title: Chirality inversion in the bilirubin molecular exciton.
abstract: The bichromophoric pigment bilirubin acts as a molecular exciton in its UV-visible and circular dichroism (CD) spectroscopy. In both polar and nonpolar solvents, an optically active analog, (beta R,beta 'R)-dimethylmesobilirubin-XIII alpha (1), exhibits intense bisignate CD Cotton effects in the region of its long wavelength UV-vis absorption near 400 nm: Delta epsilon(434)(max) + 337, Delta epsilon(389)(max) - 186 (CHCl(3)), and Delta epsilon(431)(max) + 285, Delta epsilon(386)(max) - 177 (CH(3)OH). However, introduction of an amine into a CHCl(3) solution of 1 causes the Cotton effect signs to become inverted, e.g., after addition of NH(3), Delta epsilon(433)(max) - 345, Delta epsilon(389)(max) + 243, and after addition of ethylene diamine, Delta epsilon(435)(max) - 420, Delta epsilon(390)(max) + 299. The sign inversions imply inversion of molecular chirality of the bilirubin and the phenomenon appears to be general for amines, including alpha,omega-diamines. 1,8-Diaminooctane was found to be more effective than longer or shorter chain analogs in producing CD sign inversion.
authors.affiliation: Chemistry Department, University of Nevada, Reno, Nevada 89557-0020, USA.
authors.forename: S E
authors.initials: SE
authors.lastname: Boiadjiev
authors.forename: D A
authors.initials: DA
authors.lastname: Lightner
mesh_terms: D001663:Bilirubin / Q000737:chemistry*; D002942:Circular Dichroism; D006860:Hydrogen Bonding; D008968:Molecular Conformation; D013237:Stereoisomerism
chemical_list: D001663:Bilirubin