SPECIFIC INTERACTIONS BETWEEN SODIUM DEOXYCHOLATE AND ITS WATER-INSOLUBLE ANALOGS - MECHANISMS FOR PREMICELLE AND MICELLE FORMATION OF SODIUM DEOXYCHOLATE

Interactions between sodium deoxycholate (NaDC, host) and its water-insoluble analogues (guests) have been studied in water (pH 10) to clarify the mechanisms for the premicelle and micelle formation of NaDC. Turbidity measurements have been used as a convenient method to study the interactions between the guest and host molecules. At least two alpha-hydroxy groups attached to the C-3 and C-12 positions of a steroid nucleus are required for the guest steroids to interact with NaDC below the critical micelle concentration. This strongly suggests the formation of a hydrogen-bonded dimer of NaDC as a premicelle whose formation is assisted by the hydrophobic environment provided by the alpha-plane of the steroid. The guest steroids having a hydroxy group at the C-3 position and a polar head group at the C-24 position, which can participate in hydrogen bonding, are solubilized by the NaDC micelles. The results support the mechanism for the NaDC micelle formation involving hydrogen bonding between the C-3 hydroxy group of a premicelle and the C-24 carboxylate anion of another premicelle.