Magnetic Properties of Mn-Doped Amorphous SiO2 Matrix

Samples of Mn-doped amorphous SiO2 matrix with manganese concentration 0.7 and 3 at.% have been prepared by a sol-gel method. Transmission electron microscopy analysis has shown that the samples contain agglomerates of amorphous silica particles 10 - 20 nm in size. Two types of Mn-rich particles are dispersed in silica matrix, smaller nanoparticles with dimensions between 3 and 10 nm, and larger crystalline areas consisting of aggregates of the smaller nanoparticles. High-temperature magnetic susceptibility reveals that dominant magnetic phase at higher temperatures is lambda-MnO2. At temperatures below T-C = 43 K strong ferrimagnetism originating from the minor Mn3O4 phase masks the relatively weak magnetism of lambda-MnO2. Magnetic field dependence of the maximum in the zero-field-cooled magnetization for both the samples in the vicinity of 40 K, and a frequency shift of the real component of the AC magnetic susceptibility in the sample with 3 at.% Mn suggest that the magnetic moments of the smaller Mn3O4 nanoparticles with dimensions below 10 nm are subject to thermally activated blocking process just below the Curie temperature T-C. The low-temperature maximum in the zero-field-cooled magnetization observed for both the samples below 10 K indicates possible spin glass freezing of the magnetic moments in the geometrically frustrated Mn sublattice of the lambda-MnO2 crystal structure.12th Annual YUCOMAT Conference, Sep 06-10, 2010, Herceg Novi, Montenegr

A comparative antimicrobial and toxicological study of gold(III) and silver(I) complexes with aromatic nitrogen-containing heterocycles: synergistic activity and improved selectivity index of Au(III)/Ag(I) complexes mixture

Five aromatic nitrogen-containing heterocycles, pyridazine (pydz, 1), pyrimidine (pm, 2), pyrazine (pz, 3), quinoxaline (qx, 4) and phenazine (phz, 5) have been used for the synthesis of gold(III) and silver(I) complexes. In contrast to the mononuclear Au1-5 complexes all having square-planar geometry, the corresponding Ag1-5 complexes have been found to be polynuclear and of different geometries. Complexes Au1-5 and Ag1-5, along with K[AuCl4], AgNO3 and N-heterocyclic ligands used for their synthesis, were evaluated by in vitro antimicrobial studies against a panel of microbial strains that lead to many skin and soft tissue, respiratory, wound and nosocomial infections. All tested complexes exhibited excellent to good antibacterial activity with minimal inhibitory (MIC) values in the range of 2.5 to 100 mu g mL(-1) against the investigated strains. The complexes were particularly efficient against pathogenic Pseudomonas aeruginosa (MIC = 2.5-30 mu g mL(-1)) and had a marked ability to disrupt clinically relevant biofilms of strains with high inherent resistance to antibiotics. Moreover, the Au1-4 and Ag1-5 complexes exhibited pronounced ability to competitively intercalate double stranded genomic DNA of P. aeruginosa, which was demonstrated by gel electrophoresis techniques and supported by molecular docking into the DNA major groove. Antiproliferative effect on the normal human lung fibroblast cell line MRC5 has also been evaluated in order to determine therapeutic potential of Au1-5 and Ag1-5 complexes. Since the investigated gold(III) complexes showed much lower negative effects on the viability of the MRC5 cell line than their silver(I) analogues and slightly lower antimicrobial activity against the investigated strains, the combination approach to improve their pharmacological profiles was applied. Synergistic antimicrobial effect and the selectivity index of 10 were achieved for the selected gold(III)/silver(I) complexes mixtures, as well as higher P. aeruginosa PAO1 biofilm disruption activity, and improved toxicity profile towards zebrafish embryos, in comparison to the single complexes. To the best of our knowledge, this is the first report on synergistic activity of gold(III)/silver(I) complexes mixtures and it could have an impact on development of new combination therapy methods for the treatment of multi-resistant bacterial infections.Supplementary material: [http://cherry.chem.bg.ac.rs/handle/123456789/3334

Supplementary data for the article: Savić, N. D.; Milivojevic, D. R.; Glišić, B. D.; Ilic-Tomic, T.; Veselinovic, J.; Pavic, A.; Vasiljevic, B.; Nikodinovic-Runic, J.; Djuran, M. I. A Comparative Antimicrobial and Toxicological Study of Gold(III) and Silver(i) Complexes with Aromatic Nitrogen-Containing Heterocycles: Synergistic Activity and Improved Selectivity Index of Au(III)/Ag(i) Complexes Mixture. RSC Advances 2016, 6 (16), 13193–13206. https://doi.org/10.1039/c5ra26002g

