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Xia Lab-Radical Mass Spectrometry

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Our research program aims broadly at developing new mass spectrometry (MS) methods for bio-analysis. Research efforts are currently focused on utilizing radical reactions as a unique approach to providing the high level of structural information of proteins and lipids, such as disulfide linkage pattern and carbon-carbon double bond location. We are also developing new MS instrumentation to investigate the radical attack on biomolecules in the gas phase and characterizing a series of peptide or protein radicals which are of biological importance. 

自由基诱导解离质谱实现鞘氨醇深度结构解析

近期,瑕瑜课题组开发了一种基于CID引发的自由基诱导解离(RDD)的串联质谱分析方法应用于表征鞘氨醇的精细结构,该策略结合反相液相色谱(RPLC)分离实现了复杂生物样品中总鞘氨醇的定性定量解析。相关工作“In-Depth Characterization of Sphingoid Bases via Radical-Directed Dissociation Tandem Mass Spectrometry”近日发表在J. Am. Soc. Mass. Spectrom.上。该文第一作者为清华大学化学系博士生赵婧,通讯作者为瑕瑜教授。该课题得到国家自然科学基金(No. 22225404,22074075)的支持,北京生命科学研究所董梦秋课题组博士生罗惠为该工作提供了线虫脂质提取物样品。

鞘氨醇是鞘脂类的基本组成单元,如图1所示,鞘氨醇的头部基团、链长以及化学修饰的变化(例如甲基分支、双键和羟基化),使鞘氨醇具有广泛的结构多样性和独特的功能特性。各类生物体中均具有其代表性的鞘氨醇结构。鞘烯(SPH d18:1)是哺乳动物细胞中主要的鞘氨醇,而植物、真菌和水生生物中的鞘氨醇更具结构多样性。草药琉璃苣(Borago officinalis)中Δ8-鞘脂去饱和酶诱导在C8和C9之间形成一个C=C双键,产生SPH t18:1(Δ8);秀丽隐杆线虫(C. elegans)的代表性鞘氨醇是含有甲基支链的C17鞘氨醇。鞘氨醇类似物,如来自天然产物的化学衍生物芬戈莫德(fingolimod),已被开发成用于多发性硬化症和自身免疫性疾病的治疗药物。然而,传统的串联质谱(MS/MS)通过碰撞诱导解离(CID)在表征鞘氨醇时难以定位其链内极性基团、C=C双键和支链的位置,需要发展新方法来实现鞘氨醇精细结构的深度解析。

图一. 鞘氨醇的常见结构

CID中偶电子离子通常在电荷定向碎裂中发生共价键异裂。RDD与之不同,其碎裂与键的极性相关性低,可以沿研究者将所建立的流程应用于牛心脏和线虫中鞘氨醇的结构解析,如图三所示,所提取的脂质经过酸水解产生游离的鞘氨醇,然后进行后续的TPN-RPLC-MS/MS分析。在牛心脏中,除了主要的鞘氨醇SPH d18:0和SPH d18:1外,研究者还鉴定出含有奇数碳链(SPH d17:0)和多不饱和(SPH d18:2(4, 14) )的鞘氨醇。在线虫中,除了高丰度的SPH id17:1和SPH id17:0,研究者鉴定出10余种低丰度鞘氨醇(相对于总量<5%),并发现奇数碳链鞘氨醇均含有末端支链,偶数碳链则为直链;结合PB-MS/MS的验证,研究者还发现了一种含量约为0.03%、含有末端支链的多不饱和鞘氨醇SPH id17:2(4, 13)。着脂质的烷基链发生丰富的碎裂行为,从而得到与链修饰相对应的特征碎片。RDD方法通常需要结合化学衍生化和串联质谱技术,先在目标脂质中引入自由基前体,再在气相中活化离子释放自由基并启动RDD。最早,Blanksby小组设计将含光敏自由基前体的4-碘苯甲酸酯与鞘磷脂形成非共价复合物,通过紫外光诱导解离断裂芳香碳-碘键释放苯基自由基,从而得到鞘磷脂的酰基链上的RDD图谱。瑕瑜课题组近年来专注于采用CID来生成脂质自由基离子,引发RDD以分析脂质精细结构。赵雪等人发现鞘磷脂的碳酸氢根负离子加合物的MS2 CID可以产生磷酸乙基自由基,进而引发酰基链上的RDD通道,基于该裂解模式,鉴定得到了线虫中鞘磷脂的酰胺羟基化和烷基链中的甲基分支的相关信息。简瑞君等人利用o-苄基羟胺(o-BHA)中可解离的C-O键(键解离能量为32 kcal/mol),开发了针对支链脂肪酸的定性定量流程。3-(2,2,6,6-四甲基哌啶-1-氧甲基)-吡啶酸2,5-二氧吡咯啉-1-酯(TPN)最初由高金山课题组开发用于疏水性肽的自由基启动测序(FRIPS)。C-O键相对较低的BDE(30 kcal/mol)有助于在CID下失去2,2,6,6-四甲基哌啶-N-氧自由基(TEMPO·,156 Da),然后在肽骨架内引发RDD。瑕瑜课题组林巧红等人随后证明了TPN衍生的磷酸乙醇胺也可以经CID-RDD定位甲基分支、环丙烷和羟基修饰。在本工作中,研究者进一步扩展了TPN-RDD的应用范围,如图二所示,鞘氨醇经TPN衍生后,在CID下失去TEMPO·自由基,得到吡啶甲基自由基,该自由基可以夺取碳链上的任意质子,从而诱发RDD碎裂,由于烯丙基自由基较乙基自由基的稳定性,SPH id17:0对应的CID谱图中m/z 361(-C3H7·)的信号明显增强,且没有m/z 375(-C2H5·),与直链SPH d17:0连续相隔14 Da的特征峰不同,其28 Da间隔的特征离子可实现支链位置的鉴定。RPLC分离结合RDD的鉴定信息,我们可以通过MRM对两种异构体进行定性定量解析,检测限为5 nM。

