DIFFUSION OF MIXED MICELLES OF BILE SALT-LECITHIN IN AMYLOPECTIN GELS- A FOURIER-TRANSFORM INFRARED MICROSPECTROSCOPY APPROACH

Using Fourier transform infrared (FTIR) microspectroscopy the average translational diffusion coefficients of bile salt-lecithin mixed micel les diffusing in amylopectin gels of varying concentration were measur ed, on the assumption that the diffusion coefficient was constant duri ng diffusion. This assumption was examined based on quasielastic light scattering (QLS) measurements of the change in the mixed micellar siz e on dilution. The size increased significantly on dilution with a buf fer without the bile salt, whereas the size was almost constant on dil ution with a solution of the bile salt in the same buffer. Because bil e salt molecules in intermicellar solution (being much smaller) diffus e much faster than the mixed micelles, the mixed micelles in the diffu sing front can be treated as if diluted with the bile salt solution. T herefore their size will be constant during diffusion, validating the assumption of a constant diffusion coefficient. Based on this it is po ssible to show that the micelles diffuse with a diffusion coefficient of similar to 10(-11) m(2) s(-1), independent (within experimental err or) of the amylopectin gel concentration over the range 5%-10% w/w.