Dissociation Constants of Protonated Oxidized Glutathione in Seawater Media at Different Salinities |
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Authors: | Pasquale Crea Concetta De Stefano Frank J. Millero Silvio Sammartano Virender K. Sharma |
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Affiliation: | (1) Dipartimento di Chimica Inorganica, Chimica Analtica e Chimica Fisica Universita di Messina, Salita Sperone 31, 98166 Messina (Vill. S. Agata), Italy;(2) Rostenstiel School of Marine and Atmospheric Sciences, Marine and Atmospheric Chemistry, 4600 Rickenbacker Causeway, Miami, FL 33149, USA;(3) Chemistry Department, Florida Institute of Technology, 150 West University Boulevard, Melbourne, FL 32901, USA; |
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Abstract: | Oxidized glutathione (GSSG), which has four carboxylic and two amino groups, interacts with metal ions and may affect the bioavailability and geochemistry of metals in natural waters. In the present paper, six stepwise protonation constants KtextHi K^{text{H}}_{i} for GSSG were measured as a function of salinity, S = 5–35‰ at t = 25°C (and in NaCl/MgCl2 mixtures at different ionic strengths), in order to provide thermodynamic data for their acid base properties, which are useful for studying the interaction with metals in these media. The protonation enthalpies (ΔH i /kJ mol−1) were also determined at t = 25°C. The results were interpreted using the SIT model and Pitzer equations. The seawater model with the interaction parameters accounts for the differences between the values in NaCl and seawater. The results suggest that it is important to consider all of the ionic interactions in natural waters in examining the proton dissociation of GSSG. |
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