Guido Ennas

Characterization of Nanocrystalline γ–Fe 2 O 3 Prepared by Wet Chemical Method

Homogeneous maghemite (γ–Fe 2 O 3 ) nanoparticles with an average crystal size around 5 nm were synthesized by successive hydrolysis, oxidation, and dehydration of tetrapyridino-ferrous chloride. Morphological, thermal, and structural properties were investigated by transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and x-ray diffraction (XRD) techniques. Rietveld refinement indicated a cubic cell. The superstructure reflections, related to the ordering of cation lattice vacancies, were not detected in the diffraction pattern. Kinetics of the solid-state phase transition of nanocrystalline maghemite to hematite (α–Fe 2 O 3 ), investigated by energy dispersive x-ray diffraction (EDXRD), indicates that direct transformation from nanocrystalline maghemite to microcrystalline hematite takes place during isothermal treatment at 385 °C. This temperature is lower than that observed both for microcrystalline maghemite and for nanocrystalline maghemite supported on silica.

Diclofenac nanosuspensions: influence of preparation procedure and crystal form on drug dissolution behaviour.

The aim of this paper was to ascertain the role of drug crystalline form and preparation procedure in nanosuspension formulations in order to optimise dissolution properties of lipophilic, poorly soluble drugs, thus improving their oral bioavailability. The non-steroidal anti-inflammatory drug diclofenac acid (DCF), which is known to exist in different crystal forms, was chosen as a model drug. To this purpose, the influence of homogenization technique was studied by preparing several nanosuspensions with two different crystalline forms of the drug (DCF1 and DCF2). Particle size and size distribution, morphology, microstructure, and thermal behaviour of the different formulations were studied by photon correlation spectroscopy (PCS), scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and differential scanning calorimetry (DSC). Solubility studies of the bulk drug crystalline forms and dissolution experiments of nanosuspensions in comparison with different controls (bulk drug, physical mixtures, coarse suspensions) were carried out in different media: distilled water, simulated gastric fluid (SGF) and simulated intestinal fluid (SIF). Besides well known factors capable of affecting drug nanoparticle dissolution, results showed that drug dissolution rate in nanosuspensions is strongly affected by the drug solubility, which depends on the crystal form, and preparation procedure (high pressure homogenization process). Results demonstrated that this process partially transformed DCF2 in DCF1 while it did not have any effect on the DCF1 crystals.

Diclofenac-β-cyclodextrin binary systems: Physicochemical characterization and in vitro dissolution and diffusion studies

The aim of this work was to study the influence of β-cyclodextrin (β-CD) on the biopharmaceutic properties of diclofenac (DCF). To this purpose the physicochemical characterization of diclofenac-β-cyclodextrin binary systems was performed both in solution and solid state. Solid phase characterization was performed using differential scanning calorimetry (DSC), powder x-ray diffractometry (XRD), and Fourier transform infrared spectroscopy (FTIR). Phase solubility analyses, and in vitro permeation experiments through a synthetic membrane were performed in solution. Moreover, DCF/β-CD interactions were studied in DMSO by1H nuclear magnetic resonance (NMR) spectroscopy. The effects of different preparation methods and drug-to-β-CD molar ratios were also evaluated. Phase solubility studies revealed 1∶1 M complexation of DCF when the freeze-drying method was used for the preparation of the binary system. The true inclusion for the freeze-dried binary system was confirmed by1H NMR spectroscopy, DSC, powder XRD, and IR studies. The dissolution study revealed that the drug dissolution rate was improved by the presence of CDs and the highest and promptest release was obtained with the freeze-dried binary system. Diffusion experiments through a silicone membrane showed that DCF diffusion was higher from the saturated drug solution (control) than the freeze-dried inclusion complexes, prepared using different DCF-β-CD molar ratios. However, the presence of the inclusion complex was able to stabilize the system giving rise to a more regular diffusion profile.

Sol–gel preparation and characterization of Ni–SiO2 nanocomposites

Abstract A series of Ni–SiO2 composites, in the range 7–80 mol% of nickel, were prepared by two gelation methods with tetraethylorthosilicate (TEOS) and nickel(II) nitrate as starting materials. In the first method an aqueous solution of the salt was used while the second employed an alcoholic solution. The methods also differed in the intermediate thermal treatments of the gels. All the systems were reduced at temperatures around 500°C in flowing hydrogen and were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Nanometre sized nickel particles, homogeneously dispersed over the silica support, were observed in the samples with the smaller Ni content obtained by both methods, but only the one which made use of the alcoholic solution was successful in providing nanometre sized particles with size increasing with increasing concentration.

