A. Deriu

Magnetic, Mössbauer, and neutron diffraction investigations of W‐type hexaferrite BaZn2−xCoxFe16O27 single crystals

Macroscopic magnetic measurements, Mossbauer, and neutron diffraction studies have been carried out on BaCoxZn2−xFe16O27 [(Zn−Co)2‐W] single‐crystal hexaferrites. The extrapolated saturation magnetization values σs(0) are slightly lower than those found in the literature. Such differences have been justified as due to the different Co and Zn distributions among the tetrahedral sites.The Co ions induce a strong planar contribution to the magnetic anisotropy. At low temperature, the spin order, found from the macroscopic magnetic measurements and preliminary neutron diffraction studies, is planar, while the Mossbauer data indicate a conical order with an angle of 70° with respect to the c axis. By increasing the temperature, the cobalt anisotropy decreases and a spin reorientation to easy axis is observed.

Structure of self-organized multilayer nanoparticles for drug delivery.

The combined use of cryo-TEM, dynamic light scattering, and small-angle X-ray and neutron scattering techniques allows a detailed structural model of complex pharmaceutical preparations of soybean lecithin/chitosan nanoparticles used as drug vectors to be worked out. Charge-driven self-organization of the lipid(-)/polysaccharide(+) vesicles occurs during rapid injection, under mechanical stirring, of an ethanol solution of soybean lecithin into a chitosan aqueous solution. We conclude that beyond the charge inversion region of the phase diagram, i.e., entering the redissolution region, the initial stages of particle formation are likely to be affected by a re-entrant condensation effect at the nanoscale. This behavior resembles that at the mesoscale which is well-known for polyion/amphiphile systems. Close to the boundary of the charge inversion region, nanoparticle formation occurs under a maximum condensation condition at the nanoscale and the complexation-aggregation process is driven toward a maximum multilamellarity. Interestingly, the formulation that maximizes vesicle multilamellarity corresponds to that displaying the highest drug loading efficiency.

A magnetic and structural study of Mn, Co, and Ni substituted Fe3Ge2 hexagonal germanides

Structural (x-ray and neutron diffraction), Mossbauer, and magnetic investigations were performed in order to study Mn, Co, and Ni substituted Fe3.34Ge2 hexagonal germanides. From an x-ray diffraction analysis of Fe3.34Ge2 single crystal data Fe was found to enter exclusively 2a and 2d sites of the defective structure, while vacancies only occupy the 2d site in the congruent composition. It was also found that Ge atoms are slightly displaced from 2c site towards an adjacent vacancy in a 2d site. The preferential entrance of Mn, Co, and Ni was determined by neutron powder diffraction and Mossbauer data in the paramagnetic region. The complex Mossbauer spectra in the ferromagnetic region were interpreted in terms of a distribution of crystal field gradient directions which has its origins from the splitting of the coordinates of Ge atoms due to the presence of vacancies at 2d site. No magnetic contribution was found for Ni, while a small magnetic moment was found to be supplied by Co. In the 2a site (the on...

Mn2+, Ti4+ substituted barium ferrite

Abstract The substitution of iron by manganese in M-type barium ferrite BaFe 12 O 19 has been investigated with the aim of elucidating its effect on the magnetic and magnetostrictive properties. Substitution of up to 0.4 manganese atoms per unit formula did not affect the magnetization whilst the anisotropy and magnetostriction decreased by 30% and 20%, respectively. Higher manganese contents gave rise to large perturbations of the collinear magnetic order mainly in the plane of the 12K sublattice. The distribution of manganese among the various cation sublattices has also been derived from the analysis of the Mossbauer spectra.

3d and 4f magnetism in Nd2Fe14−xCoxB and Y2Fe14−xCoxB compounds

A systematic study of the effects of Co substitution on the crystal structure and magnetic anisotropy of Y2Fe14−xCoxB and Nd2Fe14−xCoxB has been carried out in order to clarify the different roles and contributions to the anisotropy of both rare earth and transition metals. The substitution of Co leads to an enhancement of the Curie temperature in both series of compounds. The Co has been found to provide a planar anisotropy which is larger than that of the axial anisotropy of Fe. A marked site preference has been observed. Two distinct contributions of the Co to the anisotropy have been observed.

