,5-NDC < 1,3-NDC < 1,6-NDC < 2,3-NDC < 2,7-NDC ≤ 2,6-NDC, indicating that β-CD is able to recognize the molecular structures of NDC’s. On the other hand, interactions of α- and γ-CD’s with NDC’s were very weak and nonspecific to NDC’s. The molecular structures of β-CD complexes with some NDC’s were estimated based on the ROESY spectra of the systems. Column chromatography of NDC’s using a β-CD-(2-chloromethyloxirane) polymer column showed that the retention volumes for NDC’s increased in the order of: 1,4-NDC < 1,6-NDC < 2,3-NDC < 2,7-NDC < 2,6-NDC, which agreed with the order the Ka values.