Covalent radii revisited

A new set of covalent atomic radii has been deduced from crystallographic data for most of the elements with atomic numbers up to 96. The proposed radii show a well behaved periodic dependence that allows us to interpolate a few radii for elements for which structural data is lacking, notably the noble gases. The proposed set of radii therefore fills most of the gaps and solves some inconsistencies in currently used covalent radii. The transition metal and lanthanide contractions as well as the differences in covalent atomic radii between low spin and high spin configurations in transition metals are illustrated by the proposed radii set.     

Rapid white truffle headspace analysis by proton transfer reaction mass spectrometry and comparison with solid-phase microextraction coupled with gas chromatography/mass spectrometry

The gastronomic relevance and high price of white truffle are related mainly to its unique aroma. Here we evaluate, for the first time, the possibility of characterizing in a rapid and non-destructive way the aroma of white truffles based on proton transfer reaction mass spectrometry (PTR-MS). We indicate that anonymous PTR-MS fingerprinting allows sample classification and we also compare qualitatively and quantitatively PTR-MS data with measurements made by solid-phase microextraction gas chromatography (SPME-GC) of the same samples under the same conditions. PTR-MS fragmentation data of truffle-relevant compounds are also published here for the first time. Most of the sulfur-containing compounds detected by GC and relevant for white truffle aroma have a high positive correlation with single PTR-MS peaks. Our work indicates that, after preliminary comparison with GC data, PTR-MS is a new tool for the rapid, quantitative and non-invasive characterization of white truffle by direct headspace injection without any pre-concentration.     

Charge transfer complexes of dithioxamides with dihalogens as powerful reagents in the dissolution of noble metals

Commonly involved in the recovery/refining processes of noble metals (NMs), coordination chemistry is now required by new legislation to face requirements in the selection of ligands that must combine effectiveness with low environmental impact, in order to balance sustainability with economic development for conventional applications and for the recovery of NMs from secondary sources thus helping to convert Trash in Resource. In this paper, we review the properties of dihalogen/cyclic-dithioxamide adducts as a case-study to show how suitable complexes can provide innovation in the recovery processes of NMs from secondary sources and in the gold etching process in improving the reliability of microelectronic devices. These adducts, which do not show cytotoxicity, are capable of dissolving metal palladium and even gold in a one-step reaction and under mild conditions. In particular, Me₂dazdt·2I₂ (Me₂dazdt = N,N’-dimethyl-perhydrodiazepine-2,3-dithione) has proved to be the most effective in practical applications. It has been used in the palladium recovery from model spent three way catalysts (TWC). It selectively dissolved palladium, almost quantitatively, under mild conditions, even in a complex system such as an exhaust catalytic converter, a ceramic material that has undergone severe thermal and chemical stresses. Quite satisfactory results have also been obtained in gold recovery from selected WEEE (waste from electrical and electronic equipments) scrap and from deprocessing procedures for the failure analysis of microelectronic devices.     

Synthesis and biological evaluation of novel 9-heteroaryl substituted 7-chloro-4,5-dihydro-4-oxo-1,2,4-triazolo[1,5-a]quinoxaline-2-carboxylates (TQX) as (R,S)-2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA) receptor antagonists

In this paper, we report a study on some new 4,5-dihydro-4-oxo-1,2,4-triazolo[1,5-a]quinoxaline-2-carboxylate derivatives (TQXs), bearing a nitrogen-containing heterocycle at position-9, and designed as (R,S)-2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA) receptor antagonists. These compounds ensue from the structural modification of previously reported 8-heteroaryl-TQXs which were endowed with high affinity and selectivity for the AMPA receptor. All the newly synthesized compounds were biologically evaluated for their binding at the AMPA receptor. Gly/N-methyl-D-aspartic acid (NMDA) and kainic acid (KA) high-affinity binding assays were performed to assess the selectivity of the reported derivatives toward the AMPA receptor. This study produced some new TQXs which are less potent than the reference compounds, and endowed with a mixed AMPA and Gly/NMDA receptor binding affinity. To rationalize the experimental findings, a molecular modeling study was performed by docking some TQX derivatives to the AMPA receptor model.     

