13 research outputs found
Dicopper Double-Strand Helicates Held Together by Additional π–π Interactions
The
bis-bidentate ligand, obtained from Schiff base condensation
of <i>RR</i>-1,2-cyclohexanediamine and 8-naphthylmethoxyquinoline-2-carbaldehyde
(<b>L–L</b>), forms with [Cu<sup>I</sup>(MeCN)<sub>4</sub>]ÂClO<sub>4</sub> a double strand helicate complex, made especially
stable by the presence of four definite interstrand π–π
interactions involving a quinoline subunit and a naphthylmethoxy substituent
of the two strands. The [Cu<sup>I</sup><sub>2</sub>(<b>L–L</b>)<sub>2</sub>]<sup>2+</sup> complex, which does not decompose even
on excess addition of either <b>L–L</b> or Cu<sup>I</sup>, undergoes a two electron oxidation in MeCN, through two one-electron
fully reversible steps, separated by 260 mV, as shown by cyclic voltammetry
(CV) studies. The high stability of the mixed valence complex [Cu<sup>I</sup>Cu<sup>II</sup>(<b>L–L</b>)<sub>2</sub>]<sup>3+</sup> with respect to disproportionation to [Cu<sup>I</sup><sub>2</sub>(<b>L–L</b>)<sub>2</sub>]<sup>2+</sup> and [Cu<sup>II</sup><sub>2</sub>(<b>L–L</b>)<sub>2</sub>]<sup>4+</sup> is essentially due to a favorable electrostatic term. Cu<sup>II</sup> forms with <b>L–L</b> a stable species, with a 1:1
stoichiometric ratio, but, in the absence of crystallographic data,
it was impossible to assess whether it is of mono- or dinuclear nature.
However, CV studies on an MeCN solution containing equimolar amounts
of Cu<sup>II</sup> and <b>L–L</b> showed the presence
in the reduction scan of two fully reversible waves, separated by
about 250 mV, which indicated the presence in solution of a dicopperÂ(II)
double strand helicate complex, [Cu<sup>II</sup><sub>2</sub>(<b>L–L</b>)<sub>2</sub>]<sup>4+</sup>. This work demonstrates
that additional interstrand π–π interactions can
favor the formation of unusually stable dicopperÂ(I) and dicopperÂ(II)
helicate complexes
Exploiting Micelle-Driven Coordination To Evaluate the Lipophilicity of Molecules
We present a systematic study based on the calculation
of complexation
constants between a Zn-complex solubilized in Triton X-100 micellar
solutions and a series of linear mono- and dicarboxylic acids, under
physiological pH conditions, that allowed the evaluation of the lipophilicity
of these molecules. This empirical lipophilicity parameter describes
conveniently the partition of organic molecules between hydrophobic
microdomains and water. The results can be used to predict the lipophilicity
of molecules with similar structure and allows the distinction of
intrinsic contributions of the carboxylates and of the methylene groups
to the lipophilicity of the molecule
Fabrication of Inkjet-Printed Gold Nanostar Patterns with Photothermal Properties on Paper Substrate
Inkjet
printing technology has brought significant advances in
patterning various functional materials that can meet important challenges
in personalized medical treatments. Indeed, patterning of photothermal
active anisotropic gold nanoparticles is particularly promising for
the development of low-cost tools for localized photothermal therapy.
In the present work, stable inks containing PEGylated gold nanostars
(GNSs) were prepared and inkjet printed on a pigment-coated paper
substrate. A significant photothermal effect (Δ<i>T</i> ≅ 20 °C) of the printed patterns was observed under
near infrared (NIR) excitation of the localized surface plasmon resonance
(LSPR) of the GNS with low laser intensity (<i>I</i> ≅
0.2 W/cm<sup>2</sup>). Besides the pronounced photothermal effect,
we also demonstrated, as an additional valuable effect, the release
of a model fluorescent thiol-terminated Bodipy dye (BDP-SH) from the
printed gold surface, both under bulk heating and NIR irradiation.
