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Dissociation constants of protonated methionine species in seawater media |
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| Authors: | Virender K Sharma Frank J Millero Concetta De Stefano Pasquale Crea |
| Institution: | aChemistry Department, Florida Institute of Technology, 150 West University Boulevard, Melbourne, Fl 32901 USA;bRostenstiel School of Marine Atmospheric Sciences, Marine and Atmospheric Chemistry, 4600 Rickenbacker Causeway, Miami, Fl 33149 USA;cDipartimento di Chimica Inorganica, Chimica Analtica e Chimica Fisica, Universita di Messina, Salita Sperone 31, I-98166 Messina (Vill. S. Agata), Italy |
| Abstract: | 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. |
| Keywords: | Pitzer model Thiols Methionine Seawater Dissociation constants Salinity |
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