Structural analysis of phosphatidylcholines by post-source decay matrix-assisted laser desorption/ionization time-of-flight mass spectrometry
Structural analysis of phosphatidylcholines by post-source decay matrix-assisted laser desorption/ionization time-of-flight mass spectrometry
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DOI：
10.1016/s1044-0305(03)00068-0
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发表时间：
2003-04-01
影响因子：
3.2
通讯作者：
Knowles, NR
中科院分区：
文献类型：
--
作者：
Al-Saad, KA;Siems, WF;Knowles, NR
研究了源后衰变(PSD)基质辅助激光解吸电离飞行时间质谱仪(MALDI-TOF-MS)在磷脂酰胆碱(PC)结构分析中的应用。在MALDI中，PC不产生可检测到的负离子，但可观察到[PC+H](+)和[PC+Na](+)两种阳离子。质子化的PC物种的PSD谱只包含一个对应于头部基团(m/z 184)的片段，而盐化的前体产生了许多碎片离子，包括那些来自脂肪酸损失的碎片离子。甘油主链C-1位(sn-1)的脂肪酸损失比C-2位(sn-2)的脂肪酸损失更有利。头基(磷胆碱)裂解产生的离子包括[PC+Na-59](+)、[PC+Na-183](+)和[PC+Na-205](+)，分别对应于三甲胺(TMA)、非盐化磷酸胆碱和盐化磷酸胆碱的损失。在m/z 183、146和86处观察到其他反映头基结构的片段。[PC+Na](+)与[PC+H](+)的PSD碎片模式的不同归因于Na+和H+结合的不同。当质子与磷酸基团的带负电的氧结合时，钠离子可以与PC分子的几个区域联系在一起。因此，在盐化的PC中，磷酸基团中带负电荷的氧的分子间相互作用，以及多个位置的钠缔合，可以导致复杂和特征的离子碎裂模式。Sn-1脂肪酸基团的优先损失可以通过形成能量上有利的六元环中间体来解释，而不是在sn-2脂肪酸基团丧失之前形成的五元环中间体。
The utility of post-source decay (PSD) matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was investigated for the structural analysis of phosphatidylcholine (PC). PC did not produce detectable negative molecular ion from MALDI, but positive ions were observed as both [PC+H](+) and [PC+Na](+). The PSD spectra of the protonated PC species contained only one fragment corresponding to the head group (m/z 184), while the sodiated precursors produced many fragment ions, including those derived from the loss of fatty acids. The loss of fatty acid from the C-1 position (sn-1) of the glycerol backbone was favored over the loss of fatty acid from the C-2 position (sn-2). Ions emanating from the fragmentation of the head group (phosphocholine) included [PC+Na-59](+), [PC+Na-183](+) and [PC+Na-205](+), which corresponded to the loss of trimethylamine (TMA), non-sodiated choline phosphate and sodiated choline phosphate, respectively. Other fragments reflecting the structure of the head group were observed at m/z 183, 146 and 86. The difference in the fragmentation patterns for the PSD of [PC+Na](+) compared to [PC+H](+) is attributed to difference in the binding of Na+ and H+. While the proton binds to a negatively charged oxygen of the phosphate group, the sodium ion can be associated with several regions of the PC molecule. Hence, in the sodiated PC, intermolecular interaction of the negatively charged oxygen of the phosphate group, along with sodium association at multiple sites, can lead to a complex and characteristic ion fragmentation pattern. The preferential loss of sn-1 fatty acid group could be explained by the formation of an energetically favorable six-member ring intermediate, as apposed to the five-member ring intermediate formed prior to the loss of sn-2 fatty acid group.