Alternative low-cost approach to the synthesis of magnetic iron oxide nanoparticles by thermal decomposition of organic precursors.

A new approach to thermal decomposition of organic iron precursors is reported, which results in a simpler and more economical method to produce well crystallized γ-Fe2O3 nanoparticles (NPs) with average sizes within the 3-17 nm range. The NPs were characterized by TEM, SAED, XRD, DLS-QELS, Mössbauer spectroscopy at different temperatures, FT-IR and magnetic measurements. The obtained γ-Fe2O3 NPs are coated with oleic acid and, in a lower quantity, with oleylamine (about 1.5 nm in thickness). It was shown that changing operative variables allows us to tune the average particle diameters and obtain a very narrow or monodisperse distribution of sizes. The γ-Fe2O3 NPs behave superparamagnetically at room temperature and their magnetization saturation is reduced by about 34% in comparison with bulk maghemite. The results indicate that the distance between two neighbour NPs, generated by the coating, of about 3 nm is insufficient to inhibit interparticle magnetic interactions when the average diameter is 8.8 nm. The good quality of the NPs, obtained through the present low-cost and easy-handling process, open a new perspective for future technological applications.

Effect of the curing conditions on the properties of an acrylic denture base resin microwave-polymerised.

OBJECTIVES: The aim of this study is to evaluate the effect of the different conditions of curing on the residual monomer levels, hardness and impact strength of a microwave-polymerised acrylic resin. METHODS: The material was polymerised in a microwave oven in four different conditions of power and curing time. The kinetics of release of residual monomer in water was evaluated by spectrophotometric method up to 24 h. The hardness of the sample was determined by the Rockwell method and the impact strength tested by the Charpy method. The results were subjected to statistical analysis using ANOVA and Tukey's test for comparison. RESULTS: The levels of residual monomer were found dependent upon the curing conditions and they were correlated with the values of impact strength. Significant differences were observed in this property regarding the analysed conditions (p<0.001). CONCLUSIONS: From the appropriate selection of power and time of curing of the resin, it is possible to optimise the level of residual monomer and a low cytotoxicity keeping at the same time the best mechanical properties.

A vanadium/aspirin complex controlled release using a poly(beta-propiolactone) film. Effects on osteosarcoma cells.

A delivery system for vanadium was developed using poly(beta-propiolactone) (PbetaPL) films. The release kinetics of a complex of vanadium (IV) with aspirin (VOAspi) was evaluated with films prepared from polymers of different molecular weights, as well as with variable drug load. A sustained release of vanadium over 7 days was achieved. The drug release kinetics depends on contributions from two factors: (a) diffusion of the drug; and (b) erosion of the PbetaPL film. The experimental data at an early stage of release were fitted with a diffusion model, which allowed determination of the diffusion coefficient of the drug. VOAspi does not show strong interaction with the polymer, as demonstrated by the low apparent partition coefficient (approximately 10(-2)). UMR106 osteosarcoma cells were used as a model to evaluate the anticarcinogenic effects of the VOAspi released from the PbetaPPL film. VOAspi-PbetaPL film inhibited cell proliferation in a dose-response manner and induced formation of approximately half of the thiobarbituric acid reactive substances (TBARS), an index of lipid peroxidation. compared to that with free VOAspi in solution. The unloaded PbetaPL film did not generate cytotoxicity, as evaluated by cell growth and TBARS. Thus, the polymer-embedded VOAspi retained the antiproliferative effects showing lower cytotoxicity than the free drug. Results with VOAspi-PbetaPL films suggest that this delivery system may have promising biomedical and therapeutic applications.

Revision of a theoretical expression for gas-liquid chromatographic retention.

In this communication, we revise some aspects of the [ideal gas/Van der Waals fluid] partition, derived in an earlier publication. The general character of the conclusions concerning the dependence of the partial molar free energy of solution, deltaGs(n), on the chain length, n, of linear solute molecules is shown through the relationship with more general partition formulations. Simultaneously, the correction of an error in the expression of the retention time dependence on the phase ratio of the chromatographic column, beta, is carried out. The misleading source of this error was redundant accounting in the solute translational contribution to deltaGs(n).

Adsorption of an ionic homopolypeptide to a flat surface induced by pH change.

This paper presents a model for pH-dependent adsorption of an ionic homopolypeptide with secondary structure on a flat surface. This model is developed by generalization of a discrete model of semistiff chain with short-range interaction, between homopolypeptide chain and surface. The presence of intramolecular repulsive interaction as well as secondary structure is introduced here by modified Zimm-Bragg stabilization parameters. The model predicts that in the case of low degree of ionization, the adsorption behaviour of an ionic and non-ionic homopolypeptide are qualitatively similar (i.e. both show a second-order phase-transition, characteristic of this phenomenon). We also illustrate the prediction of the model about the critical absorption energy in the case of selective interaction, and show that a discontinuity in the melting-temperature behaviour appears when the pH is tuned to a critical pH value (pHc).