Retinal phototoxicity induced by hydrochlorothiazide after exposure to a UV tanning device

Abstract UV radiation is known to cause acute and chronic eye and skin damage. The present case report describes the occurrence of hydrochlorothiazide-induced retinal phototoxicity immediately after exposure to UV light emanated from a sunbed in a 40-year-old myopic woman. During the tanning session she had always worn UV protective eyewear, except for a few minutes when she took the protective goggles off to put her spectacles on to locate and turn the timer switch off. At baseline her visual acuity was 10/25 in OD and 10/80 in OS. Fundus examination revealed the presence of retinal lesions in both eyes. More specific tests confirmed the presence of a phototoxic macular damage. Hydrochlorothiazide was discontinued, and she was recommended to wear UV filtering glasses. Over the follow-up period (12 months), a slow and progressive visual acuity recovery in both eyes occurred. At the last check the visual acuity improvement was of about 60% from baseline in both eyes. Fundus examination showed only a juxtafoveal flat pigmented scar of the retinal pigment epithelium in both eyes, milder in OD. The constant rise in the number of sunbed users makes the knowledge of UV-related side effects a problem that cannot be postponed further. Awareness of the general public about the harmful effects of UV exposure must represent one of the leading preventive health strategies. Therefore, a careful analysis of the medical history before the admission to a sunbed session throughout a questionnaire could represent an economic and effective measure to avoid further cases of a phototoxic macular damage in patients taking photosensitizing compounds.     

Pristine and Al-doped hematite printed films as photoanodes of <Emphasis Type="Italic">p</Emphasis>-type dye-sensitized solar cells

We hereby propose a non-expensive method for the deposition of pure and Al-doped hematite photoanodes in the configuration of thin films for the application of dye-sensitized solar cells (DSSC). The electrodes have been prepared from hematite nanoparticles that were obtained by thermal degradation of a chemical precursor. The particles have been used in the preparation of a paste, suitable for both screen printing and doctor blade deposition. The paste was then spread on fluorine-doped tin oxide (FTO) to obtain porous hematite electrodes. The electrodes have been sensitized using N3 and D5 dyes and were characterized through current/voltage curves under simulated sun light (1 sun, AM 1.5) with a Pt counter electrode. Al-doping of hematite showed interesting changes in the physical and electrochemical characteristics of sensitized photoanodes since we could notice the growth of AlFe₂O₄ (hercynite) as a secondary crystal phase into the oxides obtained by firing the mixtures of two chemical precursors at different molar ratios. Pure and Al-doped hematite electrodes have been used in a complete n-type DSSCs. The kinetics of charge transfer through the interface dye/electrolyte was studied and compared to that of a typical p-type DSSC based on NiO photocathodes sensitized with erythrosine B. The results suggest a potential application of both Fe₂O₃ and Fe₂O₃/AlFe₂O₄ as photoanodes of a tandem DSSC.     

Observational Aspects of Magnetic Reconnection at the Earth’s Magnetosphere

Magnetic field reconnection has shown to be the dominant process in the solar wind-Earth’s magnetosphere interaction. It enables mass, momentum, and energy exchange between different plasma regimes, and it is regarded as an efficient plasma acceleration and heating mechanism. Reconnection has been observed to occur in laboratory plasmas, at planetary magnetospheres in our Solar System, and the Sun. In this work, we focus on analyzing the characteristics of magnetic reconnection at the Earth’s magnetosphere according to spaceborne observations in the vicinity of our planet. Firstly, the locations where magnetic field reconnection are expected to occur within the vast magnetospheric region are addressed, and is shown how they are influenced by changes in the interplanetary magnetic field direction. The main magnetic field and plasma signatures of magnetic reconnection are discussed from both theoretical and observational points of view. Spacecraft observations of ion inertial length scale reconnection are also presented.     

Vibrational Quenching in Near-Infrared Emitting Lanthanide Complexes: A Quantitative Experimental Study and Novel Insights

Two series of novel NIR-emissive complexes of Nd³⁺, Sm³⁺, Er³⁺ and Yb³⁺ with two different β-diketonate ligands (L₁=4,4,4-trifluoro-1-phenyl-1,3-butadione and L₂=4,4,4-trifluoro-1-(4-chlorophenyl)-1,3-butadione) are reported. The neutral triphenylphosphine oxide (tppo) ligand was used to replace coordinated water molecules in the first coordination sphere of the as-obtained [Ln(L₁₍₂₎)₃(H₂O)₂] complexes to afford water-free [Ln(L₁₍₂₎)₃(tppo)₂] molecular species. Upon replacement of water molecules by tppo units, the NIR emission lifetimes of the Nd³⁺, Er³⁺and Sm³⁺complexes increase by about one order of magnitude up to values of ≈9, 8 and 113 ms while Yb³⁺ complexes reach intrinsic quantum yields as high as to Φ_Yb=6.5 %., which are remarkably high for fully hydrogenated complexes. Vibrational quenching by CH and OH oscillators has been quantitatively assessed by implementing the Förster's model of resonance energy transfer on the basis of experimental data. This study demonstrates that highly efficient NIR-emitting lanthanide complexes can be obtained with facile, cheap and accessible syntheses through a rational design.