6 research outputs found
EPR Characterization of Copper(II) Complexes of PAMAM-Py Dendrimers for Biocatalysis in the Absence and Presence of Reducing Agents and a Spin Trap
Polyamidoamine (PAMAM)
dendrimers at different generations (from
G2 to G6) were functionalized with pyridine (Py) groups at the external
surface, and their complexation behavior with CuÂ(II) at increasing
molar ratios between the ions and the Py groups was analyzed in the
absence and presence of reducing agents and a spin trap. These CuÂ(II)âdendrimer
complexes may be used as antitumor and antiamyloidogenesis drugs,
similarly to other CuÂ(II)âdendrimer complexes, and as biocatalysts.
Indeed, they have revealed to selectively catalyze molecular oxygen
reduction to generate reactive oxygen species (ROS). A computer-aided
electron paramagnetic resonance (EPR) study of these complexes allowed
us to identify different complexes by increasing the CuÂ(II)/Py molar
ratio for the different generations. Binuclear EPR-silent complexes
were formed at the highest generations. The differently complexed
CuÂ(II) ions showed a different capability to be reduced, starting
from the most exposed at the dendrimer surface bearing a stable CuÂ(II)âPy<sub>2</sub> coordination. CuÂ(II)âG5 showed peculiar structural
properties which probably favored its activity as biocatalyst. The
spin trap was able to capture hydroxyl radicals, which became clearly
EPR visible after all CuÂ(II) ions were reduced to CuÂ(I). This method
may be used as a platform to study interactions of CuÂ(II) in nanosized
macromolecules for biomedical purposes, mainly in biocatalysis involving
redox reactions and formation of ROS
Effect of Hydrogenated Cardanol on the Structure of Model Membranes Studied by EPR and NMR
Hydrogenated cardanol (HC) is known
to act as an antiobesity, promising
antioxidant, and eco-friendly brominating agent. In this respect,
it is important to find the way to transport and protect HC into the
body; a micellar structure works as the simplest membrane model and
may be considered a suitable biocarrier for HC. Therefore, it is useful
to analyze the impact of HC in the micellar structure and properties.
This study reports a computer aided electron paramagnetic resonance
(EPR) and <sup>1</sup>H NMR investigation of structural variations
of cetyltrimetylammonium bromide (CTAB) micelles upon insertion of
HC at different concentrations and pH variations. Surfactant spin
probes inserted in the micelles allowed us to get information on the
structure and dynamics of the micelles and the interactions between
HC and CTAB. The formation of highly packed HC-CTAB mixed micelles
were favored by the occurrence of both hydrophobic (chainâchain)
and hydrophilic (between the polar and charged lipid heads) interactions.
These interactions were enhanced by neutralization of the acidic HC
heads. Different HC localizations into the micelles and micellar structures
were identified by changing HC/CTAB relative concentrations and pH.
The increase in HC concentration generated mixed micelles characterized
by an increased surfactant packing. These results suggested a rod-like
shape of the mixed micelles. The increase in pH promoted the insertion
of deprotonated HC into less packed micelles, favored by the electrostatic
headâhead interactions between CTAB and deprotonated-HC surfactants
Effect of Hydrogenated Cardanol on the Structure of Model Membranes Studied by EPR and NMR
Hydrogenated cardanol (HC) is known
to act as an antiobesity, promising
antioxidant, and eco-friendly brominating agent. In this respect,
it is important to find the way to transport and protect HC into the
body; a micellar structure works as the simplest membrane model and
may be considered a suitable biocarrier for HC. Therefore, it is useful
to analyze the impact of HC in the micellar structure and properties.
This study reports a computer aided electron paramagnetic resonance
(EPR) and <sup>1</sup>H NMR investigation of structural variations
of cetyltrimetylammonium bromide (CTAB) micelles upon insertion of
HC at different concentrations and pH variations. Surfactant spin
probes inserted in the micelles allowed us to get information on the
structure and dynamics of the micelles and the interactions between
HC and CTAB. The formation of highly packed HC-CTAB mixed micelles
were favored by the occurrence of both hydrophobic (chainâchain)
and hydrophilic (between the polar and charged lipid heads) interactions.
These interactions were enhanced by neutralization of the acidic HC
heads. Different HC localizations into the micelles and micellar structures
were identified by changing HC/CTAB relative concentrations and pH.
