TY - JOUR
T1 - Imidazole and imidazolium porphyrins
T2 - Gas-phase chemistry of multicharged ions
AU - Ramos, Catarina I.V.
AU - Pereira, Patrícia M.R.
AU - Santana-Marques, M. Graça
AU - De Paula, Rodrigo
AU - Simões, Mário M.Q.
AU - Neves, M. Graça P.M.S.
AU - Cavaleiro, José A.S.
PY - 2014/5
Y1 - 2014/5
N2 - 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.
AB - 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.
KW - electrospray mass spectrometry
KW - gas-phase chemistry
KW - imidazole porphyrins
KW - imidazolium porphyrins
KW - multicharged ions
UR - http://www.scopus.com/inward/record.url?scp=84900033480&partnerID=8YFLogxK
U2 - 10.1002/jms.3350
DO - 10.1002/jms.3350
M3 - Article
C2 - 24809898
AN - SCOPUS:84900033480
SN - 1076-5174
VL - 49
SP - 371
EP - 379
JO - Journal of Mass Spectrometry
JF - Journal of Mass Spectrometry
IS - 5
ER -