氟甲卡西酮异构体的质谱识别和计算化学研究

李霄炜; 林香丽; 周轩宇; 柯星; 范一雷; 徐雨; 徐嘉伟

doi:10.7538/zpxb.2025.0004

浙江警察学院，全省毒品防控技术研究重点实验室，浙江杭州　310053

中国科学院福建省物质结构研究所，结构化学国家重点实验室，福建福州　350002

中国科学院大学化学科学学院，北京　101408

国家毒品实验室浙江分中心，浙江杭州　310053

通讯作者: 徐雨; 徐嘉伟

中图分类号: O657.63

Mass Spectrometry Identification and Computational Chemistry Study of Fluoromethcathinone Isomers

Zhejiang Key Laboratory of Drug Prevention and Control Technology, Zhejiang Police College, Hangzhou 310053, China

State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002, China

School of Chemical Science, University of Chinese Academy of Sciences, Beijing 101408, China

National Anti-Drug Laboratory Zhejiang Regional Center, Hangzhou 310053, China

Corresponding authors: Yu XU ; Jia-wei XU

MSC: O657.63

摘要: 合成卡西酮是一类新精神活性物质，具有成瘾性强、种类多、更新快、结构相似等特点。3-氟甲卡西酮（3-FMC）和4-氟甲卡西酮（4-FMC）是第二代合成卡西酮类物质氟甲卡西酮的2种位置异构体，其结构非常相近，对二者的准确定性分析是当前司法鉴定中的一个难题。本文采用气相色谱-四极杆-飞行时间串联质谱（GC-QTOF MS）和高效液相色谱-四极杆-轨道阱串联质谱（LC-Q-Orbitrap/MS）技术，结合计算化学方法研究位置异构体3-FMC和4-FMC的质谱裂解模式和裂解机理。结果表明，3-FMC的苯环侧链易断裂并产生碎片离子m/z 58。由于氟原子具有较强的吸电子诱导效应，使苯环邻位和对位的电子云密度发生显著变化，导致不同位置异构体的苯环侧链发生了不同的裂解方式。其中，3-FMC苯环上侧链易发生异裂失去1分子CH₄生成碎片离子m/z 148，而4-FMC苯环上侧链易发生均裂并失去1分子CH₃·生成碎片离子m/z 149。进一步利用密度泛函理论，根据相对吉布斯自由能筛选裂解可能生成片段的结构，确认最稳定的异构体碎片离子。质谱分析实验结果与计算化学结论一致，本研究为准确鉴定氟甲卡西酮异构体3-FMC和4-FMC提供了参考依据。

关键词:

Abstract: Synthetic cathinones are a class of new psychoactive substances, characterized by strong addictiveness, great diversity, rapid updates, and similar structures. Among them, 3-fluoromethcathinone (3-FMC) and 4-fluoromethcathinone (4-FMC) are two positional isomers of the second-generation synthetic cathinone, fluoromethcathinone. Their structures are very similar, therefore, the accurate qualitative analysis of these isomers remains a challenge in current judicial appraisals. In this study, the fragmentation patterns of positional isomers 3-FMC and 4-FMC were investigated by gas chromatography-quadrupole time-of-flight mass spectrometry (GC-QTOF MS) and liquid chromatography-Q-Orbitrap mass spectrometry (LC-Q-Orbitrap/MS). Then, the mass differences of 3-FMC and 4-FMC fragments were further analyzed by the relationship between chemical structures and fragment ion abundances. Computational studies further demonstrated the experimental results using Gibbs free energy profiles and electronic properties of possible fragments. In addition, the fragmentation mechanisms of 3-FMC and 4-FMC were investigated by applying density functional theory calculation, which can more accurately elucidate the mass spectral behavior and structure characteristics of compounds as reflected by mass spectrometric data. The results showed that the side chain of the benzene ring in 3-FMC is prone to break and generate a fragment ion at m/z 58. It was found that the electron cloud densities at the ortho and para positions of the benzene ring change significantly due to the strong electron-withdrawing inductive effect of the fluorine atom. This, in turn, leads to different fragmentation patterns of the benzene ring side chains of different positional isomers. Specifically, the side chain on the benzene ring of 3-FMC is prone to heterolytic cleavage to lose one molecule of CH₄ and generate a fragment ion with m/z 148. In contrast, the side chain on the benzene ring of 4-FMC tends to homolytic cleavage to lose one molecule of CH₃· and generate a fragment ion at m/z 149. Structures of possible fragments were screened based on relative Gibbs free energy to confirm the most stable isomer of fragment ions. The first stage of fragmentation with one H₂O loss is a variant of α-hydroxy N-phenylimines rearrangement reaction, which consists of three steps of σ-migration and acts as the rate-determinant step of the fragmentation process to form the four-membered ring side chain fragment (m/z 164, IM6). Further theoretical prediction was conducted using relative Gibbs free energy. All possible isomers that retain the fluorophenyl structure are screened to determine the most stable structure. The results of the fragmentation patterns obtained from computational chemistry are consistent with the experimental results of mass spectrometry analysis. The study provides an important reference and a basis for the accurate identification of the fluoromethcathinone isomers 3-FMC and 4-FMC.

