National Institute Of Materials Physics - Romania

Composites of magnetite (Fe3O4) nanoparticles dispersed in a polydimethylsiloxane (PDMS) matrix were prepared by a molding process. Two types of samples were obtained by free polymerization with randomly dispersed particles and by polymerization in an applied magnetic field. The magnetite nanoparticles were obtained from magnetic micrograins of acicular goethite (alpha-FeOOH) and spherical hematite (alpha-Fe2O3), as demonstrated by XRD measurements. The evaluation of morphological and compositional properties of the PDMS:Fe3O4 composites, performed by SEM and EDX, showed that the magnetic particles were uniformly distributed in the polymer matrix. Addition of magnetic dispersions promotes an increase of thermal conductivity compared with pristine PDMS, while further orienting the powders in a magnetic field during the polymerization process induces a decrease of the thermal conductivity compared with the un-oriented samples. The shape of the magnetic dispersions is an important factor, acicular dispersions providing a higher value for thermal conductivity compared with classic commercial powders with almost spherical shapes.

The electrochemical behavior and the interaction of the immunosuppressive drug azathioprine (AZA) with deoxyribonucleic acid (DNA) were investigated using voltammetric techniques, mass spectrometry (MS), and scanning electron microscopy (SEM). The redox mechanism of AZA on glassy carbon (GC) was investigated using cyclic and differential pulse (DP) voltammetry. It was proven that the electroactive center of AZA is the nitro group and its reduction mechanism is a diffusion-controlled process, which occurs in consecutive steps with formation of electroactive products and involves the transfer of electrons and protons. A redox mechanism was proposed and the interaction of AZA with DNA was also investigated. Morphological characterization of the DNA film on the electrode surface before and after interaction with AZA was performed using scanning electron microscopy. An electrochemical DNA biosensor was employed to study the interactions between AZA and DNA with different concentrations, incubation times, and applied potential values. It was shown that the reduction of AZA molecules bound to the DNA layer induces structural changes of the DNA double strands and oxidative damage, which were recognized through the occurrence of the 8-oxo-deoxyguanosine oxidation peak. Mass spectrometry investigation of the DNA film before and after interaction with AZA also demonstrated the formation of AZA adducts with purine bases.

The structure of the IrQ(ppy)(2) organometallic dual phosphorescent compound was experimentally and theoretically investigated. The Metal-to-Ligand Charge Transfer toward the phenylpiridine and quinoline ligands explains its dual phosphorescence property. The IrQ(ppy)(2) organometallic's electronic properties extend the absorption spectra toward the lower energies than Ir(ppy)(3) due to the bandgap reduction induced by the quinoline ligand. The magneto-optical measurements reveal A-terms, which are produced by splitting the triplet states and B-terms, which arise when the electronic levels are mixed in the magnetic field. The IrQ(ppy)(2) molecule's transport properties confirm an ambipolar character, consisting of a higher hole transport character induced by the phenyilpiridine ligands and a lower electron transport character induced by the quinoline ligand. (C) 2021 Elsevier B.V. All rights reserved.

Gold nanoparticles (similar to 10 nm) were deposited on titanium dioxide nanoparticles (similar to 21 nm) and the material obtained was characterized using IR, UV-Vis, N-2 adsorption-desorption isotherm, DLS, EDS (EDX), TEM, XPS, and XRD techniques. It was found that the methylene blue dye is degraded in the presence of this material when using hydrogen peroxide as the oxidant. Tests were performed at 2, 4, 6, and 24 h, with hydrogen peroxide contents varying from 1 to 5 mg/mL. Longer exposure time and a higher content of oxidant led to the degradation of methylene blue dye at up to 90%. The material can be reused several times with no loss of activity.

The effect of temperature on the features of the crystal and magnetic structures, as well as the magnetic properties of the solid solution of SrFe10.8In1.2O19 hexaferrite was investigated. The appearance of ferroelectric properties was detected at room temperature, which contradicts the generally accepted opinion on the description of the crystal structure of hexaferrites within the framework of the centrosymmetric P6(3)/mmc (No. 194) space group. The reasons of spontaneous polarization in solid solutions of hexaferrites remain controversial. No deviation from the collinear magnetic structure was found in the investigated temperature range from 1.5 to 350 K, while the thermal expansion of the unit cell was practically absent in the range from 1.5 to 50 K. The crystal structure of hexaferrites was considered in the framework of both centrosymmetric P6(3)/mmc and non-centrosymmetric P6(3)mc space groups, which allowed us to associate the emerging spontaneous polarization with unequal distortions of neighboring oxygen polyhedra.

