1993 Volume 41 Issue 9 Pages 1616-1620
The interaction of sodium salicylate and naphazoline hydrochloride with polyvinylpyrrolidones having four different molecular weights (10, 25, 40, and 360kDa), and with the micelles of non-ionic surfactant polyoxyethylene n-dodecylethers having various numbers of oxyethylene units (5, 6, 7, and 8) were investigated using the freezing point depression method. The advantages of this method are that the binding parameters can be rapidly obtained by a simple procedure using a commercially available osmometer. Based on the colligative properties, the binding parameters were calculated. The data were expressed in the form of nonlinear Scatchard plots. The results suggested that salicylate and naphazoline were bound to two kinds of binding sites on a molecule of polyvinylpyrrolidone or to a micelle of polyoxyethylene n-dodecylether; the primary binding site exhibited a high affinity but a low capacity for the drug, while the second binding site has a lower affinity and a high capacity; that is, the interaction on the second binding site could be described as non-specific binding. For the interactions of drugs with polyvinylpyrrolidone, the number of N-vinyl-2-pyrrolidone units (monomer) that interacted with one molecule of salicylate and naphazoline were fairly constant, and from 10 to 14 and from 21 to 30, respectively. For the interactions of drugs with a micelle of polyoxyethylene n-dodecylether, the number of polyoxyethylene n-dodecylether molecules which interacted was also nearly constant at 3 to 4 and 5 to 6, respectively.