图二. TPN-RDD实现鞘氨醇精细结构解析的示意图及其应用于SPH d17:0和SPH id17:1的MS2 CID谱图,LC谱图和定量曲线。

研究者将所建立的流程应用于牛心脏和线虫中鞘氨醇的结构解析,如图三所示,所提取的脂质经过酸水解产生游离的鞘氨醇,然后进行后续的TPN-RPLC-MS/MS分析。在牛心脏中,除了主要的鞘氨醇SPH d18:0和SPH d18:1外,研究者还鉴定出含有奇数碳链(SPH d17:0)和多不饱和(SPH d18:2(4, 14) )的鞘氨醇。在线虫中,除了高丰度的SPH id17:1和SPH id17:0,研究者鉴定出10余种低丰度鞘氨醇(相对于总量<5%),并发现奇数碳链鞘氨醇均含有末端支链,偶数碳链则为直链;结合PB-MS/MS的验证,研究者还发现了一种含量约为0.03%、含有末端支链的多不饱和鞘氨醇SPH id17:2(4, 13)。

图三. TPN-RPLC-MS/MS应用于复杂样品中鞘氨醇解析示意图,以及牛心和线虫中鉴定出的鞘氨醇信息和对应的色谱洗脱时间。

总的来说,本工作所开发的分析流程具有研究各种生物系统中鞘脂代谢的潜力。目前受TPN中NHS的特异性限制,尚不能应用于缺乏游离胺基的完整复杂鞘脂,如神经酰胺、鞘磷脂和鞘糖脂,为了克服这一限制,未来的工作可尝试发展与复杂鞘脂形成共价或非共价复合物的RDD试剂。

 

编辑:赵婧

审核:乔利鹏,瑕瑜

本文链接:In-Depth Characterization of Sphingoid Bases via Radical-Directed Dissociation Tandem Mass Spectrometry | Journal of the American Society for Mass Spectrometry (acs.org)

快速正交分离和异构体解析质谱法深度分析磷脂组成

近期,清华大学化学系瑕瑜教授课题组与清华大学药学院尹航教授课题组以及北京大学第一医院巩艳青泌尿外科副研究员合作在Nature Communications杂志上发表了题为 “Deep-profiling of phospholipidome via rapid orthogonal separations and isomer-resolved mass spectrometry” 的文章。论文第一作者为清华大学化学系2018级博士生夏天,通讯作者为瑕瑜教授。在该研究中,作者将亲水作用色谱(HILIC)、捕集离子淌度(TIMS)及异构体解析串联质谱(MS/MS)有机集成,发展了具有数据自动解析能力的磷脂组深度分析系统,实现多种生物样品磷脂组的快速、灵敏、高覆盖定性定量分析。

生物样品的脂质组通常包含数千种脂质分子,并伴有多种脂质同分异构体和同重分析物,且各类脂质浓度跨越6-8个数量级。目前脂质常用分析方法是通过液相色谱(LC)结合质谱(MS)进行分析,然而脂质研究领域仍缺乏快速有效的脂质异构体通用分离方案。此外,即使脂质异构体成功得到分离,但由于缺乏标准品,也难以指认出它们的具体结构。

针对上述脂质分析挑战,作者开发一种新型的脂质组学分析流程,该分析流程融合了HILIC和TIMS的正交分离能力与异构体解析MS/MS技术,并具有快速(液相色谱运行时间<10分钟)、灵敏度高(在nM级别检测生物样品中的磷脂)和覆盖范围广等独特的分析优势,可以提供磷脂的C=C位置信息和PC的sn位置信息。同时,使用自制软件LipidNovelist进行数据分析,实现脂质异构体的质谱数据自动解析。

如图1所示,为了准确解析磷脂的结构,作者构建了一个3步数据采集的分析流程。分析流程的第一步是在负离子模式下进行非靶向质谱数据采集,通过6.5分钟的HILIC-TIMS-MS运行,实现在脂质总组成水平上的相对定量,并尽可能多的检测磷脂的链组成信息,同时分析PC的sn位置。采用非靶向的数据采集方式使得在每个LC运行中采集超过5000张MS2 CID谱图,覆盖八个主要磷脂类别。

分析流程的第二步则是在C=C位置水平上对磷脂进行分析,对脂质提取物进行离线2',4',6'-三氟苯乙酮(triFAP) PB衍生化反应,接着对PB衍生的脂质进行了靶向MS/MS分析,PB-MS/MS数据可导入到自制的数据处理软件LipidNovelist中,实现在C=C位置水平上对磷脂结构进行鉴定。分析流程的第三步创建了一个样品专属的总脂肪酸(TFA)数据库,其中包含样品中各类TFA的C=C位置信息。在对磷脂的triFAP PB-MS/MS质谱数据进行分析时,会将样品专属的TFA数据库用作先验知识,提高对磷脂双键位置的准确鉴定。

图1    磷脂精细结构解析的分析流程。

作者使用牛肝极性脂质提取物对所建立的分析流程进行基准测试,鉴定出400多种磷脂的C=C位置,并绘制了许多磷脂的C=C位置异构体和PC的sn-异构体的相对含量。与之前的HILIC-在线丙酮PB-MS/MS分析流程相比(Nat. Commun. 2019, 10 (1), 79),由于灵敏度提高,脂质鉴定数目翻倍。

 

图2  通过HILIC-MS2 CID、HILIC-TIMS-MS2 CID和HILIC-TIMS-PB-MS2 CID技术鉴定牛肝中磷脂的链组成和C=C位置信息。

接着,在对RAW 264.7巨噬细胞磷脂组的分析过程中,作者发现了大量不寻常的脂肪酰基不饱和位点。通过将总脂肪酸谱的变化与去饱和酶活性的变化(包括SCD1和FADS2)相关联,证实了这些不寻常双键位置异构体的存在。作者从RAW 264.7细胞中鉴定出超过一千种不同的磷脂结构;这些结构多样性也突出了脂质组异构体分析的必要性。

在脂质精细结构水平进行定量还对疾病诊断具有意义。与正常对照相比,人膀胱癌组织中多种异构体显示出显著的组成变化(图3),如果不区分异构体,这种变化将被掩盖。总的来说,该分析流程为磷脂的精细结构解析提供了一个全面且易于采用的解决方案,可应用于基础研究和临床研究。

感谢国家自然科学基金委(No. 22225404)、国家科技部重点研发计划(2018YFA0800903)提供的经费支持。

图3  在C=C位置和sn位置水平分析人膀胱癌组织和正常组织中的磷脂(N=6)

 

