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Chirality inversion in the bilirubin molecular exciton
1Chemistry Department, University of Nevada, Reno, Nevada 89557-0020, USA.
Chirality
|April 24, 2001
Summary
Chirality of bilirubin analogs can be inverted by amines, demonstrated through circular dichroism (CD) spectroscopy. This molecular chirality inversion phenomenon is general for amines and depends on the amine
Area of Science:
- * Spectroscopy
- * Chemical Physics
- * Organic Chemistry
Background:
- * Bilirubin, a bichromophoric pigment, functions as a molecular exciton.
- * Optically active bilirubin analogs exhibit bisignate circular dichroism (CD) Cotton effects.
- * These effects are observed in the UV-visible absorption region near 400 nm in various solvents.
Purpose of the Study:
- * To investigate the effect of amine addition on the chirality of bilirubin analogs.
- * To determine if the observed chirality inversion is a general phenomenon for amines.
- * To explore the influence of amine chain length on the inversion efficiency.
Main Methods:
- * UV-visible spectroscopy
- * Circular dichroism (CD) spectroscopy
- * Chirality measurements in polar and nonpolar solvents (CHCl(3), CH(3)OH)
- * Addition of various amines (NH(3), ethylene diamine, 1,8-diaminooctane)
Main Results:
- * (beta R,beta 'R)-dimethylmesobilirubin-XIII alpha (1) shows intense bisignate CD Cotton effects in CHCl(3) and CH(3)OH.
- * Addition of amines to a CHCl(3) solution of (1) caused inversion of the CD Cotton effect signs.
- * 1,8-Diaminooctane was most effective among tested diamines in inducing CD sign inversion.
Conclusions:
- * The observed sign inversions in CD spectra indicate a reversal of molecular chirality in bilirubin analogs.
- * This chirality inversion phenomenon is general for amines, including alpha,omega-diamines.
- * The effectiveness of diamines in inducing chirality inversion is dependent on their chain length.
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