JMS letters
•
macrocycle oxidation by loss of a hydrogen atom (–H ). After the
initial formation of a radical at the β-pyrrole position, the reaction
may proceed through the formation of β–β linkages between the
two porphyrin rings in the μ-O-bridged dimer. The oxidation reaction
of metalloporphyrins with silver hexafluorophosphate or via an
anode is one of the most widely used methods in porphyrin
synthesis for connecting the porphyrin macrocycle directly through
meso–meso or other positions including meso-β, β–β, and fused
Acknowledgements
This work was supported by Fundação para a Ciência e a Tecnologia
(
FCT, Portugal), European Union, QREN, FEDER and COMPETE, projects
NORTE-07-0162-FEDER-000048, NORTE-07-0124-FEDER-000066/
7, PEst-C/EQB/LA0006/2011 and the R&D project PTDC/EQU-
6
EQU/121677/2010 and the Programme for Scientific Re-equipment,
contract REDE/1517/RMN/2005, with funds from POCI 2010 (FEDER)
and Fundação para a Ciência e a Tecnologia (FCT).
[12,13]
linkages.
The mechanism proposed involves the reaction of a
radical cation with a neutral metalloporphyrin, the regioselectivity
for meso or β-pyrrolic positions being determined by differences in
Yours,
[13]
the HOMO orbitals of the metalloporphyrins.
Cross-linking be-
a
a
a
tween the two rings would explain further losses of H , while stabiliz-
André M. N. Silva, * António Aguiar, Salete S. Balula, Ana M. G.
2
a
b
ing the porphyrin dimer and preventing its dissociation.
Unfortunately, the ion at m/z 2067.72 did not prove to be
sufficiently stable or to be present in an amount that could afford
Silva and Maria Rangel
a
REQUIMTE/Departamento de Química e Bioquímica, Faculdade
de Ciências Universidade do Porto, Rua do Campo Alegre s/n,
4169-007 Porto Portugal
3
an additional fragmentation step (MS ), thus preventing its structural
characterization.
+
Fragmentation of [(μ-OH)(FeTPFPP)2] with HCD [Fig. 3(B)]
b
REQUIMTE/Instituto de Ciências Biomedicas de Abel Salazar
produced two predominant fragment ions at m/z 1027.96939
Universidade do Porto, Rua Jorge Viterbo Ferreira, 228, 4050-313
Porto Portugal
and 1023.95818, showing the cleavage of the μ-O-bridged
porphyrin dimer into its monomer species [FeTPFPP] (m/z
+
1027.97) and a further loss of four hydrogen atoms (m/z 1023.96).
Further investigations will be required to understand why the
preferable CID fragmentation pathways of the μ-O-bridged References
porphyrin dimer seem to favor loss of hydrogen atoms over
[
1] A. Aguiar, S. Ribeiro, A. M. N. Silva, L. Cunha-Silva, B. De Castro, A. M.
G. Silva, S. S. Balula, Appl. Catal. Gen. 2014, 478, 267.
dimer dissociation or other characteristic neutral losses such as
those found for the monomer fragmentation. Fragmentation of
[2] C.-C. Guo, X.-Q. Liu, Y. Liu, Q. Liu, M.-F. Chu, X.-B. Zhang, J. Mol. Catal.
A: Chem. 2003, 192, 289.
+
the [FeTPFPP] monomer (m/z 1027.97) both with HCD or CID
•
[3] E. V. Kudrik, P. Afanasiev, L. X. Alvarez, P. Dubourdeaux, M.
Clemancey, J.-M. Latour, G. Blondin, D. Bouchu, F. Albrieux, S. E.
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resulted in cumulative losses of hydrogen (m/z 1, –H ), hydrogen
fluoride (m/z 20, –HF), pentafluorobenzyl radical (m/z 166, –C
and pentafluorobenzene (m/z 167, –C H) as previously described
6 5
F
•),
6 5
F
[14]
in the literature.
[
[
5] R. S. Brown, C. L. Wilkins, Anal. Chem. 1986, 58, 3196.
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μ-O-bridged iron porphyrin dimers are becoming widely
utilized in a number of technological applications and these
experiments show that ESI instruments may become an impor-
tant tool in the characterization of these chemical systems.
Given the right choice of solvent, MS may report on the solution
speciation of monomer – dimer equilibria. Such capability may
prove useful when μ-O-bridged iron porphyrin dimers are used
in chemical catalysis, allowing the study of catalyst stability,
reaction mechanisms, and degradation products. Furthermore,
it was shown that the gas phase chemistry of monomers and
dimers differs significantly, and that a combination of CID and
HCD fragmentation modes may not only provide structural
information but also give insight into the chemical properties
of these molecules.
[
[
[
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[
[
[
[
J. Mass Spectrom. 2014, 49, 763–765
Copyright © 2014 John Wiley & Sons, Ltd.
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