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首页> 外文期刊>Journal of mass spectrometry: JMS >Imidazole and imidazolium porphyrins: gas-phase chemistry of multicharged ions
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Imidazole and imidazolium porphyrins: gas-phase chemistry of multicharged ions

机译：咪唑和咪唑卟啉：多电荷离子的气相化学

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Electrospray ionization mass spectrometry/mass spectrometry in the positive ion mode was used to investigate the gas-phase chemistry of multicharged ions from solutions of porphyrins with 1,3-dimethylimidazolium-2-yl (DMIM) and 1-methylimidazol-2-yl (MIm) meso-substituents. The studied compounds include two free bases and 12 complexes with transition metals (Cu(II), Zn(II), Mn(III), and Fe(III)). The observed multicharged ions are either preformed or formed during the electrospraying process by reduction or protonation and comprise closed-shell and hypervalent mono-radical and bi-radical ions. The observed extensive and abundant fragmentation of the DMIM and MIm meso-substituents is a characteristic feature of these porphyrins. Fragments with the same mass values can be lost from the meso-substituents either as charged or neutral species and from closed-shell and hypervalent radical ions. Reduction processes are observed for both the free bases and the metallated DMIM porphyrins and occur predominantly by formation of hypervalent radicals that fragment, at low energy collisions, by loss of methyl radicals with formation of the corresponding MIm functionalities. These findings confirm that, when using electrospray ionization, reduction is an important characteristic of cationic meso-substituted tetrapyrrolic macrocycles, always occurring when delocalization of the formed hypervalent radicals is possible. For the Fe(III) and Mn(III) complexes, reduction of the metal centers is also observed as the predominant fragmentation of the corresponding reduced ions through losses of charged fragments testifies. The fragmentation of the closed-shell ions formed by protonation of the MIm porphyrins mirrors the fragmentation of the closed-shell ions of their DMIM counterparts.
机译：正离子模式下的电喷雾电离质谱/质谱用于研究卟啉与1,3-二甲基咪唑-2-基（DMIM）和1-甲基咪唑-2-基（ MIm）中位取代基。研究的化合物包括两个游离碱和12个与过渡金属（Cu（II），Zn（II），Mn（III）和Fe（III））的配合物。所观察到的多电荷离子在电喷雾过程中通过还原或质子化而预先形成或形成，并且包含闭壳离子和高价单自由基和双自由基离子。观察到的DMIM和MIm中位取代基广泛而丰富的碎片化是这些卟啉的特征。具有相同质量值的片段可能会从带电荷或中性的中位取代基以及封闭的壳和高价自由基离子中丢失。对于游离碱和金属化的DMIM卟啉都观察到还原过程，并且主要通过形成高价自由基而发生，该低价自由基在低能量碰撞时会断裂，由于甲基自由基的损失而形成相应的MIm官能团。这些发现证实，当使用电喷雾电离时，还原是阳离子内消旋取代的四吡咯大环的重要特征，当形成的高价基团可能离域时，总是发生还原。对于Fe（III）和Mn（III）配合物，还观察到金属中心的减少，因为相应的还原离子主要由于带电碎片的损失而破碎。 MIm卟啉质子化形成的闭壳离子的碎片反映了其DMIM对应物的闭壳离子的碎片。

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