C. Castellano

X-ray and neutron reflectivity study of solid-supported lipid membranes prepared by spin coating

We present a study of x-ray synchrotron radiation and neutron reflectivity on solid-supported lipid membranes prepared by spin coating. This technique has the advantage of allowing the control of the number of lipid layers by varying the deposition parameters. The experiments were performed on the cationic lipid 1,2-dioleoyl-3-trimethylammonium-propane chloride salt (DOTAP), the neutral lipid 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), the lipid mixture (DOTAP-DOPC), and the complex (DOTAP-DOPC∕DNA) deposited on wafers. Only single neutral lipids or lipid-peptide mixtures were deposited on solid substrate using the spin coating technique and characterized. Results on the structure of the deposited lipid layers indicate that DNA contributes to the order in the lipoplexes.

Glass transition temperature of water confined in lipid membranes as determined by anelastic spectroscopy

The research of gene delivery vehicles used in gene therapy is focused on nonviral vectors like lipid membranes. Such vectors, nonimmunogenic and biodegradable, are formed by complexation of DNA with a mixture of cationic lipids and a neutral colipid which improve the transfection efficiency. A main topic related to lipid membrane dynamics is their capability to spontaneously confine water. At present the value of the glass transition temperature (Tg) is largely debated and determined only by some indirect methods. Here the authors show that anelastic spectroscopy allows the confined water Tg value to be directly identified in several lipid mixtures.

Local structure of hole-doped manganites: influence of temperature and applied magnetic field

We report an extended x-ray absorption fine-structure investigation on the Mn K absorption edge in La1-xCaxMnO3 as a function of temperature and magnetic field. The results provide microscopic evidence that the modifications in the local structure around Mn atomic sites, as a function of temperature and applied magnetic field, are directly related to the magneto-transport properties of these materials.

Crystal and magnetic structure of Cr- and Ni-substituted(La0.50Ca0.50)MnO3

The crystal and magnetic structure of (La0.50Ca0.50)(Mn1−xBx)O3 (x = 0.00, 0.03, 0.08; B = Cr, Ni) has been investigated between 5 and 300 K by means of dc magnetic measurements and neutron powder diffraction followed by Rietveld refinement. In the pristine compound an orthorhombic to monoclinic phase transition is detected on cooling, accompanied by a CE-type antiferromagnetic (AFM) ordering arising. Ni2+ and Cr3+ substitutions have similar effects on the structural and magnetic properties of (La0.50Ca0.50)MnO3, despite the fact that these ions are characterized by different external electronic configurations. After substitution, the orthorhombic to monoclinic phase transition is hindered. As a consequence, charge and orbital orderings are suppressed, as is the superexchange; double exchange takes place inducing ferromagnetic (FM) interactions. No evidence for stable magnetic interaction between Cr3+ or Ni2+ and the neighbouring Mn ions was detected. Nevertheless, in the Ni-substituted samples a detectable quantity of monoclinic phase forms during cooling, inside which AFM interactions take place. The amount of this secondary monoclinic phase decreases on increasing Ni substitution; the global FM magnetic moment decreases as well, due to a spin-cluster glass-type state arising. As a result a FM state is found to coexist with a spin-cluster glass-type state.

Structural and magnetic properties of Cu substituted manganites studied by EXAFS and dc magnetization measurements

Abstract We report extended X-ray absorption fine structure (EXAFS) measurements at the Mn K-edge and dc magnetic measurements performed on (La 1− x Ca x )(Mn 1− y Cu y )O 3 samples ( x xa0=xa00.37 and 0.75 and y xa0=xa00.03 or 0.08), thus comparing the effects determined by the partial Mn substitution with Jahn–Teller Cu 2+ ions with those induced by the already studied analogous substitution of Mn with non-Jahn-Teller Cr 3+ . Hence, in the present paper we complete our study on the influence of chemical Mn site substitutions on the nanoscale phase inhomogeneity characteristic of these strongly correlated electron systems. We observe that the Cu 2+ substitution determines two very different effects in the two compositions belonging from the opposite sides of the phase diagram. In the x xa0=xa00.37 case it weakens the ferromagnetic ordering thus favouring the antiferromagnetic charge ordered phase component, while in the x xa0=xa00.75 one it does not significantly modify the charge ordering already present in the system, differently from what previously observed in presence of non-Jahn-Teller Cr 3+ substitution.

Dynamics of the low temperature inhomogeneous phase in manganese perovskites

The anelastic spectra of

Dynamics of liposomes gene vectors studied by anelastic spectroscopy

La_{1-x}Ca_xMnO_3

Ordering and lyotropic behavior of a silicon-supported cationic and neutral lipid system studied by neutron reflectivity

with x=0.40 have been measured in a wide temperature range. The ferromagnetic–paramagnetic and the structural orthorhombic–trigonal phase transitions are clearly identified and the nature of an elastic energy loss peak just below

Extended x-ray absorption fine structure study of the MnAs local structure at the phase transitions

T_C

Local Structure and Dynamic Properties of Mn Substituted Manganites Studied by EXAFS and Anelastic Spectroscopy

is discussed. Its temperature and frequency dependences are typical of the dynamic susceptibilities of phase inhomogeneous or frustrated compounds like relaxor ferroelectric perovskites or spin glasses. Then at low temperature these systems seem to be characterized by a phase separation scenario presenting a glass-like dynamics. The bases of a forthcoming quantitative study have been identified.