Key words:

氟甲卡西酮异构体的质谱识别和计算化学研究

通讯作者: 徐雨;

通讯作者: 徐嘉伟

1. 浙江警察学院，全省毒品防控技术研究重点实验室，浙江杭州　310053

2. 中国科学院福建省物质结构研究所，结构化学国家重点实验室，福建福州　350002

3. 中国科学院大学化学科学学院，北京　101408

4. 国家毒品实验室浙江分中心，浙江杭州　310053

收稿日期: 2025-01-10

录用日期: 2025-06-17

关键词:

Mass Spectrometry Identification and Computational Chemistry Study of Fluoromethcathinone Isomers

Corresponding author: Yu XU ;

Corresponding authors: Jia-wei XU

1. 浙江警察学院，全省毒品防控技术研究重点实验室，浙江杭州　310053

2. 中国科学院福建省物质结构研究所，结构化学国家重点实验室，福建福州　350002

3. 中国科学院大学化学科学学院，北京　101408

4. 国家毒品实验室浙江分中心，浙江杭州　310053

Received Date: 2025-01-10

Accepted Date: 2025-06-17

Keywords:

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近年来，新精神活性物质（NPS）在世界范围内流行，其成瘾性强、易合成且难以管控，造成了严重的社会危害^[1]。目前，全球已出现近1 000种NPS，主要包括合成大麻素、合成卡西酮、苯乙胺、色胺和苯环己哌啶等，其中，合成卡西酮类多达140种，常被不法分子以“浴盐”“清洗剂”“植物肥料”等名义售卖。滥用合成卡西酮会产生幻觉、幻听等精神病症状，严重时还会伴有失眠、食欲不振、抑郁、焦虑、自残等副作用^[2-4]，甚至会攻击他人^[5]。但因其生产工艺简单、原料易得，且多通过网上销售，使得合成卡西酮的监管和打击难度极大，现已成为近年来国际禁毒领域最突出的难题之一。

合成卡西酮主要是不法分子通过对卡西酮或甲卡西酮进行细微的结构修饰获得的，因此存在许多结构类似物。4-氟甲卡西酮（4-FMC）是甲卡西酮的氟取代衍生物，是继第一代合成卡西酮4-甲卡西酮之后的第二代合成卡西酮类物质^[6]，于1952年首次合成，2015年被列管。3-氟甲卡西酮（3-FMC）是4-FMC的位置异构体，其结构示于图1。尽管两者化学性质相似，能产生相似的兴奋和致幻效果^[7]，但包括我国在内的很多国家尚未对3-FMC进行列管。因此，准确鉴定3-FMC和4-FMC对毒品犯罪案件中毒品鉴定和吸毒认定具有重要意义。

合成卡西酮的结构分析主要采用液相色谱-质谱（LC-MS）、气相色谱-质谱（GC-MS）、红外光谱（IR）、核磁共振波谱（NMR）等方法。Archer等^[8]开发了一种使用FTIR和¹⁹F NMR快速测定氟甲基卡氮二酮位置异构体的方法。然而，IR和NMR因灵敏度不足，不适用于复杂混合物分析^[9]。色谱-质谱技术具有质量范围宽、分辨率高、检测精度高等特点，适用于复杂混合物中目标物质的快速筛查，因而被广泛应用于新型毒品的结构鉴定^[10-12]。Liu等^[13]采用液相色谱-飞行时间质谱和气相色谱-静电场轨道阱高分辨质谱，系统研究了3种新合成卡西酮类物质的质谱裂解途径。

本文采用液相色谱-四极杆-静电场轨道阱高分辨质谱（LC-Q-Orbitrap/MS）和气相色谱-四极杆飞行时间质谱（GC-QTOF MS），对氟甲卡西酮位置异构体3-FMC和4-FMC在电子电离质谱（EI-MS）和电喷雾电离-碰撞诱导解离串联质谱（ESI-CID-MS/MS）模式下产生的主要碎片离子和裂解过程进行分析，并结合密度泛函理论计算方法研究其裂解机理，以更准确地阐明异构体的质谱行为和结构特征，为法庭科学实验室鉴定合成卡西酮提供参考。

