Development of nickel-based magnetoliposomes

Liposomes entrapping nickel-based magnetic nanoparticles (magnetoliposomes) were prepared and characterized.This work was supported by FEDER through the COMPETE Program and by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Project of CFUM [PEst-C/FIS/UI0607/2011 (F-COMP-01-0124-FEDER-022711)]. FCT is also acknowledged for the PhD grant of A.R.O. Rodrigues (SFRH/BD/90949/2012)

Magnetoliposomes based on magnetite nanoparticles

In this work, magnetic nanoparticles of magnetite were prepared by soft chemical methods, using different surfactants as templating media. These nanoparticles were either covered with a lipid bilayer, forming dry magnetoliposomes, or entrapped in liposomes - aqueous magnetoliposomes.FCT, FEDER, COMPETE/QREN/EU for financial support to CFUM (Strategic Project PEst-C/FIS/UI0607/2011) and to the research project PTDC/QUI/81238/2006 (FCOMP-01-0124-FEDER-007467)

Magnetoliposomes based on nickel/silica core/shell nanoparticles

In this work, magnetic nanoparticles of nickel core with silica shell were prepared by soft chemical methods, using tetraethyl orthosilicate (TEOS) and different surfactants as templating media. These nanoparticles were either covered with a lipid bilayer or entrapped in liposomes.FCT, FEDER, COMPETE/QREN/EU for financial support to CFUM (Strategic Project PEst-C/FIS/UI0607/2011) and to the research project PTDC/QUI/81238/2006 (FCOMP-01-0124-FEDER-007467)

The phase transition sequence of betaine arsenate investigated by infrared reflectivity

The ac-polarized infrared reflectivity spectra of betaine ortho-arsenic acid single crystals have been measured throughout the ferroelastic–ferroelectric phase transition observed near Tc2 = 120 K. The monoclinic symmetry of the system was explicitly taken into account and a three-polarization technique used for the first time to investigate in detail the critical behaviour of the Bu polar phonons. The results show that near the THz frequency range, the usual approximation of considering the system as pseudoorthorhombic fails, giving rise to errors in the determination of the optical parameters. The obtained spectroscopic data indicate that the phase diagram and the physical mechanism involved in the stabilization of ferroelectricity in betaine arsenate (BA) are more complex than the prevalent view of a simple ordering process in bistable hydrogen bonds

The infrared dielectric tensor and axial diepersion in ceasium L-malate monohydrate

Caesium hydrogen L-malate monohydrate (CsH(C4H4O5)H2O) is a novel coordination compound of L-malic acid and caesium that crystallizes into a monoclinic structure and shows promising properties for application as a piezoelectric, pyroelectric and electro-optic material. In the present work we use polarized infrared reflectivity measurements to investigate the dielectric tensor of the material in the spectral range of 40–4000 cm−1. The use of a three-polarization technique allows us to obtain from the reflectivity data the parameters that characterize the B phonons with wavevectors varying in the plane perpendicular to the monoclinic axis. Consequently, we are able to monitor the frequency dependence of the orientation of the principal dielectric axes in this plane. Using these results we can evaluate the role of polar phonons in the low frequency dielectric response, characterize the dielectric tensor in the terahertz frequency range and describe the axial optical and dielectric dispersion over the frequency range investigated

Structure and dielectric characterization of a new A site deficient La5 3MgTaO6 perovskite

he crystal structure of new A site deficient La5 3MgTaO6 perovskite was investigated by neutron, X ray and electron diffraction. Neutron and X ray powder diffraction spectra were refined in the monoclinic I2 m space group, with the parameters of the unit cell a 5.6304 2 angstrom, b 5.6226 2 angstrom, c 7.9434 2 angstrom and beta 90.04 1 degrees. This structural model presumes a random distribution of the vacancies and takes into account both a rock salt type Mg2 Ta5 cation ordering and a a c 0 configuration of the octahedral tilting. Electron diffraction showed that the crystal structure is more complex at the local level due to a short range vacancy ordering. This observation in combination with the symmetry analysis leads to the conclusion that the C2 m symmetry with 2 root 2a p x 2 root 2a p x 2a p supercell is more adequate for the description of the crystal structure in the local level. Dielectric measurements performed in a wide frequency range were correlated with the crystal structure and compared with other ordered double perovskites. Far infrared spectroscopy was used to characterize the lattice contribution to the dielectric response at the microwave frequencies. The complex dielectric function was evaluated and extrapolated down to the gigahertz range. The effect of the vacancies on the intrinsic dielectric losses is discussed based on the spatial phonon correlation model. c 2006 Elsevier Inc. All rights reserve

