Nuclear magnetic resonance studies on micelle formation by promethazine hydrochloride

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Abstract
The pmr spectra of solutions of promethazine hydrochloride in D2O have been obtained as a function of concentration above and below the critical micellar concentration of the drug. Chemical shifts were obtained relative to an external standard of a 20% promethazine solution (micellar). The shifts of the spectrum of the hydrophilic NH(CH3)2 group to higher fields on increasing concentration were explained by the increased dissociation of the group at the micelle surface, an effect illustrated by the decrease in bulk pH at the critical micelle concentration. Diamagnetic shifts of the aromatic ring protons are compatible with the non-polar environment and a parallel stacking of the phenothiazine rings in the interior of the micelle.