Supplementary material for: [https://doi.org/10.1039/c5ra26002g]Related to published version: [http://cherry.chem.bg.ac.rs/handle/123456789/2041

Sol-gel as a Method to Tailor the Magnetic Properties of Co1+yAl2-yO4

The magnetic properties of mesoscopic materials are modified by size and surface effects. We present a sol-gel method used to tailor these effects, and illustrate it on Co1+yAl2-yO4 spinel. Nanocomposites made of spinel oxide Co1+yAl2-yO4 particles dispersed in an amorphous SiO2 matrix were synthesized. Samples with various mass fractions -x of Co1+yAl2-yO4 in composite, ranging from predominantly SiO2 (x = 10 wt%) to predominantly spinel (x = 95 wt%), and with various Co concentrations in spinel y were studied. The spinel grain sizes were below 100 nm with a large size distribution, for samples with predominant spinel phase. Those samples showed Curie-Weiss paramagnetic behavior with antiferromagnetically interacting Co ions (theta approximate to -100 K). The grain sizes of spinel stays confined in 100 nm range even in the spinel samples diluted with as low as 5 wt% concentration of amorphous SiO2. For the samples with predominant SiO2 the crystalline nanoparticles are well separated and of size of around 100 nm, but with presence of much smaller spinel nanoparticles of about 10 nm. The magnetic properties of the samples with predominant silica phase showed complex behavior, spin-glass magnetic freezing at the lowest temperatures and lower absolute value of theta and consequently lower exchange constant

Supplementary data for the article: Savić, N. D.; Milivojevic, D. R.; Glišić, B. D.; Ilic-Tomic, T.; Veselinovic, J.; Pavic, A.; Vasiljevic, B.; Nikodinovic-Runic, J.; Djuran, M. I. A Comparative Antimicrobial and Toxicological Study of Gold(III) and Silver(i) Complexes with Aromatic Nitrogen-Containing Heterocycles: Synergistic Activity and Improved Selectivity Index of Au(III)/Ag(i) Complexes Mixture. RSC Advances 2016, 6 (16), 13193–13206. https://doi.org/10.1039/c5ra26002g

Supplementary material for: [https://doi.org/10.1039/c5ra26002g]Related to published version: [http://cherry.chem.bg.ac.rs/handle/123456789/2041

Magnetic properties of Mn-oxide nanoparticles dispersed in an amorphous SiO2 matrix

Samples of Mn-oxide nanoparticles dispersed in an amorphous SiO2 matrix with manganese concentration 0.7 and 3 at% have been synthesized by a sol-gel method. Transmission electron microscopy analysis has shown that the samples contain agglomerates of amorphous silica particles 10-20 nm in size. Insilica matrix two types of Mn-rich particles are dispersed, smaller nanoparticles with dimensions between 3 and 10 nm, and larger crystalline areas consisting of aggregates of the smaller nanoparticles. High temperature magnetic susceptibility study reveals that dominant magnetic phase at higher temperatures is lambda-MnO2. At temperatures below T-C = 43 K strong ferrimagnetism originating from the minor Mn3O4 phase masks the relatively weak magnetism of lambda-MnO2 with antiferromagnetic interactions. Magnetic field dependence of the maximum in the zero-field-cooled magnetization for both the samples in the vicinity of 40 K, and a frequency shift of the real component of the ac magnetic susceptibility in the sample with 3 at% Mn suggest that the magnetic moments of the smaller Mn3O4 nanoparticles with dimensions below 10 nm are exposed to thermally activated blocking process just below the Curie temperature T-C. Appearance of a maximum in the zero-field-cooled magnetization for both the samples below 10 K indicates possible spin glass freezing of the magnetic moments at low temperatures which might occur in the geometrically frustrated Mn sublattice of the lambda-MnO2 crystal structure. (C) 2010 Elsevier B.V. All rights reserved

Synthesis and densification of single-phase mayenite (C12A7)

