Ratio of entropy to enthalpy in thermal transitions in biological tissues

Steven L. Jacques

Research output: Contribution to journalArticlepeer-review

47 Scopus citations


Thermal transitions in biological tissues that have been reported in the literature are summarized in terms of the apparent molar entropy (ΔS) and molar enthalpy (ΔH) involved in the transition. A plot of ΔS versus ΔH for all the data yields a straight line, consistent with the definition of free energy, ΔG= ΔH+ TΔS. Various bonds may be involved in cooperative bond breakage during thermal transitions; however, for the sake of description, the equivalent number of cooperative hydrogen bonds can be cited. Most of the tissue data behave as if 10 to 20 hydrogen bonds are cooperatively broken during coagulation, with one transition, the expression of heat shock protein, involving 90 cooperative hydrogen bonds. The data are consistent with ΔS=a+bΔH, where a = -327.5 J/(mol K) and b=31.47X 10-4 K-1. If each additional hydrogen bond adds 19X103 J/mol to ΔH, then each additional bond adds 59.8 J/(mol · K) to ΔS. Hence, the dynamics of irreversible thermal transitions can be described in terms of one free parameter, the apparent number of cooperative hydrogen bonds broken during the transition.

Original languageEnglish (US)
Article number041108
JournalJournal of biomedical optics
Issue number4
StatePublished - Jul 2006


  • Thermal effects
  • X ray
  • X ray lasers

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Biomaterials
  • Atomic and Molecular Physics, and Optics
  • Biomedical Engineering


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