Optical phonons in R2BaMO5 oxides with M=Co, Ni, Cu, and R=a rare earth

High-pressure synthesis and magnetic properties of tetragonal R2BaCuO5 (R = Sm and Eu)

We report the experimental discovery of a new structural phase of well-known orthorhombic R ₂BaCuO₅ (R = Sm and Eu), exhibiting a tetragonal crystal structure with space group P4∕mbm. The high-pressure tetragonal phase is isostructural with the brown phase R ₂BaCuO₅ (R = La, Pr, and Nd). In this structure, the Cu ions form an isolated square planar environment, contrary to the orthorhombic phase, where the Cu ions are located in a distorted square pyramid. Magnetization and specific heat measurements reveal the long-range antiferromagnetic order of the Cu²⁺ and/or Sm³⁺ moments for the Sm-sample, with the magnetic specific heat accounting for only 35% of the magnetic entropy. Interestingly, the Eu-sample remains paramagnetic down to the lowest temperature. The high Curie-Weiss temperature of -140 K and magnetic entropy of 3% of the expected value indicates that the system is highly frustrated. We estimated the isothermal entropy change and investigated the magnetocaloric effect for Eu₂BaCuO₅, and the maximum entropy change detected at a field of 70 kOe at 3 K reaches 5.6 J kg^-1K^-1.

Synthesis, Structure and Impact of 5-Aminoorotic Acid and Its Complexes with Lanthanum(III) and Gallium(III) on the Activity of Xanthine Oxidase

The superoxide radical ion is involved in numerous physiological processes, associated with both health and pathology. Its participation in cancer onset and progression is well documented. Lanthanum(III) and gallium(III) are cations that are known to possess anticancer properties. Their coordination complexes are being investigated by the scientific community in the search for novel oncological disease remedies. Their complexes with 5-aminoorotic acid suppress superoxide, derived enzymatically from xanthine/xanthine oxidase (X/XO). It seems that they, to differing extents, impact the enzyme, or the substrate, or both. The present study closely examines their chemical structure by way of modern methods-IR, Raman, and 1H NMR spectroscopy. Their superoxide-scavenging behavior in the presence of a non-enzymatic source (potassium superoxide) is compared to that in the presence of an enzymatic source (X/XO). Enzymatic activity of XO, defined in terms of the production of uric acid, seems to be impacted by both complexes and the pure ligand in a concentration-dependent manner. In order to better relate the compounds' chemical characteristics to XO inhibition, they were docked in silico to XO. A molecular docking assay provided further proof that 5-aminoorotic acid and its complexes with lanthanum(III) and gallium(III) very probably suppress superoxide production via XO inhibition.

Theoretical and Experimental Vibrational Characterization of Biologically Active Nd(III) Complex

The neodymium(III) complex of orotic acid (HOA) was synthesized and its structure determined by means of analytical and spectral analyses. Detailed vibrational analysis of HOA, sodium salt of HOA, and Nd(III)–OA systems based on both the calculated and experimental spectra confirmed the suggested metal–ligand binding mode. Significant differences in the IR and Raman spectra of the complex were observed as compared to the spectra of the ligand. The calculated vibrational wavenumbers, including IR intensities and Raman scattering activities, for the ligand and its Nd(III) complex were in good agreement with the experimental data. The vibrational analysis performed for the studied species, orotic acid, sodium salt of orotic acid, and its Nd(III) complex helped to explain the vibrational behaviour of the ligand’s vibrational modes, sensitive to interaction with Nd(III). In this paper we also report preliminary results about the cytotoxicity of the investigated compounds. The cytotoxic effects of the ligand and its Nd(III) complex were determined using the MTT method on different tumour cell lines. The screening performed revealed that the tested compounds exerted cytotoxic activity upon the evaluated cell lines.

SrMnO3 Thermochromic Behavior Governed by Size-Dependent Structural Distortions

The influence of particle size in both the structure and thermochromic behavior of 4H-SrMnO3 related perovskite is described. Microsized SrMnO3 suffers a structural transition from hexagonal (P63/mmc) to orthorhombic (C2221) symmetry at temperature close to 340 K. The orthorhombic distortion is due to the tilting of the corner-sharing Mn2O9 units building the 4H structural type. When temperature decreases, the distortion becomes sharper reaching its maximal degree at ∼125 K. These structural changes promote the modification of the electronic structure of orthorhombic SrMnO3 phase originating the observed color change. nano-SrMnO3 adopts the ideal 4H hexagonal structure at room temperature, the orthorhombic distortion being only detected at temperature below 170 K. A decrease in the orthorhombic distortion degree, compared to that observed in the microsample, may be the reason why a color change is not observed at low temperature (77 K).

FT-IR and FT-Raman study of Nasicon type phosphates, ASnFe(PO4)3 [A=Na2, Ca, Cd]

FT-Raman and FT-IR spectra of ASnFe(PO4)3 [A=Na2, Ca, Cd] were recorded and analyzed. The bands were assigned in terms of the vibrational group frequencies of SnO6 octahedral and PO4 tetrahedral. The spectral analysis shows that the symmetry of corner shared octahedral (SnO6) and the tetrahedral (PO4) are lowered from their free ion symmetry state. The presence of Fe3+ ions disrupts the S-N-O-S-N chain in the structure. This causes distortion of SnO6 and PO4 in the structure of all the compounds. Also it is seen that there are two distinct PO4 tetrahedra of different P-O bond lengths. One of these tetrahedra is linearly distorted in all the title compounds. The PO4 frequencies and bond lengths are calculated theoretically and are in agreement with the experimental values. The presence of PO4 polyanion in the structure can reduce the redox energy and hence reduce the metal oxygen covalency strength in the structure.

Enhanced Microwave Absorption Properties of Intrinsically Core/shell Structured La(0.6)Sr(0.4)MnO(3) Nanoparticles

The intrinsically core/shell structured La(0.6)Sr(0.4)MnO(3) nanoparticles with amorphous shells and ferromagnetic cores have been prepared. The magnetic, dielectric and microwave absorption properties are investigated in the frequency range from 1 to 12 GHz. An optimal reflection loss of -41.1 dB is reached at 8.2 GHz with a matching thickness of 2.2 mm, the bandwidth with a reflection loss less than -10 dB is obtained in the 5.5-11.3 GHz range for absorber thicknesses of 1.5-2.5 mm. The excellent microwave absorption properties are a consequence of the better electromagnetic matching due to the existence of the protective amorphous shells, the ferromagnetic cores, as well as the particular core/shell microstructure. As a result, the La(0.6)Sr(0.4)MnO(3) nanoparticles with amorphous shells and ferromagnetic cores may become attractive candidates for the new types of electromagnetic wave absorption materials. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s11671-009-9374-y) contains supplementary material, which is available to authorized users.