Physicochemical Study of Bile Salt-Polymer Micellar Aggregates

The micellar behavior of Sodium Deoxycholate (NaDC), a bile salt in presence of a neutral water soluble polymer Poly(vinylpyrrolidone) (PVP) has been investigated at four different temperatures (10-40 degrees C) using conductometric, tensiometric, viscometric and fluorometric methods. NaDC is found to associate co-operatively with the polymer beyond a critical concentration, saturate the polymer completely and then undergo micellization at a higher concentration. The counter-ion binding capacity to the micelles is considerably reduced in presence of PVP. The thermodynamic properties of micellization and interfacial adsorption depend on the polymer concentration and the entropic contributions are observed to control the complexation process. The NaDC-PVP aggregate exhibits polyelectrolytic behavior. The aggregation number (N) and polarity index (I-1/I-3) of the NaDC-PVP mixed entities have been explored by pyrene fluorescence probing technique. The values of N and I-1/I-3 are found to be affected by [PVP] and temperature: the N values decrease with temperature while those of I-1/I-3 show increasing trend. The dependence of N and I-1/I-3 values on [PVP] and temperature reveal interesting insights into the NaDC-PVP complexation phenomenon.