聚天冬氨酸酸解离常数的测定

Determination of the Dissociation Constants of Polyaspartic Acid

采用pH电位滴定法,利用先进的BEST程序,针对聚羧酸在水溶液中解离及平衡常数测定的复杂性,构建了聚天冬氨酸(PASP)在水溶液中解离的H4L和H2L两种模型,分别测得了相应的各级酸解离常数,并得到了PASP在不同pH条件下的物种分布曲线。在35℃,I=0.1时,对于H4L模型,各级酸解离常数的pKa值为:2.27、3.66、4.22、5.40;对于H2L模型,相应的pKa值为2.92、4.84。研究结果表明,两种模型计算结果均能与实验结果很好吻合,但H4L模型误差更小,因此是一种更为合理的模型。

By means of pH potentiometric titration, the dissociation equilibrium of polyaspartic acid （PASP） was studied. Computer program BEST edited by Martell has been used to calculate the dissociation constants of PASP. Considering the complexity of the dissociation of polyaspartic acid in aqueous solution, two models including H4 L and H2 L were constructed to simulate the dissociation process of PASP. All levels of the dissociation constants of PASP for two models were determined. As for two models, the corresponding values of pK,i were listed as follows： 2.27,3.66,4.22,5.40 for H4L and 2.02,4.84 for H2 L under the condition of 35 ℃ and/（ionic strength） =0. 1. The results showed that the model H4L was relative better than H2L, because, for H4L, the corresponding error was less and the matching between the experimental and calculating data was better. As a function of pH, the distribution state of different species of PASP in aqueous solution was also given out according to the experimental and calculating results.