Enzymatic catalysis in cosolvent modified pressurized organic solvents

Marazban Sarkari, Barbara L. Knutson, Ching Shih Chen

Research output: Contribution to journalArticlepeer-review

8 Scopus citations


An important advantage of carrying out enzymatic catalysis in organic media is the increased solubility of hydrophobic substrates. This study compares a model lipase catalyzed esterification of cholesterol using vinyl acetate (VA) in two such nontraditional media: high-pressure hexane and supercritical (SCF) ethane. The effect of using one of the reactants (VA) as a cosolvent to increase the solubility of the other reactant (cholesterol) in SCF ethane has been investigated. The thermodynamic activity of water (a(w)) in the reaction media was controlled by the direct addition of the salt hydrate pair Na4P2O7/Na4P2O7,10H2O. The a(w) of the salt hydrate system is shown to be a function of pressure and its variation over the pressure range 104-173 bar has been estimated. The initial reaction rate in pressurized hexane was found to vary linearly with the cholesterol concentration. The reaction rate was also a function of pressure-the effect being more pronounced in ethane than in hexane. This is consistent with the large negative partial molar volumes observed in SCFs, although the sign of the resulting activation volume differs from previous investigations of lipase-catalyzed reactions in SCFs. When corrected for substrate concentration, the initial rate of catalysis in SCF ethane was determined to be greater than in pressurized hexane over the conditions investigated. This study shows that proper solvent choice can be used to regulate reaction rates in pressurized solvents.

Original languageEnglish
Pages (from-to)258-264
Number of pages7
JournalBiotechnology and Bioengineering
Issue number3
StatePublished - Nov 5 1999


  • Cosolvent effect
  • Enzymatic catalysis
  • Pressurized organic solvent
  • Supercritical fluids
  • Water activity

ASJC Scopus subject areas

  • Biotechnology
  • Bioengineering
  • Applied Microbiology and Biotechnology


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