1. 实验部分

1.1. 主要仪器与装置

GC-QTOF MS气相色谱-质谱联用仪：美国安捷伦公司产品，配有自动进样器；Dionex Ultimate 3000液相色谱仪、Thermo Q Extractive四极杆-静电场轨道阱高分辨质谱仪：美国赛默飞公司产品。

1.2. 主要材料与试剂

甲醇、乙腈：HPLC级，德国默克公司产品；甲酸：HPLC级，ROE Scientific Inc公司产品；3-FMC（CAS号：1049677-77-1；分子式：C₁₀H₁₂FNO；分子质量：181.21）和4-FMC（CAS号：447-40-5；分子式：C₁₀H₁₂FNO；分子质量：181.21）标准品：上海原思标物科技有限公司产品；水：由Millipore Milli-Q-Gradient净化系统制得。

1.3. 样品制备

用甲醇分别溶解3-FMC和4-FMC对照品。GC-QTOF MS、LC-Q-Orbitrap/MS分析浓度分别为1 mg/L、100  μg/L。

1.4. 实验条件

1.4.1. GC-MS条件

色谱条件：HP-5MS毛细管柱（30 m×250 μm，0.25 μm）；进气温度300 ℃；柱流速1.0 mL/min；分流比40:1；载气为氦气（纯度＞99.9%）；升温程序为初始温度50 ℃，保持3 min，以20 ℃/min升至320 ℃，保持13 min。

质谱条件：EI电离源（70 eV），质量扫描范围m/z 25～200，离子源温度230 ℃，四极杆温度150 ℃。

1.4.2. LC-MS条件

色谱条件：Hypersil GOLD VANQUISH色谱柱（100 mm×2.1 mm, 1.9 μm）；流动相为乙腈（A）和1%甲酸水溶液（B）；梯度洗脱条件为0～2 min（95%B），2～9.5 min（95%～5%B），9.5～12 min（5%B）；流动相流速0.3 mL/min；进样量10 μL。

质谱条件：加热电喷雾电离源正离子模式（HESI⁺）；质量扫描范围m/z 160～600；碰撞气体为氮气；喷淋电压3 800 V；毛细管温度350 ℃；传动毛细管温度350 ℃；全扫描数据采集方式：full MS-ddMS²；质量分辨率14 000，自动增益控制（AGC）目标为3×10⁶，最大注射时间（IT）50 ms；质量分辨率35 000，AGC目标1×10⁵，最大IT 50 ms；隔离窗为m/z 4。

1.4.3. 数据处理

使用Gaussian16程序，在(U)M06-2X-D3/def2-SVP理论^[14-16]水平下对各稳定结构和过渡态进行几何优化和频率计算。使用ORCA（5.0.2版本）程序，在RI-DLPNO-CCSD（T）/cc-pVTZ理论能级^[17-19]和相应的辅助基组^[20]下获得单点能量，并在对应质谱条件的温度和101.325 kPa下计算吉布斯自由能的热力学校正量。

3. 结论

本工作采用GC-QTOF MS和LC-Q-Orbitrap/MS研究氟甲卡西酮位置异构体3-FMC和4-FMC的质谱裂解模式。GC-QTOF MS结果表明，3-FMC和4-FMC具有相似的碎片离子和离子丰度。LC-Q-Orbitrap/MS结果表明，尽管3-FMC和4-FMC具有相似的碎片离子，但碎片离子m/z 148和149的丰度明显不同。这是因为氟原子具有较强的吸电子诱导效应，可以显著降低苯环的电子云密度，尤其是苯环邻、对位的电子云密度。因此，苯环侧链上的甲氨基会发生不同的裂解反应，导致碎片离子m/z 148和149的丰度不同。密度泛函理论研究进一步证实了该实验结果，并根据吉布斯自由能谱和电子性质推导出详细的裂解途径：第一步裂解（失去1分子H₂O）是α-羟基N-苯基亚胺重排反应的变体，由3步α-迁移构成，形成四元环侧链碎片离子（m/z 164, IM6），此过程为决速步骤；第二步通过相对吉布斯自由能进行理论预测，对所有保留氟苯基结构的可能异构体进行筛选，确定最稳定结构。综上，LC-Q-Orbitrap/MS法可准确有效地鉴别氟甲卡西酮位置异构体3-FMC和4-FMC，为合成卡西酮的鉴定和管控提供依据。

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