In an attempt to investigate how a nonionic polymer, hydroxypropyl methylcellulose (HPMC), interacts with a cationic surfactant, hexadecyltrimethylammonium bromide (CTAB), a dialysis method was employed for directly measuring the HPMC-CTAB interaction. The result showed that an interaction existed between CTAB and HPMC, and the higher the HPMC concentration the greater the fraction of CTAB bound. The shift in the UV spectra represents the change in the microenvironment. UV spectroscopy was employed to indicate the location of substrates, alpha-NA, IBA, and oil red O, in the CTAB micelles. The study of solubility as a function of CTAB concentration was the method used for determining the binding constants of the substrates. The addition of HPMC decreased the binding constants of the substrates to the micelles. It implied that the HPMC-CTAB interaction influenced the substrate binding regions. The IBA binding constant was also determined using a potentiometric titration method. The results agreed well between the two methods.2009 Wiley-Liss, Inc. and the American Pharmacists Association
