COMPLEXATION OF NAPHTHYLETHANOLS WITH BETA-CYCLODEXTRIN

The complexation behavior of 1-naphthyl-1-ethanol (1-NpOH) and 2-napht hyl-1-ethanol (2-NpOH) with beta-cyclodextrin (beta-CD) was studied by employing several spectroscopic techniques. In the case of 1-NpOH, on ly a complex with 1:1 stoichiometry is formed with beta-CD, which. has an equilibrium constant that is smaller than that observed for the 1: 1 complex between beta-CD and 2-NpOH. Excimer emission was observed in the presence of beta-CD for solutions containing high 2-NpOH concentr ations. This excimer emission was ascribed to a complex with 2:2 beta- CD/2-NpOH stoichiometry. In addition, H-1 NMR data suggest that 2-NpOH is axially incorporated into the beta-CD cavity. Only in the case of 2-NpOH was a broadening of the signals corresponding to the aromatic p rotons observed in the presence of beta-CD. This broadening was attrib uted to the formation of the 2:2 complex. The dynamics of NpOH complex ation was investigated by using the quenching methodology for triplet states. The entry rate constants for the 1:1 complex of 1-NpOH and 2-N pOH are (4.7 +/- 1.9) x 10(8) M-1 s(-1) and (2.9 +/- 1.6) x 10(8) M-1 s(-1), respectively, whereas the exit rate constants for the two compo unds are (4.8 +/- 1.8) x 10(5) s(-1) and (1.8 +/- 0.7) x 10(5) s(-1). In the case of 2-NpOH, we were able for the first time to estimate the rate constant for the dissociation of a beta-CD 2:2 complex ((0.2-2.5 ) x 10(3) s(-1)), showing that the dynamics for complexes including mo re than one cyclodextrin are remarkably slower than the dynamics obser ved for 1:1 complexes.