7 research outputs found
Amperometric Quantification of SāNitrosoglutathione Using Gold Nanoparticles: A Step toward Determination of SāNitrosothiols in Plasma
S-Nitrosothiols (RSNOs) are carriers
of nitric oxide (NO) and have
important biological activities. We propose here the use of gold nanoparticles
(AuNPs) and NO-selective amperometric microsensor for the detection
and quantification of S-nitrosoglutathione (GSNO) as a step toward
the determination of plasma RSNOs. AuNPs were used to decompose RSNOs
with the quantitative release of free NO which was selectively detected
with a NO microsensor. The optimal [GSNO]/[AuNPs] ratio was determined,
corresponding to an excess of AuNP surface relative to the molar GSNO
amount. Moreover, the influence of free plasma thiols on this method
was investigated and a protocol based on the blocking of free thiols
with iodoacetic acid, forming the carboxymethyl derivative of the
cysteine residues, is proposed
Simultaneous Electrochemical Speciation of Oxidized and Reduced Glutathione. Redox Profiling of Oxidative Stress in Biological Fluids with a Modified Carbon Electrode
The
simultaneous electrochemical quantification of oxidized (GSSG)
and reduced glutathione (GSH), biomarkers of oxidative stress, is
demonstrated in biological fluids. The detection was accomplished
by the development of a modified carbon electrode and was applied
to the analysis of biological fluids of model organisms under oxidative
stress caused by lead intoxication. Nanocomposite molecular material
based on cobalt phthalocyanine (CoPc) and multiwalled carbon nanotubes
functionalized with carboxyl groups (MWCNT<sub>f</sub>) was developed
to modify glassy carbon electrodes (GCE) for the detection of reduced
and oxidized glutathione. The morphology of the nanocomposite film
was characterized by scanning electron microscopy (SEM) and profilometry.
The electrochemical behavior of the modified electrode was assessed
by cyclic voltammetry (CV) to determine the surface coverage (Ī)
by CoPc. The electrocatalytic behavior of the modified electrode toward
reduced (GSH) and oxidized (GSSG) forms of glutathione was assessed
by CV studies at physiological pH. The obtained results show that
the combined use of CoPc and MWCNT<sub>f</sub> results in an electrocatalytic
activity for GSH oxidation and GSSG reduction, enabling the simultaneous
detection of both species. Differential pulse voltammetry reveals
detection limits of 100 Ī¼M for GSH and 8.3 Ī¼M for GSSG,
respectively. The potential interference from ascorbic acid, cysteine,
glutamic acid, and glucose was also studied, and the obtained results
show limited effects from these species. Finally, the hybrid electrode
was used for the determination of GSH and GSSG in rat urine and plasma
samples, intoxicated or not by lead. Both glutathione forms were detected
in these complex biological matrixes without any pretreatment. Our
results portray the role of GSH and GSSG as markers of oxidative stress
in live organisms under lead intoxication
Tictoid Expanded Pyridiniums: Assessing Structural, Electrochemical, Electronic, and Photophysical Features
In regard to semirigid donorāspacerāacceptor
(DāSāA)
dyads devised for photoinduced charge separation and built from an
unsaturated spacer, there exists a strategy of design referred to
as āgeometrical decouplingā that consists in introducing
an inner-S twist angle approaching 90Ā° to minimize adverse D/A
mutual electronic influence. The present work aims at gaining further
insights into the actual impact of the use of bulky substituents (R)
of the alkyl type on the electronic structure of spacers (S) of the
oligo-<i>p</i>-phenylene type, which can be critical in
the functioning of derived dyads. To this end, a series of 12 novel
expanded pyridiniums (EPs), regarded as model SāA assemblies,
was synthesized and its structural, electronic, and photophysical
properties were investigated at both experimental and theoretical
levels. These EPs result from the combination of 4 types of pyridinium-based
acceptor moieties with the three following types of S subunits connected
at position 4 of the pyridinum core: xylyl (X), xylyl-phenyl (XP),
