Adolfo Lai

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.

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.

Study of dimethyl-substituted benzene derivatives by 13C nuclear magnetic resonance spectroscopy and INDO MO calculations

A 13C n.m.r. investigation of some substituted dimethyl benzenes is reported. The spectral analysis were carried out by the iterative Laocoon III and a spin-simulation program furnished carbon–proton coupling constants that have been rationalized with the aid of the FPT–INDO MO calculations. The angular dependences of the calculated 3JC,CHO and 1JCHO coupling constants have been analysed and the preferred conformations are discussed.

Imazalil–cyclomaltoheptaose (β-cyclodextrin) inclusion complex: preparation by supercritical carbon dioxide and 13C CPMAS and 1H NMR characterization

An inclusion complex between imazalil (IMZ), a selected fungicide, and cyclomaltoheptaose (beta-cyclodextrin, betaCD) was obtained using supercritical fluid carbon dioxide. The best preparation conditions were determined, and the inclusion complex was investigated by means of 1H NMR spectroscopy in aqueous solution and 13C CPMAS NMR spectroscopy in the solid state. Information on the geometry of the betaCD/IMZ complex was obtained from ROESY spectroscopy, while the dynamics of the inclusion complex in the kilohertz range was obtained from the proton spin-lattice relaxation times in the rotating frame, T(1rho) (1H).

NMR Investigation of Imidazolium-Based Ionic Liquids and Their Aqueous Mixtures

(1)H and (13)C NMR spectroscopy is employed to investigate the interaction of water with two imidazolium-based ionic liquids (ILs), 1-hexyl-3-methylimidazolium bromide ([C(6)mim]Br) and 1-octyl-3-methylimidazolium bromide ([C(8)mim]Br), at IL concentrations well above the critical aggregation concentration (CAC). The results are compared with those of the neat samples. To this aim, a detailed analysis of the changes in the (1)H chemical shifts, (13)C relaxation parameters, and 2D ROESY data due to the presence of water is performed. The results for both neat ILs are consistent with a packed structure where head-to-head, head-to-tail, and tail-to-tail contacts occur and where the site of maximal mobility restriction is at the polar head. At the lowest investigated water content, the presence of water influences mainly the environment around the IL polar head, slowing down the motional dynamics of the aromatic ring with respect to the alkyl chain. At higher water contents this difference diminishes, the motional freedom of the whole molecule increasing. The presence of ROESY cross-peaks between protons in the polar and apolar IL regions, as well as between protons in non-neighboring alkyl groups, at all investigated water contents suggests that the alkyl tails are not fully segregated in hydrophobic domains, as expected for micelle-like structures.

Characterization of the ionization and spectral properties of sulfonephthalein indicators. Correlation with substituent effects and structural features.

The pK values of the second ionization of a set of substituted sulfonephthaleins are studied by spectrophotometry and (13)C NMR spectroscopy. A study of the correlation between equilibrium and spectral data on the one hand and the substituent effects on the other is presented, using the dual substituent analysis of Swain and Lupton. This shows a complete dependence of pK values on the F field variable, and of the wavelengths of the bands of basic forms on the R resonance variable.

Group IIB metal and VIB metal-carbonyl thiomorpholin-3-thione derivatives

Abstract Using thiomorpholin-3-thione (ts) as ligand the complexes M(CO)5ts (where M = Cr, Mo, W), which are yellow, crystalline, non-electrolyte and diamagnetic, were obtained. Complexes of the types MX2ts2 and MX2ts (M = Zn, Cd, Hg; X = Cl, Br, I) were obtained as diamagnetic and non-electrolyte compounds. On the basis of i.r. and PMR spectra we suggest that the Cr, Mo and W-pentacarbonyl-derivatives have C4ν symmetry and are S-bonded through the thioketonic group, while all the IIB group derivatives seem to be N-bonded.

Study of the nanoparticle/matrix interactions in Y2O3–SiO2 samples

Two Y2O3–SiO2 nanocomposites with 10 and 30 wt.% yttrium oxide were obtained by a sol–gel method, and characterized by TEM, X-ray diffraction, FTIR, 29Si MAS and CPMAS NMR spectroscopy. It was found that small (2–3 nm) amorphous yttria nanoparticles are homogeneously dispersed in the silica matrix. Their size does not appear to grow with thermal treatment up to 900 °C nor with yttria content. The silica interacts strongly at the interface with yttria nanoparticles through hydrogen bonds, sometime mediated by bridging water molecules, but also via direct Si–O–Y bonds.

XRD, TEM IR and 29Si MAS NMR characterization of NiO-SiO2 Nanocomposites

The present study focuses on the structural properties of a NiO-SiO2nanocomposite with 14 mol % of nickel oxide obtained by a sol-gel method and a gradual heating the gel in the 350–900°C range. NiO nanoparticles and their dispersion in the amorphous silica matrix were studied through TEM and XRD. The behaviour at the nanoparticle/matrix interface was investigated through IR and 29Si MAS NMR spectroscopy comparing the spectra of the nanocomposite with that of a silica sample obtained with the same preparation method and submitted to the same thermal treatments. The results indicate that nanoparticles, formed in cavities of the silica matrix, act as an obstacle towards the spontaneous silica polymerization process with heat treatments.

Binding of Ru(II) polyazaaromatic complexes to DNA: A 23Na NMR spin-lattice relaxation study

The possibility of using sodium-23 spin-lattice relaxation rate measurements to probe the interaction modes of Ru11 polyazaaaromatic complexes with DNA is investigated. The following complexes are considered: Ru(phen)3(2+) (phen = 1.10-phenanthroline), Ru(phen)2HAT2+ (HAT = 1,4,5,8,9,12-hexaazatriphenylene), and Ru(diMeTAP)3(2+) (diMeTAP = 2,7-dimethyl-1,4,5,8-tetraazaphenanthrene). The addition of Ru(diMeTAP)3(2+) to a solution of NaDNA leads to a decrease in the sodium-23 spin-lattice relaxation rate (R1) similar to the effect observed upon addition of Mg2+. This indicates that Ru(diMeTAP)3(2+) interacts like Mg2+ with DNA and consequently that the electrostatic interaction dominates the association with DNA, Ru(phen)3(2+) and Ru(phen)2HAT2+ diminish R1 more efficiently than Mg2+, in a manner similar to ethidium bromide, which is known for its intercalation properties. Thus interactions other than electrostatic occur between these two complexes and DNA. These results are in agreement with data obtained from other techniques, according to which Ru(phen)3(2+) and Ru(phen)2HAT2+ are located partially inside the DNA double helix, in contrast to Ru(diMeTAP)3(2+) which remains in the ionic atmosphere around the phosphate backbone.