MICELLAR AGGREGATES OF SODIUM GLYCOCHOLATE AND SODIUM TAUROCHOLATE AND THEIR INTERACTION COMPLEXES WITH BILIRUBIN-IX-ALPHA - STRUCTURAL MODELS AND CRYSTAL-STRUCTURE

Sodium glycocholate (NaGC) and taurocholate (NaTC) have been studied b y means of X-ray and circular dichroism (CD) measurements, using bilir ubin-IXalpha (BR) as probe molecule, together with potential-energy ca lculations. Helical models for the micellar aggregates of NaGC and NaT C were inferred from crystal structures solved by X-ray analysis. Sinc e it is known that chiral molecules, micellar aggregates and macromole cules select preferentially or exclusively one of the two enantiomeric conformers of BR, CD spectra of BR in submicellar and micellar aqueou s solutions of NaGC and NaTC were recorded as a function of pH and BR concentration in order to verify these helical models and the enantios elective ability of the bile salt monomers and micellar aggregates. Po tential-energy calculations supported the CD experimental results and provided reasonable bile salt-BR interaction models. The behaviour of NaGC and NaTC is compared with that of sodium deoxycholate (NaDC), pre viously studied. The CD spectra of the bile salt-BR systems seem to al low characterisation of the typical structure of the bile salt micella r aggregates.