The relevance of point defects in studying silica-based materials from bulk to nanosystems

The macroscopic properties of silica can be modified by the presence of local microscopic modifications at the scale of the basic molecular units (point defects). Such defects can be generated during the production of glass, devices, or by the environments where the latter have to operate, impacting on the devices’ performance. For these reasons, the identification of defects, their generation processes, and the knowledge of their electrical and optical features are relevant for microelectronics and optoelectronics. The aim of this manuscript is to report some examples of how defects can be generated, how they can impact device performance, and how a defect species or a physical phenomenon that is a disadvantage in some fields can be used as an advantage in others

Structure of the FeBTC Metal\u2013Organic Framework: A Model Based on the Local Environment Study

The local environment of iron in FeBTC, a metal organic framework commercially known as Basolite F300, is investigated combining XANES and EXAFS studies of the iron K-edge. The building block of the FeBTC can be described as an iron acetate moiety. Dehydration induces a change in the coordination of the first shell while preserving the network. We propose that the local structure around Fe atoms does not undergo a rearrangement, thus, leading to the formation of an open site. The analysis conveys that the FeBTC is a disordered network of locally ordered blocks

Investigation by raman spectroscopy of the decomposition process of HKUST-1 upon exposure to air

We report an experimental investigation by Raman spectroscopy of the decomposition process of Metal-Organic Framework (MOF) HKUST-1 upon exposure to air moisture (T=300 K, 70% relative humidity). The data collected here are compared with the indications obtained from a model of the process of decomposition of this material proposed in literature. In agreement with that model, the reported Raman measurements indicate that for exposure times longer than 20 days relevant irreversible processes take place, which are related to the occurrence of the hydrolysis of Cu-O bonds. These processes induce small but detectable variations of the peak positions and intensities of the main Raman bands of the material, which can be related to Cu-Cu, Cu-O, and O-C-O stretching modes. The critical analyses of these changes have permitted us to obtain a more detailed description of the process of decomposition taking place in HKUST-1 upon interaction with moisture. Furthermore, the reported Raman data give further strong support to the recently proposed model of decomposition of HKUST-1, contributing significantly to the development of a complete picture of the properties of this considerable deleterious effect

Sensing of transition metals by top-down carbon dots

Carbon quantum dots (CQDs) are a new class of carbon-rich materials with a range of unique optical and structural properties. They can be defined as carbon nanoparticles, with sizes in the range of 1–10 nm, displaying absorption and emission activities in the UV-VIS range. Depending on the structure, CQDs display a wide variability of properties, which provides the possibility of finely tuning them for several applications. The great advantages of CQDs are certainly the ease of synthesis, non-toxicity, and the strong interactions with the surrounding environment. Based on this, CQDs are especially promising as selective chemosensors. The present study reports on carbon quantum dots synthesized with a top-down (TD) approach, and characterized by different optical, spectroscopic, and morphological techniques to identify the selectivity for metal ions belonging to the first transition series. In particular, the study focuses on the interaction between two samples, namely TD and TDA, featuring different surface functionalization, and heavy metal ions. Their sensing towards Co2+, Cu2+, Fe3+, Zn2+, and Ni2+ has been tested by fluorescence (PL), steady state absorption spectroscopy, and time-resolved PL spectroscopy, in order to determine the fluorescence quenching. We found a PL quenching in the presence of concentrations of metal salts starting from 0.5 µM, and a selectivity towards the interacting ions, depending on CQDs’ surface features paving the way for their use for sensing

Time scales of epidemic spread and risk perception on adaptive networks

Incorporating dynamic contact networks and delayed awareness into a contagion model with memory, we study the spreading patterns of infectious diseases in connected populations. It is found that the spread of an infectious disease is not only related to the past exposures of an individual to the infected but also to the time scales of risk perception reflected in the social network adaptation. The epidemic threshold $p_{c}$ is found to decrease with the rise of the time scale parameter s and the memory length T, they satisfy the equation $p_{c} =\frac{1}{T}+ \frac{\omega T}{a^s(1-e^{-\omega T^2/a^s})}$. Both the lifetime of the epidemic and the topological property of the evolved network are considered. The standard deviation $\sigma_{d}$ of the degree distribution increases with the rise of the absorbing time $t_{c}$, a power-law relation $\sigma_{d}=mt_{c}^\gamma$ is found

A comparative study of top-down and bottom-up carbon nanodots and their interaction with mercury ions

We report a study of carbon dots produced via bottom-up and top-down routes, carried out through a multi-technique approach based on steady-state fluorescence and absorption, time-resolved fluorescence spectroscopy, Raman spectroscopy, infrared spectroscopy, and atomic force microscopy. Our study focuses on a side-to-side comparison of the fundamental structural and optical properties of the two families of fluorescent nanoparticles, and on their interaction pathways with mercury ions, which we use as a probe of surface emissive chromophores. Comparison between the two families of carbon dots, and between carbon dots subjected to different functionalization procedures, readily identifies a few key structural and optical properties apparently common to all types of carbon dots, but also highlights some critical differences in the optical response and in the microscopic mechanism responsible of the fluorescence. The results also provide suggestions on the most likely interaction sites of mercury ions at the surface of carbon dots and reveal details on mercury-induced fluorescence quenching that can be practically exploited to optimize sensing applications of carbon dots

