Self Association of Bile Salts in Aqueous Medium - A Spectroscopic Investigation using Diphenylhexatriene

Abstract

The physiological importance of bile salts lies in their ability to solubilise cholesterol, dietary lipids and fat soluble vitamins in the gastrointestinal tract. The detergent action of bile salts is mainly due to their micelle-forming capacity hence these are known as “biosurfactants”. Owing to its physiological importance, proper understanding of the micellisation process of bile salts is essential in the evaluation of their biological activities. The sensitivity of a fluorescent molecule to its immediate environment makes fluorescence a versatile technique to be used for acquiring important information about micelles and micellisation process. 1,6-Diphenylhexatriene (DPH) is one of the most sensitive fluorescent probes used for such studies. Using the fluorescence intensity of DPH, CMC of sodium taurocholate and sodium taurodeoxycholate was evaluated and found to be 17 mM and 7 mM, respectively. It was found that the fluorescence intensity of DPH in cholate micelles is less than that in corresponding deoxycholate micelles for a given concentration of DPH and under similar experimental conditions. Detailed spectrophotometric study revealed that deoxycholate micelles provide a hydrophobic environment for DPH hence the preferred form for DPH in deoxycholate micelles is the trans-form and the intensity is high, whereas cholate micelles provide a hydrophilic environment for DPH hence it exists in the cis-form and as a result of which fluorescence intensity is low.