These preliminary results suggest the way of the development of a
new class of low-cost, disposable, and smart devices for localized
thermal treatments combined with temperature-triggered drug release
Self-assembled monolayers of Prussian blue nanoparticles with photothermal effect
<p>A photo-responsive antibacterial surface was prepared grafting non-toxic Prussian blue nanoparticles on a functionalized glass surface. Colloidal Prussian blue was synthesized as nanoparticles with cubic shape and grafted on a polyamine-functionalized SiO<sub>2</sub> surface, obtaining a good coverage and a homogeneous distribution of the nanocubes. Irradiation of these samples in the so-called ‘bio-transparent window’ of the near-infrared allows to exert a triggered antibacterial effect.</p
Optical Method for Predicting the Composition of Self-Assembled Monolayers of Mixed Thiols on Surfaces Coated with Silver Nanoparticles
With a simple optical
method, based on UV–vis absorption spectra on glass slides,
it is possible to predict the composition of self-assembled monolayers
of mixed thiols, grafted on monolayers of silver nanoparticles. Glass
slides are modified with the layer-by-layer technique, first forming
a monolayer of mercaptopropyltrimethoxysilane, then grafting a monolayer
of silver nanoparticles on it. These surfaces are further coated by
single or mixed thiol monolayers, by dipping the slides in toluene
solutions of the chosen thiols. Exchange constants are calculated
for the competitive deposition between the colorless 1-dodecanethiol
or PEG5000 thiol and BDP-SH, with the latter being a thiol-bearing
molecule containing the strongly absorbing BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene)
moiety, synthesized on purpose. The constants are calculated by determining
the fraction of BDP-SH deposited on the surface from a solution with
a given molar fraction, directly measuring the absorption spectra
of BDP-SH on the slides. Then, the exchange constant for the competitive
deposition between 1-dodecanethiol and PEG5000 thiol is calculated
by combining their exchange constants with BDP-SH. This allows to
predict the fraction of the two colorless thiols coating the silver
nanoparticles slides obtained from a toluene solution with a given
molar fraction, for example, of PEG5000 thiol. The correctness of
the calculated surface fraction is verified by studying the coating
competition between 1-dodecanethiol and a PEG5000 thiol remotely modified
with a strongly absorbing fluorescein fragment
Antibacterial Activity of Glutathione-Coated Silver Nanoparticles against Gram Positive and Gram Negative Bacteria
In the present paper, we study the mechanism of antibacterial
activity
of glutathione (GSH) coated silver nanoparticles (Ag NPs) on model
Gram negative and Gram positive bacterial strains. Interference in
bacterial cell replication is observed for both cellular strains when
exposed to GSH stabilized colloidal silver in solution, and microbicidal
activity was studied when GSH coated Ag NPs are (i) dispersed in colloidal
suspensions or (ii) grafted on thiol-functionalized glass surfaces.
The obtained results confirm that the effect of dispersed GSH capped
Ag NPs (GSH Ag NPs) on Escherichia coli is more intense because it can be associated with the penetration
of the colloid into the cytoplasm, with the subsequent local interaction
of silver with cell components causing damages to the cells. Conversely,
for Staphylococcus aureus, since the
thick peptidoglycan layer of the cell wall prevents the penetration
of the NPs inside the cytoplasm, the antimicrobial effect is limited
and seems related to the interaction with the bacterial surfaces.