本文编辑:夏天

本文审核:瑕瑜  简瑞君

本文链接:https://doi.org/10.1038/s41467-023-40046-x

基于自由基诱导解离串联质谱与Paternò-Büchi衍生深度解析氧化磷脂酰乙醇胺

氧化甘油磷脂酰乙醇胺(oxPEs)是一类生物活性脂类,在各种生理、病理过程中扮演着复杂的角色。传统的质谱方法不能提供oxPEs中OH及C=C的准确位置信息;对于OH来说,其诊断离子往往缺乏足够的特异性。近日,清华大学化学系瑕瑜教授课题组在Analytical Chemistry发表了以“Characterization of Oxidized Glycerophosphoethanolamines via Radical-Directed Dissociation Tandem Mass Spectrometry and the Paternò-Büchi Derivatization”为题的文章,该文第一作者为清华大学化学系博士生林巧红。该课题得到了国家自然科学基金(No. 22225404)和国家重点研发计划(No. 2018YFA0800903)的支持。在这项工作中,作者报道了一种可对oxPE实现深入结构表征的组合策略,如图1所示,此策略包括:自由基诱导解离串联质谱(RDD-MS/MS)定位OH基团及Paternò-Büchi衍生偶合串联质谱(PB-MS/MS)定位C=C。

图1

此前,作者用自由基引发剂3-(2,2,6,6-Tetramethylpiperidin-1-yloxymethyl)-picolinic acid 2,5-dioxopyrrolidin-1-yl ester(TPN)或5-(2,2,6,6-tetramethylpiperidin-1-yloxymethyl) nicotinic acid 2,5-dioxopyrrolidin-1-yl ester(TBN)对PE进行衍生化,并在MS2 CID下高效产生了脂质自由基离子(丢失TEMPO)。在本文中,作者发现TPN/TBN衍生产物在负离子MS2 CID下可产生脂质自由基离子(TPN,m/z 900.6),随后发生在脂肪酰基链上的RDD生成了可指示OH位点的诊断离子m/z 829.5、801.5、799.5(图2a),其中m/z 829.5的RDD机理如图2b所示。量子化学计算结果表明,在空间上脂质自由基离子中的OH位于吡啶甲基自由基附近,吡啶甲基自由基优先夺取OH中氢原子,其活化能(15.4 kcal/mol)低于夺取与OH相邻的烯丙基氢的活化能(63.9 kcal/mol)。TPN/TBN-RDD鉴定OH位点的灵敏度可达nM,且可诱导OH两侧C-C裂解,比传统的鉴定方法更具有可信度。

图2

接着,作者建立了基于TPN -RDD的反相色谱工作流程,并对PE 16:0/HETE、PE 16:0/HODE的一系列OH位置异构体进行了OH位点分析。由于RDD无法提供oxPE中的C=C位置信息,作者还开发了针对oxPE的PB-MS/MS方法。经过PB反应试剂筛选,苯甲酰甲酸甲酯(MB)能够提供较高的PB反应产率(43%)及丰度较高的C=C诊断离子,因此被选作oxPE的PB反应试剂。作者通过制备色谱对OH位置异构体进行分离,而后对各异构体分别进行PB-MS/MS分析,发现PB-MS/MS可同时提供oxPE中共轭及非共轭C=C的位置信息。更重要的是,对于那些RDD只能对其OH位点进行定域的结构来说,如11-HETE,结合PB-MS/MS所提供的C=C位置信息,便可以进一步确定OH位点。

最后,作者利用基于TPN-RDD的反相色谱工作流程对大豆15-脂氧合酶(15-LOX)的牛肝脂质提取物中的oxPE进行了OH位点鉴定,一共鉴定出24种具有特定OH位点的oxPE分子,这些oxPE的OH位点均在n-6位。以PE 38:5(OH)为例,其被鉴定为PE 18:1_20:4(15-OH)、18:0_20:5(15-OH)、16:0_22:5(17-OH)的OH位置异构体混合物,其中16:0_22:5(17-OH)与18:1_20:4(15-OH)同时存在C=C位置构体。

图3

综上,这项工作提供的这样一种结合策略可以实现oxPEs中OH和C=C位置解析。RDD-MS/MS能够明确鉴定或限制oxPEs中的OH位点;作为RDD的补充,PB-MS/MS则提供共轭及非共轭C=C位置信息。此外,RDD方法可以很容易地结合到RPLC-MS/MS工作流程中,从而能够高灵敏(LOD ~1 nM)地从复杂混合物中鉴定oxPE分子。

 

本文编辑:林巧红

本文审核:瑕瑜 简瑞君

本文链接:https://doi.org/10.1021/acs.analchem.3c00792

1. Gas-phase radical ion chemistry

Radical ions, which consist of unpaired electrons, offer distinct gas-phase ion chemistry as compared to the even-electron species. Radical chemistry can be utilized to tackle challenging problems, such as differentiating isomeric structures, which would otherwise not be solved by traditional MS analysis of even-electron ions of the biomolecules. We are developing MS instrumentation and methods to facilitate radical reactions for either in the vacuum or in ambient air.

1. Radical reactions at the interface of ESI-MS.

Radicals or excited neutrals are generated via air discharge or UV photolysis and subsequently reacted with ions entrained in the ESI plume.  Radical reactions are subsequently monitored and characterized in situ by MS analysis. Reactions of peptides and lipids with various radical species have been investigated, including •OH, •CH2OH, excited state of (CH3)2CO.  Novel analytical applications based on these reactions have been developed.

AC; 2010, 82, 2856JASMS., 2011, 22, 922Analyst, 2013, 138, 2840;JASMS, 2014, 25, 1192.

 

2. Ion/radical reactions in a linear ion trap mass spectrometer.

A first linear ion trap mass spectrometer capable of studying reactions between the mass-selected ions and radicals has been recently developed and tested in collaboration with Prof. Zheng Ouyang from Biomedical Engineering at Purdue. This instrument uses a rectilinear ion trap as the mass analyzer and gas-phase reactor, an ESI as the source of the bimolecular ions, a pulsed pyrolysis valve for the generating an intense radical beam, and a glow discharge electron impact (GDEI) source for radical characterization. This MS platform can facilitate mechanistic studies on the radical attack to biomolecules that are of biological significance

 

3. Chemistry of bio-radical ions.

Through radical relations at ESI-MS interface, our group has synthesized and studied cysteine sulfinyl radical in the gas phase (Cys-SO•), which has a wide relevance to radical-induced oxidation of proteins, however, has been poorly characterized due to its transient nature in the condensed phases. Different from carbon-centered radicals, we have discovered that sulfinyl radical has a dual property of being acting as a base or a radical via combined experimental and theoretical approaches. The base property allows the formation of proton bridging between the radical site and the neighboring amino acid residues and thus contributes to the overall structural and chemical property of a polypeptide.