and xylyl-tolyl (XT). From comparison of collected data with those
already reported for eight other EPs based on the same A components
but linked to S fragments of two other types (i.e., phenyl, P, and
biphenyl, PP), the following quantitative order in regard to the pivotal
S-centered HOMO energy perturbation was derived (sorted by increasing
destabilization): <i>P</i> < X āŖ PP ā<
XP ā< XT. This indicates that spacers (S) are primarily
distinguished on the basis of their mono- or biaryl composition and
secondarily by their number of methyl substituents (R). The electron-donating
inductive contribution of methyl substituents (HOMO destabilization)
more than counterbalances the effect of conjugation disruption (HOMO
stabilization). This ācompensation effectā suggests
that mildly electron-withdrawing hindering groups are better suited
for āgeometrical decouplingā, given that high-energy
S-centered occupied MOs can assist charge recombination within DāSāA
dyads
Tictoid Expanded Pyridiniums: Assessing Structural, Electrochemical, Electronic, and Photophysical Features
In regard to semirigid donorāspacerāacceptor
(DāSāA)
dyads devised for photoinduced charge separation and built from an
unsaturated spacer, there exists a strategy of design referred to
as āgeometrical decouplingā that consists in introducing
an inner-S twist angle approaching 90Ā° to minimize adverse D/A
mutual electronic influence. The present work aims at gaining further
insights into the actual impact of the use of bulky substituents (R)
of the alkyl type on the electronic structure of spacers (S) of the
oligo-<i>p</i>-phenylene type, which can be critical in
the functioning of derived dyads. To this end, a series of 12 novel
expanded pyridiniums (EPs), regarded as model SāA assemblies,
was synthesized and its structural, electronic, and photophysical
properties were investigated at both experimental and theoretical
levels. These EPs result from the combination of 4 types of pyridinium-based
acceptor moieties with the three following types of S subunits connected
at position 4 of the pyridinum core: xylyl (X), xylyl-phenyl (XP),
and xylyl-tolyl (XT). From comparison of collected data with those
already reported for eight other EPs based on the same A components
but linked to S fragments of two other types (i.e., phenyl, P, and
biphenyl, PP), the following quantitative order in regard to the pivotal
S-centered HOMO energy perturbation was derived (sorted by increasing
destabilization): <i>P</i> < X āŖ PP ā<
XP ā< XT. This indicates that spacers (S) are primarily
distinguished on the basis of their mono- or biaryl composition and
secondarily by their number of methyl substituents (R). The electron-donating
inductive contribution of methyl substituents (HOMO destabilization)
more than counterbalances the effect of conjugation disruption (HOMO
stabilization). This ācompensation effectā suggests
that mildly electron-withdrawing hindering groups are better suited
for āgeometrical decouplingā, given that high-energy
S-centered occupied MOs can assist charge recombination within DāSāA
dyads
Rhenium Complexes Based on 2āPyridyl-1,2,3-triazole Ligands: A New Class of CO<sub>2</sub> Reduction Catalysts
A series of [ReĀ(N^N)Ā(CO)<sub>3</sub>(X)] (N^N = diimine and X = halide) complexes based on 4-(2-pyridyl)-1,2,3-triazole
(pyta) and 1-(2-pyridyl)-1,2,3-triazole (tapy) diimine ligands have
been prepared and electrochemically characterized. The first ligand-based
reduction process is shown to be highly sensitive to the nature of
the isomer as well as to the substituents on the pyridyl ring, with
the peak potential changing by up to 700 mV. The abilities of this
class of complexes to catalyze the electroreduction and photoreduction
of CO<sub>2</sub> were assessed for the first time. It is found that
only Re pyta complexes that have a first reduction wave with a peak
potential at ca. ā1.7 V vs SCE are active, producing CO as
the major product, together with small amounts of H<sub>2</sub> and
formic acid. The catalytic wave that is observed in the CVs is enhanced
by the addition of water or trifluoroethanol as a proton source. Long-term
