Ramos Catarina I V, Pereira Patrícia M R, Santana-Marques M Graça, De Paula Rodrigo, Simões Mário M Q, Neves M Graça P M S, Cavaleiro José A S
Mass Spectrometry Laboratory, QOPNA, Department of Chemistry, University of Aveiro, 3810-193, Aveiro, Portugal.
J Mass Spectrom. 2014 May;49(5):371-9. doi: 10.1002/jms.3350.
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.
采用正离子模式的电喷雾电离质谱/质谱法研究了带有1,3 - 二甲基咪唑 - 2 - 基（DMIM）和1 - 甲基咪唑 - 2 - 基（MIm）中位取代基的卟啉溶液中多电荷离子的气相化学性质。所研究的化合物包括两种游离碱以及12种与过渡金属（Cu(II)、Zn(II)、Mn(III)和Fe(III)）形成的配合物。观察到的多电荷离子要么是预先形成的，要么是在电喷雾过程中通过还原或质子化形成的，包括闭壳层以及高价单自由基和双自由基离子。观察到DMIM和MIm中位取代基广泛且丰富的碎片化是这些卟啉的一个特征。具有相同质量值的碎片可以作为带电或中性物种从中位取代基以及闭壳层和高价自由基离子中丢失。在游离碱和金属化的DMIM卟啉中均观察到还原过程，并且主要通过形成高价自由基而发生，这些高价自由基在低能碰撞时通过甲基自由基的丢失而碎片化，形成相应的MIm官能团。这些发现证实，在使用电喷雾电离时，还原是阳离子中位取代四吡咯大环的一个重要特征，当形成的高价自由基能够离域时总是会发生。对于Fe(III)和Mn(III)配合物，还观察到金属中心的还原，因为相应还原离子通过带电碎片的丢失而发生的主要碎片化证明了这一点。MIm卟啉质子化形成的闭壳层离子的碎片化反映了其DMIM对应物闭壳层离子的碎片化情况。
