Chiara Milanese

Synthesis, Characterization and Antibacterial Activity against Gram Positive and Gram Negative Bacteria of Biomimetically Coated Silver Nanoparticles

In the present work, we describe a simple procedure to produce biomimetically coated silver nanoparticles (Ag NPs), based on the postfunctionalization and purification of colloidal silver stabilized by citrate. Two biological capping agents have been used (cysteine Cys and glutathione GSH). The composition of the capped colloids has been ascertained by different techniques and antibacterial tests on GSH-capped Ag NPs have been conducted under physiological conditions, obtaining values of Minimum Inhibitory Concentration (MIC) of 180 and 15 μg/mL for Staphylococcus aureus and Escherichia coli, respectively. The antibacterial activity of these GSH capped NPs can be ascribed to the direct action of metallic silver NPs, rather than to the bulk release of Ag(+).

Reactive growth of niobium silicides in bulk diffusion couples

Abstract The diffusion-controlled growth of niobium silicides (NbSi 2 and Nb 5 Si 3 ) was studied in Nb/Si and Nb/NbSi 2 bulk diffusion couples annealed at 1200–1350 °C for 2–24 h. Both compounds were found to grow as parallel layers, according to the parabolic rate law. The concept of the integrated diffusion coefficient is used to describe the growth kinetics of the two silicides. The corresponding activation energy is 263 kJ/mol for Nb 5 Si 3 and 304 kJ/mol for NbSi 2 . The activation energy (in eV) scales as 0.98 T m (K)/1000 for Nb 5 Si 3 and as 1.4 T m (K)/1000 for NbSi 2 in agreement with the general behavior observed for many transition metal silicides. The position of the Kirkendall plane inside the Nb 5 Si 3 layer developed in Nb/NbSi 2 couples indicates that, in the present temperature range, the diffusion of Si in Nb 5 Si 3 is considerably faster than that of Nb.

Reactive diffusion in the system vanadium–silicon

Abstract The diffusion-controlled growth of vanadium silicides (V 3 Si, V 5 Si 3 , V 6 Si 5 , VSi 2 ) was studied on bulk V–Si diffusion couples annealed for 2–36 h at 1150–1390°C. The layer growth kinetics was parabolic for all of the silicides. Only at 1150 and 1200°C was an induction period observed before the formation of a continuous V 6 Si 5 layer. The parabolic growth constants of the II kind for the exclusive growth of each silicide from the adjacent phases were calculated from the parabolic constants of the I kind measured on the V–Si diffusion couples. The rate constants of the II kind were in turn related to the diffusion properties of the silicides. As a result, the interdiffusion coefficient, taking into account the diffusion of both elements, was obtained for each phase. The resulting activation energies were 240 kJ mol −1 for V 3 Si, 250 kJ mol −1 for V 5 Si 3 and 190 kJ mol −1 for VSi 2 . The activation energies scale well with the melting point of the compounds. For V 6 Si 5 , the activation energy is strongly dependent on the set of thermodynamic data used in the calculation owing to the uncertainty in the decomposition temperature of this phase.

Combustion synthesis of mechanically activated powders in the Nb–Si system

The effect of the mechanical activation of the reactants on the self-propagating high-temperature synthesis (SHS) of niobium silicides was investigated. SHS experiments were performed on reactant powder blends of composition Nb:Si = 1:2 and Nb:Si = 5:3 pretreated for selected milling times. A self-sustaining reaction could be initiated when a sufficiently long milling time was employed. At short milling times, the reactions self-extinguished or propagated in an unsteady mode. Combustion peak temperature, wave velocity, and product composition were markedly influenced by the length of the milling treatment. Single-phase products could be obtained for sufficiently long milling times. Observation of microstructural evolution in quenched reactions together with isothermal experiments allowed clarification of the mechanism of the combustion process and the role played by the mechanical activation of the reactants.

Field activated combustion synthesis of the silicides of vanadium

Abstract The synthesis of vanadium silicides was investigated using the field-activated combustion synthesis technique. For all V–Si compounds, self-sustaining combustion reactions could be obtained when fields above a threshold value were imposed. Monophasic products were obtained only for the starting compositions V:Si=l:2 and V:Si=5:3. For all other compositions the reaction produced a polyphasic mixture. No significant variation of phase composition was observed with an increase in field strength. In contrast with other systems, the field was seen to have a weak effect on the combustion macrokinetic parameters. This was interpreted on the basis of the large electrical conductivity of the reaction products, driving a large part of the electric flux away from the reaction front. The reaction mechanism was investigated through the use of quenching experiments. Only the VSi 2 and V 5 Si 3 phases were observed in the leading edge of the combustion front, with the other phases forming from solid–solid interactions in the afterburn. These results have been compared with observations relative to the mechanism of silicides formation in isothermal solid–solid and solid–liquid diffusion couples.

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 poly(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 T = 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.

