MOLECULAR RECOGNITION OF NAPHTHALENEDICARBOXYLIC ACID REGIOISOMERS BYCYCLODEXTRINS

Complexation of cyclodextrins (CD's) with some regioisomers of naphtha lenedicarboxylic acid (NDC) was examined in 0.1 mol dm(-3) NaHCO3 at 2 5 degrees C by means of H-1 NMR spectroscopy, together with the measur ement of induced circular dichroism spectra of NDC's with the addition of CD's. The H-1 NMR spectra of 2,6- and 2,7-NDC's showed characteris tic AB-type patterns, which changed continuously with increasing CD co ncentration in accord with the Pople theory. The binding constants (K- a) for beta-CD complexes with NDC's increased in the order of: 1,4-NDC approximate to 1,5-NDC < 1,3-NDC < 1,6-NDC < 2,3-NDC < 2,7-NDC less t han or equal to 2,6-NDC, indicating that beta-CD is able to recognize the molecular structures of NDC's. On the other hand, interactions of alpha- and gamma-CD's with NDC's were very weak and nonspecific to NDC 's. The molecular structures of beta-CD complexes with some NDC's were estimated based on the ROESY spectra of the systems. Column chromatog raphy of NDC's using a beta-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 th e order the K-a values.