Effects of mobility in a population of Prisoner's Dilemma players

We address the problem of how the survival of cooperation in a social system depends on the motion of the individuals. Specifically, we study a model in which Prisoner's Dilemma players are allowed to move in a two-dimensional plane. Our results show that cooperation can survive in such a system provided that both the temptation to defect and the velocity at which agents move are not too high. Moreover, we show that when these conditions are fulfilled, the only asymptotic state of the system is that in which all players are cooperators. Our results might have implications for the design of cooperative strategies in motion coordination and other applications including wireless networks.Comment: 4 pages with 4 figures. APS format. Final version to be published in PR

Streptomyces coelicolor Vesicles: Many Molecules to Be Delivered

Streptomyces coelicolor is a model organism for the study of Streptomyces, a genus of Gram-positive bacteria that undergoes a complex life cycle and produces a broad repertoire of bioactive metabolites and extracellular enzymes. This study investigated the production and characterization of membrane vesicles (MVs) in liquid cultures of S. coelicolor M145 from a structural and biochemical point of view; this was achieved by combining microscopic, physical and -omics analyses. Two main populations of MVs, with different sizes and cargos, were isolated and purified. S. coelicolor MV cargo was determined to be complex, containing different kinds of proteins and metabolites. In particular, a total of 166 proteins involved in cell metabolism/differentiation, molecular processing/transport, and stress response were identified in MVs, the latter functional class also being important for bacterial morpho-physiological differentiation. A subset of these proteins was protected from degradation following treatment of MVs with proteinase K, indicating their localization inside the vesicles. Moreover, S. coelicolor MVs contained an array of metabolites, such as antibiotics, vitamins, amino acids, and components of carbon metabolism. In conclusion, this analysis provides detailed information on S. coelicolor MVs under basal conditions and on their corresponding content, which may be useful in the near future to elucidate vesicle biogenesis and functions. IMPORTANCE Streptomycetes are widely distributed in nature and characterized by a complex life cycle that involves morphological differentiation. They are very relevant in industry because they produce about half of all clinically used antibiotics, as well as other important pharmaceutical products of natural origin. Streptomyces coelicolor is a model organism for the study of bacterial differentiation and bioactive molecule production. S. coelicolor produces extracellular vesicles that carry many molecules, such as proteins and metabolites, including antibiotics. The elucidation of S. coelicolor extracellular vesicle cargo will help us to understand different aspects of streptomycete physiology, such as cell communication during differentiation and response to environmental stimuli. Moreover, the capability of these vesicles for carrying different kinds of biomolecules opens up new biotechnological possibilities related to drug delivery. Indeed, decoding the molecular mechanisms involved in cargo selection may lead to the customization of extracellular vesicle content

Fluorescent Boron Oxide Nanodisks as Biocompatible Multi-messenger Sensors for Ultrasensitive Ni2+^{2+} Detection

Boron-based nanocomposites are very promising for a wide range of technological applications, spanning from microelectronics to nanomedicine. A large variety of B-based nanomaterials has been already observed, such as borospherene, B nanotubes and nanoparticles, and boron nitride nanoparticles. However, their fabrication usually involves toxic precursors or leads to very low yields or small boron atom concentration. In this work, we report the synthesis of nanometric B$_{2}$O$_{3}$ nanodisks, a family of nanomaterials with a quasi-2D morphology capable of intense fluorescence in the visible range. Such as boron-based nanomaterial, which we synthesized by pulsed laser ablation of a boron target, is water-dispersible and nontoxic, and displays a highly crystalline structure. Moreover, its bright blue photoluminescence is highly sensitive and selective for the presence of Ni$^{2+}$ ions in solution, down to extremely small concentrations in the picomolar range. The results are very promising in view of the use of such novel B$_{2}$O$_{3}$ nanodisks as ultrasensitive multi-messenger Ni$^{2+}$ nanosensors

Characterization of E'delta and triplet point defects in oxygen deficient amorphous silicon dioxide

We report an experimental study by electron paramagnetic resonance (EPR) of gamma ray irradiation induced point defects in oxygen deficient amorphous SiO2 materials. We have found that three intrinsic (E'gamma, E'delta and triplet) and one extrinsic ([AlO4]0) paramagnetic centers are induced. All the paramagnetic defects but E'gamma center are found to reach a concentration limit value for doses above 10^3 kGy, suggesting a generation process from precursors. Isochronal thermal treatments of a sample irradiated at 10^3 kGy have shown that for T>500 K the concentrations of E'gamma and E'delta centers increase concomitantly to the decrease of [AlO4]0. This occurrence speaks for an hole transfer process from [AlO4]0 centers to diamagnetic precursors of E' centers proving the positive charge state of the thermally induced E'gamma and E'delta centers and giving insight on the origin of E'gamma from an oxygen vacancy. A comparative study of the E'delta center and of the 10 mT doublet EPR signals on three distinct materials subjected to isochronal and isothermal treatments, has shown a quite general linear correlation between these two EPR signals. This result confirms the attribution of the 10 mT doublet to the hyperfine structure of the E'delta center, originating from the interaction of the unpaired electron with a nucleus of 29Si (I=1/2). Analogies between the microwave saturation properties of E'gamma and E'delta centers and between those of their hyperfine structures are found and suggest that the unpaired electron wave function involves similar Si sp3 hybrid orbitals; specifically, for the E'delta the unpaired electron is supposed to be delocalized over four such orbitals of four equivalent Si atoms.Comment: Approved for publication in Physical Review