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Isomers and Rotamers of DCM in Methanol and in Gas Phase Probed by Ion Mobility Mass Spectrometry in Combination with High Performance Liquid Chromatography.
The Journal of Physical Chemistry B ( IF 2.8 ) Pub Date : 2020-05-07 , DOI: 10.1021/acs.jpcb.0c00097 Piyali Chatterjee 1 , Subhra Sankar Dutta 1 , Tapas Chakraborty 1
The Journal of Physical Chemistry B ( IF 2.8 ) Pub Date : 2020-05-07 , DOI: 10.1021/acs.jpcb.0c00097 Piyali Chatterjee 1 , Subhra Sankar Dutta 1 , Tapas Chakraborty 1
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An integrated method of ion mobility mass spectrometry and high-performance liquid chromatography (HPLC) has been used to investigate the isomeric distribution of a popular fluorescent dye DCM (4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran) in methanol solution. Chromatographic separation of DCM isomers in methanol has been performed by probing the molecular mass (DCMH+), and two distinctly separated peaks are observed at retention times 3.73 (peak-I) and 3.87 (peak-II) min, where the latter one appears nearly twice as intense as the former. However, peak-I appears much weaker compared to peak-II if the chromatogram is recorded by optical probing at the absorption maximum of this dye (467 nm). The ion mobility (IM) spectra of DCMH+ ions corresponding to each of the LC-separated factions show three common peaks A, B, and C, with collision cross-section (CCS) values of 174, 185, and 197 Å2, respectively, but their relative intensities in the two IM spectra appear in opposite sequences. The three IM peaks have been assigned by considering the theoretically calculated CCS values of 13 possible isomers of DCMH+ ions. The IM spectral features also reveal that isomeric interconversions occur during the ESI process. Electronic structure calculations have been used to optimize the geometries of the four isomers of solvated DCM and the corresponding protomeric structures of DCMH+. The isomerization pathways and associated energy barriers have also been calculated. The gas-phase protomers are found to follow a completely different sequence of stability as compared to the neutral isomers. The analysis reveals that peak-I corresponds to one of the cis isomers, whereas peak-II arises due to cumulative contributions of the other three isomers. The absorption spectrum of DCM in methanol is simulated from the computed spectral profiles of the isomers which indicates a distribution of trans1, trans2, cis1, and cis2 isomers as 33.5, 61.5, 2.0, and 3.0%, respectively. The fragmentation behavior of DCMH+ ions in a collision-induced dissociation experiment has been found to be isomer dependent.
中文翻译：
离子淌度质谱结合高效液相色谱探测甲醇中和气相中DCM的异构体和旋转异构体。
离子淌度质谱和高效液相色谱（HPLC）的集成方法已用于研究流行的荧光染料DCM（4-（二氰基亚甲基）-2-甲基-6-（4-二甲基氨基苯乙烯）- 4 H-吡喃）的甲醇溶液。通过探测分子量（DCMH +）进行了DCM异构体在甲醇中的色谱分离，在保留时间3.73（peak-I）和3.87（peak-II）min处观察到两个明显分离的峰，后一个出现几乎是前者的两倍。但是，如果通过光学探测在该染料的最大吸收值（467 nm）下记录了色谱图，则峰I与峰II相比要弱得多。DCMH +的离子迁移率（IM）光谱对应于每个LC-分离派别的离子显示三种常见的峰A，B，和C，与碰撞截面（CCS）的174值，185，和197埃2，分别，但它们的相对强度在两个IM光谱以相反的顺序出现。通过考虑DCMH +离子的13种可能异构体的理论计算CCS值来分配三个IM峰。IM光谱特征还揭示了在ESI过程中发生异构体互变。电子结构计算已用于优化溶剂化DCM的四个异构体的几何形状以及DCMH +的相应原型结构。还已经计算出异构化途径和相关的能垒。与中性异构体相比，发现气相启动子遵循完全不同的稳定性顺序。分析显示峰-I对应于一个顺式异构体，而峰-II是由于其他三个异构体的累积贡献而产生的。DCM的在甲醇中的吸收光谱是从指示的分布的同分异构体的所计算的光谱曲线的模拟反-1，TRANS2，CIS1和CIS2异构体33.5，61.5，2.0和3.0％之间。DCMH +的碎片行为 在碰撞诱导的离解实验中，离子是依赖于异构体的。
更新日期：2020-05-07
中文翻译：
离子淌度质谱结合高效液相色谱探测甲醇中和气相中DCM的异构体和旋转异构体。
离子淌度质谱和高效液相色谱（HPLC）的集成方法已用于研究流行的荧光染料DCM（4-（二氰基亚甲基）-2-甲基-6-（4-二甲基氨基苯乙烯）- 4 H-吡喃）的甲醇溶液。通过探测分子量（DCMH +）进行了DCM异构体在甲醇中的色谱分离，在保留时间3.73（peak-I）和3.87（peak-II）min处观察到两个明显分离的峰，后一个出现几乎是前者的两倍。但是，如果通过光学探测在该染料的最大吸收值（467 nm）下记录了色谱图，则峰I与峰II相比要弱得多。DCMH +的离子迁移率（IM）光谱对应于每个LC-分离派别的离子显示三种常见的峰A，B，和C，与碰撞截面（CCS）的174值，185，和197埃2，分别，但它们的相对强度在两个IM光谱以相反的顺序出现。通过考虑DCMH +离子的13种可能异构体的理论计算CCS值来分配三个IM峰。IM光谱特征还揭示了在ESI过程中发生异构体互变。电子结构计算已用于优化溶剂化DCM的四个异构体的几何形状以及DCMH +的相应原型结构。还已经计算出异构化途径和相关的能垒。与中性异构体相比，发现气相启动子遵循完全不同的稳定性顺序。分析显示峰-I对应于一个顺式异构体，而峰-II是由于其他三个异构体的累积贡献而产生的。DCM的在甲醇中的吸收光谱是从指示的分布的同分异构体的所计算的光谱曲线的模拟反-1，TRANS2，CIS1和CIS2异构体33.5，61.5，2.0和3.0％之间。DCMH +的碎片行为 在碰撞诱导的离解实验中，离子是依赖于异构体的。
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