蛋氨酸在KCl溶液中的解离常数与活度系数

采用改变pH法在25、30和35℃下测定了质量浓度为0.25~4.0 mol/kg的KCl水溶液中蛋氨酸的解离常数，计算得到了蛋氨酸的质子化焓；采用电动势法在25℃测量了0.025~0.200 mol/kg蛋氨酸溶液中浓度为0.1~1 mol/kg的KCl的活度系数，计算得到了KCl溶液中蛋氨酸的活度系数。结果表明，蛋氨酸在KCl水溶液中的解离常数随温度上升而减小、随KCl浓度增加而增大；25℃下，蛋氨酸在KCl水溶液中的活度系数随蛋氨酸浓度增大先减小后增大。运用德拜-休克尔模型和Pitzer模型对解离常数和活度系数的实验数据进行拟合，得到了相关参数，结果表明Pitzer模型的可靠性较好。

Dissociation constants and activity coefficients of methionine in KCl aqueous solutions

The dissociation constants of methionine in KCl aqueous solutions with the molality of 0.25—4.0 mol/kg at 25℃, 30℃ and 35℃ were determined by changing the pH value, and the protonation enthalpies of methionine species were calculated. Methionine activity coefficients of 0.1—1 mol/kg KCl in 0.025—0.200 mol/kg DL-methionine solution were measured by electromotive force method at 25℃, and the activity coefficients of methionine in KCl aqueous solutions were calculated. The results showed that the dissociation constants of methionine in KCl aqueous solution decreased with the increase of temperature and increased with the increase of KCl concentration. The activity coefficients of methionine in KCl aqueous solutions at 25°C decreased first and then increased with the increase of methionine concentration. Debye-Huckel model and Pitzer model were used to fit the experimental datas of dissociation constants and activity coefficients, and the relevant parameters were obtained. The results show that the reliability of the Pitzer model is better.