Sol-gel deposition of silica films on silicate glasses: Influence of the presence of lead in the glass or in precursor solutions

Many lead silicate historical glasses suffer degradation phenomena often observed as color changes and iridescence caused by lead ions leaching from the outer layers of the glass. In order to repair and to prevent these phenomena, glasses with large amounts of lead (6.7 and 14.3 at.% of lead) have been coated with silica films at neutral pH by dipping them in a precursor solution of TEOS (tetraethyl orthosilicate), ethyl alcohol and deionized water without any other acid or basic catalyst. Experiments with long dipping times (24 h) and temperatures around 20 °C have been performed to evaluate the role of lead ions of the glass as a catalyst. Silica films of very good quality and optical transparency have been also obtained on lead-free, soda-lime glasses by adding catalytic amounts of Pb(NO₃)₂ instead of HCl to the precursor solution. The films have been characterized by optical microscopy, AFM (Atomic Force Microscopy), XPS (X-ray Photoelectron Spectroscopy) and SIMS (Secondary Ion Mass Spectrometry).     

Influence of electronic and structural effects on the oxidative behavior of nickel porphyrins

With the aim of better understanding the electronic and structural factors which govern electron-transfer processes in porphyrins, the electrochemistry of 29 nickel(II) porphyrins has been examined in dichloromethane containing either 0.1 M tetra-n-butylammonium perchlorate (TBAP) or tetra-n-butylammonium hexafluorophosphate (TBAPF(6)) as supporting electrolyte. Half-wave potentials for the first oxidation and first reduction are only weakly dependent on the supporting electrolyte, but E(1/2) for the second oxidation varies considerably with the type of supporting electrolyte. E(1/2) values for the first reduction to give a porphyrin pi-anion radical are effected in large part by the electronic properties of the porphyrin macrocycle substituents, while half-wave potentials for the first oxidation to give a pi-cation radical are affected by the substituents as well as by nonplanar deformations of the porphyrin macrocycle. The potential difference between the first and second oxidations (Delta/Ox(2) - Ox(1)/) is highly variable among the 29 investigated compounds and ranges from 0 mV (two overlapped oxidations) to 460 mV depending on the macrocycle substituents and the anion of the supporting electrolyte. The magnitude of Delta/Ox(2) - Ox(1)/ is generally smaller for compounds with very electron-withdrawing substituents and when TBAP is used as the supporting electrolyte. This behavior is best explained in terms of differences in the binding strengths of anions from the supporting electrolyte (ClO(4)(-) or PF(6)(-)) to the doubly oxidized species. A closer analysis suggests two factors which are important in modulating Delta/Ox(2) - Ox(1)/ and thus the binding affinity of the anion to the porphyrin dication. One is the type of pi-cation radical (a proxy for the charge distribution in the dication), and the other is the conformation of the porphyrin macrocycle (either planar or nonplanar). These findings imply that the redox behavior of porphyrins can be selectively tuned to display separate or overlapped oxidation processes.     

Binding properties of a polyclonal antibody directed towards lead complexes

A previously described conjugate of 8-hydroxyquinoline and bovine serum albumin was complexed with lead(II), (8-hydroxyquinoline to metal ion ratio 2:1) and used as an immunogen to produce polyclonal antibodies against lead in chickens. Antibodies obtained from a first blood sample during a standard immunisation procedure showed very promising features (dynamic range of the assay was 1 to 1000 ng l(-1)). Nevertheless, proceeding with the immunisation caused a complete loss of the recognition of the complex. A modified brief immunisation procedure was carried out and, in this case, the immunogen proved to be sufficiently stable in vivo to produce antibodies that selectively bound to the lead(II) complex (in the same 2:1 ratio used as an immunogen). Since the antiserum obtained cannot reach the same performance levels as the first one, standard curves were obtained by adding the free 8-hydroxyquinoline to the solution, which enables 2:1 complexes to be more easily formed. Cross-reactivity and dependence from buffer were investigated, showing at least 10-fold lower binding to non-target divalent metal ions compared to lead(II). MES buffer (pH = 6.0) gave more sensitive but very imprecise curves, whereas Tris (pH = 8.5) allows higher precision but lower sensitivity to be observed.     

Transport of atmospheric pollutants in a semi-rural area of central Italy

An environmental monitoring program aimed to the evaluation of the air quality in the surroundings of Gallese (near Viterbo, in central Italy) was carried out from July 1998 to July 2000. The goal of the program was the comprehension of the transport and transformation mechanisms of nitrogen and sulphur pollutants, and the evaluation of photochemical smog episodes. In this framework, a wide range of atmospheric pollution events was studied, and for many of them it was possible to detect the main source of the pollution. We report in this paper the interpretation of ozone episodes, sulphur dioxide episodes and sea-salts episodes, due to transport from the urban area of Rome, the industrial area of Narni-Tarni and the coastal areas of the Tyrrhenian Sea, respectively.     

