Gas-Phase Ion/Ion Reactions to Enable Radical-Directed Dissociation of Fatty Acid Ions: Application to Localization of Methyl Branching
Gas-Phase Ion/Ion Reactions to Enable Radical-Directed Dissociation of Fatty Acid Ions: Application to Localization of Methyl Branching
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DOI：
10.1021/acs.analchem.3c04510
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发表时间：
2024-02-14
影响因子：
7.4
通讯作者：
McLuckey，Scott A.
中科院分区：
文献类型：
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作者：
Shenault，De'Shovon M.;Fabijanczuk，Kimberly C.;McLuckey，Scott A.
脂肪酸和脂肪酯的碳链上的甲基支化是脂肪酸和脂肪酯遇到的结构变化之一。脂肪酸/酯链的支化在细菌物种中尤其突出，例如在皮脂和皮脂中。通过质谱 (MS) 来确定支链与异构直链物种的区别以及支化的定位可能具有挑战性。凝聚相衍生化策略通常与分离结合使用，最常用于解决支链脂肪酸的鉴定和表征。在这项工作中，提出了一种气相离子/离子策略，该策略避免了凝聚相衍生化，并将自由基位点引入脂肪酸离子中以促进自由基定向解离（RDD）。气相方法还直接适用于通过碰撞诱导从含有脂肪酯的脂质类解离而产生的脂肪酸阴离子。具体来说，与两个三联吡啶配体结合的二价镁络合物，每个配体包含一个((2,2,6,6-四甲基-1-哌啶-1-基)氧基)(TEMPO)部分，用于电荷反转脂肪酸阴离子。在其中一个配体和剩余配体的 TEMPO 基团轻易丢失后，自由基位点被引入到复合物中。随后的复合物碰撞诱导解离 (CID) 表现出优先裂解，定位分支位点。该方法以异、反异和类异戊二烯支链脂肪酸和完整甘油磷脂进行说明，并应用于源自枯草芽孢杆菌的支链和直链脂肪酸的混合物。
Methyl branching on the carbon chains of fatty acids and fatty esters is among the structural variations encountered with fatty acids and fatty esters. Branching in fatty acid/ester chains is particularly prominent in bacterial species and, for example, in vernix caseosa and sebum. The distinction of branched chains from isomeric straight-chain species and the localization of branching can be challenging to determine by mass spectrometry (MS). Condensed-phase derivatization strategies, often used in conjunction with separations, are most commonly used to address the identification and characterization of branched fatty acids. In this work, a gas-phase ion/ion strategy is presented that obviates condensed-phase derivatization and introduces a radical site into fatty acid ions to facilitate radical-directed dissociation (RDD). The gas-phase approach is also directly amenable to fatty acid anions generated via collision-induced dissociation from lipid classes that contain fatty esters. Specifically, divalent magnesium complexes bound to two terpyridine ligands that each incorporate a ((2,2,6,6-tetramethyl-1-piperidine-1-yl)oxy) (TEMPO) moiety are used to charge-invert fatty acid anions. Following the facile loss of one of the ligands and the TEMPO group of the remaining ligand, a radical site is introduced into the complex. Subsequent collision-induced dissociation (CID) of the complex exhibits preferred cleavages that localize the site(s) of branching. The approach is illustrated withiso-,anteiso-, and isoprenoid branched-chain fatty acids and an intact glycerophospholipid and is applied to a mixture of branched- and straight-chain fatty acids derived fromBacillus subtilis.