CaCl2在甘氨酸+水和丙氨酸+水混合溶剂中的活度系数

利用离子选择性电极(ISE)测定了298.15 K时CaCl2在甘氨酸+水和丙氨酸+水混合溶剂中的活度系数. CaCl2的质量摩尔浓度变化范围为0.01～0.20 mol/kg, 氨基酸的质量摩尔浓度变化范围为0.10～0.40 mol/kg. 用Debye-Hückel扩展方程和Pitzer方程进行理论计算得到的活度系数基本一致. 依据McMillan-Mayer理论, 计算了CaCl2从纯水到氨基酸水溶液的标准转移Gibbs自由能, 利用最小二乘法拟合求得了对相互作用参数(gEA)和盐效应常数(ks). 讨论了这两种氨基酸的加入对CaCl2的活度系数、热力学稳定性及盐效应常数的影响.

Activity Coefficients of CaCl2 in Glycine+Water and Alanine+Water Mixtures at 298.15 K

Activity coefficients of CaCl2 in glycine+water and alanine+water mixtures at 298.15 K were determined by cell potential measurements using ion selective electodes(ISE). The molalities of CaCl2 ranged from 0.01 to 0.20 mol/kg, and those of amino acides ranged from 0.1 to 0.4 mol/kg. The cell potentials were analyzed by the Debye-Hückel extended equation and the Pitzer equation to calculate activity coefficients. The results obtained from the two theoretical models are in good agreement with each other. Standard transfer Gibbs free energy, pair interaction parameters(gEA) and salting constants(ks) were also evaluated. The results are disscussed in terms of the stereo-chemistry of amino acid molecules and structures and electrostatical interaction models. Activity coefficient of CaCl2 increases with increasing of molalities of amino acids. Standard transfer Gibbs free energy decreases with increasing molalities of amino acids, indicating that the interactions of the amino acides with CaCl2 are thermodynamically attractive in aqueous solution. Values of gEA are negative, indicating that the interactions of these two amino acides with CaCl2 result mainly from the electrostatical attraction.