The increase in HC concentration generated mixed micelles characterized
by an increased surfactant packing. These results suggested a rod-like
shape of the mixed micelles. The increase in pH promoted the insertion
of deprotonated HC into less packed micelles, favored by the electrostatic
headâhead interactions between CTAB and deprotonated-HC surfactants
Copper(II) Complexes with 4âCarbomethoxypyrrolidone Functionalized PAMAM-Dendrimers: An EPR Study
The
internal flexibility and interacting ability of PAMAM-dendrimers
having 4-carbomethoxypyrrolidone-groups as surface groups (termed
Gn-Pyr), which may be useful for biomedical purposes, and ion traps
were investigated by analyzing the EPR spectra of their copperÂ(II)
complexes. Increasing amounts (with respect to the Pyr groups) of
copperÂ(II) gave rise to different signals constituting the EPR spectra
at room and low temperature corresponding to different coordinations
of Cu<sup>2+</sup> inside and outside the dendrimers. At low Cu<sup>2+</sup> concentrations, CuN<sub>4</sub> coordination involving the
DAB core is preferential for G3- and G5-Pyr, while G4-Pyr shows a
CuN<sub>3</sub>O coordination. CuN<sub>2</sub>O<sub>2</sub> coordination
into the external dendrimer layer was also contributing to G3- and
G4-Pyr spectra. The structures of the proposed copperâdendrimer
complexes were also shown. G4-Pyr displays unusual binding ability
toward CuÂ(II) ions. Mainly the remarkably low toxicity shown by G4-Pyr
and its peculiar binding ability leads to a potential use in biomedical
fields
EPR and Rheological Study of Hybrid Interfaces in GoldâClayâEpoxy Nanocomposites
With the aim to obtain new materials
with special properties to
be used in various industrial and biomedical applications, ternary
âgoldâclayâepoxyâ nanocomposites and their
nanodispersions were prepared using clay decorated with gold nanoparticles
(AuNPs), at different gold contents. Nanocomposites structure was
characterized by X-ray diffraction (XRD), scanning electron microscopy
(SEM), and transmission electron microscopy (TEM). Rheology and electron
paramagnetic resonance (EPR) techniques were used in order to evaluate
the molecular dynamics in the nanodispersions, as well as dynamics
at interfaces in the nanocomposites. The percolation threshold (i.e.,
the filler content related to the formation of long-range connectivity
of particles in the dispersed media) of the gold nanoparticles was
determined to be Ď<sub>p</sub> = 0.6 wt % at a fixed clay content
of 3 wt %. The flow activation energy and the relaxation time spectrum
illustrated the presence of interfacial interactions in the ternary
nanodispersions around and above the percolation threshold of AuNPs;
these interfacial interactions suppressed the global molecular dynamics.
It was found that below Ď<sub>p</sub> the free epoxy polymer
chains ratio dominated over the chains attracted on the gold surfaces;
thus, the rheological behavior was not significantly changed by the
presence of AuNPs. While, around and above Ď<sub>p</sub>, the
amount of the bonded epoxy polymer chains on the gold surface was
much higher than that of the free chains; thus, a substantial increase
in the flow activation energy and shift in the spectra to higher relaxation
times appeared. The EPR signals of the nanocomposites depended on
the gold nanoparticle contents and the preparation procedure thus
providing a fingerprint of the different nanostructures. The EPR results
from spin probes indicated that the main effect of the gold nanoparticles
above Ď<sub>p</sub>, was to form a more homogeneous, viscous
and polar clayâepoxy mixture at the nanoparticle surface. The
knowledge obtained from this study is applicable to understand the
role of interfaces in ternary nanocomposites with different combinations
of nanofiller
Self-Assembled Ligands Targeting TLR7: A Molecular Level Investigation
Toll-like
receptors (TLRs) are pattern recognition transmembrane
proteins that play an important role in innate immunity. In particular,
TLR7 plays a role in detecting nucleic acids derived from viruses
and bacteria. The huge number of pathologies in which TLR7 is involved
has led to an increasing interest in developing new compounds targeting
this protein. Several conjugation strategies were proposed for TLR7
agonists to increase the potency while maintaining a low toxicity.
In this work, we focus the attention on two promising classes of TLR7
compounds derived from the same pharmacophore conjugated with phospholipid
and polyethylene glycol (PEG). A multidisciplinary investigation has
been carried out by molecular dynamics (MD), dynamic light scattering
(DLS), electron paramagnetic resonance (EPR), and cytotoxicity assessment.
DLS and MD indicated how only the phospholipid conjugation provides
the compound abilities to self-assemble in an orderly fashion with
a maximal pharmacophore exposition to the solvent. Further EPR and
cytotoxicity experiments highlighted that phospholipid compounds organize
in stable aggregates and well interact with TLR7, whereas PEG conjugation
was characterized by poorly stable aggregates at the cells surface.
The methodological framework proposed in this study may be used to
investigate, at a molecular level, the interactions generally occurring
between aggregated ligands, to be used as drugs, and protein receptors