EFFECTS OF PH ON THE ABSORPTION, EMISSION AND LIGHT-SCATTERING SPECTROSCOPY OF BILIRUBIN AND XANTHOBILIRUBIC ACID IN SODIUM TAUROCHOLATE SOLUTION

Electronic absorption, differential absorption and emission spectra, a s well as light scattering intensities, have been obtained for solutio ns of the bile pigment bilirubin in the presence of the bile salt sodi um taurocholate over the pH range 5.0-8.0. Similar measurements were p erformed on the dipyrrinone analog compound xanthobilirubic acid. The results are interpreted in terms of hydrophobic solubilization of mono meric bilirubin at alkaline pH, and formation of hydrophobic mixed agg regates of pigment and bile salt at lower pH, with the size of the bil irubin aggregates increasing as the pH decreases. The data are consist ent with a model of co-micellization of pigment and bile salt, and als o suggest that the chemistry of these complexes is determined mainly b y the structural properties of the tetrapyrrole.