A. Pires

Room temperature magnetocaloric effect and refrigerant capacitance in La0.7Sr0.3MnO3 nanotube arrays

High aspect ratio La0.7Sr0.3MnO3 nanotube (NT) arrays have been synthesized using nitrates based sol-gel precursor by nanoporous anodized aluminum oxide template assisted method. Their phase purity and microstructures were analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive x-ray spectroscopy. Magnetocaloric effect (MCE) of as prepared NTs was investigated by means of field dependence magnetization measurements. Significant magnetic entropy change, −△SM = 1.6 J/kg K, and the refrigerant capacitance, RC = 69 J/kg, were achieved near the transition temperature at 315 K for 5 T. For comparison, a bulk sample was also prepared using the same precursor solution which gives a value of −△SM = 4.2 J/kg K and a RC = 165 J/kg. Though the bulk sample exhibits higher △SM value, the NTs present an expanded temperature dependence of −△SM curves that spread over a broad temperature range and assured to be appropriate for active magnetic refrigeration. The diminutive MCE observed in mangani...

Magnetocaloric effect in La0.7Ca0.3MnO3 nanotube arrays with broad working temperature span

We have studied the magnetic entropy change of highly ordered La0.7Ca0.3MnO3 nanotube arrays synthesized by template assisted sol-gel method in temperatures ranging from 179 to 293 K and in magnetic fields up to 5 T. From the measurements of isothermal magnetization, we have calculated the maximum isothermal magnetic entropy change of −△SM = 1.9 J/kg K around the Curie temperature at 236 K for a field of 5 T. The nanotubes present lower magnetic entropy change compared with their bulk counterpart (−△SM = 4.8 J/kg K) which was prepared by the same sol-gel route. Such diminished magnetic entropy change observed in nanotubes is explained by the disordered magnetic states which are created on the surface sites of nanograins due to the larger surface to volume ratio. However, the nanotubes present an expanded magnetic transition that extends over a wide temperature range and suggest that such manganite nanotubes could be used for magnetic refrigeration with broad working temperature span.

Magnetoliposomes as carriers for promising antitumor thieno[3,2-b]pyridin-7-arylamines: photophysical and biological studies

Magnetoliposomes containing superparamagnetic manganese ferrite nanoparticles were tested as nanocarriers for two new promising antitumor drugs, a N-(3-methoxyphenyl)thieno[3,2-b]pyridin-7-amine (1) and a N-(2-methoxy-phenyl)thieno[3,2-b]pyridin-7-amine (2). The fluorescence emission of both compounds was studied in different polar and non-polar media, evidencing a strong intramolecular charge transfer character of the excited state of both compounds. These in vitro potent antitumor thienopyridine derivatives were successfully incorporated in both aqueous and solid magnetoliposomes, with encapsulation efficiencies higher than 75%. The magnetic properties of magnetoliposomes containing manganese ferrite nanoparticles were measured for the first time, proving a superparamagnetic behaviour. Growth inhibition assays on several human tumor cell lines showed very low GI50 values for drug-loaded aqueous magnetoliposomes, comparing in most cell lines with the ones previously obtained using the neat compounds. These results are important for future drug delivery applications using magnetoliposomes in oncology, through a dual therapeutic approach (simultaneous chemotherapy and magnetic hyperthermia).

Magnetoliposomes containing magnesium ferrite nanoparticles as nanocarriers for the model drug curcumin

Magnesium ferrite nanoparticles, with diameters around 25 nm, were synthesized by coprecipitation method. The magnetic properties indicate a superparamagnetic behaviour, with a maximum magnetization of 16.2 emu g−1, a coercive field of 22.1 Oe and a blocking temperature of 183.2 K. These MgFe2O4 nanoparticles were used to produce aqueous and solid magnetoliposomes, with sizes below 130 nm. The potential drug curcumin was successfully incorporated in these nanosystems, with high encapsulation efficiencies (above 89%). Interaction by fusion between both types of drug-loaded magnetoliposomes (with or without PEGylation) and models of biological membranes was demonstrated, using FRET or fluorescence quenching assays. These results point to future applications of magnetoliposomes containing MgFe2O4 nanoparticles in cancer therapy, allowing combined magnetic hyperthermia and chemotherapy.