Mariano Casu

IR and NMR study of nanoparticle-support interactions in a Fe2O3-SiO2 nanocomposite prepared by a sol-gel method

The interaction of iron oxide with the silica matrix in a Fe2O3-SiO2 nanocomposite prepared by a sol-gel method has been investigated using Near-, Mid-, and Far-IR, and 29Si MAS-, and 1H NMR techniques. Samples of nanocomposites and of pure silica obtained by the same preparation procedure and subjected to the same thermal treatments have been examined. Spectroscopic data indicate that the Fe2O3 nanoparticles interact with the silica or silanol groups at the surface of the cavities in which they form. This result allowed us to propose a model for the nanoparticle/silica interface.

Sulpiride activates the firing rate and tyrosine hydroxylase activity of dopaminergic neurons in unanesthetized rats

The effect of i.v. sulpiride on the firing rate of dopaminergic neurons in the substantia nigra, pars compacta (SN-DA cells) and tyrosine hydroxylase (TH) activity in the caudate nucleus was studied. In rats, paralyzed with succinylcholine and artificially respirated, (-)-sulpiride (10-50 mg/kg) produced a dose-related increase in the firing rate of SN-DA cells and in TH activity. On the contrary, in rats anesthetized with halothane, (-)-sulpiride (up to 50 mg/kg) activated neither dopaminergic firing nor TH activity. However, (-)-sulpiride (10-25 mg/kg) readily reversed the inhibitory effect of i.v. apomorphine (25 micrograms/kg) on dopaminergic firing in both anesthetized and unanesthetized rats. Since sulpiride fails to inhibit DA-sensitive adenylate cyclase, it may be concluded that DA receptors, whose blockade results in increased dopaminergic firing and TH activation, are not coupled with this enzyme. Moreover, the results indicate that the mechanism responsible for firing and TH stimulation is inhibited by halothane anesthesia. The latter significantly decreased also the stimulant effect of i.v. haloperidol on striatal TH activity.

Effect of muscimol, a gaba-mimetic agent, on dopamine metabolism in the mouse brain

Abstract The intraperitoneal injection of muscimol at the dose of ranging from 0.5 to 5 mg/kg produced hypomotility, catalepsy and loss of righting reflex in mice. These effects were associated with an initial brief fall followed by a more sustained increase in homovanillic acid and dihydroxyphenylacetic acid levels, without changes in dopamine concentration. Diazepam potentiated the effect of muscimol in motor activity and on dopamine metabolism.

CO escape from myoglobin with metadynamics simulations

The relatively small size of myoglobin makes it suitable for the investigation of the ligand escape process in respiratory proteins and, in general, an ideal model system for the study of the more general structure‐function paradigm. In this work, we use Molecular Dynamics simulations combined with an accelerated algorithm, the metadynamics, to probe the escape of CO from myoglobin. Our approach permits to quantitatively describe the escape process via the reconstruction of the associated free energy surface. Additionally, hints on the involvement of a larger numbers of residues than hitherto assumed in the gating process are extracted from our data. Proteins 2008.

Failure of ketamine to interact with opiate receptors.

Ketamine, an anesthetic agent endowed with several morphine-like effects, failed to displace 3H-dihydromorphine or 3H-methionine-enkephalin from opiate receptors in the rat brain synaptosomal-mitochondrial membrane preparations. Furthermore, ketamine-induced analgesia in rats was not antagonized by naloxone, suggesting that this effect is not mediated by opiate receptors.

XRD, TEM and 29Si MAS NMR study of sol-gel ZnO-SiO2 nanocomposites

X-Ray amorphous ZnO nanoparticles homogeneously dispersed in a silica matrix were evidenced in ZnO-SiO 2 nanocomposites obtained by a sol-gel method and heated to 700°C. TEM observations indicated that the particle size slowly increases with temperature and zinc oxide content, reaching an upper limit of 12 nm. Through a comparison of the 29 Si MAS NMR data of the nanocomposites and silica samples, obtained by the same preparation method, it was possible to observe that reaction occurs between ZnO and silica on heating, which causes a depolymerization of the host matrix with the formation of low condensation groups. This result is discussed in terms of interactions between nanoparticles and the silica matrix at the nanoparticle/matrix interface. A further increase in temperature (900°C) results in the formation of the β-Zn 2 SiO 4 crystalline phase.