Love et al. J. Am. Chem. Soc., 2013, 135, 6226

Tan et al. J Phys. Chem. A, 2014, 118 ,11828

 

We also systematically investigated the inter- and intra-molecular reactivity of the sulfinyl radicals. They showed that the cysteine sulfinyl radical can react with a disulfide bond or a thiol group within a peptide, which has implications to radical-induced disulfide bond scrambling.

Using functionalized sulfinyl radical as a precursor of glycyl-type radical, we have also developed an experimental approach based on tandem mass spectrometry to correlate the electronic property of the connecting groups to the stability of glycyl-type radical species (Angew. Chem., Int. Ed., 2014, 53, 1887-1890, featured as the front cover and the “hot article”).

Tan et al. Angew. Chem. Int. Ed. 2014, 53, 1887

4. Application of radical chemistry for bio-analysis Analysis of unsaturated lipids:

Facile determination of C=C bond locations of lipids is a long-standing challenge for lipid analysis using MS. Intact lipid analysis via conventional low energy collisional activation tandem mass spectrometry does not provide information for the C=C location because much higher energies are required for cleaving C-C or C=C bonds and thus no fragments specific to the C=C locations can be produced. Utilizing the high reactivity of C=C with radicals or electrophilic excited state molecules, our group has recently developed coupling Paternò–Büchi (PB) reaction with MS/MS for highly confident C=C bond location determination in lipids (Angew. Chem., Int. Ed, 2014, 53, 2592-2596). This PB-MS/MS strategy is currently being developed for unsaturated lipid C=C location isomer characterization and quantitation of biological samples (tissue, cell lines, plasma), application to shotgun and separation based lipidomics, biomarker discovery, and bio-imaging.

Ma and Xia, Angew. Chem. Int. Ed. 2014, 53, 2592

 

2. PB-MS/MS developed by our group

42. Tian Xia, Xue Jin, Donghui Zhang, Jitong Wang, Ruijun Jian, Hang Yin, Yu Xia*, "Alternative fatty acid desaturation pathways revealed by deep profiling of total fatty acids in RAW 264.7 cell line", J. Lipid. Res. 2023.

https://doi.org/10.1016/j.jlr.2023.100410

41.  Qiaohong Lin, Ruijun Jian, Shengzhuo Wang, Yu Xia*, "Characterization of Oxidized Glycerophosphoethanolamines via Radical-Directed Dissociation Tandem Mass Spectrometry and the Paternò–Büchi Derivatization", Anal. Chem. 2023, 95, 25, 9422–9427.

https://doi.org/10.1021/acs.analchem.3c00792

40.  Tian Xia, Feng Zhou, Donghui Zhang, Xue Jin, Hengxue Shi, Hang Yin, Yanqing Gong, Yu Xia*, "Deep-profiling of phospholipidome via rapid orthogonal separations and isomer-resolved mass spectrometry", Nat. Commun., 202314, 4263.

https://doi.org/10.1038/s41467-023-40046-x

39.  Hengxue Shi, Zhenshu Tan, Xiangyu Guo, Hanlin Ren, Shengzhuo Wang, Yu Xia*, "Visible-Light Paternò–Büchi Reaction for Lipidomic Profiling at Detailed Structure Levels", Anal. Chem. 2023, 95, 11, 5117–5125.

https://doi.org/10.1021/acs.analchem.3c00085

38.  Wenpeng Zhang, Ruijun Jian, Jing Zhao, Yikun Liu, Yu Xia*, "Deep-lipidotyping by mass spectrometry: recent technical advances and applications", Journal of Lipid Research, 2022.

https://doi.org/10.1016/j.jlr.2022.100219

37.  Donghui Zhang, Qiaohong Lin, Tian Xia, Jing Zhao, Wenpeng Zhang, Zheng Ouyang* and Yu Xia*, "LipidOA: A Machine-Learning and Prior-Knowledge-Based Tool for Structural Annotation of Glycerophospholipids", Anal. Chem. 2022, 94, 48, 16759–16767.

https://doi.org/10.1021/acs.analchem.2c03505

36. Hai-Fang Li, Jing Zhao, Wenbo Cao, Wenpeng Zhang, Yu Xia*, and Zheng Ouyang*, “Site-Specific Photochemical Reaction for Improved C=C Location Analysis of Unsaturated Lipids by Ultraviolet Photodissociation” Research, 2022, Article ID 9783602, Published: 12 Feb 2022

https://doi.org/10.34133/2022/9783602

35. Xiaoxiao Ma, Wenpeng Zhang, Zishuai Li, Yu Xia* and Zheng Ouyang*, Enabling High Structural Specificity to Lipidomics by Coupling Photochemical Derivatization with Tandem Mass Spectrometry. Acc. Chem. Res. 2021, 54, 20, 3873–3882.

https://doi.org/10.1021/acs.accounts.1c00419

34. Zishuai Li, Simin Cheng, Qiaohong Lin, Wenbo Cao, Jing Yang, Minmin Zhang, Aijun Shen, Wenpeng Zhang, Yu Xia, Xiaoxiao Ma* and Zheng Ouyang*, "Single-cell lipidomics with high structural specificity by mass spectrometry" Nature Communications, 2021, 12, 2869.

https://doi.org/10.1038/s41467-021-23161-5

33. Qiaohong Lin, Pengyun Li, Mengxuan Fang, Donghui Zhang, and Yu Xia*, “Deep Profiling of Aminophospholipids Reveals a Dysregulated Desaturation Pattern in Breast Cancer Cell Lines” Anal. Chem. 2021, Publication Date:December 21

https://doi.org/10.1021/acs.analchem.1c03494

32. Jing Zhao, Mengxuan Fang, Yu Xia*, “A Liquid Chromatography-Mass Spectrometry Workflow for In-Depth Quantitation of Fatty Acid Double Bond Location Isomers”J. Lipid. Res. 2021, Available online 24 August .

