Resonance Raman spectroscopy of bilirubins and their complexes.
Yang, Bijun
1992
Abstract
Resonance Raman spectra of bilirubin IX$\alpha$, III$\alpha$, XIII$\alpha$, mesobilirubin XIII$\alpha$, $\alpha$,$\alpha\sp\prime$-dimethyl mesobilirubin XIII$\alpha$ (meso), and $\alpha{,}\alpha\sp\prime$-dimethyl mesobilirubin XIII$\alpha$ (racemic) in alkaline aqueous and/or chloroform solutions are reported. Partial band assignments of bilirubin IXa are proposed. The model compounds confirm assignments of bands of the Raman spectrum of bilirubin IX$\alpha$ to each of the two different pyrromethenones. Resonance Raman spectra of mesobilirubin IV$\alpha$, vinylneoxanthobilirubinic acid and vinylisoneoxanthobilirubinic acid in alkaline aqueous solution and of the t-butylammonium salt of bilirubin IX$\alpha$ are used to define markers for presence or absence of internal hydrogen bonds. Interactions of bilirubin dianion with sphingomyelin, phosphatidyl choline, phosphatidyl ethanolamine, and phosphatidyl glycerol liposomes are studied. The Raman evidence suggests that in the bilirubin dianion/sphingomyelin liposome complex the intramolecular hydrogen bonds between propionate groups and lactam NH/CO are ruptured. It is proposed that in the complex the bilirubin propionates form ion pairs with the quaternary ammonium ion of the choline moiety of sphingomyelin. The Raman studies also show that the interactions of bilirubin with the other three phospholiposome are weaker than the interaction between bilirubin and sphingomyelin. The intramolecular hydrogen bonds of bilirubin dianion in these complexes are largely maintained. 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 infrared and Raman spectra of the target molecules. The results of the calculations are compared to the spectra of bilirubin IX$\alpha$ and various model compounds in the solid state and solution. Raman spectra of bilirubin gallstone, bilirubin IX$\alpha$ solid, calcium bilirubinate (neutral and acid form), potassium bilirubinate, and cholesterol are reported. The result confirms that pigment gallstone is mainly composed of bilirubin ion salts and acid bilirubin. Cholesterol is not a major constituents in this region. The Raman study shows that in neutral form of calcium bilirubinate, the intramolecular hydrogen bonds between the propionic acids and lactams are ruptured, while in the acid form of calcium bilirubinate and potassium bilirubinate the ridge-tile conformation of bilirubin is maintained, or at least half of its folded structure is maintained.Other Identifiers
(UMI)AAI9227032
Subjects
Chemistry, Analytical
Types
Thesis
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