Harnessing the Liquid‐Phase Exfoliation of Graphene Using Aliphatic Compounds: A Supramolecular Approach

The technological exploitation of the extraordinary properties of graphene relies on the ability to achieve full control over the production of a high‐quality material and its processing by up‐scalable approaches in order to fabricate large‐area films with single‐layer or a few atomic‐layer thickness, which might be integrated in working devices. A simple method is reported for producing homogenous dispersions of unfunctionalized and non‐oxidized graphene nanosheets in N‐methyl‐2‐pyrrolidone (NMP) by using simple molecular modules, which act as dispersion‐stabilizing compounds during the liquid‐phase exfoliation (LPE) process, leading to an increase in the concentration of graphene in dispersions. The LPE‐processed graphene dispersion was shown to be a conductive ink. This approach opens up new avenues for the technological applications of this graphene ink as low‐cost electrodes and conducting nanocomposite for electronics.     

Quantification of cyclic dipeptides from cultures of Lactobacillus brevis R2Δ by HRGC/MS using stable isotope dilution assay

Lactic acid bacteria (LAB) play an important role as natural preservatives in fermented food and beverage systems, reducing the application of chemical additives. Thus, investigating their antifungal compounds, such as cyclic dipeptides, has gained prominence. Previous research has primarily focussed on isolation of these compounds. However, their precise quantification will provide further information regarding their antifungal performance in a complex system. To address this, deuterated labelled standards of the cyclic dipeptides cyclo(Leu-Pro), cyclo(Pro-Pro), cyclo(Met-Pro) and cyclo(Phe-Pro) were synthesized, and stable isotope dilution assays were developed, enabling an accurate quantification of cyclo(Leu-Pro), cyclo(Pro-Pro), cyclo(Met-Pro) and cyclo(Phe-Pro) in MRS-broth and wort. Quantitative results showed that, in the Lactobacillus brevis R2Δ fermented MRS-broth, the concentrations of cyclo(Leu-Pro), cyclo(Pro-Pro) and cyclo(Phe-Pro) were significantly higher (P?<?0.05), than in wort for cyclo (Leu-Pro) when compared with their controls. This indicates that the formation of these three cyclic dipeptides is related to L. brevis R2Δ metabolism. Furthermore, this represents the first report of cyclic dipeptides quantification using stable isotope dilution assays in LAB cultures both in vitro and in a food system.     

Drug–Polymer Interactions in Hydrogel‐based Drug‐Delivery Systems: An Experimental and Theoretical Study

In drug‐delivery systems, drug transport is a key step, but the interpretation of the transport mechanism is still controversial. Here, we investigated a promising hydrogel library loaded with the anticonvulsant drug ethosuximide (ESM). The self‐diffusion coefficient of ESM was measured using two methods: a direct and advanced measurement with a pulsed field gradient spin‐echo (PFGSE) method, using an NMR spectrometer equipped with high‐resolution magic angle spinning (HR‐MAS) probe, and an indirect one based on fitting in vitro drug‐delivery data. Starting from the experimental data a mathematical model without fitted parameters was developed and all the phenomena involved, that is, adsorption and diffusion, were considered. At low drug concentrations, adsorption prevails and consequently the diffusivity in the gels is lower than that in water. At high drug concentrations, where all adsorption sites are saturated, the diffusion in the gels is similar to that in a water solution. This study may pave the way for better device design.     

Development of lasers for spaceborne Doppler wind lidar applications

During the course of years, various activities have been carried out at CESI (incorporating now former CISE Innovative Technologies labs) on Doppler wind lidar (DWL) for spaceborne applications. Historically, the first activities were related to the development of a CO₂ laser transmitter for the DWL development with coherent (heterodyne) detection technique. More recently, efforts have been directed to the technology of neodymium solid-state laser transmitter with direct detection (edge technique). Presently, a work in course involves a team of European firms including CESI and is devoted to the breadboarding of a diode-pumped UV laser for DWL application.     

Amorphization and recrystallization of ion implanted Si nanocrystals probed through their luminescence properties

In this paper the amorphization of Si nanocrystals (nc) by ion beam irradiation and the subsequent recrystallization are investigated in detail. The luminescence properties of Si nanocrystals embedded within a SiO₂ matrix are used as a probe of the damaging effects generated by high-energy ion beam irradiation. Samples have been irradiated with 2 MeV Si⁺ ions at different doses, in the range between 1×10⁹ and 1×10¹⁶ cm⁻². By increasing the ion dose, the nc-related photoluminescence (PL) strongly decreases after a critical dose value. It is shown that the lifetime quenching alone cannot quantitatively explain the much stronger PL drop, but the total number of emitting centers has to diminish too. Moreover, we studied the recovery of the amorphized Si nc by performing thermal annealings. It is demonstrated that the recovery of the PL properties of completely amorphized Si nc is characterized by a single activation energy, whose value is 3.4 eV. Actually, this energy is associated to the transition between the amorphous and the crystalline phases of each Si grain. The recrystallization kinetics of Si nanostructures is demonstrated to be very different from that of a bulk system.     

Erbium-doped Si nanocrystals: optical properties and electroluminescent devices

In the last decade, a strong effort has been devoted towards the achievement of efficient light emission from silicon. Among the different approaches, rare-earth doping and quantum confinement in Si nanostructures have shown great potentialities. In the present work, the synthesis and properties of low-dimensional silicon structures in SiO₂ will be analyzed. All of these structures present a strong room temperature optical emission, tunable in the visible by changing the crystal size. Moreover, Si nanocrystals (nc) embedded in SiO₂ together with Er ions show a strong coupling with the rare earth. Indeed each Si nc absorbs energy which is then preferentially transferred to the nearby Er ions. The signature of this interaction is the strong increase of the excitation cross section for an Er ion in the presence of Si nc with respect to a pure oxide host. We will show the properties of Er-doped Si nc embedded within Si/SiO₂ Fabry–Pérot microcavities. Very narrow, intense and highly directional luminescence peaks can be obtained. Moreover, the electroluminescence (EL) properties of Si nc and Er-doped Si nc in MOS devices are investigated. It is shown that an efficient carrier injection at low voltages and quite intense room temperature EL signals can be achieved, due to the sensitizing action of Si nc for the rare earth. These data will be presented and the impact on future applications discussed.     

Artificial Molecular Ratchets: Tools Enabling Endergonic Processes

Non-equilibrium chemical systems underpin multiple domains of contemporary interest, including supramolecular chemistry, molecular machines, systems chemistry, prebiotic chemistry, and energy transduction. Experimental chemists are now pioneering the realization of artificial systems that can harvest energy away from equilibrium. In this tutorial Review, we provide an overview of artificial molecular ratchets: the chemical mechanisms enabling energy absorption from the environment. By focusing on the mechanism type—rather than the application domain or energy source—we offer a unifying picture of seemingly disparate phenomena, which we hope will foster progress in this fascinating domain of science.