Spectrometric and 2D NMR studies on the complexation of chlorophenols with cyclodextrins

The formation and structure of inclusion complexes of alpha- and beta -cyclodextrins with 2-chlorophenol (2CP), 3-chlorophenol (3CP), 4-chlorophenol (4CP), 2,4-dichlorophenol (24DCP), 2,6-dichlorophenol (26DCP) and 3,4-dichlorophenol (34DCP) have been studied by UV-VIS and H-1 NMR spectroscopy. Both cyclodextrins were found to form 1 : 1 inclusion complexes. Binding constants estimated from titration studies revealed that the stability of the complexes was highly dependent on the structure and polarity of the chlorophenol and on the cyclodextrin used. In general, weaker binding constants were observed for a given chlorophenol with beta -cyclodextrin than with beta -cyclodextrin. The weakest binding constants (K-b < 200 M-1) were obtained for the ortho-substituted chlorophenols (2CP and 26DCP) and the largest binding constants were obtained between para-chlorophenols (4CP, 24DCP and 34DCP) and <beta>-cyclodextrin. 2D-TROESY studies of chlorophenol-cyclodextrin complexes in D2O provided insight into the structure of the complexes.