controlled potential electrolysis experiments gave total Faradaic
yield close to 100%. In particular, functionalization of the triazolyl
ring with a 2,4,6-tri-<i>tert</i>-butylphenyl group provided
the catalyst with a remarkable stability
Rhenium Complexes Based on 2āPyridyl-1,2,3-triazole Ligands: A New Class of CO<sub>2</sub> Reduction Catalysts
A series of [ReĀ(N^N)Ā(CO)<sub>3</sub>(X)] (N^N = diimine and X = halide) complexes based on 4-(2-pyridyl)-1,2,3-triazole
(pyta) and 1-(2-pyridyl)-1,2,3-triazole (tapy) diimine ligands have
been prepared and electrochemically characterized. The first ligand-based
reduction process is shown to be highly sensitive to the nature of
the isomer as well as to the substituents on the pyridyl ring, with
the peak potential changing by up to 700 mV. The abilities of this
class of complexes to catalyze the electroreduction and photoreduction
of CO<sub>2</sub> were assessed for the first time. It is found that
only Re pyta complexes that have a first reduction wave with a peak
potential at ca. ā1.7 V vs SCE are active, producing CO as
the major product, together with small amounts of H<sub>2</sub> and
formic acid. The catalytic wave that is observed in the CVs is enhanced
by the addition of water or trifluoroethanol as a proton source. Long-term
controlled potential electrolysis experiments gave total Faradaic
yield close to 100%. In particular, functionalization of the triazolyl
ring with a 2,4,6-tri-<i>tert</i>-butylphenyl group provided
the catalyst with a remarkable stability
Single-Step versus Stepwise Two-Electron Reduction of Polyarylpyridiniums: Insights from the Steric Switching of Redox Potential Compression
Contrary to 4,4ā²-dipyridinium (i.e., archetypal
methyl viologen),
which is reduced by two single-electron transfers (stepwise reduction),
the 4,1ā²-dipyridinium isomer (so-called āhead-to-tailā
isomer) undergoes two electron transfers at apparently the same potential
(single-step reduction). A combined theoretical and experimental study
has been undertaken to establish that the latter electrochemical behavior,
also observed for other polyarylpyridinium electrophores, is due to
potential compression originating in a large structural rearrangement.
Three series of branched expanded pyridiniums (EPs) were prepared: <i>N</i>-aryl-2,4,6-triphenylpyridiniums (Ar-<b>TP</b>), <i>N</i>-aryl-2,3,4,5,6-pentaphenylpyridiniums (Ar-<b>XP</b>), and <i>N</i>-aryl-3,5-dimethyl-2,4,6-triphenylpyridinium
(Ar-<b>DMTP</b>). The intramolecular steric strain was tuned
via <i>N</i>-pyridinio aryl group (Ar) phenyl (Ph), 4-pyridyl
(Py), and 4-pyridylium (qPy) and their bulky 3,5-dimethyl counterparts,
xylyl (Xy), lutidyl (Lu), and lutidylium (qLu), respectively. Ferrocenyl
subunits as internal redox references were covalently appended to
representative electrophores in order to count the electrons involved
in EP-centered reduction processes. Depending on the steric constraint
around the <i>N</i>-pyridinio site, the two-electron reduction
is single-step (Ar = Ph, Py, qPy) or stepwise (Ar = Xy, Lu, qLu).
This steric switching of the potential compression is accurately accounted
for by ab initio modeling (Density Functional Theory, DFT) that proposes
a mechanism for pyramidalization of the N<sub>pyridinio</sub> atom
coupled with reduction. When the hybridization change of this atom
is hindered (Ar = Xy, Lu, qLu), the first reduction is a one-electron
process. Theory also reveals that the single-step two-electron reduction
involves couples of redox isomers (electromers) displaying both the
axial geometry of native EPs and the pyramidalized geometry of doubly
reduced EPs. This picture is confirmed by a combined UVāvisāNIR
spectroelectrochemical and time-dependent DFT study: comparison of
in situ spectroelectrochemical data with the calculated electronic
transitions makes it possible to both evidence the distortion and
identify the predicted electromers, which play decisive roles in the
electron-transfer mechanism. Last, this mechanism is further supported
by in-depth analysis of the electronic structures of electrophores
in their various reduction states (including electromeric forms)