INVESTIGADORES
NEUMAN Nicolas Ignacio
congresos y reuniones científicas
Título:
Synthesis, Characterization and HNO Binding Properties of Metalocorroles
Autor/es:
MIGUEL A. MORALES; NICOLÁS I. NEUMAN; JUAN PELLEGRINO; FABIO DOCTOROVICH
Lugar:
Chascomús
Reunión:
Encuentro; IV LABIC Fourth Latin American Meeting on Biological Inorganic Chemistry V WOQUIBIO Fifth Workshop on Bioinorganic Chemistry; 2014
Institución organizadora:
UBA, UNR, CONICET, AGENCIA, Workshop Argentino de Química Bioinorgánica
Resumen:
Session I- Bioinspired and Biomimetic Coordination Chemistry
P5.-Synthesis, Characterization and HNO Binding Properties of Metalocorroles
Miguel A. Morales,1 Nicolás I. Neuman,1,2 Juan Pellegrino1 and Fabio Doctorovich1
1 INQUIMAE/DQIAyFQ, FCEN, Universidad de Buenos Aires, Argentina
2 Departamento de Física, FBCB, Universidad Nacional del Litoral, Argentina
mmorales@qi.fcen.gov.ar
INTRODUCTION
Corroles are contracted tetrapyrrolic
macrocycles which possess a direct pyrrolepyrrole
bond. Corrole synthesis was first
inspired by natural occurence of vitamin B12,
which is a derivatized cobalt corrin (reduced
corrole).1 In 1999 two facile syntheses of
corroles were reported,2,3 which led to a
geometrical increase in the number of studies of
these compounds and their properties. Corroles
have several interesting properties. They
stabilize metals in high oxidation states, which
has applications in catalysis, have several
photochemical applications, such as singlet
oxygen generation (ref) and bind small ligands
such as O2, NO and HNO (azanone). Our
group´s interest in HNO was intensified lately
due to the finding that several biologically
relevant reductants are capable to reduce NO to
HNO in physiological conditions (see poster by
M. Muñoz et al.) In this work we will sinthesize
corroles and study the reductive binding of
HNO by Co(III) and Fe(III) corroles, which
could lead to new useful HNO sensors.
EXPERIMENTAL METHODS
Corroles were synthesized according to refs. 4
and 5, by acid-catalyzed condensation of
substituted benzaldehyde and pyrrole, followed
by oxidative ring-closure of a tetrapyrrolic
intermediate using p-chloranyl. The resulting
corroles (deep green) were purified by column
chromatography using silica-gel and
dichloromethane (DCM)/hexanes mixtures.
Metallation was achieved by refluxing a
DCM/MeOH solution of corrole and a metal salt
such as Fe(SO4)2 or Co(Acetate)2. All products
were characterized by UV-visible and NMR
spectroscopy. Their electrochemical properties
were studied by cyclic voltammetry and UV-vis
spectroelectrochemistry (results not shown
here).
HNO binding was measured by mixing iron or
cobalt corrole with HNO donor Piloty's acid
(PA)6 and 2,6-lutidine (base) and following the
UV-vis spectral changes.
RESULTS AND DISCUSSION
Figure 1 shows the UV-vis spectra of free base
tris-meso-(4-nitrophenyl)- (NO2C), tris-meso-
(4-methoxyphenyl)- (MeOC), tris-meso-
(phenyl)- (PhC), and tris-meso-(2,6-
dichlorophenyl)corrole (diClC). The spectra of
PhC, MeOC and diClC show a split Soret band
in the 400-420 nm region and two to four Qbands
in the 500-700 nm region. NO2C shows a
broader Soret band at 455 nm.
Fig. 1. UV-vis spectra of free base corroles.
Free base corroles are unstable, and they have to
be kept in the dark during purification and
stored in the dark under inert gas atmosphere.
Upon metallation the corroles become much
more stable, but still the oxidation state of the
metal may change if not stored under inert
atmosphere.
Figure 2 shows the UV-vis spectra of
Co(IV)MeOC, Co(III)MeOC, and the product of
the reaction Co(III)MeOC with HNO donor
Piloty´s acid. Reaction of the reduced cobalt
corrole with PA is very fast, and in EtOH
doesn´t require addition of a base to initiate
decomposotion of PA to produce HNO.
Fig. 2. UV-vis spectra of Co(IV)MeOC,
Co(III)MeOC, and Co(III)MeOC plus Piloty´s
Acid.
Alternatively, Co(IV)MeOC reaction with
Piloty´s acid as a function of time was followed
spectrophotometrically and required hours to
completion.
A proposed mechanism, based on previous work
in cobalt porphyrins,7 is the following
HNO Co(III)Cor Co(III)(NO− )Cor H+ + ® +
Instead, Co(IV)MeOC is likely coordinated
with an oxo- or hidroxo- group which slows the
direct metal-HNO reaction. Further
characterization of the reaction mechanism is
underway.
Additionally, studies on HNO binding to
Fe(IV)(diClC) were performed as with
CoMeOC. Fe(III)(NO)(diClC) was
characterized by FTIR and NMR. Further, EPR
studies were performed on Fe(III)(NO)(diClC)
and its one-electron reduced product. The nNO
frequency change upon reduction was around -
185 cm-1, indicative of a high NO centred
reduction. The oxidized complex shows no EPR
signal, but the reduced complex shows an
isotropic hyperfine split signal (I = 1), which
upon freezing becomes highly anisotropic. This
signal is indicative of coordinated NO?.
CONCLUSIONS
We have synthesized and characterized a series
of corroles and cobalt metallocorroles using
UV-vis spectroscopy, NMR and electrochemical
methods. We have also observed that
Co(III)MeOC binds HNO at a considerable rate,
and is thus promising in the development of an
HNO sensing system. Finally an iron nitrosyl
corrole was isolated and characterized, as well
as its one-electron reduction product. These
studies are underway with other nitrosyl corrole
complexes.
REFERENCES
1. Aviv-Harel I. et al., CEJ (2009), 15:8382-
8394
2. Paolesse R. et al., CC (1999), 1307-1308
3. Gross Z. et al., ACIEE. (1999), 38(10):1427-
1429
4. Gryko D.T. et al., OBC (2003), 1(2):350-357
5. Koszarna B. et al., JOC (2006), 71(10):3707-
3717
6. Bonner F.T. et al. IC (1992), 31:2514:2519
7. Suárez, S. et al., AC (2013), 85:10262-10269
ACKNOWLEDGMENTS
The authors would like to thank CONICET,
UBA and ANPCyT for providing financial
support to this project. MAM, NIN and JP thank
CONICET for a fellowship grant. FD is a
member of CONICET.