Department of Chemistry, Purdue University, West Lafayette, IN 47907-2084, USA.
J Am Soc Mass Spectrom. 2013 Jan;24(1):30-7. doi: 10.1007/s13361-012-0506-8. Epub 2012 Dec 4.
Gas-phase modification of carboxylic acid functionalities is performed via ion/ion reactions with carbodiimide reagents [N-cyclohexyl-N'-(2-morpholinoethyl)carbodiimide (CMC) and [3-(3-Ethylcarbodiimide-1-yl)propyl]trimethylaminium (ECPT)]. Gas-phase ion/ion covalent chemistry requires the formation of a long-lived complex. In this instance, the complex is stabilized by an electrostatic interaction between the fixed charge quaternary ammonium group of the carbodiimide reagent cation and the analyte dianion. Subsequent activation results in characteristic loss of an isocyanate derivative from one side of the carbodiimide functionality, a signature for this covalent chemistry. The resulting amide bond is formed on the analyte at the site of the original carboxylic acid. Reactions involving analytes that do not contain available carboxylic acid groups (e.g., they have been converted to sodium salts) or reagents that do not have the carbodiimide functionality do not undergo a covalent reaction. This chemistry is demonstrated using PAMAM generation 0.5 dendrimer, ethylenediaminetetraacetic acid (EDTA), and the model peptide DGAILDGAILD. This work demonstrates the selective gas-phase covalent modification of carboxylic acid functionalities.
通过与碳二亚胺试剂[N-环己基-N'-(2-吗啉代乙基)碳二亚胺（CMC）和[3-(3-乙基碳二亚胺-1-基)丙基]三甲基铵（ECPT）]的离子/离子反应来实现羧酸官能团的气相修饰。气相离子/离子共价化学需要形成长寿命的配合物。在这种情况下，配合物通过碳二亚胺试剂阳离子的固定电荷季铵基团与分析物二阴离子之间的静电相互作用来稳定。随后的激活导致碳二亚胺官能团一侧特征性地失去异氰酸酯衍生物，这是这种共价化学的特征。在原始羧酸的位置在分析物上形成酰胺键。不包含可用羧酸基团的分析物（例如，已转化为钠盐）或不具有碳二亚胺官能团的试剂不会发生共价反应。使用 PAMAM 代 0.5 树突、乙二胺四乙酸（EDTA）和模型肽 DGAILDGAILD 证明了这种化学性质。这项工作证明了羧酸官能团的选择性气相共价修饰。
