Determination of association constants in cyclodextrin/drug complexation using the Scatchard plot: application to beta-cyclodextrin-anilinonaphthalenesulfonates.
The appropriate Scatchard equation was developed for a system involving the formation of 1:1 and 1:2 substrate:cyclodextrin complexes. Simulation of this system was performed under the most common experimental conditions encountered in this type of study. The use of the equation allows for nonlinear least-squares estimation of the association constants. The interaction of the model compounds 1-anilino-8-naphthalenesulfonate (1,8-ANS) and 2(p-toluidinyl)-6-naphthalenesulfonate (2,6-TNS) with beta-cyclodextrin (beta-CD) was used to evaluate the theoretical model. Binding experiments were performed using either potentiometric titration or fluorimetric detection. The experimental data for 1,8-ANS/beta-CD fit well to the 1:1 binding model, with an association constant of 87 +/- 1 M-1. The association constants of the 1:1 and 1:2 2,6-TNS/beta-CD complexes utilizing direct potentiometry were 3737 +/- 6 and 149 +/- 2 M-1. It is shown that fluorimetry can give biased estimates for the association constants of the complexation 2,6-TNS/beta-CD, since the assumption of an equivalent quantum yield of bound species is not valid.
Sideris
E E
EE
Department of Pharmacy, University of Athens, Greece.
Valsami
G N
GN
Koupparis
M A
MA
Macheras
P E
PE
D000817:Anilino Naphthalenesulfonates / Q000737:chemistry*; D003505:Cyclodextrins / Q000737:chemistry*; D004566:Electrodes; D007202:Indicators and Reagents; D007700:Kinetics; D008954:Models, Biological; D013050:Spectrometry, Fluorescence
D000817:Anilino Naphthalenesulfonates; D003505:Cyclodextrins; D007202:Indicators and Reagents