Structure and organization of phospholipid/polysaccharide nanoparticles

In recent years nanoparticles and microparticles composed of polymeric or lipid material have been proposed as drug carriers for improving the efficacy of encapsulated drugs. For the production of these systems different materials have been proposed, among them phospholipids and polysaccharides due to their biocompatibility, biodegradability, low cost and safety. We report here a morphological and structural investigation, performed using cryo-TEM, static light scattering and small angle neutron and x-ray scattering, on phospholipid/saccharide nanoparticles loaded with a lipophilic positively charged drug (tamoxifen citrate) used in breast cancer therapy. The lipid component was soybean lecithin; the saccharide one was chitosan that usually acts as an outer coating increasing vesicle stability. The microscopy and scattering data indicate the presence of two distinct nanoparticle families: uni-lamellar vesicles with average radius 90 A and multi-lamellar vesicles with average radius 440 A. In both families the inner core is occupied by the solvent. The presence of tamoxifen gives rise to a multi-lamellar structure of the lipid outer shell. It also induces a positive surface charge into the vesicles, repelling the positively charged chitosan molecules which therefore do not take part in nanoparticle formation.

Protein–membrane interaction: effect of myelin basic protein on the dynamics of oriented lipids

Abstract We have studied the effect of physiological amounts of myelin basic protein (MBP) on pure dimyristoyl l -α-phosphatidic acid (DMPA) oriented membranes. The investigation has been carried out using several complementary experimental methods to provide a detailed characterization of the proteo-lipid complexes. In particular, taking advantage of the power of the quasi-elastic neutron scattering (QENS) technique as optimal probe in biology, a significant effect is suggested to be induced by MBP on the anisotropy of lipid dynamics across the liquid–gel phase transition. Thus, the enhancement of the spatially restricted, vertical translation motion of DMPA is suggested to be the main responsible for the increased contribution of the out of plane lipid dynamics observed at 340 K.

Elastic incoherent neutron scattering as a probe of high pressure induced changes in protein flexibility.

We report here the results of elastic incoherent neutron scattering experiments on three globular proteins (trypsin, lysozyme and beta-lactoglobulin) in different pressure intervals ranging from 1 bar to 5.5 kbar. A decrease of the mean square hydrogen fluctuations, u(2), has been observed upon increasing pressure. Trypsin and beta-lactoglobulin behave similarly while lysozyme shows much larger changes in u(2). This can be related to different steps in the denaturing processes and to the high propensity of lysozyme to form amyloids. Elastic incoherent neutron scattering has proven to be an effective microscopic technique for the investigation of pressure induced changes in protein flexibility.

Dynamics of hydrated starch saccharides

We report here elastic neutron scattering data on glucose and on two of its polymeric forms: amylose and amylopectin. We have covered the hydration range from the dry state to about 0.6 g water/g dry saccharide. The data indicate, in all the analysed systems, the presence of a dynamic glass-like transition similar to that observed in hydrated proteins. The fact that this feature is observed also in a relatively small molecule like glucose confirms the hypothesis already put forward by other authors, that this transition in biomolecular species is essentially triggered and driven by the interaction of the macromolecule with the network of fluctuating H-bond of the solvent.

X-ray diffraction and Mössbauer spectroscopy of the core/shell iron/iron oxide system

Abstract Iron–iron oxide nanocomposites obtained by inert gas condensation techniques have been studied by X-ray diffraction and Mossbauer spectroscopy as a function of particle size in the 5–25xa0nm range, i.e. as a function of the oxide volume fraction. The oxide (spinel) phase is characterised by small grain size and high atomic disorder. The thermal relaxation in the supposedly ferrimagnetic order of the oxide is reduced by magnetic polarisation of the iron core. The oxide Mossbauer spectrum has been fitted with two broad sextets with different dependence on the particle size of the hyperfine field distribution.