CH3NH3SnxPb1–xBr3 Hybrid Perovskite Solid Solution: Synthesis, Structure, and Optical Properties

We report the synthesis and characterization of a MASnxPb1-xBr3 (MA = methylammonium; nominal x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, 1) solid solution. The original synthetic method developed allowed one to obtain single-phase materials with homogeneous Sn/Pb distribution. All of the samples prepared are cubic, and the unit cell linearly decreases with increasing x value. The optical response indicates a linear trend (Vegards law) of the band gap with increasing Sn content from 2.20 eV (x = 0) to 1.33 eV (x = 1), thus extending light absorption into the near-IR.

Silver nanoparticles synthesized and coated with pectin: An ideal compromise for anti-bacterial and anti-biofilm action combined with wound-healing properties.

The synthesis of Ag nanoparticles from Ag+ has been investigated, with pectin acting both as reductant and coating.∼100% Ag+ to Ag(0) one-pot conversion was obtained, yielding p-AgNP, i.e. an aqueous solution of pectin-coated spherical Ag nanoparticles (d=8.0±2.6nm), with a<1ppm concentration of free Ag+ cation. Despite the low free Ag+ concentration and low Ag+ release with time, the nature of the coating allows p-AgNP to exert excellent antibacterial and antibiofilm actions, comparable to those of ionic silver, tested on E. coli (Gram-) and S. epidermidis (Gram+) both on planctonic cells and on pre- and post-biofilm formation conditions. Moreover, p-AgNP were tested on fibroblasts: not only p-AgNP were found to be cytocompatible but also revealed capable of promoting fibroblasts proliferation and to be effective for wound healing on model cultures. The antibacterial activity and the wound healing ability of silver nanoparticles are two apparently irreconcilable properties, as the former usually requires a high sustained Ag+ release while the latter requires low Ag+ concentration. p-AgNP represents an excellent compromise between opposite requirements, candidating as an efficient medication for repairing wounds and/or to treat vulnerable surgical site tissues, including the pre-treatment of implants as an effective prophylaxis in implant surgery.

Radiation-induced grafting of carbon nanotubes on HPLC silica microspheres: theoretical and practical aspects

Multi-walled carbon nanotubes (MWCNTs) were grafted for the first time by γ-radiation onto silica microspheres in the presence of polybutadiene (PB) as the linking agent, obtaining a novel hybrid material with chromatographic properties, with an alternative approach to the existing procedures. The synthesis involves the one-pot γ-radiation-induced grafting of MWCNTs onto silica microspheres in the presence of PB as a linking agent. PB also serves as a coating layer of the silica particles, to which MWCNTs are anchored through stable chemical bonds formed via radical chain reaction with the polymer. The product (MWCNT-PB-modified silica) resulted in MWCNT bundles interlaying the silica particles which acted as a support and as a spacer. This new material highlights the unquestionable properties of CNTs also when grafted in a composite, thus allowing the disposition of a more robust material whose properties are still related to the nanotube structure. The grafting was confirmed by Raman spectroscopy. The surface area, determined by BET isotherms, resulted in 132 m(2) g(-1), about 34% lower than that of pure silica, pointing to the cross-linking effect of PB in the silica matrix. The evaluation of MWCNT-PB-modified silica as a LC stationary phase was performed by separation of aromatics, with satisfactory resolution and reproducibility, while structural selectivity was proved by isomer separation. A good resolution was obtained also for acid/basic compounds as barbiturates. A comparison with a commercial C18 sorbent highlighted the advantage in using the CNT column for separating aromatic hydrocarbons. Control experiments on the PB-coated silica column proved the key role of MWCNTs in the chromatographic performance.

Preparation and characterization of carprofen co-crystals

Carprofen co-crystals with selected co-formers were prepared by solvent evaporation and wet/dry grinding methods. Their effective formation was investigated by thermal analysis, FT-IR, X-ray single crystal and powder diffraction and SEM-EDS. This last technique has been applied for the first time to co-crystals since it provides unambiguous confirmation of co-crystal formation. Among the investigated co-formers we studied, only 4,4′-dipyridyl yields co-crystals. Two different crystal structures are obtained when the molar ratio of carprofen : 4,4′-dipyridyl is 2 : 1 (triclinic cell) and 1 : 1.5 (monoclinic cell). The asymmetric triclinic cell (Z = 2) contains two carprofen and two half 4,4′-dipyridyl moieties while the monoclinic cell (Z = 4) contains a single carprofen, and one and a half 4,4′-dipyridyl moieties. Several hydrogen-bond supramolecular synthons can be identified in the solid state. For both the 2 : 1 and 1 : 1.5 co-crystals, the main hydrogen-bond interaction consists of an O–H⋯N heterosynthon involving, as a donor, the COOH group of carprofen and, as a H-acceptor, the nitrogen of a 4,4′-dipyridyl molecule. The two co-crystals have characteristic FT-IR spectra and slightly different melting temperatures. X-Ray powder diffraction patterns of the 1 : 1 and 1 : 2 compositions reveal a mixture of phases, whose amount is quantified with Rietveld analysis.