INVESTIGADORES
BARI Sara Elizabeth
congresos y reuniones científicas
Título:
The Relationship between Sulfide Species and Iron Porphyrinates: A Theoretical and Experimental Approach
Autor/es:
BARI, SARA E.; SURKIN, NICOLAS; DABROWSKI, SERGIO G.; BOUBETA, FERNANDO; BOECCHI, LEONARDO; MARTÍ, MARCELO A.; ROSENSTEIN, RUTH; E
Lugar:
New Mexico, USA
Reunión:
Conferencia; Sixth International Conference on Porphyrins and Phthalocyanines (ICPP-6); 2010
Resumen:
ICPP-6_book.indb
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The toxic
and stinky gas hydrogen sulfide (H2S) has been recently promoted to
the category of gasotransmitter for its participation in the cardiovascular
system, particularly in vasodilation and blood pressure control. At
physiological conditions (pH =7.4), dissolved H2S is partially
deprotonated (pKa1=6.9), and both H2S and hydrosulfide
(SH-) are available to display their coordination chemistry, where
probably lies their biochemical impact. In fact, a couple of hemeproteins have
been proved to bind sulfide species with very high affinity, opening the discussion
about the role of hemeproteins in H2S biochemistry.[1][2]
Interestingly, the active sites of these hemeproteins do not exhibit common
features, making it very difficult to rationalize the affinity results in
molecular terms. Recently, the synthesis and crystal structures of two hydrosulfide
iron (II) porphyrinates have been successfully achieved.[2]
Since the
molecular determinants controlling sulfide affinity to hemeproteins are not
well established, we focused in the characterization of the binding of SH2,
SH-, S2- to heme model compounds from a theoretical and
experimental perspective.
We performed
quantum mechanics simulation at the DFT level, to understand how sulfide
species are affected upon binding to the heme group. We used an iron(III)
porphine model coordinated to imidazole, with SH2, SH- or
S2- as sixth ligand ((Im)FeIII(SH2), (Im)FeIII(SH-), (Im)FeIII(S2-)), in
order to characterize the structural parameters, the distribution of charges,
and the IR frequencies for each system. Far-IR frequencies characterize the
Fe-S stretching for the three ligands: 318 and 380 cm-1, 336 and 393
cm-1, and 346 and 383 cm-1 for (Im)FeIII(SH2), (Im)FeIII(SH-), (Im)FeIII(S2-), respectively,
being weaker the lower frequencies in the three cases. The calculated stretching frequencies for the
S-H bond are 2709 and 2687 cm-1 (asymmetric and symmetric modes in
(Im)FeIII(SH2) respectively), and 2665 cm-1 for (Im)FeIII (SH-).
The reaction
was studied experimentally using buffered solutions of TPPSFeIII (10-5M
in buffer AcO-/AcOH, pH=6.5, 25ºC, anaerobic conditions) and freshly
prepared solutions of commercial SHNa; the evolution of the reaction was
followed by UV/Vis spectroscopy. In our hands, the isolated TPPSFeIII
system yielded the expected and well characterized reduction product.
Conversely, preparations of TPPSFeII (lmax= 428nm) afforded an uncharacterized reaction
intermediate, that evolved to a new species (lmax= 418 and 536 nm).
We are currently performing IR and Raman spectroscopies
and computational studies of iron (II) model systems to gain further insight in
structural characterization.
References
1. BD Nguyen, X Zhao, K Vyas, G N La Mar,
RA Lile, EA Brucker, GN Phillips Jr., JS Olson
JB
Wittenberg J Biol Chem. 1998, 273, 9517-26.
2. FN Nicoletti, A Comandini, A
Bonamore, L Boechi, FM Boubeta, A Feis, G Smulevich, A Boffi,
Biochemistry, 2010 (in press).
3. JW
Pavlik,BC Noll, AG Oliver,
CE Schulz, WR Scheidt, Inorg. Chem. 2010, 49, 1017-26.