https://doi.org/10.1016/j.jlr.2021.100110

31. Qingyuan Hu, Yu Xia*, Xiaoxiao Ma*, “Comprehensive Structural Characterization of Lipids by Coupling Paternò–Büchi Reaction and Tandem Mass Spectrometry”, In: Hsu FF. (eds) Mass Spectrometry-Based Lipidomics. Methods in Molecular Biology, vol 2306. Humana, New York, NY.

https://doi.org/10.1007/978-1-0716-1410-5_4

30. Tian Xia, Ming Yuan, Yongwei Xu, Feng Zhou, Kate Yu*, and Yu Xia*, “Deep Structural Annotation of Glycerolipids by the Charge-Tagging Paterno–Büchi Reaction and Supercritical Fluid Chromatography–Ion Mobility Mass Spectrometry", Anal. Chem. 2021, 93, 23, 8345–8353

https://pubs.acs.org/doi/10.1021/acs.analchem.1c01379

29. Hanlin Ren, Alexander Triebl, Sneha Muralidharan, Markus R. Wenk*, Yu Xia* and Federico Torta*, "Mapping the Distribution of Double Bond Location Isomers in Lipids across Mouse Tissues", Analyst, 2021,146, 3899-3907

https://doi.org/10.1039/D1AN00449B

28. X. Ma, Y. Xia, "Unsaturated Lipid Analysis via Coupling the Paternò–Büchi Reaction with ESI-MS/MS", Lipidomics. 2020: 148-174.

27. Xue Zhao, Gang Wu, Wenpeng Zhang, Mengqiu Dong, and Yu Xia*, "Resolving Modifications on Sphingoid Base and N-Acyl Chain of Sphingomyelin Lipids in Complex Lipid Extracts", Anal. Chem. 2020, 92, 21, 14775–14782

https://doi.org/10.1021/acs.analchem.0c03502

26. Jing Zhao, Xiaobo Xie, Qiaohong Lin, Xiaoxiao Ma, Pei Su, Yu Xia*, "Next-Generation Paternò–Büchi Reagents for Lipid Analysis by Mass Spectrometry", Anal. Chem. 2020, 92, 19, 13470–13477

https://pubs.acs.org/doi/10.1021/acs.analchem.0c02896

25. Elissia T. Franklin, Yu Xia*, "Structural elucidation of triacylglycerol using online acetone Paternò–Büchi reaction coupled with reversed-phase liquid chromatography mass spectrometry" , Analyst. 2020, 145, 6532-6540.

https://doi.org/10.1039/D0AN01353F

24. Elissia Franklin, Samuel Shields, Jeffrey Manthorpe, Jeffrey C. Smith, Yu Xia, Scott A. Mcluckey*, "Coupling Headgroup and Alkene Specific Solution Modifications with Gas-Phase Ion/Ion Reactions for Sensitive Glycerophospholipid Identification and Characterization", J. Am. Soc. Mass Spectrom. 2020, 31, 4, 938–945.

https://doi.org/10.1021/jasms.0c00001

23. Wenpeng Zhang*, Bing Shang, Zheng Ouyang, Yu Xia*, "Enhanced Phospholipid Isomer Analysis by Online Photochemical Derivatization and RPLC-MS", Anal. Chem. 2020, 92, 9, 6719–6726.

https://doi.org/10.1021/acs.analchem.0c00690

22. Tian Xia, Hanlin Ren, Wenpeng Zhang, Yu Xia*, "Lipidome-Wide Characterization of Phosphatidylinositols and Phosphatidylglycerols on C=C Location Level", Analytica Chimica Acta, 2020, 1128, 107-115.

http://dx.doi.org/10.1016/j.aca.2020.06.017

21. Wenbo Cao, Simin Cheng, Jing Yang, Wenpeng Zhang, Zishuai Li, Qinhua Chen, Yu Xia, Zheng Ouyang*, Xiaoxiao Ma*, "Large-scale lipid analysis with C=C location and sn-position isomer resolving power", Nat Commun, 2020, 11, 375.

https://www.nature.com/articles/s41467-019-14180-4

20. 马潇潇,胡清源,瑕瑜*, "Paternò-Büchi(PB)反应与串联质谱结合实现不饱和脂质精确结构解析", 分析测试学报, 2020, 39(1), 19-27.

http://new.fxcsxb.com/fxcsxb/ch/reader/view_abstract.aspx?file_no=20200103&flag=1

19. Xiaobo Xie, Jing Zhao, Miao Lin, Jinlan Zhang, Yu Xia*, "Profiling of Cholesteryl Esters by Coupling Charge Tagging Paternò-Büchi Reaction and Liquid Chromatography-Mass Spectrometry", Anal. Chem. 2020, 92, 12, 8487–8496.

https://doi.org/10.1021/acs.analchem.0c01241

18. Haifang Li, Wenbo Cao, Xiaoxiao Ma, Xiaobo Xie, Yu Xia, Zheng Ouyang*, "Visible-Light-Driven [2 + 2] Photocycloadditions between Benzophenone and C=C Bonds in Unsaturated Lipids", J. Am. Chem. Soc. 2020, 142, 7, 3499–3505.

https://doi.org/10.1021/jacs.9b12120

17. Wenpeng Zhang, Bing Shang, Yu Xia, "Comprehensive Characterization of Phospholipid Isomers in Human Platelets", J. Anal. Test., 2020, 4, 210–216.

https://link.springer.com/article/10.1007/s41664-020-00137-w

16. Q. Lin, D. Zhang, Y. Xia*, "Analysis of Ether Glycerophosphocholines at the Level of C=C Locations from Human Plasma", Analyst, 2020, 145, 513-522.

https://doi.org/10.1039/C9AN01515A

15. X. Zhao, W. Zhang, D. Zhang, X. Liu, W. Cao, Q. Chen, Z. Ouyang, Y. Xia*, "A Lipidomic Workflow Capable of Resolving sn- and C=C Location Isomers of Phosphatidylcholines", Chem. Science, 2019, 10, 10740-10748.

https://doi.org/10.1039/C9SC03521D

14. Y. Su, J. Page, X. Ma, R. Shi, Y. Xia*, Zheng Ouyang*, "Mapping Lipid C=C Location Isomers in Organ Tissues by Coupling Photochemical Derivatization and Rapid Extractive Mass Spectrometry", Int. J. Mass Spectrom. 2019, 445, 116206

https://doi.org/10.1016/j.ijms.2019.116206

13. Elissia T. Franklin, Stella K. Betancourt, Caitlin E. Randolph, Scott A. McLuckey* , and Yu Xia* ,"In-depth structural characterization of phospholipids by pairing solution photochemical reaction with charge inversion ion/ion chemistry",  Anal Bioanal Chem. 2019, 411, 4739–4749.

