ABSTRACT
Clustering of magnetic nanoparticles can drastically change their collective magnetic properties, which in turn may influence their performance in technological or biomedical applications. Here, we investigate a commercial colloidal dispersion (FeraSpinTMR), which contains dense clusters of iron oxide cores (mean size around 9 nm according to neutron diffraction) with varying cluster size (about 18-56 nm according to small angle x-ray diffraction), and its individual size fractions (FeraSpinTMXS, S, M, L, XL, XXL). The magnetic properties of the colloids were characterized by isothermal magnetization, as well as frequency-dependent optomagnetic and AC susceptibility measurements. From these measurements we derive the underlying moment and relaxation frequency distributions, respectively. Analysis of the distributions shows that the clustering of the initially superparamagnetic cores leads to remanent magnetic moments within the large clusters. At frequencies below 105 rad s-1, the relaxation of the clusters is dominated by Brownian (rotation) relaxation. At higher frequencies, where Brownian relaxation is inhibited due to viscous friction, the clusters still show an appreciable magnetic relaxation due to internal moment relaxation within the clusters. As a result of the internal moment relaxation, the colloids with the large clusters (FS-L, XL, XXL) excel in magnetic hyperthermia experiments.
ABSTRACT
The structural and magnetic properties of magnetic multi-core particles were determined by numerical inversion of small angle scattering and isothermal magnetisation data. The investigated particles consist of iron oxide nanoparticle cores (9 nm) embedded in poly(styrene) spheres (160 nm). A thorough physical characterisation of the particles included transmission electron microscopy, X-ray diffraction and asymmetrical flow field-flow fractionation. Their structure was ultimately disclosed by an indirect Fourier transform of static light scattering, small angle X-ray scattering and small angle neutron scattering data of the colloidal dispersion. The extracted pair distance distribution functions clearly indicated that the cores were mostly accumulated in the outer surface layers of the poly(styrene) spheres. To investigate the magnetic properties, the isothermal magnetisation curves of the multi-core particles (immobilised and dispersed in water) were analysed. The study stands out by applying the same numerical approach to extract the apparent moment distributions of the particles as for the indirect Fourier transform. It could be shown that the main peak of the apparent moment distributions correlated to the expected intrinsic moment distribution of the cores. Additional peaks were observed which signaled deviations of the isothermal magnetisation behavior from the non-interacting case, indicating weak dipolar interactions.
ABSTRACT
An attempt has been undertaken to evaluate the aetiology of urinary tract infections in a large group of patients and to determine the resistance to ciprofloxacin during therapy, and the efficacy of the drug in treating of urinary tract infections. 52 patients with urinary tract infections were treated with ciprofloxacin. Ciprobay by BAYER was used in coated 500 mg tablets twice a day and intravenous solutions in 200 mg dosages every 12 hours for 10-14 days depending on the clinical condition. Microbiological tests were made according to general methods. Sensitivity evaluation to ciprofloxacin was done using E-tests by AB Biodisk and dilution tests. The most common a etiology of urinary tract infections were Gram-negative Enterobacteriaceae rods, mainly E. coli. Ciprofloxacin gave the best results against Enterobacteriaceae rods (100% eradications). In other infections, effective therapy was possible after determining of the sensitivity in vitro. S. haemolyticus bacteria tended significantly towards resistance to ciprofloxacin during therapy.
Subject(s)
Anti-Infective Agents/therapeutic use , Ciprofloxacin/therapeutic use , Urinary Tract Infections/drug therapy , Ciprofloxacin/pharmacology , Drug Administration Schedule , Drug Resistance, Microbial , Humans , Microbial Sensitivity Tests , Urinary Tract Infections/microbiologyABSTRACT
The study was aimed at observation of influence of subinhibitory doses of selected beta-lactam antibiotics (cefuroxime, ceftazidime, thienamycin) and of ciprofloxacin on morphology and physiology of S. aureus and E. coli. The bacteria were subjected to action of these antibiotics in various subinhibitory concentrations in fluid Mueller-Hinton medium at 37 degrees C for 18 hours, and morphological changes in bacterial cells were observed in light and electronic microscope. In case of E. coli changes appeared as presence of elongated forms, while S. aureus formed giant cells with changes in staining. It was found that intensity of these morphological changes was proportional to concentrations of antibiotics. For determination of influence of tested antibiotics on growth of bacteria they were cultured in the fluid Mueller-Hinton medium containing antibiotics in concentrations of 4, 1 1/4 MIC. The culture lasted for 6 hours, and number of bacterial cells in 1 ml of the medium was periodically determined. Distinct inhibition of growth of bacterial cells was proportional to the used concentrations of antibiotics. Described in this paper morphological changes of bacteria found confirmation in change of their physiology expressed as inhibition of bacterial cell growth.
