Laboratoire Analyse et Modélisation pour la Biologie et l'Environnement UMR 8587, Université d'Evry Val d'Essonne-CNRS, Evry, France.
Electrophoresis. 2009 Oct;30(20):3582-90. doi: 10.1002/elps.200900261.
Ca(2+) complexation by both sulfate and selenate ligands was studied by CE. The species were observed to give a unique retention peak as a result of a fast equilibrium between the free ions and the complexes. The change in the corresponding retention time was interpreted with respect to the equilibrium constant of the complexation reaction. The results confirmed the formation of CaSO(4)(aq) and CaSeO(4)(aq) under our experimental conditions. The formation data were derived from the series of measurements carried out at about 15, 25, 35, 45 and 55 degrees C in 0.1 mol/L NaNO(3) ionic strength solutions, and in 0.5 and 1.0 mol/L NaNO(3) ionic strength solutions at 25 degrees C. Using a constant enthalpy of reaction enabled to fit all the experimental data in a 0.1 mol/L medium, leading to the thermodynamic parameters: Delta(r)G(0.1M)(25 degrees C)=-(7.59+/-0.23) kJ/mol, Delta(r)H(0.1 M)=5.57+/-0.80 kJ/mol, and Delta(r)S(0.1 M)(25 degrees C)=44.0+/-3.0 J mol(-1) K(-1) for CaSO(4)(aq) and Delta(r)G(0.1 M)(25 degrees C)=-(6.66+/-0.23) kJ/mol, Delta(r)H(0.1 M)=6.45+/-0.73 kJ/mol, and Delta(r)S(0.1 M)(25 degrees C)=44.0+/-3.0 J mol(-1) K(-1) for CaSeO(4)(aq). Both formation reactions were found to be endothermic and entropy driven. CaSO(4)(aq) appears to be more stable than CaSeO(4)(aq) by 0.93 kJ/mol under these experimental conditions, which correlates with the difference of acidity of the anions as expected for interactions between hard acids and hard bases according to the hard and soft acids and bases theory. The effect of the ionic medium on the formation constants was successfully treated using the Specific ion Interaction Theory, leading to significantly different binary coefficients epsilon(NA+,SO(2-)(4)) = -(0.15 +/- 0.06) mol/kg-1 and epsilon(NA+,SO(2-)(4)) = -(0.26 +/- 0.10) mol/kg-1.
钙（2+）与硫酸盐和硒酸盐配体的络合作用通过 CE 进行了研究。观察到这些物质由于自由离子与配合物之间的快速平衡而产生独特的保留峰。相应保留时间的变化根据络合反应的平衡常数进行了解释。结果证实了在我们的实验条件下形成了 CaSO(4)(aq)和 CaSeO(4)(aq)。形成数据是从在约 15、25、35、45 和 55°C 下在 0.1 mol/L NaNO(3)离子强度溶液中和在 25°C 下在 0.5 和 1.0 mol/L NaNO(3)离子强度溶液中进行的一系列测量中得出的。使用恒定的反应焓使得能够在 0.1 mol/L 介质中拟合所有实验数据，得出热力学参数：Delta(r)G(0.1M)(25 摄氏度)=-(7.59+/-0.23) kJ/mol，Delta(r)H(0.1 M)=5.57+/-0.80 kJ/mol，Delta(r)S(0.1 M)(25 摄氏度)=44.0+/-3.0 J mol(-1) K(-1) 对于 CaSO(4)(aq)和 Delta(r)G(0.1 M)(25 摄氏度)=-(6.66+/-0.23) kJ/mol，Delta(r)H(0.1 M)=6.45+/-0.73 kJ/mol，Delta(r)S(0.1 M)(25 摄氏度)=44.0+/-3.0 J mol(-1) K(-1) 对于 CaSeO(4)(aq)。这两种形成反应均被发现是吸热和熵驱动的。在这些实验条件下，CaSO(4)(aq)比 CaSeO(4)(aq)稳定 0.93 kJ/mol，这与根据硬酸和硬碱理论预期的阴离子酸度差异相关，因为它们是硬酸和硬碱之间相互作用的结果。使用特殊离子相互作用理论成功地处理了离子介质对形成常数的影响，导致显著不同的二元系数 epsilon(NA+,SO(2-)(4)) = -(0.15 +/- 0.06) mol/kg-1 和 epsilon(NA+,SO(2-)(4)) = -(0.26 +/- 0.10) mol/kg-1。