Isolation and 13C-NMR characterization of an insoluble proteinaceous fraction from substantia nigra of patients with Parkinson's disease

Neuromelanin is a dark brown pigment suspected of being involved in the pathogenesis of Parkinsons disease. This pigment can be isolated from normal human substantia nigra by a procedure that includes an extensive proteolytic treatment. In this study we used such a procedure to extract the neuromelanin pigment from a pool of substantia nigra from patients affected by Parkinsons disease. 13C Cross polarization magic angle spinning nuclear magnetic resonance spectroscopy and electron paramagnetic resonance spectroscopy were used to characterize the solid residue obtained from the extraction procedure. We found that the pigment extracted from the substantia nigra of parkinsonian patients was mainly composed of highly cross‐linked, protease‐resistant, lipo‐proteic material, whereas the neuromelanin macromolecule appears to be only a minor component of this extract. A synthetic model of melanoprotein has been prepared by enzymatic oxidation of dopamine in the presence of albumin. Once it has undergone the same proteolytic treatment, this model system yields a 13C‐NMR spectrum which is similar to that observed for the parkinsonian midbrain extract. These results are consistent with the view that oxidative stress has a relevant role in the pathogenesis of Parkinsons disease.

Synthesis, characterisation and optical properties of nanocrystalline Y2O3–Eu3+ dispersed in a silica matrix by a deposition–precipitation method

A Eu3+-doped-yttria–silica nanocomposite was synthesized through a deposition–precipitation technique. Yttria nanocrystalline particles with a mean size of 12 nm, dispersed in an amorphous silica matrix, were evidenced by XRD and TEM in a sample treated at 900 °C. The nanoparticles are coated with an amorphous layer visible in the HRTEM micrographs; this amorphous layer is likely to interact with the silica matrix through Si–O–Y bonds, which is consistent with 29Si NMR MAS results. The nanocomposite treated at 1000 °C partially evolves to give an α-Y2Si2O7 crystalline phase. The luminescence spectra of the nanocomposites indicate that the sites in which the Eu3+ ions are accommodated are disordered. On the other hand, the decay times of the 5D0 emission are rather long in the present nanocomposites studied herein, indicating that multiphonon relaxation is not effective in quenching the luminescence. The reduced coupling to OH vibrations in the materials under investigation could be ascribed to the presence of the amorphous layer coating the nanoparticles and effectively shielding the Eu3+ ion from the silanol groups.

Synthesis, characterization and optical spectroscopy of a Y2O3–SiO2 nanocomposite doped with Eu3+

Abstract A Y2O3–SiO2 nanocomposite doped with Eu3+ was obtained by the sol–gel technique and characterized by powder X-ray diffraction, transmission electron microscopy, 29 Si NMR and laser-excited luminescence spectroscopy. It was found that small (2–3 nm) Y2O3 nanoparticles, whose size does not appear to change for heat treatments in the range 500–900 °C, interact at the interface with the SiO2 matrix. Luminescence spectroscopy seems to indicate that the Eu3+ ion is preferentially located inside the highly disordered Y2O3 nanoparticles. These luminescent nanocomposites form a class of materials which could find applications in the field of phosphors.

Interaction of metergoline with striatal dopamine system.

Abstract The intragastric of intraperitoneal administration of metergoline (2.5–10 mg/kg) stimulates dopamine (DA) synthesis in the rat and mouse brain. In vitro, metergoline blocks DA-sensitive adenylate cyclase and displaces H 3 -haloperidol from specific binding sites in striatal homogenates.