49 ISSN: 1469-0667 © IM Publications LLP 2008 doi: 10.1255/ejms.908 All rights reserved EUROPEAN JOURNAL OF MASS SPECTROMETRY Porphyrin derivatives are involved in vital functions such as respiration and photosynthesis. Lately, these derivatives have been used for the production of new materials and applied as catalysts, as receptor models in molecular recognition and in medicine. 1–3 As far as biomedical applications are concerned, formulations based on porphyrins are already being marketed, namely for cancer therapy and the treatment of aged-related macular degeneration. The potential of these compounds for gene regulation therapies, drug targeting, inactivation of microorganisms and viruses is also well recognised. 1–6 For all these applications, compounds with adequate structural features are required. This fact explains the great effort devel- Electrospray tandem mass spectrometry of b -nitroalkenyl meso-tetraphenylporphyrins Eduarda M.P. Silva, a Pedro Domingues, b João P.C. Tomé, a M. Amparo F. Faustino, a M. Graça P.M.S. Neves, a Augusto C. Tomé, a Daniel Dauzonne, c Artur M.S. Silva, a José A.S. Cavaleiro, a António J. Ferrer-Correia b and M. Rosário M. Domingues b * a Organic Chemistry Group, Department of Chemistry, University of Aveiro, 3810–193 Aveiro, Portugal b Mass Spectrometry Group, Department of Chemistry, University of Aveiro, 3810–193 Aveiro, Portugal. E-mail: mrd@ua.pt mrd@ua.pt c UMR 176 CNRS, Institut Curie, Section de Recherche, 26 rue d’Ulm, 75248 Paris cedex 05, France b-Nitroalkenyl meso-tetraphenylporphyrins [b-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 b-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 b-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. Keywords: electrospray, tandem mass spectrometry, porphyrins, nitroalkenes, nitro compounds Introduction E.M.P. Silva et al., Eur. J. Mass Spectrom. 14, 49–59 (2008) Received: 1 February 2008 n Revised: 5 March 2008 n Accepted: 11 March 2008 n Publication: 31 March 2008