Intermolecular interactions in sodium deoxycholate micelles: An NMR study involving a spin-labeled cholestane

A ¹H and ¹³C NMR study of the interaction between sodium deoxycholate (NaDC) micelles and a nitroxide probe (cholestane spin-label, CSL) is presented. It is shown that CSL primarily interacts with the β face of NaDC. The ¹H NMR relaxation data enable the spatial geometry of the interaction to be defined. van der Waals energy calculations show that the CSL-NaDC interaction corresponds to a minimum if a helical model, previously proposed, is assumed for the NaDC micelle. At high concentrations of CSL, the CSL-NaDC interaction changes and the α face of NaDC may also become involved in the interaction.