Ultraviolet and nuclear magnetic resonance studies of the solubilization of chlorzoxazone by alkyltrimethylammonium halides

• Published in: Journal of colloid and interface science 1983-01, Vol.92 (2), p.396-402
• Main Authors: Chen, Chih-Ming J, Frank, Sylvan G
• Format: Article
• Language: English
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/0021-9797(83)90161-3

From comparisons of the spectra of chlorzoxazone before and after solubilization in solutions of Tween 80, sodium lauryl sulfate, and cetyltrimethylammonium bromide (CTAB), the most significant changes were found for the cationic CTAB. Subsequent studies of the interaction of chlorzoxazone with CTAB indicated that the quaternary ammonium group induces the ionization of chlorzoxazone from its nonionic keto form to its ionized enolate form. From changes in the UV absorbance of chlorzoxazone after solubilization in solutions of CTAB, the binding constant of chlorzoxazone with the CTAB micelles (5.51 × 10 4 M −1) and the approximate number of binding sites (8) were calculated by Sepulveda's method, modified to include the critical micelle concentration. Furthermore, NMR studies of the more soluble chlorzoxazone-dodecyltrimethylammonium chloride (DTAC) systems indicated that chlorzoxazone was located in the palisade layer of the DTAC micelles with its carbonyl oxygen close to the surface and chlorine atom facing inward toward the nonpolar core of the micelles.