Mayenite (C12A7) powders have been synthesized by self-combustion method (glycine/nitrate procedure - GNP and a newly suggested modified glycine/nitrate procedure - MGNP). The MGNP is derived from the GNP by substituting a portion of Al-nitrate with the less expensive Al-acetate. The effect of synthesis conditions of both procedures on the phase evolution was studied. Mayenite samples, obtained by using GNP and MGNP, followed by thermal treatment in air, were analyzed by using XRD method. The obtained results showed that crystallization started at 900 degrees C for the GNP and at 750 degrees C for the MGNP while below these temperatures samples are amorphous. Also, only observed phase was mayenite for MGNP, while a secondary phase is present in samples synthesized by using GNP. Scanning electron microscopy (SEM), electron paramagnetic resonance (EPR) and nuclear magnetic resonance spectroscopy (NMR) were used to characterize the pure mayenite phase at room temperature. Sintering behavior was studied by dilatometry. A relative density of 94% is obtained at 1300 degrees C. (C) 2016 Elsevier Ltd. All rights reserved

Magnetic properties of ultrasmall iron-oxide nanoparticles

The work presents structural and magnetic properties of ultrasmall magnetic nanoparticles consisting of inorganic iron oxide core and organic ester shell, dispersed in an organic fluid, synthesized via polyol route. The structure analysis shows that nanoparticles are crystalline, less than 3 nm in size, mutually clearly separated. The magnetic properties are in accordance with the size of the nanoparticles and do not indicate interparticle interactions. The particles show pure superparamagnetic behavior with very low blocking temperature. ZFCFC bifurcation and ac susceptibility peaks are at temperatures T-B LT 12 K. The properties of fluid were compared with dried powder sample. Drying of fluid brings about interactions between the magnetic nanoparticles that considerably affect spin dynamics of the particles. The surface of nanoparticles has a significant influence on their behavior. The Mssbauer parameters indicate existence of gamma-Fe2O3 core and non-stoichiometric surface layer. Magnetic field dependent magnetization analysis suggests smaller apparent size of the particles d(0) = 0.56 nm. High magnetic anisotropy due to surface layer anisotropy was measured to be of the order 10(6) erg/cm(3) that is two orders of magnitude higher than that in bulk material. (C) 2014 Elsevier B.V. All rights reserved

Biofilm-forming ability and infection potential of Pseudomonas aeruginosa strains isolated from animals and humans

Pseudomonas aeruginosa has been amongst the top 10 'superbugs' worldwide and is causing infections with poor outcomes in both humans and animals. From 202 P. aeruginosa isolates (n = 121 animal and n = 81 human), 40 were selected on the basis of biofilm-forming ability and were comparatively characterized in terms of virulence determinants to the type strain P. aeruginosa PAO1. Biofilm formation, pyocyanin and hemolysin production, and bacterial motility patterns were compared with the ability to kill human cell line A549 in vitro. On average, there was no significant difference between levels of animal and human cytotoxicity, while human isolates produced higher amounts of pyocyanin, hemolysins and showed increased swimming ability. Non-parametric statistical analysis identified the highest positive correlation between hemolysis and the swarming ability. For the first time an ensemble machine learning approach used on the in vitro virulence data determined the highest relative predictive importance of the submerged biofilm formation for the cytotoxicity, as an indicator of the infection ability. The findings from the in vitro study were validated in vivo using zebrafish (Danio rerio) embryos. This study highlighted no major differences between P. aeruginosa species isolated from animal and human infections and the importance of pyocyanin production in cytotoxicity and infection ability

Magnetic properties and magnetic relaxation in a suspension of CoFe2O4 nanoparticles

We present a study of dynamic magnetic properties of superparamagnetic CoFe2O4 nanoparticles of average size 5.9 nm suspended in an organic liquid. The relaxation times of the particle magnetic moments are found to be strongly dependent on the size of the particles, and also considerably dependent on interparticle interactions. Besides the lower frequency peak, an additional much faster relaxation is observed in the frequency dependence of the imaginary part of the ac magnetic susceptibility below the freezing point of the liquid. It is found that a large contribution to the magnetic relaxation of the lower frequency peak originates from the particles of dimensions 6.3-5.1 nm with interparticle interactions in the range 25-82 K, which correspond to nearer-neighbor particles. Much faster relaxation indicates that its significant part arises from the particles of dimensions 5.8-5.0 nm with interactions in the range 1-52 K which include also more distant neighbors. (C) 2013 AIP Publishing LLC