Bourcier Sophie, Hoppilliard Yannik
Laboratoire des Mécanismes Réactionnels, Unité Mixte de recherche CNRS 7651, Ecole Polytechnique, 91128 Palaiseau Cedex, France.
Rapid Commun Mass Spectrom. 2009 Jan;23(1):93-103. doi: 10.1002/rcm.3852.
This work presents the use of neutral losses (NL) for the identification of compounds related to the metabolism of tyrosine. The mass spectra of all the studied compounds, recorded at several collision energies, are compared. The fragmentation mechanism of protonated molecules, MH(+), is explained by combining collision-induced dissociation (CID) mass spectra and density functional theory (DFT) calculations. The results show that the first fragmentation is the elimination from MH(+) of a neutral molecule including a functional group of the linear chain. Three primary neutral losses are observed: 17 u (NH(3)), 18 u (H(2)O) and 46 u (H(2)O+CO) characterizing amino, hydroxyl and carboxylic functions on the linear chain. The presence and abundance of ions corresponding to these losses are dependent on (i) the position of the functional group on the linear chain, (ii) the initial localisation of the protonating hydrogen, and (iii) the substitution of the aromatic ring. For compounds including a functional group on the benzylic carbon atom, the investigation of the other functions requires the knowledge of secondary fragmentations. Among these secondary fragmentations we have retained the loss of NH(3) from MH-18u and the loss of ketene from MH-17u. Experimentally these fragmentations are detected using losses of 35 u and 59/73 u. In other words, NL35 identifies hydroxy and amino compounds and NL 46 and/or NL59/73 identify carboxylic acids. The search for characteristic neutral losses is used for the analysis of compounds in a mixture and the analysis of biological fluid. We show that selective search of several neutral losses allows also the unambiguous differentiation of isomers and gives the opportunity to identify compounds in biological fluids.
这项工作展示了利用中性丢失（NL）来鉴定与酪氨酸代谢相关的化合物。比较了在几种碰撞能量下记录的所有研究化合物的质谱。通过结合碰撞诱导解离（CID）质谱和密度泛函理论（DFT）计算，解释了质子化分子MH(+)的碎裂机制。结果表明，首次碎裂是从MH(+)中消除一个包含直链官能团的中性分子。观察到三种主要的中性丢失：17 u（NH₃）、18 u（H₂O）和46 u（H₂O + CO），它们分别表征直链上的氨基、羟基和羧基官能团。对应这些丢失的离子的存在和丰度取决于：（i）直链上官能团的位置；（ii）质子化氢的初始定位；（iii）芳环的取代情况。对于在苄基碳原子上包含一个官能团的化合物，对其他官能团的研究需要了解二级碎裂。在这些二级碎裂中，我们保留了MH - 18u中NH₃的丢失以及MH - 17u中乙烯酮的丢失。实验上，这些碎裂通过35 u和59/73 u的丢失来检测。换句话说，NL35鉴定羟基和氨基化合物，NL 46和/或NL59/73鉴定羧酸。对特征性中性丢失的搜索用于混合物中化合物的分析以及生物流体的分析。我们表明，对几种中性丢失的选择性搜索还能明确区分异构体，并为鉴定生物流体中的化合物提供机会。
