Isabella Natali Sora

Photophysical properties of N-alkylated azahelicene derivatives as DNA intercalators: counterion effects.

In this work, three compounds having the same organic moiety (N-methyl-5-azahelicenium salts) but different counterions (I-, NO3- and COOCF3-) have been investigated in buffered aqueous solutions and in the presence of DNA to give information on the counterion effects on the binding. In particular, the absorption spectra, fluorescence quantum yields and fluorescence lifetimes in aqueous solution for free organic molecules have been determined by steady-state and time-resolved spectrofluorimetric measurements. The obtained values are compared with those of the chromophores in the presence of increasing concentrations of DNA. The results allow determination of the association constants (K(a)) and the number of base couples per chromophore molecule (n) by means of the McGhee Von Hippel model. The binding parameters are strongly affected by the nature of counterions since the highest K(a) value was determined for the compound having COOCF3-; on the other hand the NO3- derivative is able to interact with the highest number of binding sites. The morphology and structural properties of the DNA-chromophore complexes were investigated by circular dichroism (CD) and atomic force microscopy (AFM). The data revealed that I- and COOCF3- derivatives preferentially form intercalation complexes, while the NO3- salt is able to form intercalation and grove binding complexes at the same time.

Use of admixtures in organic-contaminated cement-clay pastes

In this work microstructure, porosity and hydration degree of cement-based solidified/stabilized wasteforms were studied before assessing their leaching behaviour. 2-Chloroaniline was chosen as a model liquid organic pollutant and included into cement pastes, which were also modified with different admixtures for concrete: a superplasticizer based on acrylic-modified polymer, a synthetic rubber latex and a waterproofing agent. An organoclay, modified with an ammonium quaternary salt (benzyl-dimethyl-tallowammonium, BDMTA), was added to the pastes as pre-sorbent agent of the organic matter. All the samples were dried up to constant weight in order to stop the hydration process at different times during the first 28 days of curing, typically, after 1 day (1d), 7 days (7d) and 28 days. Then, the microstructure of the hardened cement-clay pastes was investigated by powder X-ray diffraction (XRD). The hydration degree and porosity were studied by thermal analysis (TG/DTA) and mercury intrusion porosimetry (MIP), respectively. For samples cured for 28 days a short-term leach test set by Italian regulation for industrial waste recycling (D.M. 5 February 1998) was performed. The best results showed a 5% release of the total initial amount of organic pollutant.

Synthesis, crystal structure and crystal packing of diaza[5]helicenes

Analysis of the crystalline packing of known aza[5]helicenes is presented together with some newly synthesized diaza[5]helicenes species, characterized by NMR spectroscopy and X-ray diffraction. The comparison with carbo[5]helicenes and monoaza[5]helicenes emphasizes the importance of the “shape factor” (responsible of the isomorphism between some species in the series) as well as the lack of a unique supramolecular effect organizing the molecules in the crystals (responsible for the polymorphism observed for some compounds).

Quantum Mechanics Calculations, Basicity and Crystal Structure: The Route to Transition Metal Complexes of Azahelicenes

Quantum mechanics density functional calculations provided gas-phase electron distributions and proton affinities for several mono- and diaza[5]helicenes; computational results, together with experimental data concerning crystal structures and propensity to methylation of the nitrogen atom(s), provide a basis for designing azahelicene complexes with transition metal ions.

Immobilization of organic pollutants in cement pastes admixed with organophilic materials

The results of 2-chloroaniline (2-CA) immobilization experiments in cement matrices, using an organophilic clay modified with phenolic resins as pre-sorbent, are shown. The 2-CA suspended in water was kept in contact with the organoclay for 24 h, and the slurry obtained was then admixed with ordinary Portland cement (OPC) without additional water, to obtain a firm solid waste. Six cement—clay pastes were prepared with the same water-to-cement ratio (0.50 wt/wt), but with different slurry composition (water-to-organoclay ratio equal to 10 and 5 wt/wt, respectively) and different amounts of 2-CA suspended in water, namely 5000, 15 000, and 25 000 ppmw (weight). Dynamic leach tests were performed on solidified monoliths in order to assess the successful immobilization of the 2-CA. Moreover, X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy analyses were carried out.

