Phloroglucinol and derived compounds comprise a huge class of secondary metabolites widely distributed in plants and brown algae. A vast array of biological activities, including antioxidant, ...anti-inflammatory, antimicrobial, and anticancer has been associated to this class of compounds. In this review, the available data on the antiviral and antibacterial capacity of phloroglucinols have been analyzed. Some of these compounds and derivatives show important antimicrobial properties in vitro. Phloroglucinols have been shown to be effective against viruses, such as human immunodeficiency virus (HIV), herpes or enterovirus, and preliminary data through docking analysis suggest that they can be effective against SARS-CoV-19. Also, some phloroglucinols derivatives have shown antibacterial effects against diverse bacteria strains, including Bacillus subtilis and Staphylococcus aureus, and (semi)synthetic development of novel compounds have led to phloroglucinols with a significantly increased biological activity. However, therapeutic use of these compounds is hindered by the absence of in vivo studies and scarcity of information on their mechanisms of action, and hence further research efforts are required. On the basis of this consideration, our work aims to gather data regarding the efficacy of natural-occurring and synthetic phloroglucinol derivatives as antiviral and antibacterial agents against human pathogens, which have been published during the last three decades. The recollection of results reported in this review represents a valuable source of updated information that will potentially help researchers in the development of novel antimicrobial agents.
The electrical behavior of textured YBaCo2O5+δ thin layers (100, 150, and 240 nm) grown on SrTiO3 substrates was investigated by means of complex impedance and transport measurements. Strong ...dependence of the electrical properties of the layers on the frequency, temperature, and thickness was observed. A semiconducting-like behavior was verified for the investigated films. The impedance spectra (semicircle arcs) were well modeled in terms of equivalent electrical circuits. The circuital analysis allowed for distinguishing between capacitive and resistive contributions to the impedance. The insulating phase and the dielectric relaxation were modeled by means of a conventional resistor-capacitor element connected in parallel. The conductivity data was adequately fit to Jonscher's law, σac = σdc + Aωn. Values of the n exponent lower than 1 were obtained in the temperature range measured. The value of the real part of the dielectric permittivity (ε′r) grew as the temperature was increased and the frequency lowered. An activation energy of ~70 meV was determined from the impedance data. High values of the dielectric loss (tanδ) were observed in the lower frequency region and at the higher temperatures measured. Separate measurements on blank SrTiO3 substrates were also carried out in the present study for comparison.
•Highly-quality, YBaCo2O5±δ thin films were deposited on SrTiO3 by dc sputtering.•Uniformity in the oxygen content throughout the films was verified.•Dielectric response was investigated as a function of frequency, thickness and temperature.•Capacitive and resistive contributions to the impedance were clearly identified.•An activation energy of ~70 meV was determined for the films.
Dimensionally Stable Anodes (Sb2O5-doped Ti/RuO2-ZrO2) are synthesized at four different Zr/Ru molar ratios using the Pechini method to account for the effects of ZrO2 content on the active chlorine ...formation. X-ray diffraction for ternary catalysts reveal co-deposited phases consisting of a tetragonal crystalline structure (P42/mnm) for RuO2, and two phases corresponding to monoclinic (P2/m) and tetragonal (P42/mnm) crystalline structures for ZrO2. SEM micrographs show that ZrO2 alters grain growth and film morphology as its content is increased. Electrochemical tests performed in 1 mol L−1 H2SO4 and 0.1 mol L−1 NaCl demonstrate that the kinetic rate to perform the oxygen evolution reaction (OER) decreases with the simultaneous augment of ZrO2 and Sb2O5 compositions in the ternary anode, while in the ZrO2 absence, Sb2O5 catalyzes the OER (Ti/SbRu) compared to the Ti/Ru and ternary electrodes. Although the chlorine evolution reaction (CER) preferentially occurs by the suppression of OER in chloride media, the CER rate mainly increases due to the rise of the ZrO2 content. This finding is corroborated with an iodometric method using UV-Vis spectroscopy, which shows that the electro-generation capacity to form active chlorine species is significantly enhanced when ZrO2 is added, compared to Ti/RuO2 and Sb2O5 doped Ti/RuO2 materials. Accelerated life tests conducted with all catalysts indicate that all ternary anodes present failure times considerably longer than Ti/Ru, Ti/SbRu and Ti/RuZr electrodes, suggesting a stability enhancement due to the combined presence of Sb and Zr species.
(Fe30Cu70)96B4 (FCB) alloys were produced in an induction furnace and then reduced in size by mechanical milling in stainless steel vials in an Ar atmosphere. Structural, morphological, and magnetic ...characterization techniques were used to investigate the evolution of powder alloys as a function of their milling time (0, 12, 24, 36, 48, and 60 h). Structural analysis by X-ray diffraction confirmed that all samples exhibit a crystalline fcc structure and space group Fm-3 m. As the milling time increases, the induced stress increments, leading to changes in the lattice parameter value and atomic volume. Thus, lattice parameter values are approximately in the range a = 0. 3614–0.3626 nm. TEM analysis confirmed that after 12 h of milling, the FCB system was made up of nanoparticles with diameters between 6 and 8.2 nm. ZFC-FC measurements revealed that the samples are ferromagnetic at room temperature. Nevertheless, due to the particle's nanometric size, a superparamagnetic-like behavior was evidenced with a blocking temperature (TB) below 60 K. M(H) loops were fitted using a distribution of Langevin functions, obtaining a maximum saturation magnetization Ms ~ 25 emu/g after 24 h of milling. Likewise, the FCB system is magnetically soft a room temperature with coercive field values below (132 Oe). Finally, Mössbauer spectroscopy showed that the superparamagnetic-like behavior could be associated with the Cu matrix's nanoparticle size and Fe atom behavior.