Experiments on GSH Ag NPs grafted on glass allowed us to elucidate
more precisely the antibacterial mechanism, showing that the action
is reduced because of GSH coating and the limitation of the translational
freedom of NPs
Thermal and Chemical Stability of Thiol Bonding on Gold Nanostars
The
stability of thiol bonding on the surface of star-shaped gold
nanoparticles was studied as a function of temperature in water and
in a set of biologically relevant conditions. The stability was evaluated
by monitoring the release of a model fluorescent dye, Bodipy-thiol
(BDP-SH), from gold nanostars (GNSs) cocoated with polyÂ(ethylene glycol)
thiol (PEG-SH). The increase in the BDP-SH fluorescence emission,
quenched when bound to the GNSs, was exploited to this purpose. A
maximum 15% dye release in aqueous solution was found when the bulk
temperature of gold nanostars solutions was increased to <i>T</i> = 42 °C, the maximum physiological temperature. This fraction
reduces 3–5% for temperatures lower than 40 °C. Similar
results were found when the temperature increase was obtained by laser
excitation of the near-infrared (NIR) localized surface plasmon resonance
of the GNSs, which are photothermally responsive. Besides the direct
impact of temperature, an increased BDP-SH release was observed upon
changing the chemical composition of the solvent from pure water to
phosphate-buffered saline and culture media solutions. Moreover, also
a significant fraction of PEG-SH was released from the GNS surface
due to the increase in temperature. We monitored it with a different
approach, that is, by using a coating of α-mercapto-ω-amino
PEG labeled with tetramethylrhodamine isothiocyanate on the amino
group, that after heating was separated from GNS by ultracentrifugation
and the released PEG was determined by spectrofluorimetric techniques
on the supernatant solution. These results suggest some specific limitations
in the use of the gold–thiolate bond for coating of nanomaterials
with organic compounds in biological environments. These limitations
come from the duration and the intensity of the thermal treatment
and from the medium composition and could also be exploited in biological
media to modulate the in vivo release of drugs
Temperature and pH Stimuli-Responsive System Delivers Location-Specific Antimicrobial Activity with Natural Products
Smart materials with controlled stimuli-responsive functions
are
at the forefront of technological development. In this work, we present
a generic strategy that combines simple components, physicochemical
responses, and easy fabrication methods to achieve a dual stimuli-responsive
system capable of location-specific antimicrobial cargo delivery.
The encapsulated system is fabricated by combining a biocompatible
inert polymeric matrix of poly(dimethylsiloxane) (PDMS) and a bioactive
cargo of saturated fatty acids. We demonstrate the effectiveness of
our approach to deliver antimicrobial activity for the model bacteria Escherichia coli. The system responds to two control
variables, temperature and pH, delivering two levels of antimicrobial
response under distinct combinations of stimuli: one response toward
the planktonic media and another response directly at the surface
for sessile bacteria. Spatially resolved Raman spectroscopy alongside
thermal and structural material analysis reveals that the system not
only exhibits ON/OFF states but can also control relocation and targeting
of the active cargo toward either the surface or the liquid media,
leading to different ON/OFF states for the planktonic and sessile
bacteria. The approach proposed herein is technologically simple and
scalable, facing low regulatory barriers within the food and healthcare
sectors by using approved components and relying on fundamental chemical
processes. Our results also provide a proof-of-concept platform for
the design and easy fabrication of delivery systems capable of operating
as Boolean logic gates, delivering different responses under different
environmental conditions
A Molecular Thermometer for Nanoparticles for Optical Hyperthermia
We
developed an all-optical method to measure the temperature on
gold (nanorods and nanostars) and magnetite nanoparticles under near-infrared
and radiofrequency excitation by monitoring the excited state lifetime
of Rhodamine B that lies within ≅20 nm from the nanoparticle
surface. We reached high temperature sensitivity (0.029 ± 0.001
ns/°C) and low uncertainty (±0.3 °C). Gold nanostars
are ≅3 and ≅100 times more efficient than gold nanorods
and magnetite nanoparticles in inducing localized hyperthermia
Gold Branched Nanoparticles for Cellular Treatments
Under the action of near-infrared radiation, shape anisotropic
gold nanoparticles emit two-photon luminescence and release heat.
Accordingly, they have been proposed for imaging, photothermal therapies
and thermo-controlled drug delivery. In all these applications particular
care must be given to control the nanoparticle – cell interaction
and the thermal efficiency of the nanoparticles, while minimizing
their intrinsic cytotoxicity. We present here the characterization
of the cell interaction of newly developed branched gold nanostars,
obtained by laurylsulfobetaine-driven seed-growth synthesis. The study
provides information on the size distribution, the shape anisotropy,
the cellular uptake and cytotoxicity of the gold nanostars as well
as their intracellular dynamic behavior by means of two-photon luminescence
imaging, fluorescence correlation spectroscopy and particle tracking.
The results show that the gold nanostars are internalized as well
as the widely used gold nanorods and are less toxic under prolonged
treatments. At the same time they display remarkable two-photon luminescence
and large extinction under polarized light in the near-infrared region
of the spectrum, 800–950 nm. Gold nanostars appear then a valuable
alternative to other elongated or in-homogeneous nanoparticles for
cell imaging