Terras raras: aplicações industriais e biológicas

PMMA or PVDF films blended with β-diketonate tetrakis EuIII or TbIII complexes used as downshifting coatings of near-UV LEDs

Luminescent Ln^III complexes incorporated in polymeric films exhibit narrow emission bands and absorption within the near-UV/blue spectral range, and enhanced phostability, which qualify them to be explored for solid-state lighting. Herein, (C₂₆H₅₆N)[Eu(dbm)₄] and Na[Tb(acac)₄], (C₂₆H₅₆N⁺ = didodecyldimethylammonium, dbm^- =1,3-diphenyl-1,3-propanedionate, acac^- = acetylacetonate), were dispersed in PMMA or PVDF films to protect them from degradation, and the obtained blends were applied as downshifting coatings on near-UV emitter LEDs. Upon such excitation, both Eu^III and Tb^III complexes emit red or green light with absolute emission quantum yields of 6.4 and 99%, respectively. The complex amount within films influences the photophysical parameters due to multiphotonic deactivation, and formation of agglomerates. For the PMMA-based LED prototypes, the Ln^III emission is well-observed while for the PVDF ones, only a poor Ln^III emission is detected due to their opacity. Therefore, the PMMA-based systems are better candidates to be used as luminescent coatings of near-UV LEDs for solid-state lighting.

Acute toxicity of single and combined rare earth element exposures towards Daphnia similis

The increasing use of Rare Earth Elements (REE) in emerging technologies, medicine and agriculture has led to chronic aquatic compartment contamination. In this context, this aimed to evaluate the acute toxic effects of lanthanum (La), neodymium (Nd) and samarium (Sm), as both single and binary and ternary mixtures on the survival of the microcrustacean Daphnia similis. A metal solution medium with (MS) and without EDTA and cyanocobalamin (MSq) as chelators was employed as the assay dilution water to assess REE bioavailability effects. In the single exposure experiments, toxicity in the MS medium decreased following the order La > Sm > Nd, while the opposite was noted for the MSq medium, which was also more toxic than the MS medium. The highest MS toxicity was observed for the binary Nd + La (1:1) mixture (EC₅₀ 48 h of 11.57 ± 1.22 mg.L^-1) and the lowest, in the ternary Sm + La + Nd (2:2:1) mixture (EC₅₀ 48 h 41.48 ± 1.40 mg.L^-1). The highest toxicity in the MSq medium was observed in the single assays and in the binary Sm + Nd (1:1) mixture (EC₅₀ 48 h 10.60 ± 1.57 mg.L^-1), and the lowest, in the ternary Sm + La + Nd (1:2:2) mixture (EC₅₀ 48 h 36.76 ± 1.54 mg.L^-1). Concerning the MS medium, 75 % of interactions were additive, 19 % antagonistic, and 6 % synergistic. In the MSq medium, 56 % of interactions were synergistic and 44 % additive. The higher toxicity observed in the MSq medium indicates that the absence of chelators can increase the concentrations of more toxic free ions, suggesting that the MS medium should be avoided in REE assays. Additive interactions were observed in greater or equivalent amounts in both media and were independent of elemental mixture ratios. These findings improve the understanding of environmental REE effects, contributing to the establishment of future guidelines and ecological risk calculations.

Molecular Docking Study of Antibiotics, Anti-Inflammatory Drugs and [Eu(TTA)3⋅AMX] Complex as COVID-19 Biomarker through Interaction of Its Main Protease (Mpro)

Coronavirus Acute Respiratory Syndrome (SARS-CoV-2) is a very recent viral infection and has generated one of the world’s biggest problems of all time. There is no scientific evidence and clinical trials to indicate that possible therapies have shown results in suspected or confirmed patients other than the use of immunizations. Given the above, some substances are being studied to be applied to contain their spread and further damage. This work aims to perform an in silico study of amoxicillin, widely known as an antibiotic and used to prevent bacterial infections and a possible biomarker made from a complex with Europium (Eu). It was shown to have the ability to interact with the COVID-19 protein in Mpro protease as ligands. The study was conducted using the AutoDock Vina with Lamarckian genetic model algorithm (GA) combined with the estimation of grid-based energy in rigid and flexible conformation. Compared to affinity energy, amoxicillin presented [Formula: see text][Formula: see text]kcal/mol, which was better than its co-crystallized ligand in the study. The Europium complex, where its synthesis was also demonstrated in this work, presented energy of [Formula: see text][Formula: see text]kcal/mol with hydrogen bonds and possible color change when UV light was applied. For the choice of the best poses in the simulation, the neural network parameter, NNScore2, was used. It can be affirmed that this study is still introductory but promising both in the treatment and identification of the virus.

