Luzeli Moreira da Silva

Cobalt–chromium (Co–Cr) alloys are valued in biomedicine for their mechanical performance and relative bioinertness. Here, Co–Cr alloys containing tantalum (Ta; 0, 3, 6, and 9 wt %) were synthesized by electric-arc melting to assess how Ta content influences bulk and surface properties across scales. X-ray Diffraction (XRD), Vickers Microhardness, Wettability, Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS), and Atomic Force Microscopy/Kelvin Probe Force Microscopy (AFM/KPFM) were employed. Bioactivity and biocompatibility were evaluated by immersion in simulated body fluid (SBF) and cell-viability assays. Ta addition promoted the coexistence of Co allotropes (εCo and αCo) and the formation of a secondary TaCo2 phase, resulting in a dendritic microstructure. Microhardness increased significantly, reaching 466 ± 27 HV0.5 for 9 wt % Ta (≈77% above the Ta-free alloy). Surface-potential mapping revealed ≈1500% higher local potential differences and composition-dependent work function distribution, indicating Ta-driven electronic heterogeneity. The alloys were cytocompatible under extract exposure conditions, suggesting that Ta-induced surface changes may indirectly modulate the biological response. SBF tests confirmed improved in vitro bioactivity, with apatite nucleation on all alloys; the 6 wt % Ta composition produced the thickest Ca/P-rich layer (∼1.3 μm). Overall, Ta addition modulated the microstructure, localized deformation resistance, surface electronic response, and in vitro biological behavior of Co–Cr alloys, with 6 wt % Ta showing the most balanced response among the investigated compositions.

Multiphase alloys with sequential long-range magnetic order represent an intriguing approach to overcoming an intrinsic limitation of single-phase magnetocaloric materials by broadening the operational temperature window and enhancing thermal coupling between phases. In this study, we investigate a dysprosium–platinum–indium (Dy–Pt–In) alloy with a nominal composition of 35 wt% Dy, 41 wt% Pt, and 24 wt% In, synthesized by arc melting and characterized in terms of its structural, microstructural, magnetic, and magnetocaloric properties. Rietveld refinement of X-ray diffraction data, combined with scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) analyses, revealed a multiphase alloy composed of a DyPtIn, DyPt2In, and dysprosium–platinum (DyPt) intermetallic phases. The alloy exhibit three magnetic transitions: two successive ferromagnetic (FM) transitions at 32.5 and 23.0 K, and a field-dependent antiferromagnetic-like transition at 7.5 K, which together sustain an nearly constant adiabatic temperature change of ~2.1 K across a broad temperature range (2.5–57 K) and a maximum magnetic entropy change of ~6.3 J/kg·K for a field variation of 50 kOe. The results demonstrate the potential of Dy–Pt–In multiphase systems to extend the working temperature span and enhance the performance of cryogenic magnetic refrigeration (MR) applications.

In this study, a Gd–Pt–In composite was synthesized by arc melting. Powder X-ray diffraction, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) analyses confirmed the composite composition formed by a matrix phase of GdPtIn, comprising 76% of the sample, and a dispersed phase (21%) formed by GdPt. Magnetic and specific heat measurements revealed two ferromagnetic transitions in the composite at 67 and 63.5 K. These successive transitions provide a very broad curve for both the magnetic entropy change (−ΔS _M) and adiabatic temperature change (ΔT _ad) magnetocaloric parameters, generating a wide temperature range with a significant magnetocaloric effect (MCE) and a substantial relative cooling power (RCP). For a magnetic field change (ΔH) of 50 kOe, the maximum magnetic entropy change (−ΔS _M ^max) reached 6 J/kg K, with a corresponding RCP value of 368 J/kg. The excellent magnetocaloric properties of the Gd–Pt–In composite position it as a promising candidate for low-temperature magnetic refrigeration applications. Furthermore, these findings offer valuable insights for the ongoing search for effective refrigerant materials, particularly those exhibiting multiple successive magnetic phase transitions.