Fibres of poly(methyl methacrylate) were obtained by electrospinning, subjected to coating with a gold layer and then attached on a thin polyethylene terephthalate substrate in order to obtain flexible electrodes for biosensing applications. The morphology of these electrodes, investigated by scanning electron microscopy showed multilayers of random oriented fibres of approx. 400 nm diameter. The electrochemical characterization of these flexible electrodes was performed by cyclic voltammetry and electrochemical impedance spectroscopy in acid and neutral media, in the absence and in the presence of redox probes, proving their superior performance (e.g. 5fold current density value) when compared to planar gold electrodes obtained on silicon wafers. The electrodes obtained from conductive electrospun polymeric fibres nets were tested by cyclic voltammetry and amperometry for the detection of hydrogen peroxide with a sensitivity of 0.84 mA cm-2 mM-1 and a detection limit of 20.40 ?M. The immobilization of the model enzyme glucose oxidase at the surface of the gold-coated electrospun polymeric fibres electrode was investigated and the obtained biosensor was applied for glucose determination in aqueous solutions by fixed potential amperometry with a sensitivity of 3.10 ?A cm-2 mM-1, a detection limit of 0.33 mM, and reduced interferences. Also, the practical applicability of the biosensor was tested for the detection of glucose in artificial sweat and serum samples.

Peppers are consumed all over the world, have several benefits to human health, such as antioxidant properties that can prevent diseases related to free radicals such as cardiovascular, inflammatory diseases, cancer, among others. This work aimed to evaluate the antioxidant capacity (AOC) of 36 varieties of peppers through ABTS and DPPH radical scavenging, electroanalytical assays, and to verify the vasorelaxant properties of selected samples. The greater the amount of capsaicin found in the extracts, the higher the AOC the greater the vasorelaxation. Naga had the highest scoring for antioxidant capacity, pout showed the lowest antioxidant capacity, vase pyramid intermediate level, whereas the capsaicin content followed the same trend. Extracts from all pepper varieties studied presented vasorelaxant properties in independent and dependent endothelial pathways.

The 20S proteasome enzyme complex is involved in the proteolytic degradation of misfolded and oxidatively damaged proteins and is a focus of medical research for the development of compounds with pharmaceutical properties, which are active in cancer cells and/or neurodegenerative diseases. The present study aims to develop a biosensor for investigating the 20S proteasome activity and inhibition by means of electrochemical methods. The 20S proteasome is best immobilized at the electrode surface through bio-affinity interactions with antibodies that target different subunits on the 20S proteasome, enabling the investigation of the effect of an enzyme's orientation on biosensor response. The enzymatic activity is analyzed by fixed potential amperometry with the highest sensitivity of 24 mu A cm(-2) mM(-1) and a LOD of 0.4 mu M. The detection principle involves the oxidation of an electroactive probe that is released from the enzyme's substrates upon proteolysis. The most sensitive biosensor is then used to study the multicatalytic activity of the 20S proteasome, i.e. the caspase-, trypsin- and chymotrypsin-like activity, by analyzing the biosensor's sensitivity towards different substrates. The behavior of the immobilized 20S proteasome is investigated as a function of substrate concentration. The kinetic parameters are derived and compared with those obtained when the enzyme was free in solution, with K-0.5 values being one to two orders of magnitude lower in the present case. Two 20S inhibitors, epoxomicin and bortezomib, are investigated by analyzing their influence on the 20S biosensor response. The proposed analytical method for proteasome activity and inhibitor screening has the main advantage of being cost-effective compared to the ones typically employed.

Three commercial powders of MgB2 were tested in vitro by MTS and LDH cytotoxicity tests on the HS27 dermal cell line. Depending on powders, the toxicity concentrations were established in the range of 8.3-33.2 mu g/ml. The powder with the lowest toxicity limit was embedded into polyvinylpyrrolidone (PVP), a biocompatible and biodegradable polymer, for two different concentrations. The self-replenishing MgB2-PVP composite materials were coated on substrate materials (plastic foil of the reservoir and silicon tubes) composing a commercial urinary catheter. The influence of the PVP-reference and MgB2-PVP novel coatings on the bacterial growth of Staphylococcus aureus ATCC 25923, Enterococcus faecium DMS 13590, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, in planktonic and biofilm state was assessed in vitro at 6, 24, and 48 h of incubation time. The MgB2-PVP coatings are efficient both against planktonic microbes and microbial biofilms. Results open promising applications for the use of MgB2 in the design of anti-infective strategies for different biomedical devices and systems.

In the present study, a new low-cost bioceramic nanocomposite based on porous hydroxyapatite (HAp) and cetyl trimethyl ammonium bromide (CTAB) as surfactant was successfully obtained by a simple chemical co-precipitation. The composition and structure of the HAp-CTAB were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), scanning electron microscope (SEM) equipped with an energy dispersive X-ray (EDX) spectrometer, and N-2 adsorption/desorption analysis. The capacity of HAp-CTAB nanocomposites to remove the lead ions from aqueous solutions was studied by adsorption batch experiments and proved by Langmuir and Freundlich models. The Pb2+ removal efficiency of HAp-CTAB biocomposite was also confirmed by non-destructive ultrasound studies. The cytotoxicity assays showed that the HAp-CTAB nanocomposites did not induce any significant morphological changes of HeLa cells after 24 h of incubation or other toxic effects. Taken together, our results suggests that the obtained porous HAp-CTAB powder could be used for the decontamination of water polluted with heavy metals, such as Pb2+.