On the aggregation of bilirubins using vapor pressure osmometry

✍ Scribed by Stefan E. Boiadjiev; David A. Lightner

• Publisher: Journal of Heterocyclic Chemistry
• Year: 2000
• Tongue: English
• Weight: 586 KB
• Volume: 37
• Category: Article
• ISSN: 0022-152X
• DOI: 10.1002/jhet.5570370431

✦ Synopsis

Abstract

Bilirubin and its analogs are carboxylic acids that engage in intramolecular hydrogen bonding and are thus thought to be monomelic in solution, although the evidence for the molecularity in solution is indirect. Contrastingly, the dimethyl esters favor intermolecular hydrogen bonding and are thought to be dimeric, yet they, like the bilirubin (acids), exhibit essentially no concentration dependence of their NH nmr chemical shifts upon dilution from 10^−2^ to 10^−5^ (or even 10^−6^) M in chloroform‐d. Vapor phase osmometry (vpo) studies of chloroform solutions of eight bilirubins and their dimethyl esters clearly indicate that the former are monomelic, while the latter are dimeric — except when a β‐methyl group (but not an α*‐methyl) is present in each methyl propionate chain. Bilirubin mono‐esters might be monomelic or dimeric in solution. Using vpo to study some seven mono‐esters or mono acids, we found that the pigments were monomelic in chloroform.