Simulated weathering tests of photocatalytic paint containing LaFeO3

The effects of simulated weathering tests on water paints based upon a silicate binder, containing a LaFeO3 photocatalyst, were investigated by measuring their self-cleaning performances. Paint samples were exposed to accelerated ageing tests using a climatic chamber, which simulated weathering effects such as UV radiation, rainwater and conspicuous temperature and humidity variations. Samples were subsequently stained by Procion Red PX4B dye and the color degradation of the taint onto the solid phase was followed through UV-vis diffuse reflectance spectra (DRS). The dye discoloration percentage after 360 h visible light irradiation was 78 % for not weathered samples, and 67 % for weathered ones.

Structural Studies of Doped Lanthanum Orthoferrites of Interest for SOFCs

Traditional LSM (La1-xSrxMnO3-w) SOFC cathode material shows some drawbacks operating below 800 °C, in particular poor oxygen ion conduction, which limits the active area of the electrode to the three phase boundary (TPB) between electrolyte, electrode and gas phase at the interface. A strategy to overcome this problem consists in the development of materials with both good oxygen ion and electronic conductivity, in which oxygen ions catalytically dissociated on the surface are able to reach the electrolyte by diffusion in the bulk of the cathode. La1-xSrxFeO3-w has been proposed as possible SOFC cathode, in search for a high activity at lower temperatures with respect to LSM. The aim of the work is the structural study of alternative cathodic materials for intermediate temperature solid oxide fuel cells, mainly based on ABO3 perovskite-type lanthanum ferrite. Within this framework the effects of A (La)-site doped with Sr or B (Fe)-site doped with Ta on the crystal structures of these materials were investigated by X-ray powder diffraction (XRPD). In conjunction with the experimental results, the microscopic mechanisms of the doping effect were discussed providing deeper understanding into structure-property relations.

Ageing of Lanthanum Strontium Copper Orthoferrite Powders for Sensing Layers

Nanosized powders of lanthanum strontium copper orthoferrites La0.8Sr0.2Fe1-xCuxO3-w (LSFC) have been recently proposed as sensing component in chemical sensors for humidity detection. The LSFC powders were prepared by citrate auto-combustion of dry gel obtained from a solution of corresponding nitrates in a citric acid solution. The aged powders were investigated by chemical and structural analysis using X-ray Photoelectron Spectroscopy (XPS), Infrared Spectroscopy and X-Ray Powder Diffraction as a total loss of their sensing properties has been observed after about one year storage of the sensors at room temperature in the laboratory. The detection of surface hydroxides and carbonates species as well as very large Sr and Cu excess within the surface area were important results.

Copper Doped Lanthanum Strontium Ferrite as Cathode for La0.8Sr0.2Ga0.8Mg0.2O3

A “cobalt free” cathode material with stoichiometric composition La0.8Sr0.2Fe0.8Cu0.2O3 (LSFCu) was specifically developed for La0.8Sr0.2Ga0.8Mg0.2O3 (LSGM) electrolyte. The chemical stability with LSGM electrolyte was investigated by structural and morphological analysis. The electrochemical properties of LSFCu dense pellets were investigated in the temperature range 600–750°C by electrochemical impedance spectroscopy (EIS). LSFCu/LSGM/LSFCu symmetrical cells were prepared and Area Specific Resistance (ASR) values, directly depending on the rate limiting step of the oxygen reduction reaction, were evaluated. Fuel cells were prepared using LSFCu as cathode material on LSGM pellet and electrochemical tests were performed and compared to similar fuel cells prepared by using commercial La0.6Sr0.4Fe0.8Co0.2O3(LSFCo). The maximum current density and power density recorded for LSFCu and LSFCo were comparable demonstrating that Cu can be used as substitutes Co.