pH Optimization of Amidation via Carbodiimides
pH Optimization of Amidation via Carbodiimides
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DOI：
10.1021/ie401724m
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发表时间：
2013-09-25
影响因子：
4.2
通讯作者：
Carnali, Joseph O.
中科院分区：
文献类型：
--
作者：
Madison, Stephen A.;Carnali, Joseph O.
使用碳二亚胺来产生胺反应试剂是修饰蛋白质、核酸和含有羧酸基的小分子有机化合物的一种受欢迎的方法，反之亦然。优化酰胺化的规则以前没有被定量地提出，但当使用昂贵的荧光染料进行修饰时，这种优化是至关重要的。本文系统地研究了1-乙基-3-[3-二甲氨基丙基]碳二亚胺盐酸盐(EDAC)将含胺染料与羧甲基纤维素钠(NaCMC)偶联的反应条件，重点考察了偶联胺基团pK(A)的作用。反应活性与羧甲基纤维素钠的部分去质子化、碳二亚胺的部分去质子化、含胺染料的部分去质子化以及反应物和中间体的相对稳定性的乘积成正比：(α(CMC))(1-α(EDAC))(α(胺))S-f。通过与实验数据的比较，该产物对给定胺基团pKa的pH依赖性可以用来确定S-f的pH依赖性。用PK(A)取代第二个含胺染料，并倒置上述步骤，可以半定量地预测pH条件，以优化其酰胺化反应。结果表明，一般可用的pK(A)值和上述形式的S-f可以用来优化碳二亚胺辅助酰胺化反应。
The use of carbodiimides to create an amine-reactive reagent is a favored means of modifying proteins, nucleic acids, and small-molecule organic compounds containing carboxylic acid groups, or vice versa. The rules for optimizing the amidation have not previously been presented quantitatively, but such optimization is critical when modifying with an expensive fluorescent dye. In this study, the reaction conditions for attaching an amine-containing dye to sodium carboxymethyl cellulose (NaCMC) via 1-ethyl-3[3-dimethylaminopropyl]carbodiimide hydrochloride (EDAC) are systematically examined, with an emphasis on the role played by the pK(a) of the coupling amine group. The reactivity is reasoned to be proportional to the product of the fractional deprotonation of NaCMC, the fractional protonation of the carbodiimide, the fractional deprotonation of the amine-containing dye, and the relative stability of the reactants and intermediates: (alpha(CMC))(1 - alpha(EDAC))(alpha(amine))S-f. The pH dependence of this product for a given amine group pKa can be used, by comparison to experimental data, to determine the pH dependence of S-f. Substitution of the pK(a) for a second amine-containing dye and inverting the above procedure gives a semiquantitative prediction of the pH conditions to optimize its amidation. The results suggest that generally available pK(a) values and the above form of S-f can be used to optimize carbodiimide assisted amidation.