Koval Dusan, Kasicka Václav, Jirácek Jirí, Collinsová Michaela
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Prague, Czech Republic.
Electrophoresis. 2006 Dec;27(23):4648-57. doi: 10.1002/elps.200600133.
A CE method was used for the determination of acidity constants (pK(a)) of a series of ten phosphinic pseudopeptides, which varied in number and type of ionogenic groups. Effective electrophoretic mobilities were measured in the 1.8-12.0 pH range in the BGEs of constant ionic strength of 25 mM. Effective electrophoretic mobilities, corrected to standard temperature of 25 degrees C, were subjected to non-linear regression analysis and the obtained apparent pK(a) values were recalculated to thermodynamic pK(a)'s by extrapolation to zero ionic strength according to the extended Debye-Hückel model. The pK(a) values of the phosphinic acid group fell typically in the 1.5-2.25 interval, C-terminal carboxylic groups in the 2.94-3.50 interval, carboxylic groups of the lateral chain of glutamate and aspartate in the 4.68-4.97 interval, imidazolyl moiety of histidine in the 6.55-8.32 interval, N-terminal amino groups in the 7.65-8.28 interval and epsilon-amino group of the lateral chain of lysine in the 10.46-10.61 interval. Further, separation of diastereomers of the phosphinic pseudopeptides was investigated in achiral BGEs. Evaluation of the resolution of the diastereomers as a function of pH of the BGE revealed that most suitable pH region for separation of the diastereomers is around the pK(a) values of the central phosphinic acid group of the pseudopeptides. Successful separation of some diastereomers was, however, achieved in the neutral and alkaline BGEs as well.
采用毛细管电泳法测定了一系列十种次膦酸假肽的酸度常数（pK(a)），这些假肽的离子ogenic基团的数量和类型各不相同。在25 mM恒定离子强度的背景电解质（BGE）中，于1.8 - 12.0 pH范围内测量有效电泳迁移率。将校正到25℃标准温度的有效电泳迁移率进行非线性回归分析，并根据扩展的德拜 - 休克尔模型，通过外推至零离子强度，将获得的表观pK(a)值重新计算为热力学pK(a)。次膦酸基团的pK(a)值通常在1.5 - 2.25区间，C端羧基在2.94 - 3.50区间，谷氨酸和天冬氨酸侧链羧基在4.68 - 4.97区间，组氨酸的咪唑基部分在6.55 - 8.32区间，N端氨基在7.65 - 8.28区间，赖氨酸侧链的ε - 氨基在10.46 - 10.61区间。此外，在手性背景电解质中研究了次膦酸假肽非对映体的分离。将非对映体的分离度作为背景电解质pH的函数进行评估，结果表明，分离非对映体最合适的pH区域大约在假肽中心次膦酸基团的pK(a)值附近。然而，在中性和碱性背景电解质中也成功实现了一些非对映体的分离。
