Abstract
The self-association of three bile salts has been studied by sedimentation equilibrium and vapor pressure osmometry. Sedimentation equilibrium experiments were performed on solutions of sodium cholate and sodium ursodeoxycholate at 25(DEGREES)C. At 31(DEGREES)C and at the human body temperature, 37(DEGREES)C, the association behavior of these two compounds was examined by vapor pressure osmometry. A number of possible models were tested against the association data. A Type IV SEK (sequential, equal equilibrium constant) model gave a good description of the observed associations of both bile salts at all three temperatures. This association is defined by the following equilibria: (UNFORMATTED TABLE FOLLOWS) 2P(,1) (DBLARR) P(,2) P(,2) + P(,n-2) (DBLARR) P(,n) (n = 4,6,8,...) (TABLE ENDS) where P(,1) is the associating monomer. The self-association of sodium deoxycholate was also studied by vapor pressure osmometry at 37(DEGREES)C. This enabled a direct comparison to be made of the association of the three bile salts at 37(DEGREES)C. The self-association of sodium deoxycholate was best described by the Type IV SEK model with a dimerization equilibrium constant, k(,12), of 0.150 1/g and a stepwise equilibrium constant, k, of 2.5 1/g and a nonideal term, BM(,1), of -0.0055 1/g. For sodium cholate values of k(,12) = 0.081 1/g, k = 0.46 1/g and BM(,1) = -0.0133 1/g were found. The degree of association of sodium deoxycholate was much greater than that of sodium cholate even though the two molecules differ only in the respect that sodium deoxycholate lacks a hydroxyl group at the 7(alpha) position of the steroid nucleus. The association of sodium ursodeoxycholate was slightly weaker than that of sodium cholate with k(,12) = 0.038 1/g, k = 0.39 1/g and BM(,1) = -0.0214 1/g. From the values of the equilibrium constants for the association of sodium cholate and sodium ursodeoxycholate at 25(DEGREES), 31(DEGREES) and 37(DEGREES)C the thermodynamic parameters (DELTA)G('0), (DELTA)H('0) and (DELTA)S('0) were determined. No dependence of the association of these compounds upon temperature was observed within the limits of precision of these experiments.
Beckerdite, John Michae (1983). The self-association of bile salts in isotonic saline. Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -578133.