This paper presents a comprehensive investigation of a Tutton crystal, rubidium cobalt sulfate hexahydrate Rb₂Co-(SO₄)₂(H₂O)₆, detailing its synthesis and characterizing its structural (PXRD), vibrational (FT-IR and Raman), thermal (TG and DSC), and optical (UV-vis-NIR) properties. Complementary, calculations using density functional theory (DFT) were implemented to estimate electronic band structure and assign optical phonon modes identified through FT-IR and Raman spectra. The material was prepared by the slow solvent evaporation method and crystallized, having P2₁/a-space group in the monoclinic system (unit cell parameters a = 9.204(9) Å, b = 12.467(2) Å, c = 6.246(3) Å, β = 106.02(5)°, and V = 688.93(4) ų). Hirshfeld surface analysis and void calculations revealed a densely packed structure stabilized by strong O···H/H···O hydrogen bonds, followed by O···Co/Co···O contacts, with a void volume of only 1.4%. Thermograms show a full dehydration at ≈ 384 K (ΔH = 301.15 kJ/mol). While electronic band structure indicates an electronic bandgap of 3.00 eV, dominated by Co²⁺ d-orbital contributions, the optical measurements display an optical bandgap of ≈ 4.13 eV, attributed to ligand-to-metal charge transfer bands involving electron donation from the nonbonding orbitals of H₂O to the Co²⁺ orbitals. The optical absorbance (200-300 nm) transmittance (300-420 nm/580-1100 nm) windows underscore the potential of Rb₂Co-(SO₄)₂(H₂O)₆ crystal.

This study presents the synthesis, physicochemical characterization, and biological evaluation of a novel ternary nickel(II) complex with isoleucine and 1,10-phenanthroline ligands, [Ni(Phen)(Ile)₂]∙6H₂O, designed as a potential antitumor agent. Single-crystal X-ray diffraction revealed a monoclinic structure (C2-space group) with an octahedral Ni(II) coordination involving Phen and Ile ligands. A Hirshfeld surface analysis highlighted intermolecular interactions stabilizing the crystal lattice, with hydrogen bonds (H···H and O···H/H···O) dominating (99.1% of contacts). Density functional theory (DFT) calculations, including solvation effects (in water and methanol), demonstrated strong agreement with the experimental geometric parameters and revealed higher affinity to the water solvent. The electronic properties of the complex, such as HOMO−LUMO gaps (3.20–4.26 eV) and electrophilicity (4.54–5.88 eV), indicated a charge-transfer potential suitable for biological applications through interactions with biomolecules. Raman and infrared spectroscopic studies showed vibrational modes associated with Ni–N/O bonds and ligand-specific deformations, with solvation-induced shifts observed. A study using ultraviolet–visible–near-infrared absorption spectroscopy demonstrated that the complex remains stable in solution. In vitro cytotoxicity assays against MCF-7 (breast adenocarcinoma) and HCT-116 (colorectal carcinoma) cells showed dose-dependent activity, achieving 47.6% and 65.3% viability reduction at 100 μM (48 h), respectively, with lower toxicity to non-tumor lung fibroblasts (GM07492A, 39.8%). Supporting the experimental data, we performed computational modeling to examine the pharmacokinetic profile, with particular focus on the absorption, distribution, metabolism, and excretion properties and drug-likeness potential.

Tutton salts have received considerable attention due to their potential applications in thermochemical energy storage (TCHS) systems. This technology requires high-purity materials that exhibit reversible dehydration reactions, significant variations in dehydration enthalpy, and high-temperature melting points. In this study, K₂Cu(SO₄)₂(H₂O)₆ Tutton salt in the form of single crystals was grown using the slow solvent evaporation method. Their structural, morphological, and thermal characteristics are presented and discussed, as well as temperature-induced phase transformations. At room temperature, the salt crystallizes in a monoclinic structure belonging to the P2₁/a space group, which is typical for Tutton salts. The lack of precise control over the solvent evaporation rate during crystal growth introduced structural disorder, resulting in defects on the crystal surface, including layer discontinuities, occlusions, and pores. Thermoanalytical analyses revealed two stages of mass loss, corresponding to the release of 4 + 2 coordinated H₂O molecules—four weakly coordinated and two strongly coordinated to the copper. The estimated dehydration enthalpy was ≈ 80.8 kJ/mol per mole of H₂O. Powder X-ray diffraction measurements as a function of temperature showed two phase transformations associated with the complete dehydration of the starting salt occurring between 28 and 160 °C, further corroborating the thermal results. The total dehydration up to ≈ 160 °C, high enthalpy associated with this process, and high melting point temperature make K₂Cu(SO₄)₂(H₂O)₆ a promising candidate for TCHS applications.