Spectrometric and 2D NMR studies on the complexation of chlorophenols withcyclodextrins

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