Claudia Nadejde

Chemically modified nanoparticles surface for sensing bacterial loading--experimental study based on fluorescence stimulation by iron ions.

The influence of iron ions supplied from magnetite nanoparticles with chemically modified surface on Pseudomonas aeruginosa germ was aimed--with experimental and theoretical approach of the intensity of the fluorescent signal emitted by the pyoverdine like siderophores. As the coated magnetic nanoparticles could function as probes, the possibility of designing a chemical device was considered based on the sensing of iron reduction from Fe(3+) into the more soluble Fe(2+), for detecting various levels of contamination (10 ÷ 10(8) cell/ml) of biological specimens and environmental samples. The proposed mathematical model estimated the fluorescence intensity due to siderophore synthesized by Pseudomonas, considering that the parameter describing the ion-bacteria interaction depends differently on the cell density for different magnetite nanoparticle coatings: linear dependence was found in the case of sodium oleate coating while power function was revealed for tetramethyl ammonium coating of magnetite nanocores, in both cases magnetite suspension being supplied in the same concentration (0.1 μl/ml). The calculated values of fluorescence intensity fitted the experimental data corresponding to magnetite supplied bacteria with graph slopes close to the unit and correlation coefficients of 0.999 and 0.996, while for the control samples, where that parameter was zeroed, correlation coefficient was found of 0.999.

Wet milling versus co-precipitation in magnetite ferrofluid preparation

Various uses of ferrofluids for technical applications continuously raise interest in the improvement and optimization of the preparation methods. This paper deals with the preparation of finely granulated magnetite particles coated with oleic acid in hydrocarbon suspensions following either chemical co-precipitation from iron salt precursors or wet milling of micron size mag- netite powder with the goal to compare the benefits and disadvantages of each method. Microstructural measurements showed that both methods gave similar- sized magnetite particles of 10-15 nm. The wet-milled magnetite suspension had a higher saturation magnetization than that obtained in the relatively rapid co-precipitation synthesis. The different efficacies of ferrophase incorporation into kerosene could be related to the different mechanisms of oleic acid bond- ing to the surface of the nanoparticles. Comparative data showed that wet milling represents a viable alternative to the traditional co-precipitation method since despite of longer processing time, the impact of chemicals on the envi- ronment and remnant water in the final product could be avoided.

Molecular modelling and spectral investigation of some triphenyltetrazolium chloride derivatives

The molecular parameters of 2,3,5-triphenyl-2H-tetrazolium chloride (TTC) and some compounds based on triphenylformazans (TPFs) — resulting from the enzymatic transformation of TTC, were subjected to comparative investigation on the basis of semi-empirical quantum-chemical simulations, revealing some changes in dipole moment and polarisability in the TPFs in comparison with TTC. Chemical shift due to substituents was discussed using electronic absorption bands in the UV-VIS range recorded for diluted solutions in various solvents as well as the absorption spectra recorded in the infrared range for KBr dispersions. The correlation of the spectral shift of the electronic absorption bands with a specific function on the solvent refractive index, as recommended by theoretical studies focused on solute-solvent interactions, revealed the major role played by dispersive and induction forces. For several solvents, a different behaviour could be assigned to specific interactions overlapping with universal solute-solvent interactions.

Functionalized magnetic nanoparticles: Synthesis, characterization, catalytic application and assessment of toxicity

Cost-effective water cleaning approaches using improved treatment technologies, for instance based on catalytic processes with high activity catalysts, are urgently needed. The aim of our study was to synthesize efficient Fenton-like photo-catalysts for rapid degradation of persistent organic micropollutants in aqueous medium. Iron-based nanomaterials were chemically synthesized through simple procedures by immobilization of either iron(II) oxalate (FeO) or iron(III) citrate (FeC) on magnetite (M) nanoparticles stabilized with polyethylene glycol (PEG). Various investigation techniques were performed in order to characterize the freshly prepared catalysts. By applying advanced oxidation processes, the effect of catalyst dosage, hydrogen peroxide concentration and UV-A light exposure were examined for Bisphenol A (BPA) conversion, at laboratory scale, in mild conditions. The obtained results revealed that BPA degradation was rapidly enhanced in the presence of low-concentration H2O2, as well as under UV-A light, and is highly dependent on the surface characteristics of the catalyst. Complete photo-degradation of BPA was achieved over the M/PEG/FeO catalyst in less than 15 minutes. Based on the catalytic performance, a hierarchy of the tested catalysts was established: M/PEG/FeO > M/PEG/FeC > M/PEG. The results of cytotoxicity assay using MCF-7 cells indicated that the aqueous samples after treatment are less cytotoxic.

Magnetic Submicron Powder Preparation and Characterization

The goal of this experimental study was to present a comparative analysis of iron oxides powders obtained by two alternative methods, i.e. the co-precipitation at high temperature from aqueous reaction medium of iron oxides and, respectively, the solvent free method for the preparation magnetite at room temperature. Vibrational absorption spectra evidenced the dominancy of magnetite in both samples, while the X-ray diffractograms revealed the submicron size as well as the presence of additional iron oxide, in the second sample prepared by solvent free method.