https://doi.org/10.1007/s00216-018-1537-1

12. R. Zou, W. Cao, L. Chong, W. Hua, H. Xu, Y. Mao, J. Page, R. Shi, Y. Xia, Tony Y. Hu, W. Zhang*, and Z. Ouyang*, "Point-of-Care Tissue Analysis Using Miniature Mass Spectrometer", Anal. Chem. 2019, 91, 1, 1157–1163

https://doi.org/10.1021/acs.analchem.8b04935

11. X. Xie, Y. Xia*, "Analysis of Conjugated Fatty Acid Isomers by the Paternò-Büchi Reaction and Trapped Ion Mobility Mass Spectrometry", Anal. Chem. 2019, 91, 7173-7180.

https://doi.org/10.1021/acs.analchem.9b00374

10. W. Zhang, S. Chiang, Z. Li, Q. Chen, Y. Xia, Z. Ouyang*, "A Polymer Coating Transfer Enrichment for Direct Mass Spectrometry Analysis of Lipids in Biofluid Samples", Angew. Chem., Int. Ed., 2019, 58, 6064-6069.

https://doi.org/10.1002/anie.201900011

9. W. Zhang, D. Zhang, Q. Chen, J. Wu, Z. Ouyang*, Y. Xia*, "Online photochemical derivatization enables comprehensive mass spectrometric analysis of unsaturated phospholipid isomers", Nat. Commun., 2019, 10, 79.

https://www.nature.com/articles/s41467-018-07963-8

8. L. Chong, R. Tian, R. Shi, Z. Ouyang*, and Y. Xia*, "Coupling the Paternò-Büchi (PB) Reaction With Mass Spectrometry to Study Unsaturated Fatty Acids in Mouse Model of Multiple Sclerosis", Front. Chem. 2019, 7:807.

https://doi.org/10.3389/fchem.2019.00807

7. F. Tang*, C. Guo, X. Ma, J. Zhang, Y. Su, R. Tian, R. Shi, Y. Xia, X. Wang, Z. Ouyang*, "Rapid in situ Profiling of Lipid C=C Location Isomers in Tissue Using Ambient Mass Spectrometry with Photochemical Reactions", Anal. Chem. 2018, 90, 5612-5619

https://doi.org/10.1021/acs.analchem.7b04675

6. J. Li, S. Condello, J. T. Pepin, X. Ma, Y. Xia, T. D. Hurley, D. Matei*, and J. Cheng*, “Lipid Desaturation Is a Metabolic Marker and Therapeutic Target of Ovarian Cancer Stem Cells”, Cell Stem Cell, 2017, 20, 3, 301-314

https://doi.org/10.1016/j.stem.2016.11.004

5. J. Ren, E.T. Franklin, Y. Xia*, "Uncovering Structural Diversity of Unsaturated Fatty Acyls in Cholesteryl Esters via Photochemical Reaction and Tandem Mass Spectrometry", J. Am. Soc. Mass Spectrom. 2017, 28, 1432-1441

https://doi.org/10.1021/jasms.8b05584

4. X. Ma, X. Zhao, J. Li, W. Zhang, J.-X. Cheng, Z. Ouyang*, Y. Xia*, "Photochemical Tagging for Quantitation of Unsaturated Fatty Acids by Mass Spectrometry", Anal. Chem. 2016, 88, 8931–8935

https://doi.org/10.1021/acs.analchem.6b02834

3. C. A. Stinson, Y. Xia*, "A Method of coupling Paternò-Büchi reaction with direct infusion ESI-MS/MS for locating C=C bond in glycerophospholipids", Analyst, 2016, 141, 3696-3704

https://doi.org/10.1039/C6AN00015K

2. X. Ma, L. Chong, R. Tian, R. Shi, T. Y. Hu, Z. Ouyang*, Y. Xia*, "Identification and quantitation of lipid C=C location isomers: a shotgun lipidomics approach enabled by photochemical reaction", Proc. Natl. Acad. Sci. USA, 2016, 113, 2573-2578. Featured by C&E News and Nature Methods

https://doi.org/10.1073/pnas.1523356113

1. X. Ma and Y. Xia*, "Pinpointing Double Bonds in Lipids by Paternò–Büchi Reactions and Mass Spectrometry", Angew. Chem., Int. Ed, 2014, 53, 2592-2596.

https://doi.org/10.1002/anie.201310699

3. Advances of PB-MS/MS by other research groups around the world.(2017-2023)

52. Chen M.; Wang R.; Ren Q. X.; Li B.; Li P.*; Yang H.*; Gao W.*; Analysis of unsaturated fatty acids by supercritical fluid chromatography tandem mass spectrometry coupled with online Paternò-Büchi reaction. Microchemical Journal. 2023, 109551.

https://doi.org/10.1016/j.microc.2023.109551

51. Guo X. Y.; Cao W. B.; Fan X. M.; Guo Z. Y.; Zhang D. H.; Zhang H. Y.; Ma X. X.; Dong J. H.; Wang Y. F. *; Zhang W. P. *; Ouyang Z.*; Tandem Mass Spectrometry Imaging Enables High Definition for Mapping Lipids in Tissues. Angew Chem Int Ed Engl. 2023, 62, 9, e202214804

https://doi.org/10.1002/anie.202214804

50. Cheng S. M.; Xie Z. N.; Hu Q. Y.; Qian Y.; Ma X. X.*; Familiarizing Undergraduate Students with Advanced Mass Spectrometry Techniques: An Example of Detailed Lipid Structure Characterization. J. Chem. Educ. 2023, 100, 3, 1270–1276.

https://doi.org/10.1021/acs.jchemed.2c00824

49. Cheng S. M.; Zhang D. H.; Feng J. X.; Hu Q. Y.; Tan A.; Xie Z. N.; Chen Q. H.; Huang H. M.; Wei Y.; Ouyang Z.*; Ma X. X.*; Metabolic Pathway of Monounsaturated Lipids Revealed by In-Depth Structural Lipidomics by Mass Spectrometry. Research, 2023, 6, 0087.

