Pham Huong T, Julian Ryan R
Department of Chemistry, University of California , Riverside, California 92521, United States.
Anal Chem. 2014 Mar 18;86(6):3020-7. doi: 10.1021/ac403754j. Epub 2014 Feb 27.
Phosphatidylethanolamines (PE) and phosphatidylcholines (PC) are important phospholipids frequently present in many types of cells. In some cases, PE has been equated with PC because they are chemically very similar and are often isomeric species. In this study, we demonstrate that noncovalent complexation between PE and 18-crown-6 ether (18C6) can be used to quantitatively mass shift and separate PE from PC phospholipids. Detection of PE is also more sensitive by approximately an order of magnitude with addition of 18C6. This noncovalent complexation approach is used to separate and quantitatively characterize PE in a soy bean asolectin extract. 18C6 (modified with an iodobenzoyl moiety) can also be used to efficiently generate radical PE lipids following photoactivation in the gas phase. Subsequent collisional activation of these lipid radical ions leads to radical directed dissociation (RDD), which generates unique fragment ions relative to dissociation of comparable even electron ions. Interestingly, RDD produces fragment ions that reveal carbon bonding features within the lipid acyl chain substituents, such as double bond location or the presence of branching. Furthermore, several novel and abundant fragments were observed in unsaturated lipids. Mechanisms that can account for the high abundance of some of these product ions are proposed.
磷脂酰乙醇胺（PE）和磷脂酰胆碱（PC）是许多类型细胞中常见的重要磷脂。在某些情况下，PE被等同于PC，因为它们在化学上非常相似，且常常是同分异构体。在本研究中，我们证明PE与18-冠-6醚（18C6）之间的非共价络合可用于使PE的质量发生定量偏移，并将其与PC磷脂分离。加入18C6后，对PE的检测灵敏度也提高了约一个数量级。这种非共价络合方法用于分离和定量表征大豆浓缩卵磷脂提取物中的PE。18C6（用碘苯甲酰部分修饰）在气相光活化后也可用于高效生成自由基PE脂质。随后对这些脂质自由基离子进行碰撞活化会导致自由基定向解离（RDD），相对于类似的偶电子离子解离，它会产生独特的碎片离子。有趣的是，RDD产生的碎片离子揭示了脂质酰基链取代基内的碳键特征，如双键位置或分支的存在。此外，在不饱和脂质中观察到了几个新的且丰度较高的碎片。本文提出了一些可以解释其中一些产物离子丰度较高的机制。
