Equilibrium swelling of pigment gallstones: Evidence for network polymer structure

Brian E. Black, Stephen H. Carr*, Hideki Ohkubo, J. Donald Ostrow

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

25 Scopus citations


A major component of pigment gallstones (PS) is a black, insoluble substance. It has been suggested that this pigment material might be a highly crosslinked polymer, and if such were the case, it should imbibe solvent (swell) to the maximum permitted by the crosslinks of its macromolecular network. We measured the equilibrium amount, qeq, by which pulverized, desiccated PS swells in different liquids, including isotonic aqueous buffers at pH values from 1.5–11.5. For ionic strengths ≥ 0.15, the dependence of qeq on pH exhibits a broad titration curve with a midpoint near pH 7. qeq was < 1.2 in methanol, dimethylformamide, dimethylsulfoxide, and chloroform. The ir absorbance from vinyl groups in the black pigment was only one‐eighth that of unconjugated bilirubin, the primary chemical building block of PS; this implicates vinyl groups in the formation of a polymer network. The rise in qeq with increasing pH suggests that the carboxyl groups are free to ionize and are therefore not involved in the covalent bonds that make the crosslinked polymer. A network polymer structure would account for the inability to dissolve PS in those solvents in which unconjugated bilirubin is soluble.

Original languageEnglish (US)
Pages (from-to)601-610
Number of pages10
Issue number3
StatePublished - Mar 1982

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Biomaterials
  • Organic Chemistry


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