https://doi.org/10.34133/research.0087

48. Hu W. Y.; Han Y. H.*; Selective Characterization of Olefins by Paternò–Büchi Reaction with Ultrahigh Resolution Mass Spectrometry. Anal. Chem. 2023.

https://doi.org/10.1021/acs.analchem.3c02966

47. Freitas D. P.; Yan X.*; In situ droplet-based on-tissue chemical derivatization for lipid isomer characterization using LESA. Analytical and Bioanalytical Chemistry 2023, 415, 4197–4208.

https://doi.org/10.1007/s00216-023-04653-3

46. Lu H. Y.; Zhang H.; Li L. J.*; Chemical tagging mass spectrometry: an approach for single‑cell Omics. Analytical and Bioanalytical Chemistry. 2023.

https://doi.org/10.1007/s00216-023-04850-0

45. Kanter J. P.; Honold P. J.; Luh D.; Heiles S., Spengler B.; Fraatz M. A.; Zorn H.; Hammer A. K.*; Biocatalytic Production of Odor-Active Fatty Aldehydes from Fungal Lipids. J. Agric. Food Chem. 2023, 71, 21, 8112–8120

https://doi.org/10.1021/acs.jafc.3c01972

44. Wang D. H.; Brenna J. T.*, and Shchepinov M. S.*; Quantitative High-Field NMR- and Mass Spectrometry-Based Fatty Acid Sequencing Reveals Internal Structure in Ru-Catalyzed Deuteration of Docosahexaenoic Acid. Anal. Chem. 2022, 94, 38, 12971–12980.

https://doi.org/10.1021/acs.analchem.2c00923

43. Kanter J.P.; Honold P. J.; Lüke D.; Heiles S.; Spengler B.; Fraatz M. A.; Harms C.; Ley J. P.; Zorn H.; Hammer A. K.*; An enzymatic tandem reaction to produce odor-active fatty aldehydes. Appl. Microbiol. Biotechnol. 2022, 106, 6095–6107

https://doi.org/10.1007/s00253-022-12134-3

42. Bednařík A.*; Prysiazhnyi V.; Bezdeková D.; Soltwisch J.; Dreisewerd K.; Preisler J.*; Mass Spectrometry Imaging Techniques Enabling Visualization of Lipid Isomers in Biological Tissues. Anal. Chem. 2022, 94, 12, 4889–4900.

https://doi.org/10.1021/acs.analchem.1c05108

41. Bechtella L.; Walrant A.*; Structural Bases for the Involvement of Phosphatidylinositol-4,5-bisphosphate in the Internalization of the Cell-Penetrating Peptide Penetratin. ACS Chem. Biol. 2022, 17, 6, 1427–1439.

https://doi.org/10.1021/acschembio.1c00974

40. Cerrato A.; Capriotti A. L.*; Novel Aza-Paternò-Büchi Reaction Allows Pinpointing Carbon–Carbon Double Bonds in Unsaturated Lipids by Higher Collisional Dissociation. Anal. Chem. 2022, 94, 38, 13117–13125.

https://doi.org/10.1021/acs.analchem.3c02966

39. Christiana M.;Kokotou M. G.*; Liquid Chromatography-Mass Spectrometry (LC-MS) Derivatization-Based Methods for the Determination of Fatty Acids in Biological Samples. Molecules 202227(17), 5717

https://doi.org/10.3390/molecules27175717

38. Sun C. L.*; Wan X.*; A novel on-tissue cycloaddition reagent for mass spectrometry imaging of lipid C=C position isomers in biological tissues. Chinese Chemical Letters 2022, 33, 2073-2076.

https://doi.org/10.1016/j.cclet.2021.08.034

37. Hynds H. M.;Hines K. M.*; Ion Mobility Shift Reagents for Lipid Double Bonds Based on Paternò–Büchi Photoderivatization with Halogenated Acetophenones. J. Am. Soc. Mass Spectrom. 2022, 33, 10, 1982–1989

https://doi.org/10.1021/jasms.2c00211

36. Chen Y. Y.; Xie C. Y.; Wang X. X.; Cao G. D.; Ru. Y.; Song Y. Y.; Iyaswamy A.; Li M.; Wang J. N.*; Cai Z. W.*; 3Acetylpyridine On-Tissue Paterno−Buchi Derivatization Enabling High Coverage Lipid C=C Location-Resolved MS Imaging in Biological Tissues. Analytical Chemistry, 2022.

https://doi.org/10.1021/acs.analchem.2c03089

35. Feng, G. F.; Gao, M.; Wang L.W.; Chen J. Y.; Hou M. L.; Wan Q. Q.; Lin Y.; Xu G. Y.; Qi X. T.; Chen S. M.*; Dual-resolving of positional and geometric isomers of C=C bonds via bifunctional photocycloaddition-photoisomerization reaction system. Nature Communications, 2022, 13, 2652

https://doi.org/10.1038/s41467-022-30249-z

34. Mao, R.; Li, W.; Ji, P.; Ding, H.; Teka, T.; Zhang, L.; Fu, Z.; Fu, X.; Kaushal, S.; Dou, Z.*; Han, L.*; An efficient and sensitive method on the identification of unsaturated fatty acids in biosamples: Total lipid extract from bovine liver as a case study. Journal of Chromatography A, 2022, 1675, 463176

https://doi.org/10.1016/j.chroma.2022.463176

33. Sun, J.; Liu, R. X.; Li, S.; Li, W. *; M. L. Gross*; Nanoparticles and photochemistry for native-like transmembrane protein footprinting. Nature Communications, 2021, 12, 7270

https://doi.org/10.1038/s41467-021-27588-8

32. Han, Y.; Chen, P.; Li, Z.; Wang, X.; Sun, C. *; Multi-wavelength visible-light induced [2+2] cycloaddition for identification of lipid isomers in biological samples. Journal of Chromatography A, 2022, 1662, 462742

https://doi.org/10.1016/j.chroma.2021.462742

31. Liu, Z.; S. Rochfort*; Regio-distribution and double bond locations of unsaturated fatty acids in phospholipids of bovine milk. Food Chemistry, 2021, Available online 2 November.

