Ks. Cameron et L. Fielding, NMR diffusion spectroscopy as a measure of host-guest complex association constants and as a probe of complex size, J ORG CHEM, 66(21), 2001, pp. 6891-6895
The complexes of cyclohexylacetic acid and cholic acid with beta -cyclodext
rin were studied by NMR diffusion coefficient measurements. The diffusion c
oefficient of the 1:1 cyclohexylacetic acid/beta -cyclodextrin complex, K-a
= 1800 +/- 100 M-1, is slightly slower (3.23 +/- 0.07 x 10(-6) cm(2) s(-1)
) than that of beta -cyclodextrin (3.29 +/- 0.07 x 10(-6) cm(2) s(-1)). The
diffusion coefficient of the 1:1 cholic acid/beta -cyclodextrin complex, K
-a 5900 +/- 800 M-1, is significantly slower (2.93 +/- 0.07 x 10(-6) cm(2)
s(-1)) than that of beta -cyclodextrin. The results indicate that caution s
hould be exercised when studying host-guest complexation by the so-called '
single point' technique. A novel data treatment is introduced which takes i
nto account the diffusion behavior of all of the species when determining K
-a. Experimentally determined diffusion coefficients of complexes are also
a useful probe of the size of host-guest complexes.