Carbon-13 and proton NMR studies of the interaction of tricyclic antidepressant drugs with micellar aggregates

C-13 NMR relaxation parameters including T1, the spin-lattice relaxation time, and NOE, the nuclear Overhauser effect, have been measured for mixtures of tricyclic antidepressants (TCAs) and sodium dodecyl sulfate (SDS) micelles. The relaxation parameters were measured at 75 and 100 MHz and were interpreted in terms of the overall and internal motion of these micellar aggregates. It is suggested that the drug molecules are partitioned almost totally within the SDS micelle, resulting in significant increases in micellar volume and a reduction in mobility of SDS alkyl chains. The mobility of the TCA molecules was also examined by using chemical shift data and 2D NMR techniques. It is found that the TCA molecules adopt an extended conformation, with the tricyclic moiety occupying the hydrophobic region of the micelle and the dimethylammonium moiety residing at the micelle/water interface.