22 research outputs found
The Reference Site Collaborative Network of the European Innovation Partnership on Active and Healthy Ageing
Understanding the Role of Hyponitrite in Nitric Oxide Reduction
Herein, we review the preparation and coordination chemistry of cis and trans isomers of hyponitrite, [N2O2](2-). Hyponitrite is known to bind to metals via a variety of bonding modes. In fact, at least eight different bonding modes have been observed, which is remarkable for such a simple ligand. More importantly, it is apparent that the cis isomer of hyponitrite is more reactive than the trans isomer because the barrier of N2O elimination from cis-hyponitrite is lower than that of trans-hyponitrite. This observation may have important mechanistic implications for both heterogeneous NOx reduction catalysts and NO reductase. However, our understanding of the hyponitrite ligand has been limited by the lack of a general route to this fragment, and most instances of its formation have been serendipitous
Studies of Iron(III) Porphyrinates Containing Silanethiolate Ligands
The
chemistry of several ironĀ(III) porphyrinates containing silanethiolate
ligands is described. The complexes are prepared by protonolysis reactions
of silanethiols with the ironĀ(III) precursors, [FeĀ(OMe)Ā(TPP)] and
[FeĀ(OH)Ā(H<sub>2</sub>O)Ā(TMP)] (TPP = dianion of <i>meso-</i>tetraphenylporphine; TMP = dianion of <i>meso-</i>tetramesitylporphine).
Each of the compounds has been fully characterized in solution and
the solid state. The stability of the silanethiolate complexes versus
other ironĀ(III) porphyrinate complexes containing sulfur-based ligands
allows for an examination of their reactivity with several biologically
relevant small molecules including H<sub>2</sub>S, NO, and 1-methylimidazole.
Electrochemically, the silanethiolate complexes display a quasi-reversible
one-electron oxidation event at potentials higher than that observed
for an analogous arenethiolate complex. The behavior of these complexes
versus other sulfur-ligated ironĀ(III) porphyrinates is discussed
Studies of Iron(III) Porphyrinates Containing Silanethiolate Ligands
The
chemistry of several ironĀ(III) porphyrinates containing silanethiolate
ligands is described. The complexes are prepared by protonolysis reactions
of silanethiols with the ironĀ(III) precursors, [FeĀ(OMe)Ā(TPP)] and
[FeĀ(OH)Ā(H<sub>2</sub>O)Ā(TMP)] (TPP = dianion of <i>meso-</i>tetraphenylporphine; TMP = dianion of <i>meso-</i>tetramesitylporphine).
Each of the compounds has been fully characterized in solution and
the solid state. The stability of the silanethiolate complexes versus
other ironĀ(III) porphyrinate complexes containing sulfur-based ligands
allows for an examination of their reactivity with several biologically
relevant small molecules including H<sub>2</sub>S, NO, and 1-methylimidazole.
Electrochemically, the silanethiolate complexes display a quasi-reversible
one-electron oxidation event at potentials higher than that observed
for an analogous arenethiolate complex. The behavior of these complexes
versus other sulfur-ligated ironĀ(III) porphyrinates is discussed
<i>Treponema denticola</i> Superoxide Reductase: In Vivo Role, in Vitro Reactivities, and a Novel [Fe(Cys)<sub>4</sub>] Site
In vitro and in vivo results are presented demonstrating
that superoxide
reductase (SOR) from the air-sensitive oral spirochete, <i>Treponema
denticola</i> (Td), is a principal enzymatic scavenger of superoxide
in this organism. This SOR contains the characteristic non-heme [FeĀ(His)<sub>4</sub>Cys] active sites. No other metal-binding domain has been
annotated for Td SOR. However, we found that Td SOR also accommodates
a [FeĀ(Cys)<sub>4</sub>] site whose spectroscopic and redox properties
resemble those in so-called 2Fe-SORs. Spectroscopic comparisons of
the wild type and engineered Cys ā Ser variants indicate that
three of the Cys ligands correspond to those in [FeĀ(Cys)<sub>4</sub>] sites of ācanonicalā 2Fe-SORs, whereas the fourth
Cys ligand residue has no counterpart in canonical 2Fe-SORs or in
any other known [FeĀ(Cys)<sub>4</sub>] protein. Structural modeling
is consistent with iron ligation of the ānoncanonicalā
Cys residue across subunit interfaces of the Td SOR homodimer. The
Td SOR was isolated with only a small percentage of [FeĀ(Cys)<sub>4</sub>] sites. However, quantitative formation of stable [FeĀ(Cys)<sub>4</sub>] sites was readily achieved by exposing the as-isolated protein
to an iron salt, a disulfide reducing agent and air. The disulfide/dithiol
status and iron occupancy of the Td SOR [FeĀ(Cys)<sub>4</sub>] sites
could, thus, reflect intracellular redox status, particularly during
periods of oxidative stress