EFFECTS OF KRYPTOFIX-222 ON VOLUMETRIC AND TRANSPORT-PROPERTIES OF DILUTED AQUEOUS-SOLUTIONS OF SODIUM GLYCODEOXYCHOLATE

The viscosity and the density of sodium glycodeoxycholate (NaGDO) in pure water and in water + 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane(C222) mixtures have been measured at 5 and 25-degrees-C in order to investigate the specific role of ionic solvation on the modification of the micellar properties of the bile salt caused by the complexation of sodium counterion with C222. The hydrodynamic volumes (V(eta)) of NaGDO in water-macrobicyclic solutions, lower than those in pure water, have been justified in terms of the electrical shielding of sodium ion by the hosting macrocycle. Significant differences between V(eta) and the apparent molal volume (PHI(v)) were also found. These discrepancies have been attributed to the solvent molecules interacting with solute and involved in the flow process. The feature of the apparent molal volumes of NaGDO in aqueous solutions containing Kryptofix 222 is very peculiar; namely, PHI(v), progressively increases up to a maximum occurring at the equivalent ratio between cryptate and bile salt concentrations. This phenomenon has been related to the collapse of the cation hydration shell occurring in the complexation process.