Ag2Mo3O10·2H2O nanorods under high pressure: In situ Raman spectroscopy.

This work presents a pressure-dependent behavior of silver trimolybdate dihydrate (Ag2Mo3O10·2H2O) nanorods using in situ Raman scattering. The Ag2Mo3O10·2H2O nanorods were obtained by the hydrothermal method at 140 °C for 6 h. The structural and morphological characterization of the sample was performed by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). Pressure-dependent Raman scattering studies were performed on Ag2Mo3O10·2H2O nanorods up to 5.0 GPa using a membrane diamond-anvil cell (MDAC). The vibrational spectra under high pressure showed splitting and emergence of new bands above 0.5 GPa and 2.9 GPa. Reversible phase transformations under pressure were observed in silver trimolybdate dihydrate nanorods: Phase I - ambient phase (1 atm - 0.5 GPa) â†’ Phase II (0.8 GPa - 2.9 GPa) â†’ Phase III (above 3.4 GPa).

In situ high-temperature Raman scattering study of monoclinic Ag2Mo2O7 microrods.

In this work, we present a temperature-dependent behavior of monoclinic silver dimolybdate (m-Ag2Mo2O7) microrods using in situ Raman scattering. The m-Ag2Mo2O7 microrods were obtained by the conventional hydrothermal method at 423 K for 24 h. The structural and morphological characterization of the sample has been done by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Temperature-dependent Raman scattering measurements were performed on m-Ag2Mo2O7 microrods, and the results show an irreversible first-order structural phase transition at 698 K-723 K and the melting process at 773 K. Changes in the Raman spectra confirm the phase transition from the P21/c monoclinic structure to the P-1 triclinic structure. No morphological changes were observed during the structural phase transition of the sample at 723 K. Time-dependent optical microscopy at 773 K showed the growth of nanowires on the Ag2Mo2O7 microrods in the triclinic structure.

Temperature-dependent phonon dynamics of Ag3PO4 microcrystals.

In this work, we present the study of the temperature-dependent behavior of silver orthophosphate (Ag3PO4) microcrystals using in situ Raman scattering. The Ag3PO4 as-synthesized microcrystals were prepared by the precipitation method and characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman and infrared spectroscopy, and differential scanning calorimetry (DSC). Temperature-dependent phonon dynamics were performed on Ag3PO4 microcrystals and pointed to a first-order phase transition in the temperature range 500-515 °C: Phase I (25-500 °C) â†’ Phase II (515-590 °C). The phase transition is reversible and a temperature hysteresis was observed during the heating - cooling process: Phase II (590-470 °C) â†’ Phase I (455-25 °C). The reversible phase transition is related to the distortion of the tetrahedral symmetry of PO4 caused by the decrease in the crystalline order. DSC analysis confirmed the results of temperature-dependent Raman spectroscopy.

Temperature-induced isostructural phase transition on NaCe(MoO4)2 system: A Raman scattering study.

Temperature-dependent Raman spectroscopic study has been performed on scheelite-type sodium­cerium molybdate - NaCe(MoO4)2 - in the temperature range 113-873 K. This study provides phonon properties of NaCe(MoO4)2, which are very important to understand the mechanism governing eventual phase transitions undergone by the structure, since phonons are very sensitive to structural changes. The ambient scheelite phase remains stable in a low-temperature range (113-293 K), and no relevant modification is observed in the Raman spectra. However, the experiments reveal the existence of one reversible phase transition at high-temperature. The vibrational spectra of NaCe(MoO4)2 system showed anomalies above 748 K, where overlaps of some bands and the appearance of a band at 458 cm-1 are observed. These modifications were attributed to an isostructural phase transition and a discussion about the possible mechanism of this transformation is furnished.

Antibacterial properties and modulation analysis of antibiotic activity of NaCe(MoO4)2 microcrystals.

This study reports the antibacterial properties and modulation analysis of antibiotic activity by NaCe(MoO4)2 microcrystals as well as their structural and morphological characterization. Evaluation of the antibacterial and antibiotic-modulating activity was carried out using the broth microdilution method. The Minimum Inhibitory Concentrations (MICs) of the compounds were expressed as the geometric mean of the triplicate values obtained through the use of Resazurin. Compound concentrations in the plates ranged from 512 to 0.5 µg/mL. Regarding its direct antibacterial activity, NaCe(MoO4)2 had a MIC ≥ 1024 µg/mL against all studied strains. As for its modulatory effect, it presented synergism with the antibiotic Gentamicin against the S. aureus strain and with Norfloxacin against E. coli, causing a reduction of 75% and 60%, respectively, in the antibiotic quantity required to have the same effect on the strain in study.

Modulation of antibiotic effect by Fe2(MoO4)3 microstrutures.

In this study, we report the antibacterial activity and modulation of antibiotic activity by Fe2(MoO4)3 microstructures obtained by the hydrothermal route without use of surfactants or organic additives. This material was characterized by X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM) images. The XRD pattern showed that the Fe2(MoO4)3 crystallize in a monoclinic structure without secondary phases. Raman spectroscopy confirms the formation of Fe2(MoO4)3. SEM images show that the Fe2(MoO4)3 obtained have ball-of-yarn shaped morphology. In the antibacterial assays, strains of Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus were assayed by microdilution method to evaluate the antibacterial and modulatory-antibiotic activity with antibiotics as gentamicin, norfloxacin and imipenem. Against all bacteria, the Minimum Inhibitory Concentration (MIC) was Fe2(MoO4)3 ≥ 1024 µg/mL. This high MIC result must be associated with the fact of the iron be an essential microelement to the bacterial growth. However, when the Fe2(MoO4)3 was assayed in association with the antibiotics was observed an antagonistic effect demonstrated by an enhance of the MIC. This fact is associated directly with the pro-oxidative properties of metallic oxides. These compounds enhance the production of free radicals, as H2O2 and superoxide ions that can affect the cell structures as cell membrane and cell wall. Other effect is associated with the possible coordination of the metal, performing bonds with the chemical structure of the antibiotics, reducing their activity. Our results indicated that nanocompounds as Fe2(MoO4)3 can not be used as antimicrobial products for clinical usage, neither directly and neither in association with antibiotics.

ß-Ag2MoO4 microcrystals: Characterization, antibacterial properties and modulation analysis of antibiotic activity.

This study reports the antibacterial properties and modulation analysis of antibiotic activity by ß-Ag2MoO4 microcrystals as well as their structural and vibrational characterization. The silver molybdate was obtained by the conventional hydrothermal method, and the structural, vibrational and morphological properties of the sample were determined using X-ray diffraction, Raman spectroscopy and scanning electron microscopy images. ß-Ag2MoO4 microcrystals obtained show spinel-type cubic structure (Fd-3m) with irregular shapes. The evaluation of antibacterial and modulatory-antibiotic activity was performed using the microdilution method to determine the Minimum Inhibitory Concentration (MIC) of the ß-Ag2MoO4 and antibiotics alone and associated with the silver molybdate. The ß-Ag2MoO4 modulates the antibiotic activity against all bacteria assayed in a synergistic (as the norfloxacin and gentamicin against S. aureus and gentamicin against E. coli) or an antagonistic form (as the norfloxacin against E.coli and P. aeruginosa). The reversion of antibiotic resistance by combinations with Ag2MoO4 could be a novel strategy to combat infections caused by multiple drug resistance (MDR) pathogens. Our results indicate that these silver molybdates present a clinically relevant antibacterial activity and enhanced the antibiotic activity of some antibiotics against MDR strain of S. aureus and E. coli, being an interesting alternative to combat antibiotic-resistant bacterial infectious agents.