Fe-Co-B amorphous alloy powder by chemical reduction

Fine boride powders, prepared by reactions between sodium or potassium borohydride and aqueous (or alcoholic) solutions of transition metal salts have long been known to be good catalysts for hydrogenation reactions. New interest around them has recently grown, because they were found to exhibit amorphous structure. Classical chemical reactions may thus offer a simple route to prepare amorphous metal powders, paralleling more sophisticated methods so far used to reach the same goal. To explore the potential of these reactions, we considered the system Fe-Co-B with the aim of examining the characteristics of the product obtained in the easiest way and without any particular precautions. The structure of the amorphous alloy appears to be different from that of materials with a similar Me/B ratio prepared via melt spinning.

Cross-linked chitosan/liposome hybrid system for the intestinal delivery of quercetin

Quercetin is a flavonoid with antioxidant/anti-inflammatory properties, poorly absorbed when administered orally. To increase its bioavailability and optimize its release in the intestine, a hybrid system made of liposomes coated with cross-linked chitosan, named TPP-chitosomes, was developed and characterized by light scattering, transmission electron microscopy, differential scanning calorimetry, X-ray powder diffraction and Turbiscan® technology. The TPP-chitosomes were nanosized (∼180 nm), fairly spherical in shape and unilamellar. The actual coating of the surface of liposomes with the cross-linked chitosan was demonstrated by Small-Angle X-ray Scattering. The release of quercetin in simulated gastric and intestinal pH was investigated, the results showing that the system provided resistance to acidic conditions, and promoted the release in alkaline pH, mimicking the intestinal environment. The proposed hybrid system represents a promising combination of nanovesicles and chitosan for the delivery of quercetin to the intestine in the therapy of oxidative stress/inflammation related disorders.

PEGylation and preliminary biocompatibility evaluation of magnetite–silica nanocomposites obtained by high energy ball milling.

High energy ball milling (HEBM) has been used for the first time to prepare PEGylated magnetite-silica (Fe(3)O(4)-SiO(2)) nanocomposites intended to be used for biological purposes. Surface amine groups were introduced by a silanization reaction involving 3-aminopropyl triethoxysilane (APTS) followed by PEGylation to yield long-term stable and stealth nanocomposites of 200nm in diameter. The efficient coverage by PEG chains was shown by isothermal titration calorimetry (ITC) where PEGylated nanocomposites did not interact with BSA compared to non-PEGylated counterparts which led to a significant change in enthalpy. By cell viability (MTT) assays and cell morphology investigations, it was evidenced that PEGylated Fe(3)O(4)-SiO(2) nanocomposites did not provide any appreciable cytotoxicity on J774 macrophage and MCF-7 breast cancer cell lines. Furthermore, noticeable internalization was evidenced by J774 cells with PEGylated Fe(3)O(4)-SiO(2) nanocomposites in contrast to MCF-7 cells, in good agreement with the respective tendency of each cell line for endocytosis.

Iron and Iron-oxide on Silica Nanocomposites Prepared by the Sol-gel Method

γ-Fe 2 O 3 /SiO 2 and Fe/SiO 2 nanocomposites, with a Fe/Si molar ratio of 0.25, were prepared by the sol-gel method starting from ethanolic solutions of tetraethoxysilane and iron (III) nitrate. After gelation the xerogelswere oxidated or reduced. Samples were investigated by transmission electron microscopy, x-ray diffraction, differential scanning calorimetry, and thermogravimetry. Magnetic properties of the samples were investigated at room temperature (RT) and at 77 K. Nanometric particles supported in the silica matrix were obtained in all cases. Bigger particles (10 nm) were obtained in the case of Fe/SiO 2 nanocomposites with respect to the γ-Fe 2 O 3 /SiO 2 samples (5-8 nm). A slight effect of sol dilution on particle size was observed only in the case of γ-Fe 2 O 3 /SiO 2 nanocomposites. A superparamagnetic behavior was shown at RT only by γ-Fe 2 O 3 /SiO 2 nanocomposites. Iron-based composites exhibited coercivity values higher than 700 Oe at RT.

The synthesis of nanocrystalline nickel boride powders by ball milling of elemental components

Solid state reaction induced by ball milling the elemental components has been investigated on Ni60B40 and Ni80B20 mixtures by means of transmission electron microscopy, X-ray diffraction and differential scanning calorimetry. The time evolution of the reaction is similar in the two samples, although slower in Ni80B20. Reaction begins with the formation of o-Ni3B and of a disordered phase. The final products are nanocrystalline o-Ni3B and unreacted nickel in Ni80B20 and nanocrystalline t-Ni2B in Ni60B40. Different milling conditions, tested on the Ni60B40 sample, do not modify the path but affect the rate of the solid state reaction.

Structure and chemical durability of zinc-containing glasses

Abstract The structural role of Zn(II) in borosilicate glasses has been investigated by comparing X-ray diffraction data from a glass of the system Na2OLi2OZnOSiO2B2O2 with those obtained from a Zn-free borosilicate matrix and from a sample having nearly the same composition, but containing CoO instead of ZnO. Difference radial distribution curves were calculated in order to determine the environment of Zn(II) and Co(II) atoms. It is concluded that both transition metal atoms are surrounded by approximately four oxygen neighbours at distances expected for fourfold coordination.