Behaviors of Sodium Taurocholate and Sodium Taurodeoxycholate in Binary Mixed Micelles of Bile Salt and Nonionic Surfactant

Abstract

Behavior of sodium taurocholate (NaTC) and sodium deoxycholate (NaTDC) in binary mixed micelles consisting of bile salt and octaethylene glycol mono-n-decyl ether (C10E8) has been studied on the basis of micellar compositions, polarities of interior of intramicelles, mean aggregation numbers, and 1H-NMR measurements, respectively. Micellar compositions for both the NaTC−C10E8 system and NaTDC−C10E8 system tended to change from C10E8-rich micelles to bile-salt-rich micelles with the mole fraction of bile salts from the results of both theoretical calculations using critical micellar concentration (cmc) and the micellar polarity, and also a microenvironment of intramicelles for the NaTDC−C10E8 system was more hydrophobic than that for the NaTC−C10E8 system. Mean aggregation numbers of mixed micelles for both systems abruptly decreased with the increase of mole fraction of bile salts in the range of the low mole fraction, but mean aggregation numbers for the NaTDC−C10E8 system were larger than those for NaTC−C10E8 system. Furthermore, from the results of 1H-NMR measurements, the methyl group protons at the 18, 19, and 21 positions in NaTC molecules were found to have a slight freedom with an increase of mole fraction of NaTC, but those of NaTDC were found to be restricted with an increase of mole fraction of NaTDC.