Abstract: In this paper, UV and CD spectra of bilirubin and bile salts-bilirubin in aqueous solution have been simulated by. means of "PPP-SCF-CI-DV", quantum chemical programme, in order to clarify the conformations of bilirubin and its complexes with bile salts. The torsional angles between two dipyrrole chromophores of bilirubin were pos-tulated changing from 104° to 112°, after binding with bile salts and the intramole-cularly hydrogen bonded states of bilirubin still are kept; the separation between two absorption peakes in both UV and CD spectrum increases in presence of bile salts, it is interpreted by that one dipyrrole chromophores of billrubin are combined with bile salts mainly; the difference of CD spectrum which are produced by dihydroxy and trihydroxy bile salts may be explained by enantio-selective binding.

Key words: Bilirubin, Bile salts, Quantum chemistry calculation