Thermo-solvatochromism of zwitterionic probes in binary mixtures of tetramethylurea and water: Relevance to gelation of lysozyme solutions

M. A. Da Silva, C. T. Martins, E. P.G. Arêas, O. A. El Seoud

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Solutions of lysozyme in mixtures of tetramethylurea, TMU, and water, W, undergo "gelation" above a certain critical composition, at room temperature; the threshold composition for gelation shows some dependence on temperature. Lysozyme gelation in TMU/W has been explained by solvent-induced protein unfolding, due to the protein exposure to a more hydrophobic microenvironment. This preferential solvation can be readily quantified from the study of polarity indicators, serving as simple models for the protein domains. Thermo-solvatochromism of two indicators, 2,6-diphenyl-4-(2,4,6- triphenylpyridinium-1-yl) phenolate, and 4-[(E)2-(1-methylpyridinium-4-yl) ethenyl] phenolate, has been studied in mixtures of TMU-W, from 10 to 60°C. Both probes are preferentially solvated by TMU and, more efficiently, by the hydrogen-bonded species, TMU-W. The maximum concentration of the latter is close to the "critical" threshold mole fraction of water (ca. 0.8.) at which lysozyme gelation occurs. As TMU is added to water the protein, by analogy to polarity indicators, undergoes progressive solvation by less polar, hydrophobic microenvironment leading, at a critical composition, to its unfolding with concomitant gelation of the solution.

Original languageEnglish
Pages (from-to)1135-1145
Number of pages11
JournalPolish Journal of Chemistry
Issue number5-6
Publication statusPublished - May 2007


  • Lysozyme
  • Polarity indicators
  • Protein gelation
  • Tetramethylurea
  • Thermo-solvatochromism

ASJC Scopus subject areas

  • Chemistry(all)

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