title: Modeling the acid-base properties of glutathione in different ionic media, with particular reference to natural waters and biological fluids.
abstract: The acid-base properties of γ-L-glutamyl-L-cysteinyl-glycine (glutathione, GSH) were determined by potentiometry (ISE-H(+), glass electrode) in pure NaI((aq)) and in NaCl((aq))/MgCl(2(aq)), and NaCl((aq))/CaCl(2(aq)) mixtures, at T = 298.15 K and different ionic strengths (up to I(c) ~ 5.0 mol L(-1)). In addition, the activity coefficients of glutathione were also determined by the distribution method at the same temperature in various ionic media (LiCl((aq)), NaCl((aq)), KCl((aq)), CsCl((aq)), MgCl(2(aq)), CaCl(2(aq)), NaI((aq))). The results obtained were also used to calculate the Specific ion Interaction Theory (SIT) and Pitzer coefficients for the dependence on medium and ionic strength of glutathione species, as well as the formation constants of weak Mg(j)H( i )(GSH)((i+2j-3)) and Ca(j)H(i)(GSH)((i+2j-3)) complexes. Direct calorimetric titrations were also carried out in pure NaCl((aq)) and in NaCl((aq))/CaCl(2(aq)) mixtures at different ionic strengths (0.25 ≤ I (c )/mol L(-1) ≤ 5.0) in order to determine the enthalpy changes for the protonation and complex formation equilibria in these media at T = 298.15 K. Results obtained are useful for the definition of glutathione speciation in any aqueous media containing the main cations of natural waters and biological fluids, such as Na(+), K(+), Mg(2+), and Ca(2+). Finally, this kind of systematic studies, where a series of ionic media (e.g., all alkali metal chlorides) is taken into account in the determination of various thermodynamic parameters, is useful for the definition of some trends in the thermodynamic behavior of glutathione in aqueous solution.
authors: Dipartimento di Chimica Inorganica, Chimica Analitica e Chimica Fisica, Università di Messina, Vle F Stagno D'Alcontres 31, 98166 Messina, Vill. S Agata, Italy.
authors: Rosalia Maria
authors: RM
authors: Cigala
authors: Francesco
authors: F
authors: Crea
authors: Concetta
authors: C
authors: De Stefano
authors: Gabriele
authors: G
authors: Lando
authors: Demetrio
authors: D
authors: Milea
authors: Silvio
authors: S
authors: Sammartano
mesh_terms: D000465:Algorithms; D001826:Body Fluids / Q000737:chemistry; D002021:Buffers; D002122:Calcium Chloride / Q000737:chemistry; D002151:Calorimetry; D005978:Glutathione / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D015636:Magnesium Chloride / Q000737:chemistry; D008954:Models, Biological; D008956:Models, Chemical; D009994:Osmolar Concentration; D010084:Oxidation-Reduction; D011199:Potentiometry; D012965:Sodium Chloride / Q000737:chemistry; D013816:Thermodynamics; D017186:Titrimetry; D014867:Water / Q000737:chemistry
chemical_list: D002021:Buffers; D015636:Magnesium Chloride; D014867:Water; D012965:Sodium Chloride; D005978:Glutathione; D002122:Calcium Chloride