Xh. Shen et al., STUDIES OF THE INCLUSION COMPLEXATION BETWEEN A 3H-INDOLE AND BETA-CYCLODEXTRIN IN THE PRESENCE OF UREA, SODIUM DODECYL-SULFATE, AND 1-PROPANOL, Langmuir, 13(22), 1997, pp. 5830-5836
The interaction of amino)phenyl)-3,3-dimethyl-5-carboethoxy-3H-indole
(4) with beta-cyclodextrin (beta-CD) in the presence of urea, sodium d
odecyl sulfate (SDS), and 1-propanol, respectively, were studied by ab
sorption and steady-state fluorescence measurements. It was found that
the addition of urea gives rise to a remarkable decrease in K-1, the
association constant for the 1:1 (guest:host) inclusion complex, and a
much more decrease in K-2, the association constant for the 1:2 inclu
sion complex. The linear correlations between In K-2 and molecular vol
umes of some 3H-indoles in the absence and presence of urea, respectiv
ely, indicate the hydrophobic nature of the interaction of 4 with eith
er beta-CD or urea. This result also shows that the urea effect study
is an effective way to characterize the hydrophobic nature of the inte
ractions between cyclodextrins (CDs) and guest molecules. Using 4 as a
fluorescent probe, the interaction of SDS with beta-CD was investigat
ed through a competitive method. The formation of 1:1 and 1:2 inclusio
n complexes between SDS and beta-CD was confirmed. The association con
stants K-1' for the 1:1 complex and K-2' for the 1:2 complex were esti
mated to be 26800 +/- 2500 and 440 +/- 90 M-1, respectively. Effect of
1-propanol on the inclusion complexation between 4 and beta-CD was al
so investigated, The mechanism that 1:1:1 but not 1:2:2 ternary comple
xes of 4, 1-propanol, and beta-CD are formed was demonstrated to be op
erative by a nonlinear regression routine. On the addition of either u
rea, SDS, or 1-propanol into the 4-beta-CD binary system, the fluoresc
ence quantum yields (Phi(F)) are significantly reduced suggesting that
4 transfers from the relatively nonpolar environments to polar enviro
nments.