Fluorescent probe study of sulfonamide binding to povidone.

The possibility of using a fluorescent probe technique for the study of drug-providone (I) interactions was investigated. 1-Anilino-8-naphthalenesulfonate (II) was used as the probe. Sulfanilamide, sulfacetamide, and sulfabenzamide were used as the binding competitors. Both sulfacetamide and sulfabenzamide decreased the fluorescence intensity of the I-II complex, while sulfanilamide increased the intensity. The fluorescence depression was greater with sulfabenzamide than with sulfacetamide, indicating that the former is more strongly bound to povidone. Since sulfabenzamide has a greater hydrophobic group (phenyl) than sulfacetamide (methyl), the binding of these sulfonamides to povidone is probably at least partially hydrophobic in nature. The enhanced fluorescence intensity of the I-II complex in the presence of sulfanilamide is believed to involve hydrogen bonding in which the sulfanilamide acts as an intermediary between I and II. Double reciprocal plots for the I-II and sulfonamide-I interactions were employed to obtain a binding constant of 3.2 X 10(4) M-1 for the I-II interaction. The association constants for sulfacetamide and sulfabenzamide were calculated by means of the Klotz equation to be 13.4 and 56.8 M-1, respectively. The povidone molecules appear to have 1.28 binding sites for these compounds under the experimental conditions.