•A new route to homogenization of FeCuB metastable alloy systems by casting and mechanical alloying is reported.•Structural and magnetic properties were carefully investigated and found to be influenced by particle size.•Mechanical alloying technique has been fully employed to prepare FeCuB nanoparticles alloys.•The combination of the two techniques casting and mechanical alloys promote the incorporation of Fe into the Cu matrix.
A novel ferromagnetic state coexisting with ferroelectric ordering at room temperature in strained BiFeO3 (BFO) thin films grown using a sputtering technique on La0.7Sr0.3MnO3/SiO2/Si(100) (LSMO/SOS) ...substrates is reported. The properties of BFO films with different thicknesses (tBFO = 15, 50, 70, 120, and 140 nm) on 40 nm LSMO layers are explored. 012 out-of-plane highly textured BFO/LSMO stacks grew with rhombohedral structures. LSMO layers are nanostructured in nature, constituted by ferromagnetic single-domain nanoregions induced by the constrain of the SiO2 surface, with TC ∼200 K and high coercive field (HC) of ∼1100 Oe at 2.5 K. BFO films grew epitaxially nanostructured on LSMO, exhibiting ∼4 nm spherical nanoregions. The BFO layers show typical antiferromagnetic behavior (in a greater volume fraction) when made thicker (tBFO > 70 nm). The thinner films (tBFO < 50 nm) display ferromagnetic behavior with TC > 400 K, HC ∼ 1600 Oe for 15 nm and ∼1830 Oe for 50 nm. We propose that such ferromagnetic behavior is originated by the establishment of a new magnetic configuration in the Fe3+OFe3+ sublattice of the BFO structure, induced by strong hybridization at the interface as consequence of superexchange coupling interactions with the ferromagnetic Mn3+OMn3+/Mn4+ sublattice of LSMO. All BFO layers show excellent ferroelectric and piezoelectric properties (coercive field ∼ 740 kV/cm, and d33 = 23 p.m./V for 50 nm; ∼200 kV/cm and 55 p.m./V for 140 nm), exhibiting 180° and 109° DWs structures depending on the thickness. Such multiferroic properties predict the potential realization of new magneto-electronic devices integrated with Si technology.
A structural and physical properties study on ferroelectric (K0·44Na0·52Li0.04)0.97La0·01Nb0·9Ta0·1O3 ceramics with monocrystalline grains of orthorhombic (O) and tetragonal (T) perovskite phases ...coexisting at room temperature (RT) is presented. Different sintering temperatures were evaluated. XRD analysis demonstrates high crystalline quality of both phases with volume fractions depending of the sintering temperature. SEM shows grain facets and morphologies of both phases in all samples. Raman analysis confirms the dopant incorporation and the coexistence of both phases. The contributions of each phase in the dielectric response are deconvoluted using the frequency-temperature dielectric analysis. The orthorhombic-to-tetragonal (TO-T) and tetragonal-to-cubic (TT-C) phase transition temperatures shift ~100 °C below those reported for pure-KNN in all samples, as consequence of the Li, La, and Ta doping combination. Li doping promotes T-phase grain growth and decreases TO-T below RT. La incorporation promotes the O-phase grain growth and decreases TO-T and TT-C. The optimal sintering temperature is 1180 °C with 50-50 volume fractions of T-O phases. Piezoresponse studies show a complex 180°-domain structure.
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•Lead free Li/La doped KNNTa ceramic is constituted by coexisting tetragonal and orthorhombic structured grains.•Li doping promotes tetragonal grain growth and La incorporation promotes the orthorhombic grain growth.•Li and La combination shifts the FE-FE transition below room temperature.•The coexistence of two phases provides better room temperature functionality for applications.
Abstract
A Fe
32
Cu
64
B
4
(FeCuB) alloy was obtained by using an induction furnace under an argon atmosphere. Parameters suitable in the casting processes like voltage, temperature and cooling times ...were optimized. Once the FeCuB alloy was melted and solidified, X-ray diffraction (XRD) and surface morphology analysis were performed through optical and scanning electron microscopy (SEM-EDX). The results showed that complete diffusion of the precursor elements (Fe, Fe2B, Cu) requires thermal homogenization treatments (2 and 4 hours) at 750° as suggested from phase diagram of FeCuB simulation. The XRD analysis revealed that the primary crystallization consists of a mixture of the fcc-FeCuB (79%) and bcc-FeCuB (21%), with a = 3.62Å, spatial group Fm-3m and a = 2.86Å, spatial group Im-3m respectively. Micrographic images show an average grain distribution of
∼
135
µ
m. Finally, long times of homogenization (4 hours) allow a greater uniformity and redistribution of grain boundaries, resulting in the formation of an equiaxed grain structure in the alloy.
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