Normal coordinate analysis of bilirubin vibrational spectra: Effects of intramolecular hydrogen bonding

Abstract

Normal coordinate analyses are presented for half-bilirubin molecules. Calculations for the A---B pyrromethenone include intramolecular hydrogen bonds, while those for the C---D chromophore exclude intramolecular hydrogen bonds. Valence force-field parameters have been optimized to correlate closely with the IR and Raman spectra of the target molecules. The results of the calculations are compared with the spectra of bilirubin IXa and various model compounds in the solid state and solution.