Dissociation constants of protonated methionine species in seawater media

✍ Scribed by Virender K. Sharma; Frank J. Millero; Concetta De Stefano; Pasquale Crea

• Book ID: 104041471
• Publisher: Elsevier Science
• Year: 2007
• Tongue: English
• Weight: 377 KB
• Volume: 106
• Category: Article
• ISSN: 0304-4203
• DOI: 10.1016/j.marchem.2007.04.008

✦ Synopsis

The dissociation constants (pK 1 ⁎ and pK 2 ⁎ ) 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 pK 2 ⁎ values were lower than the values in NaCl at the same ionic strength while the pK 1 ⁎ 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 Mg 2+ complexes and Pitzer interaction parameters for Mg 2+ with methionine. The seawater model with the interaction parameters accounts for the differences between the value of pK 1 ⁎ and pK 2 ⁎ 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.