Ionic liquids as stationary phases in gas chromatography: Determination of chlorobenzenes in soils

The present research focuses on the evaluation of different ionic liquid (IL) stationary phases in gas chromatography. The different IL columns were evaluated in terms of peak resolution (R_s) and peak symmetry for the separation of the chlorobenzenes. The determination of chlorobenzenes in soil samples by means of the optimal IL stationary phase (SLB‐IL82) is proposed as an application. Soil pretreatment was based on a simplified quick, easy, cheap, effective, rugged, and safe extraction procedure and a large injection volume via a programed temperature vaporizer working in solvent vent mode. The retention time of the chlorobenzenes increased as the polarity of the IL column decreased. SLB‐IL82 is the stationary phase that provides the best values as regards R_s and asymmetry factor. Soil sample blanks were spiked with the analytes before subjecting the sample to the extraction process. The existence of a matrix effect was checked and the analytical characteristics of the method were determined in a fortified garden soil sample. The method provided good linearity, good repeatability and reproducibility values, and the LODs were in the 0.1–4.7 μg/kg range. Two fortified soil samples were applied to validate the proposed methodology.     

Solvent extraction with organophosphorus extractants in environmental samples: determination of cadmium(II) in natural water

In this work, Cd(II) extraction in natural waters by organophosphorus extractants as organic phase, as well as its back-extraction in an acidic media, has been studied. Cadmium extraction behavior at natural waters’ pH conditions (values in the range 7–8) was studied with two different extractants and co-ions, obtaining the highest extraction efficiency when using 0.1M Cyanex 272 in kerosene as organic phase and 0.1 M NO₃ ^? as co-ion. Once they were selected, the effect on the extraction efficiency of sample pH, buffer concentration, extraction time, Cyanex 272 concentration as well as back-extractant concentration, was studied. The presence of the main inorganic and organic ligands in the sample was also studied, observing that extraction efficiency was affected most significantly when chlorides were present, with a decrease of about 14%, proving negligible for the others. Under the selected conditions, spiked real samples were successfully analyzed.      

Paths to synchronization on complex networks

The understanding of emergent collective phenomena in natural and social systems has driven the interest of scientists from different disciplines during decades. Among these phenomena, the synchronization of a set of interacting individuals or units has been intensively studied because of its ubiquity in the natural world. In this Letter, we show how for fixed coupling strengths local patterns of synchronization emerge differently in homogeneous and heterogeneous complex networks, driving the process towards a certain global synchronization degree following different paths. The dependence of the dynamics on the coupling strength and on the topology is unveiled. This study provides a new perspective and tools to understand this emerging phenomena.     

Practical aspects of electron energy-loss spectroscopy (EELS) calculations using FEFF8

We discuss the application of the ab initio program FEFF8 to calculations of electron energy-loss spectroscopy (EELS), focusing in particular on core-loss spectra. FEFF8 is based on a self-consistent, real space multiple scattering formalism. We focus on issues relevant to practical simulations, including the construction of well-converged potentials, the treatment of inelastic losses and exchange-correlation potentials and the core-hole. We also discuss how to account for experimental conditions, for example, sample orientation and finite temperature effects such as Debye-Waller factors. Finally we discuss the interpretation of the spectra in terms of electronic structure and local projected density of states (LDOS). As an explicit example, we illustrate various features of the code by application to the ionization edges of GaN.     

Heterocyclic compounds as antiviral drugs: Synthesis,structure–activity relationship and traditional applications

A virus outbreak challenges the economic, medical, and public health infrastructure worldwide. More than one virus capable of triggering diseases have been identified per year since 1972, which requires the development of new ways of treatment and prevention, however, such processes are not rapid and easy. With the pandemic scenario experienced since early 2020, several drugs with well-known purposes have gained prominence, due to speculation of their use in the treatment against the new coronavirus. Among the main drugs studied, the vast majority contain a heterocyclic structure. In this review, we presented the traditional and efficient synthesis of 15 drugs that have been studied for the COVID-19 treatment, containing in their structure heterocycles like indole, quinoline, pyrimidone, tetrahydrofuran, pyrrolidine, triazole, pyridazine, pyrazole, pyrrolopyrimidine, azetidine, pyrrolotriazine, pyrazine, tetrahydropyran, benzofuran, spiroketal, and thiazole. Furthermore, we have shown the original applications, as well as their structure–activity relationship and what is their situation as a drug candidate against COVID-19. Thus, the objective was to consolidate the main synthetic and pharmacological aspects involving clinically developed heterocycles that at some point were presented as promising against SARS-CoV-2.     

