Abstract
Fourier transform infrared (FTIR)-attenuated total reflection (ATR) spectroscopy and viscometry were applied to study the micellization of two bile lipids, sodium taurochenodeoxycholate (NaTCDC) and sodium glycocholate (NaGC), in aqueous solutions. The CH2 stretching bands of the bile lipid hydrocarbon region were shifted to higher frequencies suggesting initial critical micellization at 2.5 mM for NaTCDC and 9 mM for NaGC. An abrupt enhancement of the absorption intensity of the CH3 groups of the sterol rings in bile lipids were under conformational strain at 3.5 mM NaTCDC and 9 mM NaGC. Viscometry measurements showed abrupt changes in viscosities in the region of critical micellar concentration (CMC) of both bile lipids. Both infrared and viscometry studies confirmed the onset of conformational strains in tightly packed lipid micelles at their CMC. In addition, FTIR/ATR spectroscopy has defined the specific hydrophobic interactions which bring about critical micellization of bile lipids.
Highlights
Fourier transform infrared (FT1R)-attenuated total reflection (ATR) spectroscopy and viscometry were applied to study the micellization of two bile lipids, sodium taurochenodeoxycholate (NaTCDC) and sodium glycocholate (NaGC), in aqueous solutions
We have studied the vibrational properties of the aliphatic bonds in bile salt molecules by Fourier transform infrared spectroscopy (FTIR) spectroscopy and micellar growth properties by viscometry in order to understand the physical-chemical factors that lead to critical micellar concentration (CMC) formation and aggregation of bile lipids
I R spectroscopy has allowed us to examine the mechanism of CMC formation
Summary
Fourier transform infrared (FT1R)-attenuated total reflection (ATR) spectroscopy and viscometry were applied to study the micellization of two bile lipids, sodium taurochenodeoxycholate (NaTCDC) and sodium glycocholate (NaGC), in aqueous solutions. Viscometry measurements showed abrupt changes in viscosities in the region of critical micellar concentration (CMC) of both bile lipids. Over a narrow concentration range, referred to as the critical micellar concentration (CMC), some bile salts exhibit critical self-association with a strong cooperative interaction of a number of bile salt monomers to form a micelle [1] We have studied those physical chemical features that affected the C M C formation of NaEDC and NaGC, by using infrared (IR) spectroscopic and viscometric methods. IR spectroscopy of biliary lipids in aqueous solutions has been hampered because of the intense absorption of water We have overcome this problem and have measured the I R spectra of bile salts in water by using FTIR in conjunction with attenuated total reflectance (ATR) cylindrical cell. Since the formation of micelles is associated with an increase in the hydrodynamic radius (Rh) of aggregates in solution, and since viscometric methods are sensitive to changes in Rh, we were able to measure small but significant changes in viscosity during micellar formation
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