Conformation and intermolecular interation of the antidepressant drugs nitroxazepine and imipramine in aqueous solutions and model membranes

Complete assignments of the proton magnetic resonance spectra of nitroxazepine and imipramine have been made using 1D and 2D techniques. The drugs are found to aggregate through stacking intereactions between the tricyclic moieties at higher concentrations in aqueous solutions. The changes in the chemical shifts with increasing concentration of the two antidepressant drugs show qualitative agreement with the stacking patterns and conformations observed in crystal structures. The conformations of the propyl moiety of the two drugs in aqueous solution and in lipid bilayers are very different. In D2O, the drugs exist in an extended chain conformation which is similar to the crystal structure. In lipid bilayers they acquire a folded structure. The folded structures probably facilitate the binding of the hydrophobic regions of the drugs to the interior of lipid bilayers