New Ideas for Understanding the Structure and Magnetism in AgF2: Prediction of Ferroelasticity

In the search for new high-temperature superconductors, it has been proposed that there are strong similarities between the fluoroargentate AgF₂ and the cuprate La₂CuO₄. We explored the origin of the possible layered structure of AgF₂ by studying its parent high-symmetry phase and comparing these results with those of a seemingly analogous cuprate, CuF₂. Our findings first stress the large differences between CuF₂ and AgF₂. Indeed, the parent structure of AgF₂ is found to be cubic, naturally devoid of any layering, even though Ag²⁺ ions occupy trigonal sites that, nevertheless, allow the existence of a Jahn-Teller effect. The observed Pbca orthorhombic phase is found when the system is cooperatively distorted by a local E⊗e trigonal Jahn-Teller effect around the silver sites that creates both geometrical and magnetic layering. While the distortion implies that two Ag²⁺−F⁻ bonds increase their distance by 15 % and become softer, our simulations indicate that covalent bonding and interlayer electron hopping is strong, unlike the situation in cuprate superconductors, and that, in fact, exfoliation of individual planes might be a harder task than previously suggested. As a salient feature, these results prove that the actual magnetic structure in AgF₂ is a direct consequence of vibronic contributions involved in the Jahn-Teller effect. Finally, our findings show that, due to the multiple minima intrinsic to the Jahn-Teller energy surface, the system is ferroelastic, a property that is strongly coupled to magnetism in this argentate.     

The Photophysics and Photochemistry of Melanin- Like Nanomaterials Depend on Morphology and Structure

Melanin-like nanomaterials have found application in a large variety of high economic and social impact fields as medicine, energy conversion and storage, photothermal catalysis and environmental remediation. These materials have been used mostly for their optical and electronic properties, but also for their high biocompatibility and simplicity and versatility of preparation. Beside this, their chemistry is complex and it yields structures with different molecular weight and composition ranging from oligomers, to polymers as well as nanoparticles (NP). The comprehension of the correlation of the different compositions and morphologies to the optical properties of melanin is still incomplete and challenging, even if it is fundamental also from a technological point of view. In this minireview we focus on scientific papers, mostly recent ones, that indeed examine the link between composition and structural feature and photophysical and photochemical properties proposing this approach as a general one for future research.     

Optimized IR synchrotron beamline design

Synchrotron infrared beamlines are powerful tools on which to perform spectroscopy on microscopic length scales but require working with large bending‐magnet source apertures in order to provide intense photon beams to the experiments. Many infrared beamlines use a single toroidal‐shaped mirror to focus the source emission which generates, for large apertures, beams with significant geometrical aberrations resulting from the shape of the source and the beamline optics. In this paper, an optical layout optimized for synchrotron infrared beamlines, that removes almost totally the geometrical aberrations of the source, is presented and analyzed. This layout is already operational on the IR beamline of the Brazilian synchrotron. An infrared beamline design based on a SOLEIL bending‐magnet source is given as an example, which could be useful for future IR beamline improvements at this facility.     

Ab Initio Study on the Stability of NgnBe2N2, NgnBe3N2 and NgBeSiN2 Clusters

The global minima of Be₂N₂, Be₃N₂ and BeSiN₂ clusters are identified using a modified stochastic kick methodology. The structure, stability and bonding nature of these clusters bound to noble gas (Ng) atoms are studied at the MP2/def2‐QZVPPD level of theory. Positive Be?Ng bond dissociation energy, which gradually increases down Group 18 from He to Rn, indicates the bound nature of Ng atoms. All of the Ng‐binding processes are exothermic in nature. The Xe and Rn binding to Be₂N₂ and Be₃N₂ clusters and Ar?Rn binding to BeSiN₂ are exergonic processes at room temperature; however, for the lighter Ng atoms, lower temperatures are needed. Natural population analysis, Wiberg bond index computations, electron density analysis, and energy decomposition analysis are performed to better understand the nature of Be?Ng bonds.