Dipartimento di Chimica Inorganica, Chimica Analitica e Chimica Fisica, Università di Messina, Vle F Stagno D'Alcontres 31, 98166 Messina, Vill. S Agata, Italy.
Amino Acids. 2012 Aug;43(2):629-48. doi: 10.1007/s00726-011-1110-0. Epub 2011 Oct 14.
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.
γ-L-谷氨酰-L-半胱氨酰-甘氨酸（谷胱甘肽，GSH）的酸碱性质通过电位法（ISE-H(+)，玻璃电极）在纯 NaI((aq)) 和 NaCl((aq))/MgCl(2(aq)) 以及 NaCl((aq))/CaCl(2(aq)) 混合物中测定，温度为 298.15 K，离子强度不同（最高可达 I(c)~5.0 mol L(-1))。此外，还通过分布法在相同温度下在各种离子介质（LiCl((aq))、NaCl((aq))、KCl((aq))、CsCl((aq))、MgCl(2(aq))、CaCl(2(aq))、NaI((aq))) 中测定了谷胱甘肽的活度系数。所得到的结果还用于计算特定离子相互作用理论（SIT）和 Pitzer 系数，以表示谷胱甘肽物种对介质和离子强度的依赖性，以及形成常数弱 Mg(j)H( i )(GSH)((i+2j-3)) 和 Ca(j)H(i)(GSH)((i+2j-3)) 配合物。还在纯 NaCl((aq)) 和 NaCl((aq))/CaCl(2(aq)) 混合物中进行了直接量热滴定，在不同的离子强度（0.25≤I(c)/mol L(-1)≤5.0）下，以确定在 T = 298.15 K 时这些介质中质子化和配合物形成平衡的焓变。所得到的结果对于在含有天然水和生物体液主要阳离子（如 Na(+)、K(+)、Mg(2+) 和 Ca(2+)）的任何水溶液中定义谷胱甘肽形态学非常有用。最后，这种系统研究，其中在测定各种热力学参数时考虑了一系列离子介质（例如，所有碱金属氯化物），对于定义谷胱甘肽在水溶液中的热力学行为的某些趋势非常有用。
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