Dissociation constants of protonated methionine species in seawater media

Virender K. Sharma, Frank J. Millero, Concetta De Stefano, Pasquale Crea

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


The dissociation constants (pK1* and pK2*) for methionine have been measured in artificial seawater as a function of salinity (S = 5 to 35) and temperature (5 to 45 °C). The seawater pK2* values were lower than the values in NaCl at the same ionic strength while the pK1* values in seawater were lower only at S = 35. In an attempt to understand these differences, we have made measurements of the constants in Na-Mg-Cl solutions at 25 °C. The measured values have been used to determine the formation of Mg2+ complexes and Pitzer interaction parameters for Mg2+ with methionine. The seawater model with the interaction parameters accounts for the differences between the value of pK1* and pK2* between NaCl and seawater. This study demonstrates that it is important to consider all of the ionic interactions in natural waters when examining the dissociation of organic acids.

Original languageEnglish (US)
Pages (from-to)463-470
Number of pages8
JournalMarine Chemistry
Issue number3-4
StatePublished - Aug 2007


  • Dissociation constants
  • Methionine
  • Pitzer model
  • Salinity
  • Seawater
  • Thiols

ASJC Scopus subject areas

  • Oceanography
  • Chemistry(all)
  • Environmental Chemistry
  • Water Science and Technology


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