https://doi.org/10.1016/j.foodchem.2021.131515

30. Deng, J.; Yang, Y.*; Zeng, Z.; Xiao, X.; Li, J.; Luan, T.*; Discovery of Potential Lipid Biomarkers for Human Colorectal Cancer by In-Capillary Extraction Nanoelectrospray Ionization Mass Spectrometry. Analytical Chemistry, 2021, 93, 38, 13089–13098

https://doi.org/10.1021/acs.analchem.1c03249

29. Zhang, J.; Guo, C.; Huo, X.; Ma, X.; Li, X.; Zeper, A.; Chu, Y.; Wang, X.; Tang, F.; Unsaturated lipid isomeric imaging based on the Paternò–Büchi reaction in the solid phase in ambient conditions. Talanta, 2021, 235, 122816.

https://doi.org/10.1016/j.talanta.2021.122816

28. Sun, C; Ma, C; Li, L; Han, Y; Wang, D; Wan,X; "A novel on-tissue cycloaddition reagent for mass spectrometry imaging of lipid C=C position isomers in biological tissues", Chinese Chemical Letters, 2021, Available online 12 August.

https://doi.org/10.1016/j.cclet.2021.08.034

27. Huang, W.; Zhou. H.; Yuan, M.; Lan, L.; Hou, A.; Ji, S. Comprehensive Characterization of the Chemical Constituents in Platycodon Grandiflorum by an Integrated Liquid Chromatography-Mass Spectrometry Strategy. Journal of Chromatography A, 2021, 1654, 462-477.

https://doi.org/10.1016/j.chroma.2021.462477

26. Yang Y. Coupling Paternò-Büchi Reaction with Ambient NanoESI-MS for Identification of Unsaturated Triacylglycerols in Peanut Oils. Journal of Chinese Mass Spectrometry Society, 2021, 42(4): 455-461.

http://www.jcmss.com.cn/EN/10.7538/zpxb.2021.0032

25. Wang, D.; Park, H.; Wang, Z.; Lacombe, R.S.; Shmanai, V.V.; Bekish, A.V.; Schmidt, K.; Shchepinov, M.S.; Brenna, J.T.“Toward Quantitative Sequencing of Deuteration of Unsaturated Hydrocarbon Chains in Fatty Acids" Analytical Chemistry, 2021, 93, 8238–8247

https://doi.org/10.1021/acs.analchem.1c01016

24. Xu, S.; Lv, X.; Wu, B.; Xie, Y.; Wu, Z.; Tu, X.; Chen, H.; Wei, F. Pseudotargeted Lipidomics Strategy Enabling Comprehensive Profiling and Precise Lipid Structural Elucidation of Polyunsaturated Lipid-Rich Echium Oil. Journal of Agricultural and Food Chemistry, 2021

https://doi.org/10.1021/acs.jafc.0c07268

23. Wäldchen, F.; Mohr, F.; Wagner, A.H.; Heiles, S. "Multifunctional reactive MALDI matrix enabling high-lateral resolution dual polarity MS imaging and lipid C= C position-resolved MS2 imaging." Analytical Chemistry. 2020, 92, 14130–14138

https://doi.org/10.1021/acs.analchem.0c03150

22. Jeck, V.; Froning, M.; Tiso, T.; Blank, L. M.; Hayen, H. "Double bond localization in unsaturated rhamnolipid precursors 3-(3-hydroxyalkanoyloxy) alkanoic acids by liquid chromatography–mass spectrometry applying online Paternò–Büchi reaction." Analytical and bioanalytical chemistry, 2020, 412, 5601-5613.

https://link.springer.com/article/10.1007/s00216-020-02776-5

21.Maddox, S. W., Olsen, S. S., Velosa, D. C., Burkus-Matesevac, A., Peverati, R., & Chouinard, C. D. Improved Identification of Isomeric Steroids using the Paternò-Büchi Reaction with Ion Mobility-Mass Spectrometry. Journal of the American Society for Mass Spectrometry, 2020, 31, 2086–2092

https://doi.org/10.1021/jasms.0c00215

20. Xu, S.; Wei, F.; Xie, Y.; Wu, B.; Lv, X.; Qin, Z.; Chen, H. Localisation of C=C Bond and Absolute Quantification of Unsaturated Fatty Acids in Vegetable Oils based on Photochemical Derivatisation Reaction Coupled with Mass Spectrometry. International Journal of Food Science & Technology, 2020, 55,  2883-2892

https://doi.org/10.1111/ijfs.14546

19. Li, P.; Deng, J.; Xiao, N.; Cai, X.; Wu, Q.; Lu, Z.; Du, B. "Identification of polyunsaturated triacylglycerols and CC location isomers in sacha inchi oil by photochemical reaction mass spectrometry combined with nuclear magnetic resonance spectroscopy." Food chemistry, 2020, 307, 125568.

https://doi.org/10.1016/j.foodchem.2019.125568

18. Zhu, Y.; Wang, W.; Yang, Z. "Combining Mass Spectrometry with Paternò-Büchi Reaction to Determine Double-bond Positions in Lipids at the Single-cell Level." Analytical Chemistry, 2020, 92, 11380–11387

https://doi.org/10.1021/acs.analchem.0c02245

17. Xu, S.; Wu, B.; Oresic, M.; Xie, Y.; Yao, P.; Wu, Z.; Wei, F. "Double Derivatization Strategy for High-Sensitivity and High-Coverage Localization of Double Bonds in Free Fatty Acids by Mass Spectrometry." Analytical Chemistry, 2020, 92, 6446-6455.

https://doi.org/10.1021/acs.analchem.9b05588

16. Feng, G.; Hao, Y.; Wu, L.; Chen, S. "A visible-light activated [2+ 2] cycloaddition reaction enables pinpointing carbon–carbon double bonds in lipids." Chemical Science, 2020, 11, 7244-7251.

https://doi.org/10.1039/D0SC01149E

15. Esch, P.; Heiles, S. "Investigating C=C Positions and Hydroxylation Sites in Lipids Using Paternò–Büchi Functionalization Mass Spectrometry." Analyst, 2020, 145, 2256-2266.

https://doi.org/10.1039/C9AN02260K

14. Wäldchen, F.; Spengler, B.; Heiles, S. "Reactive Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry Imaging Using an Intrinsically Photoreactive Paternò–Büchi Matrix for Double-Bond Localization in Isomeric Phospholipids." Journal of the American Chemical Society, 2019, 141, 11816-11820.

https://doi.org/10.1021/jacs.9b05868

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