Nonhydrolytic synthesis of high-quality anisotropically shaped brookite TiO2 nanocrystals

A surfactant-assisted nonaqueous strategy, relying on high-temperature aminolysis of titanium carboxylate complexes, has been developed to access anisotropically shaped TiO2 nanocrystals selectively trapped in the metastable brookite phase. Judicious temporal manipulation of precursor supply to the reaction mixture enables systematic tuning of the nanostructure geometric features over an exceptionally wide dimensional range (30-200 nm). Such degree of control is rationalized within the frame of a self-regulated phase-changing seed-catalyzed mechanism, in which homogeneous nucleation, on one side, and heterogeneous nucleation/growth processes, on the other side, are properly balanced while switching from the anatase to the brookite structures, respectively, in a continuous unidirectional crystal development regime. The time variation of the chemical potential for the monomer species in the solution, the size dependence of thermodynamic structural stability of the involved titania polymorphs, and the reduced activation barrier for brookite nucleation onto initially formed anatase seeds play decisive roles in the crystal-phase- and shape-tailored growth of titania nanostructures by the present approach.     

Temperature-Dependent Dynamical Evolution in Coum/SBE-β-CD Inclusion Complexes Revealed by Two-Dimensional FTIR Correlation Spectroscopy (2D-COS)

A combination of Fourier transform infrared spectroscopy in attenuated total reflectance geometry (FTIR-ATR) and 2D correlation analysis (2D-COS) was applied here for the first time in order to investigate the temperature-dependent dynamical evolution occurring in a particular type of inclusion complex, based on sulfobutylether-β-cyclodextrin (SBE-β-CD) as hosting agent and Coumestrol (7,12-dihydorxcoumestane, Coum), a poorly-soluble active compound known for its anti-viral and anti-oxidant activity. For this purpose, synchronous and asynchronous 2D spectra were calculated in three different wavenumber regions (960–1320 cm⁻¹, 1580–1760 cm⁻¹ and 2780–3750 cm⁻¹) and over a temperature range between 250 K and 340 K. The resolution enhancement provided by the 2D-COS offers the possibility to extract the sequential order of events tracked by specific functional groups of the system, and allows, at the same time, the overcoming of some of the limits associated with conventional 1D FTIR-ATR analysis. Acquired information could be used, in principle, for the definition of an optimized procedure capable to provide high-performance T-sensitive drug carrier systems for different applications.     

Validation of the copper(i)-catalyzed azide-alkyne coupling in ionic liquids. Synthesis of a triazole-linked C-disaccharide as a case study

The first study of a copper(I)-catalyzed azide-alkyne click reaction in ionic liquids (ILs) is reported. The cycloaddition of a sugar azide with a sugar acetylene (CuI, i-Pr2EtN, 80 degrees C) was carried out in 10 ILs as well as in standard molecular solvents (toluene and DMF) to give the 1,4-disubstituted triazole-linked C-disaccharide. The highest yields (84 and 95%) were registered in Ammoeng 110 and [C(8)dabco][N(CN)(2)]. The latter solvent was recycled in four subsequent reactions without loss of the reaction efficiency. Reactions carried out in the absence of the Hünig's base afforded mixtures of 1,4- and 1,5-disubstituted triazole regioisomers.     

An original route to newly-functionalized indoles and carbazoles starting from the ring-opening of nitrothiophenes

The multifaceted behavior of nitrobutadienes deriving from the initial ring-opening of nitrothiophenes finds a further clear-cut example in their Michael-type acceptor reactivity towards indole. Thus, depending on the starting diene, either newly-functionalized indoles or carbazoles are produced, the latter as the result of an appealing double (intermolecular + intramolecular) Michael-type addition to a nitrovinylic moiety. The outcome encompasses motifs for both mechanistic and synthetic interest in the field of heterocycles endowed with possible pharmacological activity.     

Purcell effect observation in erbium doped lithium niobate photonic crystal structures

In this study, we investigate the emission from a photonic crystal (PC) structure fabricated in Er-doped LiNbO₃ crystal. We report the linear, non-linear, and saturated output intensity as the pumping power is increased. The measurements are taken inside the PC and on the bulk substrate. Purcell effect can be observed in the experimental results in the presence of the PC.     

Synthesis and surface properties of microphase separated or nanostructured coatings based on hybrid and fluorinated acrylic copolymers

Coating materials characterised by intrinsic inhomogeneity or nanostructured morphology can display unique interfacial (e.g. surface and adhesion) and bulk (e.g. mechanical, thermal) properties, when heterophasic or self-segregating components are obtained by suitable design of the constitutive copolymers' structure. With the purpose of obtaining intrinsically photostable low-surface energy coating materials characterised by good penetration into porous substrates and variable response of the adhesive and polymer-air interface, fluorinated acrylic-based copolymers and water-borne acrylic-organosilane hybrids have been considered. For the latter, dispersed phase polymerisation procedures based on combined emulsion copolymerisation and hydrolysis-polycondensation of organosilane precursors have been adopted.