Dissociation Constants of Protonated Oxidized Glutathione in Seawater Media at Different Salinities

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 K H i for GSSG were measured as a function of salinity, S = 5-35% at t = 25°C (and in NaCl/ MgCl 2 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 (DH 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.

Physico-Chemical Controls on Seawater

“…Organic acids studied include citric (Crea et al, 2004), cysteine (Sharma et al, 2005), methionine (Sharma et al, 2007), and glutathione (Crea et al, 2010). These include the ionization of organic acids, solubility of nonelectrolytes, and the formation of ion complexes.…”

Ionic Strength Dependence of Dioxovanadium(V) Complexation with Ethylene Glycol-bis(2-aminoethylether)-N,N,N′,N′-tetraacetic Acid

“…There are many papers in the literature about the SIT. − Sammartano et al proposed a modified version of the SIT approach, in which the specific coefficients are expressed as a function of I normalε = normalε ∞ + false( normalε 0 − normalε ∞ false) false( I + 1 false) − 1 where ε ∞ is the value of ε for I → ∞ and ε 0 is the value of ε for I → 0. ε ∞ could be defined as follows normalε ∞ = normalε ∞ false( 0 false) + normalε ∞ false( 1 false) I The results were satisfactory in the whole range 0.1 < I /mol·kg −1 < 6 . Equation comes from the need for adding a term which takes into account the formation of weak (or even very weak) ion pairs …”

“…There are many papers in the literature about the SIT. [26][27][28][29][30][31][32] Sammartano et al 32 proposed a modified version of the SIT approach, in which the specific coefficients are expressed as a function of…”

Complexation of Dioxovanadium(V) with D-(-)-Quinic Acid at Different Ionic Strengths Using Different Models Based on the Debye-Hückel Theory

“…12 shows the non-specific long-range contribution of the electrostatic region, while the second reflects the contribution due to short-range ion-ion, ion-neutral, or neutralneutral interactions in accordance with the Brønsted postulate that ε(j, k) = 0 if ions have the same charge sign. There are many papers in the literature about the SIT [29][30][31][32][33][34][35][36]. Sammartano [29] proposed a modified version of the SIT approach in which the specific coefficients are expressed as a function of I by:…”