Structure and dielectric characterization of a new A-site deficient La5/3MgTaO6 perovskite

The crystal structure of new A-site deficient Lasj3MgTa06 perovskite was investigated by neutron, X-ray and electron diffraction. Neutron and X-ray powder diffraction spectra were refined in the monoclinic 12/m space group, with the parameters of the unit cell a = 5.6304(2)A, b = 5.6226(2) A, c = 7.9434(2)A and p= 90.04(1)". This structural model presumes a random distribution of the vacancies and takes into account both a rock salt-type Mg2+ /Ta5+ cation ordering and a-a-co configuration of the octahedral tilting. Electron diffraction showed that the crystal structure is more complex at the local level due to a short-range vacancy ordering. This observation in combination with the symmetry analysis leads to the conclusion that the C2/m symmetry with 2.J2ap x 2.J2ap x 2ap supercell is more adequate for the description of the crystal structure in the local level. Dielectric measurements performed in a wide frequency range were correlated with the crystal structure and compared with other ordered double perovskites. Far-infrared spectroscopy was used to characterize the lattice contribution to the dielectric response at the microwave frequencies. The complex dielectric function was evaluated and extrapolated down to the gigahertz range. The effect of the vacancies on the intrinsic dielectric losses is discussed based on the spatial phonon correlation model

Magnetic Liposomes based on Nickel Ferrite Nanoparticles for biomedical applications

Nickel ferrite nanoparticles with superparamagnetic behavior at room temperature were synthesized by a coprecipitation method. These magnetic nanoparticles were either covered with a lipid bilayer, forming dry magnetic liposomes (DMLs), or entrapped in liposomes, originating aqueous magnetoliposomes (AMLs). A new and promising method for the synthesis of DMLs is described. The presence of the lipid bilayer in DMLs was confirmed by FRET (Förster Resonance Energy Transfer) measurements between the fluorescent-labeled lipids NBD-C12-HPC (NBD acting as donor) included in the second lipid layer and rhodamine B-DOPE (acceptor) in the first lipid layer. An average donor-acceptor distance of 3 nm was estimated. Assays of the non-specific interactions of magnetoliposomes with biological membranes (modeled using giant unilamellar vesicles, GUVs) were performed. Membrane fusion between both aqueous and dry magnetoliposomes and GUVs was confirmed by FRET, which is an important result regarding applications of these systems both as hyperthermia agents and antitumor drug nanocarriers.This work was supported by FEDER through the COMPETE/QREN/EU Program and by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Project of CFUM [PEst-C/FIS/UI0607/2013 (F-COMP-01-0124-FEDER-022711)]. FCT, POPH-QREN and FSE are acknowledged for the PhD grant of A.R.O. Rodrigues (SFRH/BD/90949/2012) and for financial support to MAP-Fis PhD Programme

Infrared reflectivity study of the phase transitions in sodium ammonium sulphate dihydrate

This work reports a detailed infrared reflectivity investigation of the phase transitions in single crystals of sodium ammonium sulfate dihydrate (SASD). The polarized reflectivity spectra allow us to follow the temperature dependence of the polar vibrational modes and detect the critical behaviour of the vibrational parameters through the two low temperature structural phase transitions observed in the compound. The results obtained show that the mechanism of the transitions in SASD is complex, involving a strong coupling between pseudo-spins and phonons. In the paraelectric phase, the driving mechanism of the first phase transition (Tc1 = 95 K) appears to be related to a relaxation with a characteristic frequency that is much lower than the phonon frequencies. In the temperature range corresponding to the first ferroelectric phase (Tc1 > T > Tc2 = 79 K), the dynamics of the lattice change considerably and the parameters characterizing several vibrational modes display anomalous temperature dependences. The second phase transition occurring at Tc2 is marked by an important and discontinuous change of the spectral shape, indicating that a considerable lattice distortion is involved