Fractal and reactive dimensions of some ursodeoxycholic acid salts

Six salts of ursodeoxycholic acid, a bile acid largely administered for the dissolution of cholesterol gallstones, were obtained as powders by lyophilization of their aqueous solutions. The salts were prepared using lithium, sodium and potassium hydroxide; and using arginine, pyrrolidine ethanol and Tris as organic bases. Thermal, microscopy and EDAX analysis were carried out to identify the nature of the salts. Using the parameters of fractal geometry, fractal surface dimension (D-S) and reactive dimension (D-R) to dissolution were also obtained. The very low values (2.02-2.15) for the fractal dimension (D-S) of the particle surface suggest that, except in the case of the lithium (2.29) and pyrrolidine ethanol (2.43) salts, the particles thus obtained are characterized by smooth and regular surfaces. The D-R for most salts were found to be higher than the corresponding D-S and in a very narrow range of values (2.79-2.84). This fact was briefly discussed and compared with previous results obtained with other surfactants. The behaviour of the salt with the Tris base was considered separately. (C) 1998 Elsevier Science B.V. All rights reserved.