Novel Approaches of Nanoceria with Magnetic, Photoluminescent, and Gas-Sensing Properties

The modification of CeO₂ with rare-earth elements opens up a wide range of applications as biomedical devices using infrared emission as well as magnetic and gas-sensing devices, once the structural, morphological, photoluminescent, magnetic, electric, and gas-sensing properties of these systems are strongly correlated to quantum electronic transitions between rare-earth f-states among defective species. Quantitative phase analysis revealed that the nanopowders are free from secondary phases and crystallize in the fluorite-type cubic structure. Magnetic coercive field measurements on the powders indicate that the substitution of cerium with lanthanum (8 wt %), in a fluorite-type cubic structure, created oxygen vacancies and led to a decrease in the fraction of Ce species in the 3+ state, resulting in a stronger room-temperature ferromagnetic response along with high coercivity (160 Oe). In addition to the magnetic and photoluminescent behavior, a fast response time (5.5 s) was observed after CO exposure, indicating that the defective structure of ceria-based materials corresponds to the key of success in terms of applications using photoluminescent, magnetic, or electrical behaviors.

Cysteine-Functionalized Chitosan Magnetic Nano-Based Particles for the Recovery of Light and Heavy Rare Earth Metals: Uptake Kinetics and Sorption Isotherms

Cysteine-functionalized chitosan magnetic nano-based particles were synthesized for the sorption of light and heavy rare earth (RE) metal ions (La(III), Nd(III) and Yb(III)). The structural, surface, and magnetic properties of nano-sized sorbent were investigated by elemental analysis, FTIR, XRD, TEM and VSM (vibrating sample magnetometry). Experimental data show that the pseudo second-order rate equation fits the kinetic profiles well, while sorption isotherms are described by the Langmuir model. Thermodynamic constants (ΔG°, ΔH°) demonstrate the spontaneous and endothermic nature of sorption. Yb(III) (heavy RE) was selectively sorbed while light RE metal ions La(III) and Nd(III) were concentrated/enriched in the solution. Cationic species RE(III) in aqueous solution can be adsorbed by the combination of chelating and anion-exchange mechanisms. The sorbent can be efficiently regenerated using acidified thiourea.

Biosorption and desorption of lanthanum(III) and neodymium(III) in fixed-bed columns with Sargassum sp.: perspectives for separation of rare earth metals

Rare earth (RE) metals are essentials for the manufacturing of high-technology products. The separation of RE is complex and expensive; biosorption is an alternative to conventional processes. This work focuses on the biosorption of monocomponent and bicomponent solutions of lanthanum(III) and neodymium(III) in fixed-bed columns using Sargassum sp. biomass. The desorption of metals with HCl 0.10 mol L(-1) from loaded biomass is also carried out with the objective of increasing the efficiency of metal separation. Simple models have been successfully used to model breakthrough curves (i.e., Thomas, Bohart-Adams, and Yoon-Nelson equations) for the biosorption of monocomponent solutions. From biosorption and desorption experiments in both monocomponent and bicomponent solutions, a slight selectivity of the biomass for Nd(III) over La(III) is observed. The experiments did not find an effective separation of the RE studied, but their results indicate a possible partition between the metals, which is the fundamental condition for separation perspectives.

New highly luminescent hybrid materials: terbium pyridine-picolinate covalently grafted on kaolinite

Luminescent hybrid materials derived from kaolinite appear as promising materials for optical applications due to their specific properties. The spectroscopic behavior of terbium picolinate complexes covalently grafted on kaolinite and the influence of the secondary ligand and thermal treatment on luminescence are reported. The resulting materials were characterized by thermal analysis, element analysis, X-ray diffraction, infrared absorption spectroscopy, and photoluminescence. The thermogravimetric curves indicated an enhancement in the thermal stability up to 300 °C for the lanthanide complexes covalently grafted on kaolinite, with respect to the isolated complexes. The increase in the basal spacing observed by X-ray diffraction confirmed the insertion of the organic ligands into the basal space of kaolinite, involving the formation of a bond between Al-OH and the carboxylate groups, as evidenced by infrared spectroscopy. The luminescent hybrid material exhibited a stronger characteristic emission of Tb(3+) compared to the isolated complex. The excitation spectra displayed a broad band at 277 nm, assigned to a ligand-to-metal charge transfer, while the emission spectra presented bands related to the electronic transitions characteristic of the Tb(3+) ion from the excited state (5)D(4) to the states (7)F(J) (J=5, 4, and 3), with the 4→5 transition having high intensity with green emission.

Biomass in Batch Systems: Physicochemical Evaluation of Kinetics and Adsorption Models

This work evaluated kinetic and adsorption physicochemical models for the biosorption process of lanthanum, neodymium, europium, and gadolinium by Sargassum sp. in batch systems. The results showed: (a) the pseudo-second order kinetic model was the best approximation for the experimental data with the metal adsorption initial velocity parameter in 0.042-0.055 mmol.g-1.min-1 (La < Nd < Gd < Eu); (b) the Langmuir adsorption model presented adequate correlation with maximum metal uptake at 0.60-0.70 mmol g-1 (Eu < La < Gd < Nd) and the metal-biomass affinity parameter showed distinct values (Gd < Nd < Eu < La: 183.1, 192.5, 678.3, and 837.3 L g-1, respectively); and (c) preliminarily, the kinetics and adsorption evaluation did not reveal a well-defined metal selectivity behavior for the RE biosorption in Sargassum sp., but they indicate a possible partition among RE studied.