Silva Eduarda M P, Domingues Pedro, Tomé João P C, Faustino M Amparo F, Neves M Graça P M S, Tomé Augusto C, Dauzonne Daniel, Silva Artur M S, Cavaleiro José A S, Ferrer-Correia António J, Domingues M Rosário M
Organic Chemistry Group, Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal.
Eur J Mass Spectrom (Chichester). 2008;14(1):49-59. doi: 10.1255/ejms.908.
Beta-nitroalkenyl meso-tetraphenylporphyrins [beta-TPPCHC(NO(2))R)], as free-bases and Zn(II) complexes, were studied by electrospray mass spectrometry (ESI-MS). Under this ionisation condition the M + H ions are formed. The fragmentation pattern of the resulting M + H ions were studied by electrospray tandem mass spectrometry (ESI-MS/MS). The ESI-MS/MS of beta- nitroalkenylporphyrins, either as free-bases or as Zn(II) complexes, show several interesting features, distinct from the typical behaviour of nitro compounds. For the studied compounds, common main fragmentation patterns are observed, namely characteristic losses of NO(2), HNO(2), 2OH, RNO(2), RCNO, RCNO(2), RCH(2)NO(2), C(6)H(5) plus NO(2) and the formation of the protonated macrocycle, TPP + H or ZnTPP + H. However, depending on the presence or absence of the metal and the nature of the R substituent, important differences are observed on the relative abundances of the ions formed by the same fragmentation pathway. The presence of bromine in the alkenyl group leads to a peculiar behaviour, since the main fragmentation pattern corresponds to the combined elimination of the bromine atom with the typical nitro group fragments. When R = Br, the loss of the nitro group occurs in low relative abundance (11-16%). However, when R = CH(3), the relative abundance of the ion due to the loss of HNO(2) changes drastically from 100%, observed for the free-base porphyrin, to 29% in the case of the Zn(II) complex. These variations of the relative abundance of the fragment corresponding to the loss of the nitro moiety (typically considered as a diagnostic fragment) can induce to an erroneous interpretation of their MS/MS spectra. Some fragmentations are observed only for the free-base porphyrins, namely the loss of CH(NO(2)R and HNO(2) plus C(2)H(2), while the loss of OH, H(2)O, OH plus H(2)O and RCCH plus H(2)O is observed only for the complexes. Unusual and unexpected fragmentations are also observed, namely the losses of RCNO, RCNO(2) and HNO(2) plus C(2)H(2). This work demonstrates that valuable structural information about the beta-nitroalkenyl substituents linked to meso- tetraarylporphyrins can be achieved using MS/MS. These results can also be useful for the interpretation of the mass spectra of other nitroalkenyl substituted compounds.
以游离碱和锌（II）配合物形式存在的β-硝基烯基中位四苯基卟啉[β-TPPCHC(NO₂)R]，通过电喷雾质谱法（ESI-MS）进行了研究。在这种电离条件下，会形成M + H离子。通过电喷雾串联质谱法（ESI-MS/MS）研究了所得M + H离子的碎裂模式。β-硝基烯基卟啉无论是游离碱形式还是锌（II）配合物形式，其ESI-MS/MS都显示出一些有趣的特征，与硝基化合物的典型行为不同。对于所研究的化合物，观察到了常见的主要碎裂模式，即NO₂、HNO₂、2OH、RNO₂、RCNO、RCNO₂、RCH₂NO₂、C₆H₅加NO₂的特征性损失以及质子化大环卟吩 + H或锌卟吩 + H的形成。然而，根据金属的存在与否以及R取代基的性质，在相同碎裂途径形成的离子的相对丰度上观察到了重要差异。烯基中溴的存在导致了一种特殊行为，因为主要碎裂模式对应于溴原子与典型硝基碎片的联合消除。当R = Br时，硝基的损失以较低的相对丰度（11 - 16%）发生。然而，当R = CH₃时，由于HNO₂损失产生的离子的相对丰度从游离碱卟啉的100%急剧变化到锌（II）配合物情况下的29%。对应于硝基部分损失的碎片（通常被视为诊断性碎片）相对丰度的这些变化可能会导致对其MS/MS光谱的错误解释。仅在游离碱卟啉中观察到了一些碎裂，即CH(NO₂)R和HNO₂加C₂H₂的损失，而仅在配合物中观察到了OH、H₂O、OH加H₂O以及RCCH加H₂O的损失。还观察到了不寻常和意外的碎裂，即RCNO、RCNO₂和HNO₂加C₂H₂的损失。这项工作表明，使用MS/MS可以获得与中位四芳基卟啉相连的β-硝基烯基取代基的有价值的结构信息。这些结果对于解释其他硝基烯基取代化合物的质谱也可能有用。
