Strategy to Probe the Local Atomic Structure of Luminescent Rare Earth Complexes by X-ray Absorption Near-Edge Spectroscopy Simulation Using a Machine Learning-Based PyFitIt Approach.

Rare earth(III) ß-diketonates are highly remarkable luminophores in the visible spectral region among the rare earth compounds, owing to the efficient contribution from the 4f-4f intraconfigurational transitions. To get detailed structural insight into the RE3+ sites (RE = Eu, Gd, and Sm), X-ray absorption near-edge spectroscopy (XANES) can be very potent in probing the local chemical environment around the RE3+ ion. In this work, a PyFitIt machine learning approach was employed as a new strategy to simulate the Eu, Gd, and Sm L3-edge XANES and thereby determine the local atomic structure of the luminescence RE3+ ß-diketonate complexes, [Eu(tta)3(H2O)2], [C4mim][Eu(dbm)4], [Gd(tta)3(H2O)2], and [Sm(dbm)3(phen)] (tta, 3-thenoyltrifluoroacetonate; dbm, dibenzoylmethane; phen, phenanthroline; and C4mim, 1-butyl-3-methylimidazolium bromide). Continuous Cauchy wavelet transform validated the PyFitIt calculated XANES by visualizing very efficiently the coordination geometries, composed of O and O/N backscatterers around the RE3+ (RE = Eu and Gd) and Sm3+ ions, respectively, as a pinkish-red color map in the two-dimensional images of the corresponding complexes. Extended X-ray absorption fine structure fit in Artemis also corroborated the three-dimensional structures generated by PyFitIt XANES simulation for all the compounds. Though, relatively slightly higher bond distance values for the Sm3+ complex are due to the higher atomic radius of the Sm3+ ion when compared to the Eu3+ and Gd3+ complexes. Meanwhile, higher Debye-Waller factor (σ2) values for the [C4mim][Eu(dbm)4] when compared to the [Eu(tta)3(H2O)2] indicated the structure disorder, owing to the distortion in the local geometry. It is noteworthy that the optical properties, described mainly by the Ωλ (λ = 2 and 4) 4f-4f intensity parameters, are very sensitive to the local coordination environment around the Eu3+ ion. Thus, a close agreement between the experimental and theoretically calculated Ωλ parameter values confirmed that the PyFitIt calculated square antiprismatic structures are precisely similar to the real structures of the Eu3+ complexes.

In vitro and in vivo efficacy of zinc oxide green nanoparticles against multidrug-resistant Salmonella Typhi.

Antibiotic resistance is an increasing threat, requiring novel therapeutic solutions. Metal nanoparticles e.g., zinc oxide nanoparticles (ZnO NPs) exhibited the potential against many bacterial pathogens. Strains of Salmonella enterica serovar Typhi resistant to ceftriaxone were reported first from Pakistan in 2016. Since then, S. Typhi is a pathogen of concern globally owing to its rapidly emerging resistance potential against many last resort antibiotics. In the present study, in vitro and in vivo antimicrobial activity of ZnO NPs against multidrug resistant (MDR) and extensively drug resistant (XDR) Salmonella Typhi strains from Pakistan was evaluated. Zinc oxide green nanoparticles (ZnO GNPs), synthesized from Aloe vera, were characterized by SEM, XRD, UV-vis and Raman spectroscopy. In vitro antibacterial activity of two different concentrations of ZnO GNPs (7 and 15%) was checked using agar well diffusion method. Further, broth microdilution and time kill assays were performed using the ZnO GNPs. In vivo assays were conducted in BALB/c mice sepsis models. In all the three methods, agar well diffusion assay broth microdilution and time kill assay, different zinc oxide dihydrate precursor concentrations had shown the antibacterial activity. The minimum inhibitory concentration (MIC) of ZnO GNPs nanoparticles against MDR and XDR S. Typhi strains was found as 16 to 64 µg/ml. In vivo experiment has shown a significant decrease in CFU/ml in the mice treated with ZnO GNPs as compared to the control group. Our findings have revealed that ZnO GNPs have significant antibacterial activity against MDR and XDR S. Typhi, both in vitro and in vivo.

Structure-property correlations, defect driven magnetism and anomalous temperature dependence of magnetic coercivity in PbTi1-xFexO3 (0 ≤x≤ 0.5) systems.

The search for new multiferroic materials is on the rise due to their potential applications in an advanced generation of highly efficient multifunctional devices. Here we report a series of PbTi1-xFexO3 (0 ≤x≤ 0.5) samples prepared by a solid-state reaction method. Structural analysis suggests that doping of Fe introduces oxygen vacancies along the c-axis (aliovalent substitution; Fe3+→ Ti4+), local distortions and microstrains in the PbTiO3 lattice which triggered the partial structural transformation from tetragonal to cubic. This has been confirmed using structural analysis tools such as X-ray diffraction, Fourier Transform Infrared Spectroscopy, Raman spectroscopy, and Mössbauer spectroscopy. The presence of oxygen vacancies was further confirmed by refining the site occupancies through Rietveld refinement. Mössbauer measurements confirmed that Fe ions exist in the 3+ state and change in coordination of some Fe3+ ions from octahedral to tetrahedral points towards the oxygen deficiency in the system. Raman studies confirm the presence of all ordinary and quasi phonon modes in Fe doped PbTiO3 samples. The overlapping and weakening of modes are related to the structural changes/transformation. The modes' shifting to lower wavenumbers is ascribed to the increase in the average atomic mass at Ti-sites. The induced ferromagnetism in the system increases with an increase in the Fe content and can be explained on the basis of the F-center exchange mechanism. Moreover, we found an anomalous temperature-dependent trend in the magnetic coercivity (decrease in coercivity as the temperature is decreased) which can be explained in terms of a low-temperature decrease in an effective magnetic anisotropy when the effects of magneto-electric coupling are included. The existence of well-developed ferroelectric and ferromagnetic hysteresis loops confirmed the multiferroic nature of the system. The increase in the value of the dielectric constant at 1 MHz with an increase in the Fe content is attributed to the increase in resistivity of the system due to the formation of immobile defect dipole complexes.