Insights into the Capillary Electrophoresis Separation of Heparin Disaccharides from Nuclear Magnetic Resonance, p<i>K</i><sub>a</sub>, and Electrophoretic Mobility Measurements
作者:Stacie L. Eldridge、Layne A. Higgins、Bailey J. Dickey、Cynthia K. Larive
DOI:10.1021/ac901218q
日期:2009.9.1
Determination of the pKa values of heparin disaccharide functional groups can provide insights into the nature of glycosaminoglycan (GAG)−protein interactions and prove useful for optimization of the charged-based separations typically used in GAG analysis. In order to gain a better understanding into the capillary electrophoresis (CE) separation process, the pKa values of the carboxylate and primary amine moieties of 11 heparin disaccharide standards were determined through 1H NMR detected pH titrations. These pKa values were used to calculate the effective net charge of each disaccharide and compared to the electrophoretic mobilities measured by CE. Although a different migration order had been reported by other researchers, our results indicate a strong positive correlation between the two measurements, consistent with the migration order observed in our CE separations. The effect of mutarotation was also examined by 1H NMR. Mutarotation equilibrium constants favored the α anomer over the β conformation. pKa values determined for both anomers of the four disaccharide standards containing a GlcN primary amine indicated that the β anomer of the GlcN residue was more acidic. Partial separation of these anomers was achieved in CE separations using either formic acid or phosphate buffer.
测定肝素二糖官能团的 pKa 值可以深入了解糖胺聚糖(GAG)-蛋白质相互作用的性质,并有助于优化通常用于 GAG 分析的带电分离。为了更好地了解毛细管电泳(CE)分离过程,我们通过 1H NMR 检测 pH 滴定法测定了 11 种肝素二糖标准物质的羧酸基和伯胺基的 pKa 值。这些 pKa 值用于计算每种双糖的有效净电荷,并与 CE 测得的电泳迁移率进行比较。虽然其他研究人员报告了不同的迁移顺序,但我们的结果表明这两种测量结果之间存在很强的正相关性,与我们在 CE 分离中观察到的迁移顺序一致。我们还通过 1H NMR 研究了互变的影响。对含有 GlcN 伯胺的四种二糖标准的两种异构体测定的 pKa 值表明,GlcN 残基的 β 异构体酸性更强。在使用甲酸或磷酸盐缓冲液进行 CE 分离时,可实现这些异构体的部分分离。